Effects of limitation stress and of disruptive stress on induced ...
Effects of limitation stress and of disruptive stress on induced ...
Effects of limitation stress and of disruptive stress on induced ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Vol. 427: 83–94, 2011<br />
doi: 10.3354/meps09044<br />
INTRODUCTION<br />
Herbivory is an important biotic factor affecting algal<br />
biomass, abundance, <str<strong>on</strong>g>and</str<strong>on</strong>g> distributi<strong>on</strong> (Lubchenco &<br />
Gaines 1981, Van Alstyne et al. 2001). The effects <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
mesograzer c<strong>on</strong>sumpti<strong>on</strong> <strong>on</strong> algal individuals may last<br />
over relatively l<strong>on</strong>g periods because grazed individuals<br />
are rarely killed (Dethier et al. 2005). C<strong>on</strong>sequently,<br />
the capacity to limit grazing to a tolerable level should<br />
be <str<strong>on</strong>g>of</str<strong>on</strong>g> substantial selective advantage. Such resistance<br />
*Email: fweinberger@ifm-geomar.de<br />
MARINE ECOLOGY PROGRESS SERIES<br />
Mar Ecol Prog Ser<br />
Published April 12<br />
<str<strong>on</strong>g>Effects</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>stress</str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>disruptive</str<strong>on</strong>g><br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g> <strong>on</strong> <strong>induced</strong> antigrazing defense in the<br />
bladder wrack Fucus vesiculosus<br />
Florian Weinberger 1, *, Sven Rohde 1, 2 , Yv<strong>on</strong>ne Oschmann 1 , Laila Shahnaz 1, 3 ,<br />
Sergey Dobretsov 1, 4 , Martin Wahl 1<br />
1Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany<br />
2ICBM, Carl-v<strong>on</strong>-Ossietzky Universität Oldenburg, Schleusenstrasse 1, 26382 Wilhelmshaven, Germany<br />
3Sindh Institute <str<strong>on</strong>g>of</str<strong>on</strong>g> Urology <str<strong>on</strong>g>and</str<strong>on</strong>g> Transplantati<strong>on</strong>, Civil Hospital, Karachi 74200, Pakistan<br />
4Department <str<strong>on</strong>g>of</str<strong>on</strong>g> Marine Science <str<strong>on</strong>g>and</str<strong>on</strong>g> Fisheries, College <str<strong>on</strong>g>of</str<strong>on</strong>g> Agricultural <str<strong>on</strong>g>and</str<strong>on</strong>g> Marine Sciences, Sultan Qaboos University,<br />
Al Khoud 123, PO Box 34, Muscat, Sultanate <str<strong>on</strong>g>of</str<strong>on</strong>g> Oman<br />
ABSTRACT: We assessed the effects <str<strong>on</strong>g>of</str<strong>on</strong>g> light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> temperature shift <strong>on</strong> palatability <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
<strong>induced</strong> antiherbivore defense in the brown alga Fucus vesiculosus L. Incubati<strong>on</strong> for 2 wk at light<br />
intensities above the compensati<strong>on</strong> point <str<strong>on</strong>g>of</str<strong>on</strong>g> photosynthesis <str<strong>on</strong>g>and</str<strong>on</strong>g> in the absence <str<strong>on</strong>g>of</str<strong>on</strong>g> grazers increased<br />
the palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus <str<strong>on</strong>g>and</str<strong>on</strong>g> its subsequent c<strong>on</strong>sumpti<strong>on</strong> by the omnivorous isopod Idotea<br />
baltica Pallas. This effect correlated with an increased C:N ratio <str<strong>on</strong>g>and</str<strong>on</strong>g> mannitol c<strong>on</strong>tent in the algal tissue,<br />
presumably due to increased photosynthetic carb<strong>on</strong> fixati<strong>on</strong>. Mannitol, the primary product <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
photosynthesis in F. vesiculosus, proved to be a feeding cue for I. baltica, <str<strong>on</strong>g>and</str<strong>on</strong>g> depleti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the mannitol<br />
pool may therefore account for the reduced palatability during light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>. At light intensities<br />
above the compensati<strong>on</strong> point <str<strong>on</strong>g>of</str<strong>on</strong>g> photosynthesis, F. vesiculosus resp<strong>on</strong>ded with decreasing<br />
palatability when it was exposed to I. baltica grazing. Irrespective <str<strong>on</strong>g>of</str<strong>on</strong>g> the preceding light regime, such<br />
defense inducti<strong>on</strong> was prevented during incubati<strong>on</strong> under light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>. Thus, under low light,<br />
defense inducti<strong>on</strong> is not <strong>on</strong>ly inhibited, but also less necessary due to the relative absence <str<strong>on</strong>g>of</str<strong>on</strong>g> feeding<br />
cues. Upward or downward shifts in water temperature by approximately 10°C also inhibited<br />
inducible defense in F. vesiculosus. However, such shifts did not affect algal growth <str<strong>on</strong>g>and</str<strong>on</strong>g> were therefore<br />
the c<strong>on</strong>sequence <str<strong>on</strong>g>of</str<strong>on</strong>g> an impairment <str<strong>on</strong>g>of</str<strong>on</strong>g> specific defense-related comp<strong>on</strong>ents rather than <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
resource <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>, unless compensatory growth was given priority over defense.<br />
KEY WORDS: Alga–herbivore interacti<strong>on</strong> · Defense inducti<strong>on</strong> · Idotea · Seaweed–herbivore<br />
interacti<strong>on</strong> · Stress effects<br />
Resale or republicati<strong>on</strong> not permitted without written c<strong>on</strong>sent <str<strong>on</strong>g>of</str<strong>on</strong>g> the publisher<br />
may be either c<strong>on</strong>stitutive (stable in intensity) or regulated,<br />
i.e. deployed in the presence <str<strong>on</strong>g>of</str<strong>on</strong>g> grazers <str<strong>on</strong>g>and</str<strong>on</strong>g> re -<br />
duced when grazing stops. Resistance in general is the<br />
sum effect <str<strong>on</strong>g>of</str<strong>on</strong>g> various different traits reducing edibility,<br />
such as tissue toughness or presence <str<strong>on</strong>g>of</str<strong>on</strong>g> chemical<br />
deterrents. The known examples <str<strong>on</strong>g>of</str<strong>on</strong>g> regulated algal<br />
resistance against herbivores are almost exclusively<br />
based up<strong>on</strong> biochemical mechanisms (Jormalainen &<br />
H<strong>on</strong>kanen 2008), which affect palatability <str<strong>on</strong>g>and</str<strong>on</strong>g> may be<br />
either activated or <strong>induced</strong>. In the case <str<strong>on</strong>g>of</str<strong>on</strong>g> activati<strong>on</strong>,<br />
© Inter-Research 2011 · www.int-res.com<br />
OPEN PEN<br />
ACCESS CCESS
84<br />
tissue disrupti<strong>on</strong> by herbivores provokes a transfor -<br />
mati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> pre-formed metabolites into active defense<br />
compounds (Paul & Van Alstyne 1992, Cetrulo & Hay<br />
2000, Van Alstyne et al. 2001). Such activated defenses<br />
need to be stimulated <str<strong>on</strong>g>and</str<strong>on</strong>g> in this sense may be c<strong>on</strong>si -<br />
dered regulated. However, they are basically c<strong>on</strong>stitutive,<br />
because the defensive precursors are produced<br />
before herbivory occurs <str<strong>on</strong>g>and</str<strong>on</strong>g> have to be stored <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
maintained independently <str<strong>on</strong>g>of</str<strong>on</strong>g> the presence <str<strong>on</strong>g>of</str<strong>on</strong>g> grazers<br />
(Paul & Van Alstyne 1992, Karban & Baldwin 1997). As<br />
activated defense, <strong>induced</strong> defense needs stimulati<strong>on</strong>,<br />
but defense genes instead <str<strong>on</strong>g>of</str<strong>on</strong>g> defensive precursor compounds<br />
are activated. The occurrence <str<strong>on</strong>g>of</str<strong>on</strong>g> inducible<br />
chemical defenses following herbivory, or mechanical<br />
simulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> herbivory, is well documented for a large<br />
number <str<strong>on</strong>g>of</str<strong>on</strong>g> terrestrial plants (Karban & Baldwin 1997,<br />
Agrawal 2005). Recent research suggests that <strong>induced</strong><br />
resistance is also comm<strong>on</strong> am<strong>on</strong>g macroalgae (Toth &<br />
Pavia 2007, Jormalainen & H<strong>on</strong>kanen 2008, Rohde &<br />
Wahl 2008), <str<strong>on</strong>g>and</str<strong>on</strong>g> in some cases molecular signals may<br />
indicate the presence or activity <str<strong>on</strong>g>of</str<strong>on</strong>g> potential enemies to<br />
the alga <str<strong>on</strong>g>and</str<strong>on</strong>g> induce a de novo synthesis <str<strong>on</strong>g>of</str<strong>on</strong>g> defensive<br />
compounds (Coleman et al. 2007).<br />
Several theories postulate selective advantages <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
<strong>induced</strong> defense (Agrawal & Karban 1999), e.g. where<br />
c<strong>on</strong>sumpti<strong>on</strong> pressure is variable (Karban & Baldwin<br />
1997). The gene-to-gene model predicts a reduced<br />
risk <str<strong>on</strong>g>of</str<strong>on</strong>g> enemy adaptati<strong>on</strong> to <strong>induced</strong> defensive traits<br />
(Keen 1990), while the cost-allocati<strong>on</strong> model postulates<br />
an energetic advantage when defenses are <strong>on</strong>ly<br />
produced when needed (Cr<strong>on</strong>in 2001). Defense costs<br />
are difficult to detect (Strauss et al. 2002) <str<strong>on</strong>g>and</str<strong>on</strong>g> their<br />
existence has been questi<strong>on</strong>ed (Mole 1994). However,<br />
a meta-analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> 88 studies investigating plantherbivore<br />
interacti<strong>on</strong>s found evidence <str<strong>on</strong>g>of</str<strong>on</strong>g> direct costs<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>stitutive <str<strong>on</strong>g>and</str<strong>on</strong>g> <strong>induced</strong> defense in 57% <str<strong>on</strong>g>and</str<strong>on</strong>g> 52%<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> all cases, respectively (Strauss et al. 2002). While<br />
numerous studies dem<strong>on</strong>strated defense inducti<strong>on</strong><br />
against herbivores in marine macroalgae in recent<br />
years (reviewed in Toth & Pavia 2007), so far n<strong>on</strong>e<br />
have rigorously dem<strong>on</strong>strate incurring costs (e.g. Pansch<br />
et al. 2009, Appelhans et al. 2010; but see Dworjanyn<br />
et al. 2006 for costs <str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>stitutive defense<br />
against fouling).<br />
Because regulated defenses are dynamic, they may<br />
be particularly pr<strong>on</strong>e to envir<strong>on</strong>mental <str<strong>on</strong>g>stress</str<strong>on</strong>g>. Numerous<br />
terrestrial studies have dem<strong>on</strong>strated interactive<br />
effects <str<strong>on</strong>g>of</str<strong>on</strong>g> envir<strong>on</strong>mental <str<strong>on</strong>g>and</str<strong>on</strong>g> biotic factors <strong>on</strong> plant<br />
performance, but corresp<strong>on</strong>ding marine work is scarce<br />
(Dethier et al. 2005). The abiotic envir<strong>on</strong>ment <str<strong>on</strong>g>of</str<strong>on</strong>g>ten<br />
determines the resources that are available to an<br />
organism. A reducti<strong>on</strong> in resource availability can<br />
result either from direct <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> or indirectly from<br />
the <str<strong>on</strong>g>disruptive</str<strong>on</strong>g> physiological effects <str<strong>on</strong>g>of</str<strong>on</strong>g> extreme envir<strong>on</strong>mental<br />
c<strong>on</strong>diti<strong>on</strong>s (Dethier et al. 2005). Both disrup-<br />
Mar Ecol Prog Ser 427: 83–94, 2011<br />
tive <str<strong>on</strong>g>stress</str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>stress</str<strong>on</strong>g> could therefore affect<br />
the macroalgal capacity to induce defenses — if they<br />
are costly <str<strong>on</strong>g>and</str<strong>on</strong>g> if resource shortage is not buffered by<br />
energy stores or re-allocati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> resources from other<br />
processes such as growth. In the present study, we<br />
investigated the effects <str<strong>on</strong>g>of</str<strong>on</strong>g> both <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>stress</str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
<str<strong>on</strong>g>disruptive</str<strong>on</strong>g> <str<strong>on</strong>g>stress</str<strong>on</strong>g> <strong>on</strong> <strong>induced</strong> defense in the rockweed<br />
Fucus vesiculosus, <str<strong>on</strong>g>and</str<strong>on</strong>g> we hypothesized that <str<strong>on</strong>g>stress</str<strong>on</strong>g><br />
inflicted by light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> <str<strong>on</strong>g>disruptive</str<strong>on</strong>g> temperature<br />
shifts weakens the algal defensive performance.<br />
Fucus vesiculosus occurs in boreal <str<strong>on</strong>g>and</str<strong>on</strong>g> cold temperate<br />
z<strong>on</strong>es <str<strong>on</strong>g>of</str<strong>on</strong>g> the north Atlantic <str<strong>on</strong>g>and</str<strong>on</strong>g> is the main macroalgal<br />
c<strong>on</strong>stituent <str<strong>on</strong>g>of</str<strong>on</strong>g> the upper littoral z<strong>on</strong>e in the western<br />
Baltic (Rönnbäck et al. 2007). Several abiotic <str<strong>on</strong>g>stress</str<strong>on</strong>g>es<br />
are comm<strong>on</strong> in this habitat, <str<strong>on</strong>g>and</str<strong>on</strong>g> some <str<strong>on</strong>g>of</str<strong>on</strong>g> them have<br />
been predicted to increase in the course <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>on</strong>going<br />
climate change. According to most climate-change<br />
scenarios, <str<strong>on</strong>g>stress</str<strong>on</strong>g> caused by high temperature, high<br />
nutrient load, fluctuating salinity, <str<strong>on</strong>g>and</str<strong>on</strong>g> low light will<br />
increase (IPCC Core Writing Team et al. 2007, BACC<br />
Author Team 2008). Presumably due to increased light<br />
<str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> (resulting from a combined l<strong>on</strong>g-term effect<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> eutrophicati<strong>on</strong> favoring plankt<strong>on</strong> blooms <str<strong>on</strong>g>and</str<strong>on</strong>g> epi -<br />
biosis), F. vesiculosus has already retreated from the<br />
deeper parts <str<strong>on</strong>g>of</str<strong>on</strong>g> its distributi<strong>on</strong> range in the western<br />
Baltic, which 35 yr ago extended to a depth <str<strong>on</strong>g>of</str<strong>on</strong>g> 10 m <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
nowadays goes <strong>on</strong>ly to depths shallower than 2 to 3 m<br />
(Vogt & Schramm 1991). However, in the western<br />
Baltic, F. vesiculosus shows positive growth to a depth<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> 5 to 6 m in summer at least (Rohde et al. 2008, Wahl<br />
et al. 2010) <str<strong>on</strong>g>and</str<strong>on</strong>g> is capable <str<strong>on</strong>g>of</str<strong>on</strong>g> tolerating periods <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
severe light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> weeks to m<strong>on</strong>ths due to its<br />
capacity to store assimilated carb<strong>on</strong> in the form <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
mannitol <str<strong>on</strong>g>and</str<strong>on</strong>g> polysaccharides such as laminaran or<br />
alginate (Bidwell et al. 1972, Lehvo et al. 2001,<br />
Obluchinskaya et al. 2002). Prol<strong>on</strong>ged winter periods<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> occur not <strong>on</strong>ly north <str<strong>on</strong>g>of</str<strong>on</strong>g> the Arctic circle<br />
(Voskoboinikov et al. 2006), but also in the western<br />
Baltic, where mean light intensities at the lower distributi<strong>on</strong><br />
limit <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus fall below the light compensati<strong>on</strong><br />
point <str<strong>on</strong>g>of</str<strong>on</strong>g> photosynthesis from the end <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
October to mid-March (Wahl et al. 2010). During such<br />
c<strong>on</strong>diti<strong>on</strong>s, the tissue c<strong>on</strong>centrati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> mannitol <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
alginate in F. vesiculosus drops by 60 to 70%, while net<br />
growth may c<strong>on</strong>tinue under a net energy deficit for up<br />
to 2 mo (Lehvo et al. 2001, Obluchinskaya et al. 2002).<br />
Thus, the disappearance <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus from the<br />
depth range between 3 <str<strong>on</strong>g>and</str<strong>on</strong>g> 5 m requires additi<strong>on</strong>al<br />
explanati<strong>on</strong>s other than the direct light-reducti<strong>on</strong><br />
effect.<br />
Besides light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>, other potential abiotic<br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g>ors for Fucus vesiculosus are the <strong>on</strong>going <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
predicted shifts in temperature <str<strong>on</strong>g>and</str<strong>on</strong>g> its fluctuati<strong>on</strong>s.<br />
While 20°C is the highest water temperature that we<br />
find for periods l<strong>on</strong>ger than weeks within the natural
distributi<strong>on</strong> range <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus (Lüning 1990),<br />
water temperature is already close to this limit in the<br />
upper 5 m <str<strong>on</strong>g>of</str<strong>on</strong>g> the western Baltic from June through<br />
August (M. Wahl unpubl.) <str<strong>on</strong>g>and</str<strong>on</strong>g> is predicted to rise by<br />
3 to 5°C in the course <str<strong>on</strong>g>of</str<strong>on</strong>g> this century (BACC Author<br />
Team 2008). Moreover, F. vesiculosus may already<br />
experience ex tremely warm (30 to 40°C) <str<strong>on</strong>g>and</str<strong>on</strong>g> fluctuating<br />
c<strong>on</strong>diti<strong>on</strong>s during periods <str<strong>on</strong>g>of</str<strong>on</strong>g> air exposure in summer<br />
(Pears<strong>on</strong> et al. 2009 for Portugal <str<strong>on</strong>g>and</str<strong>on</strong>g> Cornwall,<br />
Wahl et al. 2010 for the western Baltic). Thermal<br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g> may either impact F. vesiculosus directly or<br />
affect its biotic interacti<strong>on</strong>s (Wahl et al. 2010), e.g. by<br />
provoking changes in its palatability or antifeeding<br />
protecti<strong>on</strong>.<br />
Various aspects <str<strong>on</strong>g>of</str<strong>on</strong>g> the defensive mechanisms in<br />
Fucus vesiculosus have been studied since the report<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> antifeeding properties by Geiselman & McC<strong>on</strong>nell<br />
(1981). F. vesiculosus induces defenses in resp<strong>on</strong>se to<br />
clipping (Van Alstyne 1988, Yates & Peckol 1993,<br />
Hemmi et al. 2004), as well as in resp<strong>on</strong>se to natural<br />
herbivory by its main c<strong>on</strong>sumer in the western Baltic,<br />
the isopod Idotea baltica (Rohde et al. 2004). I. baltica<br />
grazing results in reduced palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus<br />
to this omnivore, <str<strong>on</strong>g>and</str<strong>on</strong>g> this effect is due to a changed<br />
chemical compositi<strong>on</strong>, dem<strong>on</strong>strated by palatability<br />
tests <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus using freeze-dried <str<strong>on</strong>g>and</str<strong>on</strong>g> pelleted<br />
material (Rohde et al. 2004), which is devoid <str<strong>on</strong>g>of</str<strong>on</strong>g> all thallus<br />
structure.<br />
The effect <str<strong>on</strong>g>of</str<strong>on</strong>g> nutrient <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> (e.g. Yates & Peckol<br />
1993, Pavia & Brock 2000), as well as <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>disruptive</str<strong>on</strong>g><br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g>es such as UV radiati<strong>on</strong> (Cr<strong>on</strong>in & Hay 1996,<br />
Pavia et al. 1997) or desiccati<strong>on</strong> (Dethier et al. 2005), <strong>on</strong><br />
macroalgal defense has been investigated in a few<br />
studies. The results are somewhat c<strong>on</strong>troversial, both<br />
finding <str<strong>on</strong>g>and</str<strong>on</strong>g> refuting <str<strong>on</strong>g>stress</str<strong>on</strong>g> effects <strong>on</strong> defense. It must<br />
be noted that in most <str<strong>on</strong>g>of</str<strong>on</strong>g> these studies, tissue c<strong>on</strong>centrati<strong>on</strong>s<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> phlorotannins were used as a proxy <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong><br />
defense. However, Idotea baltica, like many other<br />
marine c<strong>on</strong>sumers <str<strong>on</strong>g>of</str<strong>on</strong>g> algae (Targett & Arnold 1998), is<br />
not deterred by phlorotannin (Jormalainen et al. 2001)<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> grows well when fed with Fucus vesiculosus rich<br />
in phlorotannin (Hemmi & Jormalainen 2004). As with<br />
most other alga-herbivore interacti<strong>on</strong>s, the relevant<br />
defensive compounds in the interacti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus<br />
with I. baltica are still unknown. Moreover, a<br />
reduced palatability may not <strong>on</strong>ly result from in -<br />
creased c<strong>on</strong>centrati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> defensive compounds, but<br />
also from lower c<strong>on</strong>centrati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> feeding cues, which<br />
again are unknown in most instances. C<strong>on</strong>sequently, a<br />
direct measurement <str<strong>on</strong>g>of</str<strong>on</strong>g> palatability is necessary when<br />
assessing the trade-<str<strong>on</strong>g>of</str<strong>on</strong>g>f between defensive costs <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g>.<br />
We therefore analyzed the effect <str<strong>on</strong>g>of</str<strong>on</strong>g> Idotea baltica<br />
grazing at different naturally occurring <str<strong>on</strong>g>stress</str<strong>on</strong>g> levels,<br />
from weak to severe, <strong>on</strong> the subsequent palatability<br />
Weinberger et al.: Stress modulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong> defense 85<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus to I. baltica. To distinguish<br />
between <str<strong>on</strong>g>stress</str<strong>on</strong>g> effects <strong>on</strong> overall palatability <str<strong>on</strong>g>and</str<strong>on</strong>g> <strong>on</strong><br />
chemical determinants <str<strong>on</strong>g>of</str<strong>on</strong>g> palatability, we ran feeding<br />
assays quantifying the preference <str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica for<br />
either live F. vesiculosus (characterized by mechanical<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> chemical properties) or for pelleted F. vesiculosus<br />
(characterized by chemical properties <strong>on</strong>ly). We<br />
(1) compared the inducibility <str<strong>on</strong>g>of</str<strong>on</strong>g> changes in both types<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> palatability, <str<strong>on</strong>g>and</str<strong>on</strong>g> we will call such changes ‘in -<br />
duced defense’. We assessed the effect <str<strong>on</strong>g>of</str<strong>on</strong>g> light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g><br />
up<strong>on</strong> (2) photosynthesis <str<strong>on</strong>g>and</str<strong>on</strong>g> (3) food quality<br />
(mannitol c<strong>on</strong>tent <str<strong>on</strong>g>and</str<strong>on</strong>g> C:N ratio) <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus. We<br />
also assessed the effects <str<strong>on</strong>g>of</str<strong>on</strong>g> (4) light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
(5) previous temperature shifts up<strong>on</strong> <strong>induced</strong> defense<br />
in F. vesiculosus. We present the findings from a<br />
series <str<strong>on</strong>g>of</str<strong>on</strong>g> experiments, <str<strong>on</strong>g>and</str<strong>on</strong>g> evaluate feeding assays<br />
based up<strong>on</strong> effect sizes, in order to facilitate comparis<strong>on</strong>s<br />
am<strong>on</strong>g experiments.<br />
MATERIALS AND METHODS<br />
All Fucus vesiculosus individuals used were collected<br />
from a rocky shore in the Kiel Fjord, western<br />
Baltic (54° 26’ N, 10° 11’ E), where they form dense,<br />
almost m<strong>on</strong>ospecific st<str<strong>on</strong>g>and</str<strong>on</strong>g>s in the first meter below<br />
the water surface. The algae were transferred in coolers<br />
from the upper subtidal z<strong>on</strong>e (0.2 to 0.7 m) to the<br />
laboratory, freed from grazers, <str<strong>on</strong>g>and</str<strong>on</strong>g> maintained at<br />
15°C in aerated seawater until required (
86<br />
Biosciences). For the highest light level, reflectors<br />
were installed above the fluorescent tubes. For lower<br />
light levels, either no reflectors were installed, the elevati<strong>on</strong><br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> the lamps over the aquarium was increased,<br />
or a window screen was mounted be tween the lights<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> aquaria. For complete preventi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> irradiati<strong>on</strong>,<br />
aquaria were covered with black plastic sheet. The<br />
light:dark period was 12:12 h in experiments c<strong>on</strong>ducted<br />
in winter (October to March) <str<strong>on</strong>g>and</str<strong>on</strong>g> 16:8 h in<br />
experiments c<strong>on</strong>ducted in summer (April to September).<br />
The daily mean <str<strong>on</strong>g>of</str<strong>on</strong>g> photosynthetically active radiati<strong>on</strong><br />
(PAR) was calculated as:<br />
PAR × Light exposure time (h) / 24 h (2)<br />
For an overview <str<strong>on</strong>g>of</str<strong>on</strong>g> the light <str<strong>on</strong>g>and</str<strong>on</strong>g> temperature combinati<strong>on</strong>s<br />
that were tested in the different defenseinducti<strong>on</strong><br />
experiments, see Table 1.<br />
At the beginning <str<strong>on</strong>g>of</str<strong>on</strong>g> each defense-inducti<strong>on</strong> experiment,<br />
6 to 12 Fucus vesiculosus individuals (for the<br />
Mar Ecol Prog Ser 427: 83–94, 2011<br />
Table 1. Defense-inducti<strong>on</strong> experiments. Sea surface temperature (SST) is the<br />
mean water temperature (recorded in intervals <str<strong>on</strong>g>of</str<strong>on</strong>g> 8 min) during 2 wk prior to the<br />
collecti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus. Corresp<strong>on</strong>dingly, ambient photosynthetically<br />
active radiati<strong>on</strong> (PAR) is the mean PAR reaching the sea surface during these<br />
2 wk (also recorded in intervals <str<strong>on</strong>g>of</str<strong>on</strong>g> 8 min during day <str<strong>on</strong>g>and</str<strong>on</strong>g> night). Temperature<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> mean PAR are the c<strong>on</strong>diti<strong>on</strong>s during defense inducti<strong>on</strong>. n: number <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
replicates (individual F. vesiculosus specimens that were treated)<br />
M<strong>on</strong>th SST Ambient Treat- Temp. Mean Feeding n<br />
(°C) PAR ment (°C) PAR assay<br />
(µE m –2 s –1 ) no. (µE m –2 s –1 )<br />
Mar 2006 0.8 95.5 1 15 37.5 Live 12<br />
2 15 15 Live 12<br />
3 20 37.5 Live 12<br />
4 20 15 Live 12<br />
Jan 2007 6.5 22.9 5 15 40 Live 8<br />
6 15 25 Live 8<br />
7 15 10 Live 8<br />
Apr 2007 9.2 223.8 8 15 40 Live 8<br />
9 15 25 Live 8<br />
10 15 5 Live 8<br />
May 2007 10.5 470.2 11 15 37.5 Pellet 8<br />
12 15 5 Pellet 8<br />
May 2008 13.7 594.7 13 8 46.7 Live + pellet 8<br />
14 12 46.7 Live + pellet 8<br />
15 16 46.7 Live + pellet 8<br />
16 21 46.7 Live + pellet 8<br />
17 23 46.7 Live + pellet 8<br />
Aug 2008 18.7 333.5 18 8 46.7 Live + pellet 8<br />
19 11 46.7 Live + pellet 8<br />
20 15 46.7 Live + pellet 8<br />
21 20 46.7 Live + pellet 8<br />
22 22 46.7 Live + pellet 8<br />
Feb–Mar 2.2 92.7 23 15 0 Live + pellet 6<br />
2009 24 15 15 Live + pellet 6<br />
25 15 32.5 Live + pellet 6<br />
26 15 62 Live + pellet 6<br />
exact number <str<strong>on</strong>g>of</str<strong>on</strong>g> replicates, see Table 1) <str<strong>on</strong>g>of</str<strong>on</strong>g> equal size<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> without severe grazing damage or epibi<strong>on</strong>ts were<br />
collected (1 algal individual was comprised <str<strong>on</strong>g>of</str<strong>on</strong>g> the tissue<br />
growing from a single holdfast). They were divi -<br />
ded into a sufficient amount <str<strong>on</strong>g>of</str<strong>on</strong>g> comparable apical<br />
pieces <str<strong>on</strong>g>of</str<strong>on</strong>g> 4 to 5 g that each individual could be incubated<br />
both in the presence <str<strong>on</strong>g>and</str<strong>on</strong>g> absence <str<strong>on</strong>g>of</str<strong>on</strong>g> Idotea<br />
baltica under each light <str<strong>on</strong>g>and</str<strong>on</strong>g> temperature c<strong>on</strong>diti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> a<br />
given experiment.<br />
Defense inducti<strong>on</strong> was inferred from the feeding<br />
preference <str<strong>on</strong>g>of</str<strong>on</strong>g> Idotea baltica am<strong>on</strong>g Fucus vesiculosus<br />
individuals that were previously exposed or unexposed<br />
to I. baltica. To assess this, pieces from each<br />
F. vesiculosus individual were r<str<strong>on</strong>g>and</str<strong>on</strong>g>omly distributed to<br />
the pairs <str<strong>on</strong>g>of</str<strong>on</strong>g> aquaria in all light <str<strong>on</strong>g>and</str<strong>on</strong>g> temperature c<strong>on</strong>diti<strong>on</strong>s<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> allowed to acclimatize for 3 d under the given<br />
c<strong>on</strong>diti<strong>on</strong>s. After acclimatizati<strong>on</strong>, inducti<strong>on</strong> was initiated.<br />
To this end, <strong>on</strong>e aquarium <str<strong>on</strong>g>of</str<strong>on</strong>g> a replicate pair <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
aquaria under each treatment combinati<strong>on</strong> received a<br />
defined number <str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica individu-<br />
als (5 to 8 in different experiments,<br />
depending <strong>on</strong> the size <str<strong>on</strong>g>of</str<strong>on</strong>g> the animals<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> corresp<strong>on</strong>ding to approximately<br />
35 mg dry weight in all experiments),<br />
while the sec<strong>on</strong>d aquarium was left<br />
grazer-free. Grazers <str<strong>on</strong>g>and</str<strong>on</strong>g> abiotic <str<strong>on</strong>g>stress</str<strong>on</strong>g>ors<br />
or <str<strong>on</strong>g>stress</str<strong>on</strong>g> combinati<strong>on</strong>s were<br />
allowed to act for the following 14 d.<br />
Net biomass change during the<br />
treatment phase was quantified as<br />
wet-weight change. For this purpose,<br />
algal pieces from aquaria with <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
without grazers were carefully blotted<br />
dry <str<strong>on</strong>g>and</str<strong>on</strong>g> weighed to the nearest 0.001 g<br />
at both the beginning <str<strong>on</strong>g>and</str<strong>on</strong>g> end <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />
trial.<br />
For the analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> C:N ratio <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
mannitol c<strong>on</strong>tent, Fucus vesiculosus<br />
pieces from aquaria with <str<strong>on</strong>g>and</str<strong>on</strong>g> without<br />
grazers were frozen (–20°C), freezedried,<br />
ground in a cooled mill (IKA),<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> stored in a freezer (–20°C). The<br />
C:N ratio was analyzed according to<br />
Sharp (1974) using a Carlo Erba NA-<br />
1500-CNS-analyzer. Mannitol was<br />
extracted <str<strong>on</strong>g>and</str<strong>on</strong>g> analyzed as described in<br />
Vas’kovs kii & Isai (1972), with the difference<br />
that periodate oxidati<strong>on</strong> was<br />
stopped after 10 s.<br />
Feeding assays. After the treatment<br />
phase, the palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus<br />
exposed versus unexposed to<br />
grazing was compared in 2-way choice<br />
feeding assays, using naive Idotea<br />
baltica as a grazer. Two different
assays were used in this test phase. In <strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> these<br />
assays, F. vesiculosus was tested alive (‘live assay’),<br />
while in the sec<strong>on</strong>d assay F. vesiculosus was <str<strong>on</strong>g>of</str<strong>on</strong>g>fered as<br />
food pellets (‘pellet assay’).<br />
The live assay was c<strong>on</strong>ducted as follows. Grazed<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> ungrazed Fucus vesiculosus pieces (<strong>on</strong>e piece <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
each) from the same individual alga <str<strong>on</strong>g>and</str<strong>on</strong>g> light/<br />
temperature c<strong>on</strong>diti<strong>on</strong> were carefully blotted dry,<br />
weighed, <str<strong>on</strong>g>and</str<strong>on</strong>g> transferred to a 2.9 l aquarium c<strong>on</strong>taining<br />
seawater, to which a defined number <str<strong>on</strong>g>of</str<strong>on</strong>g> Idotea<br />
baltica were added (3 to 5 in different experiments,<br />
depending <strong>on</strong> the size <str<strong>on</strong>g>of</str<strong>on</strong>g> the animals <str<strong>on</strong>g>and</str<strong>on</strong>g> corresp<strong>on</strong>ding<br />
to approximately 20 mg <str<strong>on</strong>g>of</str<strong>on</strong>g> dry weight in all<br />
experiments). Additi<strong>on</strong>al grazed <str<strong>on</strong>g>and</str<strong>on</strong>g> ungrazed algal<br />
pieces (<strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> each) were weighed <str<strong>on</strong>g>and</str<strong>on</strong>g> transferred to<br />
another aquarium to serve as c<strong>on</strong>trols for autogenic<br />
changes in mass during the bioassay (Peters<strong>on</strong> &<br />
Renaud 1989). The algal pieces were reweighed after<br />
3 d <str<strong>on</strong>g>and</str<strong>on</strong>g> the biomass c<strong>on</strong>sumed was calculated as:<br />
Biomass c<strong>on</strong>sumed = T0 × (Cf/C0) – Tf (3)<br />
where T0 <str<strong>on</strong>g>and</str<strong>on</strong>g> Tf were wet weights <str<strong>on</strong>g>of</str<strong>on</strong>g> the algae before<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> after the feeding trials, <str<strong>on</strong>g>and</str<strong>on</strong>g> C0 <str<strong>on</strong>g>and</str<strong>on</strong>g> Cf were the<br />
weights <str<strong>on</strong>g>of</str<strong>on</strong>g> the growth c<strong>on</strong>trols; i.e. Cf/Co represents<br />
autogenic changes in mass (Sotka et al. 2002).<br />
For the pellet assay, grazed <str<strong>on</strong>g>and</str<strong>on</strong>g> ungrazed algal<br />
pieces from the same individual <str<strong>on</strong>g>and</str<strong>on</strong>g> light/temperature<br />
c<strong>on</strong>diti<strong>on</strong> were frozen, lyophilized, <str<strong>on</strong>g>and</str<strong>on</strong>g> ground<br />
for 2 min in a cooled mill (IKA). The algal powder<br />
was stored in airtight plastic tubes in a freezer<br />
(–20°C) until food pellets were prepared as follows:<br />
180 mg <str<strong>on</strong>g>of</str<strong>on</strong>g> agar (Carl Roth) were mixed with 2.5 ml <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
dei<strong>on</strong>ized water <str<strong>on</strong>g>and</str<strong>on</strong>g> heated to boiling in a microwave<br />
oven. The diluted agar was then poured into a mixture<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> 0.5 g Fucus vesiculosus powder <str<strong>on</strong>g>and</str<strong>on</strong>g> 2 ml <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
dei<strong>on</strong>ized water, <str<strong>on</strong>g>and</str<strong>on</strong>g> after short stirring with a spatula,<br />
the mixture was poured <strong>on</strong>to wax paper that was<br />
covered by mosquito gauze (mesh size: 1 × 1 mm). A<br />
sec<strong>on</strong>d piece <str<strong>on</strong>g>of</str<strong>on</strong>g> wax paper was used as cover <str<strong>on</strong>g>and</str<strong>on</strong>g> the<br />
mixture was compressed with a panel until it gelled.<br />
After removal <str<strong>on</strong>g>of</str<strong>on</strong>g> the wax paper, the mixture <str<strong>on</strong>g>of</str<strong>on</strong>g> agar<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> F. vesiculosus powder had attached to the net,<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> squares <str<strong>on</strong>g>of</str<strong>on</strong>g> defined size (7 × 7 or 15 × 15 cells in<br />
different experiments) were cut out. Two pellets c<strong>on</strong>taining<br />
powder from grazed <str<strong>on</strong>g>and</str<strong>on</strong>g> ungrazed parts <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
the same individual <str<strong>on</strong>g>and</str<strong>on</strong>g> the same light/temperature<br />
c<strong>on</strong>diti<strong>on</strong> were placed into a Petri dish (Greiner; 9 cm<br />
diameter) after <strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> them had been marked by<br />
removal <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>on</strong>e corner (1 to 3 squares). We shifted the<br />
marking am<strong>on</strong>g treatments to r<str<strong>on</strong>g>and</str<strong>on</strong>g>omize its potential<br />
effect <strong>on</strong> grazer behavior. For each F. vesiculosus<br />
individual <str<strong>on</strong>g>and</str<strong>on</strong>g> light/temperature c<strong>on</strong>diti<strong>on</strong>, 3 Petri<br />
dishes were prepared in this way as pseudo-replicates.<br />
Averaging the grazer preferences across these<br />
3 dishes helped to reduce the variability am<strong>on</strong>g<br />
Weinberger et al.: Stress modulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong> defense<br />
87<br />
grazer individuals. One Idotea baltica individual <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
30 ml seawater were added to each Petri dish before<br />
they were incubated in darkness at 15°C. The incubati<strong>on</strong><br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> the Petri dishes was stopped individually<br />
when 25 to 75% <str<strong>on</strong>g>of</str<strong>on</strong>g> at least 1 <str<strong>on</strong>g>of</str<strong>on</strong>g> the 2 pellets had been<br />
eaten. Petri dishes where food detached from the<br />
mosquito net or no c<strong>on</strong>sumpti<strong>on</strong> took place within<br />
48 h were not evaluated. In all other Petri dishes, the<br />
c<strong>on</strong>sumed <str<strong>on</strong>g>and</str<strong>on</strong>g> remaining amounts <str<strong>on</strong>g>of</str<strong>on</strong>g> both pellets<br />
were quantified by counting the number <str<strong>on</strong>g>of</str<strong>on</strong>g> squares<br />
that had <str<strong>on</strong>g>and</str<strong>on</strong>g> had not been c<strong>on</strong>sumed by I. baltica,<br />
respectively.<br />
The pellet assay was also used in order to quantify<br />
the feeding preference <str<strong>on</strong>g>of</str<strong>on</strong>g> Idotea baltica for pellets<br />
c<strong>on</strong>taining <str<strong>on</strong>g>of</str<strong>on</strong>g> not c<strong>on</strong>taining mannitol (Roth). Pure agar<br />
is not c<strong>on</strong>sumed by I. baltica, <str<strong>on</strong>g>and</str<strong>on</strong>g> a sample <str<strong>on</strong>g>of</str<strong>on</strong>g> dried<br />
Ulva sp., a green macroalga devoid <str<strong>on</strong>g>of</str<strong>on</strong>g> mannitol (Kylin<br />
1915), was therefore used as main ingredient <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />
pellets instead <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus powder, <str<strong>on</strong>g>and</str<strong>on</strong>g> either<br />
mixed with mannitol or not.<br />
Net photosynthesis. Net photosynthesis under the<br />
different light treatments was estimated by measuring<br />
O 2 producti<strong>on</strong> with a Clark-type GOX20 oxygen electrode<br />
(Greisinger Electr<strong>on</strong>ic). The electrode was calibrated<br />
in seawater from the Kiel Fjord that was extensively<br />
bubbled with air or N 2, in order to obtain fully<br />
oxygenated or anoxic water, respectively. Aquaria<br />
c<strong>on</strong>taining 2.9 l <str<strong>on</strong>g>of</str<strong>on</strong>g> seawater, an oxygen electrode, <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
Fucus vesiculosus at a density <str<strong>on</strong>g>of</str<strong>on</strong>g> 10 g l –1 were sealed<br />
air-tight with adhesi<strong>on</strong> film (Melitta Toppits) <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
exposed at 15°C to the light intensities used in the<br />
treatment phase. The water in the aquaria was mixed<br />
using a magnetic stirrer. O 2 c<strong>on</strong>centrati<strong>on</strong>s in the water<br />
were recorded for 30 min, <str<strong>on</strong>g>and</str<strong>on</strong>g> rates <str<strong>on</strong>g>of</str<strong>on</strong>g> net producti<strong>on</strong><br />
or c<strong>on</strong>sumpti<strong>on</strong> were calculated.<br />
Data analysis. St<str<strong>on</strong>g>and</str<strong>on</strong>g>ardized effect sizes were calculated<br />
in order to allow for comparis<strong>on</strong>s am<strong>on</strong>g different<br />
defense-inducti<strong>on</strong> experiments. For the live assay,<br />
which records absolute amounts <str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>sumed biomass<br />
<strong>on</strong> a c<strong>on</strong>tinuous scale, the effect size g was calculated<br />
according to Hedges (1981) as:<br />
g = (T – C)/s* (4)<br />
where T <str<strong>on</strong>g>and</str<strong>on</strong>g> C represent the average biomass c<strong>on</strong>sumed<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> previously grazed <str<strong>on</strong>g>and</str<strong>on</strong>g> ungrazed Fucus<br />
vesiculosus, respectively, <str<strong>on</strong>g>and</str<strong>on</strong>g> s* is the pooled st<str<strong>on</strong>g>and</str<strong>on</strong>g>ard<br />
deviati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> both groups. The value g was biascorrected<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> 95% c<strong>on</strong>fidence intervals (CI) <str<strong>on</strong>g>of</str<strong>on</strong>g> g were<br />
c<strong>on</strong>structed (Hedges & Oilkin 1985).<br />
For the pellet assay, which recorded numbers <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
gauze squares c<strong>on</strong>sumed by Idotea baltica in the pellets<br />
<strong>on</strong> a n<strong>on</strong>-c<strong>on</strong>tinuous scale, the effect size was w,<br />
which is the approximate relative risk <str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>sumpti<strong>on</strong><br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> a given pellet type. To calculate this size, the gauze<br />
squares counted in different pseudo-replicates <str<strong>on</strong>g>of</str<strong>on</strong>g> the
88<br />
same individual <str<strong>on</strong>g>and</str<strong>on</strong>g> test c<strong>on</strong>diti<strong>on</strong> were summed<br />
(Fisher & van Belle 1993). The value w was then calculated<br />
as an odds ratio<br />
w = [(0.5 + t + )/(0.5 + t – )]/[(0.5 + c + )/(0.5 + c – )]<br />
(Fisher & van Belle 1993)<br />
where t represents numbers <str<strong>on</strong>g>of</str<strong>on</strong>g> squares <str<strong>on</strong>g>of</str<strong>on</strong>g> pellets<br />
c<strong>on</strong>taining grazed Fucus or mannitol; c represents<br />
the same for pellets c<strong>on</strong>taining ungrazed Fucus or no<br />
mannitol; + <str<strong>on</strong>g>and</str<strong>on</strong>g> – indicate squares that were eaten<br />
or not eaten, respectively. Binominal proporti<strong>on</strong> 95%<br />
CI <str<strong>on</strong>g>of</str<strong>on</strong>g> w were c<strong>on</strong>structed according to Fisher & van<br />
Belle (1993). CI <str<strong>on</strong>g>of</str<strong>on</strong>g> w that exclude 1 indicate a sig -<br />
nificant associati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> eaten <str<strong>on</strong>g>and</str<strong>on</strong>g> not-eaten mesh<br />
am<strong>on</strong>g both pellets <str<strong>on</strong>g>and</str<strong>on</strong>g> thus a significant preference<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica for <strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> these (χ 2 test, p = 0.05; Fisher<br />
& van Belle 1993). Both g <str<strong>on</strong>g>and</str<strong>on</strong>g> log(w) indicate a preference<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica for grazed F. vesiculosus when<br />
they are >0, while effect sizes
Fig. 1. Fucus vesiculosus. C<strong>on</strong>centrati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> mannitol in tissue<br />
after incubati<strong>on</strong> at different light intensities <str<strong>on</strong>g>and</str<strong>on</strong>g> in the presence<br />
(grazed) <str<strong>on</strong>g>and</str<strong>on</strong>g> absence (ungrazed) <str<strong>on</strong>g>of</str<strong>on</strong>g> Idotea baltica.<br />
Treatments 23 to 26 in Table 1; data are mean ± 95% CI.<br />
Different letters indicate light intensities that resulted in significantly<br />
different mannitol c<strong>on</strong>centrati<strong>on</strong>s (2-way ANOVA;<br />
Table S1 in the supplement)<br />
Weinberger et al.: Stress modulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong> defense<br />
Even in the absence <str<strong>on</strong>g>of</str<strong>on</strong>g> grazers, a significant<br />
weight loss <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus was observed at subcompensati<strong>on</strong><br />
irradiance (5 µE m –2 s –1 ; Fig. 2B). In c<strong>on</strong>trast,<br />
light intensities above the light-compensati<strong>on</strong><br />
point allowed for positive growth in ungrazed algae.<br />
Net growth in previously grazed algae at all light<br />
intensities tended to be lower than in previously<br />
ungrazed algae. This effect was significant at 25 <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
40 µE m –2 s –1 (Fig. 2B; Table S3A in the supplement). In<br />
the presence <str<strong>on</strong>g>of</str<strong>on</strong>g> grazers, F. vesiculosus always tended<br />
to lose biomass except for previously grazed algae (i.e.<br />
with <strong>induced</strong> defenses, see below), which gained biomass<br />
under the highest irradiance (Fig. 2C). The difference<br />
in wet-weight increase between <strong>induced</strong> <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
un<strong>induced</strong> F. vesiculosus at 40 µE m –2 s –1 was significant<br />
(p < 0.05) when the Wilcox<strong>on</strong> test was used. However,<br />
2-way ANOVA detected neither a significant<br />
overall effect <str<strong>on</strong>g>of</str<strong>on</strong>g> grazing during the treatment phase,<br />
nor a significant interactive effect <str<strong>on</strong>g>of</str<strong>on</strong>g> grazing <str<strong>on</strong>g>and</str<strong>on</strong>g> PAR<br />
(Table S3B in the supplement). Overall, preceding<br />
grazing (treatment phase) seemed to reduce Idotea<br />
baltica c<strong>on</strong>sumpti<strong>on</strong> during the test phase (Fig. 2D).<br />
Nearly no c<strong>on</strong>sumpti<strong>on</strong> was observed with previously<br />
Fig. 2. Fucus vesiculosus. (A) C:N ratios, (B,C) growth, <str<strong>on</strong>g>and</str<strong>on</strong>g> (D) palatability after 14 d <str<strong>on</strong>g>of</str<strong>on</strong>g> treatment at 15°C <str<strong>on</strong>g>and</str<strong>on</strong>g> at 3 different light<br />
intensities with <str<strong>on</strong>g>and</str<strong>on</strong>g> without the presence <str<strong>on</strong>g>of</str<strong>on</strong>g> Idotea baltica. Treatments 8 to 10 in Table 1; data are mean ± 95% CI. (A) C:N ratios<br />
at the end <str<strong>on</strong>g>of</str<strong>on</strong>g> the treatment phase. (B,C) Growth rates in the (B) absence or (C) presence <str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica after previous presence or absence<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> the grazer. (D) C<strong>on</strong>sumpti<strong>on</strong> by I. baltica in a 2-way choice assay. The grazers could choose between living thallus pieces<br />
that had <str<strong>on</strong>g>and</str<strong>on</strong>g> had not been exposed to I. baltica during the preincubati<strong>on</strong> period. Different letters indicate light intensities (A,C) or<br />
treatments (B) that are significantly different (2-way ANOVA; Tables S3 & S4 in the supplement). *Significantly different data<br />
after treatment with <str<strong>on</strong>g>and</str<strong>on</strong>g> without grazers (Wilcox<strong>on</strong> test, p < 0.05). PAR: photosynthetically active radiati<strong>on</strong><br />
89
90<br />
grazed F. vesiculosus irrespective <str<strong>on</strong>g>of</str<strong>on</strong>g> light c<strong>on</strong>diti<strong>on</strong>s.<br />
In c<strong>on</strong>trast, the c<strong>on</strong>sumpti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> previously ungrazed<br />
algae increased with irradiance. At 40 µE m –2 s –1 but<br />
not at lower irradiance, the preference for previously<br />
ungrazed F. vesiculosus relative to previously grazed<br />
F. vesiculosus was significant (Wilcox<strong>on</strong> test).<br />
Exposure <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus to relatively high light<br />
thus seemingly increases its attractiveness for Idotea<br />
baltica. An additi<strong>on</strong>al experiment was therefore c<strong>on</strong>ducted<br />
in order to test the hypothesis that I. baltica is<br />
attracted by mannitol, the main primary product <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
photosynthesis in F. vesiculosus. Food pellets c<strong>on</strong>taining<br />
as the basic reference ingredient ground Ulva sp.<br />
(naturally devoid <str<strong>on</strong>g>of</str<strong>on</strong>g> mannitol) <str<strong>on</strong>g>and</str<strong>on</strong>g> mannitol or no mannitol<br />
were <str<strong>on</strong>g>of</str<strong>on</strong>g>fered to I. baltica in 2-way choice assays<br />
(Fig. 3). Increasing mannitol c<strong>on</strong>centrati<strong>on</strong> resulted in<br />
increasing preference <str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica. This effect was significant<br />
(χ 2 test, p < 0.05) when mannitol was present at<br />
natural c<strong>on</strong>centrati<strong>on</strong>s (–17.5 mg g –1 ).<br />
Further experiments c<strong>on</strong>ducted at 15 to 16°C c<strong>on</strong>firmed<br />
that the defense inducibility is light-dependent<br />
(Fig. 4). A logistic dose-resp<strong>on</strong>se functi<strong>on</strong> could be<br />
fitted to these data (r 2 = 0.7316, p = 0.044; Fig. 4A).<br />
According to this functi<strong>on</strong>, the necessary mean daily<br />
PAR for inducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> a half-maximal reducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
palatability was 3.6 µE m –2 s –1 (95% CI: 0.6 to 20.5 µE<br />
m –2 s –1 ). Because <str<strong>on</strong>g>of</str<strong>on</strong>g> the data variability, no significant<br />
linear or logistic regressi<strong>on</strong> between the effect size<br />
obtained in assays with living Fucus vesiculosus <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
the mean daily light intensity during the preincubati<strong>on</strong><br />
was detected (Fig. 4B; p < 0.05). However, as in the<br />
pellet assay, the 2 lowest light intensities tested (0 <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
5 µE m –2 s –1 ) resulted in the 2 highest (least negative)<br />
effect sizes.<br />
Regressi<strong>on</strong> analysis further revealed that no significant<br />
correlati<strong>on</strong> between the effect sizes obtained with<br />
both bioassays <str<strong>on</strong>g>and</str<strong>on</strong>g> the mean outdoor light intensity in<br />
Fig. 3. Idotea baltica. Feeding preference for food pellets c<strong>on</strong>taining<br />
mannitol at different c<strong>on</strong>centrati<strong>on</strong>s, relative to pellets<br />
devoid <str<strong>on</strong>g>of</str<strong>on</strong>g> mannitol. Data are mean ± 95% CI<br />
Mar Ecol Prog Ser 427: 83–94, 2011<br />
Fig. 4. Fucus vesiculosus <str<strong>on</strong>g>and</str<strong>on</strong>g> Idotea baltica. Feeding preference<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica for <strong>induced</strong> F. vesiculosus that had been<br />
treated at 15°C at different light intensities. Effect sizes < 0 indicate<br />
reduced palatability after exposure to I. baltica. (A)<br />
F. vesiculosus was <str<strong>on</strong>g>of</str<strong>on</strong>g>fered freeze-dried in an artificial diet.<br />
Treatments 11, 12, 15, 20, <str<strong>on</strong>g>and</str<strong>on</strong>g> 23 to 26 in Table 1. Solid line<br />
represents the best fitting logistic dose-resp<strong>on</strong>se functi<strong>on</strong><br />
(dashed lines are 95% CI; n = 8). (B) F. vesiculosus was <str<strong>on</strong>g>of</str<strong>on</strong>g>fered<br />
alive. Mean ±95% CI. Treatments 1, 2, 5 to 10, 15, 20, <str<strong>on</strong>g>and</str<strong>on</strong>g> 23<br />
to 26 in Table 1. PAR: photosynthetically active radiati<strong>on</strong><br />
Kiel Fjord (ranging from 22.9 to 594.7 µE m –2 s –1 ;<br />
Table 1) during the 2 wk prior to Fucus vesiculosus collecti<strong>on</strong><br />
existed (data not shown).<br />
Temperature effects<br />
In a first experiment, Fucus vesiculosus was collected<br />
in March, when the mean ambient water temperature<br />
was 0.8°C. The material was treated with <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
without Idotea baltica, at mean daily light intensities <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
15 <str<strong>on</strong>g>and</str<strong>on</strong>g> 37.5 µE m –2 s –1 , <str<strong>on</strong>g>and</str<strong>on</strong>g> at each light c<strong>on</strong>diti<strong>on</strong> at<br />
15 <str<strong>on</strong>g>and</str<strong>on</strong>g> 20°C. ANOVA revealed that light affected<br />
growth significantly, while temperature had no overall<br />
effect, but interacted with light (Table S4A in the supplement;<br />
Fig. 5A). Irrespective <str<strong>on</strong>g>of</str<strong>on</strong>g> the light regime,<br />
I. baltica grazing during the treatment phase resulted<br />
in reduced palatability at 15°C, but not at 20°C
Fig. 5. Fucus vesiculosus. Growth rates during (A) <str<strong>on</strong>g>and</str<strong>on</strong>g> results<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> feeding assays after (B) treatment at different light <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
temperature combinati<strong>on</strong>s. Growth was measured as change<br />
in biomass (±95% CI) during the treatment phase. *Significant<br />
differences in the palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> grazed <str<strong>on</strong>g>and</str<strong>on</strong>g> ungrazed<br />
specimens (Wilcox<strong>on</strong> test, p < 0.05). Treatments 1 to 4 in<br />
Table 1. PAR: photosynthetically active radiati<strong>on</strong><br />
(Fig. 5B; Wilcox<strong>on</strong> test, p < 0.05). ANOVA c<strong>on</strong>firmed<br />
that temperature, but not light, affected the palatability<br />
reducti<strong>on</strong> after grazing significantly, while light<br />
interacted with temperature (Table S4B in the supplement).<br />
The experiment was repeated in May with Fucus<br />
vesiculosus that had been collected at 14°C. This time<br />
the algae were treated at <strong>on</strong>ly <strong>on</strong>e light c<strong>on</strong>diti<strong>on</strong><br />
(mean daily PAR: 35 µE m –2 s –1 ), but over a larger temperature<br />
range. In order to exclude possible temperature<br />
effects during the subsequent 2-way choice feeding<br />
assay, they were <str<strong>on</strong>g>of</str<strong>on</strong>g>fered in pelleted form at a<br />
st<str<strong>on</strong>g>and</str<strong>on</strong>g>ard temperature <str<strong>on</strong>g>of</str<strong>on</strong>g> 15°C. In this sec<strong>on</strong>d experiment,<br />
the algae were able to induce defenses between<br />
8 <str<strong>on</strong>g>and</str<strong>on</strong>g> 21°C, but not at 23°C (Fig. 6A). The experiment<br />
was repeated in the same way in August with F.<br />
vesiculosus that had been collected at a mean ambient<br />
water temperature <str<strong>on</strong>g>of</str<strong>on</strong>g> 20°C. This time the algae<br />
<strong>induced</strong> defenses between 15 <str<strong>on</strong>g>and</str<strong>on</strong>g> 22°C, but not at 8<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> 11°C (Fig. 6B).<br />
Irrespective <str<strong>on</strong>g>of</str<strong>on</strong>g> the ambient temperature during collecti<strong>on</strong><br />
(tested with material collected at 0.8, 6.5, 9.2,<br />
Weinberger et al.: Stress modulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong> defense<br />
Fig. 6. Fucus vesiculosus <str<strong>on</strong>g>and</str<strong>on</strong>g> Idotea baltica. Relative feeding<br />
preference (effect size log(w) ± 95% CI) <str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica for food<br />
pellets c<strong>on</strong>taining F. vesiculosus that had been collected at<br />
(A) 18.7°C (Treatments 18 to 22 in Table 1) <str<strong>on</strong>g>and</str<strong>on</strong>g> (B) 13.7°C<br />
(Treatments 14 to 17 in Table 1) <str<strong>on</strong>g>and</str<strong>on</strong>g> exposed or unexposed to<br />
I. baltica at identical photosynthetically active radiati<strong>on</strong> levels<br />
(46.5 µE m –2 s –1 ), but different temperatures. Effect sizes < 0<br />
indicate that previous exposure to I. baltica resulted in reduced<br />
palatability for I. baltica. *Significant differences in the<br />
palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> grazed <str<strong>on</strong>g>and</str<strong>on</strong>g> ungrazed F. vesiculosus (Wilcox<strong>on</strong><br />
test, p < 0.05)<br />
10.5, 14, <str<strong>on</strong>g>and</str<strong>on</strong>g> 20°C), Fucus vesiculosus was always<br />
capable <str<strong>on</strong>g>of</str<strong>on</strong>g> a defense resp<strong>on</strong>se when the treatment was<br />
c<strong>on</strong>ducted at a mean daily PAR <str<strong>on</strong>g>of</str<strong>on</strong>g> 35 to 40 µE m –2 s –1<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> a temperature <str<strong>on</strong>g>of</str<strong>on</strong>g> 15°C (data not shown).<br />
DISCUSSION<br />
Both light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>stress</str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> <str<strong>on</strong>g>disruptive</str<strong>on</strong>g> <str<strong>on</strong>g>stress</str<strong>on</strong>g><br />
resulting from temperature shifts may impair the<br />
capacity <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus for defense inducti<strong>on</strong><br />
against grazing by Idotea baltica. We found comparable<br />
results with both bioassay types employed, both<br />
using live algae or rec<strong>on</strong>stituted algae as feed. Each<br />
assay has certain advantages <str<strong>on</strong>g>and</str<strong>on</strong>g> disadvantages. The<br />
live assay allows for quantificati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the overall<br />
palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus, which may depend up<strong>on</strong><br />
chemical as well as structural traits. However, the possibility<br />
that F. vesiculosus changes its palatability<br />
91
92<br />
while the assay is c<strong>on</strong>ducted cannot be fully excluded,<br />
which probably accounts for the relatively large variability<br />
in the data. More stringent test c<strong>on</strong>diti<strong>on</strong>s are<br />
possible with the pellet assay, which results in less<br />
variability. However, this assay <strong>on</strong>ly quantifies chemical<br />
properties, since the algal structure is destroyed.<br />
The c<strong>on</strong>gruent results obtained with both assays suggest<br />
that variati<strong>on</strong>s in the palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus<br />
after different treatments must be primarily due to<br />
variable chemical defense <str<strong>on</strong>g>and</str<strong>on</strong>g>/or attracti<strong>on</strong>.<br />
In Fucus vesiculosus, the light-compensati<strong>on</strong> point <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
net photosynthesis varies with seas<strong>on</strong>. At the Danish<br />
Belt, a PAR <str<strong>on</strong>g>of</str<strong>on</strong>g> approximately 35 µE m –2 s –1 was re -<br />
quired to compensate for respirati<strong>on</strong> between April<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> September, compared to 15 µE m –2 s –1 between<br />
October <str<strong>on</strong>g>and</str<strong>on</strong>g> February (Middelboe et al. 2006). Corresp<strong>on</strong>ding<br />
with these data, respirati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus<br />
from Kiel was in the present study compensated at<br />
17 µE m –2 s –1 in early March, while positive growth in<br />
summer was impossible when the mean daily PAR was<br />
attracted I. baltica. Mannitol accumulati<strong>on</strong> during light<br />
exposure may therefore increase the attractiveness <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
F. vesiculosus. Such increased attracti<strong>on</strong> should result<br />
in increased feeding pressure <str<strong>on</strong>g>and</str<strong>on</strong>g> in an increased<br />
requirement <str<strong>on</strong>g>of</str<strong>on</strong>g> additi<strong>on</strong>al (<strong>induced</strong>) defense.<br />
The proposed scenario corresp<strong>on</strong>ds with the fact that<br />
Idotea baltica is virtually absent from Fucus vesiculosus<br />
in the German Baltic Sea <str<strong>on</strong>g>and</str<strong>on</strong>g> in winter, but not<br />
from other algae in the close vicinity <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus<br />
(Weinberger et al. 2008). Since the presence <str<strong>on</strong>g>of</str<strong>on</strong>g> I. bal -<br />
tica al<strong>on</strong>e is not sufficient to induce antifeeding<br />
defense, c<strong>on</strong>sumpti<strong>on</strong> is required (Rohde et al. 2004)<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> an absence <str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>sumpti<strong>on</strong> due to low palatability<br />
at low light c<strong>on</strong>diti<strong>on</strong>s should result in no triggering <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
defense. The questi<strong>on</strong> therefore arises whether anti -<br />
feeding defenses are not <strong>induced</strong> under light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g><br />
because the resources are lacking or because the<br />
necessity is not created. A definite answer will perhaps<br />
<strong>on</strong>ly be possible <strong>on</strong>ce the <strong>induced</strong> compounds have<br />
been identified <str<strong>on</strong>g>and</str<strong>on</strong>g> the resources <str<strong>on</strong>g>and</str<strong>on</strong>g> signaling pathways<br />
required for their producti<strong>on</strong> are known.<br />
In additi<strong>on</strong> to low-light <str<strong>on</strong>g>stress</str<strong>on</strong>g>, abrupt changes in<br />
water temperature in either directi<strong>on</strong> by 7 to 8°C<br />
impaired the ability <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus to induce<br />
defense. Absolute temperatures were not important.<br />
Given that approximately 20°C is the highest l<strong>on</strong>gterm<br />
water temperature within the natural distributi<strong>on</strong><br />
range <str<strong>on</strong>g>of</str<strong>on</strong>g> F. vesiculosus (Lüning 1990), we expected<br />
that upward shifts <str<strong>on</strong>g>of</str<strong>on</strong>g> temperature to 20°C or more<br />
should exert <str<strong>on</strong>g>stress</str<strong>on</strong>g>, while downward shifts from 19°C<br />
should release <str<strong>on</strong>g>stress</str<strong>on</strong>g>. However, both shifts impaired<br />
the capacity for <strong>induced</strong> defense. At the same time,<br />
these shifts did not prevent algal growth, which indicates<br />
that a possible resource depleti<strong>on</strong> due to <str<strong>on</strong>g>disruptive</str<strong>on</strong>g><br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g> was not as severe as under light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>.<br />
Possibly, abrupt temperature shifts caused the (temporary)<br />
dysfuncti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> specific enzymes or other cellular<br />
comp<strong>on</strong>ents relevant for defense inducti<strong>on</strong>. Apparently,<br />
short-term oscillati<strong>on</strong>s in temperature during air<br />
exposure do not definitely disrupt defense inducti<strong>on</strong> in<br />
F. vesiculosus, because this capacity is present in fieldcollected<br />
material even from the most shallow depths,<br />
where temperature fluctuati<strong>on</strong>s can be extreme.<br />
In c<strong>on</strong>clusi<strong>on</strong>, the present study indicates that the <strong>induced</strong><br />
defense <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus against its main c<strong>on</strong>sumer<br />
in the western Baltic Sea requires exceeding a<br />
minimum threshold <str<strong>on</strong>g>of</str<strong>on</strong>g> light <str<strong>on</strong>g>and</str<strong>on</strong>g> stable temperature c<strong>on</strong>diti<strong>on</strong>s.<br />
Induced defense against Idotea baltica is mainly<br />
employed during phases <str<strong>on</strong>g>of</str<strong>on</strong>g> str<strong>on</strong>g photosynthesis, when<br />
the tissue is rich in mannitol <str<strong>on</strong>g>and</str<strong>on</strong>g> attractive for the herbivore.<br />
During phases <str<strong>on</strong>g>of</str<strong>on</strong>g> light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>, <strong>induced</strong> defense<br />
is largely inhibited. However, this is compensated by reduced<br />
attracti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> I. baltica, due to a reduced c<strong>on</strong>tent <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
mannitol. F. vesiculosus thus appears capable <str<strong>on</strong>g>of</str<strong>on</strong>g> coping<br />
with its main c<strong>on</strong>sumer in the Baltic Sea even during pe-<br />
Weinberger et al.: Stress modulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong> defense<br />
riods <str<strong>on</strong>g>of</str<strong>on</strong>g> relatively severe light-<str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>stress</str<strong>on</strong>g>. Different<br />
from light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>, abrupt shifts <str<strong>on</strong>g>of</str<strong>on</strong>g> water temperature<br />
by 7°C or more rarely (if ever) occur in Fucus vesiculosis<br />
habitats. For this reas<strong>on</strong>, F. vesiculosus may not have<br />
evolved the capacity to compensate with alternative<br />
mechanisms for the disrupti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong> defense by<br />
temperature <str<strong>on</strong>g>stress</str<strong>on</strong>g>.<br />
Acknowledgements. K. David, A.-L. Lopez, <str<strong>on</strong>g>and</str<strong>on</strong>g> W. Weßels<br />
provided tremendous help in different experiments. This<br />
study was facilitated by a Deutsche Bundesstiftung Umwelt<br />
(DBU) fellowship to S.R.<br />
LITERATURE CITED<br />
93<br />
Agrawal AA (2005) Future directi<strong>on</strong>s in the study <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>induced</strong><br />
plant resp<strong>on</strong>ses to herbivory. Entomol Exp Appl 115:<br />
97–105<br />
Agrawal AA, Karban R (1999) Why <strong>induced</strong> defenses may be<br />
favored over c<strong>on</strong>stitutive strategies in plants. In: Tollrian<br />
R, Harvell C (eds) The ecology <str<strong>on</strong>g>and</str<strong>on</strong>g> evoluti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> inducible<br />
defenses. Princet<strong>on</strong> University Press, Princet<strong>on</strong>, NJ,<br />
p 45–61<br />
Appelhans YS, Lenz M, Medeiros HE, Perez da Gama BA,<br />
Pereira RC, Wahl M (2010) Stressed, but not defenceless:<br />
no obvious influence <str<strong>on</strong>g>of</str<strong>on</strong>g> irradiati<strong>on</strong> levels <strong>on</strong> antifeeding<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> antifouling defences <str<strong>on</strong>g>of</str<strong>on</strong>g> tropical macroalgae. Mar Biol<br />
157:1151–1159<br />
BACC Author Team (2008) Assessment <str<strong>on</strong>g>of</str<strong>on</strong>g> climate change for<br />
the Baltic Sea Basin. Springer-Verlag, Berlin<br />
Bidwell RGS, Percival E, Smestad B (1972) Photosynthesis <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
metabolism <str<strong>on</strong>g>of</str<strong>on</strong>g> marine algae. VIII. Incorporati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> 14 C into<br />
the polysaccharides metabolized by Fucus vesiculosus during<br />
pulse labelling experiments. Can J Bot 50:191–197<br />
Cetrulo GL, Hay ME (2000) Activated chemical defenses in<br />
tropical versus temperate seaweeds. Mar Ecol Prog Ser<br />
207:243–253<br />
Coleman RA, Ramchunder SJ, Moody AJ, Foggo A (2007) An<br />
enzyme in snail saliva induces herbivore-resistance in a<br />
marine alga. Funct Ecol 21:101–106<br />
Corotto FS, O’Brien MR (2002) Chemosensory stimuli for the<br />
walking legs <str<strong>on</strong>g>of</str<strong>on</strong>g> the crayfish Procambarus clarkia. J Chem<br />
Ecol 28:1117–1130<br />
Cr<strong>on</strong>in G (2001) Resource allocati<strong>on</strong> in seaweeds <str<strong>on</strong>g>and</str<strong>on</strong>g> marine<br />
invertebrates: chemical defense patterns in relati<strong>on</strong> to<br />
defense theories. In: McClintock J, Baker B (eds) Marine<br />
chemical ecology. CRC Press, Boca Rat<strong>on</strong>, FL, p 325–353<br />
Cr<strong>on</strong>in G, Hay ME (1996) Susceptibility to herbivores<br />
depends <strong>on</strong> recent history <str<strong>on</strong>g>of</str<strong>on</strong>g> both the plant <str<strong>on</strong>g>and</str<strong>on</strong>g> animal.<br />
Ecology 77:1531–1543<br />
Dethier MN, Williams SL, Freeman A (2005) Seaweeds under<br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g>: manipulated <str<strong>on</strong>g>stress</str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> herbivory affect critical lifehistory<br />
functi<strong>on</strong>s. Ecol M<strong>on</strong>ogr 75:403–418<br />
Dworjanyn SA, Wright JT, Paul NA, De Nys R, Steinberg PD<br />
(2006) Cost <str<strong>on</strong>g>of</str<strong>on</strong>g> chemical defence in the red alga Delisea<br />
pulchra. Oikos 113:13–22<br />
Fisher LD, van Belle G (1993) Biostatistics: a methodology for<br />
the health sciences. John Wiley & S<strong>on</strong>s, New York, NY<br />
Franke HD, Janke M (1998) Mechanisms <str<strong>on</strong>g>and</str<strong>on</strong>g> c<strong>on</strong>sequences <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
intra- <str<strong>on</strong>g>and</str<strong>on</strong>g> interspecific interference competiti<strong>on</strong> in Idotea<br />
baltica (Pallas) <str<strong>on</strong>g>and</str<strong>on</strong>g> Idotea emarginata (Fabricius) (Crustacea:<br />
Isopoda): a laboratory study <str<strong>on</strong>g>of</str<strong>on</strong>g> possible proximate<br />
causes <str<strong>on</strong>g>of</str<strong>on</strong>g> habitat segregati<strong>on</strong>. J Exp Mar Biol Ecol 227:1–21<br />
Geiselman JA, McC<strong>on</strong>nell OJ (1981) Polyphenols in brown<br />
algae Fucus vesiculosus <str<strong>on</strong>g>and</str<strong>on</strong>g> Ascophyllum nodosum:
94<br />
chemical defenses against the marine herbivorous snail,<br />
Littorina littorea. J Chem Ecol 7:1115–1133<br />
Hedges LV (1981) Distributi<strong>on</strong> theory for Glass’s estimator <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
effect size <str<strong>on</strong>g>and</str<strong>on</strong>g> related estimators. J Educ Stat 6:107–128<br />
Hedges LV, Oilkin I (1985) Statistical methods for metaanalysis.<br />
Academic Press, Orl<str<strong>on</strong>g>and</str<strong>on</strong>g>o, FL<br />
Hemmi A, Jormalainen V (2004) Geographic covariati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
chemical quality <str<strong>on</strong>g>of</str<strong>on</strong>g> the host alga Fucus vesiculosus with<br />
fitness <str<strong>on</strong>g>of</str<strong>on</strong>g> the herbivorous isopod Idotea baltica. Mar Biol<br />
145:759–768<br />
Hemmi A, H<strong>on</strong>kanen T, Jormalainen V (2004) Inducible resistance<br />
to herbivory in Fucus vesiculosus: durati<strong>on</strong>, spreading<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> variati<strong>on</strong> with nutrient availability. Mar Ecol Prog<br />
Ser 273:109–120<br />
IPCC Core Writing Team, Pachauri RK, Reisinger A (2007)<br />
Climate change 2007: synthesis report. C<strong>on</strong>tributi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
Working Groups I, II <str<strong>on</strong>g>and</str<strong>on</strong>g> III to the Fourth Assessment<br />
Report <str<strong>on</strong>g>of</str<strong>on</strong>g> the Intergovernmental Panel <strong>on</strong> Climate<br />
Change. IPCC Secretary, Geneva<br />
Jormalainen V, H<strong>on</strong>kanen T (2008) Macroalgal chemical<br />
defenses <str<strong>on</strong>g>and</str<strong>on</strong>g> their roles in structuring temperate marine<br />
communities. In: Amsler CD (ed) Algal chemical ecology.<br />
Springer-Verlag, Berlin, p 75–90<br />
Jormalainen V, H<strong>on</strong>kanen T, Heikkilä N (2001) Feeding preferences<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> performance <str<strong>on</strong>g>of</str<strong>on</strong>g> a marine isopod <strong>on</strong> seaweed<br />
hosts: cost <str<strong>on</strong>g>of</str<strong>on</strong>g> habitat specializati<strong>on</strong>. Mar Ecol Prog Ser<br />
220:219–230<br />
Karban R, Baldwin IT (1997) Induced resp<strong>on</strong>se to herbivory.<br />
University <str<strong>on</strong>g>of</str<strong>on</strong>g> Chicago Press, Chicago, IL<br />
Keen NT (1990) Gene-for-gene complementarity in plant<br />
pathogen interacti<strong>on</strong>s. Annu Rev Genet 24:447–463<br />
Kylin H (1915) Untersuchungen über die Biochemie der<br />
Meeresalgen. Hoppe-Seyler’s Z Physiol Chem 94:337–429<br />
Lehvo A, Bäck S, Kiirikki M (2001) Growth <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus<br />
L. (Phaeophyta) in the Northern Baltic proper: energy<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> nitrogen storage in seas<strong>on</strong>al envir<strong>on</strong>ment. Bot Mar<br />
44:345–350<br />
Lubchenco J, Gaines SD (1981) A unified approach to marine<br />
plant-herbivore interacti<strong>on</strong>s. 1. Populati<strong>on</strong>s <str<strong>on</strong>g>and</str<strong>on</strong>g> communities.<br />
Annu Rev Ecol Syst 12:405–437<br />
Lüning K (1990) Seaweeds: their envir<strong>on</strong>ment, biogeography<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> ecophysiology. John Wiley, New York, NY<br />
Middelboe AL, S<str<strong>on</strong>g>and</str<strong>on</strong>g>-Jensen K, Binzer T (2006) Highly predictable<br />
photosynthetic producti<strong>on</strong> in natural macroalgal<br />
communities from incoming <str<strong>on</strong>g>and</str<strong>on</strong>g> absorbed light. Oecologia<br />
150:464–476<br />
Mole S (1994) Trade-<str<strong>on</strong>g>of</str<strong>on</strong>g>fs <str<strong>on</strong>g>and</str<strong>on</strong>g> c<strong>on</strong>straints in plant-herbivore<br />
defense theory: a life-history perspective. Oikos 71:3–12<br />
Obluchinskaya ED, Voskoboinikov GM, Galynkin VA (2002)<br />
C<strong>on</strong>tents <str<strong>on</strong>g>of</str<strong>on</strong>g> alginic acid <str<strong>on</strong>g>and</str<strong>on</strong>g> fuccidan in Fucus algae <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />
Barents Sea. Appl Biochem Microbiol 38:186–188<br />
Pansch C, Cerda O, Lenz M, Wahl M, Thiel M (2009) C<strong>on</strong>sequences<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> light reducti<strong>on</strong> for anti-herbivore defense <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
bioactivity against mussels in for seaweed species from<br />
northern-central Chile. Mar Ecol Prog Ser 381:83–97<br />
Paul VJ, Van Alstyne KL (1992) Activati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> chemical<br />
defenses in the tropical green algae Halimeda spp. J Exp<br />
Mar Biol Ecol 160:191–203<br />
Pavia H, Brock E (2000) Extrinsic factors influencing phloro -<br />
tannin producti<strong>on</strong> in the brown alga Ascophyllum nodo -<br />
sum. Mar Ecol Prog Ser 193:285–294<br />
Pavia H, Cervin G, Lindgren A, Aberg P (1997) <str<strong>on</strong>g>Effects</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> UV-<br />
B radiati<strong>on</strong> <str<strong>on</strong>g>and</str<strong>on</strong>g> simulated herbivory <strong>on</strong> phlorotannins in<br />
the brown alga Ascophyllum nodosum. Mar Ecol Prog Ser<br />
157:139–146<br />
Pears<strong>on</strong> G, Lago-Lest<strong>on</strong> A, Mota C (2009) Frayed at the<br />
edges: selective pressure <str<strong>on</strong>g>and</str<strong>on</strong>g> adaptive resp<strong>on</strong>se to abiotic<br />
Editorial resp<strong>on</strong>sibility: Charles Peters<strong>on</strong>,<br />
Morehead City, North Carolina, USA<br />
Mar Ecol Prog Ser 427: 83–94, 2011<br />
<str<strong>on</strong>g>stress</str<strong>on</strong>g>ors are mismatched in low diversity edge populati<strong>on</strong>s.<br />
J Ecol 97:450–462<br />
Peters<strong>on</strong> CH, Renaud PE (1989) Analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> feeding preference<br />
experiments. Oecologia 80:82–86<br />
Rohde S, Wahl M (2008) Antifeeding defense in baltic<br />
macroalgae: inducti<strong>on</strong> by direct grazing versus waterborne<br />
cues. J Phycol 44:85–90<br />
Rohde S, Molis M, Wahl M (2004) Regulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> anti-herbivore<br />
defence by Fucus vesiculosus in resp<strong>on</strong>se to various<br />
cues. J Ecol 92:1011–1018<br />
Rohde S, Hiebenthal C, Wahl M, Karez R, Bisch<str<strong>on</strong>g>of</str<strong>on</strong>g> K (2008)<br />
Decreased depth distributi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus vesiculosus (Phaeophyceae)<br />
in the Western Baltic: effects <str<strong>on</strong>g>of</str<strong>on</strong>g> light deficiency<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> epibi<strong>on</strong>ts <strong>on</strong> growth <str<strong>on</strong>g>and</str<strong>on</strong>g> photosynthesis. Eur J Phycol<br />
43:143–150<br />
Rönnbäck P, Kautsky N, Pihl L, Troell M, Söderqvist T,<br />
Wennhage H (2007) Ecosystem goods <str<strong>on</strong>g>and</str<strong>on</strong>g> services from<br />
Swedish coastal habitats: identificati<strong>on</strong>, valuati<strong>on</strong>, <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
implicati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> ecosystem shifts. Ambio 36:534–544<br />
Sharp JH (1974) Improved analysis for particulate organic<br />
carb<strong>on</strong> <str<strong>on</strong>g>and</str<strong>on</strong>g> nitrogen from seawater. Limnol Oceanogr<br />
19:984–989<br />
Sotka EE, Taylor RB, Hay ME (2002) Tissue-specific inducti<strong>on</strong><br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> resistance to herbivores in a brown seaweed: the importance<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> direct grazing versus waterborne signals from<br />
grazed neighbors. J Exp Mar Biol Ecol 277:1–12<br />
Strauss YS, Rudgers JA, Lau JA, Irwin RE (2002) Direct <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
ecological costs <str<strong>on</strong>g>of</str<strong>on</strong>g> resistance to herbivory. Trends Ecol<br />
Evol 17:278–285<br />
Targett NM, Arnold TM (1998) Predicting the effects <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
brown algal phlorotannins <strong>on</strong> marine herbivores in tropical<br />
<str<strong>on</strong>g>and</str<strong>on</strong>g> temperate oceans. J Phycol 34:195–205<br />
Toth GB, Pavia H (2007) Induced herbivore resistance in seaweeds:<br />
a meta-analysis. J Ecol 95:425–434<br />
Van Alstyne KL (1988) Herbivore grazing increases polyphenolic<br />
defenses in the intertidal brown alga Fucus distichus.<br />
Ecology 69:655–663<br />
Van Alstyne KL, Dethier MN, Duggins D (2001) Spatial patterns<br />
in macroalgal chemical defenses. In: McClintock JB,<br />
Baker BJ (eds) Marine chemical ecology. CRC, Boca<br />
Rat<strong>on</strong>, FL, p 301–324<br />
Vas’kovskii VE, Isai SV (1972) Determinati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the amount<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> mannitol in brown seaweeds. Khimiya Prirodnykh<br />
Soedinenii 8(5):596–600. English translati<strong>on</strong> Chem Nat<br />
Comp :566–569<br />
Vogt H, Schramm W (1991) C<strong>on</strong>spicuous decline <str<strong>on</strong>g>of</str<strong>on</strong>g> Fucus in<br />
Kiel Bay (Western Baltic): What are the causes? Mar Ecol<br />
Prog Ser 69:189–194<br />
Voskoboinikov GM, Makarov MV, Ryzhik IV (2006) Changes<br />
in the compositi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> photosynthesis pigments <str<strong>on</strong>g>and</str<strong>on</strong>g> cellular<br />
structure <str<strong>on</strong>g>of</str<strong>on</strong>g> the brown algae Fucus vesiculosus L. <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
F. serratus L. from the Barents Sea during a prol<strong>on</strong>ged<br />
period <str<strong>on</strong>g>of</str<strong>on</strong>g> darkness. Russ J Mar Biol 32:20–27<br />
Wahl M, Shahnaz L, Dobretsov S, Saha M <str<strong>on</strong>g>and</str<strong>on</strong>g> others (2010)<br />
The ecology <str<strong>on</strong>g>of</str<strong>on</strong>g> antifouling resistance in the bladder wrack<br />
Fucus vesiculosus: patterns <str<strong>on</strong>g>of</str<strong>on</strong>g> micr<str<strong>on</strong>g>of</str<strong>on</strong>g>ouling <str<strong>on</strong>g>and</str<strong>on</strong>g> antimicrobial<br />
protecti<strong>on</strong>. Mar Ecol Prog Ser 411:33–48<br />
Weinberger F, Buchholz B, Karez R, Wahl M (2008) The invasive<br />
alga Gracilaria vermiculophylla in the Baltic Sea:<br />
adapti<strong>on</strong> to brackish water may compensate for light <str<strong>on</strong>g>limitati<strong>on</strong></str<strong>on</strong>g>.<br />
Aquat Biol 3:251–264<br />
White TCR (1984) The abundance <str<strong>on</strong>g>of</str<strong>on</strong>g> invertebrate herbivores<br />
in relati<strong>on</strong> to the availability <str<strong>on</strong>g>of</str<strong>on</strong>g> nitrogen in <str<strong>on</strong>g>stress</str<strong>on</strong>g>ed food<br />
plants. Oecologia 63:90–105<br />
Yates JL, Peckol P (1993) <str<strong>on</strong>g>Effects</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> nutrient availability <str<strong>on</strong>g>and</str<strong>on</strong>g><br />
herbivory <strong>on</strong> polyphenolics in the seaweed Fucus vesiculosus.<br />
Ecology 74:1757–1766<br />
Submitted: August 16, 2010; Accepted: January 17, 2010<br />
Pro<str<strong>on</strong>g>of</str<strong>on</strong>g>s received from author(s): March 18, 2011