A guide to the deep-water sponges of - NMFS Scientific Publications ...
A guide to the deep-water sponges of - NMFS Scientific Publications ...
A guide to the deep-water sponges of - NMFS Scientific Publications ...
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8 Pr<strong>of</strong>essional Paper <strong>NMFS</strong> 12<br />
Bering Sea each year – more than four times <strong>the</strong> weight<br />
<strong>of</strong> corals landed <strong>the</strong>re as fisheries bycatch (<strong>NMFS</strong> 5 ).<br />
All emergent epifauna are susceptible <strong>to</strong> disturbance<br />
from fishing gear (S<strong>to</strong>ne, 2006) and most species <strong>of</strong><br />
<strong>deep</strong>-<strong>water</strong> <strong>sponges</strong> are <strong>to</strong> some degree vulnerable <strong>to</strong><br />
disturbance (also see Hogg et al., 2010, for a recent<br />
review). Fishing operations affect <strong>the</strong> seafloor from<br />
depths <strong>of</strong> 27 m <strong>to</strong> about 1200 m in <strong>the</strong> Aleutian Islands,<br />
with most effort at depths shallower than 200 m (S<strong>to</strong>ne,<br />
2006). The degree <strong>to</strong> which a particular gear type affects<br />
sponge habitat depends on its configuration (i.e.,<br />
physical area <strong>of</strong> contact), operation (i.e., physical forces<br />
on <strong>the</strong> seafloor), spatial and temporal intensity <strong>of</strong> operation,<br />
seafloor bathymetry and substratum type, and<br />
<strong>the</strong> resiliency <strong>of</strong> <strong>sponges</strong> <strong>to</strong> disturbance. Both direct<br />
and indirect effects from fishing activities on <strong>sponges</strong><br />
likely occur. Direct effects include removal as bycatch,<br />
damage caused by physical contact, or detachment<br />
from <strong>the</strong> seafloor and translocation <strong>to</strong> unsuitable habitat.<br />
Indirect effects include increased vulnerability <strong>to</strong><br />
predation, especially for <strong>sponges</strong> detached from <strong>the</strong><br />
seafloor, and habitat alteration. Fur<strong>the</strong>rmore, <strong>the</strong>re<br />
is some evidence that reproduction is suppressed in<br />
damaged shallow-<strong>water</strong> scleractinian corals due <strong>to</strong> a<br />
reallocation <strong>of</strong> energy reserves <strong>to</strong> tissue repair and<br />
regeneration (Wahle, 1983), and similar effects may<br />
occur in <strong>sponges</strong>.<br />
Most <strong>of</strong> <strong>the</strong> fac<strong>to</strong>rs that control <strong>the</strong> degree <strong>to</strong> which<br />
<strong>sponges</strong> provide habitat structure are <strong>the</strong> same fac<strong>to</strong>rs<br />
that control <strong>the</strong> degree <strong>to</strong> which <strong>the</strong>y are vulnerable <strong>to</strong><br />
disturbance. For example, large species with arborescent<br />
growth forms are more likely <strong>to</strong> be contacted by<br />
passing fishing gear. Species such as Plakina tanaga have<br />
low vulnerability <strong>to</strong> disturbance due <strong>to</strong> <strong>the</strong>ir encrusting<br />
habitus and absence in areas where bot<strong>to</strong>m trawling is<br />
known <strong>to</strong> occur. Some species such as Poecillastra tenuilaminaris<br />
are highly vulnerable <strong>to</strong> disturbance due <strong>to</strong><br />
<strong>the</strong>ir large size and high relative abundance. Artemisina<br />
stipitata is moderately vulnerable <strong>to</strong> disturbance due <strong>to</strong><br />
its large size, erect form, and presence in areas where<br />
bot<strong>to</strong>m trawling and longline fishing are known <strong>to</strong> occur.<br />
Some <strong>sponges</strong>, for example those with holdfast<br />
structures ra<strong>the</strong>r than root-like attachment systems, may<br />
be more vulnerable <strong>to</strong> detachment, and it is unknown<br />
if intact but o<strong>the</strong>rwise undamaged <strong>sponges</strong> detached<br />
from <strong>the</strong> substrate (e.g., roller <strong>sponges</strong>; Reiswig, unpubl.<br />
data, 2010) can survive.<br />
The recovery rate <strong>of</strong> disturbed benthic ecosystems in<br />
Alaskan <strong>water</strong>s is <strong>of</strong> keen interest <strong>to</strong> fisheries managers<br />
but is still little more than conjecture due <strong>to</strong> limited<br />
5 National Marine Fisheries Service. 2004. Final programmatic<br />
supplemental groundfish environmental impact statement for Alaska<br />
groundfish fisheries. Alaska Region, NOAA, <strong>NMFS</strong>, P.O. Box<br />
21668, Juneau, AK 99802-1668.<br />
knowledge <strong>of</strong> species distribution and basic life his<strong>to</strong>ry<br />
processes. Rates <strong>of</strong> recovery will depend on growth rates<br />
and rates <strong>of</strong> sexual and asexual reproduction or speed <strong>of</strong><br />
regeneration, which are unknown for most species. Two<br />
key components <strong>of</strong> ecosystem persistence are resistance<br />
(i.e., <strong>the</strong> ability <strong>to</strong> resist changes from disturbance) and<br />
resiliency (i.e., <strong>the</strong> ability <strong>to</strong> absorb changes and <strong>the</strong><br />
speed with which it returns <strong>to</strong> its original condition)<br />
(Holling, 1973). In <strong>the</strong> case <strong>of</strong> <strong>sponges</strong>, resistance <strong>to</strong><br />
disturbance depends largely on <strong>the</strong>ir physical size, morphology,<br />
and distribution relative <strong>to</strong> <strong>the</strong> disturbance.<br />
We know from studies in <strong>the</strong> Aleutian Islands and Gulf<br />
<strong>of</strong> Alaska that benthic emergent epifauna, especially<br />
<strong>sponges</strong>, have low resistance <strong>to</strong> fishing gear disturbance<br />
(Freese et al., 1999; S<strong>to</strong>ne, 2006; Heifetz et al., 2009;<br />
S<strong>to</strong>ne, unpubl. data, 2004–2005). We know little about<br />
<strong>the</strong> resiliency <strong>of</strong> emergent epifauna, however.<br />
Resiliency depends on several fac<strong>to</strong>rs, including<br />
growth rate, recruitment rate, and reproductive ecology.<br />
Like <strong>deep</strong>-<strong>water</strong> corals, <strong>sponges</strong> have life his<strong>to</strong>ry<br />
attributes such as slow growth rates and high longevity<br />
(Day<strong>to</strong>n, 1979), indicating that long periods <strong>of</strong> time<br />
would be necessary for habitats dominated by <strong>sponges</strong><br />
<strong>to</strong> recover from disturbance (Freese, 2001). Growth<br />
rates for <strong>deep</strong>-<strong>water</strong> <strong>sponges</strong> are generally slow (see<br />
above) and <strong>the</strong>refore inherently difficult <strong>to</strong> study.<br />
Reference sites, such as undersea cables that provide<br />
a known time-line for recruitment and subsequent<br />
growth, show promise in studies <strong>of</strong> sponge habitat recovery<br />
(Levings and McDaniel, 1974) but have not yet<br />
been identified or targeted for such study in Alaska.<br />
The only known study <strong>to</strong> address <strong>the</strong> recovery dynamics<br />
<strong>of</strong> <strong>sponges</strong> in Alaska reported no visually detectable<br />
growth or regeneration one year post-disturbance with<br />
a bot<strong>to</strong>m trawl (Freese, 2001). Due <strong>to</strong> <strong>the</strong> opportunistic<br />
nature <strong>of</strong> that study (observations were subjective, not<br />
quantifiable; not repeatable since specimens were not<br />
georeferenced; and made in an area subjected <strong>to</strong> high<br />
background disturbance), <strong>the</strong> findings are questioned.<br />
Contrastingly, a study conducted <strong>of</strong>f <strong>the</strong> sou<strong>the</strong>astern<br />
coast <strong>of</strong> <strong>the</strong> U.S. indicated that some <strong>sponges</strong> were<br />
capable <strong>of</strong> recovering completely within one year from<br />
damage caused by a research trawl (Van Dolah et al.,<br />
1987).<br />
Moni<strong>to</strong>ring bycatch <strong>of</strong> <strong>sponges</strong><br />
Appendix II provides a list <strong>of</strong> all <strong>sponges</strong> for which we<br />
have provided species descriptions in this <strong>guide</strong>. For<br />
each species, <strong>the</strong> importance as fish habitat and <strong>the</strong> vulnerability<br />
<strong>to</strong> disturbance from fishing activities is ranked<br />
from low (1) <strong>to</strong> high (3). Ranks for <strong>the</strong> two measures<br />
are averaged <strong>to</strong> provide a score. We recommend that<br />
species with scores greater than 2.0 be considered a