11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 10: Ecological Processes on Today's Reef Ecosystems
10-49
Interactive Effects Of Competition And Microhabitat On Juvenile Survival in A
Coral Reef Fish
Mary BONIN* 1,2 , Glenn ALMANY 1,2 , Maya SRINIVASAN 2 , Geoffrey JONES 1,2
1 ARC Centre of Excellence for Coral Reef Studies, Townsville, Australia, 2 Marine and
Tropical Biology, James Cook University, Townsville, Australia
Microhabitat type and competition for preferred microhabitats can influence patterns of
abundance and mortality in coral reef fish communities, however the relative influence
and interaction between these two factors is not well understood. In Kimbe Bay, Papua
New Guinea, we used surveys to quantify microhabitat use in two live-coral specialist
damselfishes (Pomacentridae), Chrysiptera parasema and Dascyllus melanurus. We then
used a patch reef experiment to test how intra- and interspecific competition interacts
with two types of microhabitat to influence survival of juvenile C. parasema. Surveys
demonstrated that C. parasema and D. melanurus utilize similar coral microhabitats; 72%
of C. parasema and 85% of D. melanurus used corymbose and bottlebrush growth forms
of Acropora. One microhabitat type, Pocillopora spp. coral, was used by D. melanurus
but not C. parasema. The patch reef experiment revealed that microhabitat type had the
strongest influence on survival of C. parasema. In the absence of interspecific
competitors, approximately 90% of C. parasema survived for 5 days after transplantation
to bottlebrush Acropora compared to only 30% survival on Pocillopora. In both
microhabitats, interspecific competition with D. melanurus, but not intraspecific
competition, decreased survival of C. parasema. The interspecific effect of D. melanurus
was greater in the more structurally-complex microhabitat; on Acropora reefs,
interspecific competition resulted in a 34% decrease in C. parasema survival compared to
19% on Pocillopora reefs. This study demonstrates that interspecific competition and
microhabitat type can interact to influence survival in coral reef fishes, though whether
and how these factors influence survival will depend on the behavioural attributes and
strength of habitat associations among potential competitors.
10-50
Differential Effect Of Early Post-Settlement Processes On The Abundance Of Two
Concurrently Settling Coral Reef Fishes
Henri VALLES* 1 , Donald KRAMER 1 , Wayne HUNTE 2
1 Biology, McGill University, Montreal, QC, Canada, 2 Biology, University of the West
Indies, Cave Hill, Barbados
To examine the magnitude, spatial variability and causes of early density-independent
(DI) and density-dependent (DD) post-settlement losses in coral reef fishes, we
monitored density of Sparisoma (Scaridae) and Stegastes partitus (Pomacentridae) on
three reefs in Barbados (West Indies) for 3-3.5 months following a period of high
recruitment and fitted the data to a modified Beverton-Holt model. To assess whether
surveys missed early DD mortality, we compared recruitment on reefs to that on standard
monitoring units (SMURFs) that excluded predators. Recruitment was >11x (Sparisoma)
and >3x (S. partitus) greater than the initial number of large juveniles/ adults. Mortality
was very high (Sparisoma 97%; S. partitus 91%), indicating that post-settlement
processes were more important than settlement in determining local density. Mortality
did not vary significantly across sites. After 3-3.5 months, Sparisoma densities were
similar to those before recruitment. S. partitus densities increased, but increases did not
match among-site differences in recruitment, indicating that post-settlement processes
differed spatially. DI effects did not vary significantly between taxa or sites. DD effects
were one order of magnitude higher for Sparisoma than for S. partitus, possibly due to
lower availability of refuge microhabitat for Sparisoma. DD effects varied significantly
across sites for S. partitus, but not Sparisoma, perhaps because of lower precision in
density estimates for Sparisoma. Among-site differences in DD effects for S. partitus
were associated with differences in recruitment rates and substrate. Predator density was
similar across sites. Recruit density on the reefs mirrored captures in SMURFs, indicating
that surveys did not miss important DD predation. Our findings suggest that substrate
influences rates of DD mortality and therefore local population dynamics, but with
markedly different strength for different taxa.
10-51
Living in a Washing Machine: Differing Capacities to Capture Prey Under Divergent
Velocity/Turbulence Conditions Reflect Microhabitat Differences of Two Chaenopsid
Blennies
Raymond CLARKE* 1 , Christopher FINELLI 2 , Edward BUSKEY 3
1 Department of Biology, Sarah Lawrence College, Bronxville, NY, 2 Department of Biology and
Marine Biology, University of North Carolina Wilmington, Wilmington, NC, 3 The University
of Texas at Austin Marine Science Institute, Port Aransas, TX
Wave-generated oscillating water flow on coral reefs creates a challenge for the fishes that live
there, but it also creates opportunities. Roughhead blennies (Acanthemblemaria aspera) and
spinyhead blennies (A. spinosa) live in holes in dead coral skeletons from which they make
rapid forays to capture passing prey, primarily copepods. On coral reefs throughout the
Caribbean, spinyheads occupy locations in tall corals while roughheads reside close to the reef
surface. Spinyheads have metabolic rates 1.5 times higher than those of roughheads. Our study
involves (1) measuring water speeds and flow patterns both generally and within blenny feeding
volumes, (2) videotaping blennies feeding in the field and (3) studying blenny feeding patterns
and success in flumes. The flume studies include wild-caught calanoids (Acartia tonsa) as prey
and water flow regimes that replicate those measured in the field. Spinyheads experience
greater velocity and turbulence and possess a more fixed attack pattern, focusing primarily on
planktonic prey whereas roughheads feed primarily on benthic prey but periodically shift to
planktonic prey under low flow conditions. Spinyheads attack at greater distances and at greater
rates under all conditions. Both species attack more frequently during the slack stage of the
wave cycle, but spinyheads attack over a greater proportion of the wave cycle than do
roughheads. Spinyheads also have greater capture success than roughheads under fast smooth
flow and all turbulent water conditions. These data reveal in some detail the ways in which
these blennies are adapted to different microhabitats thus facilitating coexistence in the same
reef zones.
10-52
Micropredator Gnathiid Isopods Reduce Larval Damselfish Persistence By Affecting
Performance
Alexandra GRUTTER* 1 , Angela CREAN 1 , Lynda M CURTIS 1 , Armand M KURIS 2 , Robert
R WARNER 2 , Mark I MCCORMICK 3
1 School of Integrative Biology, The University of Queesland, St. Lucia Queesland, Australia,
2 Ecology, Evolution, and Marine Biology, Univeristy of California Santa Barbara, Santa
Barbara, CA, 3 ARC Centre of Excellence for Coral Reef Studies and School of Marine and
Tropical Biology, James Cook University, Townsville Queensland, Australia
Traditional hypothesis for the pelagic phase of demersal coral reef fishes are not strongly
supported by the data. An alternative hypothesis is that they migrate to the pelagic environment
to disrupt or avoid transmission of infectious agents. On the Great Barrier Reef, gnathiid
isopods (mobile micropredators) are one of the most common ectoparasites of fish. Gnathiid
effects on small fishes were used as a model for the consequences of keeping larvae on the reef.
Nothing is known of how gnathiids affect the performance and survival of juveniles in the wild.
We therefore tested the effect of gnathiids on the swimming performance, oxygen consumption,
and survival of the common damselfish Pomacentrus amboinensis in nature. Of juvenile fish
sampled at dawn and during the day, 3.5% and 0% had a gnathiid respectively, however, this
difference was not significant. In the laboratory, most gnathiids (79%) remained attached to
juvenile fish for up to 6 h and all fish survived exposure to the gnathiids. When tested in pairs in
a double-laned swim chamber, settlement-stage fish that had previously been fed on by a
gnathiid ceased swimming first in 77% of the trials. They also had a 14% lower critical
swimming speed compared to fish not exposed to a gnathiid. Previously parasitized settlementstage
fish had a 32% higher oxygen consumption rate than did unexposed fish. When tagged
settlement-stage fish were placed in pairs on dead coral patches in the wild and monitored, the
previously parasitized fish disappeared from the reef first in 67% of the trials. Our analysis
indicates that gnathiid isopods significantly decrease the performance of young P. amboinensis.
This may affect their survival and successful establishment on the reef. Micropredation by
gnathiids may therefore contribute to selection pressure for a pelagic stage.
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