11th ICRS Abstract book - Nova Southeastern University

22-50
Changes in Ecosystem Structure Induce Trade-Offs in Storage And Reproduction
Across Fishes From Multiple Trophic Levels
Sheila WALSH* 1 , Benjamin RUTTENBURG 1,2 , Scott HAMILTON 3 , Mary
DONOVAN 3 , Stuart SANDIN 1
1 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA,
2 Marine Science Institute, University of California, Santa Barbara, Santa Barbara,
3 Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA
Ecosystem structures characterized by different predation, competition, and resource
regimes may select for specific energy allocation strategies at the organismal level.
Shifts in energy allocation between somatic storage and reproduction may ultimately
have consequences that scale back up to the ecosystem level. We tested the effect of
changes in ecosystem structure on total weight, liver weight, and gonad weight for five
species of fish, each representing a different trophic level. We collected fishes from a
cross-island and a within-island gradient of predator biomass to control for biogeographic
and regional-scale oceanographic effects. The gradients also represent gradients in
resource availability. Fish weight at length decreased with increasing predator biomass
for all species except the top predator. The effect was increasing with decreasing trophic
level, suggesting that lower trophic level species were also affected by decreasing
resource availability. Liver weight at weight of unreproductive fishes showed a similar
pattern to total weight. Gonad weight at weight, however, showed differences in the
direction of the effect across trophic levels. Gonad weight decreased for higher trophic
level fishes but increased for lower trophic level fishes. The difference in the effect on
reproductive allocations may be due to the compounded effects of increased mortality
and decreased resource availability. The trend of decreasing weight at length with
decreasing fishing pressure, a proxy for predator biomass, was found to be general when
our data were compared to published data from other regions. Our results indicate a
community-wide response in energy allocation to changes in ecosystem structure.
Ecosystems dominated by predators and coral may actually increase fish community
productivity by inducing shifts in energy allocation away from storage and toward
reproduction. However, the net effect will depend on the relative contribution of and
interactions between somatic and population growth.
Oral Mini-Symposium 22: Coral Reef Associated Fisheries
195