Meeting Abstract

P1.50  Monday, Jan. 4  Reduced herbivory by Caribbean sea urchins in response to chemical cues of a known predator PARISH, E.R.*; TURNER, T.; Univ. of the Virgin Islands eddieparish@gmail.com

Non-consumptive, indirect effects can contribute to trophic cascades as well as to changes in prey species morphology, yet many ecological studies only consider direct consequences of predation when examining predator-prey relationships. To test for trait-mediated indirect interactions (TMIIs), we examined a system on Caribbean coral reefs where herbivorous urchins, including Diadema antillarum and Echinometra viridis, decrease macroalgae and thereby increase juvenile coral survival. Diadema antillarum and E. viridis are preyed upon by fishes as well as invertebrates, yet no previous study has examined whether these urchins change their behavior in response to chemical cues from predators. To test this hypothesis, urchins were placed in individual 38 L buckets down current of a separate aquaria housing a helmet shell Cassis tuberosa, a known urchin predator. Each trial was paired with a control aquarium in which no predator was up-current of urchins. Urchins were fed a known amount of the red alga Acanthophora spicifera ad libitum for 24 h. The amount of A. spicifera consumed was calculated by the difference between initial and final weights. In two experiments TMIIs were demonstrated: D. antillarum and E. viridis consumed significantly less algae in the perceived presence of C. tuberosa (t-test, p < 0.001). Both small and large D. antillarum and E. viridis reduced foraging rates in the assumed presence of C. tuberosa. Diadema antillarum and E. viridis altered their behaviors in response to chemical cues from potential predators, which may have positive indirect effects on macroalgae communities through a release in grazing pressure.