Plasticity in the Sclerites of a Gorgonian Coral: Tests of Water Motion, Light Level, and Damage Cues.

The gorgonian coral Briareum asbestinum contains skeletal elements (sclerites) that vary in length and density within and among local populations. Data from previous work suggested that the sclerite compositions of colonies may be altered in response to environmental cues such as predator damage, water motion, and light level. To test these hypotheses, colonies from shallow reefs were transplanted to racks at a single location where the three environmental factors of interest were artificially manipulated. After 9-14 weeks of growth, sclerite morphologies and densities had not changed in response to shading or to water-motion reductions that mimicked deep-water conditions. However, colonies did respond significantly to two types of simulated predator damage. Following tip amputation, sclerites in the regenerated tips of damaged colonies were shorter and more dense than in the controls. In contrast, mid-branch scarring caused colonies to produce longer sclerites at lower densities. Since long sclerites deter feeding by predatory snails, the increase in sclerite length in response to scarring of mid-branch regions may function as an inducible defense.