Trophic biology of stylophora pistillata larvae: Evidence from stable isotope analysis

The successful recruitment of planktonic larvae to coral reefs is essential for the continued existence of these highly diverse ecosystems. Feeding strategies may affect recruitment success and potentially determine species distribution by controlling the dispersal range of the larvae. Our aim here was to ascertain the feeding strategies of planula larvae of the coral Stylophora pistillata by using stable isotopes. Planula larvae, fragments of parental colonies, and 3 potential food types were analyzed for carbon and nitrogen stable isotope compositions and C/N ratios. We found that planulae were depleted in ¹³C when compared to parental tissues, whereas their C/N ratios were 2-fold higher. Following lipid extraction, there were no significant differences in d¹³C values and C/N ratios between lipid-free planulae and parental colonies. This indicates that the differences in d13C originate in the lipid content of the planulae and not from any isotopic fractionation that may occur during embryological development. Controlled feeding experiments were conducted using phytoplankton, zooplankton, and bacteria. Despite the presence of an oral opening, the planulae did not show any feeding behavior, and the stable isotope data corroborated the observations of no feeding. Moreover, following 2 wk of starvation in the dark, planulae started to utilize their lipid and protein reservoirs. These results stress the importance of the photosynthates translocated from the algal symbionts to these planulae as an energy source.