Food supply influences survival of Diadema antillarum larvae

Caribbean coral reefs have become increasingly degraded in recent decades, in part due to the loss of a keystone invertebrate herbivore, the sea urchin Diadema antillarum. Most D. antillarum populations have failed to recover from an epizootic in the 1980’s that extinguished 99% of D. antillarum throughout the Caribbean. D. antillarum have a biphasic life history, including benthic adults that reproduce via broadcast spawning, and pelagic larvae that feed and develop in the plankton for up to 90 days. Hindrances to D. antillarum population recovery may occur at several stages throughout their complex life history: low fertilization success at low population densities of benthic adults, high mortality during the pelagic larval stage, and recruitment failure of juveniles due to low-quality habitat provided by degraded reefs. Here, we examine the effects of food supply on the growth and survival of D. antillarum larvae in vitro. Replicate D. antillarum larval cultures (n=3 per treatment) were fed phytoplankton at high (1000 cells/mL), medium (450 cells/mL), and low (100 cells/mL) concentrations, which are representative of the natural variation in phytoplankton densities found in the northern Caribbean. Growth rates were similar between feeding treatments, but larvae fed high food concentrations survived longer than medium or low food concentrations. If high food concentrations can enhance larval survival, successful D. antillarum dispersal and recruitment may depend on the distribution of phytoplankton in the ocean. Oceanographic features that boost phytoplankton concentrations, such as upwelling eddies, may provide ideal habitat for D. antillarum larvae.