Crown-of-thorns starfish complete their larval phase eating only nitrogen-fixing <i>Trichodesmium</i> cyanobacteria.

Abstract

Cyanobacteria of the genus <i>Trichodesmium</i> form extensive blooms that supply new N to nutrient-poor marine ecosystems. Yet little is known about what eats <i>Trichodesmium</i>. In this laboratory study, we show that one of the greatest threats to coral reefs, predatory crown-of-thorns starfish (CoTS), <i>Acanthaster</i> sp., completes their larval phase feeding solely on <i>Trichodesmium</i>. We observed <i>Trichodesmium erythraeum</i> CMP1985 in the stomachs of larvae using florescence microscopy and traced the assimilation of nitrogen from labeled trichomes into larval tissues using stable isotopes. Some larvae fed <i>T. erythraeum</i> were morphologically ready to become benthic juveniles after 19 days. Given that <i>Trichodesmium</i> can be food for CoTS, reported increases in <i>Trichodesmium</i> could be a driving factor in the heightened frequency of CoTS population irruptions that have devastated coral reefs in past decades. Future studies could test this through investigating the diets of wild larvae and incorporating <i>Trichodesmium</i> abundance into models of CoTS population dynamics.