While examining a relationship between the occurrence of winter storms and variations in the growth rate of larvae off Tasmania, we found several lines of evidence that suggest that the food chain supporting the larvae of the region’s dominant midwater predator is not based on phytoplankton, as we had expected, but rather on microbial decomposition of seagrass detritus. Seagrass detritus is known to be important in food webs of benthic coastal communities, but extensive utilization of buoyant seagrass detritus by planktonic microheterotrophs has not been reported. Offshore transport of seagrass detritus by storms occurs frequently and such detritus may be a common and important, but highly variable, source of production for coastal planktonic ecosystems.