Feeding on survival-food: gelatinous plankton as a source of food for anchovies

Abstract

The gelatinous zooplankton, composed by members of different phyla (Cnidaria, Ctenophora, Tunicata), are usually neglected in most studies about energy transfer in the marine trophic web, and often it is assumed that such soft-bodied fauna are trophic ‘dead ends’ in the food webs. In recent years, however, it has been shown that many fish species feed extensively on gelatinous zooplankton, while other species may feed on them occasionally when other food is scarce. We found that anchovies, Engraulis anchoita Hubbs & Marini, 1935, shoaled close to the Río de la Plata surface salinity front, where dense aggregations of the salp, Iasis zonaria (Pallas, 1774), were detected acoustically in May, 1994. Densities of non-gelatinous zooplankton were low at this interface, and anchovies fed on the salps. In this paper, we describe the environmental and biological conditions that led a normally planktivorous filter feeder E. anchoita to prey on gelatinous plankton.