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

The gelatinous zooplankton, composed by members of different phyla (Cnidari a, Ctenophora, Tunicata), are usually neglected in most studies about energ y transfer in the marine trophic web, and often it is assumed that such sof t-bodied fauna are trophic 'dead ends' in the food webs. In recent years, h owever, it has been shown that many fish species feed extensively on gelati nous zooplankton, while other species may feed on them occasionally when ot her food is scarce. We found that anchovies, Engraulis anchoita Hubbs & Mar ini, 1935, shoaled close to the Rio de la Plata surface salinity front, whe re dense aggregations of the salp, Iasis zonaria (Pallas, 1774), were detec ted acoustically in May, 1994. Densities of non-gelatinous zooplankton were low at this interface, and anchovies fed on the salps. In this paper, we d escribe the environmental and biological conditions that led a normally pla nktivorous filter feeder E. anchoita to prey on gelatinous plankton.