Seasonal variation of gelatinous plankton consumption by fish in the South-western Atlantic Ocean: a question of strategy

Abstract

Gelatinous plankton is an important food resource for several species of fishes in theSouthwestern Atlantic Ocean. Some fish depend heavily on these organisms and arespecialized to feed on ctenophores, salps and medusae, while others only consumegelatinous plankton occasionally. We hypothesize that consumption of gelatinous planktonby fishes represents an alternative food resource when primary prey are not available duringcold periods in the study area. To determine seasonal variations of gelatinous planktonconsumption by fishes, data samples were grouped into cold and warm periods. A total of64,567 stomachs belonging to 106 species of fish were analysed, of which 32,943 (51%)contained food items. Of those containing food items, 2719 (8.2%), from 38 fish species,contained gelatinous items. Fourteen species ingested gelatinous in warm period, nine incold period, and 15 in both periods. The proportion of stomachs with gelatinous wassignificantly greater during the cold period. Ctenophores were the most predominant prey inboth periods, followed by salps and medusae. Consumption of ctenophores, salps andmedusae was unevenly distributed within the area during the different periods. Classificationmethods (group average sorting utilizing Bray?Curtis similarity measures based on log (X + 1)identified eight areas of consumption. SIMPER (similarity percentages) analyses revealed thatnine fish species contributed most to gelatinous plankton consumption. The seasonal andspatial variation of gelatinous consumption by fish would be related to the availability offood in each period. Strategies of gelatinous consumption, including survival, feedingopportunities and prey specialization, are discussed.