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 the Southwestern Atlantic Ocean. Some fish depend heavily on these organisms and are specialized to feed on ctenophores, salps and medusae, while others only consume gelatinous plankton occasionally. We hypothesize that consumption of gelatinous plankton by fishes represents an alternative food resource when primary prey are not available during cold periods in the study area. To determine seasonal variations of gelatinous plankton consumption by fishes, data samples were grouped into cold and warm periods. A total of 64,567 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 in cold period, and 15 in both periods. The proportion of stomachs with gelatinous was significantly greater during the cold period. Ctenophores were the most predominant prey in both periods, followed by salps and medusae. Consumption of ctenophores, salps and medusae was unevenly distributed within the area during the different periods. Classification methods (group average sorting utilizing Bray-Curtis similarity measures based on log (X + 1) identified eight areas of consumption. SIMPER (similarity percentages) analyses revealed that nine fish species contributed most to gelatinous plankton consumption. The seasonal and spatial variation of gelatinous consumption by fish would be related to the availability of food in each period. Strategies of gelatinous consumption, including survival, feeding opportunities and prey specialization, are discussed.

Demersal fish predators of gelatinous zooplankton in the Northeast Pacific Ocean

“…The collections analyzed in this study mostly occurred during the summer months (87.9% of total diet collections were from May to September), as this is the primary period when demersal fishes are surveyed in the study region. However, as shown by Mianzan et al (1996) andDiaz Briz et al (2018), incidence of predation on gelatinous zooplankton can be higher for some taxa during other seasons, when alternative crustacean or fish prey may not be as readily available. Due to lower metabolic rates during these cooler seasons, predators may be able to subsist on prey types with lower energy content (Doyle et al 2007) relative to the summer period.…”

Molecular approach indicates consumption of jellyfish by commercially important fish species in a coastal Mediterranean lagoon

“…In the field, gilthead seabreams prey mainly on polychaetes, small fishes, crustaceans, gastropods and bivalves but adapt their diet to local prey availability (Pita et al 2002;Escalas et al 2015). Therefore, we suspect that the high abundance and accessibility of A. coerulea medusae during the bloom periods, benefit this opportunistic predator by providing a suitable source of food when its preferred prey are less accessible (Marques et al 2016;Díaz Briz et al 2018).…”

“…Gelatinous organisms are digested rapidly and often destroyed or shrunk by preservative methods (Arai 2005). Although gut contents still provide new evidences of the importance of jellyfish as prey (Díaz Briz et al 2018), contemporary studies have been using new techniques to identify jellyfish predators, such as stable isotope analysis, animal-borne cameras, remotely operated vehicles and molecular analysis (Hays et al 2018). Due to these modern techniques, the list of jellyfish predators has been growing and now includes commercially important fishes such as herring (Clupea harengus), whiting (Merlangius merlangus), bluefin tuna (Thunnus thynnus) and swordfish (Xiphias gladius) (Cardona et al 2012;Lamb et al 2017).…”

Population demographics and growth rate of Salpa thompsoni on the Kerguelen Plateau

“…Although the above mentioned apex predators mainly consume crustaceans and fish, recent genetic studies highlighted the dietary significance of gelatinous zooplankton, including salps for fish and penguins (e.g. Cavallo et al, 2018;Diaz Briz et al, 2018;Clarke et al, 2019). It is, therefore, particularly important to assess the impact that S. thompsoni may have on the local pelagic ecosystem as both a potential competitor or as a micronektonic prey.…”