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

* This research was conducted at Instituto de Investigaciones Marinas y Costeras (IIMyC), Universidad Nacional de Mar del Plata (UNMdP), Buenos Aires, Argentina.

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.

KEYWORDS:

• Seasonality
• fish predation
• gelatinous plankton
• strategy of consumption

Acknowledgements

We are especially grateful to Dr Dale Calder of the Royal Ontario Museum for revising the grammar and style of this manuscript and to our friend Laura Carlino for her help on the English of the early version. Also, Diego Giberto (INIDEP-CONICET) for providing a critical review on the early manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

* This research was conducted at Instituto de Investigaciones Marinas y Costeras (IIMyC), Universidad Nacional de Mar del Plata (UNMdP), Buenos Aires, Argentina.

Additional information

Funding

This work was supported by the Consejo Nacional de Investigaciones Científicas y Técnicas [grant number PIP 2012-0152]; Universidad Nacional de Mar del Plata [grant number EXA 734/15, UNMdP]. LDB is supported by CONICET fellowship. This is INIDEP contribution No. 2133.