Influence of copepod size and behaviour on vulnerability to predation by the scyphomedusa Aurelia aurita

Abstract

The influence of copepod prey size and behaviour upon Aurelia aurita medusae predation rates was investigated. There was no significant difference in predation rates across a 4-fold (250 to 987 mm) prey size range (heat-killed developmental stages of Acartia tonsa). Any behavioural differences (e.g. swimming speed, escape response) across live A. tonsa developmental stages had no significant effect upon their susceptibility to predation. In addition, Aurelia aurita ingestion rates were similar upon adult males and females of a copepod that exhibit similar swimming speeds (A. tonsa), as well as upon both adult sexes of a copepod with contrasting swimming behaviour
(Oithona similis). An encounter model indicated that the size and speed of Aurelia aurita overwhelmed the differences in size and swimming speeds of these prey by largely determining encounter rates. However, overall, heat-killing prey lead to significantly higher predation rates than those upon live prey. This may be attributed to the escape response of live prey, which is not included in the encounter model. The capture efficiency of Aurelia aurita was low (,9%), but high ingestion rates may be achieved through the large encounter rates of this cruising predator.

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ORCID for Cathy H. Lucas: orcid.org/0000-0002-5929-7481

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