Feeding rates of the jellyfish Aurelia aurita on fish larvae
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We quantified feeding rates of field caught Aurelia aurita feeding on yolk sac cod (Gadus morhua) larvae in a series of incubation experiments. A short-time (~1 h) functional response experiment with a wide range of prey concentrations (0.5–16 prey l−1, initial concentration) revealed that ingestion rates increased linearly over this range, such that clearance rates were similar between the different prey concentrations. This suggests that A. aurita is capable of efficiently utilizing dense prey patches. This indication was further supported by a linear increase of prey captured by A. aurita during 2.5 h of feeding at extremely high prey concentration (>200 prey l−1). Clearance rate in darkness scaled with jellyfish diameter to a power of ~1.7 for jellyfish 3.9–9.5 cm in diameter. The jellyfish did not alter their umbrella pulse frequency in response to presence of fish larvae. There were no significant differences between A. aurita feeding rates in light and darkness for yolk sac prey ages 0–7 days (at 7.5°C). Although prey vision and escape abilities of fish may develop rapidly during early larval ontogeny, these factors apparently have little impact on interactions with predators such as A. aurita during the yolk sac stage.
KeywordsClearance Rate Fish Larva Encounter Rate Gelatinous Zooplankton Prey Concentration
We thank Laurianne Gandon and Anne Goarant for catching jellyfish, Frank Midtøy for advice on rearing cod larvae and Erling Otterlei, SagaFjord Sea Farm AS (Stord, Norway) for providing cod eggs. Thomas Kiørboe kindly commented on an earlier draft. This work formed part of the EUROGEL project funded by the European Commission (EVK3-CT-2002–00074). The experiments comply with the current laws of Norway, where the experiments were performed.
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