Prey selection patterns ofChrysaora fuscescensin the northern California Current

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Abstract

Chrysaora fuscescens is the most abundant large scyphomedusae in the northern California Current (NCC), a productive upwelling system. We quantified the diet and prey selection of C. fuscescens at stations off the Oregon and Washington coasts during the summer of 2014. The major prey items ingested were copepods, cladocerans and gelatinous taxa, and comprised 4–77% of gut contents. Northern anchovy eggs (Engraulis mordax) were a dominant prey item at stations near the Columbia River, comprising 40% of gut contents. Prey selection indices showed that though copepods dominated gut contents, C. fuscescens preferentially ingested slow-moving, non-motile prey including fish eggs and gelatinous taxa and negatively selected for more motile prey such as copepods. Clearance rates and ingestion rates varied by three orders of magnitude for the different zooplankton taxa but, on average, fish eggs and gelatinous taxa were cleared at higher rates than more commonly ingested prey items such as copepods. Daily carbon ration reached 10% of body carbon but had an average value of 2%, suggesting that some medusae may be food limited. These results highlight medusae predation on ichthyoplankton and can inform ecosystem models in the NCC.

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