Trophic ecology of the neustonic cnidarian Velella velella in the northern California Current during an extensive bloom year: insights from gut contents and stable isotope analysis
Aggregations of the neustonic hydrozoan Velella velella occur periodically in the northern California Current. Despite the regular occurrence of notable bloom events in this productive upwelling zone, little is known about their trophic ecology. We used gut content and stable isotope analyses (SIA) to elucidate V. velella prey selectivity and trophic niche to address their potential impacts on the marine ecosystem. The dominant prey items ingested by V. velella colonies were non-motile prey including cladocerans and northern anchovy (Engraulis mordax) eggs, though copepods were also common in gut contents. Removal rates of northern anchovy eggs could be magnified in bloom years and in areas of high spawning biomass. Stable isotope analysis revealed differences in isotopic niche width and overlap among V. velella based on latitudinal gradients and to a lesser extent on V. velella size and demonstrates the need for continued work to fully understand the trophic ecology of this unique neustonic organism.
We acknowledge Curtis Roegner for providing the neuston samples and Toby Auth for assistance in identifying fish eggs and larvae, along with members of the Weis lab at Oregon State University, especially Jack Koch, for guidance and laboratory work with V. velella symbionts. For stable isotope direction, we would like to thank Jennifer McKay at the Oregon State University Stable Isotope Facility for her expertise. We thank Curtis Roegner, Elizabeth Daly, Rich Zabel, Jennifer Purcell and two anonymous reviewers for comments on the manuscript.
We acknowledge the support of Oregon Sea Grant (R/ECO-33-Sutherland). We also appreciate the NOAA Fisheries Northwest Fisheries Science Center for providing ship, logistic, and salary support.
Compliance with ethical standards
All national and institutional guidelines for the use of animals were followed.
Conflict of interest
All authors declare that they have no conflict of interest.
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