Stratification onset and dissipation influences gelatinous zooplankton abundance and diversity

Shelf seas are biologically productive and can oscillate between vertically mixed (fall/winter) and stratified conditions (spring/summer). The latter scenario, often driven by solar heating and relatively low wind speeds, favors aggregations that are especially relevant to consumers that rely on concentrated prey resources. Gelatinous zooplankton are an abundant group of consumers that encompass a wide range of feeding strategies, from grazers to predators, suggesting their responses to stratification and mixed conditions may differ among genera or functional groups. Resolving these dynamics is critical for understanding the diversity of trophic pathways and broader properties of shelf food webs. Using in situ imaging systems, we measured the fine-scale abundances of gelatinous zooplankton in well-mixed and stratified conditions from both the South Atlantic Bight and Gulf of Mexico. A 50-km transect in the northern Gulf of Mexico, just south of Perdido Bay (Florida, USA), showed that the diversity of gelatinous zooplankton increased with more intense stratification in the summer. Many groups of hydromedusae and siphonophores (identified to the genus level) displayed low spatial overlap, even when associated with similar water mass properties. Doliolids were one of the only groups to consistently occupy the pycnocline - an area often associated with high concentrations of marine snow. Future work will determine if aggregations are consistent among years and how these distributions of gelatinous zooplankton influence diets and trophic structure in shelf food webs.

Presentation Preference: Oral

Primary Presenter: Adam Greer, University of Georgia, Skidaway Institute of Oceanography (atgreer@uga.edu)

Authors:

Adam Greer, University of Georgia, Skidaway Institute of Oceanography  (atgreer@uga.edu)

Luciano Chiaverano, Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP)  (lchiaverano@inidep.edu.ar)

Nele Weigt, University of Georgia, Skidaway Institute of Oceanography  (nweigt@uga.edu)

Laura Treible, Savannah State University  (treiblel@savannahstate.edu)

Jay Brandes, University of Georgia, Skidaway Institute of Oceanography  (Jay.Brandes@skio.uga.edu)

Marc Frischer, University of Georgia, Skidaway Institute of Oceanography  (Marc.Frischer@skio.uga.edu)