Copepod, Ctenophore, and Schyphomedusae Control in Structuring the Chesapeake Bay Summer Mesohaline Planktonic Food Web

Abstract

The Chesapeake Bay has undergone substantial cultural eutrophication for the past century, leading to elevated nutrient loads and accompanying phytoplankton response. High winter-spring flow and nutrient loading leads to elevated spring diatom biomass (bottom up control). In the summer, however, bottom up control of mesohaline plankton dynamics is difficult to identify, while top-down control, from jellyfish on ctenophores, ctenophores on the copepod Acartia tonsa, and A. tonsa control of rotifers and ciliates, is apparent. Using a long-term data set (1987–2002), predator abundances that appear to control their primary prey have been identified for mesohaline Chesapeake Bay and tributary stations. It appears that Acartia tonsa at >5–8 L⁻¹ exerts substantial grazing pressure on rotifers and ciliates, ~10–20 mL ctenophore m⁻³ limit A. tonsa densities, and >0.05 jellyfish m⁻³ control ctenophores. Expected bottom up control of the plankton community below these thresholds could not be identified, however, suggesting multiple physical, chemical, and biological limits might be interacting in space and time to prevent elucidation of the bottom up system drivers of plankton dynamics.

Kevin G. Sellner and Stella G. Sellner

The Sellner’s met in the early 1980s after Kevin hired Stella to expand microzooplankton taxonomy for the ongoing plankton monitoring program he had been invited to implement for Maryland’s portion of Chesapeake Bay in 1984. Following receipt of his M.S. from the Baruch Institute of the University of South Carolina and his Ph.D. from Dalhousie, Kevin had joined the Academy of Natural Sciences in Philadelphia in 1978 and subsequently transferred to its Benedict Estuarine Research Laboratory on the Patuxent River, Chesapeake Bay, in 1981. Stella joined the plankton group from the USDA’s Carbohydrate Analysis Laboratory and the two began a three decade collaboration, including marriage in 1995, on phytoplankton-zooplankton interactions for the Chesapeake Bay and Gulf of Finland, focusing on describing the seasonal succession of taxa in tidal fresh to polyhaline reaches of the former as well as phytoplankton-zooplankton relationships in algal blooms of the two systems. Kevin shifted from the lab to administering the initial US multi-agency Federal program ECOHAB (Ecology and Oceanography of Harmful Algal Blooms) for several years, overseeing peer and panel review for approximately $50 M of projects on Alexandrium, Karenia, Pfiesteria, Karlodinium, and Pseudo-nitzschia. Stella remained at the laboratory while it transitioned to the Morgan State University PEARL (Patuxent Environmental and Aquatic Research Laboratory) where she became the Education Coordinator and directed the NOAA-funded PLANS (PLankton And Nutrient Studies) science program in Calvert County, Maryland high schools. Kevin returned to the Chesapeake to direct the 6-institution Chesapeake Research Consortium in 2001, committed to fostering multi-institution, multi-discipline research and transferring basic research results to the management community of the basin; he was also able to pursue research on mitigating cyanobacteria blooms in the region which he continues today. Kevin and Stella recently retired to pursue other “fun” science opportunities as they enjoy Frederick, MD, USA culture, nature, and history.