Fisheries production is intimately related to both the supply of new nitrogen to the ecosystem (biogeochemical perspective) and to plankton trophic relationships that determine how primary productivity is made available to fish and other organisms (trophic perspective). Here in the FSU Plankton Ecology and Biogeochemistry Lab we are working with colleagues from many partner institutions to unravel linkages between the trophic and biogeochemical perpectives and to predict zooplankton concentrations (and fisheries prey limitation) in the Gulf of Mexico. With funding from NASA and NOAA we are taking field-based and model-based approaches to tackle this long-standing topic.

 

Our NOAA RESTORE Act Grant-funded project (with the University of Hawaii, Scripps Institution of Oceanography, and Southeast Fisheries Science Center) is designed to address the relative importance of bottom-up ecosystem limitation (nitrate uptake and nitrogen fixation) and zooplankton community structure (e.g. protists vs copepods vs appendicularians) in controlling survival and growth rates of larval bluefin tuna. These tuna are economically important throughout the Atlantic but spawn only in oligotrophic regions of the Gulf of Mexico and Mediterranean Sea. We seek to improve fisheries stock assessments by determining the important processes structuring the ecosystems where these fish thrive. Specifically we will determine: 1) Whether these ecosystems rely on upwelled nitrate (which would lead to decreased production if the ocean becomes more stratified) or nitrogen fixation (in which case the community is less dependent on allochthonous nutrient sources). 2) Whether shifts in community structure (e.g. from appendicularians to poecilastomatoid copepods, which are both preferred prey of tuna larvae but have very different trophic levels) alter the efficiency with which primary production is transmitted to tuna larvae. Our project involves and interdisciplinary team and extensive fieldwork on two month long cruises in the Gulf of Mexico in 2017 and 2018.

 

Our NASA-funded grant (with collaborators at Horn Point Laboratory) focuses on using satellite and modeling products to predict zooplankton concentrations for incorporation into fisheries models. This project takes the view that crustacean zooplankton, with their long lifetimes and migratory behavior, should not be measured as "concentrations". Instead, predicting their dynamics and interactions with other organism requires a Lagrangian, individual-based approach in which organisms are allowed to grow, reproduce, and die in the model over a period of weeks to months. Our challenge is to couple this Lagrangian approach with a typical Eulerian approach used for nutrients and single-celled plankton in the Gulf of Mexico.