Project: Fecal Pellets of Doliolids and Copepods: Two Different Microworlds?

High primary productivity on wide subtropical continental shelves has been related to upwellings generated by western boundary currents. Studies on the U.S. southeastern (SE) shelf have revealed frequent occurrences of patches of pelagic tunicates which can rapidly colonize the SE shelf and consume a large percentage of the primary productivity. Since these tunicates are, as compared to copepods, rather inefficient in utilizing the ingested phytoplankton, large amounts of the ingested organic matter should be available to other consumers which might represent different microworlds. While among the neritic metazoa calanoid copepods have been considered the main consumers of larger phytoplankton cells, among protists heterotrophic dinoflagellates can feed on such cells. Neritic salps and doliolids, because of their occasional occurrence, were only seen as occasional major consumers. Doliolids are now known to occur predictably on the SE shelf through much of the year, and because of their inefficient use of phytoplankton, their effects on the shelf food web might be considerable. This project will investigate processes related to the early decomposition of doliolid fecal pellets and compare these processes to pellet decomposition of co-occurring calanoid copepods. The investigators will test several hypotheses related to the main question: How do the early decomposition rates of fecal pellets of doliolids and copepods compare, and how are they related to the abundance, size and processes of heterotrophic prokaryotes? As the feeding processes differ between calanoid copepods and doliolids, major differences in early decomposition are expected. This should influence the pelagic microbial loop of productive subtropical shelves.

The research focuses on a central theme, processing of biogenic material, within the diverse field of marine plankton, marine biogeochemistry, and shelf oceanography, and therefore will be of interest well beyond the specific focus of the project. Because thaliacean abundance is a common feature of western boundary continental shelf environments, the findings of this study will be applicable well beyond the South Atlantic Bight.