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. Moreover, the project will target three important education and broader impact themes: 1) Teacher education; 2) Demographic diversification of future ocean scientists; and 3) Strengthening international science collaboration. To help bridge the gap between research and K-12 students and teacher communities, a collaboration with an ongoing science teacher program sponsored by The Georgia Aquarium and NOAA (Rivers to Reef Educator Workshop) the investigators will interact with 96 K-12 in-service science teachers and provide them with oceanographic research experience and novel insights into the specific questions currently being addressed in plankton ecology. By supporting undergraduate students (largely African American) through a well established relationship with Savannah State University, the project will contribute to the effort to increase the diversity of future ocean scientists and professionals. Finally, a strong component of collaboration with colleagues in Germany and Norway will further the scientific objectives of the project and strengthen collaborations between US and European biological oceanographers.
?" from January 2011 to December 2014 (Grant 1031263). The goal of our study was to compare early decomposition rates of fecal pellets of doliolids with those of calanoid copepods, and their relation to abundances, sizes and processes of heterotrophic prokaryotes. It had been known that zooplankton fecal pellets, mainly produced by copepods, contribute significantly to the ocean’s carbon cycle. Our findings showed that pellets produced by doliolids (Tunicata, Thaliacea) on the U.S. southeastern subtropical continental shelf differed from those of the mostly studied planktonic copepods: They are produced at a far higher rate, contain far higher amounts of carbon and nitrogen, and can be readily accessed by prokaryotes. As doliolids occur abundantly to being temporarily dominant on numerous continental shelves (e.g. Agulhas Bank, Ivory Coast, Southeastern Australia, most of the Brazilian Coast, coastal regions of Japan, the Gulf of Mexico, the U.S. west coast and the U.S. southeastern shelf), they contribute significantly to the carbon production and cycle in subtropical Ocean Margins as they are producing organic matter via extraordinary asexual production rates as well as pellet production rates. Our findings from the 4-year study contributed the following: Doliolids pellets sink at a lower rate than copepod pellets of similar carbon content, are faster colonized by prokaryotes than copepod pellets, and serve as food for heterotrophic dinoflagellates, copepods and thaliacea. In essence, such pellets’ extended residence time in the water column implies that they will hardly reach the sea floor. We also found that such doliolids readily ingested dispersed oil globules (several microns diameter, Fig.1 and Fig.2) in the presence of environmental amounts of phytoplankton without disturbing the feeders. That process leads to a prolonged stay of such oil globules in the water column as such pellets sink only very slowly. Similar to the U.S. southeastern shelf, doliolids can occur intermittently in large numbers in the Gulf of Mexico. Our findings reveal that fecal pellets of doliolids and planktonic copepods indeed represent different environments for microbes i.e. are indeed Different Microworlds. Our results represent not only an initial contribution towards understanding the ecological significance of fecal pellets of vastly different zooplankton taxa but also on the existence and persistence of their producers, the doliolids.
