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OBJECTIVES: Atlantic menhaden (Brevoortia tyrannus) is a key forage species on the Atlantic coast that forms a direct link between primary productivity and fisheries production. Ecosystem-Based Management (EBM) requires an understanding of the linkage between climate, plankton communities, and forage fish dynamics, but is poorly understood. Identification of food organisms by traditional methods is difficult due to their small size and the effects of digestive processes. Molecular techniques can provide unambiguous forensic tools to identify stomach species. This project is to develop and verify molecular techniques, based on cox1 DNA, to provide an unambiguous tool to identify species in stomach contents of these fish and to compare them with those found in plankton. Existing molecular databases (National Center for Biotechnology Information and Barcode of Life) will be utilized for identification of gut and plankton species. The expertise of a plankton biologist will be utilized to verify species identification.
METHODOLOGY: This project will utilize the molecular technique of barcoding to provide an unambiguous forensic tool to identify stomach contents of menhaden, using the 650 bp mitochondrial cytochrome c oxidase 1 (cox1) DNA. Identification by barcoding will be verified by traditional microscopic methods. Stomach contents will be compared to plankton composition. An initial feasibility study will collect menhaden and ambient plankton. Plankton composition will be determined by traditional observational methods, as well as by barcoding. The first step will be to verify that species recognized by traditional methods give rise to the expected Cox1 signatures. The second step will be to demonstrate that phytoplankton species fed to captive menhaden can be identified by barcoding analysis. The methodology will be used to compare menhaden diets with plankton composition, collaborating with NOAA supported collection activities to investigate the effects of climate change on diet and feeding of menhaden in nearshore ecosystems.
RATIONALE: Menhaden is one of the primary forage fishes in the Chesapeake Bay and plays a key role in the food chain. It is the primary prey of the Bay's most targeted predatory fishes and supports the biggest volume fishery in the Bay. However, in recent years, production of young menhaden in the Chesapeake Bay has declined sharply and a link between environmental variability and the productivity of forage fishes is under investigation. Although most forage fish species are not federally managed, many of their predators are. Multiple programs within NOAA/NMFS actively monitor forage fish and study their ecological interactions and the effects of climate changes. Thus, NOAA has become actively engaged in research on forage fish ecology, and this study will develop and verify the methodology needed to fill an important gap in our understanding of their importance for nearshore ecosystems.