NCCOS Project Explorer (NPE)

Analysis of Sources of Primary Production Supporting Fisheries in Marine Protected Areas and Coastal Ecosystems(2009)

Project Description:
Information on the food sources and trophic position of the fish occupying Marine Protected Areas will provide resource managers with insight on the degree and mechanisms by which alterations in the oceanographic regime vs. changes in the reef benthic environment will affect fishery productivity. Information on food sources supporting reef fish production can also help in the determination of the appropriate boundaries for Marine Protected Areas (MPA). We are currently collaborating with fishery scientists and coral reef ecologists at several MPA. The Papahanaumokuakeain the Northwest Hawaiian Islands is a relatively pristine coral reef ecosystem that exhibits a trophic structure dominated by apex predators. Preliminary estimates are that sharks and jacks constitute over 50% of the fish biomass associated with the reefs. This suggests an abundant source of primary production available to herbivores, which must be heavily preyed upon. It is unknown whether the bulk of this primary production is autochthonous, that is, associated with the reef environment and surrounding sediments, or allochthonous, that is, associated with the North Pacific Gyre and brought in to the reef ecosystem on ocean currents. Autochthonous production would be primarily associated with benthic algae and coral organisms, while allochthonous production would be associated with oceanic phytoplankton production. These two sources of primary production are distinguishable by their stable C isotope signature, or 13C value. The C isotope signatures of fish and shark tissue will provide an index of the amount of benthic (autochthonous) and planktonic (allochthonous) production supporting fishery production. N isotopes do not differ much between benthic and pelagic primary producers in oceanic environments, but they are excellent indicators of the trophic position of consumers. Compared to their food, consumer organisms are enriched in 15N in a significant and predictable pattern, and so can be used to determine whether a fish is feeding 2, 3, 4 or more steps above the base of the food chain.

Expected Outcome:
Food web models, based on stable isotope analysis of fish, shark and plant tissue, will provide an estimate of the importance of pelagic (phytoplankton) primary production to fishery production in the Papahanaumokuakea National Monument (PNM). Food web models of apex predators in the PNM will provide an estimate of the trophic level at which sharks and jacks are feeding in a relatively pristine ecoystem, helping resource managers to determine effects of anthropogenic fishing pressure on reef ecosystems. Food web models of fish collected from shallow coastal ocean envirnoments, such as the West Florida Shelf, which lack signifcant reef ecosystems, will help determine the sources of primary production supporting fish production in these nearshore environments. The potential contribution of benthic primary producers, including seagrasses and benthic algae, to coastal ocean food webs is an important parameter in forecasting the response of coastal ocean productivity to such perturbations as storms, harmful algal blooms, and other sources of turbidity which reduce the amount of light reaching the bottom. Food web models of MPA in coral reef envrionments can help determine the degree to which fish typically associated with the coral reef strucutre may rely on surrounding benthic habitats, including seagrass beds, for food. In turn, these findings will help resource managers determine the appropriate boundaries for MPA designation.