ABSTRACT
Classically, phytoplankton losses have been attributed primarily to zooplankton grazing. Within the past decade there has been increased evidence that microzooplankton and bacteria also mediate the oxidation of phytoplankton, especially in the oligotrophic central ocean gyres. On the continental margins, however, export of shelf phytoplankton to the adjacent ocean basins may also occur. The Shelf Edge Exchange Processes (SEEP) program is a multidisciplinary effort aimed at quantifying the various fates of phytoplankton of the Northeast Continental Shelf ecosystem of the United States. The results of the first SEEP field program, conducted off the coast of Long Island, New York and Martha's Vineyard, Massachusetts, in 1984, suggested that about 35% of the spring phytoplankton production was consumed by herbivorous zooplankton, 45% was oxidized on the shelf by microbes and the benthos, and the remainder was possibly exported to the interior of the adjacent ocean basin and slope sediments. In the second SEEP program, conducted off the Delmarva Peninsula from March 1988 to May 1989, phytoplankton and zooplankton biomass, current speed and direction, incident irradiance, soluble oxygen, as well as temperature and salinity were continuously measured at 10 moorings by state-of-the-art instrumentation. The results revealed that a single pulse of phytoplankton, constituting a bloom, does not occur in the spring, that phytoplankton and zooplankton biomass are highly coherent, and that on a time scale of 2 to 10 days, physical processes dominate the dynamics between primary and secondary producers. The results imply that understanding food chain dynamics requires a much higher temporal resolution of components than has heretofore been available, and that on the continental shelf, fisheries are more likely to be limited by recruitment and mortality than food availability.
