FOOD WEB ANALYSIS OF A PLANKTONIC SYSTEM OFF SOUTHERN CALIFORNIA

The California Basin Study program (CaBS) has measured carbon and nitrogen flows between some of the compartments of a planktonic system off Southern California. We have used an inverse analysis approach to infer those flows which were not measured in order to develop a more complete description of the planktonic food web. We then analyzed these results by using network analysis and by following the movement of imaginary tracers through the food web. Results suggest that detritus was a crucial part of the food web, with a substantial fraction of algal production flowing directly to it. Detrital production of dissolved organic matter (DOM), along with leakage from grazers, were the dominant sources of bacterial food. Bacteria did not provide an important path for the movement of organic matter to the larger mesozooplankton. Although mesozoa were not the dominant grazers of algal production, they were important for the movement of material below the euphotic zone, accounting for nearly half of the downward flux. Flows of carbon and nitrogen were quite different because Of Carbon respiration. Nitrogen removal from the euphotic zone was influenced by high dissolved organic nitrogen (DON) concentrations. The effects of DON and dissolved organic carbon (DOC) in euphotic zone elemental cycling imply that an element used to trace new production will have a different removal rate from the euphotic zone unless it also has a comparable dissolved organic phase. More experimental effort needs to be devoted to detrital dynamics, as well as those of sub-copepod sized grazers.