Biomass and productivity in Monterey Bay, California: contribution of the large phytoplankton

The contribution of large phytoplankton to the standing stock and productiv ity of the eastern-boundary ecosystem of Monterey Bay, California, was eval uated during 1992 and 1993, using size fractionation. Eight cruises sampled the variability of the bay both spatially (within the upwelling plume and offshore) and temporally (during upwelling and non-upwelling seasons, El Ni no and non-El Nino years). The larger cell sized (> 5 mu m) autotrophs cont ributed significantly to chlorophyll, particulate nitrogen, and new and pri mary productivity in most cruises. This was especially noticeable above a t hreshold nutrient concentration of 10-12 mu M nitrate. Pooling the entire d ataset, there were good linear relationships between biomass and productivi ty parameters measured using GF/F and 5 mu m filters. The contribution of t he > 5 mu m size fraction was greatest at higher biomass concentrations and productivity rates, supporting the idea that to reach maximal values, larg e cells are required, There were linear trends with Chl:PON ratio of close to 1, and C-14: (NO3)-N-15 uptake ratio of about 10 in both total and > 5 m u m size fractions. These large cells are major contributors to carbon and nitrogen productivity in Monterey Bay. (C) 2000 Elsevier Science Ltd. All r ights reserved.