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

The contribution of large phytoplankton to the standing stock and productivity of the eastern-boundary ecosystem of Monterey Bay, California, was evaluated 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 Niño and non-El Niño years). The larger cell sized (>5 μm) autotrophs contributed significantly to chlorophyll, particulate nitrogen, and new and primary productivity in most cruises. This was especially noticeable above a threshold nutrient concentration of 10–12 μM nitrate. Pooling the entire dataset, there were good linear relationships between biomass and productivity parameters measured using GF/F and 5 μm filters. The contribution of the >5 μm size fraction was greatest at higher biomass concentrations and productivity rates, supporting the idea that to reach maximal values, large cells are required. There were linear trends with Chl : PON ratio of close to 1, and 14C : 15NO3 uptake ratio of about 10 in both total and >5 μm size fractions. These large cells are major contributors to carbon and nitrogen productivity in Monterey Bay.