Phytoplankton play a central role in biogeochemical cycles. Simply measuring biomass and production is not sufficient; a detailed assessment of the community structure is necessary to elucidate the population dynamics, annual variability and responses to short-term physical events. The objectives of this project are: (1) to determine the composition of the phytoplankton community at the GOFS Hawaii Ocean Time-series station, (2) to estimate the contribution of the different algal populations to the total biomass, and (3) to understand depth distribution and temporal patterns and to elucidate annual variability. In order to characterize and quantify the different populations of cells of the phytoplankton community a number of different techniques will be employed. Flow cytometry will allow rapid discrimination of different groups such as eukaryotic picoplankton, Synechococcus - cyanobacteria, and the newly discovered prochlorophytes. It will provide an efficient and quantitative way to measure cell concentration and to quantitate pigment fluorescence and scatter signature on a single-cell basis. Immunofluorescence techniques, using antibodies specifically targeted at prokaryotic (Synechococcus) and eukaryotic (e.g. prasinophytes, coccolithophorids) groups and pigment analyses (by HPLC and spectrofluorometry) will permit further refinement of the taxonomic composition of the community. The latter will be specifically helpful for the smaller eukaryotes and for the prochlorophyte component which has a unique divinyl-chlorophyll signature and which is believed to be very important in oligotrophic waters. This project will provide the first detailed time-series data on the structure of the phytoplankton community in the central Pacific gyre. The results will complement the core measurements made at station ALOHA by adding a quantitative analysis of the primary producer community, which will serve as a basis for future realistic modeling efforts. Contrasting our findings with a parallel project to be conducted by S.W. Chisholm and R.J. Olson (MIT/WHOI) at the GOFS Bermuda site, where phytoplankton exhibits pronounced seasonal variability, will reinforce the value of both studies.
