PHYTOPLANKTON COMMUNITY COMPOSITIONS IN THE WESTERN EQUATORIAL PACIFIC DETERMINED FROM CHLOROPHYLL AND CAROTENOID PIGMENT DISTRIBUTIONS

The chlorophyll and carotenoid pigment compositions of particulate matter from 11 locations in the western equatorial Pacific were analysed by high performance liquid chromatography (HPLC). Chlorophyll a (Chl a) concentrations were generally low, as is common in oligotrophic waters, but they differed by more than an order of magnitude between locations (0.01-0.34 μgl-1). Chlorophyll b concentrations were high at most stations, and higher than Chl a at one site on the equator. Major carotenoids included zeaxanthin, 19′-hexanoyloxyfucoxanthin and 19′-butanoyloxyfucoxanthin. Peridinin, prasinoxanthin and fucoxanthin were present in low concentrations at every station (0-16 ng l-1), but alloxanthin was found at only three sites. The concentrations of marker pigments were used in conjuction with Chl a/pigment ratios characteristics of the different algal classes to derive the composition (by class) of the phytoplankton communities. These calculations suggest that the phytoplankton communities are dominated by algal classes which mainly contain nanoplanktonic species. Prymnesiophytes were abundant at most stations, whereas green algae, cyanobacteria and prochlorophytes were important in specific areas. Although diatoms are usually the major source of fucoxanthin in productive water bodies, in these equatorial watersprymnesiophyte contributions were much more important. Diatoms were not abundant at any station. Community composition and biomass showed greater variation than has been reported for other oligotrophic regions, probably due to local features such as water mixing near the equator and off the coast of Papua New Guinea. Some of the advantages and limitations of HPLC analysis of marker pigments for the determination of phytoplankton community compositions in oceanic waters are discussed. © 1990.