A quantitative study of phytoplankton from the equatorial Pacific

The hydrography and abundance of phytoplankton were studied at three stations located in the equatorial Pacific, March 1957. Water bottle samples preserved with neutralized formalin were used for the phytoplankton study, which included the smaller forms of diatoms, dinoflagellates and coccolithophorids. Difficulties in obtaining reliable estimates in the case of poor populations were overcome by a simple concentration technique.

The quantity of phytoplankton, computed as number of cells under 0·1 m², was found to be much the same as the maximal figure for the Sargasso Sea and the amount obtained before and after the time of maximal population in the antarctic and subantarctic Pacific.

In the equatorial Pacific phytoplankton abundance was restricted to the upper 50 to 100 m. Maxima in the numbers of diatoms were found nearer the surface than those of dinoflagellates, while the coccolithophorids showed different patterns in their vertical distribution. “Olivgrüne Zellen” (Hentschel) were present at the greatest sampling depths.

A pennate diatom species, athecate dinoflagellates and certain small coccolithophorids were the most numerous forms observed.

Circumstantial evidence of seasonal variation is discussed.