PHYTOPLANKTON AND CIILOROPHYLL IN THE GERLACHE AND BRANSFIELD STRAITS OF ANTARCTICA1

Studies wcrc: mndc on the phytoplankton and chloropl~yll (1 content of waters in the Gcrlathe and Bransficld Straits of Antarctica during Dcccmbcr 1958 and January 1959. Rich communities of diatoms, snch as ?‘lzaZussiosiIa, CoscinotZiscz48, Eucfmpin, and SUnecLcr, and the chrysophyccan Phaeocystis were obscrvccl at numerous stations in the Gcrlacbc Strait and the western part of Bransficld Strait. Dinoflagcllatcs wcrc very SCR~CC: in this region. Antibiotic activity of the plankton was associated with Phaeocystis. The eastern arca of Bransficld Strait, near the tip of the Antarctic Peninsula, was almost dcvoicl of phytoplankton at all dcptl1s. Chlorophyll CL cletcrminations agreed in gcncral with observations on the: abunclancc of phytoplankton. Chlorophyll a ranged up to about 27 mg/m” of water, and the amount of pigmcnt in snrface waters was invcrscly rclatccl to total depth of the water. During the Antarctic summer of 1958-59, an opportunity was offered for studies on phytoplankton productivity in the marinc waters along the western coast of the Antarctic Peninsula. Although our main effort was directed toward the verification and extension of observations on the antibiotic properties of phytoplankton (Sieburth 1959; Sieburth and Rurkholdcr 1959), it scemcd worth while to devote some attention to the distribution of phytoplankton communities and the chlorophyll cz content of the plant plankton in the region indicated. In view of the dcpcndencc of Antarctic birds and fishes upon the photosynthetic plankton, it is important to gain some detailed knowledge concerning the seasonal, geographic and vertical distribution of the plankton and the factors that regulate primary production, As an index of the potential photosynthetic capacity of the plankton, it was decided to determine the quantitative occurrence of chlorophyll a. Because of the lim’ This study was mntlc possible through the logistic support of the Ilydrogrnphic Service and the Naval Antarctic Group of the Argcntinc Navy and financial support by the U. S. Office of Naval Rcsearch ( Nonr-2352 ( 02) ), the Arctic Institute of North Amcricn ( ONR 232), Brooklyn Botanic Garden ant1 Virginia Polytechnic Tnstitutc. ited time available for this work, only about 50 stations were studied, mainly in the region between the South Shetland Islands and the Antarctic Peninsula. Earlier studies of the phytoplankton in the southern ocean have been devoted chiefly to floristic aspects that were of special interest to the various cxpcditions, such as the ChdZengm Expedition, the Voyage of the Relpica, IXscovcry Expeditions, etc. Valuable observations on the species of phytoplankton have been recorded during recent campaigns of the Argcntinc Naval Hydrographic Service ( Frcnguelli and Orlando 1958), but few results have yet appeared in available publications. In an extensive trcatisc on phytoplankton pcriodicity in Antarctic surface waters, I-Iart (1942) has pointed out how the plant plankton is almost entirely diatomaceous in the southern ocean that occupies more than 12 million square miles. Hart expressed the relative abundance of phytoplankton, taken in net hauls from 100 m to the surface, in terms of chlorophyll units, and showed that the more important spccics of diatoms had a completely circumpolar distribution in the oceanic belt extending around the Antarctic continent. The circumpolar distribution of plankton species was cmphasizccl in a paper by Baker ( 1954). Among the earliest treatises on Antarctic,