In general, early studies of plankton of the Southern Ocean, and of the Pacific Sector of the Southern Ocean in particular, are closely linked to the history of exploration of the Antarctic continent and its surrounding seas. J.D. Hooker, the famed botanist and surgeon of the Erebus and Terror Expeditions (1839-43), collected the first plankton samples in Antarctic waters. Hooker sent samples collected between Cape Horn and the Ross Sea to the German diatomist, C.G. Ehrenberg, who published the first paper on Antarctic diatoms in 1844. At about the same time, Dumont d'Urville published an interesting account of the Antarctic waters in his "Voyage au Pole Sud et dans l'Oceanie", noting the rich plant and animal life. During the following three-quarters of a century, extensive collection of Antarctic phytoplankton was conducted by members of such celebrated expeditions as the Challenger (1873-76), Belgica (1897-99), Valdivia (1898-99), Gauss (1901-08), Scotia (1902-04), Pourquoi Pas? (1908-10) and Meteor (1925). The Discovery II investigations (1925-39, 1950-61) substantially increased our knowledge of the distribution and abundance of the phytoplankton and zooplankton populations, especially krill, in the Atlantic, Indian and Pacific Sectors of the Southern Ocean.

In the Pacific Sector of the Southern Ocean, systematic studies of the plankton commenced in the mid-1950s and early 1960s with the cruises of the Russian ships Ob, Slava and Vitiaz, the United States Navy ship, Eltanin, as well as with the numerous Japanese Antarctic Research Expeditions (JARE). As a result of these investigations, a large body of valuable data was obtained on the geographic and temporal distributions of phytoplankton and zooplankton populations, especially for the high latitudes of the South Pacific. El-Sayed (1970a), Knox (1970) and Bary (1970) provided comprehensive reviews of the knowledge about plankton of the South Pacific accumulated up until the late 1960s. Moreover, in a paper on the abundance, composition and distribution of phytoplankton in the Pacific Antarctic, Hasle (1969) gave an excellent overview of the history of phytoplankton investigations of the Southern Ocean up to that time.

Study of the structure and function of the Antarctic marine ecosystem began in the southwestern Pacific Sector of the Antarctic with Eltanin Cruise 38 (March to May 1969). This cruise (together with Eltanin Cruises 46 and 51 in the Indian and Pacific Sectors, respectively) constitutes a landmark in the history of ecosystem-oriented study of the seas surrounding Antarctica (El-Sayed, 1973; McWhinnie, 1973). Eltanin Cruise 51 completed an integrated study of the biology, chemistry and physical oceanography of the Ross Sea which served as a prelude to the Ross Ice Shelf Project (RISP) investigations in the late 1970s. Research efforts in the early 1980s, under the auspices of the program, Biological Investigations of Marine Antarctic Systems and Stocks (BIOMASS) has enhanced our knowledge of the plankton populations in the Pacific Sector of the Southern Ocean, although not to the same extent as the Atlantic and Indian Sectors. The publications by Heywood and Whitaker (1984) and Everson (1984b) provide recent comprehensive overviews of the Southern Ocean phytoplankton and Zooplankton, respectively.

Knowledge about the plankton and, for that matter, about other biological components of the Pacific Sector of the Antarctic lags behind that of the better-studied waters of the Atlantic Sector. In addition, while the broad distributional features of Antarctic plankton are now known, many ecological questions remain unanswered. Fortunately, due to the circumpolar nature of the Southern Ocean, knowledge gained in one sector can be applied to other sectors, provided that due allowances are made for characteristic hydrographic and environmental conditions (Hart, 1942). The reader should keep these allowances in mind, as information provided in this chapter is not strictly limited to the Pacific Sector of the Antarctic.

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