Despite the great strides made in recent years in the study of the Antarctic marine ecosystem, in part stimulated by the prospect of harvesting its marine living resources, our knowledge of the plankton in the Pacific Sector of the Southern Ocean is far from satisfactory and lags behind that of the better studied Atlantic Sector. Research carried out under the BIOMASS programme has, to some extent, ameliorated this deficiency.
Phytoplankton biomass in the Pacific Sector varies spatially and temporally as a function of a variety of physical, chemical and biological factors; notable among these are light, temperature, water column stability and grazing. Phytoplankton investigations carried out to date underscore four important points : (1) that the phytoplankton biomass and primary production rates vary by at least one to two orders of magnitude; (2) that the seasonal variabilities of phytoplankton biomass and productivity are overshadowed by geographical variations in these parameters; (3) that, like the Atlantic and Indian Sectors, Pacific Sector waters, in general, display their richness mainly in coastal regions; and (4) that Pacific Sector waters do not show an outstandingly high rate of primary production.
The copepods constitute the bulk of the Antarctic mesoplankton (accounting for an average of about 70% of its total biomass) with the chaetognaths as distant second. Most, if not all, Antarctic zooplankton species are circumpolar in distribution; however, they frequently show centres of concentrations at different depths or in different latitudes. Hydrographie conditions play an important role in the distribution of Southern Ocean zooplankton. For instance, the Subtropical Convergence and the Polar Front act as effective barriers to the distribution of some organisms. As to the zooplankton standing crop, it is difficult to arrive at reasonable estimates of their biomass because of problems related to sampling techniques, patchy distribution, and seasonal vertical migration.
Krill investigations carried out in recent years have contributed substantially to our knowledge of the biology, distribution, longevity, food and feeding behavior of this organism. However, much remains to be learned, as even the estimates of krill biomass are still a matter of controversy.
As a result of the recent investigations carried out on phytoplankton/zoo-plankton/krill interrelationships, we may find it necessary to modify our concept of the structure and function of the Antarctic marine ecosystem. In light of these investigations we are being forced to re-examine the classical description of a simple food chain from diatoms-» krill—» whales. Recent studies on Antarctic bacterioplankton, dissolved organic matter, nanoplankton, picoplankton, sea ice-algae and krill food sources suggest the presence of hitherto overlooked pathways through which a major part of the avilable energy may be flowing. A new paradigm of the Antarctic ocean's food web is now emerging (Fig. 8.17). This paradigm may contain yet other strands, so that the classic pathway may constitute only a part of the energy flow within the Antarctic marine ecosystem.
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