to a small autumn peak. After the breakup of the seasonal pycnocline, 

 the winter impoverishment of the epipelagic zone begins. 



In the extreme south, the maximum of zooplankton lags behind the 

 maximum of phytoplankton by only a month. This is not a result of more 

 rapid development of the zooplankton. The reason is that the early onset 

 of winter causes earlier descent of plankters from the surface waters. 

 As a result, some species do not succeed in completing their development 

 and descend at younger stages. 



The difference in time of onset of the maxima for plants and 

 animals is reflected in their spatial distribution as well. The ring of 

 phytoplankton bloom is always located further south than the ring of the 

 summer maximum biomass of zooplankton (Voronina, 1970a, b). In the period 

 preceding the peak of the zooplankton, the maximum concentrations of 

 both groups of organisms usually coincide in the upper layer of the 

 epipelagic zone. Later, they diverge: First, as a result of the over- 

 utilization of phytoplankton. its absolute maximum shifts deeper than 

 the maximum of its consumers; at the end of the season, most of the mass 

 of animals descends into the subsurface layer, while the maximum of algae 

 remains nearer the surface. 



The great amplitude of fluctuations in the population of algae 

 and the long period of underutil ization of the primary production are 

 characteristics of the low degree of balance in the cycles of phytoplankton 

 and zooplankton in the Antarctic. However, the degree of imbalance 

 apparently experiences significant local fluctuations, depending on the 

 hydrologic specifics and the composition of the zooplankton. Wherever, 

 due to a sharp thermocline, the copepods of the winter pool cannot reach 

 the productive layer (Voronina, 1970a, 1974), primary production is still 

 more underutilized than elsewhere. The situation is quite different at 

 the Antarctic Convergence, where the descent of the water decreases 

 primary production, but the quantity of zooplankton increases due to the 

 arrival of allochthonic material. As a result, the ratio of biomasses 

 of phytoplankton and phytophages is significantly lower here than in other 

 areas and, correspondingly, the degree of its utilization increases. The 

 maximum balance for the Antarctic is achieved in waters where the plankton 

 is dominated by euphausiids, particularly E^. superba , which do not perform 

 seasonal migrations (Voronina, 1970a, b). These large crustaceans, in 

 the post-larval period, are constantly present in the surface water mass and, 

 immediately after the beginning of vegetation, can consume the primary 

 production. 



Such is the annual cycle in the Antarctic pelagic zone. The data for 

 the Subantarctic are too sparse, and can be utilized only for a brief 

 description. The occurrence of great seasonal fluctuations in the quantity 

 of phytoplankton indicates that the cycle here is also unstable. However, 

 the existence of two generations of most phytophages and their rapid 

 development (thanks to the warmer temperatures) should decrease the period 

 of underutilization of primary production and result in a greater degree 

 of balance between the first two trophic levels. These ideas are confirmed 

 by data on the distribution of bottom sediment in the Southern Ocean. 



106 



