THE PRODUCTION O F MARINE PLANKTON
173
coastal waters were far greater ( x 20 to x 40) than in the “slope”
water (some x lo), but the average volume of zooplankton in the
coastal zone was about 4 times greater than in the “slope” area. In the
Sargasso Sea, Clarke found that the average volume of plankton hauls
was much less - only approximately one-quarter that of the “slope”
stations. The seasonal fluctuation in the Sargasso was negligible.
Foxton (1956) also found that the mean volume of zooplankton
increased fairly steadily from the subtropics through the sub-antarctic
to Antarctic areas. He believes that the standing crop in the Antarctic
was at least 4 times that of tropical southern areas; even then the
Antarctic plankton may not have been adequately sampled. There
was some indication of a reduction at the highest latitudes. Certainly in
the northern hemisphere at the very highest lakitudes it appears that
the biomass of zooplankton is very much reduced. Zenkevitch (1963)
has summarized the general quantitative distribution of zooplankton in
northern seas. Allowing for the fact that the zooplankton in very cold
seas may be richer in the lower layers, it appears from the work of
Russian investigators that the total biomass of zooplankton is very low
in the Polar basin. In the area north of Siberia the markedly lower
salinity may affect the biomass, but the gene]-a1 low productivity of
Polar waters is reflected in the low zooplankton crop. Figure 11
illustrates the remarkable rise in zooplankton density from low numbers
in the warmer Pacific seas, through high numbers in boreal waters, and
the very sharp reduction in really Arctic areas. As regards the Arctic
and sub-Arctic seas of the U.S.S.R., Zenkevitch points out that the
south-western Barents Sea is by far the most productive. A zooplankton biomass up to 2 000 mg/m3 was recorded in the summer in
some areas, but even for the whole Barents Sea, the mean annual biomass is quoted as 140 mg/m3. As compared with this, the biomass in
the colder seas is much lower; thus in the Laptev Sea and the eastern
Siberian Sea Zenkevitch quotes Jashnov that even in the summer, the
biomass does not exceed 72 mg/m3 on average. But Zenkevitch points
out that in the more central Arctic basin there seems to be a very significant decrease in zooplankton. He quotes only 12 mg/m3 in the upper
100 metres; a rise to nearly 30 mg/m3 in an intermediate layer; but only
some 7 mg/m3 in the deep layer below 800 metrlss. Johnson (1963) also
refers to the low standing crop of zooplankton in the Arctic basin. This
agrees with the very low primary production.
A summary of the biomass of zooplankton, as measured by displacement volume, is given by Bigelow and Sears (1939) for areas of the
northern Atlantic. Seas around Iceland, the Faroes and the north of
Scotland appear to be especially rich. Bigelow and Sears suggest that the
continental shelf waters off the north-east coast of U.S.A. rank next in
173
coastal waters were far greater ( x 20 to x 40) than in the “slope”
water (some x lo), but the average volume of zooplankton in the
coastal zone was about 4 times greater than in the “slope” area. In the
Sargasso Sea, Clarke found that the average volume of plankton hauls
was much less - only approximately one-quarter that of the “slope”
stations. The seasonal fluctuation in the Sargasso was negligible.
Foxton (1956) also found that the mean volume of zooplankton
increased fairly steadily from the subtropics through the sub-antarctic
to Antarctic areas. He believes that the standing crop in the Antarctic
was at least 4 times that of tropical southern areas; even then the
Antarctic plankton may not have been adequately sampled. There
was some indication of a reduction at the highest latitudes. Certainly in
the northern hemisphere at the very highest lakitudes it appears that
the biomass of zooplankton is very much reduced. Zenkevitch (1963)
has summarized the general quantitative distribution of zooplankton in
northern seas. Allowing for the fact that the zooplankton in very cold
seas may be richer in the lower layers, it appears from the work of
Russian investigators that the total biomass of zooplankton is very low
in the Polar basin. In the area north of Siberia the markedly lower
salinity may affect the biomass, but the gene]-a1 low productivity of
Polar waters is reflected in the low zooplankton crop. Figure 11
illustrates the remarkable rise in zooplankton density from low numbers
in the warmer Pacific seas, through high numbers in boreal waters, and
the very sharp reduction in really Arctic areas. As regards the Arctic
and sub-Arctic seas of the U.S.S.R., Zenkevitch points out that the
south-western Barents Sea is by far the most productive. A zooplankton biomass up to 2 000 mg/m3 was recorded in the summer in
some areas, but even for the whole Barents Sea, the mean annual biomass is quoted as 140 mg/m3. As compared with this, the biomass in
the colder seas is much lower; thus in the Laptev Sea and the eastern
Siberian Sea Zenkevitch quotes Jashnov that even in the summer, the
biomass does not exceed 72 mg/m3 on average. But Zenkevitch points
out that in the more central Arctic basin there seems to be a very significant decrease in zooplankton. He quotes only 12 mg/m3 in the upper
100 metres; a rise to nearly 30 mg/m3 in an intermediate layer; but only
some 7 mg/m3 in the deep layer below 800 metrlss. Johnson (1963) also
refers to the low standing crop of zooplankton in the Arctic basin. This
agrees with the very low primary production.
A summary of the biomass of zooplankton, as measured by displacement volume, is given by Bigelow and Sears (1939) for areas of the
northern Atlantic. Seas around Iceland, the Faroes and the north of
Scotland appear to be especially rich. Bigelow and Sears suggest that the
continental shelf waters off the north-east coast of U.S.A. rank next in