T H E PRODUCTION O F MARINE !?LANKTON
171
strate the relative abundance of zooplankton i n colder, boreal waters as
compared with the low crop in warm seas. Jespersen (1924) found that
although there may be considerable variations in zooplankton abundance in warmer waters, for instance, in the Atlantic considerably
greater quantities of zooplankton were found north of the Azores than
off the American coast and near Bermuda, the boreal regions were much
richer. Thus in subtropical and tropical regions, plankton volumes
varied from less than a litre to two litres an hour; in the northern
Atlantic west of Ireland, Jespersen found volumes approaching 7-8
litres per hour; and in the colder seas north of Scotland much greater
amounts approaching 18 or 19 litres per hour. I n general, Jespersen
suggests that for the open oceans the average crop of zooplankton in
cold northern waters is at least some eight times that of tropical seas.
Such waters are characterized by low nutrient level and poor production. Wherever in tropical regions upwelling brings nutrients to the
surface, increased primary production is accompanied by richer zooplankton. King and Hida (1957) have recentby recorded a new area of
abundance in the region of upwelling and divergence in the equatorial
central Pacific. A summary of the varying standing crops of zooplankton in different oceanic regions is given by Hela and Laevastu
(1962).
One of the problems in comparing zooplankton production at low and
high latitudes is that the seasonal abundance of zooplankton shows very
wide changes at higher latitudes. By contrast, though there is usually
some seasonal change and though different species may breed at different times of the year, in general in warm seas .bhe fluctuations are comparatively small. In Indian waters the zooplankton as a whole shows
some fluctuations in abundance over the year and this is probably
associated with the monsoon affecting phytoplankton production.
Wickstead (1958) demonstrated changes similar to the spring and
autumn peak of zooplankton production in the Singapore Straits,
probably associated with monsoon weather conditions. Moore ( 1949)
suggested for waters round Bermuda that the zooplankton under these
more oceanic conditions showed relatively little seasonal fluctuation,
and Menzel and Ryther (196lb) found a small spring maximum of zooplankton in the Sargasso Sea, but as a whole the fluctuation was small
with a low standing crop of zooplankton. Bsharah (1957) found in the
Florida current region a small seasonal fluctuation in plankton, but the
maximum averaged no more than two or three times that for the
remainder of the year.
By contrast in temperate and high latitudes the abundance of
plankton in spring and summer shows a remarkable increase over
winter, and frequently there may be a peak production in late summer
171
strate the relative abundance of zooplankton i n colder, boreal waters as
compared with the low crop in warm seas. Jespersen (1924) found that
although there may be considerable variations in zooplankton abundance in warmer waters, for instance, in the Atlantic considerably
greater quantities of zooplankton were found north of the Azores than
off the American coast and near Bermuda, the boreal regions were much
richer. Thus in subtropical and tropical regions, plankton volumes
varied from less than a litre to two litres an hour; in the northern
Atlantic west of Ireland, Jespersen found volumes approaching 7-8
litres per hour; and in the colder seas north of Scotland much greater
amounts approaching 18 or 19 litres per hour. I n general, Jespersen
suggests that for the open oceans the average crop of zooplankton in
cold northern waters is at least some eight times that of tropical seas.
Such waters are characterized by low nutrient level and poor production. Wherever in tropical regions upwelling brings nutrients to the
surface, increased primary production is accompanied by richer zooplankton. King and Hida (1957) have recentby recorded a new area of
abundance in the region of upwelling and divergence in the equatorial
central Pacific. A summary of the varying standing crops of zooplankton in different oceanic regions is given by Hela and Laevastu
(1962).
One of the problems in comparing zooplankton production at low and
high latitudes is that the seasonal abundance of zooplankton shows very
wide changes at higher latitudes. By contrast, though there is usually
some seasonal change and though different species may breed at different times of the year, in general in warm seas .bhe fluctuations are comparatively small. In Indian waters the zooplankton as a whole shows
some fluctuations in abundance over the year and this is probably
associated with the monsoon affecting phytoplankton production.
Wickstead (1958) demonstrated changes similar to the spring and
autumn peak of zooplankton production in the Singapore Straits,
probably associated with monsoon weather conditions. Moore ( 1949)
suggested for waters round Bermuda that the zooplankton under these
more oceanic conditions showed relatively little seasonal fluctuation,
and Menzel and Ryther (196lb) found a small spring maximum of zooplankton in the Sargasso Sea, but as a whole the fluctuation was small
with a low standing crop of zooplankton. Bsharah (1957) found in the
Florida current region a small seasonal fluctuation in plankton, but the
maximum averaged no more than two or three times that for the
remainder of the year.
By contrast in temperate and high latitudes the abundance of
plankton in spring and summer shows a remarkable increase over
winter, and frequently there may be a peak production in late summer