172
J . E . G . R A Y M O N T
or early autumn. The amplitude from winter minimum to annual
maximum may be a t least 40 times, with inshore waters (cf. Russell and
Colman, 1934) showing fluctuations far greater than 40 times. High
latitudes may show an enormous increase in zooplankton volumes over
the productive season (cf. Fish, 1954 for the Labrador Sea).
A typical cycle of zooplankton seasonal changes in northern temperate waters comes from the work of Harvey et al. (1935); from a
minimum in January - February there was a rise in zooplankton to a
maximum in spring and a second maximum occurs in late summer. The
zooplankton was dominated by copepods. Deevey (1956) dealing with
the zooplankton in Long Island Sound and Block Island Sound also
found marked seasonal fluctuation in zooplankton with the maximum
in summer. Wiborg (1954) recorded a spring or early summer peak in
zooplankton and a second rise between August and October, the chief
contributor to this reproductive cycle being the copepods. Digby (1954)
observed a later summer maximum for Greenland waters when the
volume was some 20 times that of the winter minimum. Fish ( 1 9 5 4 and
Kielhorn (1952) found very great changes in zooplankton abundance
between summer and winter with a maximum about July and August
in waters of the Labrador Sea. Comparative work in the Antarctic
(e.g. Mackintosh, 1934; 1937) suggests that a rapid increase in the zooplankton occurs during the spring and summer and that a peak value is
achieved during the Antarctic summer, about February. By the late
summer the population is declining again and reaches low values over
winter.
To some extent, however, this pattern can be changed by vertical
migration. Foxton (1956) has stated that seasonal variations in plankton
volume in the Antarctic are much reduced if sampling is continued
down to at least a thousand metres depth. Hansen (1960) also refers to
this problem of vertical migration and the biomass of zooplankton with
reference to the Norwegian Sea. Hansen was investigating mainly the
upper 50 metres, and in the open Norwegian Sea the average biomass
in June was some 30 times that for the minimum period in November/
December. This, however, was partly explained by a marked migration
especially of copepods. I n coastal waters, where some of the neritic
copepods remained nearer the surface, the fluctuation between summer
and winter was not nearly so great.
Despite seasonal fluctuations, however, zooplankton at high latitudes
tends to be more abundant than in warm waters, and at any latitude
neritic plankton tends to be richer. Clarke (1940) investigated the waters
south-east of New York and found them to be very much richer than in
the area of mixing between the continental slope and the Gulf Stream
to the south-east. The fluctuations between winter and summer in the
J . E . G . R A Y M O N T
or early autumn. The amplitude from winter minimum to annual
maximum may be a t least 40 times, with inshore waters (cf. Russell and
Colman, 1934) showing fluctuations far greater than 40 times. High
latitudes may show an enormous increase in zooplankton volumes over
the productive season (cf. Fish, 1954 for the Labrador Sea).
A typical cycle of zooplankton seasonal changes in northern temperate waters comes from the work of Harvey et al. (1935); from a
minimum in January - February there was a rise in zooplankton to a
maximum in spring and a second maximum occurs in late summer. The
zooplankton was dominated by copepods. Deevey (1956) dealing with
the zooplankton in Long Island Sound and Block Island Sound also
found marked seasonal fluctuation in zooplankton with the maximum
in summer. Wiborg (1954) recorded a spring or early summer peak in
zooplankton and a second rise between August and October, the chief
contributor to this reproductive cycle being the copepods. Digby (1954)
observed a later summer maximum for Greenland waters when the
volume was some 20 times that of the winter minimum. Fish ( 1 9 5 4 and
Kielhorn (1952) found very great changes in zooplankton abundance
between summer and winter with a maximum about July and August
in waters of the Labrador Sea. Comparative work in the Antarctic
(e.g. Mackintosh, 1934; 1937) suggests that a rapid increase in the zooplankton occurs during the spring and summer and that a peak value is
achieved during the Antarctic summer, about February. By the late
summer the population is declining again and reaches low values over
winter.
To some extent, however, this pattern can be changed by vertical
migration. Foxton (1956) has stated that seasonal variations in plankton
volume in the Antarctic are much reduced if sampling is continued
down to at least a thousand metres depth. Hansen (1960) also refers to
this problem of vertical migration and the biomass of zooplankton with
reference to the Norwegian Sea. Hansen was investigating mainly the
upper 50 metres, and in the open Norwegian Sea the average biomass
in June was some 30 times that for the minimum period in November/
December. This, however, was partly explained by a marked migration
especially of copepods. I n coastal waters, where some of the neritic
copepods remained nearer the surface, the fluctuation between summer
and winter was not nearly so great.
Despite seasonal fluctuations, however, zooplankton at high latitudes
tends to be more abundant than in warm waters, and at any latitude
neritic plankton tends to be richer. Clarke (1940) investigated the waters
south-east of New York and found them to be very much richer than in
the area of mixing between the continental slope and the Gulf Stream
to the south-east. The fluctuations between winter and summer in the