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major fisheries are actually found on the continental shelves and slopes on both sides, where
the degree of hydrodynamic heterogeneity is largest. More generally, these factors would
explain, according to Cushing (1989), why the great fisheries of the world are based on
diatoms and their> 5 /Lm successors in the spring bloom (and, in upwelling areas, the larger
flagellates) .
TYPE 4. PRODUCTION BY SMALL AND LARGE CELLS, STANDING STOCK
DOMINATED BY SMALL CELLS
A good example of this type of ecosystem is found in the oceanic waters of the Alaskan Gyre
in the North Pacific Ocean (Ocean Weather Station P), as recently reviewed by Parsons and
Lalli (1988) and Miller and SUPER Group (1988). One of the major features in the annual
cycle there (Fig. 7) is that little increase in chlorophyll a standing stock takes place with
respect to the winter background level, although the integrated annual production is similar
to that measured in the North Atlantic at OWS I, where a well-defined spring bloom occurs
(Fig. 6). At any time, the phytoplankton standing stock near OWS P mainly consists of small
flagellates; larger diatoms, however, are also present in small numbers, and eventually
dominate samples incubated in the absence of zooplankton (McAllister et al., 1960). Biomass
increase by large diatoms is therefore suppressed by grazing, but the large cells do effectively
contribute to primary production. The annual increase in primary production takes place rather
progressively; not inconsistently with Sverdrup's (1953) critical depth model, it is associated
with a change in the depth of the mixed layer but, because there is a permanent halocline at
about 100 m, this change is much less sharp than in areas with a spring bloom. The relatively
weak temporal hydrodynamic heterogeneity of the environment would contribute to explaining
why significant primary production is found year-round.
Production by small cells is normally transferred to microheterotrophs. In the Alaskan Gyre,
large protozoan standing stocks are present in winter but, according to Parsons and Lalli
(1988), they are eaten away by large copepods belonging to the genus Neocalanus at the onset
of the productive season. As in Type 3 above, these copepods overwinter at the last
copepodite stage and reproduce in the spring. What is peculiar to the Alaskan Gyre, according
major fisheries are actually found on the continental shelves and slopes on both sides, where
the degree of hydrodynamic heterogeneity is largest. More generally, these factors would
explain, according to Cushing (1989), why the great fisheries of the world are based on
diatoms and their> 5 /Lm successors in the spring bloom (and, in upwelling areas, the larger
flagellates) .
TYPE 4. PRODUCTION BY SMALL AND LARGE CELLS, STANDING STOCK
DOMINATED BY SMALL CELLS
A good example of this type of ecosystem is found in the oceanic waters of the Alaskan Gyre
in the North Pacific Ocean (Ocean Weather Station P), as recently reviewed by Parsons and
Lalli (1988) and Miller and SUPER Group (1988). One of the major features in the annual
cycle there (Fig. 7) is that little increase in chlorophyll a standing stock takes place with
respect to the winter background level, although the integrated annual production is similar
to that measured in the North Atlantic at OWS I, where a well-defined spring bloom occurs
(Fig. 6). At any time, the phytoplankton standing stock near OWS P mainly consists of small
flagellates; larger diatoms, however, are also present in small numbers, and eventually
dominate samples incubated in the absence of zooplankton (McAllister et al., 1960). Biomass
increase by large diatoms is therefore suppressed by grazing, but the large cells do effectively
contribute to primary production. The annual increase in primary production takes place rather
progressively; not inconsistently with Sverdrup's (1953) critical depth model, it is associated
with a change in the depth of the mixed layer but, because there is a permanent halocline at
about 100 m, this change is much less sharp than in areas with a spring bloom. The relatively
weak temporal hydrodynamic heterogeneity of the environment would contribute to explaining
why significant primary production is found year-round.
Production by small cells is normally transferred to microheterotrophs. In the Alaskan Gyre,
large protozoan standing stocks are present in winter but, according to Parsons and Lalli
(1988), they are eaten away by large copepods belonging to the genus Neocalanus at the onset
of the productive season. As in Type 3 above, these copepods overwinter at the last
copepodite stage and reproduce in the spring. What is peculiar to the Alaskan Gyre, according