Pacific Polar Biome
333
the eastern shelf of this sea with lower chlorophyll in midshelf. On the southeastern shelf,
high rates of primary production persist during the summer in the lee of the Aleutian
Islands rather than in the highly turbulent flow through, for instance, Unimak Pass.
Although diatoms are thought to have dominated phytoplankton biomass in the
Bering Sea for many years, this may have changed recently. During the very warm years
1997–98, there was an unprecedented incursion of the coccolithophore Emiliana huxleyi
into the Bering Sea (Olson and Strom, 2002) and this organism has since become a
major component of the autotrophic biomass there. Images obtained from the MODIS
sensors confirm that the Bering Sea is now one of the very few places in the oceans
where coccolithophore blooms reach biomasses >10 mg C m
−3 . The Okhotsk Sea remains
relatively free of such blooms.
In the inner and middle shelf domain the zooplankton fauna is characterized by the
copepods Calanus pacificus (= C. glacialis of Heinrich, 1962a; Motoda and Minoda, 1974),
together with several species of Pseudocalanus and Acartia longiremis and other biota.
The euphausiid Thysanoessa raschii dominates the early spring zooplankton, followed by
C. pacificus during early summer. In this area, C. pacificus passes the winter as stage 5
copepodites (C5s), presumably in deep water beyond the shelf edge. Springer et al. (1989)
computed that the demand of these herbivorous copepods, and their associated biota, was
such that they were capable of modifying standing stocks of algae and at times required
the total daily production to satisfy their needs. Of course, classic food-web models of
the Bering Sea assume that the dominant phytoplankton biomass is diatoms and that
these are transferred to higher trophic levels largely through copepods: however, Olson
and Strom (2002) propose another model that must be acknowledged. It has been shown
that some diatoms are suboptimal food for some copepods in one part of the ocean,
because of their aldehyde content, so Olson and Strom ask: “If diatoms are a sub-optimal
diet for copepods, what supports the high crustacean biomass in the SE Bering Sea?” The
assumption is based on a logical non sequitur and is perhaps another instance of William
Dickinson’s “mythic thinking” (see flyleaf); at the very least, it ignores the affirmation of
Irigoien et al. (2002) that a diatom diet has no negative effect on the reproduction
of pelagic copepods in a dozen other open ocean regions. Nevertheless, in the context
of the Bering Sea, the enquiry of Olson and Strom must be considered. They invoke
grazing rates of protistan plankton, obtained by dilution experiments, in late summer,
that appear to balance population growth of both large and small phytoplankton cells,
although bacterial cells were not included in their computations. I believe that the most
that can be said at present is that all food-web diagrams and models are to be regarded
as works in progress—and no more than that. Unfortunately, many resource ecologists
and fishery biologists have yet to understand this depressing truth.
Slope Regions Although the highest chlorophyll biomass associated with the outer
front is along the southeast shelf edge, a linear zone of relatively high chlorophyll can be
traced north to the Bering Straits. It is also characteristic that very large meanders should
be induced out over the slope and even over deep water, chlorophyll biomass remaining
very high in these excursions toward the central Bering Sea. The chlorophyll profile over
the slope follows a typical seasonal evolution: after the near-surface spring bloom, algal
growth during the summer (a 120-day growing period) continues in a deep chlorophyll
maximum (DCM) near the pycnocline, fueled by nutrients in the deeper water of the
Bering Slope Current.
The DCM of the Slope Current bifurcates around St. Lawrence Island. The eastern
part subsequently spreads over the northeastern continental slope, inducing rich benthic
fauna, and exists as a near-bottom chlorophyll maximum. The western part is significantly
enriched in the western jet current (Anadyr Current), which flows through the Bering
Straits and passes north into the Chukchi Sea. The shoaling of this flow as it enters the
333
the eastern shelf of this sea with lower chlorophyll in midshelf. On the southeastern shelf,
high rates of primary production persist during the summer in the lee of the Aleutian
Islands rather than in the highly turbulent flow through, for instance, Unimak Pass.
Although diatoms are thought to have dominated phytoplankton biomass in the
Bering Sea for many years, this may have changed recently. During the very warm years
1997–98, there was an unprecedented incursion of the coccolithophore Emiliana huxleyi
into the Bering Sea (Olson and Strom, 2002) and this organism has since become a
major component of the autotrophic biomass there. Images obtained from the MODIS
sensors confirm that the Bering Sea is now one of the very few places in the oceans
where coccolithophore blooms reach biomasses >10 mg C m
−3 . The Okhotsk Sea remains
relatively free of such blooms.
In the inner and middle shelf domain the zooplankton fauna is characterized by the
copepods Calanus pacificus (= C. glacialis of Heinrich, 1962a; Motoda and Minoda, 1974),
together with several species of Pseudocalanus and Acartia longiremis and other biota.
The euphausiid Thysanoessa raschii dominates the early spring zooplankton, followed by
C. pacificus during early summer. In this area, C. pacificus passes the winter as stage 5
copepodites (C5s), presumably in deep water beyond the shelf edge. Springer et al. (1989)
computed that the demand of these herbivorous copepods, and their associated biota, was
such that they were capable of modifying standing stocks of algae and at times required
the total daily production to satisfy their needs. Of course, classic food-web models of
the Bering Sea assume that the dominant phytoplankton biomass is diatoms and that
these are transferred to higher trophic levels largely through copepods: however, Olson
and Strom (2002) propose another model that must be acknowledged. It has been shown
that some diatoms are suboptimal food for some copepods in one part of the ocean,
because of their aldehyde content, so Olson and Strom ask: “If diatoms are a sub-optimal
diet for copepods, what supports the high crustacean biomass in the SE Bering Sea?” The
assumption is based on a logical non sequitur and is perhaps another instance of William
Dickinson’s “mythic thinking” (see flyleaf); at the very least, it ignores the affirmation of
Irigoien et al. (2002) that a diatom diet has no negative effect on the reproduction
of pelagic copepods in a dozen other open ocean regions. Nevertheless, in the context
of the Bering Sea, the enquiry of Olson and Strom must be considered. They invoke
grazing rates of protistan plankton, obtained by dilution experiments, in late summer,
that appear to balance population growth of both large and small phytoplankton cells,
although bacterial cells were not included in their computations. I believe that the most
that can be said at present is that all food-web diagrams and models are to be regarded
as works in progress—and no more than that. Unfortunately, many resource ecologists
and fishery biologists have yet to understand this depressing truth.
Slope Regions Although the highest chlorophyll biomass associated with the outer
front is along the southeast shelf edge, a linear zone of relatively high chlorophyll can be
traced north to the Bering Straits. It is also characteristic that very large meanders should
be induced out over the slope and even over deep water, chlorophyll biomass remaining
very high in these excursions toward the central Bering Sea. The chlorophyll profile over
the slope follows a typical seasonal evolution: after the near-surface spring bloom, algal
growth during the summer (a 120-day growing period) continues in a deep chlorophyll
maximum (DCM) near the pycnocline, fueled by nutrients in the deeper water of the
Bering Slope Current.
The DCM of the Slope Current bifurcates around St. Lawrence Island. The eastern
part subsequently spreads over the northeastern continental slope, inducing rich benthic
fauna, and exists as a near-bottom chlorophyll maximum. The western part is significantly
enriched in the western jet current (Anadyr Current), which flows through the Bering
Straits and passes north into the Chukchi Sea. The shoaling of this flow as it enters the