Pacific Polar Biome
335
are values significantly higher. A zooplankton profile in the eastern part of the gyre, but
seaward of the shelf-edge front, shows a biomass maximum at the pycnocline at about
45 m which suggests that the DCM described previously extends clear across the gyre
in summer. The standing stocks of diatoms near the surface in the central gyre in early
summer are lower by about one order of magnitude than at the shelf break (10
6 compared
with 10
7 cells m
−3 ).
Regional Benthic and Demersal Ecology
It has long been assumed that the large demersal fish stocks of this province are supported
by a productive shelf ecosystem, and this relationship has been the focus of two relatively
recent fisheries-oriented programs: PROBES and ISHTAR (McRoy et al., 1985; Hansell
et al., 1989). The classical supposition has been confirmed, as has the fact that the levels
of phytoplankton production apparently exceed the demands of planktonic herbivores,
and so support a very rich benthic ecosystem that is said to be the food base for the
fisheries resources, but is probably not—as I shall discuss later.
For the Bering Sea, we do have access to holistic quantitative surveys of benthic
organisms from Soviet investigations from the 1930s to the 1960s that covered the entire
shelf region. These investigations showed that the benthic infauna is dominated by lowArctic species associations, such as the circumpolar Macoma calcarea community (see
Thorson, 1957) that occupies the midshelf region (40–80 m) from the Gulf of Anadyr right
down to Bristol Bay. With the nominate species, there occurs also Mya truncata, Cardium
ciliatum, Ophiocten, Sericeum, Pectinaria granulata, and Astarte spp. With increasing sand
component in the substrate we would expect this community to be replaced by the arctic
Venus association, whereas increasing silt would lead to a Portlandia community. The
distribution of benthic biomass is very unequal, but is generally higher (220–950 g m
−2 )
on the northern shelves than on the eastern (55–169 g m
−2 ) shelf. Maximal densities are
at midshelf depth (75–100 m) on all shelves. The higher biomass on the northern shelves
is dominated by large epibenthic species (sand dollars, anemones, sponges) so that the
percentage of the benthos there that is accessible to demersal fish is relatively low: 40–50%
on the wide eastern shelf and the cold Gulf of Anadyr, 15–20% in the northern Chirikov
basin and along the northwest coast.
The relations between the benthic infauna and the population biomass of nekton
and fish are complex. The highest biomass occurs in the cold Anadyr region where the
demersal fish fauna is depauperate, and where some populations of infaunal-feeding
species (Limanda, Hippoglossoides) are small and perhaps not self-sustaining, as in the
Chukchi Sea. On the main Bering Sea shelf, these and another flatfish, Lepidopsetta
aspersa, are the only forms that are directly dependent on benthic infauna: many attempts
have been made (some reviewed by Alton, 1974) to estimate benthic production from
observed biomass and to balance this against demand by flatfish and epibenthic nekton,
but the balances obtained remain unconvincing. What is clear, however, is the lack of
direct trophic connection between the infauna of the benthos and the demersal fish
that form the bulk of fish biomass here: pollack (Theragra chalcogramma), cod (Gadus
macrocephalus), turbot (Atheresthes stomias), and others. These feed on smaller fish, which
themselves eat natant invertebrates (shrimps, amphipods, euphausiids). These, in turn,
are dependent on superficial meiobenthos and the microbial content of organic detritus.
However, the demersal ecosystem of this marginal region is in constant flux in response
to changes in environmental forcing, just as is the pelagic ecosystem. But for the demersal
system, there is an additional complication in interpreting observations: we have also
to account for the consequences of removal by commercial fisheries of a major fraction
(∼15 × 10
6 t y
−1 ) of the higher trophic-level biomass, whether of fish (principally pollack
and halibut) or crustaceans (principally the crabs Paralithodes and Chionectes). Long-term
335
are values significantly higher. A zooplankton profile in the eastern part of the gyre, but
seaward of the shelf-edge front, shows a biomass maximum at the pycnocline at about
45 m which suggests that the DCM described previously extends clear across the gyre
in summer. The standing stocks of diatoms near the surface in the central gyre in early
summer are lower by about one order of magnitude than at the shelf break (10
6 compared
with 10
7 cells m
−3 ).
Regional Benthic and Demersal Ecology
It has long been assumed that the large demersal fish stocks of this province are supported
by a productive shelf ecosystem, and this relationship has been the focus of two relatively
recent fisheries-oriented programs: PROBES and ISHTAR (McRoy et al., 1985; Hansell
et al., 1989). The classical supposition has been confirmed, as has the fact that the levels
of phytoplankton production apparently exceed the demands of planktonic herbivores,
and so support a very rich benthic ecosystem that is said to be the food base for the
fisheries resources, but is probably not—as I shall discuss later.
For the Bering Sea, we do have access to holistic quantitative surveys of benthic
organisms from Soviet investigations from the 1930s to the 1960s that covered the entire
shelf region. These investigations showed that the benthic infauna is dominated by lowArctic species associations, such as the circumpolar Macoma calcarea community (see
Thorson, 1957) that occupies the midshelf region (40–80 m) from the Gulf of Anadyr right
down to Bristol Bay. With the nominate species, there occurs also Mya truncata, Cardium
ciliatum, Ophiocten, Sericeum, Pectinaria granulata, and Astarte spp. With increasing sand
component in the substrate we would expect this community to be replaced by the arctic
Venus association, whereas increasing silt would lead to a Portlandia community. The
distribution of benthic biomass is very unequal, but is generally higher (220–950 g m
−2 )
on the northern shelves than on the eastern (55–169 g m
−2 ) shelf. Maximal densities are
at midshelf depth (75–100 m) on all shelves. The higher biomass on the northern shelves
is dominated by large epibenthic species (sand dollars, anemones, sponges) so that the
percentage of the benthos there that is accessible to demersal fish is relatively low: 40–50%
on the wide eastern shelf and the cold Gulf of Anadyr, 15–20% in the northern Chirikov
basin and along the northwest coast.
The relations between the benthic infauna and the population biomass of nekton
and fish are complex. The highest biomass occurs in the cold Anadyr region where the
demersal fish fauna is depauperate, and where some populations of infaunal-feeding
species (Limanda, Hippoglossoides) are small and perhaps not self-sustaining, as in the
Chukchi Sea. On the main Bering Sea shelf, these and another flatfish, Lepidopsetta
aspersa, are the only forms that are directly dependent on benthic infauna: many attempts
have been made (some reviewed by Alton, 1974) to estimate benthic production from
observed biomass and to balance this against demand by flatfish and epibenthic nekton,
but the balances obtained remain unconvincing. What is clear, however, is the lack of
direct trophic connection between the infauna of the benthos and the demersal fish
that form the bulk of fish biomass here: pollack (Theragra chalcogramma), cod (Gadus
macrocephalus), turbot (Atheresthes stomias), and others. These feed on smaller fish, which
themselves eat natant invertebrates (shrimps, amphipods, euphausiids). These, in turn,
are dependent on superficial meiobenthos and the microbial content of organic detritus.
However, the demersal ecosystem of this marginal region is in constant flux in response
to changes in environmental forcing, just as is the pelagic ecosystem. But for the demersal
system, there is an additional complication in interpreting observations: we have also
to account for the consequences of removal by commercial fisheries of a major fraction
(∼15 × 10
6 t y
−1 ) of the higher trophic-level biomass, whether of fish (principally pollack
and halibut) or crustaceans (principally the crabs Paralithodes and Chionectes). Long-term