Pacific Coastal Biome
395
Regional Benthic and Demersal Ecology
Systematic exploration of benthic species assemblages being no longer fashionable, I have
been able to locate no modern studies for this province, except some concerned with
environmental impact statements around oil platforms that will be of no use to us. We are
therefore still dependent on Thorson, who quotes the findings of Shelford (1935) in his
account of benthic communities here: these follow the familiar pattern of high-latitude
shelves. The Macoma baltica community on shallow mixed bottoms with low salinity,
an Amphioplus community on softer muddy deposits, the Venus fluctuosa community
on midshelf sandy deposits, the Maldane sarsi community on soft inshore muds—and
so on. I know of no modern ecological studies of benthic/pelagic interactions in this
province.
Of course, we have much more precise knowledge of the fish faunas that depend to a
large extent on these invertebrate communities: the importance of the regional fisheries
(∼60 × 10
−5 t y
−1 ) may be thanked for that. This is, zoogeographically, a marginal region
so that there is a significant gradient in species composition from east to west and, of
course, the largest concentrations of fish occur on the wider shelves in the northwestern
part of the province (PICES, undated). The diversity of the fish fauna is not great for, even
allowing for directed fishing, 10 species form >75% of the captured biomass: arrowtooth
flounder (Atheresthes stomias), Pacific ocean perch (Sebastes alutus), and Pacific halibut
(Hippoglossus stenolopus) dominate the catches.
The five species of migratory Pacific salmon (Onchorhynchus spp.) are clearly a special
case. Although it has apparently not been quantified, their life history pattern suggests
that they may represent a significant transfer of biomass from the open ocean to coastal
regions. As is well known, sockeye, chum, and pink salmon pass almost their entire
period of growth at sea in the subarctic gyre and die on returning to spawn in coastal
rivers and streams. Only chinook and coho growth is dependent on feeding in coastal
regions.
There are strong cross-shelf gradients in biomass and diversity of fish, with the highest
concentrations occurring just below the break of shelf, while the neritic regions are the
principal spawning areas and support large populations of juveniles of offshore species,
both demersal and pelagic. What the fishery science community calls “forage fish,” such
as Osmerus, are very abundant, along with >20 species of small flatfish. Pacific herring
are widespread over the shelf, with spawning areas in Prince William Sound and around
Kodiak; their abundance is highly variable, the fishery having been closed in the former
area since 1992. It is thought that this variability (at least in our modern seas) may be
due to viral and fungal infection and consequent disease. Similar variability in demersal
fish, particularly in such vulnerable species as Sebastes alutus, is largely fishery-driven; in
these latitudes, recruitment is a rather variable process. Analysis of fisheries data suggests
that a major regime shift occurred in the species composition after 1976–77, involving a
general increase in biomass that persisted until 2002, since when a decrease has set in that
is largely due to reduced abundance of walleye pollack (Pollachius). I believe that it is very
difficult to attribute causation to such changes as these, which occur in a fish ecosystem
already significantly modified from its pristine state by industrial fishing. For one thing,
population structure and growth rates are rapidly modified, so that the naturally evolved
characteristics of the life-history parameters of each species are modified so that they are
no longer the best possible fit to the natural environment. But that’s an old story, which
I discussed elsewhere in 2002.
Synopsis
Case 1—Polar irradiance-mediated production peak—The pycnocline undergoes a winter
excursion to 50 m from late summer depths of around 10 m; photic depth similarly
395
Regional Benthic and Demersal Ecology
Systematic exploration of benthic species assemblages being no longer fashionable, I have
been able to locate no modern studies for this province, except some concerned with
environmental impact statements around oil platforms that will be of no use to us. We are
therefore still dependent on Thorson, who quotes the findings of Shelford (1935) in his
account of benthic communities here: these follow the familiar pattern of high-latitude
shelves. The Macoma baltica community on shallow mixed bottoms with low salinity,
an Amphioplus community on softer muddy deposits, the Venus fluctuosa community
on midshelf sandy deposits, the Maldane sarsi community on soft inshore muds—and
so on. I know of no modern ecological studies of benthic/pelagic interactions in this
province.
Of course, we have much more precise knowledge of the fish faunas that depend to a
large extent on these invertebrate communities: the importance of the regional fisheries
(∼60 × 10
−5 t y
−1 ) may be thanked for that. This is, zoogeographically, a marginal region
so that there is a significant gradient in species composition from east to west and, of
course, the largest concentrations of fish occur on the wider shelves in the northwestern
part of the province (PICES, undated). The diversity of the fish fauna is not great for, even
allowing for directed fishing, 10 species form >75% of the captured biomass: arrowtooth
flounder (Atheresthes stomias), Pacific ocean perch (Sebastes alutus), and Pacific halibut
(Hippoglossus stenolopus) dominate the catches.
The five species of migratory Pacific salmon (Onchorhynchus spp.) are clearly a special
case. Although it has apparently not been quantified, their life history pattern suggests
that they may represent a significant transfer of biomass from the open ocean to coastal
regions. As is well known, sockeye, chum, and pink salmon pass almost their entire
period of growth at sea in the subarctic gyre and die on returning to spawn in coastal
rivers and streams. Only chinook and coho growth is dependent on feeding in coastal
regions.
There are strong cross-shelf gradients in biomass and diversity of fish, with the highest
concentrations occurring just below the break of shelf, while the neritic regions are the
principal spawning areas and support large populations of juveniles of offshore species,
both demersal and pelagic. What the fishery science community calls “forage fish,” such
as Osmerus, are very abundant, along with >20 species of small flatfish. Pacific herring
are widespread over the shelf, with spawning areas in Prince William Sound and around
Kodiak; their abundance is highly variable, the fishery having been closed in the former
area since 1992. It is thought that this variability (at least in our modern seas) may be
due to viral and fungal infection and consequent disease. Similar variability in demersal
fish, particularly in such vulnerable species as Sebastes alutus, is largely fishery-driven; in
these latitudes, recruitment is a rather variable process. Analysis of fisheries data suggests
that a major regime shift occurred in the species composition after 1976–77, involving a
general increase in biomass that persisted until 2002, since when a decrease has set in that
is largely due to reduced abundance of walleye pollack (Pollachius). I believe that it is very
difficult to attribute causation to such changes as these, which occur in a fish ecosystem
already significantly modified from its pristine state by industrial fishing. For one thing,
population structure and growth rates are rapidly modified, so that the naturally evolved
characteristics of the life-history parameters of each species are modified so that they are
no longer the best possible fit to the natural environment. But that’s an old story, which
I discussed elsewhere in 2002.
Synopsis
Case 1—Polar irradiance-mediated production peak—The pycnocline undergoes a winter
excursion to 50 m from late summer depths of around 10 m; photic depth similarly