Atlantic Polar Biome
141
development of high benthic biomass, relative diversity is not related, as one might
expect, to gravel-sand-mud ratios, or the water contents of deposits. Instead, it is related
to disturbance to the sediments by ice scour and by the feeding of gray whales and walrus.
The benthic macrofaunal communities of the Arctic shelves, below the shallow icescoured zone of the littoral, are dominated by variations of the polar Macoma and
Astarte communities, having high biomass down to about 50 m—that is to say, within the
influence of the surface water mass. On muddy sediments in this depth zone, Macoma
calcarea is associated with other bivalve mollusks, such as Mya and Leda, whereas on
sandy, coarser sediments this “boreo-arctic Macoma” association is replaced by one
dominated by Cardium ciliatum and Venus fluctuosa, the “Arctic Venus community”
(Thorson, 1957; Ellis, 1959). Deeper on the shelves, benthos of lower overall biomass is
characterized by foraminifera (Rhabdomina, Axinopsis).
A curious benthic association of considerable ecological significance is the boreoarctic Ampelisca community of Thorson (1957), which is characterized by amphipods of
the families Ampheliscidae, Isaeidae, and Phoxocephalidae that together may comprise
<85% of individuals, together with some bivalve mollusks (Cardium, Tellina), polychaetes
(Maldane, Nephthys), and various ophiuroids. These tubicolous amphipods and bivalve
mollusks are suspension feeders, utilizing the near-bottom layer of high-turbidity water,
so that benthic associations of this kind are very probably widely distributed around the
Arctic Ocean shelves where this layer is characteristic. The same association of tubicolous
amphipods has recently been encountered on the slope in northern Baffin Bay at about
500 m depth, where the density of Haploops tubicola is around 3500 ind m
−2 .
The earlier observations of benthic communities and associations of species by Thorson
and others have been confirmed in their objective reality by factor analysis of 204 quantitative benthic samples from the shelves of the northern Baffin Bay region (Thomson,
1982). By this analysis, 21 factors (each comprising one or several species) were grouped
into three species assemblages that bore sufficient resemblance to the “communities”
previously described as to suggest that these are realistic entities, comprising groups of
species having mutual interactions and requirements. Factor 2, for instance, associated six
of the nine species listed by Thorson as being characteristic of the boreo-arctic Macoma
community. We now have observations of this association from the northern Barents
Sea, both coasts of Greenland and the Canadian Arctic: it (like the other associations) is
probably circumpolar in distribution.
Unlike the rich arctic benthic communities, the associated fish are extremely reduced
in diversity compared to those associated with similar benthic communities in warm
seas. As I have already discussed in Chapter 4, this is perhaps related to the greater
uncertainty of successful recruitment from planktonic larvae in cold than in warmer seas.
The planktonic eggs of Boreogadus saida, the arctic cod, require a 45 to 90-day period
of “incubation,” whereas occlusion occurs overnight in tropical clupeids; it is chiefly
Boreogadus that should take our attention in this province, along with the Greenland
shark, halibut, and several small liparids. Liparis koefoedi is typical of the latter and is
probably circumpolar, as is Eumicropterus derjugini, a small lumpsucker occurring on the
shoaler parts of the shelves. Along the southern Greenland shelves, the bentho-pelagic
cod, Gadus morhua, was at one time very abundant but is now reduced by industrial
fishing to a small remnant.
Boreogadus saida is a small (<32 cm), slim, largely pelagic gadoid that is the key
species in the transfer of organic material from planktonic production in Arctic seas to
marine mammals and birds, for which it forms a vital source of food. It is consumed
by murres, guillemots, and kittiwakes, by harp and bearded seals, and by narwhal and
beluga. It is largely confined to cold circumpolar water, where it is widely distributed,
but its spawning concentrations in shallow water are not yet well known. It occurs at a
141
development of high benthic biomass, relative diversity is not related, as one might
expect, to gravel-sand-mud ratios, or the water contents of deposits. Instead, it is related
to disturbance to the sediments by ice scour and by the feeding of gray whales and walrus.
The benthic macrofaunal communities of the Arctic shelves, below the shallow icescoured zone of the littoral, are dominated by variations of the polar Macoma and
Astarte communities, having high biomass down to about 50 m—that is to say, within the
influence of the surface water mass. On muddy sediments in this depth zone, Macoma
calcarea is associated with other bivalve mollusks, such as Mya and Leda, whereas on
sandy, coarser sediments this “boreo-arctic Macoma” association is replaced by one
dominated by Cardium ciliatum and Venus fluctuosa, the “Arctic Venus community”
(Thorson, 1957; Ellis, 1959). Deeper on the shelves, benthos of lower overall biomass is
characterized by foraminifera (Rhabdomina, Axinopsis).
A curious benthic association of considerable ecological significance is the boreoarctic Ampelisca community of Thorson (1957), which is characterized by amphipods of
the families Ampheliscidae, Isaeidae, and Phoxocephalidae that together may comprise
<85% of individuals, together with some bivalve mollusks (Cardium, Tellina), polychaetes
(Maldane, Nephthys), and various ophiuroids. These tubicolous amphipods and bivalve
mollusks are suspension feeders, utilizing the near-bottom layer of high-turbidity water,
so that benthic associations of this kind are very probably widely distributed around the
Arctic Ocean shelves where this layer is characteristic. The same association of tubicolous
amphipods has recently been encountered on the slope in northern Baffin Bay at about
500 m depth, where the density of Haploops tubicola is around 3500 ind m
−2 .
The earlier observations of benthic communities and associations of species by Thorson
and others have been confirmed in their objective reality by factor analysis of 204 quantitative benthic samples from the shelves of the northern Baffin Bay region (Thomson,
1982). By this analysis, 21 factors (each comprising one or several species) were grouped
into three species assemblages that bore sufficient resemblance to the “communities”
previously described as to suggest that these are realistic entities, comprising groups of
species having mutual interactions and requirements. Factor 2, for instance, associated six
of the nine species listed by Thorson as being characteristic of the boreo-arctic Macoma
community. We now have observations of this association from the northern Barents
Sea, both coasts of Greenland and the Canadian Arctic: it (like the other associations) is
probably circumpolar in distribution.
Unlike the rich arctic benthic communities, the associated fish are extremely reduced
in diversity compared to those associated with similar benthic communities in warm
seas. As I have already discussed in Chapter 4, this is perhaps related to the greater
uncertainty of successful recruitment from planktonic larvae in cold than in warmer seas.
The planktonic eggs of Boreogadus saida, the arctic cod, require a 45 to 90-day period
of “incubation,” whereas occlusion occurs overnight in tropical clupeids; it is chiefly
Boreogadus that should take our attention in this province, along with the Greenland
shark, halibut, and several small liparids. Liparis koefoedi is typical of the latter and is
probably circumpolar, as is Eumicropterus derjugini, a small lumpsucker occurring on the
shoaler parts of the shelves. Along the southern Greenland shelves, the bentho-pelagic
cod, Gadus morhua, was at one time very abundant but is now reduced by industrial
fishing to a small remnant.
Boreogadus saida is a small (<32 cm), slim, largely pelagic gadoid that is the key
species in the transfer of organic material from planktonic production in Arctic seas to
marine mammals and birds, for which it forms a vital source of food. It is consumed
by murres, guillemots, and kittiwakes, by harp and bearded seals, and by narwhal and
beluga. It is largely confined to cold circumpolar water, where it is widely distributed,
but its spawning concentrations in shallow water are not yet well known. It occurs at a