Download Polar Marine Communities1

AMER. ZOOL., 34:90-99 (1994)
Polar Marine Communities1
PAUL K. DAYTON, B. J. MORDIDA, AND F. BACON
Scripps Institution of Oceanography, La Jolla, California 92093-0201
This paper offers a sweeping but very superficial review of the
marine biology of polar seas. The marine systems in the Arctic and Antarctic have in common polar positions and cold temperatures, otherwise
they are strikingly different. The Arctic has broad shallow continental
shelves with seasonally fluctuating physical conditions and a massive fresh
water impact in the northern coastal zones. However, it has a low seasonality of pack ice and little vertical mixing. In contrast, the Antarctic
has over twice the oceanic surface area, deep narrow shelves, and, except
for ice cover, a relatively stable physical environment with very little
terrestrial input. The Antarctic has great pack ice seasonality and much
vertical mixing. Primary productivity in the polar areas tends to be strongly
pulsed with the zooplankton lagging behind; however there are many
exceptions to such generalizations. Most recent research has focused on
specific patterns and processes resulting in biological hot spots such as
predictable leads in the ice, polynyas, oceanographic fronts, areas of intense
mixing, and the marginal ice zone. This review attempts to weave these
recent oceanographic studies into the geological history of each habitat
in an effort to develop a holistic understanding of the biological processes.
SYNOPSIS.
For each we consider the Arctic and the
Antarctic separately.
INTRODUCTION
Geological history and oceanographic
processes are the warp and woof of the biological understanding of any marine habitat.
These factors always must be woven into
any biological synthesis. This format is far
too broad to review the primary literature,
and this paper will rely on several detailed
reviews with the expectation that the reader
will refer to them, and from them to the
primary literature. Perhaps the most interesting question of polar marine biology
relates to the fact that the Antarctic has a
much higher species richness (Table 1) yet
lacks the ecological diversity of the Arctic.
We discuss the following topics: (1) geological origins and evolutionary histories, (2)
important processes and the dominant species, (3) higher level food webs, (4) the benthic ecology and benthic-pelagic coupling,
and (5) pressing anthropogenic problems.
ORIGIN AND EVOLUTION OF ARCTIC BIOTA
The Mesozoic Arctic was a cool temperate region, but in the late Cretaceous the
Arctic developed two large seaways connecting the subtropical Gulf of Mexico and
the tropical Tethys Sea. As the Cretaceous
ended, the connection to the Atlantic narrowed but remained open with a deep water
passage; the connection to the Pacific virtually closed. At this point the Arctic Ocean
was relatively isolated. The Cenozoic
included periods of openings to the Atlantic,
but the bathymetric Bering Strait barrier was
relatively effective until the late Pliocene
when Pacific shallow water mollusks
migrated through what may have been an
ice-free Arctic Ocean to Iceland. A perennial ice cover did not develop until 0.7-2.0
million years ago. The Quaternary Period
beginning about 1.8 million years ago had
major glacial and warm periods of about
10-20,000 year intervals with the last glaciation reaching its peak about 18,000 years
ago. The glacial periods included sea level
fluctuations of at least 85 m which exposed
1
From the symposium Science as a Way of Knowing—Biodiversity presented at the Annual Meeting of
the American Society of Zoologists, 27-30 December
1992, at Vancouver, Canada.
90
91
POLAR MARINE COMMUNITIES
TABLE 1. Number of recorded benthic species for cer- TABLE 2. Biogeographic affinities of regional Arctic
tain groups in Arctic and Antarctic*
shallow benthic fauna.*
Group
Antarctic
Arctic
Mollusks
Polychaetes
Amphipoda
Isopoda
Pycnogonid
Bryozoan
Sponges
Ascidians
875
650
470
299
100
310
300
129
224
300
262
49
29
200
200
47
* From Grebmeier and Barry, 1992.
vast areas of the large and shallow Arctic
continental shelf, resulting in the near eradication of the shelf benthic assemblages
(Dunton, 1992).
In addition to the sea level changes, the
Atlantic Arctic was periodically covered
with thick glacial ice penetrating deep into
the ocean, precluding any shallow water
assemblage. The modern biogeography of
the Arctic Ocean is a result of these Quaternary events superimposed on a very broad
and shallow continental shelf which results
in the interconnected complex of estuarine
seas, each with relatively distinct biotas.
Many of these biogeographic patterns are
becoming much better described, especially
in the Russian literature (see Dunton, 1992).
Table 2 summarizes the low endemism and
the biogeographic affinities of some of these
regions. The post-Pleistocene Arctic Ocean
faunal assemblage includes many species
with Pacific affinities on the East, and recent
Atlantic affinities in the West Arctic. The
pattern for algae is enigmatic because there
is a very strong Atlantic affinity even in
Pacific areas such as the Chukchi Sea; this
despite the fact that the north Pacific has
one of the world's most diverse floras and
there is a northern current. Clearly the biogeography of the Arctic is neither ancient
nor well established and seems to be in a
state of active colonization over the last
6,000-14,000 years (see Dunton, 1992).
ORIGIN AND EVOLUTION OF ANTARCTIC
BIOTA
The Mesozoic Antarctic was part of the
mild subtropical Gondwanaland, which
broke up in the late Cretaceous. After the
breakup, Antarctica migrated poleward
Percent species from
biogeographic area
Arctic region (n)
Chukchi (150)
Alaskan Beaufort (206)
Canadian Beaufort (266)
Canadian Archipelago
(168)
Barent'sSea(186)
Laptev Sea (152)
East Siberian (?)
Arctic Atlanendern- tic
ics
boreal
5
14
12
9
Boreal
Paci- cosmofie
poliboreal
tan
6
6
17
27
17
10
58
69
65
20
15
19
5
9
8
10
16
66
63
59
70
•From Dunton, 1992.
making possible the circum-Antarctic current which effectively isolated the continent.
As the migration increased, the convergence, divergence and upwelling systems
developed, increasing the marine isolation
and adding a great deal of oceanographic
complexity to the Southern Ocean system.
Interestingly, the continent remained subtropical to temperate until perhaps 22 million years ago. Thus the biota was of a warm
subtropical nature when it became isolated;
later it was subject to massive cooling. For
the past 20 million years or so the physical
patterns have been stable and uniform relative to other coastal systems, but there have
been many episodes of extreme glaciation,
even during the Quaternary. Thus the environment has been relatively stable with
regard to temperature, salinity and lack of
terrestrial input; however, other factors
which are not constant include light, sea ice
cover, ice disturbance, growth and recession
of large ice shelves, current variations, shortterm climate shifts such as associated with
El Ninos, etc. (reviewed by Dayton, 1990).
Biogeographers agree that most of the
Antarctic biota is very old, and it is unique
because it was first isolated for perhaps 2030 million years, and only then subject to
intense cooling, followed by the opportunity
to evolve in a relatively stable system for
perhaps another 20 million years. Given the
isolation and relatively stable environment,
the Antarctic represents a unique evolutionary laboratory. The Antarctic fauna
appears derived from three sources: (1) a
relict autochthonous fauna, (2) eurybathic
fauna emerging from deep water into the
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P. K. DAYTON ET AL.
TABLE 3. Percent Antarctic endemic species for particular groups.*
Animal groups
% species
Algal groups/regions
Fish
Amphipoda
Isopoda & Tanaidacea
Pycnogonid
Echinodermata
Bryozoa
95
90
66
>90
73
58
Chlorophyta
Subantarctic
Low Antarctic
High Antarctic
Phaeophyta
Subantarctic
Low Antarctic
High Antarctic
Rhodophyta
Subantarctic
Low Antarctic
High Antarctic
% species
16
33
67
41
73
83
70
92
100
' Algal patterns presented for regions. Data collected from other sources in Dayton, 1990.
shallower coastal zone, and (3) cool-temperate species, mostly from South America.
Most Antarctic biogeographers, especially
Dell (1972), recognize a relationship between
the Antarctic Peninsula, the Scotia Arc and
South America. We believe that this pattern
will become more apparent with better
knowledge of the South American biota.
White's (1984) and Dayton's (1990) reviews
support Hedgpeth's recognition of the large
number of circumpolar species and smaller
provinces. These groupings include (1) a
large circum-continental group, (2) species
restricted to the Bellingshausen and Weddell seas and the Antarctic Peninsula, (3)
species restricted to the Scotia Arc, and (4)
species restricted to the subantarctic islands.
Not surprisingly there is an unusually high
degree of endemism (Table 3). Assuming
endemism is a function of time and isolation, recent colonizers should have less speciation than ancient autochthonous groups,
but in most phyla autochthonous groups
have examples of both conservatism and
extensive speciation (Dell, 1972, is probably still the most complete review).
It is interesting to note that this endemism is not consistent across phyla, and most
of the endemism is found in relatively few
taxa. Examples of groups with extensive
Antarctic radiation from stem taxa can be
found in pycnogonids, gastropods, echinoderms, ascidians, and especially serolid and
arcturid isopods (reviewed by Arntz and
Gallardo, 1993). It is hard to know when
the radiation occurred, but almost the entire
Tanaidacean fauna seems to have gone
extinct during the Eocene temperature drop,
to be replaced by cold-stenothermic eurybathic species (Sieg, 1988, reviewed in Arntz
and Gallardo, 1993). Crabs represent a particularly intriguing Antarctic mystery. The
Cretaceous fossils are rich with crabs, and
the crabs persisted with no break across the
Cretaceous-Tertiary boundary into the
Eocene. At that point something happened,
perhaps associated with the Eocene cooling,
which rendered all the crabs extinct.
Although crabs remain abundant around the
sub-Antarctic Islands, they have never
returned to the Antarctic continent. Given
the prominence of crabs in the Arctic, this
Antarctic pattern is very interesting.
PRIMARY PRODUCTIVITY
Primary productivity is controlled by
many factors, but irradiance, nutrients, and
temperature are especially important in
polar seas. The amount of irradiance available to polar habitats is very strongly influenced by latitude and solar angle. These factors are invariate, but the other most
important factor influencing available irradiance is sea ice, and this is extremely variable. The amount of light attenuation is
determined by the thickness of the ice, its
condition (brine pockets, air bubbles, degree
of folding, presence of underice platelets,
and especially the presence of ice algae), and
the amount of snow cover. Of these, snow
is perhaps the most important variable as
it is extremely opaque. Nutrients are the
other important variables, and in most oceanic situations nutrients are considered the
critical limiting factor. Temperature directly
affects all biological rate processes. Often it
POLAR MARINE COMMUNITIES
93
is considered a constant in polar habitats, major sources of carbon to this system is
but in many Arctic coastal habitats the tem- terrestrial peat which is not digestible for
peratures do vary seasonally and may be most marine species.
important.
The Barents Sea is another productive area
where the high productivity results from the
Arctic
mixing of the cold Arctic and warm Atlantic
In general the Arctic Ocean is considered water masses. Primary production ranges
the world's most oligotrophic because of its from 40-80 g C/mVyr. The C/N ratios range
very high latitude and permanent ice cover from 6-8, indicative of relatively high qual(W. O. Smith and Sakshaug, 1990). How- ity food. Unlike any other Arctic water mass,
ever, its wide shallow shelves are dominated the Barents Sea has limited riverine inputs
by cold low salinity surface water from east and the shelf is deep with much of the proSiberia waters to the Greenland Sea. Sum- duction being recycled in the water column
mer river runoff and melting of the sea-ice to higher order predators.
produce large volumes of fresh water resultOne of the most important features of ice
ing in pronounced stratification and vertical covered seas are polynyas. These are prestability during the spring and summer. The dictable areas of open water within ice-covrivers also produce large volumes of sedi- ered seas which are maintained by prevailments. Nutrients tend to be high in the win- ing offshore winds and/or upwelling of
ter, but with the enhanced light conditions relatively warm water which often occurs
associated with the return of the sun and near wind sheltering land. Their study is
retreat of ice in the spring, there are high logistically difficult, but it is clear that they
levels of phytoplankton production, and the represent areas of enhanced productivity
nutrients become depleted in the summer. because nutrient levels are high, and with
The most productive areas are those areas the reduced ice cover there is usually sufof convergences of different current sys- ficient light for photosynthesis. This
tems. Grebmeier and Barry (1991), contrast enhanced productivity is the explanation for
three Arctic systems: (1) the northern Bering large populations of marine mammals and
and Chukchi seas, (2) the high Arctic Ocean birds associated with polynyas (Stirling and
with its marginal seas, and (3) the Arctic Cleator, 1981).
shelves influenced by warm Atlantic waters.
The northern Bering and Chukchi seas are Antarctica
characterized by high nutrients advected
All the above physical factors influencing
from the Gulf of Anadyr and maximum priprimary
productivity apply equally in the
mary production as high as 300 g C/mVyr.
Antarctic.
However, while the satellite seas
This area also has higher quality organic
of
the
Arctic
have many regional distinctive
matter indicated by low C/N ratios of 5-7.
The southern part of this region is one of physical and biological characteristics such
the richest fishing areas in the world, and it as salinity, sedimentation, primary producsupports high densities of marine mammals tion, etc., the Antarctic habitats are relatively constant, with less stratification and
and marine sea birds.
with nutrients rarely depleted. A major
The high Arctic Ocean and its marginal component of the ocean is the pack ice zone
seas are nutrient limited, have long seasonal which varies seasonally by a factor of 4 to
or permanent ice cover and large amounts 5 (3-5 to 17-20 million km2). As in the
of riverine seasonal input. The few data for Arctic, the marginal ice zone can be five to
the Arctic Basin marginal seas such as the seven times more productive than open
East Siberian, Laptev, Kara, northern ocean or under the sea ice (W. O. Smith and
Chukchi, Beaufort, and the Canadian Sakshaug, 1990). Despite the fact that nutriArchipelago show very low productivity, ent concentrations are relatively high in the
sometimes well under 5 g C/m2/yr and never Antarctic, primary production is remarkover 80 g C/mVyr. In this area ice algae ably low (16-100 g C/m2/yr) over vast areas
may represent the most important source of where it is limited by the deep mixed layer.
primary production. Interestingly, one of the In some areas such as nearshore habitats
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P. K. DAYTON ET AL.
and localized upwelling areas, primary production is seasonally very high (>2 g C/m2/
day). In addition the production of microalgae on the undersurface of the sea ice can
be very high in localized areas (Grebmeier
and Barry, 1991).
Many think of the system as one dominated by krill, however, there are three rather
distinct latitudinal zones for zooplankton
communities (S. L. Smith and SchnackSchiel, 1990). The northern ice-free zone
has low productivity and is dominated by
copepods (>60% of the biomass), salps,
small euphausiids, chaetognaths, etc. The
intermediate seasonal pack-ice zone has the
highest productivity and is the area dominated by the krill, Euphausia superba. The
highest concentrations of krill are over the
shelf/slope in the vicinity of fronts and
eddies. Finally, the southern permanent pack
ice zone has a short but intense phytoplankton bloom and a much more important contribution of the ice-algae. Plankton biomass
is very low and is dominated by the small
euphausiid, E. crystallorophias and the small
silverfish, Pleurogramma antarcticum.
UPPER TROPHIC LEVELS
All high level marine consumers are influenced by oceanographic processes. In polar
areas sea ice is an additional and extremely
important component of the habitat. However, the sea ice is very different in the north
and the south. In the Arctic it is consolidated and never melts except at the periphery while in the Antarctic it offers a great
deal of seasonal habitat heterogeneity, and
most of it melts in the summer. The arctic
sea ice acts to reduce primary productivity
and severely restrict access of higher predators to the water column. In the same sense,
it offers protection from polar bears and orca
for some higher predators such as ice seals.
On the other hand, the dynamic Antarctic
sea ice allows year round habitat to a wider
variety of predators such as seals and penguins. But there are no ecological analogs of
polar bears, and the sea ice offers protection
from leopard seals and orca. In both areas
polynyas are particularly important, but
because of the relative constancy of the sea
ice, they appear more important in the Arc-
tic. Finally it is important to point out that
much of what we know about the biology
of the prey species comes from the study of
the higher order predators because in many
cases they are the only means of sampling
that difficult habitat (Ainley and DeMaster,
1990).
As in other systems, polar predators tend
to forage in areas where prey are concentrated. Thus the marginal ice zones and
polynya are extremely important because
the food chain is associated with the high
levels of primary production, thus concentrating prey at all levels including prey for
the top carnivores such as polar bears, orca,
and leopard seals. In the same sense, oceanographic features such as convergences,
confluences, langmuir cells, and fronts at the
shelf break, midshelf and insular areas are
also important habitats, especially for birds.
It is important to recognize that episodic
oceanographic events at even relatively short
time scales of one season can have massive
effects on upper trophic level populations;
for example, an oceanographic shift which
caused a sharp reduction of krill apparently
also resulted in massive mortality of birds
(Heywood et al., in W. O. Smith and Sakshaug, 1990).
Arctic
The Arctic is characterized by rather distinct nearshore and offshore associations of
higher predators and these in turn have high
and low Arctic components. In the high
Arctic the upper level predators are mostly
mammals, especially in the offshore habitats where polar bears and ice seals are the
main species. The coastal habitats include
walrus and a few birds. The arctic cod (Boreogadus saida) is a key component of food
webs in all areas, but in coastal areas the
benthic community is heavily utilized by
several predators such as ducks, walrus,
bearded seals, and ringed seals. With the
exception of the polynyas, most of the predators (the whales, walrus and the birds) are
summer residents only, indicating that an
important part of their winter habitat
includes lower Arctic regions (Ainley and
DeMaster, 1990).
Lower Arctic habitats such as the inner
POLAR MARINE COMMUNITIES
shelf and shelf slope in the Bering Sea are
very different from the high Arctic and from
each other. The most obvious difference is
that most upper level predators are birds.
The inner shelf has an important benthic
component of the food web which supports
large populations and high biomass of ducks,
gray whales, walrus, and bearded seals (see
AinleyandDeMaster, 1990; Dayton, 1990).
The most important component of pelagic
prey includes copepods, euphausiids, and
gadid fish. The shelf slope habitat is much
more oceanic, with birds being the most
numerous predators, but it is a very important habitat for baleen and white whales and
fur seals. The most important prey species
are pollock, myctophid and gadid fish,
amphipods, and euphausiids (Ainley and
DeMaster, 1990).
Antarctic
The Antarctic shelf is too deep to be much
of a factor to the biology of the upper trophic
levels. The distinction between the shelf and
slope waters is blurred in the Antarctic
because so much biology is tied to the sea
ice which covers both habitats. Nevertheless, Ainley and DeMaster (1990) document
differences in the top predators which mainly
reflect important differences in the pelagic
food webs. The most important prey in the
shelf waters are squid, the small E. crystallorophias and Pleuragramma, and a few
other small fish and Crustacea. The most
common predators are crabeater seals and
adelie and emperor penguins and at higher
levels, leopard seals and orca. In some areas
weddell seals are very abundant, as are
minke whales which forage along the marginal ice zone.
The Antarctic slope waters are very different because the food webs are based on
the krill, E. superba, myctophids and squid.
In all cases the predators are much more
oceanic and include all types of whales and
birds as well as fur seals and the ubiquitous
crabeater seals. One thing that these predators share is searching behavior capable of
finding and consuming aggregated prey. The
prey aggregate in response to the oceanographic structure, but in this habitat the prey
95
also have very strong behavioral tendencies
to aggregate.
BENTHIC-PELAGIC COUPLING
The quantity and quality of the organic
carbon supplied by the pelagic system is the
major factor influencing the benthic community, and the degree to which the water
column productivity is coupled to the benthic community is variable and extremely
important. Many factors influence the coupling, especially the oceanographic factors
determining the amount of pelagic (and sea
ice algae) production, the amount of this
production recycled and advected in the
water column, and the small scale boundary
layer phenomenon at the interface. In some
Arctic areas the primary production is
almost completely recycled within the water
column, but in other, usually shallow seas,
the pelagic production is more directly
available to benthos. The amount of recycling depends upon the depth and also upon
the responsiveness of the zooplankton community.
Arctic
The benthic-pelagic coupling in the Bering
and Chukchi seas is particularly important
as these areas are fed by the extremely rich
Anadyr waters where maximum primary
production is as high as 300 g C/m2/yr and
because the seas are relatively shallow, much
of this production is available to the benthos. The food supply to the benthos is perhaps the highest in the world; this results in
very high benthic biomass, especially of
ampeliscid amphipods, and low benthic
species diversity (Grebmeier and Barry,
1991). Large demersal fishes are not common in the northern waters and the major
macro-invertebrate predators tend to be
crabs, ophiuroids, and asteroids. In some
areas these predators take a much smaller
percent of the benthic productivity, the rest
of which feeds large populations of gray
whales and walrus. This area also has higher
quality organic matter indicated by low C/N
ratios of 5-7 (Grebmeier and Barry, 1991).
The southern part of this area is one of the
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P. K. DAYTON ET AL.
richest fishing areas in the world, and it also
supports high densities of marine mammals
and marine sea birds. The lowest rates of
primary production are in the eastern Bering
Sea Alaska Coastal Water which also has
lower quality organic matter indicated by
high C/N ratios of 8-14. In contrast, the
more nutrient limited system in the Alaska
Coastal Water results in low benthic biomass and greater niche diversification of
benthic species (Grebmeier et al., 1989).
With regard to the high Arctic, there are
few data for the Arctic Basin marginal seas
such as the East Siberian, Laptev, Kara,
northern Chukchi, Beaufort, and the Canadian Archipelago. Primary production is
very limited. Despite the harsh conditions,
some of the few cobble areas in the high
Arctic support interesting kelp communities which do most of their growth in the
dark of winter (see Dunton, 1992, for this
literature), and the carbon produced by these
kelps have been traced throughout the benthic fauna (Dunton and Schell, 1987), again
emphasizing the carbon limited nature of
this system. The Barents Sea has the most
diverse bottom fauna in the Arctic. The high
productivity results from the oceanographic
mixing. The coastal zone is also unusual
because it has large populations and high
biomass of macroalgae, especially many
species of red algae, Laminaria and Fucus
(Dunton, 1992; Grebmeier and Barry, 1991).
The highest benthic biomass occurs at the
Polar Front where the main macrobenthic
species include bivalves and other large species such as crabs, sponges and echinoderms
(Grebmeier and Barry, 1991).
Antarctic
As mentioned earlier the primary production is relatively low but with localized
productive areas such as upwelling and mixing areas, fronts, etc. Furthermore as much
as 10-76% of primary production might be
cycled through bacterial loops in the water
column (Sullivan et al., 1990, reviewed in
Grebmeier and Barry, 1991); this would
reduce the relative amount of production
transferred to the benthos.
Despite this and despite the great depth,
the continental shelves are often characterized by very high benthic biomass, and in
all major macrobenthic taxa the number of
Antarctic species greatly outnumber the
Arctic species. Arntz and Gallardo (1993)
and Grebmeier and Barry (1991) report wet
wt values ranging from 0.1 g and 1,644.2
g/m2 in the Weddell Sea but only 9.1 to 57.1
in the Antarctic Peninsula area to over 4,000
g/m2 in other areas. The high Antarctic
standing stocks contrast with those of the
Arctic which rarely exceed 400 g/m2. This
contrast is very interesting because the water
column production and carbon flux to the
benthos is generally lower in the Antarctic
suggesting that other factors are important.
Somehow the decoupling of the water column from the benthos appears to limit Arctic more than Antarctic communities
(Grebmeier and Barry, 1991). This may
simply be a factor of temperature related
metabolic rates.
Grebmeier and Barry (1991) present three
general models relating the water column to
the benthos. The first describes the ice free
zones where low productivity and very deep
water results in very low carbon flux rates
to the bottom of 1-5 g C/m2/yr. Here the sediments are composed of red clays and siliceous oozes, very low carbon, and low biomass. The second model describes areas
influenced by higher mixing, fronts and seasonal ice cover. These are the richer waters
with seasonally intense phytoplankton
blooms and krill dominated zooplankton.
While there is still considerable recycling,
the bottom sediment varies from siliceous
oozes to rich sponge communities. The third
model describes continental shelves with
persistent ice cover such as McMurdo
Sound. Here the in situ primary production
is low, but there is effective advection of
carbon along the east side of the Sound
(Grebmeier and Barry, 1991).
McMurdo Sound is an especially good
example of a site with advective processes
as the east side has very high amounts of
carbon advected from the north, some benthic microalgal production and very high
densities and biomass of both infaunal and
epifaunal communities (reviewed in Dayton, 1990). At McMurdo Station there is a
dense association of sponges, and in the soft
bottom habitats there is a dense assemblage
of infauna noted for both its extraordinary
97
POLAR MARINE COMMUNITIES
densities and its remarkable equitability.
This contrasts with the west Sound habitats
bathed by waters from beneath the Ross Ice
Shelf which have very low amounts of carbon, and the benthic infauna communities
are characterized by low densities and biomass. The southern edge of McMurdo Sound
is bounded by the Ross Ice Shelf, and White
Island, over 30 km south of the edge, has a
dense population of filter feeders subsisting
on production advected under the shelf.
ANTHROPOGENIC IMPACTS
Perhaps the most common impression of
polar visitors is that the habitats are wild
and pristine. Unfortunately there are many
types of perturbations. There are persistent
rumors from the former Soviet Union of
very serious pollution including the dumping of large quantities of radioactive material and chemical pollutants into the Siberian seas. There is no knowledge of how
such poisons affect coastal ecosystems, and
it is important to learn more about how
toxicants do affect the biota and how these
effects are manifested in food webs. Minerals exploration and exploitation in the high
Arctic result in several potential perturbations about which we know very little. For
example, the noise of exploration and drilling is thought by many to significantly affect
the behavior of important species such as
bowhead whales. This is particularly serious
because much of this is done in the narrow
leads in the sea ice which serve as corridors
to vital summer feeding grounds. In addition, we can only speculate about the ramifications of high Arctic oil spills. More
southern arctic areas such as the Bering Sea
are subject to very heavy fisheries. In addition to impacting the target species, the fisheries often focus on key species such as pollock and crabs, and their exploitation may
have many ecosystem level effects. These
include resource competition with marine
species such as northern sea lions and murres
and an often staggering incidental take from
active and lost gear. Besides the northern
sea lions and murres, harbor seals and fur
seals are thought to be in serious decline as
a result of such interactions with fisheries.
Finally, heavy bottom trawling can have
extremely destructive effects on the benthic
community which can be manifested by
reducing or changing the predators and by
differentially reducing larval recruitment
which can shift the entire benthic community.
The Antarctic has no serious pollution
impacts, and it is strictly protected by an
international treaty. But none of us understands the cascading consequences of the
virtual elimination of the great whales from
the southern ocean. These effects possibly
include population explosions of krill consumers such as some penguins, fur seals
(themselves rebounding from heavy overexploitation), crabeater seals, minke whales
and possibly squid. Finfish have more
recently been overexploited and there is now
a heavy fishery on krill. Unfortunately the
giant baleen whales have shown no sign of
recovery. However, there is an international
convention which mandates a conservative
and relatively successful management of the
living resources of the Southern Ocean.
DISCUSSION
All marine communities are influenced
by food availability which ultimately comes
from primary productivity. In polar areas
marine primary production is controlled by
nutrients which are influenced by hydrographic regimes and light which is a factor
of sea ice. Both are determined directly by
oceanographic processes such as fronts
which make nutrients available and wind
and upwelling patterns which affect the sea
ice. Any ecosystem understanding must be
based on the appropriate oceanographic
processes.
Upper trophic level species are finely
tuned to oceanographic processes. Marine
birds and smaller mammals are extremely
sensitive to indications of local upwelling,
fronts, small eddies and other processes
which concentrate food. Larger mammals
and deep diving birds work larger scaled
processes, especially those which reflect predictable patterns in ice conditions. In most
marine systems a large proportion of the
productivity is consumed and recycled
within the water column, thus limiting the
amount of carbon reaching the bottom community. Exceptions occur in shallow areas
which are particularly important in the Arc-
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P. K. DAYTON ET AL.
tic Bering/Chukchi and some Barents Sea
regions. In these areas the benthic productivity is tightly coupled to the pelagic situation, and there are very large populations
of mammals such as gray whales, walrus
and bearded seals which forage on the benthos.
Benthic communities reflect the nature,
abundance, and predictability of organic
inputs, their utilization, and the amount of
important disturbance. The organic input is
critical and benthic communities track the
overlying productivity. The Arctic productivity seems to be efficiently transferred
within the foodwebs and benthic populations may have high turnover rates; the Antarctic seas offer a paradox in which the water
column has sufficient productivity to support large populations of mammals, birds,
squid, etc, but the benthic communities are
characterized by low growth rates and secondary production; these slow rates apply
even to microbial links. The Antarctic pattern of high water-column productivity and
apparently low benthic utilization is an
interesting contrast with the Arctic.
The evolutionary contrast between the
Arctic and the Antarctic is perhaps the most
interesting difference between the polar
habitats. The heavily disturbed Arctic with
its relatively young fauna and low endemism has been undergoing colonization since
the last ice age. The Antarctic, in contrast,
has the oldest and most isolated association
of marine species in the world and is characterized by a high degree of endemism. As
expected the two are profoundly different,
but the geological explanations for many of
the differences are illusory. For example,
birds and mammals aside, the water column
in the Arctic is dominated by many diverse
types offish which, properly managed, could
support large fisheries whereas the Antarctic
is characterized by invertebrates such as krill
and squid which support birds and mammals, but a small fin fishery in the 1960s
collapsed.
Perhaps more fundamental are the benthic differences between the two habitats.
The Antarctic shelf is deeper, much smaller
and in many ways simpler, despite having
more species. It lacks the crabs, sharks, most
of the benthic fishes, especially flat fishes,
many types of snails and polychaetes, and
the large extremely productive populations
of clams and ampeliscid amphipods so
characteristic of the Arctic. The Arctic benthos is much more heavily disturbed, from
both physical affects such as ice scour and
anchor ice and from bioturbation at all
scales. For example, the Arctic has many
more surface-burrowing species such as
echiuroids, polychaetes, echinoderms and
especially Crustacea. Further, in many Arctic areas there are populations of large crabs
which are extremely effective predators.
Probably most important, the Antarctic
lacks bottom-feeding fishes such as rays and
flatfish, walrus and gray whales. Although
it is one of the oldest isolated ecosystems
in the world and has a high degree of endemism, the Antarctic lacks this degree of complexity.
How is it that with all the endemism and
time of isolation, the Antarctic is so simple
relative to the young Arctic fauna? For one
thing, much of the radiation in the Antarctic
is restricted to only a few groups (algae, fish,
pycnogonids, isopods, amphipods and echinoderms); missing are some of the most
important Arctic groups (bottom fish, crabs,
bivalves, etc), most of which did occur in
the Antarctic through the Eocene and at least
in the case of shallow water balanomorph
barnacles occurred until the last ice age. A
fascinating evolutionary question is whether
this pattern results from founder groups
capable of surviving the Eocene cooling persisting in the relatively simplified, less
stressful, and predictable environment or
from some type of ecological dominance of
the founders, or perhaps the cold water
groups in the Antarctic, often with deep
water affinities, have genetic templates
which are less plastic.
With regard to exploitation, we suggest
that the traditional approach to environmental management in which conservation
efforts cannot be justified without conclusive evidence of harm is extremely dangerous. Managers tend to forget that there are
two types of errors attendant to their decisions. They usually focus on the type I error
of unnecessarily restricting a harvest which
includes the risk of the loss of revenue.
Because biology is never an absolute sci-
POLAR MARINE COMMUNITIES
ence, they find uncertainties in conservation
arguments which they use to avoid type I
errors, the recovery time for which is rapid.
Unfortunately they almost never consider
the type II error of allowing harvest which
does destroy the resource and the ecosystem; the recovery time following type II
errors almost always includes several
decades. It is common but ill-advised to
argue that use is a right rather than a privilege. We believe that resource management
must be based on some form of precautionary principle which explicitly considers the
risks to the environment and also shifts the
burden of doubt to the user to evaluate ecosystem effects of exploitation.
ACKNOWLEDGMENTS
This paper is dedicated to John H. Dearborn, perhaps the most knowledgeable polar
marine biologist in the world and certainly
one of our most helpful colleagues. Dearborn's work and this paper emphasize the
fact that all ecological, biogeographical and
evolutionary understanding depends absolutely on vibrant and well funded systematic
research. Unfortunately just when it is most
needed the science of systematics is in
marked decline. We feel that this silent crisis is extremely serious to the future of all
biology. We thank the organizers for the
invitation to participate and for their
patience. Our polar research has been funded
by the National Science Foundation.
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