THE PERIPHERAL DEEP SEAS
279
levels rise to 1.0 mg m
−3 inside the Kurile Islands, and
outside the islands in the open Pacific they increase to
5.0 mg m
−3 . Chlorophyll values above 1 mg m
−3 were
found in the Sea of Okhotsk inside the northern Kurile
Islands. Such elevated values are believed to be a
result of incursions of nutrient-richer Pacific waters
(Mordasova, 1997). Overall, Mordosova classifies the
Sea of Okhotsk as ‘eutrophic’, since it supports high
invertebrate and fish production. No data are available
for the flux of surface production to deeper waters.
Any extrapolation made from surface data will be
complicated by the flow of water into, and out of, the
Sea of Okhotsk over the deep sills between the Kurile
Islands.
THE DEEP-WATER BENTHIC FAUNA OF
PERIPHERAL DEEP SEAS
Mediterranean Sea
The most recent detailed reviews of the deep-water
fauna of the Mediterranean are given by P´ er` es (1985),
Fredj and Laubier (1985) and Laubier and Emig (1993).
When the Mediterranean was completely isolated from
the Atlantic and Indo-Pacific during the Messinian
crisis all true benthic species in the Mediterranean
became extinct (P´ er` es, 1985). Since then, there has
been colonization of deep water by species from
the deep Atlantic and from shallow waters of the
Atlantic via Mediterranean shallow water. No deep
water species are considered Lessepsian (those species
entering the Mediterraean via the Suez Canal).
P´ er` es (1985) identified two bathyal assemblages in
the western Mediterranean:
(a) the deep-sea coral assemblage
(b) the bathyal mud assemblage
The deep-sea coral assemblage
This assemblage consists of both living and dead
ahermatypic corals, which form scattered clumps but
are not widespread. Their depth range is from 300 m
down to a known maximum of 1000 m. The main
frame corals are Lophelia pertusa and Madrepora
oculata (both found commonly in the North Atlantic)
and the solitary corals Caryophyllia armata (sic) and
Desmophyllum cristagalli. The decline in the reefbuilding species is attributed to siltation resulting
from deforestation on land, and the subsequent erosion
and riverine transport of soil. Associated with both
living and dead ahermatypic corals are the gorgonians
Isidella elongata and species of Muricea and Primnoa.
The most distinctive of the polychaetes is Eunice
floridana, which lives on the coral. Truly bathyal
species include the serpulids Omphalopomopsis fimbriata and Placostegus tridentatus and the ampharetids
Acanthicolepis cousteaui and Lagisca drachi. Other
polychaetes are eurybathyic and not truly bathyal.
Characteristic molluscs include the chiton Hanleya
hanleyi as well as bivalves including species of the
genus Arca, Chlamys bruei and Spondylus gussoni.
The dominant sea urchin in this assemblage is Cidaris
cidaris and the main crustaceans Pandalina profunda
and Paromola cuvieri.
Bathyal mud assemblage
This zone extends from 200 m down to ~2500 m,
and consists of fine sediments. Compared to similar
depths in the Atlantic (see Chapter 5) this zone in
the Mediterranean may be considered impoverished,
although by contrast with other Mediterranean biotopes
this assemblage is rich in species and abundance
(P´ er` es, 1985). Most Atlantic species at this depth are
not eurybathic enough to cross the sill at Gibraltar.
The lack of colonizing species, the high temperature
of the deep Mediterranean (see above, p. 264), and
the low downward vertical flux from relatively poor
primary production at the surface, contribute to the
impoverishment of this zone. Picard (1965) and P´ er` es
(1985) have given extensive faunal lists of the species
characteristic of this zone. Polychaetes and benthic
crustaceans are particularly common but most major
groups are represented. The origin of this bathyal
fauna is still the subject of debate, but one group of
organisms (the mud-loving or pelophilous species) have
extended down to depth from relatively shallow areas,
particularly the outer or lower part of the shelf. From
200 m down, the temperature remains fairly constant;
Young et al. (1997) have shown that the embryos
and larvae of shallow species are able to tolerate the
pressures at bathyal depths, and may have penetrated
through a vertically homogeneous water column.
P´ er` es (1985) divided the bathyal mud zone into three
subzones:
(i) an upper zone containing mainly eurybathic
species;
(ii) a middle zone with high species diversity;
(iii) a lower subzone with decreased species diversity and containing species, such as Plutonaster
bifrons, not found in the two shallower zones.
Plutonaster bifrons is another species that may
279
levels rise to 1.0 mg m
−3 inside the Kurile Islands, and
outside the islands in the open Pacific they increase to
5.0 mg m
−3 . Chlorophyll values above 1 mg m
−3 were
found in the Sea of Okhotsk inside the northern Kurile
Islands. Such elevated values are believed to be a
result of incursions of nutrient-richer Pacific waters
(Mordasova, 1997). Overall, Mordosova classifies the
Sea of Okhotsk as ‘eutrophic’, since it supports high
invertebrate and fish production. No data are available
for the flux of surface production to deeper waters.
Any extrapolation made from surface data will be
complicated by the flow of water into, and out of, the
Sea of Okhotsk over the deep sills between the Kurile
Islands.
THE DEEP-WATER BENTHIC FAUNA OF
PERIPHERAL DEEP SEAS
Mediterranean Sea
The most recent detailed reviews of the deep-water
fauna of the Mediterranean are given by P´ er` es (1985),
Fredj and Laubier (1985) and Laubier and Emig (1993).
When the Mediterranean was completely isolated from
the Atlantic and Indo-Pacific during the Messinian
crisis all true benthic species in the Mediterranean
became extinct (P´ er` es, 1985). Since then, there has
been colonization of deep water by species from
the deep Atlantic and from shallow waters of the
Atlantic via Mediterranean shallow water. No deep
water species are considered Lessepsian (those species
entering the Mediterraean via the Suez Canal).
P´ er` es (1985) identified two bathyal assemblages in
the western Mediterranean:
(a) the deep-sea coral assemblage
(b) the bathyal mud assemblage
The deep-sea coral assemblage
This assemblage consists of both living and dead
ahermatypic corals, which form scattered clumps but
are not widespread. Their depth range is from 300 m
down to a known maximum of 1000 m. The main
frame corals are Lophelia pertusa and Madrepora
oculata (both found commonly in the North Atlantic)
and the solitary corals Caryophyllia armata (sic) and
Desmophyllum cristagalli. The decline in the reefbuilding species is attributed to siltation resulting
from deforestation on land, and the subsequent erosion
and riverine transport of soil. Associated with both
living and dead ahermatypic corals are the gorgonians
Isidella elongata and species of Muricea and Primnoa.
The most distinctive of the polychaetes is Eunice
floridana, which lives on the coral. Truly bathyal
species include the serpulids Omphalopomopsis fimbriata and Placostegus tridentatus and the ampharetids
Acanthicolepis cousteaui and Lagisca drachi. Other
polychaetes are eurybathyic and not truly bathyal.
Characteristic molluscs include the chiton Hanleya
hanleyi as well as bivalves including species of the
genus Arca, Chlamys bruei and Spondylus gussoni.
The dominant sea urchin in this assemblage is Cidaris
cidaris and the main crustaceans Pandalina profunda
and Paromola cuvieri.
Bathyal mud assemblage
This zone extends from 200 m down to ~2500 m,
and consists of fine sediments. Compared to similar
depths in the Atlantic (see Chapter 5) this zone in
the Mediterranean may be considered impoverished,
although by contrast with other Mediterranean biotopes
this assemblage is rich in species and abundance
(P´ er` es, 1985). Most Atlantic species at this depth are
not eurybathic enough to cross the sill at Gibraltar.
The lack of colonizing species, the high temperature
of the deep Mediterranean (see above, p. 264), and
the low downward vertical flux from relatively poor
primary production at the surface, contribute to the
impoverishment of this zone. Picard (1965) and P´ er` es
(1985) have given extensive faunal lists of the species
characteristic of this zone. Polychaetes and benthic
crustaceans are particularly common but most major
groups are represented. The origin of this bathyal
fauna is still the subject of debate, but one group of
organisms (the mud-loving or pelophilous species) have
extended down to depth from relatively shallow areas,
particularly the outer or lower part of the shelf. From
200 m down, the temperature remains fairly constant;
Young et al. (1997) have shown that the embryos
and larvae of shallow species are able to tolerate the
pressures at bathyal depths, and may have penetrated
through a vertically homogeneous water column.
P´ er` es (1985) divided the bathyal mud zone into three
subzones:
(i) an upper zone containing mainly eurybathic
species;
(ii) a middle zone with high species diversity;
(iii) a lower subzone with decreased species diversity and containing species, such as Plutonaster
bifrons, not found in the two shallower zones.
Plutonaster bifrons is another species that may