REDUCING ENVIRONMENTS OF THE DEEP-SEA FLOOR
97
Norwegian fjords to 10 000 m in trenches. Monoliferan
pogonophorans are found in sunken organic debris –
even clothing. Monoliferans and perviates are recorded
from much deeper water than the vestimentiferans of
vents and seeps. Whether this distribution relates to
depth limitations or the location of the habitats is
unknown.
Bivalves
A large amount of biomass is held in bivalves of the
families Lucinidae, Thyasiridae, Solemyidae, Mytilidae
and Vesicomyidae. Despite their long geological history and likely association with sulphide-rich habitats
(Reid and Brand, 1986), the first three families are
not common at vents. Their contribution to total
biomass and productivity at vents and seeps is probably
minor, but their deep-burrowing habit makes them
difficult to observe quantitatively or to sample from
submersibles. Lucinids, present in sediments from the
intertidal zone to the deep sea, host symbiotic bacteria
in their fleshy gills (Fisher, 1990). Their ability to
establish at very low sulphide levels suggests that these
animals may access the local concentration of sulphide
through extensive tubes which enhance interaction with
iron sulphides in the sediments (Dando et al., 1985).
Thyasirids live in burrows where sulphide levels are
usually low (Dando et al., 1986). Solemyids may lose
the gut altogether, and are most commonly known from
areas of sewage outfall or pulp log accumulation where
sulphide levels may reach 12 mM °
−1 (Childress and
Lowell, 1982).
About seventeen mussel species are known from
vents and seeps – most are in the new subfamily Bathymodiolinae (Gustafson et al., 1998). The geographic
extent of Bathymodiolus is relatively large at both vents
and seeps, although there are notable absences at the
deep seeps off Japan, seeps of the eastern Pacific, and
vents of the northeast Pacific. Distel et al. (2000) have
proposed that sunken wood and whale carcasses may
be important phylogenetic vectors in the dispersion of
seep and vent species. Mussels are recorded from a
wide range of environmental conditions, where they
may occur in groups of hundreds to thousands. Fisher
et al. (1988b) have described a broad variability
in physiological characteristics for one vent species
(Bathymodiolus thermophilus), which appears to be
related to highly variable water flow. Mussels are
common at seeps in both the Atlantic and the west
Pacific. These animals can use the abundant methane
in the seep habitat; two species are known to have
methylotrophic microbes as symbionts (Childress et al.,
1986; Cavanaugh et al., 1987).
The “giant vent clam” Calyptogena magnifica is
restricted to low-flow areas where variability in dissolved gases is reflected in several physiological indices
(Fisher et al., 1988a). Both vent and seep vesicomyids
can concentrate dissolved sulphide in their blood at
levels higher than those in the immediate environment
(Scott and Fisher, 1995). Vesicomyids are known from
nearly all seep sites described to date (Sibuet and
Olu, 1998). In Sagami Bay (“Jps” site in Fig. 4.1),
Calyptogena soyae populations reach densities of
about 1000 individuals m
−2 (Hashimoto et al., 1989).
Sulphide concentrations peak around 0.6 mmol g
−1
about 20 cm into the sediment (Hashimoto et al., 1995).
Deeper populations in the Peru Trench yield even
higher peak abundances (Olu et al., 1996a). Studies (i.e.
Juniper and Sibuet, 1987; Rosman et al., 1987) yield
glimpses of the great extent of such communities in
the deep sea and leave open the possibility that many
more such areas remain to be discovered.
Shrimps
Caridean shrimps are known from most vent regions,
and from seeps in the Gulf of Mexico, Florida and
Barbados areas. They are presently placed in the Family
Bresilidae. Phylogenetic work on one mitochondrial
locus has identified three clades within the vent/seep
shrimps, one of which is exclusive to the Mid-Atlantic
Ridge (Shank et al., 1999). Interest focused on this
group with the discovery of vents on the Mid-Atlantic
Ridge where they constitute a large part of the biomass.
Several species are known from venting chimneys
where densities reach 3000 m
−2 (Gebruk et al., 2000).
These shrimps swarm around hot fluids, and many
specimens are scarred from hot-water contact (Gebruk
et al., 1997). One species, Rimicaris exoculata, was
named for its absence of normal eyes; but a large
white organ on the dorsal carapace is capable of
gathering very dim light in the infrared wavelengths
(O’Neill et al., 1995; Van Dover et al., 1996b). Hightemperature vents emit black-body radiation which may
be visible to these animals, thus allowing them to
relocate the “smokers” if dislodged by turbulence or
their neighbours; presumably, the high sulphide levels
are needed to encourage growth of their exosymbionts
(Pelli and Chamberlain, 1989). Other vent shrimps have
similar dorsal organs, though of lesser size.
97
Norwegian fjords to 10 000 m in trenches. Monoliferan
pogonophorans are found in sunken organic debris –
even clothing. Monoliferans and perviates are recorded
from much deeper water than the vestimentiferans of
vents and seeps. Whether this distribution relates to
depth limitations or the location of the habitats is
unknown.
Bivalves
A large amount of biomass is held in bivalves of the
families Lucinidae, Thyasiridae, Solemyidae, Mytilidae
and Vesicomyidae. Despite their long geological history and likely association with sulphide-rich habitats
(Reid and Brand, 1986), the first three families are
not common at vents. Their contribution to total
biomass and productivity at vents and seeps is probably
minor, but their deep-burrowing habit makes them
difficult to observe quantitatively or to sample from
submersibles. Lucinids, present in sediments from the
intertidal zone to the deep sea, host symbiotic bacteria
in their fleshy gills (Fisher, 1990). Their ability to
establish at very low sulphide levels suggests that these
animals may access the local concentration of sulphide
through extensive tubes which enhance interaction with
iron sulphides in the sediments (Dando et al., 1985).
Thyasirids live in burrows where sulphide levels are
usually low (Dando et al., 1986). Solemyids may lose
the gut altogether, and are most commonly known from
areas of sewage outfall or pulp log accumulation where
sulphide levels may reach 12 mM °
−1 (Childress and
Lowell, 1982).
About seventeen mussel species are known from
vents and seeps – most are in the new subfamily Bathymodiolinae (Gustafson et al., 1998). The geographic
extent of Bathymodiolus is relatively large at both vents
and seeps, although there are notable absences at the
deep seeps off Japan, seeps of the eastern Pacific, and
vents of the northeast Pacific. Distel et al. (2000) have
proposed that sunken wood and whale carcasses may
be important phylogenetic vectors in the dispersion of
seep and vent species. Mussels are recorded from a
wide range of environmental conditions, where they
may occur in groups of hundreds to thousands. Fisher
et al. (1988b) have described a broad variability
in physiological characteristics for one vent species
(Bathymodiolus thermophilus), which appears to be
related to highly variable water flow. Mussels are
common at seeps in both the Atlantic and the west
Pacific. These animals can use the abundant methane
in the seep habitat; two species are known to have
methylotrophic microbes as symbionts (Childress et al.,
1986; Cavanaugh et al., 1987).
The “giant vent clam” Calyptogena magnifica is
restricted to low-flow areas where variability in dissolved gases is reflected in several physiological indices
(Fisher et al., 1988a). Both vent and seep vesicomyids
can concentrate dissolved sulphide in their blood at
levels higher than those in the immediate environment
(Scott and Fisher, 1995). Vesicomyids are known from
nearly all seep sites described to date (Sibuet and
Olu, 1998). In Sagami Bay (“Jps” site in Fig. 4.1),
Calyptogena soyae populations reach densities of
about 1000 individuals m
−2 (Hashimoto et al., 1989).
Sulphide concentrations peak around 0.6 mmol g
−1
about 20 cm into the sediment (Hashimoto et al., 1995).
Deeper populations in the Peru Trench yield even
higher peak abundances (Olu et al., 1996a). Studies (i.e.
Juniper and Sibuet, 1987; Rosman et al., 1987) yield
glimpses of the great extent of such communities in
the deep sea and leave open the possibility that many
more such areas remain to be discovered.
Shrimps
Caridean shrimps are known from most vent regions,
and from seeps in the Gulf of Mexico, Florida and
Barbados areas. They are presently placed in the Family
Bresilidae. Phylogenetic work on one mitochondrial
locus has identified three clades within the vent/seep
shrimps, one of which is exclusive to the Mid-Atlantic
Ridge (Shank et al., 1999). Interest focused on this
group with the discovery of vents on the Mid-Atlantic
Ridge where they constitute a large part of the biomass.
Several species are known from venting chimneys
where densities reach 3000 m
−2 (Gebruk et al., 2000).
These shrimps swarm around hot fluids, and many
specimens are scarred from hot-water contact (Gebruk
et al., 1997). One species, Rimicaris exoculata, was
named for its absence of normal eyes; but a large
white organ on the dorsal carapace is capable of
gathering very dim light in the infrared wavelengths
(O’Neill et al., 1995; Van Dover et al., 1996b). Hightemperature vents emit black-body radiation which may
be visible to these animals, thus allowing them to
relocate the “smokers” if dislodged by turbulence or
their neighbours; presumably, the high sulphide levels
are needed to encourage growth of their exosymbionts
(Pelli and Chamberlain, 1989). Other vent shrimps have
similar dorsal organs, though of lesser size.