90
Verena TUNNICLIFFE et al.
difficult the separate determination of temperature and
chemical influences on species distribution (Sarrazin
et al., 1999).
High-temperature sulphide chimneys must be one of
the most extreme habitats in the ocean. Measurement
of actual temperatures experienced by animals is very
difficult although values over 80ºC are reported for the
polychaete Alvinella pompejana (Chevaldonn´ e et al.,
1992; Cary et al., 1998). As conduits clog and new
orifices form, water pathways can rapidly change.
Assemblages on chimneys shift dramatically, die and/or
regrow from year to year (Fustec et al., 1987; Copley
et al., 1997; Sarrazin et al., 1997). The animals
themselves may be responsible for modifying the rock
surface and altering flow characteristics.
Faunal communities at seeps and organic remains
mostly experience ambient seawater temperatures that
range from <2ºC in deep waters to 7–8ºC at seeps
on the Louisiana Slope (MacDonald et al., 1994).
Temperature anomalies of less than 1ºC are unlikely
to influence organism distribution in non-hydrothermal
reducing habitats. However, temperatures to 21ºC were
measured in a convecting mud “lake” (Henry et al.,
1996), where the only macrofauna were symbiontcontaining sponges and vesicomyid clams around the
edges.
Chemical environment
Redox conditions in deep-sea reducing habitats range
from that of a completely anoxic milieu in which
reducing substances accumulate, and which are suitable
only for prokaryote life, to the highly reactive interface of oxic and anoxic environments where aerobic
chemosynthesis and dependent animal life flourish.
Total anoxia dominates in subsurface sediments, in
hydrothermal aquifers and within organic remains.
Oxic–anoxic interfaces are usually located on the
seafloor at vent and seep discharge points and on
or near organic remains. Subsurface mixing of oxic
and anoxic fluids can occur in hydrothermal systems,
permitting chemical oxidations and aerobic microbial
growth below the seafloor (Karl, 1995).
Common to most seafloor reducing habitats colonized by animals and/or micro-organisms is the
presence of micromolar to millimolar concentrations
of hydrogen sulphide in escaping hydrothermal fluids,
sediment pore waters or diffusing from organic remains
(Johnson et al., 1988; Naganuma et al., 1996; Barry
et al., 1997). At hydrothermal vents, organisms in
direct contact with venting fluids are usually exposed
to hydrogen sulphide. In situ chemical analysers can
describe the chemical habitat of different vent species
(Johnson et al., 1988; Sarrazin et al., 1999). Limited
data from seeps suggest that dissolved sulphide does
not escape from near-surface sediments, restricting the
utilization of sulphide to animals that extend part of
their body into the sediment to access the sulphide
(clams, lamellibrachiid vestimentiferans) or to sediment micro-organisms. Sulphide concentrations may
influence colonization patterns of vesicomyid clams
(Barry et al., 1997). Naganuma et al. (1996) found, in
sediment pore water, that sulphide concentrations and
counts of autotrophic bacteria dropped sharply within
a few decimetres of the vertebral axis of a whale
skeleton. Vesicomyid clams appear to be restricted to
sediments within 20 cm of whale bones (Bennett et al.,
1994). Sulphide is probably present in the surface
boundary layer on some areas of decaying whale bones,
as indicated by the presence of small, symbiont-bearing
bivalves, which take up sulphide through their gills.
Dissolved methane at above-background levels is
usually detectable in hydrothermal fluids, subduction
zone seeps and, of course, at hydrocarbon seeps.
Hydrothermal fluids are the most chemically complex
of the reducing solutions occurring in the marine
environment. In addition to an abundance of trace,
minor and major elements (e.g., Von Damm, 1995),
hydrothermal fluids contain most substances known to
support microbial chemosynthesis (Table 4.2), including H 2 S, CH 4 , H 2 , Fe
2+ and Mn
2+ .
ORGANIC MATTER PRODUCTION IN REDUCING
ENVIRONMENTS
Energy metabolism and carbon sources
Plant life is impossible in the total darkness of the
deep sea, thus, food resources are at a premium. The
discovery in 1977 of luxuriant oases of giant worms,
clams and mussels clustering around hydrothermal
vents over 2000 m deep (Corliss et al., 1979) came as
a complete surprise to biologists, who scrambled to
identify the food source for this unusual ecosystem.
The presence of hydrogen sulphide in hydrothermal
fluids, and an abundance of sulphide-oxidizing bacteria, were the first clues leading to the hypothesis
that faunal communities at hydrothermal vents are
Verena TUNNICLIFFE et al.
difficult the separate determination of temperature and
chemical influences on species distribution (Sarrazin
et al., 1999).
High-temperature sulphide chimneys must be one of
the most extreme habitats in the ocean. Measurement
of actual temperatures experienced by animals is very
difficult although values over 80ºC are reported for the
polychaete Alvinella pompejana (Chevaldonn´ e et al.,
1992; Cary et al., 1998). As conduits clog and new
orifices form, water pathways can rapidly change.
Assemblages on chimneys shift dramatically, die and/or
regrow from year to year (Fustec et al., 1987; Copley
et al., 1997; Sarrazin et al., 1997). The animals
themselves may be responsible for modifying the rock
surface and altering flow characteristics.
Faunal communities at seeps and organic remains
mostly experience ambient seawater temperatures that
range from <2ºC in deep waters to 7–8ºC at seeps
on the Louisiana Slope (MacDonald et al., 1994).
Temperature anomalies of less than 1ºC are unlikely
to influence organism distribution in non-hydrothermal
reducing habitats. However, temperatures to 21ºC were
measured in a convecting mud “lake” (Henry et al.,
1996), where the only macrofauna were symbiontcontaining sponges and vesicomyid clams around the
edges.
Chemical environment
Redox conditions in deep-sea reducing habitats range
from that of a completely anoxic milieu in which
reducing substances accumulate, and which are suitable
only for prokaryote life, to the highly reactive interface of oxic and anoxic environments where aerobic
chemosynthesis and dependent animal life flourish.
Total anoxia dominates in subsurface sediments, in
hydrothermal aquifers and within organic remains.
Oxic–anoxic interfaces are usually located on the
seafloor at vent and seep discharge points and on
or near organic remains. Subsurface mixing of oxic
and anoxic fluids can occur in hydrothermal systems,
permitting chemical oxidations and aerobic microbial
growth below the seafloor (Karl, 1995).
Common to most seafloor reducing habitats colonized by animals and/or micro-organisms is the
presence of micromolar to millimolar concentrations
of hydrogen sulphide in escaping hydrothermal fluids,
sediment pore waters or diffusing from organic remains
(Johnson et al., 1988; Naganuma et al., 1996; Barry
et al., 1997). At hydrothermal vents, organisms in
direct contact with venting fluids are usually exposed
to hydrogen sulphide. In situ chemical analysers can
describe the chemical habitat of different vent species
(Johnson et al., 1988; Sarrazin et al., 1999). Limited
data from seeps suggest that dissolved sulphide does
not escape from near-surface sediments, restricting the
utilization of sulphide to animals that extend part of
their body into the sediment to access the sulphide
(clams, lamellibrachiid vestimentiferans) or to sediment micro-organisms. Sulphide concentrations may
influence colonization patterns of vesicomyid clams
(Barry et al., 1997). Naganuma et al. (1996) found, in
sediment pore water, that sulphide concentrations and
counts of autotrophic bacteria dropped sharply within
a few decimetres of the vertebral axis of a whale
skeleton. Vesicomyid clams appear to be restricted to
sediments within 20 cm of whale bones (Bennett et al.,
1994). Sulphide is probably present in the surface
boundary layer on some areas of decaying whale bones,
as indicated by the presence of small, symbiont-bearing
bivalves, which take up sulphide through their gills.
Dissolved methane at above-background levels is
usually detectable in hydrothermal fluids, subduction
zone seeps and, of course, at hydrocarbon seeps.
Hydrothermal fluids are the most chemically complex
of the reducing solutions occurring in the marine
environment. In addition to an abundance of trace,
minor and major elements (e.g., Von Damm, 1995),
hydrothermal fluids contain most substances known to
support microbial chemosynthesis (Table 4.2), including H 2 S, CH 4 , H 2 , Fe
2+ and Mn
2+ .
ORGANIC MATTER PRODUCTION IN REDUCING
ENVIRONMENTS
Energy metabolism and carbon sources
Plant life is impossible in the total darkness of the
deep sea, thus, food resources are at a premium. The
discovery in 1977 of luxuriant oases of giant worms,
clams and mussels clustering around hydrothermal
vents over 2000 m deep (Corliss et al., 1979) came as
a complete surprise to biologists, who scrambled to
identify the food source for this unusual ecosystem.
The presence of hydrogen sulphide in hydrothermal
fluids, and an abundance of sulphide-oxidizing bacteria, were the first clues leading to the hypothesis
that faunal communities at hydrothermal vents are