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Other Chemosynthesis-based Ecosystems
In the 1980s, the presence of chemosynthesis-based ecosystems was highlighted
in various contexts, on ocean margins in the presence of cold seeps and in other
environments: oxygen minimum zones, bitumen outcrops, and on skeletons of
decomposing cetaceans. While cold seep animal communities are nourished by
chemosynthesis, they are also, due to their situation, nourished by organic matter
of pelagic and terrigenous origin. The lower toxicity of the fluid allows bathyal
species to enter the ecosystem, leading to far more diversified populations than
in the case of deep-sea hydrothermal vents. The study of relationships between
hydrothermal species and cold seep species shows that, during evolution, changes
have taken place between these environments, and that cold seep areas have acted
as relay areas for the dissemination of hydrothermal species. These chemosynthetic
ecosystems also possess resources in the form of methane hydrates.
Specific Seamount Ecosystems
Seamounts are prominent structures of variable size and shape, widely distributed
across the world’s ocean floors, mainly in the Pacific, but also the Atlantic and Indian
Oceans. They can reach up to 4,000 m above the ocean floor. They are most often
formed by volcanic activity and the effects of plate tectonics; some are active volcanoes and therefore feature hydrothermal ecosystems. Generally speaking, seamounts
have specific characteristics making them a special habitat for deep-sea fauna.
While abyssal plains generally have low slopes and are covered with fine sediment, seamounts can have steeper sides; their topography can be complex due to the
presence of terraces, canyons, calderas or craters; hard and soft substrates coexist in
different thicknesses and compositions. Furthermore, such relief alters the hydrodynamic conditions of surrounding water masses. It creates turbulence and sometimes
major upwellings of cold water rich in minerals, promoting high biological productivity both in pelagic and benthic areas.
The complexity of the topography and the nature of the substrate, as well as
strong hydrodynamics and a high bathymetric gradient, are influential factors in the
structure of seamounts’ faunal communities. Filter-feeding species dominate the
community of organisms fixed to hard substrates, in particular sponges and cnidaria
(including coral), which form the main part of the biomass. Fauna associated with
various crustaceans, molluscs etc. is also found. Pelagic fauna is also abundant,
with a high proportion of fish. This makes these structures a prime target for fishing, which is now known to have major destructive consequences on these ecosystems. The sediment accumulated in hollows and cracks or at the base of seamounts
is populated, like the neighbouring abyssal sediments, by many species of polychaetes, molluscs, peracarid crustaceans and other invertebrates and foraminifera.
Moreover, the composition of seamounts’ benthic communities is, like continen2 Deep-sea Environment
Other Chemosynthesis-based Ecosystems
In the 1980s, the presence of chemosynthesis-based ecosystems was highlighted
in various contexts, on ocean margins in the presence of cold seeps and in other
environments: oxygen minimum zones, bitumen outcrops, and on skeletons of
decomposing cetaceans. While cold seep animal communities are nourished by
chemosynthesis, they are also, due to their situation, nourished by organic matter
of pelagic and terrigenous origin. The lower toxicity of the fluid allows bathyal
species to enter the ecosystem, leading to far more diversified populations than
in the case of deep-sea hydrothermal vents. The study of relationships between
hydrothermal species and cold seep species shows that, during evolution, changes
have taken place between these environments, and that cold seep areas have acted
as relay areas for the dissemination of hydrothermal species. These chemosynthetic
ecosystems also possess resources in the form of methane hydrates.
Specific Seamount Ecosystems
Seamounts are prominent structures of variable size and shape, widely distributed
across the world’s ocean floors, mainly in the Pacific, but also the Atlantic and Indian
Oceans. They can reach up to 4,000 m above the ocean floor. They are most often
formed by volcanic activity and the effects of plate tectonics; some are active volcanoes and therefore feature hydrothermal ecosystems. Generally speaking, seamounts
have specific characteristics making them a special habitat for deep-sea fauna.
While abyssal plains generally have low slopes and are covered with fine sediment, seamounts can have steeper sides; their topography can be complex due to the
presence of terraces, canyons, calderas or craters; hard and soft substrates coexist in
different thicknesses and compositions. Furthermore, such relief alters the hydrodynamic conditions of surrounding water masses. It creates turbulence and sometimes
major upwellings of cold water rich in minerals, promoting high biological productivity both in pelagic and benthic areas.
The complexity of the topography and the nature of the substrate, as well as
strong hydrodynamics and a high bathymetric gradient, are influential factors in the
structure of seamounts’ faunal communities. Filter-feeding species dominate the
community of organisms fixed to hard substrates, in particular sponges and cnidaria
(including coral), which form the main part of the biomass. Fauna associated with
various crustaceans, molluscs etc. is also found. Pelagic fauna is also abundant,
with a high proportion of fish. This makes these structures a prime target for fishing, which is now known to have major destructive consequences on these ecosystems. The sediment accumulated in hollows and cracks or at the base of seamounts
is populated, like the neighbouring abyssal sediments, by many species of polychaetes, molluscs, peracarid crustaceans and other invertebrates and foraminifera.
Moreover, the composition of seamounts’ benthic communities is, like continen2 Deep-sea Environment