20
Y. Fouquet and D. Lacroix
these resources. These structures are generally large, with very sloping 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.
This complexity, together with strong hydrodynamics and a high bathymetric gradient, greatly shapes seamount communities, known today to be home to high levels of
biological diversity and biomass, also composed of fish which are already targeted by
heavy fishing activity. The endemism rate of species and connectivity between populations are related to various biotic and abiotic factors, the most important being distance
between seamounts, hydrodynamics and larval dispersal capacities. The direct and indirect consequences of exploiting the resources in these environments can be expected to
be comparable with those of the exploitation of the above-mentioned sulphide deposits.
Sediment Fauna Diversity on Abyssal Plains
Abyssal plains conducive to the formation of polymetallic nodules are located in
ocean areas characterised by a very low sedimentation rate and oligotrophic conditions (low nutrient availability) for deep-sea communities. These large stretches
generally have low slopes; they may be intersected by hills or seamounts with more
marked slopes, formed from rocky substrates. The vastest and richest nodule fields
are located in the North-East Pacific, between the Clarion and Clipperton fracture
zones at an average depth of around 5,000 m. The biological wealth of sediment environments in this zone is mainly composed of small invertebrates (tens of microns
to a few millimetres) and micro-organisms. These communities are concentrated in
the top few centimetres of sediment; their density and local diversity are high. Large
organisms are rare in this oligotrophic environment. The structure of these communities varies within the zone, due to the heterogeneity of the habitat, generated by
various factors including primary production gradients (east-west and north-south),
the topography and the presence/absence of nodules on the bottom.
The exploitation of polymetallic nodules would have direct consequences (destruction of the habitat in the area exploited) and indirect consequences (redepositing of sediment plume over a wider area) on the area’s ecosystems. The extent of the
impact would also be exacerbated by the vulnerability of abyssal benthic populations to disturbance, due to the scarcity of the majority of species and low biological
activity rates related to the oligotrophic conditions in the environment. Recolonisation and population restoration processes could take years, or even decades.
Environmental Consequences of Exploitation
Generally speaking, deep-sea mining would have various levels of impact on the
environment and on biodiversity, including local destruction of habitats and related
ecosystems, but also disturbance to the environment (water column and seabed) and
biological diversity over a more extensive area and for a far longer period of time
than the mining itself. The level of knowledge of the different potentially threatened
Y. Fouquet and D. Lacroix
these resources. These structures are generally large, with very sloping 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.
This complexity, together with strong hydrodynamics and a high bathymetric gradient, greatly shapes seamount communities, known today to be home to high levels of
biological diversity and biomass, also composed of fish which are already targeted by
heavy fishing activity. The endemism rate of species and connectivity between populations are related to various biotic and abiotic factors, the most important being distance
between seamounts, hydrodynamics and larval dispersal capacities. The direct and indirect consequences of exploiting the resources in these environments can be expected to
be comparable with those of the exploitation of the above-mentioned sulphide deposits.
Sediment Fauna Diversity on Abyssal Plains
Abyssal plains conducive to the formation of polymetallic nodules are located in
ocean areas characterised by a very low sedimentation rate and oligotrophic conditions (low nutrient availability) for deep-sea communities. These large stretches
generally have low slopes; they may be intersected by hills or seamounts with more
marked slopes, formed from rocky substrates. The vastest and richest nodule fields
are located in the North-East Pacific, between the Clarion and Clipperton fracture
zones at an average depth of around 5,000 m. The biological wealth of sediment environments in this zone is mainly composed of small invertebrates (tens of microns
to a few millimetres) and micro-organisms. These communities are concentrated in
the top few centimetres of sediment; their density and local diversity are high. Large
organisms are rare in this oligotrophic environment. The structure of these communities varies within the zone, due to the heterogeneity of the habitat, generated by
various factors including primary production gradients (east-west and north-south),
the topography and the presence/absence of nodules on the bottom.
The exploitation of polymetallic nodules would have direct consequences (destruction of the habitat in the area exploited) and indirect consequences (redepositing of sediment plume over a wider area) on the area’s ecosystems. The extent of the
impact would also be exacerbated by the vulnerability of abyssal benthic populations to disturbance, due to the scarcity of the majority of species and low biological
activity rates related to the oligotrophic conditions in the environment. Recolonisation and population restoration processes could take years, or even decades.
Environmental Consequences of Exploitation
Generally speaking, deep-sea mining would have various levels of impact on the
environment and on biodiversity, including local destruction of habitats and related
ecosystems, but also disturbance to the environment (water column and seabed) and
biological diversity over a more extensive area and for a far longer period of time
than the mining itself. The level of knowledge of the different potentially threatened