Deep-Sea Ecosystems: Biodiversity and Anthropogenic Impacts

Abstract

The oceans cover 70 per cent of the surface of the Earth. Fifty percent of the volume of these oceans is below 3000 m. The Earth is thus a blue planet and the deep sea is its largest biome. The deep sea is considered to start at 200 m depth, where light penetration is so weak that photosynthesis cannot longer be supported. This depth often coincides with the shelf break, which separates the shelf from the continental slope (200-3000 m depth), followed by abyssal plains (3000-6000 m) and hadal trenches (6000-11000 m). Continental margins are characterised by high habitat diversity, including sediment slopes, submarine canyons, cold-water corals and cold seeps amongst others, which support a high biodiversity and a variety of faunal communities. Mid-ocean ridges form a semi-continuous volcanic mountain chain around the globe, and it is here that hydrothermal vents and their exotic faunal communities are found. Away from the ridge, seamounts and knolls are underwater mountains that support rich sessile communities of filter feeders as well as fish populations. Technological developments sustain an increased understanding of the composition and function of deep-sea ecosystems, at the same time that exploration has revealed a wealth of resources, including biotic (fish, crustaceans, genetic resources) and abiotic (hydrocarbons, minerals). These resources are increasingly being targeted for commercial exploitation, with often poorly understood impacts on, and recovery potential of, deep-sea ecosystems. A better understanding of deep-sea ecosystem functioning and their response to stressors is essential for the development of robust ecosystem-based management measures that will balance resource use and environmental conservation. Future research and monitoring should incorporate assessments of cumulative impacts from different human activities, including resource extraction, waste and pollution and climate change.