Deep Sea Ecology

The open ocean covers more than 65 percent of Earth’s surface and thus represents the largest environment on our planet. Far from uniform, it encompasses a variety of different habitats spanning depths from approximately 650 feet to over 36,000 feet (average depth of over 12,300 feet). The lack of sunlight and the high hydrostatic pressures (on average approximately 400 atm) lead many to consider these environments extreme. In addition, temperatures in the deep sea are typically below 39.2°F, and as low as 28.4°F in deep Antarctic waters, which play a key role on the biodiversity distribution of deep-sea fauna (see M. Yasuhara and R. Danovaro, “Temperature Impacts on Deep-Sea Biodiversity,” Biological Reviews 91, no. 2 [2016]: 275–287). The absence of photosynthetic primary production in the deep sea results in the dominance of heterotrophic species, which depend upon the supply of organic material settling down from the photic zone or the continents. Nonetheless, chemoautotrophic bacteria and archaea that occur in hydrothermal vents and cold seeps also occur in all deep-sea sediments and contribute an important source of primary production. The deep sea hosts a wide variety of habitats and ecosystems largely defined by topographic heterogeneity and spanning from continental slopes and canyons to mid-ocean ridges, seamounts, abyssal plains, and trenches. All these massive geologic features host unique and diverse habitats that support rich assemblages and high biodiversity. Tropical coral reefs, because they support high numbers of species per unit area, and the deep sea, because it spans an enormous area, represent the two biggest repositories of marine biodiversity. High levels of endemism characterize the latter, despite the virtual absence of physical barriers. Seamounts, for example, harbor impressive species richness, and some exhibit high levels of endemism, with 30 to 50 percent of endemic invertebrate species on some seamounts. The remoteness, inaccessibility, and complexity of deep marine environments make these systems the last frontiers of scientific research and exploration on our planet. Recent discoveries, such as those enabled by the development of new technologies, the synergy of interdisciplinary skills, and the greater attention to resources and ecosystem services provided by deep-sea environments, provide strong impetus to accelerate research in these ecosystems.