The Deep Sea

This chapter explores the deep sea, which represents the largest, yet least-known, biome on earth. The environment is remarkably constant across the ocean floor: cold, dark water overlying soft, deep mud. While the high hydrostatic pressure is the most obvious physical feature of the deep, it is food supply from the surface that is the limiting factor for life on the abyssal plain. In temperate areas, the food input can be seasonal, providing cues for reproductive cycles. Due to the lack of food, the community of animals in the deep sea is at much lower densities than in shallow waters. Potentially there are millions of species inhabiting the deep-sea benthos; the main groups of large, mobile organisms are echinoderms, decapod crustaceans, and fish. Recent exploration using submersibles has revealed exciting 'island' habitats in the deep sea with a level of production and diversity higher than their surrounding environments.