Scientists have speculated that as many as 10 million species may inhabit the deep sea — biodiversity comparable to the world's richest tropical rainforests. Because deep-sea species live in rarely disturbed environments and tend to be slow growing, late maturing and endemic, they are exceptionally vulnerable to extinction. Deep-sea coral and sponge communities are largely untapped sources of natural products with enormous potential as pharmaceuticals, enzymes, pesticides, cosmetics and other commercial products.
A great deal of deep-seas biodiversity is concentrated around seamounts which are underwater mountains that rise 1,000 meters or higher from the seabed without breaking the ocean's surface. It is estimated that there may be as many as 30,000 to 100,000 seamounts worldwide. They are home to cold-water coral reefs and forests, sponge beds and hydrothermal vents, as well as the many millions of species dependent on these. And because many seamounts are located in remote surroundings — underwater islands, essentially — virtually every study finds species that were previously unknown and are endemic, meaning that they are unique to that area.
Seamounts are not only physically impressive, but like an oasis in the desert, provide an important source of food. Because of their physical characteristics and strong localized currents, they accumulate enormous quantities of plankton. The plankton, in turn, attracts a vast array of marine life, providing feeding as well as spawning grounds for myriad pelagic species, including some that have migrated across wide oceanic areas.
Home to large marine mammals, such as dolphins and whales and an extraordinary diversity of fish, together with exotic sponge and coral ecosystems, seamounts are among the world's greatest marine-biological treasures.
The deep sea is also home to remarkably rich coral systems. Once thought to inhabit only the warm and shallow waters of tropical and subtropical regions, corals have apparently been thriving in deep, dark and cold waters throughout the world for millions of years. Indeed, it is now thought that there are more coral species living in the dark ocean depths than in the tropical shallows.
Carbon dating of living cold-water coral reefs has revealed that the oldest may be 8,000 years old or more. Several of the coral species create complex reefs and ornate three-dimensional, forest-like structures that rival tropical coral systems in their size and complexity. Indeed, the oldest and tallest reef yet observed is 35 meters high.
Although scientists have only just begun to explore the ecological aspects of cold-water corals, it is clear that cold-water reefs are bustling with life, providing essential sanctuaries and nursing grounds for countless species.
Seamounts, and the cold-water corals they sustain, provide habitats for several commercial bottom-dwelling fish species, such as orange roughy, roundnose grenadier, blue ling, mirror dory and silver dory. Other species, for example, alfonsino, boar fish and blue-eye trevalla, are also attracted to these habitats. The concentrations of these fish around seamounts make them very attractive fishing grounds.
Sadly, studies show that the long life cycles and slow sexual maturation of deep-sea fish makes them particularly vulnerable to large-scale fishing activities. These species have dwelled in ecosystems that are rarely disturbed and that recover from disturbances at an exceedingly slow rate, if at all. Whole populations can be quickly fished out.