Deep Sea Ecosystems

Discovering the Deep

The most extensive ecosystem on the planet is the deep sea, with its cold dark waters at the bottom of the deep oceans. Seventy per cent (70%) of the surface of the earth is covered with water; perhaps 85% of the area and 90% of the volume is in the deep sea. Deep sea ecosystems are little known; mainly due to the difficulty of sampling these remote areas. Until recently, they were inaccessible to humans. Deep manned and remote-operated submersible vehicles are now available but are so expensive to operate that little of the deep has been visited. Discoveries include:
  • seamounts
  • hydrothermal vents, and
  • deep-sea bacteria.
The deep sea is important as a source of materials, such as manganese, and as a potential dumping site for human wastes, such as carbon dioxide.


The term seamount was introduced in 1936 to name the massive Davidson seamount off California. Today, hydrographers define a seamount as an independent feature that rises at least 1000 meters above the sea floor. The Pacific Ocean is home to about two-thirds of them, with the rest scattered across the other oceans. The peaks are typically extinct volcanoes with the bulk of the research to date focusing on their geologic origins. Researchers have visited just a few hundred of the estimated 30 000 seamounts. Fewer than 1000 even have names, and only a handful have been intensively studied.

There is growing evidence that they are home to remarkable numbers of new and unusual organisms such as fish and corals. Seamounts may also help individual animals, such as large predatory fish like hammerhead sharks, navigate long distances. Biologists want to document the productive seamount ecosystems before they are damaged by fishing trawlers or other human activity.


Bioluminescence is particularly important in deep sea ecosystems where there is no sunlight. It is also common in near-surface waters at night. Primarily produced in the ocean by myriad organisms, bioluminescence is used for mating displays, finding prey, or defense from predators. More than just an interesting curiosity of nature, bioluminescent genes and molecules are now being applied as important research tools. Basic research on jellyfish, fireflies, and other organisms has led to applications in cell biology and biomedicine.

Under the cover of darkness, zooplankton (such as the copepod depicted here) feed on phytoplankton, including dinoflagellates. However, when attacked, luminescent dinoflagellates produce a flash of light that is seen by secondary predators, such as fish, that are eager to prey on the copepod. The threat of predation to the copepod acts as a deterrent to limit its feeding on the dinoflagellate. Thus the dinoflagellate bioluminescence acts as a burglar alarm to dissuade the copepod (burglar) from attacking it because of the threat of being eaten by the fish (police).