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Abyssal plain: The flat region of the ocean floor from 4,000 to 7,000 metres.

Abyssopelagic zone: The 4,000 to 7,000 metres depth zone sea-ward of the shelf-slope break.

Acclimation: A readjustment of the physiology of an organism in response to a change in a physical parameter.

Actinians: The scientific name of sea anemones.

Ampullae: Reproductive structures found in hydrozoan corals.

Anastomose: The area where branched skeletons of stony corals fuse together where they touch.

Anthozoa: Exclusively marine cnidarians, including; sea anemones, scleractininan corals, tube anemones, sea pens, sea fans, blue coral and black coral.

Ascidians: Tunicate animals, including sea squirts and red bait.

Attenuation: Drop in light intensity due to absorption and scattering within the ocean.

Azooxanthellae: Cnidarians without symbiotic photosynthesising algae. Species described as azooxanthellae commonly feed on passing plankton and waterborne material.

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Bathyal zone: The benthic environment between the depths of 200 and 2000 metres, including the continental slope and oceanic ridges and rises.

Bathymetry: The study of the depth of the ocean.

Benthic: Anything relating to the sea floor, including organisms living in or on the seafloor.

Biodiversity: A term to describe living organisms from all systems, including terrestrial, marine and aquatic environments and the ecological complexes of which they are part.

Biomass: The amount of living material in a given area.

Bivalve: Members of the Mollusca, which have two shells connected by a hinge.

Bleaching: A phenomenon in tropical corals, bleaching occurs during periods of environmental stress when corals purge zooxanthallae, usually resulting in coral death.

Bottom trawls: A method of fishing in which a large bag-shaped net is dragged behind the vessel. The mouth of the net is kept open by various methods such as a wooden beam (beam trawl) or a large flat boards (otter trawl).

Brittle star: Marine invertebrates of the Ophiuroidea (phylum Echinodermata). They have long thin arms which set from a small disc shaped body.

Bycatch: Unwanted fish or other animals caught in fishing nets by accident. Bycatch is usually thrown back dead or dying.

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Calcareous: Made of calcium carbonate.

Carbonate mounds: Seabed features usually constructed from carbonate producing organisms and current controlled sedimentation.

Clone: Genetically identical individual usually produced asexually.

Cold seep: Cold water seeps slowly from the sea floor (the opposite of hot, hydrothermal vents); often rich in hydrogen sulphide, a compound toxic to most animal life.

Cold-water: Temperature regime not exceeding 20°C, and is meant here to draw a line between cold-water and tropical warm-water environments.

Cold-water coral ecosystems: Large aggregation of cold-water corals in terms of spatial coverage at a given locality also used to describe the associated fauna on the reef.

Colonial animals: Animals that live in groups.

Community: A group of organisms of different species that occur in the same habitat or area.

Continental margin: A zone separating the emergent continents from the deep-sea bottom; generally consists of the continental shelf, slope and rise.

Continental shelf: A gently sloping area extending from the low-water line to the depth of a marked increase in slope around the margin of a continent or island

Continental slope: A relatively steeply sloping surface lying seaward of the continental shelf.

Coral: A group of benthic anthozoans that exist as individuals or in colonies. Some species create calcium carbonate external skeletons.

Coral reef: Accretion of coral skeleton that over time rise above the sea floor.

Cosmopolitan: Animals or plants with a worldwide distribution within physical habitat limits.

Cnidarian: A phylum of animals with approximately 9000 different species. Cnidarians are radially symmetric, with tentacles originating from a central node. This phylum includes hydroids, jellyfish, anemones and corals.

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Deep-sea trenches: Narrow, elongate depressions of the deep sea floor. An example is the Marianas Trench in the Pacific Ocean.

Deep water: The water beneath the permanent thermocline that has a usually has a low and uniform temperature.

Demersal: Sinking to or lying on the bottom; living on or near the bottom and feeding on benthic organisms.

Diversity: The number of taxa in a group or place.