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.
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 zooxanthellae, 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 large flat boards (otter trawl).
Brittle star: Marine invertebrates of the Ophiuroidea (phylum Echinodermata). They have long thin arms which radiate out 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.
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, their associated fauna, and related biological, geological, chemical and physical processes driving the structure and function of these aggregations.
Colonial animals: an organism constructed of more than one genetically identical and repeated unit.
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 rises above the sea floor.
Cosmopolitan: Referring to a broad geographical distribution.
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.
Deep-sea trenches: Narrow, elongate depressions of the deep sea floor, e.g. the Marianas Trench in the Pacific Ocean, the Romanche Trench in the Atlantic Ocean.
Deep water: The water beneath the permanent thermocline that usually has a low and uniform temperature.
Demersal: Sinking to or lying on the sea floor; living on or near the bottom and feeding on benthic organisms.
Diversity: The number of or change in taxa across space and time.