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Glossary of scientific marine biological terms used in MarLIN's Biology and Sensitivity Key Information Sub-programme. Compiled from McLeod (1996) with additions from Hiscock (1998) and various other references.



Abiotic : Devoid of life.

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.

Actiniarians : The scientific name for sea anemones.

Anthozoa : A class of the phylum cnidaria that includes sea anemones, corals and sea pens.

Attenuation : Drop in light intensity due to absorption and scattering within the ocean. azoic Devoid of animal life.

Azooxanthellae : Cnidarians without symbiotic photosynthesising algae. These species commonly feed on passing plankton and waterborne material.

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Bathyal : Pertaining to the sea floor between 200 m and 4000 m (Lincoln & Boxshall, 1987).

Bathymetry : Measurement of ocean or lake depth and the study of floor topography (Lincoln & Boxshall, 1987).

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

Biodiversity : (biological diversity) "The variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems." (UN Convention on Biological Diversity, 1992).

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).

Bryozoan : The Phylum Bryozoa is characterized by sessile colonies made up of many small individuals ca 0.5 mm long called zooids. Each zooid is surrounded by a protective case, which is oval, box-like or tubular in shape. Each zooid bears a bell of ciliated tentacles called the lophophore, which is retracted if disturbed. Colonies have a wide variety of forms, including encrusting sheets or mats, soft fleshy lobes, erect twiggy growths, or bushy tufts (adapted from Ruppert & Barnes (1996) and Hayward et al. (1996)).

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

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

Cnidaria : A group of animals characterized by the possession of stinging cells, and which includes the corals, hydroids, sea anemones and jellyfish.

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.

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.

Copepod : Small crustaceans.

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.

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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.

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

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Ecology : The study of how living organisms relate to and interact with their surroundings

Ecosystem : All the organisms in a biotic community and the abiotic environmental factors with which they interact.

Endemism / Endemic: A taxa restricted in distribution to a particular geographical area and occurring nowhere else.

Epifauna: Animals living on the surface of the seabed.

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Fauna : Another term describing animals.

Foraminifera : Protozoan group which are abundant in the plankton and benthos of all oceans and possess a protective test (shell) usually composed of calcium carbonate.

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Gastropoda: A class of mollusca, most of which possess an asymmetrical spiral one-piece shell and a well-developed flattened foot. Includes snails, limpets, abalone, cowries, sea hares and sea slugs.

Global warming: Increase in global temperature caused by increasing atmospheric carbon dioxide.

Gorgonian: A type of soft coral with a horny skeleton, includes sea fans.

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Habitat: A geographical location where individuals or populations of individuals reside.

Hard coral: General term for skeletal Anthozoa, also known as 'stony coral' (see scleractinians).

High seas: This term, in municipal and international law, denotes all continuous bodies of salt water in the world that are navigable in its character and that lies outside territorial waters and maritime belts of the various countries; also called open sea.

Hydrocarbon seeps: Areas where hydrocarbons seep slowly from the sea floor, may be associated with specific faunal composition.

Hydrodynamic: Relates to the specific scientific principles that deal with the motion of fluids examples include currents and oceanic circulation.

Hydrozoa (hydroid): A class of animals from the phylum cnidaria that characteristically exhibit alternation of generations with a sessile colony - often resembling small plants - giving rise to a pelagic medusoid form by asexual budding.

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Infaunal : Organisms which live in soft sediment and are large enough to displace sediment.

Interglacial : A comparatively long warmer phase of a glacial period when considerable glacial retreat occurs.


Journal : Used to describe scientific magazines and papers.


Key species : A species which, through its predatory activities (for instance, grazing by sea urchins) or by mediating competition between prey species (for instance, by eating sea urchins), maintains community composition and structure. Removal of a keystone species leads to rapid, cascading changes in the structure they support (based on Raffaelli & Hawkins, 1996). The term is also applied here to species which provide a distinctive habitat (for instance a bed of the horse mussel Modiolus modiolus , or kelp plants Laminaria hyperborea ) and whose loss would therefore lead to the disappearance of the associated community.


Lander system : Scientific instrument designed for temporary deployment on the sea floor in order to monitor environmental parameters.

Lithoherm : Consolidated ridge-like seabed elevations composed of skeletal material such as coral rubble.

Longshore current : A current moving parallel to the shoreline.

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Macrofauna: animals exceeding 1 mm in length.

Marl: fine-grained carbonate-rich mud.

Marine Protected Area (MPA) : "Any area of intertidal or subtidal terrain, including geological and geomorphological features, together with its overlying water and associated flora, fauna, historical and cultural features, which has been reserved by law or other effective means to protect part or all of the enclosed environment." (IUCN definition, as modified by the Marine Protected Area Group, a working group of Wildlife Link's Joint Marine Group).

Marine snow : Fragile organic aggregates resulting from the collision of dissolved organic molecules or from the degradation of gelatinous substances such as larvacean houses; usually enriched with microoraganisms.

Megafauna : Animals exceeding 2 cm in length.


Nekton: Organisms with swimming abilities that permit them to move against currents.

Nutrients: Elements and compounds which are needed by organisms for maintenance and growth.


Oceanic: Associated with sea-water environments seaward of the shelf-slope break.

Oceanic Crust: The outermost layer of rock on the earth's surface, underlying the deep ocean. Oceanic crust is created at mid-ocean ridges where plates are moving apart.

Octocorallia: A subclass of the Anthozoa. Each polyp has eight tentacles extending radially from a central point.

Offshore: The comparatively flat submerged zone of variable width extending from the breaker line to the edge of the continental shelf.

Overfishing: Enormous fishing pressure resulting in fish stocks becoming overfished. Overfishing may reduce fish stocks, resulting in age structure degrading or even collapse.

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Pelagic: Living in the open-water environment, seaward of the shelf-break, also used to describe the open water environment.

Photic zone: The part of the ocean penetrated by sunlight.

Phylum: A major grouping in taxonomy.

Plankton: Passively drifting or weakly swimming organisms that are not independent of currents, including mostly microscopic algae, protozoa and larval forms of higher animals.

Polychaete: The Class Polychaeta (Phylum Annelida) are a group of truly segmented worms, characterized by extensions of each segment called 'parapodia' that bear bundles of bristles, hence the term 'many bristled' or 'poly' 'chaeta'. Cf. bristleworm.

Polyp: Typically sedentary soft-bodied component of Cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.

Population: A group of organisms of the same species inhabiting a geographical area.

Predation: The consumption of one organism by another.

Productivity: A measure of the capacity of a biological system, e.g. the amount of fish supported or reproduced by a given area in a given time.



Recruitment : The addition of new individuals to a population.

Remotely operated vehicle (ROV) : An unmanned submersible connected to the research vessel by a cable, often used to carry imaging systems and sample collectors.


Salinity : The concentration of dissolved salts in water, usually measured in parts per thousand.

Scleractinians : Corals which have a hard limestone skeleton and belong to the order Scleractinia.

Seamount : Peaks of undersea mounds which can extend several hundred metres above the sea bottom, often capped with corals (known as carbonate mounds).

Sediment : Particles of organic or inorganic matter that accumulates in loose form on the seabed.

Sessile : Permanently attached to a substratum.

Soft coral : General term for anthozoan coral without a hard skeleton.

Solitary corals : Corals composed of a single individual polyp.

Spicule : Variously shaped or sized calcareous or siliaceous skeletal elements used in the endoskeleton of sponges and echinoderms (Stachowitsch, 1992).

Storm wave base : The plane or maximum depth at which surface driven waves may impact the sea bottom during severe storms.

Stylasterids : Corals of the family Stylasteridae, including lace corals.

Symbiosis : The close association between two organisms where there is substantial mutual benefit.

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Temperate : Pertaining to the latitudinal belt between 23° 27' and 66° 33' north or south latitude, geographical regions with milder conditions than the poles and the equator. Thermocline : A depth at which the temperature of the water changes significantly.


Upwelling : The movement of nutrient-rich water from a specified depth to the surface.



Water mass : A body of water that maintains its physical identity and can be characterised by parameters such as temperature and salinity.

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Xenophyophores: Large single-celled organisms, that are common throughout the deep-sea. They are fragile organisms often no larger than a golf ball, which may resemble flattened discs, angular four-sided shapes or spheres.



Zooid : One of the individual animals connected together in a common mass constituting a colony (based on Fitter & Manuel, 1986).

Zooplankton : Tiny animals with limited ability to move, which usually drift with water currents. Includes small crustaceans and larvae of many larger animals.

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