abiotic	Non-biological factors such as temperature, that form part of the environment of an organisation.
abyssal plain	The deep and relatively flat portion of the ocean floor.
abyssopelagic zone	The 4,000 to 6,000 m depth zone, seaward of the shelf-slope break.
adaptation	A modification in organisms that makes them better suited to survive and reproduce in a particular environment.
aerobic	1. A condition or process where gaseous oxygen is present or required 2. In microbiology, Pasteur's term for microorganisms which grow only in the presence of oxygen.
albedo	Reflectivity of a surface. High albedo means that the majority of the incoming radiation is reflected (e.g. snow); low albedo means that the majority of the incoming radiation is absorbed (e.g. water).
anaerobic	Referring to a condition or process where gaseous oxygen is not present or not necessary.
analytic	A device capable of analysis.
angle of incidence	The angle that a line or beam of radiation makes with a line perpendicular to the surface at the point of incidence.
anoxia	Oxygen deficiency in the blood cells or tissues of the body in such degree as to cause psychological and physiological disturbances. Anoxia may result from a scarcity of oxygen in the medium or from an inability of the body tissue to absorb oxygen under conditions of low ambient pressure; cf. hypoxia.
antennae	One of a pair of mobile appendages on the heads of insects, crustaceans etc., that often respond to touch and taste but may be specialised for swimming.
anthropogenic	Descriptive of any factor, disturbance or material which is human-made and introduced into the environment. Term applied especially to pollutants (= derived from human sources).
appendage	Any structure growing out of the body of an organism; usually movable paired leg-like structures.
aquaculture	Production, growth and harvesting of animals or plants in marine or fresh water. Aquaculture stocks include molluscs, algae such as seaweeds and fish such as carp and trout. MARICULTURE refers to this process in salt water only.
artificial reef	Man-made structure that attracts fish and is sometimes considered a form of extensive aquaculture in which these structures provide suitable niches for fish or shellfish.
atmosphere	The gaseous envelope surrounding the Earth or any other celestial body. atom The smallest quantity of an element that can take part in a chemical reaction.
attraction	The act or quality of attracting.
autotroph	An organism which creates its own food energy from inorganic materials using light (photosynthesis) or chemical (chemosynthesis) energy. Includes plants and some bacteria.