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Abyssal plain. The deep ocean floor, an expanse of low relief at depths of 4,000 to 6,000 m


Abyssopelagic zone. The 4,000 to 6000-m-depth zone, seaward of the shelf-slope break


Acclimation. Given a change of a single parameter, a readjustment of the physiology of an organism, reaching a new steady state


Accuracy. Is the correctness of a measure when comparing to a known standard. See also resolution and precision.


Age structure. The relative abundance of different age classes in a population


Aggregated spatial distribution. A case where individuals in a space occur in clusters too dense to be explained by chance


Ahermatypic. Non-reef-building (referring to scleractinian corals)


Allele. One of several variants that can occupy a locus on a chromosome


Allopatric speciation. The differentiation of geographically isolated populations into distinct species


Allozyme. A variant of an enzyme type. These may be variants of a specific enzyme (e.g., cytochrome c) that are the products of a single genetic locus.


Amensal. Negatively affecting one or several species


Amino acids. Basic structural unit of proteins


Anadromous fish. Fish that spends most of its life feeding in the open ocean but that migrates to spawn in fresh water


Anoxic. Lacking oxygen.


Arrow worms. Members of the phylum Chaetognatha, a group of planktonic carnivores


Asexual reproduction. Reproduction of the individual without the production of gametes and zygotes


Assimilation efficiency. The fraction of ingested food that is absorbed and used in metabolism


Assortative mating. The mating of a given genotype mates with another genotype at a frequency disproportionate to that expected from random



Atoll. A horseshoe or circular array of islands, capping a coral reef system perched around an oceanic volcanic seamount


Attenuation (of light). Diminution of light intensity; explained, in the ocean, in terms of absorption and scattering


Autotrophic algae. Algae capable of photosynthesis and growth using only dissolved inorganic nutrients


Auxotrophic algae. Algae requiring a few organically derived substances, such as vitamins, along with dissolved inorganic nutrients for