bacteria	A large group of unicellular microorganisms, many of which cause disease. see also: decomposing bacteria
barometric pressure	A change in atmospheric pressure, usually altitude or weather changes.
bathypelagic zone	The 2,000 to 4,000 m depth zone seaward of the shelf-slope break.
Beggiatoa	Chemolithotrophic sulphur bacteria occurring mainly in sediments. Filaments form into thick ÔmatsÕ or bacterial plates when conditions allow.
benthic	Pertaining to the bottom terrain of water bodies; describing the portion of the aquatic environment inhabited by organisms that live on or in the sediment.
benthos	Organisms that live on or in the sediment in aquatic enviroments.
bilge water	The dirty water that collects in a vessel's bilge.
bioaccumulation	The process whereby a chemical, e.g., cadmium, is concentrated in an organism, organ or tissue at a concentration higher than that found in the environment or food.
Biochemical Oxygen Demand (BOD)	The amount of oxygen consumed by respiratory processes of bacteria and the oxidation of organic material which is measured in a water sample maintained in darkness at a specified temperature for a specified amount of time.
biodegradable	Capable of being decomposed by bacteria or other biological means.
biodiversity	1. The absolute number of species in an assemblage, community or sample; species richness. 2. A measure of the number of species and their relative abundance in a community; low diversity refers to few species or unequal abundances, high diversity to many species or equal abundances. 3. The condition of having differences with respect to a given character or trait.
biogenesis	The principle that a living organism must originate from a parent organism similar to itself.
bioluminescence	Light produced by living organisms (e.g. plankton and fishes). Most extensively developed in midwater and bottom-dwelling deep sea species (e.g. lantern fishes). Arises from (a) luminous bacteria living on the fish in a symbiotic relationship or (b) from photophores. Bioluminescence may serve as courting behaviour or as a lure for prey.
biomagnification	The accumulation of high concentrations in an organism through the retention of a compound found in low levels in the diet and water.
biomass	Any quantitative estimate of the total mass of organisms comprising all or part of a population or any other specified unit, or within a given area at a given time; measured as volume, mass (live, dead, dry or ash-free weight) or energy (joules, calories).
bioturbation	Disturbance, as by organism activity, of a sediment bed or formation.
bird	Any warm-blooded egg-laying vertebrate, characterized by a body covering of feathers and forelimbs modified as limbs.
bloom (algal)	A population burst of phytoplankton that remains within a defined part of the water column.
buoyancy	The ability to float in a liquid or to rise in a liquid, air, or other gas.