earth	The third planet from the sun, the only planet on which life is known to exist.
ebb (tide)	The movement of a tidal current away from shore or down a tidal river or estuary.
ecological efficiency	In marine ecology, the amount of energy extracted from a given trophic level divided by that supplied to the same trophic level. This is the product of two other coefficients, the ecotrophic efficiency and the growth efficiency.
ecosystem	All the organisms in a particular region and the environment in which they live. The elements of an ecosystem interact with each other in some way, and so depend on each other either directly or indirectly.
emersion	The act or an instance of emersing.
emulsification	Making or forming into an emulsion.
endemic	1. Present within a localised area 2. An endemic disease or plant.
Environmental Impact	Assessment A management tool that predicts the likely environmental impacts of projects, finds ways to reduce unacceptable impacts, shapes the project so that it is appropriate to the local environment, and presents predictions and options to decision-makers.
epibenthic	Animals and plants living above the sediment.
epifauna	Animals living on or near the ocean bottom, as opposed to infauna (animals living within the sediment).
epipelagic zone	The vertical zone where intense gradients of most of the environmental parameters (light, temperature, nutrients etc) exist. There are significant diurnal and seasonal variations and a pronounced influence from wave action.
equilibrium	1. A stable condition in which forces cancel one another 2. Any unchanging state of a body, system etc resulting from the balance of influences to which it is subjected.
erosion	1. The wearing away of, soil etc. by the action of water, ice, wind etc. 2. The act or process of eroding or the state of being eroded.
euphotic zone	For the purpose of biological investigations, it is convenient to consider the sea as divided vertically into three zones with respect to the amount of light that is present. These are: (a) the euphotic zone, which is abundantly supplied with light sufficient for the photosynthetic processes of plants (in oceans down to 80 m); (b) the disphotic zone, which is only dimly lighted and extends in the open ocean from about 80 m to 200 or more metres. No effective plant production can take place here; (c) the aphotic zone, the lightless region below the disphotic zone. The depth of the euphotic zone varies with the water's extinction coefficient, the angle of incidence of the sunlight, the length of day and cloudiness.
eurothermic	Organisms able to live in a wide temperature range.
euryhaline	Used for organisms that are capable of osmoregulating in a relatively wide range of salinities. The eel (Anguilla anguilla) and Atlantic salmon (Salmo salar) are classified as euryhaline.
eutrophication	Natural or artificial nutrient enrichment in a body of water, associated with extensive plankton blooms and subsequent reduction of dissolved oxygen.
evaporation	A change from a liquid or solid state to a vapour.
evolution	A gradual change in the characteristics of a population of animals or plants over successive generations, either by environmental influence or genetic mutation. Evolution not only refers to 'better' adaptations, but rather responses only to ambient conditions. Organisms which survive long enough to produce offspring permit the passage of their traits and genes; only those traits which are ultimately deleterious to the organism will not be available for natural selection. The most fecund individuals are therefore not necessarily the most fit.
excretion	1. The discharge of waste matter (such as urine, sweat or faeces) from the body 2. (plants) The elimination of waste matter through the leaves, roots etc.
exoskeleton	Skeleton covering the outside of the body, or situated in the skin. The exoskeleton of crustaceans consists of four layers. These are the outer, uncalcified epicuticle, the calcified exocuticle, the calcified endocuticle and the inner, uncalcified membranous layer.