Glossary of Marine Biology

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Daily estuary. An estuary in which tidal movements cause substantial changes in salinity at any one location on a daily basis


Deep layer. The layer extending from the lowest part of the thermocline to the bottom


Deep-scattering layer. Well-defined horizon in the ocean that reflects sonar; indicates a layer usually consisting of fishes, squid, or other larger zooplankton


Demographic. Referring to numerical characteristics of a population (e.g., population size, age structure)


Density. (seawater) Grams of sea water per milliliter of fluid


Density-dependent factors. Factors, such as resource availability, that vary with population density


Deposit feeder. An organism that derives its nutrition by consuming some fraction of a soft sediment


Detritus. Particulate material that enters into a marine or aquatic system. If derived from decaying organic matter it is organic detritus.


Diatom. Dominant planktonic algal form with siliceous test, occurring as a single cell or as a chain of cells


Diffusion. The net movement of units of a substance from areas of higher concentration to areas of lower concentration of that substance


Digestion efficiency. The fraction of living food that does not survive passage through a predator's gut


Dinoflagellate. Dominant planktonic algal form, occurring as a single cell, often biflagellate


Directional selection. Preferential change in a population, favoring the increase in frequency of one allele over another


Dissolved organic matter. Dissolved molecules derived from degradation of dead organisms or excretion of molecules synthesized by organisms


Disturbance. A rapid change in an environment that greatly alters a previously persistent biological community


Diversity. A parameter describing, in combination, the species richness and evenness of a collection of species. Diversity is often used as a synonym for species richness


Diversity gradient. A regular change in diversity correlated with a geographic space or gradient of some environmental factor


Ekman circulation. Movement of surface water at an angle from the wind, as a result of the Coriolis effect


El Niño-Southern Oscillation (ENSO). Condition in which warm surface water moves into the eastern Pacific, collapsing upwelling and increasing surface-water temperatures and precipitation along the west coast of North and South America


Emigration. The departure of individuals from a given area


Endosymbiotic. Being symbiotic and living within the body of an individual of the associated species


Environmental stress. Variously defined as (a) an environmental change to which an organism cannot acclimate and (b) an environmental change that increases the probability of death


Epibenthic (epifaunal or epifloral). Living on the surface of the bottom


Epidemic spawning. Simultaneous shedding of gametes by a large number of individuals


Epipelagic zone. The 0- to 150-m-depth zone, seaward of the shelf-slope break


Epiphyte. Microalgal organism living on a surface (e.g., on a seaweed frond)


Estuarine flow. Seaward flow of low-salinity surface water over a deeper and higher -alinity layer


Estuarine realms. Large coastal water regions that have geographic continuity,are bounded landward by a stretch of coastline with fresh-water input, and are bounded seaward by a salinity front


Estuary. A semienclosed body of water that has a free connection with the open sea and within which seawater is diluted measurably with freshwater that is derived from land drainage


Euphausiid. Member of an order of holoplanktonic crustacea


Eutrophic. Water bodies or habitats having high concentrations of nutrients


Evenness. The component of diversity accounting for the degree to which all species are equal in abundance, as opposed to strong dominance by one or a few species


Fecal coliform bacteria Technically, all the facultative anaerobic gram negative non-spore forming rod shaped bacteria that fermet lactose in EC medium with gas production within 24h at 44.5 degrees C. A measure of bacteria mostly originating from guts that enter waters. Believed to be correlated with disease-causing (pathogenic) bacteria.


Fecal pellets. See Pellets


Fecundity. The number of eggs produced per female per unit time (often: per spawning season)


Foliose coral. A coral whose skeletal form approximates that of a broad, flattened plate


Food chain. An abstraction describing the network of feeding relationships

in a community as a series of links of trophic levels, such as primary producers, herbivores, and primary carnivores


Food chain efficiency. Amount of energy of some other quantity extracted from a trophic level, divided by the amount of energy produced by the next-lower trophic level

Food web. A network describing the feeding interactions of the species in an area


Foraminifera. Protozoan group, individuals of which usually secrete a calcareous test; both planktonic and benthic representatives


Founder principle. A small colonizing population is genetically unrepresentative of the source of population


Freshet. An increase of water flow into an estuary during the late winter or spring, owing to increased precipitation and snow melt in the watershed


Front. A major discontinuity separating ocean currents and water masses in any combination


Fugitive species. A species adapted to colonize newly disturbed habitats