Glossary of Marine Biology



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Oceanic. Associated with sea-water environments seaward of the shelf-slope break


Oceanic ridge. A sinuous ridge rising from the deep-sea floor


Oligotrophic. Refers to water bodies or habitats with low concentrations of nutrients


Omnivory. Being able to feed in more than one distinct way (e.g., an organism capable of carnivory and herbivory)


Optimal foraging theory. A theory designed to predict the foraging behavior that maximizes food intake per unit time


Organic. Deriving from living organisms


Organic nutrients. Nutrients in the form of molecules synthesized by or originating from other organisms


Osmoconformer. An organism whose body fluids change directly with a change in the concentrations of dissolved ions in the external medium


Osmoregulator. An organism that regulates the concentration of dissolved ions in its body fluids irrespective of changes in the external medium


Osmosis. The movement of pure water across a membrane from a compartment with relatively low dissolved ions to a compartment with higher concentrations of dissolved ions


Outwelling. The outflow of nutrients from an estuary or salt-marsh system to shelf waters


Overdominance. Selection favoring heterozygotes


Oxygen dissociation curve. A curve showing the percent saturation of a blood pigment, such as hemoglobin, as a function of oxygen concentration of the fluid


Oxygen minimum layer. A depth zone, usually below the thermocline, in which dissolved oxygen is minimal


Oxygen technique (primary productivity). The estimation of primary productivity by the measurement of the rate of oxygen increase


Parapatric speciation. The differentiation into distinct species of populations experiencing some gene flow


Parasite. An organism living on or in, and negatively affecting, another organism


Particulate organic matter. Particulate material in the sea derived from the decomposition of the nonmineral constituents of living organisms


Patchiness. A condition in which organisms occur in aggregations


Pelagic. Living in the water column seaward of the shelf-slope break


Pellets. Compacted aggregations of particles resulting either from egestion (fecal pellets) or from burrow-constructing activities of marine organisms


Penetration anchor. In hydraulically burrowing organisms, any device used to penetrate and gain an initial purchase on the sediment so that the body can be thrust in farther


Peptides. Chains of amino acids; often portions of a protein molecule


pH. Measure of he acidity or basicity of water (-log10 of the activity of hydrogen ions in water)


Phenotypic plasticity. The capacity of an individual to produce different phenotypes under different conditions. Non-genetic potential variability within the range of a single individual.


Phi scale. Scale used for measuring the grain size of sediments. = -log2 (grain diameter)


Photic zone. The depth zone in the ocean extending from the surface to that depth permitting photosynthesis


Photorespiration. Enhanced respiration of plants in the light relative to dark respiration


Photosynthate. A substance synthesized in the process of photosynthesis


Photosynthetic quotient. In photosynthesis, the moles of oxygen produced, divided by the moles of carbon dioxide assimilated


Photosynthetic rate. The rate of conversion of dissolved carbon dioxide and bicarbonate ion to photosynthetic product


Phototactic. Moving in response to light


Physiological race. A geographically defined population of a species that is physiologically distinct from other populations


Phytoplankton. The photosynthesizing organisms residing in the plankton


Planktivorous. Feeding on planktonic organisms


Plankton. Organisms living suspended in the water column and incapable of moving against water currents


Planktotrophic larva. Planktonic-dispersing larva that derives its nourishment by feeding in the plankton


Planula. The planktonic larval form produced by scleractinian corals and coelenterates


Plate. Major section of the earth's crust, bounded by such features as mid-ocean ridges


Pleistocene. Period of time, going back to approximately 2 million years before the present, in which alternating periods of glaciation and deglaciation have dominated the earth's climate


Pleuston. Refers to plankton that have a float protruding above the sea surface, such as the Portugese man-of-war.


Poikilotherm. An organism whose body temperature is identical to that of the external environment


Polyp. An individual of a solitary coelenterate or one member of a coelenterate colony


Polyphyletic. Refers to a group of species that do not have one common ancestor species


Population density. Number of individuals per unit area or volume


Porifera. The phylum comprising the sponges.

PPT. A measure of the salt content of sea water in terms of kg salt per kg of water, reckoned in parts per thousand. A conductivity version of this measure is the PSU, which differs from PPT by very little, on the order of 0.02 PSU or less.

Practical Salinity. See PSU

Precision. Precision is the repeatability of a measurement. A measurement can be precise, but not accurate. See Accuracy and Resolution.


Predation. The consumption of one organism by another

Predator. An organism that consumes another living organism (carnivores and herbivores are both predators by this definition)


Primary producer. An organism capable of using the energy derived from light or a chemical substance in order to manufacture energy-rich organic compounds


Primary production. The production of living matter by photosynthesizing organisms or by chemosynthesizing organisms. Usually expressed as grams of carbon per square meter per year


Province. A geographically defined area with a characteristic set of species or characteristic percentage representation by given species


Protein polymorphism. Presence of several variants of a protein of a given type (e.g., a certain enzyme, such as carboxylase) in a population


Pseudofeces. Material rejected by suspension feeders or deposit feeders as potential food before entering the gut


PSU. Practical Salinity Units. A measure of the salt content of seawater (practical salinity), based upon electrical conductivity of a sample relative to a reference standard of sea water, which now happens to be a reference set of diluted sea water samples from the North Atlantic of known salt content. See PPT.


Pteropods. Group of holoplanktonic gastropods


Pycnocline. Depth zone within which sea-water density changes maximally


Q10 Increase of metabolic rate with an increase of 10ºC


Quantitative genetics. The study of the genetic basis of traits, usually explained in terms of the interaction of a group of genes with the environment