Science / Marine Biology Glossary

Plankton: Pelagic organisms that float through the water column, not attached to any substrate and unable to move against the currents and tides. Plankton can be further divided into phytoplankton and . . . View Full Definition

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: The number of individuals of a particular species that live within a defined area.

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 v . . . View Full Definition

Practical Salinity: See PSU

Practical Salinity Units (PSU): 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 refere . . . View Full Definition

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)

Prey: An animal that is used by other animals for food.

Primary Consumer: A heterotrophic, herbivorous organism that feeds directly on a primary producer. Urchins are a primary consumer as they feed on kelp. See also heterotroph, food chain; compare secondary consumer.

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

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

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

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

Pteropods: Group of holoplanktonic gastropods

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