Glossary of Marine Biology


G, H, I, J, K

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Gametophyte. Haploid stage in the life cycle of a plant


Generation time. The time period from birth to average age of reproduction


Genetic drift. Changes in allele frequencies that can be ascribed to random effects


Genetic locus. A location on a chromosome (possibly of a diploid organism with variants that segregate according to the rules of Mendelian heredity)


Genetic polymorphism. Presence of several genetically controlled variants in a population


Genotype. The genetic makeup of an organism, with respect to a given genetic locus, the alleles it carries


Genus. (plural: genera) The level of the taxonomic hierarchy above the species but below the family level


Geostrophic flow. Movement of water in the oceans as a combined response to the Coriolis effect and gravitational forces created by an uneven sea surface


Geotactic. Moving in response to the earth's gravitational field


GIS. Geographic Information System. A system that allows automatic location of information suitable for mapping. Usually involves a software system that takes geographic position data and other data (e.g., type of bottom sediment) in order to create a map. Data on processes (e.g., current speed) can be incorporated to make a geographic model of flow.


Global warming. Predicted increase in the earth's oceanic and atmospheric temperature, owing to additions of carbon dioxide to the atmosphere, as a result of human activities


GPS. Global Positioning System. An electronic device that uses positioning signals from satellites in order to locate precisely latitutude and longitude. Now used nearly exclusively for locating ship sampling stations at sea, but also useful for locations near and on shore.


Grab. Benthic sampling device with two or more curved metal plates designed to converge when the sampler hits bottom and grab a specified volume of bottom sediment


Grazer. A predator that consumes organisms far smaller than itself (e.g., copepods graze on diatoms)


Greenhouse effect. Carbon dioxide traps solar-derived heat in the atmosphere near the earth.

Gregarious settling. Settlement of larvae that have been attracted to members of their own species


Gross primary productivity. The total primary production, not counting the loss in respiration


Guild. A group of species, possibly unrelated taxonomically, that exploit overlapping resources


Gyre. Major cyclonic surface current systems in the oceans


Halocline. Depth zone within which salinity changes maximally


Hardy-Weinberg law. Law that states that the frequencies of genotypes in a population at a locus are determined by random mating and allele frequency


Herbivore. An organism that consumes plants


Harmful algal bloom. A bloom of (usually) planktonic microalgae belonging to a strain of a species that has a toxic harmful to marine organisms or humans consuming marine organisms.


Heritable character. A morphological character whose given state can be explained partially in terms of the genotype of the individual


Hermaphrodite. An individual capable of producing both eggs and sperm during its lifetime


Hermatypic. Reef-building


Heterotrophic algae. Algae that take up organic molecules as a primary source of nutrition


Heterozygote. With respect to a given genetic locus, a diploid individual carrying two different alleles


Highly stratified estuary. An estuary having a distinct surface layer of fresh or very-low-salinity water, capping a deeper layer of higher salinity, more oceanic water


Histogram. A multiple-bar diagram representing the frequency distribution of a group as a function of some variable. The frequency of each class is proportional to the length of its associated bar


Holoplankton. Organisms spending all their life in the water column and not on or in the sea bed


Homeotherm. An organism that regulates its body temperature despite changes in the external environmental temperature


Homozygote. With respect to a given genetic locus, a diploid individual carrying two identical alleles


Hydrographic. Referring to the arrangement and movement of bodies of water, such as currents and water masses


Hydrothermal vents. Sites in the deep ocean floor where hot, sulfur-rich water is released from geothermally heated rock


Hypothesis. A refutable statement about one or a series of phenomena


Infaunal. Living within a soft sediment and being large enough to displace sedimentary grains


Interspecific competition. Condition in which one species' exploitation of a limiting resource negatively affects another species


Interstitial. Living in the pore spaces among sedimentary grains in a soft sediment


Isotonic. Having the same overall concentration of dissolved substances as a given reference solution


Keystone species. A predator at the top of a food web, or discrete subweb, capable of consuming organisms of more than one trophic level beneath it