Glossary of Marine Biology



Copyright J. Levinton 1999

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Laminar flow. The movement of a fluid where movement of the entire fluid is regular and with parallel streamlines.


Larva. A discrete stage in many species, beginning with zygote formation and ending with metamorphosis


Larvacea. A group of planktonic tunicates that secrete a gelatinous house, used to strain unsuitable particles (large particles are rejected). An inner filter apparatus of the house, the so-called food trap or particle-collecting apparatus, is used to retain food particles.


LD50 The value of a given experimental variable required to cause 50% mortality.


Leaching. The loss of soluble material from decaying organisms


Lecithotrophic larva. A planktonic-dispersing larva that lives off yolk supplied via the egg


Leeward. The side of an island opposite from the one facing a persistent wind


Life table. A table summarizing statistics of a population, such as survival and reproduction, all broken down according to age classes


Litter. Accumulations of dead leaves in various states of fragmentation and decomposition


Locus. See Genetic locus


Logistic population growth. Population growth that is modulated by the population size relative to carrying capacity. Population growth declines as population approaches carrying capacity, and is negative when population size is greater than carrying capacity


Longshore current. A current moving parallel to a shoreline


Macrobenthos. (macrofauna or macroflora) Benthic organisms (animals or plants) whose shortest dimension is greater than or equal to 0.5 mm


Macrofauna. Animals whose shortest dimension is greater than or equal to 0.5 mm


Macrophyte. An individual alga large enough to be seen easily with the unaided eye


Macroplankton. Planktonic organisms that are 200-2,000 micrometers in size.


Mainstream flow. The flow in a part of the fluid (e.g., in a tidal creek) that is well above the bottom or well away from a surface and essentially not under the influence of the boundary layer (see boundary layer).


Mangel. See Mangrove forest.


Mangrove forest. A shoreline ecosystem dominated by mangrove trees, with associated mud flats.


Marine snow. Fragile organic aggregates, resulting from the collision of dissolved organic molecules or from the degradation of gelatinous substances such as larvacean houses. Usually enriched with microorganisms.


Marine protected area. A conservation geographic unit designed to protect crucial communities and to provide reproductive reserves for fisheries that hopefully will disperse over wider areas.


Maximum sustainable yield. In fisheries biology, the maximum catch obtainable per unit time under the appropriate fishing rate


Meiobenthos (meiofauna or meioflora). Benthic organisms (animals or plants) whose shortest dimension is less than 0.5 mm but greater than or equal to 0.1 mm


Meiofauna. Animals whose shortest dimension is less than 0.5 mm but greater than or equal to 0.1 mm


Megaplankton. Planktonic organisms that are greater than or equal to 2000 micrometers in size


Meroplankton. Organisms that spend part of their time in the plankton but also spend time in the benthos (e.g., planktonic larvae of benthic invertebrates)


Mesopelagic. The 150 -- 2000 m depth zone, seaward of the shelf-slope break


Metabolic rate. The overall rate of biochemical reactions in an organism. Often estimated by rate of oxygen consumption in aerobes


Metamorphosis. Major developmental change as the larva develops into an immature adult


Metapopulation. A group of interconnected subpopulations, usually of subequal size. The features of individuals now founnd in one subpopulation might have been determined by conditions affecting them when they were located in another subpopulation.


Microbenthos. (microfauna or microflora) Benthic organisms (animals or plants) whose shortest dimension is less than 0.1 mm


Microfauna. Animals whose shortest dimension is less than 0.1 mm


Mixing depth. The water depth to which wind energy evenly mixes the water column


Mixoplankton. Planktonic organisms that can be classified at several trophic levels. For example, some ciliates can be photosynthetic but also can ingest other plankton and are heterotrophic.


Moderately stratified estuary. An estuary in which seaward flow of surface low-salinity water and moderate vertical mixing result in a modest vertical salinity gradient


Monophyletic. Refers to a group of species that all have a single common ancestral species


Mucous-bag suspension feeder. Suspension feeder employing a sheet or bag of mucus to trap particles nonselectively


Mutualism. An interaction between two species in which both derive some benefit


Mutualistic. Conferring reciprocal benefit to individuals of two different associated species


Nanoplankton. Planktonic organisms that are 2-20 micometers in size.


Neap tides. Tides occurring when the vertical range is minimal


Nekton. Organisms with swimming abilities that permit them to move actively through the water column and to move against currents


Neritic. Seawater environments landward of the shelf-slope break


Net primary productivity. Total primary production, minus the amount consumed in respiration


Neuston. Planktonic organisms associated with the air-water interface.


Niche. A general term referring to the range of environmental space occupied by a species


Niche overlap. An overlap in resource requirements by two species


Nitrogen fixation. The conversion of gaseous nitrogen to nitrate by specialized bacteria.


No-take Reserves. Geographic areas where by law no one is allowed to fish or collect biological specimens. Rules could apply to one or all species.


Nuisance bloom. A rapid increase of one or only a few species of phytoplankton, resulting in densities high enough to cause discoloration of the surface water, possible increase of toxins, and degradation of water quality aspects such as dissolved oxygen


Nutrient cycling. The pattern of transfer of nutrients between the components of a food web


Nutrients. Those constituents required by organisms for maintenance and growth (we use this term in this book in application to plants)