Glossary of Marine Biology

 

L M N

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)