Biodiversity & Conservation

MarLIN Glossary

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M

Macrobenthos
The larger organisms of the benthos, exceeding 1 mm in length (from Lincoln & Boxshall, 1987); often applied to organisms >0.5mm. Cf. 'meiobenthos', 'microbenthos'.

Macrofauna
Animals exceeding 1 mm in length (Lincoln & Boxshall, 1987) or retained on a 1 mm or 0.5mm sieve; often applied to organisms >0.5mm. Cf. 'meiofauna', 'microfauna'.

Macroscopic
Large enough to be visible to the naked eye, typically exceeding 1mm in length.

Maerl
Twig-like unattached (free-living) calcareous red algae, often a mixture of species and including species which form a spiky cover on loose small stones - 'hedgehog stones'.

Mantle
1) In invertebrates: a dense fold of skin which secretes the shell and encloses the major organs (OED, 2005). 2) In vertebrates: referring to the dorsal surface of the shoulders.

Manubria
Plural of 'manubrium'.

Manubrium
1) Tube-like extension, bearing the mouth, that hangs down from the centre of the subumbrella of cnidarian medusae. 2) Hypostome of hydroid polyps (from Ruppert & Barnes, 1994).

Mariculture
The cultivation, under appropriate environmental conditions, of marine organisms in seawater by human effort for commercial purposes (based on Baretta-Bekker et al., 1992 and Charton & Tietjen, 1989). (See also 'aquaculture') .

Marine
Pertaining to the sea.

Marine Inlet
1) As used by the MNCR, this term covers all forms of inlet, including estuaries, enclosed bays and the sounds, straits and narrows between land masses. 2) As defined for the Habitats Directive, 'large shallow inlets and bays' are: "Large indentations of the coast where, in contrast to estuaries, the influence of freshwater is generally limited. These shallow indentations are generally sheltered from wave action and contain a great diversity of sediments and substrates with a well developed zonation of benthic communities" (European Commission 1995). 'Shallow' may be defined by the depth limit of the photic zone in open coastal waters adjoining the inlet or bay. In the UK this is interpreted for the Habitats Directive as a depth of 30 m below chart datum or shallower across at least 75% of the site."

Marine Nature Reserve
A statutory marine protected area declared in Great Britain by the Nature Conservancy Council and its successor agencies under the Wildlife and Countryside Act 1981 for the purpose of conserving marine flora or fauna or geological or physiographical features in the area and providing opportunities for study and research (from Anon., 1994). Voluntary MNRs are non-statutory protected areas agreed by local sea-users and other interested parties.

Marine Protected Area
"Any area of intertidal or subtidal terrain, including geological and geomorphological features, together with its overlying water and associated flora, fauna, historical and cultural features, which has been reserved by law or other effective means to protect part or all of the enclosed environment." (IUCN definition, as modified by the Marine Protected Area Group, a working group of Wildlife Link's Joint Marine Group).

Maritime
1) Of or related to navigation, shipping. 2) Situated, living or found close to, and having a special affinity with, the sea (based on Makins, 1991). Cf. 'marine'.

Massive
Bulky (Homes, 1979).

Mat
The dense mass that blankets the substratum.

Mean High Water Springs
The average of the heights of two successive high waters during those periods of 24 hours when the range of the tide is greatest (from Ministry of Defence, 1987).

Mean Low Water Springs
The average of the heights of two successive low waters during those periods of 24 hours when the range of the tide is greatest (from Ministry of Defence, 1987).

Medially
Towards the middle or centre (OED, 2005).

Mediterranean
An extension of the Atlantic Ocean between Europe and Africa (Charton & Tietjen, 1989) often used to describe a biogeographic region but which, according to Ekman (1953), is not a distinct faunal unit but enters into a greater one which includes the neighbouring parts of the Atlantic.

Medusiform
Disk, bell or umbrella shaped and often gelatinous (Barnes et al., 1993).

Medusoid
Disk, bell or umbrella shaped and often gelatinous (Barnes et al., 1993).

Megalopa
Post-larval stage of crabs that has a large or flexed abdomen and full complement of appendages (Ruppert & Barnes, 1994).

Megalopae
Plural of 'megalopa'.

Megalops
See 'megalopa'.

Meiobenthos
Small benthic organisms which pass through a 1 mm mesh sieve, but are retained by a 0.1mm mesh (from Lincoln & Boxshall, 1987). Typically, they inhabit interstitial space in sediments. Cf. 'macrobenthos', 'microbenthos'.

Meiofauna
Small interstitial animals which pass through a 1 mm mesh sieve but are retained by a 0.1mm mesh (from Lincoln & Boxshall, 1987). Cf. 'macrofauna', 'microfauna'.

Meroplankton
Temporary plankton consisting of pelagic stages of organisms which also have benthic stages. Mainly the larvae of sedentary organisms. (From Baretta-Bekker et al.,  1992). Cf. holoplankton.

Mesohaline
Pertaining to brackish water between 5 ‰ and 18 ‰ salinity (from McLusky, 1993).

Metagamic
Pertaining to reproductive cycles that alternate between sexual and asexual phases (Lincoln et al., 1998).

MHWS
Mean High Water Springs

Microbenthos
Microscopic benthic organisms less than 0.1 mm in length (Lincoln & Boxshall, 1987). Cf. 'macrobenthos', 'meiobenthos'.

Microfauna
Small animals less than 0.1 mm length, not visible to the naked eye (cf. 'macrofauna', 'meiofauna').

Microhabitat
A small part of the habitat which has distinct physical conditions, e.g. rock crevice.

Microscopic
Any organism which cannot be observed without the use of a microscope.

Mid-littoral
General physical terms for the area of the shore midway between the high water and low water marks.

Mid-shore
See 'mid-littoral'.

Middle Shore
See 'mid-littoral'.

Migration
Movement from one region or habitat according to the seasons (OED, 2005).

Migrations
Plural of 'migration'.

Migratory
Of organisms that move from one habitat or location to another; typically periodically or seasonally and of relatively long distance (from Lincoln et al., 1998) .

MLWS
Mean Low Water Springs

MNR
Marine Nature Reserve.

Mobile
Capable of spontaneous movement, able to move freely.

Moderately Exposed
Of wave exposure - generally coasts facing away from prevailing winds and without a long fetch, but where strong winds can be frequent (from Hiscock, 1990).

Modifier
A physical or biological feature or occurrence affecting a site which changes the characteristics of a habitat, e.g. sand-scour, wave surge, substratum mobility, freshwater run-off, grazing, or pollution.

Monitoring
The process of repetitive observation, for defined purposes, of one or more elements of the environment, according to prearranged schedules in space and time and using comparable methods for environmental sensing and data collection. Monitoring provides factual information concerning the present state and past trends in environmental behaviour (Based on UNEP definition). The term is also applied to compliance monitoring against accepted standards to ensure that agreed or required measures are followed. (Cf. 'surveillance').

Mucronate
Terminating in a point.

Mud
1) Fine particles of silt and/or clay, < 0.0625 mm diameter (from Hiscock, 1990, after Wentworth, 1922). 2) Sediment consisting of inorganic and/or organic debris with particles in this category.

Mudflat
An expanse of mud or muddy sediment in the intertidal zone. The 1991 CORINE biotopes manual (Commission of the European Communities, 1991) defines 'Mud flats and sand flats' as "Sands and muds, submerged for part of the tide, devoid of vascular plants, but usually coated by blue algae and diatoms." The EC Habitats Directive 'mudflats and sandflats not covered by seawater at low tide' uses the same definition (European Commission 1995).

Mutualism
A symbiosis in which both organisms benefit, frequently a relationship of complete dependence. (Lincoln et al., 1998) (cf. symbiosis, commensalism, parasite).

Mysid
A member of the Order Mysida (Phylum Arthropoda, Subphylum Crustacea). Cf opossum shrimp.

Mysida
The Order Mysida (Phylum Arthropoda, Subphylum Crustacea) are slender, shrimp-like crustaceans with translucent bodies, feathery appendages, a broad tail fan and obvious eyes (adapted from Hayward et al., 1996).

Mysids
Plural of 'mysid'.

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Glossary references