information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

MarLIN Glossary

lagoon (saline)

A shallow body of coastal salt water (from brackish to hypersaline) partially separated from an adjacent sea by a barrier of sand or other sediment, or less frequently, by rocks (based on Ardizzone et al., 1988). Three features serve to identify a coastal lagoon: 1) the presence of an isolating barrier beach, spit or island; 2) the retention of all or most of the water mass within the system during periods of low tide in the adjacent sea; 3) the persistence of natural water exchange between the lagoon and the parent sea - by percolation through and/or overtopping of the barrier, through inlet/outflow channels, etc. - permitting the lagoonal water to remain saline or brackish. As defined for the EC Habitats Directive, lagoons are "Expanses of shallow coastal salt water, of varying salinity and water volume, separated from the sea by sand banks or shingle, or, less frequently, by rocks. Salinity may vary from brackish water to hypersalinity depending on rainfall, evaporation and the addition of seawater from storms or from temporary flooding by the sea in winter" (European Commission 1995). Five lagoon types have been identified in Great Britain for the identification of Sites of Special Scientific Interest (Joint Nature Conservation Committee 1996). (i) Isolated saline lagoon. These are pools which are completely isolated from the sea by a barrier of rock or sediment. No seawater enters the pool by percolation, the only input of salt water occurs by limited groundwater seepage (such as in some dune pools), by overtopping of the barrier (sill) on extreme high water spring tides, or by salt water inundation during storm events. (ii) Percolation saline lagoon. These pools are separated from the sea by a permeable barrier of shingle or pebbles and small boulders. Sea water exchange occurs through the barrier to varying degrees dependent on the permeability of the barrier. (iii) Sluiced saline lagoons. These are lagoons where the ingress and egress of water from the lagoon to the open sea is modified by human mechanical interference. (iv) Silled saline lagoons. These are in many respects similar to some examples of sluiced lagoons. They are generally rocky basins which have a sill between mean high water of spring tides and mean low water of spring tides. (v) Saline lagoon inlets. These are saline lagoons where there is a permanent connection with the sea. Cf. 'pond (coastal)'.


A thin layer, plate, scale or film, especially of bone or tissue (OED, 1990).


Plural of 'lamella'.


Arranged in lamellae; lamellar (see lamella) (OED, 1990)


Lance shaped and usually elongate (Brusca, 1980).

large shallow inlet

See 'marine inlet'.


A juvenile phase differing markedly in morphology and ecology from the adult (Barnes et al.1993).


Plural of 'larva'.

lateral keel

A lateral ridge either side of the base of a fin. It is used for stability in some shark species (Lincoln et al., 1998)

lateral keels

Plural of 'lateral keel'.

lateral teeth

Of bivalve mollusc shells, projections about the shell hinge, in front of and behind the cardinal teeth and normally some distance from the beaks (Tebble, 1976).


An angular distance measured in degrees north (or south) of the equator (latitude 0°).


Development at the expense of internal resources (i.e. yolk) provided by the female (cf. planktotrophic) (Barnes et al.,1993).

life form

Structural types of organisms or growth forms that dominate or are most conspicuous in certain environmental conditions. (based on Richards et al., 1995) (cf. growth form).


Pertaining to freshwater <0.5 ‰ salinity (based on Carriker, 1967, in McLusky, 1993).


The area of the shore that is occupied by marine organisms which are adapted to or need alternating exposure to air and wetting by submersion, splash or spray. On rocky shores, the upper limit is marked by the top of the Littorina /Verrucaria belt and the lower limit by the top of the laminarian zone (Lewis, 1964). It is divided into separate subzones, particularly marked on hard substrata. Cf. 'intertidal'.

littoral fringe

The upper subzone of the littoral zone, bordering the supralittoral. It is characterized by marine lichens, littoral molluscs and algae tolerant of exposure to air for long periods; its lower boundary is characteristically the upper limit of dense barnacles. This subzone can be further subdivided into the upper and lower littoral fringes (from Hiscock, 1990) .

littoral width

The distance from High Water Spring Tides to Low Water Spring Tides, measured at right angles to the general direction of coastline.

local importance

In conservation assessment - biotopes or locations which are among the best examples or the only examples within a particular physiographic feature or area of coast but occur widely elsewhere in the coastal sector (q.v.). This was, until 1995, defined as being: "communities or areas which are widespread in similar situations but for which the one mentioned is a good example in the coastal sector under consideration". (Based on Hiscock & Mitchell, 1989.) Cf. 'international importance: species', 'national importance', 'regional importance' (biotopes or areas and species).


(Scottish) A lake. In its widest sense, it is an open, enclosed or partially enclosed body of water. (Based on Earll & Pagett, 1984.) See also 'sea loch'.


Distance in degrees east or west of the prime meridian at 0°, which runs through Greenwich, south-east England.

longshore drift

1) A current which acts parallel to the coastline, generated by an oblique wave approach or by differences in wave height along the beach, and responsible for the movement of large quantities of beach material along the shore (based on Hansom, 1988). 2) Movement of sand and shingle along the shore (Allaby & Allaby, 1990).


A circular or horse-shoe shaped fold of the body wall that encircles the mouth and bears numerous hollow ciliated tentacles (Ruppert & Barnes, 1996). A feeding organ characteristic of Bryozoa, Phoronida and Brachiopoda.


Plural of 'lophophore'.


In birds: the area between the eye and the upper part of the beak).


(Irish) see 'loch'.

lower shore

A physical term for the area of shore around low tide level, often applied where it is not possible to determine the biological subzone, for example on sediment shores (cf. 'sublittoral fringe').

Lowest Astronomical Tide

The lowest tidal level which can be predicted to occur under average meteorological conditions and any combination of astronomical conditions (from Ministry of Defence, 1987).

lunar tide

See 'astronomical tide'.


Crescent-shaped (OED, 2008).


A depressed area in front of the beaks in one or both valves, distinguished by a change in sculpture or colour (Tebble, 1976). When the entire shell is viewed from above the lunlue typically forms a heart-shaped depression (Stachowitsch, 1992).


Referring to a biogeographical region centred to the south of the British Isles and influencing the extreme south-west of the British Isles.