MarLIN Glossary

Glossary items


Special Area of Conservation


See 'bullate'.


Member of the Order Sacoglossa: shelled and slug-like opisthobranchs with a radula bearing a single row of teeth adapted for suctorial feeding on algae (Ruppert & Barnes, 1996).


A measure of the concentration of dissolved salts in seawater. Salinity is defined as the ratio of the mass of dissolved material in sea water to the mass of sea water (UNESCO, 1985). But this 'absolute' definition is not practical. Salinity was measured by a chlorinity titration but with the development of the salinometer, which utilizes conductivity, a new definition was developed. The 'practical salinity' (S) of a sea water sample is defined as the ratio of the electrical conductivity of the sample (at 15 °C, and one standard atmospheric pressure) to that of a standard solution of potassium Chloride (KCl). A ratio of 1 is equivalent to a 'practical salinity' of 35 (UNESCO, 1985). Until recently, salinity was expressed as parts per thousand (ppt or ‰). Subsequently, adoption of the 'practical salinity' gave rise to the 'practical salinity unit' (psu). However 'salinity', defined as the ratio of two quantities of the same unit, is a 'dimensionless quality', i.e. takes no units. Therefore, it is correct to speak of a salinity of 35 (UNESCO, 1985). Baretta-Bekker et al. (1992) suggested that, in most cases, where a high degree of accuracy is not required, old and new figures for salinity can be used interchangeably. However for the sake of accuracy, when referring to salinity in our on-line reviews, the units used by the original authors are quoted in the text. Freshwater is regarded as < 0.5 ‰ (limnetic), seawater as > 30 ‰ (euhaline), and brackish water as intermediate, including oligohaline, mesohaline and polyhaline waters (based on McLusky, 1993).


Areas of alluvial or peat deposits, colonized by herbaceous and small shrubby terrestrial vascular plants, almost permanently wet and frequently inundated with saline waters (from Long & Mason, 1983).


The selection of a set of data, or the collection of a quantity of material, or of a set of individuals from a population with the purpose of measuring a given characteristic of that sample (based on Dooley & Kirkpatrick, 1993).


Particles defined in three size categories based on Wentworth (1922): very coarse sand and granules (1-4 mm); medium and coarse sand (0.25-1 mm); very fine and fine sand (0.062-0.25 mm) (from Hiscock, 1990).

sand bank

Sand which rises from a level seabed towards the surface, often levelling-off in shallower depths. As defined for the EC Habitats Directive, 'sandbanks which are slightly covered by seawater all the time' are: "Sublittoral sandbanks, permanently submerged. Water depth is seldom more than 20 m below Chart Datum". They can be non-vegetated or vegetated and can include free-living species of the Corallinacea family. (European Commission 1995.)

sand flat

An expanse of sand of sandy sediment in the intertidal zone. For definition under the EC Habitats Directive, see 'mudflat'.


In west Wales - a boulder or cobble reef derived from glacial moraine, lying at shallow depth (maximum depth approximately 10 m below chart datum), completely covered at low tide, and roughly linear in shape (lit.: causeway) (based on Mills, 1991).


Botany - a modified leaf at the base of a flower stalk (OED, 2008).


A low bank in the intertidal or shallow subtidal; a mussel-bed.


A reef, especially one bordered by sediment.


Scottish form of 'scalp'


Scottish form of 'scar'.


Any organism that feeds on dead organic material.


Thriving in shaded situations, or in habitats of low light intensity (from Lincoln et al., 1998) (cf. 'cryptic', 'photophilous').


The effect of abrasion, usually by sand or gravel, on the seabed.


Hard, ridged plate usually located on either side of the body of some fish species immediately forward of the tail fin (Baretta-Bekker et al., 1992).


Hard, ridged structures usually located on either side of the body of some fish species immediately forward of the tail fin (Baretta-Bekker et al., 1992).


Strategic Environmental Assessment

sea anemone

A type of cnidarian (Order Actiniaria, Phylum Cnidaria) with a large solitary polyp, consisting of a base, a column, and a ring of tentacles around a central mouth. So called due to their resemblance to flowers.

sea anemones

Plural of 'sea anemone'.

sea cucumber

A common name for members of the Class Holothuroidea (Phylum Echinodermata), which refers to a group of 'cucumber' shaped marine organisms closely related to starfish and sea urchins.

sea loch

In Scotland - a marine inlet (q.v.) which has fjordic or fjardic features, entered by the tide (on each cycle), and with a salinity generally greater than 30 ‰. Brackish conditions may be periodically established, particularly in the surface layers (based on Earll & Pagett, 1984). As defined for the EC Habitats Directive, 'open sea lochs' are "simple glacial features which are longer than they are wide, have no entrance sill and in which the seabed slopes gradually towards the head". See also 'fjard', 'fjord'.

sea lough

Irish form of 'sea loch'.

sea spider

The common name for members of the Class Pycnogonida (Phylum Chelicerata).

sea spiders

Plural of 'sea spider'.

sea urchin

Common name for members of the Class Echinoidea (Phylum Echinodermata), characterized by a rigid test or shell, usually spherical or ovoid but occasionally flattened, and covered by mobile spines of varying length. Cf. urchin.


The sea floor.


A flowering plant (Phylum Angiospermophyta) that is adapted to living fully submerged and rooted in estuarine and marine environments. Although not true grasses, all seagrasses are monocotyledons. The group is defined by their ecology rather than their phylogeny. In British waters, seagrasses are represented by the genus Zostera (eelgrass). Several members of the genus Ruppia (tasselweeds) also occur in marine and estuarine environments. Ruppia may be considered a seagrass, although this is not accepted universally (Green & Short, 2003).


Plural (or collective noun) of 'sea grass'.


Showing periodicity related to the seasons (Lincoln et al., 1998).


Attached to a substratum but capable of movement across (or through) it (cf. 'sessile').


Particulate solid material accumulated by natural processes (from Baretta-Bekkeret al., 1992).


The scientific study of sediments.


1) A semi-independent, serially repeated unit of the body (Barnes et al., 1993). 2) In Arthropods - one of a series of units of an appendage. Also segments of the body (also referred to as somites) (based on Stachowitsch, 1992).


Breeding only once then dying (cf. iteroparous) (Barnes et al., 1993).


Measurement based on estimates or rough counts of relative quantity (density, cover) - e.g. abundance scales (cf. 'quantitative').


(conservation assessment) An assessment of the intolerance of a species or habitat to damage from an external factor and the time taken for its subsequent recovery. For example, a very sensitive species or habitat is one that is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, 'high' intolerance) and is expected to recover over a very long period of time, i.e. >10 or up to 25 years ('low'; recoverability). Intolerance and hence sensitivity must be assessed relative to change in a specific factor.


Permanently attached to a substratum (cf. 'sedentary').


The total suspended particulate matter in the water column (Lincoln et al., 1998), including plankton, nekton and both organic and inorganic suspended particulates.


Of wave exposure - coasts with a restricted fetch and/or open water window. Coasts can face prevailing winds but with a short fetch (< 20 km) or extensive shallow area offshore, or may face away from prevailing winds (Hiscock, 1990).


Beach pebbles (q.v.), normally well-rounded as a result of abrasion. In relation to coastal vegetated shingle structures, 'shingle' is considered as any sediment which has a grain size of between 2 and 200 mm (Sneddon & Randall, 1993).


A large number of fish swimming closely together (OED, 2005).


The action of forming 'shoals'.


Plural of 'shoal'.


The land along the edge of a body of water.

shore backing

The terrestrial habitat immediately behind the shore.

shore platform

A surface eroded by wave action, forming a flat rock platform in the intertidal zone (based on Ritchie, Smith & Rose 1978.) The more correct term for 'wave-cut platform' or 'abrasion platform'.


Lowest point on a submarine ridge or saddle at a relatively shallow depth, separating a basin from an adjacent sea or another basin (from Baretta-Bekker, Duursma & Kuipers, 1992). In sea lochs, sills are structures commonly formed by glaciation, found at the mouth or elsewhere along the length of the loch. Such a threshold can limit water exchange.


Fine-grained sediment particles ranging in size from 0.004 mm to 0.0625 mm (based on Wentworth, 1922).


Any extension of the mantle margin associated with incurrent or excurrent respiratory streams (Graham, 1988). In gastropods the inhalent siphon is often supported by an extension of the shell, the siphonal canal.


A flagellated groove extending from the mouth to gastrovascular cavity  providing an incurrent of water into the gastrovascular cavity of anemones and corals (adapted from Stachowitsch, 1992).


Small inhalent polyps in polymorphic octocoral colonies that drive water into the colony. The polyp has reduced tentacles or is tentacle-less and possesses a well-developed siphonoglyph (see above) (adapted from Stachowitsch, 1992).

Site of Special Scientific Interest

An area of land or water notified by the Nature Conservancy Council or its successor agencies under the Wildlife and Countryside Act 1981 as being of special nature (can include geological) conservation importance.


Low-lying rocky island or reef, often without terrestrial vegetation, and frequently swept by the sea (based on Scott & Palmer 1987).

slack water

Period in a tidal cycle usually between flood- and ebb-tide, when the strength of tidal streams is near zero.


A rock particle which is flattened and thin and corresponds to the diameter of a cobble (64-256 mm) (based on Hiscock, 1990). Also describes the type of rock which constitutes such loose-lying substrata.

soft coral

The common name for the Order Alcyonacea (Phylum Cnidaria), a group of solid fleshy bodied corals in which the thick body tissue (coenenchyme) is strengthened with calcareous spicules (adapted from Hayward et al., 1996).

soft corals

Plural of 'soft coral'.


Living alone, not gregarious.


Any deep (> 5 m depth) tidal channel between two bodies of open coastal water. Strictly, a sound is a wide expanse of water (from Earll & Pagett, 1984).


Special Protection Area

Special Area of Conservation

A site of [European] Community importance designated by the [EU] Member States through a statutory, administrative and/or contractual act where the necessary conservation measures are applied for the maintenance or restoration, at a favourable conservation status, of the natural habitats and/or the populations of the species for which the site is designated (Commission of the European Communities 1992). (This status is achieved by sites adopted by the European Commission).

Special Protection Area

A site of European Community importance designated under the Wild Birds Directive (Commission of the European Communities Council Directive 79/409/EEC of 2 April 1979 on the Conservation of Wild Birds).

species richness

The number of species in a given sample, assemblage, community, biotope, or habitat. (Lincoln et al., 1998).


A packet of sperm, produced by some species of animals (Abercrombie et al., 1973). In decapod crustaceans, the packet of sperm is formed in the vas deferens of the male, and is transferred to the female with the aid of modified first pair of pleopods (adapted from Stachowitsch, 1992).


Variously shaped or sized calcareous or siliaceous skeletal elements used in the endoskeleton of sponges and echinoderms (Stachowitsch, 1992). May be highly variable in shape, especially in holothurian echinoderms forming anchors, anchor plates, baskets, buttons and wheels. May also be termed 'deposits' in echinoderms.


Plural of 'spicule'.


Oval or round external openings of the respiratory system used in breathing (Barnes et al., 1993).


In geomorphology - a low, elongated accumulation of sediment such as sand or shingle, projecting from the shore into a water body (based on Allaby & Allaby, 1990) (cf. 'bar', 'tombolo').


An informal term for the upper supralittoral fringe, the lower terrestrial zone.


A small reproductive cell of non-flowering plants (OED, 2008).


Additional structures, produced by some kelps, above the holdfasts and below the blade, which resemble small thicker blades or may be flattened outgrowths from the stripe.


The diploid, spore producing, asexual generation in the life cycle of some plants; typically formed by the fusion of haploid gametes. (Lincoln et al., 1998).


Plural of 'sporophyte'.

spring tide

The astronomical tide of maximum range, occurring at or just after new moon and full moon. The most marked spring tides (equinoctial springs) occur at the spring and autumn equinoxes.


Site of Special Scientific Interest


The ability of an ecosystem to resist change (from Makins, 1991) (cf. 'constancy', '


Arranged like a star.


Tolerance of only a narrow range of salinities (from Lincoln & Boxshall, 1987).


Utilizing, or tolerant of, only a limited variety of food or food species (Lincoln et al., 1998).


Tolerance of a narrow range of temperatures.


Of a random variable - having a probability of distribution, usually with finite variance.


Any deep (> 5 m) tidal channel between two bodies of open coastal water. Strictly, a strait is the stretch of water between an island and its mainland (or adjacent islands) (from Earll & Pagett, 1984.)


A line on the shore comprising debris deposited by a receding tide; commonly used to denote the line of debris at the level of Extreme High Water (from Lincoln & Boxshall 1987).


Ribbon-like, in the form of a strap or ribbon.


Plural of 'stratum'

Strategic Environmental Assessment

The formalised, systematic and comprehensive process of evaluating the environmental impacts of a policy, plan or programme and its alternatives, including the preparation of a report on the evaluation and the use of the findings in publicly-accountable decision-making (Pritchard 1993) (cf. 'Environmental Assessment').


In ecology - a horizontal layer of vegetation within a stratified plant community (from Lincoln & Boxshall, 1987).


"A chemical or physical process that leads to a response within an organism, or at the levels of whole organisms or assemblages" (from Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection - GESAMP, 1995).

strobilation, strobilate

Reproduction by successive budding (Lincoln et al., 1998).


In north-west Scotland - tidal rapids (lit.: outpouring).


Appendage where the terminal segment (dactyl) folds against the blunt end of the subterminal segment (propodus), which lacks the immovable finger of a chela (see above) (Ruppert & Barnes, 1996). [View image]


The zone exposed to air only at its upper limit by the lowest spring tides, although almost continuous wave action on extremely exposed coasts may extend the upper limit high into the intertidal region. The sublittoral extends from the upper limit of the large kelps and includes, for practical purposes in nearshore areas, all depths below the littoral. Various subzones are recognised (based on Hiscock, 1985.) (Cf. 'subtidal').

sublittoral fringe

The upper part of the sublittoral zone which is uncovered by the tide. On hard substrata, the zone is characterized by the kelps Laminaria digitata and Alaria esculenta. The lower limit of this zone is marked by the upper limit of the truly sublittoral kelp Laminaria hyperborea. This species assemblage does not occur on all British coasts (based on Lewis, 1964).

suborbital stay

Bony extension (below the skin) from below the eye to the preopercle (Abercrombie et al., 1973).


Plural of 'substratum'.


Material available for colonization by plants and animals; a more correct term in this context than 'substrate'.


A physical term for the seabed below the mark of Lowest Astronomical Tide (cf. 'sublittoral').


Sequential development of plant or animal communities through time.


The lower terrestrial zone, characteristically dominated by orange and white-to-grey lichens on hard substrata with scattered salt-tolerant higher plants and mosses (from Hiscock, 1990).

surge gully

A narrow marine inlet on a small scale, usually formed by erosion of a rocky shoreline on exposed coasts. Their aspect, facing into waves, and their funnel effect, means that waves entering them become higher and of shorter wavelength, causing back-and-forth or multi-directional water movements of considerable force.

surrogate species

Species which are likely to change if the whole community is changing and therefore respond to change on behalf of the community.


A procedure by which a series of surveys is conducted in a sufficiently rigorous manner for changes in the attributes of a site (or species) to be detected over a period of time. Surveillance is often conducted to identify normal background variation ('noise') in order that abnormal changes can be identified by a monitoring programme. (From Marine Conservation Monitoring Workshop, January 1993.) The term is also applied to compliance surveillance to ensure that agreed or required measures are followed. (See also 'survey'. Cf. 'monitoring').


An inventory of the attributes of a site, area or region in terms of habitat and associated organisms (or of the distribution and/or autecological characteristics of selected species), usually by means of a standardised procedure (based on Marine Conservation Monitoring Workshop, January, 1993).

suspension feeders

Suspensivores, filter-feeders, any organisms which feed on particulate organic matter, including plankton, suspended in the water column (from Lincoln et al., 1998).


Maintaining the environment's natural qualities and characteristics and its capacity to fulfil its full range of functions, including maintenance of biodiversity (from English Nature, Planning for environmental sustainability, June 1994).

sustainable development

"Development that meets the needs of the present without compromising the ability of future generations to meet their own needs" (World Commission on Environment and Development, 1987 (the 'Brundtland' Report)).


Sea waves that have left the area where they were generated by the wind, or that have remained after the generating wind has disappeared (from Baretta-Bekker, Duursma & Kuipers 1992.)

swim bladder

An internal organ which helps fish maintain buoyancy (Holmes, 1979).


The living together in a constant and definite relationship of two different organisms (cf. commensalism, mutualism, parasite) (Brusca, 1980).


The study of the ecology of groupings of organisms, populations, communities or systems; ecological sociology (based on Lincoln et al., 1998) (cf. 'autecology').