Biodiversity & Conservation

MarLIN Glossary

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I

Importance
In the context of marine natural heritage: species or biotopes which are rare or very restricted in their distribution; species or biotopes that are in decline or have been; species or biotopes where a country has a high proportion of the regional or world population or extent; species that are keystone in a biotope by providing a habitat for other species; biotopes with a particularly high species richness; locations or biotopes that are particularly good or extensive representatives of their type. Species will also be 'important' if they are listed for protection on statutes, directives and conventions.

Imposex
An abnormality of the reproductive system in female gastropod molluscs, by which male characteristics are superimposed onto female individuals (Smith, 1980), resulting in sterility or, in extreme cases, death. This may be caused by hormonal change in response to pollution from organotin antifoulants, even at low concentrations. See 'organotin'.

Indicator Organism
An organism whose characteristics (e.g. presence or absence, population density, dispersion, reproductive success) are used as an index of attributes too difficult, inconvenient, or expensive to measure for other species, or environmental conditions of interest (Landres et al., 1988). Such characteristics may be used to indicate the degree of pollution or other environmental conditions at a particular locality. See Rowell (1994) and GESAMP (1995) for a discussion.

Infauna
Benthic animals which live within the seabed.

Infralittoral
A subzone of the sublittoral in which upward-facing rocks are dominated by erect algae, typically kelps; it can be further subdivided into the upper and lower infralittoral (based on Hiscock, 1985). The term is also used by Glémarec (1973) to refer to areas (étages) with a eurythermal environment of great seasonal and also daily and tidal amplitude. 1) lower The part of the infralittoral subzone which, on hard substrata, supports scattered kelp plants (a kelp park) or from which kelps are absent altogether and the seabed is dominated by foliose red and brown algae. It may be difficult to distinguish the lower infralittoral where grazing pressure prevents the establishment of foliose algae. 2) upper The part of the infralittoral subzone which, on hard substrata, is dominated by Laminariales forming a dense canopy, or kelp forest (based on Hiscock, 1985).

Inlet
See 'marine inlet'.

Inquilinism
A symbiotic association in which one symbiont lives in close association with another, generally in the tube or burrow or actually within a body chamber of the host (Brusca, 1980).

Intercalary
Located between the apex and base or between two other reference points such as nodes (OED, 2008).

Interface Feeder
An organism that feeds at the interface between the water column and underlying substratum.

International Importance
1) in biotopes or areas (conservation assessment) -biotopes or areas which are highly rated in a coastal sector (q.v.) are considered of international importance if they are one of the best examples or only examples present in the north-east Atlantic (North Cape, Norway to Gibraltar). This was, until 1995, defined for communities as being: "Communities which are outstandingly good examples of their type in the north-east Atlantic. Communities recorded at only a very few locations in the north-east Atlantic" (Hiscock & Mitchell 1989). Cf. 'international importance: species', 'local importance', 'national importance', 'regional importance' (biotopes or areas and species).
2) In species (conservation assessment) -species which are recorded at only a very few locations in the north-eastern Atlantic. Species recorded in higher abundance in the area under consideration than anywhere else in the north-eastern Atlantic, or where the area is one of only a few locations where large quantities are recorded (Davies et al., 1990, based on Hiscock & Mitchell, 1989). Cf. 'international importance: biotopes or areas', 'local importance', 'national importance', 'regional importance' (biotopes or areas and species).

Internode
The part of a stem between the nodes where leaves or buds are attached to the stem (OED, 2008).

Interstitial
Relating to the system of cavities and channels formed by the spaces between grains in a sediment (interstitial space).

Intertidal
The zone between the highest and lowest tides (from Lincoln et al., 1998).

Intolerance
is the susceptibility of a habitat, community or species (i.e. the components of a biotope) to damage, or death, from an external factor. Intolerance must be assessed relative to change in a specific factor.

Introduced Species
Any species which has been introduced directly or indirectly by human agency (deliberate or otherwise), to an area where it has not occurred in historical times and which is separate from and lies outside the area where natural range extension could be expected (i.e. outside its natural geographical range (q.v.)). The term includes non-established introductions ('aliens' (q.v.)) and established non-natives (q.v.), but excludes hybrid taxa derived from introductions ('derivatives').

Iridescence
Showing luminous colours which may seem to change with the viewing angle (OED, 2005).

Irish Sea
The area of sea between Great Britain and Ireland north of a line across St George's Channel from St Anne's Head to Carnsore Point in the south, and south of a line across the North Channel from Mull of Kintyre to Fair Head in the north, including all estuaries except the Firth of Clyde (Irish Sea Study Group definition, based on Shaw (1990)).

Irreplaceability
In conservation assessment - not capable of replacement if destroyed in some way. Applied to habitat features, biotopes and species.

Isobath
A line on a map connecting points of equal underwater depth; a submarine contour.

Isogamous
Having gametes of similar size, shape and behaviour (Lincoln et al., 1998).

Isohaline
A line on a map connecting places of equal salinity.

Isopod
A general term for crustaceans of the Order Isopoda.

Isopoda
The Order Isopoda (Phylum Arthropoda) are characterized by a simple flattened elongated oval body, with a distinct head, thorax and abdomen, and simple, basically identical, legs (hence 'iso' and 'pod') (adapted from Hayward et al., 1996). This group include the sea slates, gribble and woodlice.

Isopods
Plural of 'isopod'.

Isotherm
A line on a map connecting places of equal temperature.

Iteroparous
Breeding several times per lifetime (cf. semelparous) (Barnes et al., 1993).

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