Biodiversity & Conservation

MarLIN Glossary

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D

Dactylus
The moveable finger of decapod crustacean claws.

Decomposers
Organisms which feed by breaking down dead organic matter (from Lincoln et al.1998).

Delta
An accumulation of alluvial sediment, deposited where a current enters an open body of water.

Demersal
Living at or near the bottom of a sea or lake, but having the capacity for active swimming (from Lincoln et al., 1998).

Dendroid
Branching irregularly - similar to that of a root system (Prescott, 1969).

Dependency
In conservation assessment - the reliance (of a species, community or ecological process) on a particular location (for instance, a feeding, breeding, sheltering area or a migration corridor) or structure (for instance, a kelp forest, a sea grass bed, a maerl bed) for survival.

Deposit Feeders
Any organisms which feed on fragmented particulate organic matter in or on the substratum; detritivores (from Lincoln et al., 1998).

Desiccation
Removal of water; the process of drying (Lincoln et al., 1998).

Detritus
Fragmented particulate organic matter, derived from the decomposition of plant and animal remains.

Diel
Daily, pertaining to a 24 hour period (Lincoln et al., 1998).

Digitate
Having parts arranged like fingers on a hand (Holmes, 1979).

Dimorphic
Occurring in two distinct forms (usually morphological forms) (Barnes et al., 1993).

Direct Development
Development without a larval stage (cf. indirect development) (Barnes et al., 1993).

Disturbance
"A chemical or physical process caused by humans that may or may not lead to a response in a biological system within an organism or at the level of whole organisms or assemblages. Disturbance includes stresses". (from Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection - GESAMP, 1995).

Diversity
The state or quality of being different or varied (from Makins , 1991). 1) In relation to species, the degree to which the total number of individual organisms in a given ecosystem, area, community or trophic level is divided evenly over different species, i.e. measure of heterogeneity. Species diversity can be expressed by diversity indices, most of which take account of both the number of species and number of individuals per species (Based on Baretta-Bekker et al., 1992). Cf. 'evenness'; 'richness'. 2) In conservation assessment - an assessment of the richness of different types in a location (which can be large or small) including the number of different biotopes and numbers of species. The number of species present in an example of a particular biotope.

Dorsal
Relating to the upper side or back of an animal or plant (Abercrombie et al., 1973).

Dorsoventrally
Refering to the axis between the dorsal (back) and ventral (front) of an animal (OED, 2008).

Double Tide
Tides where a double peak occurs at high water or low water, usually due to complex patterns of water movement (Hawkins & Jones, 1992).

Dredge
1) The action of removing material from the seabed. 2) Bottom sampling equipment towed along the seabed for collecting benthic sediment and organisms. Dredges are also used for the commercial collection of benthic organisms, e.g. scallops, or of sediment and may be a suction or hydraulic device. Cf. 'grab'; 'trawl'.

Dune
1) Terrestrial dunes are mounds or ridges of unconsolidated windblown granular material, either bare or vegetated. 2) Subtidal and intertidal dunes are large sand or gravel ripples (mega-ripples), transported by traction in a strong current (based on Baretta-Bekker, Duursma & Kuipers 1992). The MNCR habitat classification defines these as >10 cm in height.

Dune Slack
An inter-dune hollow with a high water table (from Ritchie, Smith & Rose, 1978).

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Glossary references