Abstract
Molluscan diversity associated with sublittoral soft-bottoms was studied in Heraklion Bay as part of a long-term multidisciplinary research programme in the coastal environment of northern Crete (eastern Mediterranean). Quantitative benthic samples were collected in a pilot survey from a grid of 28 stations, followed by a seasonal sampling carried out over a seven- station transect located from 10 to 40 m depth. Univariate and multivariate analyses indicated the presence of a clear zonation along the depth gradient for the molluscan fauna and three main associations were identified in bathymetric zones parallel to the coastline. The structure of the local molluscan communities revealed the existence of an extended transition zone (ecotone) between a shallow sandy association and a deeper muddy one and a functional pattern, based on the feeding guilds, was evident along the environmental gradient. Application of graphical techniques, by using molluscan taxocoenosis, indicated a rather naturally disturbed habitat. Beta-diversity measures indicated different seasonal community adaptations to the prevailing environmental conditions. Results derived from this study revealed that beta-diversity may be a good descriptor for the assessment of the strength and breadth of sublittoral transition zones along environmental gradients.
Highlights
The European Water Framework Directive (WFD; Directive 2000/60/EC) gives emphasis to the assessment of the Ecological Quality Status (EcoQ) of coastal and transitional waters, as these highly dynamic systems are usually exposed to anthropogenic forcing
SUMMARY: Molluscan diversity associated with sublittoral soft-bottoms was studied in Heraklion Bay as part of a longterm multidisciplinary research programme in the coastal environment of northern Crete
The structure of the local molluscan communities revealed the existence of an extended transition zone between a shallow sandy association and a deeper muddy one and a functional pattern, based on the feeding guilds, was evident along the environmental gradient
Summary
The European Water Framework Directive (WFD; Directive 2000/60/EC) gives emphasis to the assessment of the Ecological Quality Status (EcoQ) of coastal and transitional waters, as these highly dynamic systems are usually exposed to anthropogenic forcing. Benthic molluscs have been used as descriptors of sublittoral soft-bottom benthic communities (Zenetos, 1996; Rueda et al, 2001), there is no information concerning their use as an appropriate taxonomic group for the detection and discrimination of community response to natural or anthropogenic-induced forcing. The detailed objectives of the present study were: (a) to describe the bathymetric distribution and seasonal variability of the sublittoral soft bottom molluscan taxocoenosis by performing a series of uni-, multivariate and graphical methods; (b) to identify the environmental factors which are instrumental in determining the molluscan community structure; and (c) to investigate the applicability of the turnover diversity measurements as a potential descriptor of the molluscan community responses to natural or anthropogenicinduced environmental perturbations in this specific coastal environment
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