Molluscan diversity along a Mediterranean soft bottom sublittoral ecotone

Abstract

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 (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.Keywords: mollusc diversity, ecotone, sublittoral, soft bottom, beta-diversity, perturbation, environmental assessment, eastern Mediterranean.RESUMEN: DIVERSIDAD MALACOLÓGICA EN UN ECOTONO SUBLITORAL MEDITERRÁNEO DE FONDOS BLANDOS. -La diversidad malacológica asociada a la zona infralitoral de fondos blandos se ha estudiado en la bahía de Heraklion como parte de un programa de investigación multidisciplinar a largo plazo en la costa norte de Creta (Mediterráneo Oriental). Muestras cuantitativas del bentos fueron recogidas durante un muestreo piloto realizado en una parrilla de 28 estaciones. A continuación se realizó un muestreo estacional en un transecto de siete estaciones situadas entre 10 y 40 m de profundidad. Los análisis univariables y multivariables indicaron la presencia de una clara zonación malacológica a lo largo del gradiente de profundidad, identificándose tres asociaciones principales en zonas batimétricas paralelas a la línea de costa. La estructura de las comunidades locales de moluscos puso de manifiesto la existencia de una extensa zona de transición (ecotono) entre la asociación de arena somera y la de fango profundo y evidenció un patrón funcional basado en los tipos de alimentación a lo largo del gradiente ambiental. La aplicación de técnicas gráficas, empleando la taxocenosis de moluscos, indicó un hábitat perturbado. Lla diversidad beta indicó diferentes adaptaciones de las comunidades estacionales a las condiciones ambientales reinantes. Los resultados obtenidos en este estudio muestran que la diversidad beta puede ser un buen descriptor para la evaluación de la capacidad y la amplitud de las zonas de transición sublitoral a lo largo de gradientes ambientales.Palab...

Seasonality and trophic diversity in molluscan assemblages from the Bay of Tunis (southern Mediterranean Sea)

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Assessment of goods and services, vulnerability, and conservation status of European seabed biotopes: a stepping stone towards ecosystem-based marine spatial management

“…Recovery may be extremely slow because of the stable (nondynamic) conditions that prevail in this biotope (Koulouri et al, 2006). Dumping of solid wastes may severely modify and pollute this biotope but such practices are currently prohibited under the London Convention and Protocol.…”

Response to oxygen deficiency (depletion): Bivalve assemblages as an indicator of ecosystem instability in the northern Adriatic Sea

“…The identification of molluscan species is much easier than the identification of all macrobenthic taxa to the generic or family level, which provided plausible results in a number of cases (e.g., Warwick et al 1990;Zenetos 1996). Therefore, using only molluscan taxocoenosis, the procedures involved in the assessment of coastal marine environments that are subjected to natural or anthropogenic-Bivalve assemblages as an indicator of ecosystem instability 1115 induced forcing, may be less time-consuming (Koulouri 2006). This study deals with communities that have experienced heavy disturbance due to oxygen crisis in northern Adriatic Sea during 1989 (Zavodnik et al 1994;Stachowitsch 1991;Degobbis et al 2000) and the subsequent decade -a period of relatively stable ecological conditions -using solely Bivalvia assemblages as an indicator of ecosystem disturbance.…”