Circalittoral biogenic habitats in the Mediterranean - oyster beds

Circalittoral oyster beds on rocky and soft bottoms comprised mainly by the Neopycnodonte cochlear. These make large mass aggregations on the bottom and support the development of other life forms such as cnidarians, bryozoans and sponges. In the Mediterranean, two species of the genus Neopycnodonte exists. Neopycnodonte cochlear and Neopycnodonte zibrowii. N. cochlear is found in waters with depths of 40-400 meters while N. zibrowii is found in deeper waters and so not included further in this assessment. This habitat  can also be found in underwater caves, in even shallow waters, indicating that the dim light is the modulator of the distribution. In the circallitoral zone, N. cochlear can cover large areas of the bottom, both muddy and rocky. Often, shells can be found growing on disgarded fishing gears, when fleets use to fish in areas where deepsea oyster exists. There are three distinct habitat components; the interstices within the oyster matrix; the biodeposits beneath the bed; and the substratum afforded by the oyster shells themselves. A diverse range of epibiota and infauna often exists in these parts of the habitat.

Indicators of quality:

Both biotic and abiotic indicators have been used to describe marine habitat quality. These include the presence of particular species, water quality parameters, levels of exposure to a particular exposure as well as more integrated indices which describe habitat function and structure, such as trophic index, or successful stages of development in habitats that have a natural cycle of change over time.

There are no known commonly agreed indicators of quality for this habitat, although particular parameters may be set in certain situations, e.g. protected features with Natura 2000 sites, where reference values may have been determined and applied on a location-specific basis. Presence, density and size range of the oyster N. cochlear can be used as an indicator of quality.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats