Neopycnodonte cochlear beds on exposed and tide-swept circalittoral rocks and cobbles

This habitat occurs in the circalittoral zone on both hard and mixed substrates. It has been recorded in exposed and tide-swept sites at depths of 60 - 150m in the Faial-Pico channel and the Formigas Bank in the Azores and in deeper waters on the upper slope of the Bay of Biscay between 200-500m. Sessile macrofauna is dominated by the oyster Neopycnodonte cochlear and the clam Chama circinata.  Some variance has been observed in the abundance of the two species although in shallower zones it may be exclusively Neopycnodonte . On hard substrates the two species growing together may build up to form a calcareous bioherm. The habitat has also been observed on mixed carbonate-volcanoclastic sediment plains where the two species form cobble to small-boulder sized clumps. N. cochlear is able to create thick mantles, serving as hard substrate for other species including foraminifera, bryozoan, ascidians, coral and sponges.

Indicators of quality:

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

The overall quality and continued occurrence of this habitat is dependent on the presence of the predominate structural species, the oyster Neopycnodonte cochlear and the clam Chama circinata species which create the biogenic structural complexity on which the associated species depend. The density and the maintenance of viable populations of these species are therefore likely to be a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats