Marmara coralligenous communities moderately exposed circalittoral rock

Coralligenous habitats are hard bottoms of biogenic origin mainly produced by the accumulation of calcareous encrusting algae growing in dim light conditions. Although more widespread in the circalittoral zone, they can also develop in the infralittoral zone, provided that light is dim enough to allow growth of the coralline algae that produce the build-up; therefore, infralittoral coralligenous concretions always develop in almost vertical walls, deep channels, or overhangs, and occupy reduced surfaces. Coralligenous bioconcretions are always very complex in structure allowing the development of several kinds of communities including those dominated by living algae (on the upper part of the concretions), suspension feeders (upper and lower part of the concretions, wall cavities, and overhangs of the build-up), borers (inside the concretions), and even soft-bottom fauna (in the sediment deposited in cavities and holes). This is a highly variable habitat that can be subdivided into different sub-habitats.

Indicators of quality:

Several indicators have been proposed to assess the health of coralligenous habitats based on the composition and abundance of species (biotic cover and conspicuous species richness), including the percent cover of different benthic assemblages (encrusting calcified Rhodophyta, non-calcified encrusting algae and fauna, turf forming algae, and sediment), boring species marks, percent cover of each species and the percentage of necrosis, Bryozoa percent cover, sludge percent cover and the builder species percent cover. Pollution has a severe impact on coralligenous outcrops where coralline algae are substituted first by Mesophyllum alternanas and latterly by Peyssonnelia rosa-marina. High water turbidity decreases diversity, especially of Bryozoans, Crustaceans and Echinoderms. However the amount of bioeroders increases, i.e. Sipunculids and boring sponges (Cliona), along with more generalist species. Mechanical disturbance and breaks of the bioconstruction with increases of turbidity and sedimentation can also be observed. Fishing can affect the abundance of certain target species  and high sedimentation rates result in overgrowth and invasion by exotic algae, altering assemblage composition.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats