Polychaete worm reefs in the Mediterranean infralittoral zone

Worm reefs are large bioconstructions built by polychaetes the most important of which in the Mediterranean are the sabellarids Sabellaria alveolata and S. spinulosa and the serpulids Hydroides dianthus and Ficopomatus enigmaticus. The development of such reefs is assured by the gregarious settlement of polychaete larvae, which occurs mainly on pre-existing reefs or their dead remains. 

Sabellaria bioconstructions can be relatively unstable and undergo a natural cycle of development and decay, they can form relatively quickly and may take the form of sheets, hummocks and reefs as well as evolving from globular formations into reef platforms. Reefs may persist in an area for many years although individual clumps may regularly form and disintegrate.  Sabellaria alveolata reefs in the Mediterranean are located between 1 to 7 m of depth where can reach 60 cm thick when they are well developed. In most sites, however, they tend to be very scattered and not particularly extensive

Most serpulids are considered to be 'secondary frame builders'. Ficopomatus enigmaticus, typically growing in coastal lagoons and brackish water lakes, can form large reefs. They can occur as a fringing reef along the rocky shoreline, forming a continuous layer that can reach up to 3 m thick, at a depth of about 1 m, or can develop as dense patch reefs growing from the bottom, with hemispherical forms called micro atolls (over 2 m height and 4 m in diameter) and with a distribution related to the depth (from 0.5 to 1.5 m).

This habitat provides a diversity of microhabitats increasing available substrate for numerous species; sheltering both hard and soft-bottom rare species which are potential colonizers of adjacent habitats; providing refuge for invertebrates including snails and crabs that may have an impact on native species communities and are attractive for some fish such as  Sygnathus abasteri, Aphanius fasciatus and Knipowitschia panizzae

Indicators of quality                                                                                                                              

The status and dynamics of the reefs must be defined integrating the physical characteristics, taking into account the degree of fragmentation of reef features (mainly produced by species which are known to degrade, smother and break up areas of Sabellaria, e.g. the mussel Mytilus galloprovinciallis), and the prevalence of different structural characteristics within the reef formations. The health of the reefs can  be determined with reference to the percentage of newly settled worms, those with crisp apertures, those with worn apertures and dead worms. 

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats