Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA5.61 Polychaete worm reefs in the Mediterranean infralittoral zone

Polychaete worm reefs in the Mediterranean infralittoral zone

Quick facts

Red List habitat type code MEDA5.61
Threat status
Europe Data Deficient
EU Data Deficient
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)


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. 

Characteristic species
For full habitat description, please download the habitat factsheet.

Threat status

Synthesis of Red List assessment

At present, the knowledge of Mediterranean worm reefs in the infralittoral is too fragmentary, with little information about extent of occurrence or its area of occupancy. There have been no quantitative analysis to determine their current conservation status and to define their dynamics, in order to evaluate threats and impacts and to highlight the conservation needs or suggest management measures and protection actions. As a result, there is insufficient data to properly assess the habitat against any of the red list criteria, and the Mediterranean Polychaete worm reefs are listed as Data Deficient for both EU 28 and EU 28+.
Red List Category Red List Criteria
Data Deficient -
Red List Category Red List Criteria
Data Deficient -

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Biological resource use other than agriculture & forestry
    • Marine and Freshwater Aquaculture
    • Intensive fish farming, intensification
    • Leisure fishing
    • Bait digging / Collection
  • Human intrusions and disturbances
    • Other human intrusions and disturbances
    • Trampling, overuse
    • Shallow surface abrasion/ Mechanical damage to seabed surface
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Pollution to surface waters by industrial plants
    • Pollution to surface waters by storm overflows
    • Other point source pollution to surface water
    • Nutrient enrichment (N, P, organic matter)
    • Marine water pollution
    • Toxic chemical discharge from material dumped at sea
  • Invasive, other problematic species and genes
    • Invasive non-native species
  • Climate change
    • Changes in abiotic conditions
    • Temperature changes (e.g. rise of temperature & extremes)
    • pH-changes
    • Water flow changes (limnic, tidal and oceanic)
    • Wave exposure changes
    • Sea-level changes

Habitat restoration potential

Serpulid reefs built by Ficopomatus are extremely dynamic in both space and time, and are characterized by very short-cycles, because they form in brackish water dynamic environment. The reefs break-down under their own weight and reform continuously. Therefore Ficopomatus is able to respond to the environmental changes and recover from damage in relatively short time. However, important variation in water flow regime and quality (especially salinity), and high human pressure can led to the disappearance of these reefs and reduce their recover capacity.
Sabellaria reefs are extremely dynamic too, they may persist in an area long time although individual clumps may regularly form and disintegrate. Usually, reefs show a cycle of development undergoing 4 different easily determined morphologies (reef compactness, tube orientation, percentage of tubes with 'sand crown', and presence/absence of epibionts on the reef surface) and defined as 'phases'. Each phase is the result of a constantly disturbed and precarious balance between physical factors (hydrodynamic forces, temperature, and local environmental conditions, such as seabed topography and water clarity), and biological factors (reproduction and recruitment mechanism of the pelagic larvae). Sabellaria alveolata can live up to 9 years, whilst S. spinulosa is a fast growing annual species so that degradation and recovery of the reefs that occurs as a response to external environmental pressure, can be different, even if in both species recruitment rates are high and recovery could be quite rapid, the speed of changes is different according to their different life cycle. As a consequence S. alveolata reefs seem to be more persistent and more abundant than S. spinulosa which, in most parts of its geographic range, is solitary or form small groups.
The limited understanding of the factors affecting recruitment success and of the source of larval supply preclude further predictions on the potential for recovery and the rate at which it might occur. Biogenic reefs can take many years to recover, and some may never recover. For example, Sabellaria spinulosa reefs have failed to recover in the Wadden Sea following their dramatic decline over recent decades. According to the life-cycle knowledge it can be hypothesised that the recover of S. alveolata may occur within at least 10 years if condition are maintained optimal, but that can last more time naturally.

Trends in extent

Average current trend in quantity

Unknown Unknown
EU28 EU28+

Trends in quality

Average current trend in quality

Unknown Unknown
EU28 EU28+

Conservation and management needs

Knowledge of this habitat is too fragmentary to determine their current health status and to define their dynamics, in order to evaluate the most important threats and impacts, to highlight the conservation needs and suggest management measures and protection actions. Understanding those parameters that influence the reef dynamics is necessary in order to develop efficient and effective management practices and policy focusing on the conservation status of large biogenic structures.

List of conservation and management needs

  • Measures related to marine habitats
    • Other marine-related measures
  • Measures related to spatial planning
    • Establish protected areas/sites
  • Measures related to hunting, taking and fishing and species management
    • Regulation/Management of fishery in marine and brackish systems
  • Measures related to special resouce use
    • Regulating/Managing exploitation of natural resources on sea


For each habitat a distribution map was produced from a wide variety of sources indicating known and potential occurrences of the habitat in 10x10 km grids within Europe. Occurrences in grid cells were given in two classes: actual distribution from relatively reliable sources (surveys, expert knowledge), and potential distribution based on models or less reliable indicators. Please download the fact sheet to see the map.

Geographic occurrence and trends

Seas Present or presence uncertain Current area of habitat (Km2) Recent trend in quantity (last 50 years) Recent trend in quality (last 50 years)
Adriatic Sea Present Unknown Unknown Unknown
Aegian-Levantine Sea
Ionian Sea and the Central Mediterranean Sea
Western Mediterranean Sea

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 943,913 >19 Unknown EOO and AOO have been calculated on the available data but this is known to be incomplete.
EU28+ >19 Unknown EOO and AOO have been calculated on the available data but this is known to be incomplete.
AOO = the area occupied by a habitat measured in number of 10x10 km grid cells.
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).

Characteristic species

Not available

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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