Worm reefs in the Atlantic littoral zone
|Red List habitat type||code NEAA2.71|
|Source||European Red List habitat factsheet|
|European Red List of habitats reports|
|European Red List of habitats (Excel table)|
The sedentary polychaete Sabellaria alveolata (honeycomb worm) is a sessile, tube-dwelling species which builds its tubes from sand and shell fragments held together with biological cement. Colonies form on fixed and stable substrates where there is a plentiful supply of sediment on the mid to lower shore. The colonies can form relatively quickly and may take the form of sheets, hummocks and reefs as well as evolving from globular formations into reef platforms. In the Bay of Mont Saint-Michel, France, they create irregularly shaped, patchy banks that cover approximately 225ha. These are considered to be the largest reef formation in Europe with worm densities estimated to reach up to 60,000 individuals/m2 and reef structures more than 2m thick. At the other extreme the S.alveolata reefs at the edge of its range on the central coast of Portugal and north of the Cumbrian coast in the UK tend to be very scattered and not particularly extensive.
S.alveolata reefs can be relatively unstable and undergo a natural cycle of development and decay. As new individuals prefer to settle on active colonies or the remains of old colonies, the age and morphology of reefs are not directly related to the age of individual worms which are typically 4-5 years with a likely maximum of 9 years. The species assemblages found on S.alveolata reefs are unique because they are composed of a mixture of species typically found on hard structures, sandy and muddy sediments as well as from subtidal, intertidal and terrestrial habitats (insect larvae).
Indicators of Quality:
The overall quality and continued occurrence of this habitat is largely dependent on the presence of S. alveolata which creates the biogenic structural complexity on which the characteristic associated communities depend. The density and the maintenance of a viable population of this species is a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage. Scientists working on the Mont-Saint-Michel S. alveolata reefs defined the vitality status of the reef by integrating the physical characteristic of the reef and its dynamics. This took into account the degree of fragmentation of reef features, cover by species which are known to degrade, smother and break up areas of S.alveolata reef (the oyster Crassostrea gigas and the mussel Mytilus galloprovinciallis) and the prevalence of different structural characteristics within the reef formations. In Morecambe Bay (UK), the health of the reefs was determined with reference to the percentage of newly settled worms, those with crisp apertures, to those with worn apertures and dead worms. A generic and universally applicable health metric has still to be developed.
Synthesis of Red List assessment
More recently, around the British Isles this habitat is considered to have been stable on a decadal scale between the 1980s- 2010s, but increased in abundance in the north of its range. In France there has been a decrease in overall extent of the reefs in Mont-Saint-Michel Bay between the 1970s and 2000s and a decline in quality for the larger reefs. In the latter case some of the changes are so drastic that they have altered the three dimensional configuration with some of the grand table-like structures that could still be seen at the beginning of the 1980s no longer present. Newly formed reefs have also been observed since 2010 in bay Mont-Saint-Michel and along the Normandy coast.
The overall trend is considered to be a decline although there are difficulties in making comparisons because changes are not limited to area covered but also the three dimensional structure of reefs.The most extensive examples of this habitat are in France where significant declines have taken place over the last 50 years.
The current Red List assessment is that although this habitat does not have a narrow geographical range and is distributed such that identified threats are unlikely to affect all localities at once, it should be considered Near Threatened for both the EU 28 and EU 28+ because of an overall decline in extent over the last 50 years.
|Red List Category||Red List Criteria|
|Red List Category||Red List Criteria|
Confidence in the assessment
Pressures and threats
- Biological resource use other than agriculture & forestry
- Marine and Freshwater Aquaculture
- Human intrusions and disturbances
- Other human intrusions and disturbances
- Trampling, overuse
- Invasive, other problematic species and genes
- Invasive non-native species
- Natural System modifications
- Human induced changes in hydraulic conditions
- Siltation rate changes, dumping, depositing of dredged deposits
- Natural biotic and abiotic processes (without catastrophes)
- Abiotic (slow) natural processes
- Interspecific faunal relations
Habitat restoration potential
Trends in extent
Average current trend in quantity
Trends in quality
Average current trend in quality
Conservation and management needs
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
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)|
|Bay of Biscay and the Iberian Coast||Present||Unknown||Unknown||Decreasing|
|Greater North 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||399,828||83||Unknown||EOO and AOO have been calculated on the available data. Although this data set is known to be incomplete the figures exceed the thresholds for threatened status.|
|EU28+||83||Unknown||EOO and AOO have been calculated on the available data. Although this data set is known to be incomplete the figures exceed the thresholds for threatened status.|
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).
|Species scientific name||English common name||Species group|
Relation to other habitat types mentioned in legal instruments
|Legal text||Annex||Name in legal text||Code in legal text||
|Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora - consolidated version 01/01/2007||Annex I: natural habitat types of community interest whose conservation requires the designation of special areas of conservation||Reefs||1170||Overlap||http://ec.europa.eu/environm...rective/index_en.htm|