Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA2.71 Worm reefs in the Atlantic littoral zone

Worm reefs in the Atlantic littoral zone

Quick facts

Red List habitat type code NEAA2.71
Threat status
Europe Near Threatened
EU Near Threatened
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)

Summary

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.  

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

Threat status

Synthesis of Red List assessment

There have been different trends in the extent and quality of this habitat across the North East Atlantic region and on various time scales. Change in abiotic conditions (temperature) resulted in significant loss of this habitat in the severe winter of 1962/3 in Europe which was the coldest since 1740 and had catastrophic effects on intertidal populations.
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.
EU
Red List Category Red List Criteria
Near Threatened A1
Europe
Red List Category Red List Criteria
Near Threatened A1

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

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
    • Competition

Habitat restoration potential

The intensity of settlement is extremely variable from year to year and place to place and once established growth can be rapid (e.g. up to 12cm/yr increase in tube length has been reported for northern France) and the worms can mature within the first year. New individuals prefer to settle on active colonies or the remains of old colonies. In-depth investigations regarding reef function, maintenance of function for degraded reefs and resilience are needed to determine the recovery capacity of this habitat.

Trends in extent

Average current trend in quantity

Decreasing Decreasing
EU28 EU28+

Trends in quality

Average current trend in quality

Unknown Unknown
EU28 EU28+

Conservation and management needs

This habitat is present within Marine Protected Areas. Specific management measures include regulation and specification of types of coast protection works to avoid changes in sedimentation regime, and regulation of intertidal fisheries to prevent break up of reefs for bait collection, or promoting access routes to aquaculture facilities that avoid reef structures. Operational measures such as hygiene requirements related to aquaculture are also important to minimise the likelihood of introducing invasive species to the shore environment. Codes of conduct and educational information on the vulnerability of these reef features can also be used to try and minimise trampling damage to the reef structures by shore users. National and European recognition of the need for protection of this habitat is also valuable as this encourages the introduction of local measures that have a direct benefit on the reefs.

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

Distribution

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)
Bay of Biscay and the Iberian Coast Present Unknown Unknown Decreasing
Celtic Seas
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.
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

The full list of characteristic species and genus are available above from the Summary. The species available in the EUNIS database are shown here.
Algae Chondrus crispus
Algae Cladostephus spongiosus
Algae Enteromorpha intestinalis
Algae Fucus serratus
Algae Mastocarpus stellatus
Algae Osmundea pinnatifida
Algae Palmaria palmata
Algae Ulva lactuca
Invertebrates Actinia equina
Invertebrates Cereus pedunculatus
Invertebrates Crassostrea gigas
Invertebrates Elminius modestus
Invertebrates Gibbula cineraria
Invertebrates Lanice conchilega
Invertebrates Littorina littorea
Invertebrates Mytilus edulis
Invertebrates Patella vulgata
Invertebrates Semibalanus balanoides
Species scientific name English common name Species group
Chondrus crispus Algae
Cladostephus spongiosus Algae
Enteromorpha intestinalis Algae
Fucus serratus Algae
Mastocarpus stellatus Algae
Osmundea pinnatifida Algae
Palmaria palmata Algae
Ulva lactuca Algae
Actinia equina Invertebrates
Cereus pedunculatus Invertebrates
Crassostrea gigas Invertebrates
Elminius modestus Invertebrates
Gibbula cineraria Invertebrates
Lanice conchilega Invertebrates
Littorina littorea Invertebrates
Mytilus edulis Invertebrates
Patella vulgata Invertebrates
Semibalanus balanoides Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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