Marine Biodiversity Data Portal - NI

Correspondence with existing habitats

Habitats Directive Annex I: Reefs

Description: Sabellaria alveolata reefs are formed by the honeycomb worm Sabellaria alveolata, a polychaete which constructs tubes in tightly packed masses with a distinctive honeycomb-like appearance. These reefs can be up to 30 cm or even 50 cm thick and take the form of hummocks, sheets or more massive formations. Reefs are mainly found on the bottom third of the shore and do not seem to penetrate far into low salinity areas. Reefs form on a variety of hard substrata, from pebbles to bedrock, in areas with a good supply of suspended sand grains from which the animals form their tubes, and include areas of sediment when an attachment has been established. The larvae are strongly stimulated to settle by the presence of existing colonies or their dead remains. S. alveolata has a very variable recruitment and the cover in any one area may vary greatly over a number of years, although in the long term reefs tend mainly to be found on the same shores.

Individual worms have a typical lifespan of 3 - 5 years, and possibly up to 9 years, but reefs themselves may last longer as a result of further settlement of worms onto existing colonies. The larvae will preferentially settle on the tubes of adults, so even small aggregations are extremely important for this priority habitat. Typically in the first two years or so, after a heavy intertidal settlement, there are few associated species. Over time, seaweeds including fucoids, Palmaria palmata, Polysiphonia spp., Ceramium spp., Enteromorpha spp. and Ulva lactuca, and animals including barnacles, dogwhelks, winkles, mussels and other bivalves such as Nucula nucleus, Sphenia binghami and Musculus discors, colonise the reef. Older reefs may increase the biodiversity and stability of what would otherwise be sand abraded rocks and boulders. Sheet-like reefs may restrict drainage of the shore, creating rockpools where there would otherwise be none.

In Northern Ireland S. alveolata aggregations are found only on shores with moderate wave action on the east coast of Co. Down. There are small aggregations in Ardglass and Minerstown, but currently the only site that meets the criteria for an S. alveolata reef is at Glassdrumman, Co. Down, as other aggregations are now much reduced in size. The smaller aggregations may qualify as reefs in future with additional larval settlement and should be monitored. This is a southern species in Britain and Ireland, reaching its northern limit on the west coast of Scotland.

Associated biotopes:

• LS.LBR.Sab – Littoral Sabellaria honeycomb worm reefs
• LS.LBR.Sab.Salv - Sabellaria alveolata reefs on sand-abraded eulittoral rock
• LS.LBR - Littoral biogenic reefs

• EUNIS code: A2.71, A2.711 and A2.7

Threats:

• Cold winters / climate change: Sabellaria alveolata reefs are at the northern end of their range in Britain and are affected by extremely cold winters, after which they may die back for many years, particularly at higher shore levels.
• Prolonged burial will cause mortality, however it can tolerate burial for a period of days or even weeks.
• Accumulations or losses of sand as a result of shoreline development, which is the major cause of loss in parts of Europe. These developments may have positive or negative effects depending on the nature of the changes.
• Trampling damage by beach users and extraction of the worms for angling bait.
• Competition for space with common mussels Mytilus edulis occurs, especially on boulder scars, but factors influencing this are unknown. Heavy settlement of mussels on S. alveolata reefs has been suspected of causing short-term destabilisation and loss of habitat.
• Variable recruitment: S. alveolata is naturally subject to very variable recruitment, but the factors influencing this are not fully understood.

References:

This habitat description has been adapted from the 1994 UK BAP Action Plan for Sabellaria alveolata reefs.