Biogenic reefs

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  3. Biogenic reefs


Biogenic reefs are made up of hard matter created by living organisms. The reefs are raised above the seabed. Reefs can grow to be several metres in height and diameter, providing important habitat for a number of species. A study of a reef in the Wash discovered 88 crevice species inhabiting the reef.

What are they?

In UK waters, they are made by blue-or horse mussels or by honeycomb-or ross tubeworms. The blue and horse mussels create reefs by binding dead and living shells together using sand and mud. The honeycomb and ross worm reefs are called Sabellaria reefs (the latin name for the worms in question) and are created by tubes of sand. They are generally found in more exposed water and shores allowing currents to deposit new sand for continual building up of the reef structure.

Where are they found?

As there are only a few species that are capable of creating biogenic reefs, they are limited in distribution. They are mainly found constantly submerged below the lowest tidal point (subtidal) but they can extend onto intertidal areas in some places. Larger distribution areas are found on the South/West and West coast and with a northern limit at the Outer Hebrides. Ireland has a few recordings.

Why are they important?

The reefs provide a surface for plants to establish and invertebrates to burrow. As a consequence they are often teeming with life – a living reef providing food and shelter for many species, similar to the coral reefs in the tropics. In intertidal habitats, the reefs created by mussels may also create rock pools thus providing a refuge for animals until the tide returns. Once again these areas are often home to many small invertebrates which hide between shells/structures.

Are they threatened?

Changes to the distribution of sand caused by physical disturbance such as dredging, trawling and construction of sea defences has a significant effect on the worms ability to generate reefs. Dredging and trawling can also act to destroy already established reefs, whilst scallop dredging can seriously damage reefs created by mussels.

Slowly generated reefs, built over a long period of time, are not quickly replaced, and the damage affects not only to the mussels and tubeworms but also the species that inhabit these living reefs.

What are The Wildlife Trusts doing to help?

Following the assent of the Marine & Coastal Access Act, four regional projects were established to identify potential Marine Conservation Zones within England. The projects are stakeholder led and Wildlife Trust staff sit on all projects, at local, regional and a national level. These projects will ultimately put forward sites to protect special areas of the sea, such as our biogenic reefs. Additional work on Marine Protected Areas is also underway in Wales and Scotland, whilst in Northern Ireland we are still campaigning for Marine legislation with a commitment to establishing these areas.

What can I do to help?

Visit to find out how you can help our marine conservation work in the UK. Depending on where you live, local Wildlife Trust volunteers help out with everything from recording marine wildlife sightings to beach cleans and educational work. Visit our Living Seas pages online or contact your local Trust to find out more.