Serpulid reefs

The organ-pipe worm Serpula vermicularis is a beautiful marine tubeworm with a showy crown of feathery tentacles, bright red, pink and orange, contrasting with its hard white tubes. Individual organ-pipe worms have an almost worldwide distribution, except for polar seas, but in a few special places, hundreds of them grow together forming bush like structures or 'reefs'

Serpulid reefs are made up of hundreds of individual worm tubes each 4-5mm in diameter and up to 150mm long. Each reef starts with a newly-settled worm building its tube on a stone or shell on the muddy seabed. More worms settle on the rock and on existing worm tubes, their open ends growing upwards and outwards. Each reef resembles a small bush, with the colourful expanded worms decorating the structure with bright flower like structures. Organ-pipe worms are very sensitive to light and vibrations, the worms rapidly retract their tentacles if disturbed and close the entrance to their tube with a cone-shaped plug. Suddenly the reef is transformed from red and orange to show just the pure white of the tubes.

Large reefs eventually become too big to support their own weight and collapse outward from the centre forming doughnut shapes. Some of the worms in the broken pieces continue to grow while others act as starter homes for more worms to attach, eventually forming new reefs

Where are they found?

Two loughs on the west coast of Ireland contain a restricted area of small reefs, and they have been reported from a coastal lagoon in Italy. There were previously reefs in Linne Mhuirich, Loch Sween, but these died out in the 1990s for reasons that are still not understood, and now only the dead worm tubes remain. Small aggregations of organ-pipe worms were found in Loch Teacuis, Morvern in 2006, these are not yet reefs, but may grow larger and proliferate to cover a greater area of sea bed. By far the best developed and largest area of serpulid reefs in the world occur in Loch Creran, west Scotland just north of Oban

The serpulid reefs in Loch Creran grow at depths of between 6 and 10m, and up to 75cm high and 1m across. The reefs form a high-rise home for a host of other animals, especially on a muddy seabed where there are few other places to hide or attach. Bright orange sponges with long tendrils are particularly abundant on some colonies, and sea firs, sea squirts and seaweeds also attach to the tubes. Spider crabs, squat lobsters, hermit crabs, starfish, small urchins and marine snails shelter or hunt on the colony, while the bristly arms of brittlestars and long, mobile tentacles of terebellid worms reach out from deep within.

Threats

Serpulid reefs are very fragile and extremely vulnerable to mechanical disturbance, for example from mobile and static fishing gear, movement of anchors and mooring chains and even divers' fins. They may also be sensitive to water quality and changes in water flow.

Protection

Because serpulid reefs are so rare they are protected by a UK Biodiversity Habitat Action Plan  . Loch Creran is also designated as a Special Area of Conservation (SAC) for its reefs, including the worm reefs

Loch Creran is managed by the Argyll Marine SAC Management Forum. The Forum coordinated by Argyll and Bute council has produced a Management Plan for the loch. The Management Plan includes a zoning map for fishing activity, a "Moorings Pack  " to help locate mooring blocks where they will not damage the serpulid reef, and guides to anchoring and diving safely in the loch.