Rocky Reefs

In 2021, Scotland celebrates the Year of Coasts and Waters, and COAST celebrates 25 years of the community of Arran’s efforts to protect our seas.

Here we bring you a little bit closer to what lies beneath our waves with a focus on the rare Rocky Reef habitats found in Scotland’s seas.

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If you have walked along any of Arran’s coastline you will know just how varied and spectacular it can be – Kildonan anyone?! – and this coastal scenery can give us some idea of what the adjacent seabed might look like.

Where the rock and boulders of the shore extend underwater they form rocky reefs which sometimes end abruptly in shallow water or, at other locations, disappear into the depths. In contrast to living reefs, rocky reefs are a result of the local geology and many of the plants and animals that live on the reef habitat actually spend their whole life attached to the rock itself.

Just like living reefs, rocky reefs support a myriad of animals.

The importance of Rocky Reefs

The island of Pladda, within the South Arran MPA, is a distinctive landmark off the southern coast of Arran. While this substantial rock outcrop is high enough to appear above the sea’s surface, nearby there are other similar rocky outcrops that are submerged below the waves, forming part of Arran’s amazing rocky reef habitats.

One such reef, known as Roraima Reef by local divers, is somewhat spectacular and is just as dramatic as its name suggests, its sheer rock walls rising abruptly from the surrounding seabed. In places this reef is carpeted by an assortment of vibrantly coloured elegant anemones which look like tightly-packed flower heads; elsewhere are clusters of the much larger orange or white plumose anemones, which can grow up to 30cm tall and are topped by a fluffy-looking circle of tentacles.

Other parts of this rocky reef are dominated by bulbous fingers of the soft coral ‘dead man’s fingers’ along with colonies of less familiar-looking marine animals such as sea firs and sea mats. Around all the life attached to the rock are bustling mobile animals which include brilliant red starfish, beautiful sea slugs and sea snails, and more familiar crabs and fish. Roraima reef is really impressive not only because of its dramatic underwater landscape but also in terms of the marine life that thrives on it.

Special Species

Our rocky reefs are home to a myriad of amazing marine life, but we’re going to take this opportunity to shout about perhaps a less known species: the Feather Star.

Feather stars are a type of Echinoderm, meaning they are related to starfish, sea urchins and sea cucumbers! Early life-stages see feather stars hatch as free-swimming larvae which very quickly attach to a substrate (rocky reefs are an ideal place) where they develop a short stalk. As they grow larger, the animal breaks off from the top of the stalk and grows claw-like “feet” (known as cirri) before continue their existence as free-living individuals. An individual can possess up to 25 cirri, which enables it to crawl pretty swiftly through its habitat.

As you look at newly settled stalked juvenile feather stars you are, in a way, looking at a living fossil. The stalk mirrors those found in the ancient fossilised ancestors – Crinoids – of this group of animals.

Take a dive with us at one of our best rocky reefs in Arran’s seas: Roraima Reef.

Human Benefits

At first glance, it may not be entirely obvious how humans can benefit from healthy rocky reef habitats; but these reefs are an essential habitat for many different mobile species, including commercially important lobsters and crab.

In shallower waters seaweeds generally dominate the reefs, with large brown kelp plants forming underwater forests together with a dense understory or smaller red seaweeds. In amongst these seaweeds larger fish such as Pollock shoal, creating ideal locations for a spot of recreational sea angling.

Further benefits provided by rocky reefs are those of natural protection; as wave energy builds the shallower reefs and bedrock act as natural breakwaters, thus reducing impacts of coastal erosion on our shorelines.

Of course, the biggest benefit we as humans gain from rocky reefs is that they are just fabulous places to scuba dive or snorkel. The abundance of life found on these reefs attracts keen water explorers from miles around, which in turn helps support the tourism trade in the area.

Threats to Rocky Reefs

Rocky reefs, by their very nature, might look as though they could withstand many pressures but, like so many parts of our underwater world, they can be damaged and degraded by a number of different activities and impacts.

  • Climate Change is causing our sea temperatures to increase and become more acidic at such a rate that animals simply cannot adapt quickly enough to survive.
  • Unregulated and/or overfishing is a threat to larger fish, such as wrasse, that live in groups within defined territories on rocky reefs. Wrasse feed around and over the reef and make use of rock crevices or purpose-built seaweed nests to lay their eggs. In recent years, wrasse species around Arran and elsewhere around Scotland and the UK have been the target of unmanaged fisheries that are supplying wrasse as cleaner fish to the salmon aquaculture industry and their numbers appear to be dwindling.
  • Large scale mechanical kelp harvesting threatens our rocky reef communities. Kelp forests found in Scotland’s seas are habitat for many species, play an important part in coastal protection, provide nursery grounds for commercially important species and are an attractive addition in the marine tourism industry.

Can we protect Rocky Reefs?

Rocky reef habitat in the Lamlash Bay No Take Zone is protected and, although the rest of the Marine Protected Area (MPA) contains a lot of rocky reef, this isn’t one of the habitats for which it was specifically designated. Nonetheless, rocky reefs and the species that live on them are an integral part of the interconnected web of life in Arran’s waters.

Elsewhere in Scotland, rocky reef habitats can be extensive and specific reef communities are protected either within MPAs or protected as Priority Marine Features – habitats and species of conservation importance.

Further afield down in Lyme Bay, the MPA designated there was done so “with the objective to recover rocky reef habitats by protecting all of the seabed”. A recent study has shown that in order for this objective to prosper all fisheries – including creel (pot) fishing – must be well managed and regulated.

Get involved to make a difference!

Rocky reefs are often found lining fishing grounds, which studies showing compositional changes to the fauna on reefs in areas where dredging takes place. Fish farming pollution, including sedimentation and chemical pollution, also causes damage to these reef habitats. How can you make a difference? Ask questions as to where your seafood is coming from – boycott farmed fish, and shop around to purchase creel-caught or hand-dived shellfish.

Please also report any invasive non-native species you find to the Scottish Environment and Rural Services (SEARS) as these adversely impact life found on our rocky reefs; a full list of invasive species can be found on the Non Native Species Secretariat website. To find out how you can engage in the management of invasive non-native species in your community, check out the Scottish Invasive Species Initiative.

Feature image courtesy of Paul Kay