For those of you new to the area, to CAOLAS or our local marine habitats, you may have wondered why Loch Sunart has been classified as a Nature Conservation Marine Protected Area (NCMPA or MPA)?

In this blog post, we will introduce you to Loch Sunart, take you under the water and give you a wee glimpse of life in the deep.

LOCH SUNART

The head of Loch Sunart sits just east of Strontian where freshwater from the Carnoch River meets the salty waters of the longest sea loch in the Highland region of Scotland. From here, the waters flow westwards on an ebb tide past Resipole Campsite, Salen Jetty, Ardnamurchan Natural History Centre and out to sea just short of the most westerly point on mainland UK near Ardnamurchan Lighthouse (an amazing place to watch marine wildlife from).

If you have visited the area before, you may well know all the places mentioned and be familiar with the landscapes surrounding Loch Sunart.

But how much do you (or us) know about life under the surface, or why Loch Sunart is an MPA?

Read on and discover the three Scottish Marine Priority Features (S-PMFs) you’ve probably never heard of under the surface…

Within Loch Sunart, many small islands create narrow channels (Gaelic: caolas) of fast-flowing water. Areas such as the Laudale Narrows (directly beneath the camera in the image above), the entrance to Loch Teacuis and around the islands of Carna and Oronsay help create the essential conditions necessary to support a diversity of marine life.

You may all never see these creatures as they generally live deep under the water, but they have been designated for protection as they are unique and rare and bring great value to the marine environment in many ways.

The designation of the Loch Sunart NCMPA complements and existing Special Area of Conservation (SAC) and is designated for its rocky reefs, otters and oak woodlands. Together these designations help protect some of Scotland’s most unique marine life, including three S-MPFs below.

Flame shells

These are brightly coloured bivalve molluscs (Limaria hians) – often described as one of the most beautiful of all British bivalves thanks to their long, vibrant orange tentacles (which cannot be retracted).

However, they are very rarely seen above the seabed. In fact, many divers have swum over flame shell beds without realising there were about 400 striking flame shells per square metre just beneath them!

The flame shells create nests by weaving together threads of byssus (a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface) with surrounding materials such as seaweed, shells, gravel, pebbles and even cobbles.

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These nests can spread to carpet the entire seabed and, in turn, create a new habitat that stabilises the sediments whilst providing an attachment surface for many additional plants and animals such as seaweeds, sponges, starfish and brittlestars. These animals increase the habitat complexity and provide shelter for yet more animal species.

A very rich variety of animals are found both within and below a flame shell bed and loss or degradation of these beds leads to destabilisation of the substrate and consequent loss of many animal species.

Due to their rarity, fragility and decline in certain areas, the flame shell beds have been incorporated into the Marine Protected Area network.

Organ pipe worm

An exciting discovery was made in 2006 when aggregations of serpulid (organ pipe) worms were found in the shallow waters of Loch Teachuis, a small arm off Loch Sunart. At the time, Loch Creran, to the south of Loch Sunart, was the only other place in Scotland where such aggregations were known to occur (more recently small aggregations have been found near the head of Loch Ailort).

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Organ pipe worms (Serpula vermicularis) are slender, widespread, polychaete (bristle) worms that live in calcareous (mostly composed of calcium carbonate) tubes attached to rocks, stones and other hard surfaces.

They occur in most Scottish sea lochs, but only as individuals!

In Loch Teachuis and Loch Creran, they aggregate together and form biogenic reefs. Loch Creran reefs may reach 75cm in height and 100cm across, but the ones in Loch Teachuis are nowhere near as large as this. These reefs create a ‘high-rise home’ for other species, such as other tubeworms, sea anemones, sea squirts and sponges, as well as many mobile crustaceans (spider crabs, hermit crabs and squat lobsters), molluscs (scallops and marine snails) and echinoderms (sea urchins, starfish and brittlestars).

Serpulids filter feed by extending a crown of bright red, orange or white feather-like tentacles (radioles) into the water to remove phytoplankton and detritus. If disturbed by light or vibrations, these can be rapidly retracted and the worm seals itself into its tube with a funnel-shaped plug or operculum. A reef, when disturbed, will suddenly transform from showing hundreds of bright red flower-like structures to just an aggregation of pure white tubes.

Serpulid reef aggregations are a priority marine features in Scotland’s seas and one of the main conservation objectives for Loch Sunart. A 2015 survey found that the loch’s small clusters of serpulids worms had deteriorated significantly. This is believed to be a natural event, and the worms will hopefully be monitored to see if there is a recovery.

Northern featherstar

Despite their appearance, Northern feather stars (Leptometra celtica) are animal. They are a species of crinoid, or feather star, related to starfish and sea urchins.

Their ten coloured (often yellow, white, or banded in red and white), slender, pinnate arms are used to catch their food, plankton and detritus from the waters that flow over them. In areas of current, they sometimes spread their arms out into a fan across the current. Where feeding conditions are good, northern feather stars can form dense beds, creating a carpet of gently swaying vivid colour on the seafloor.

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Northern feather stars are regarded as a deep water species as they are generally found at depths from 40 to 1000m. In a few parts of Loch Sunart, they can be found as shallow as 15m – perhaps reachable with just a snorkel, mask and a bit of experience!

They attach themselves to the bottom with 40 or 50 little, white legs called cirri. These are much longer than the other two species of feather star (Antedon petasus and Antedon bifida), which also live in the loch and down the west coast of Scotland and generally in shallower water. Occasionally northern feather stars will detach their cirri from the seabed, wave their ten arms and gracefully swim through the water column until they find somewhere new to settle.

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After that brief introduction to the three Scottish Marine Priority Features (S-MPFs) found in Loch Sunart, if you have any questions about them, please do get in touch.

We are currently planning a series of survey dives across Loch Sunart in 2021, and you may be able to get involved in these. If you’d like to be among the first to know about these, you’ll need to subscribe to our electronic newsletters.