Scotland’s seas are packed full of amazing life – the basking sharks that migrate to our west coast each summer are the world’s second largest fish, the Bass Rock is the world’s largest gannet colony and the cold water coral gardens on the Hebridean Slope hold some of the oldest living creatures on the planet. Some of the species that live in our seas are not just important in themselves; just like the redwood forests of the Pacific Northwest or the heather of our own peat bogs, they create and maintain the structure of our interconnected marine habitats. Here we look at where those species live, where they used to live and understand what the future may hold for them…
Healthy seabeds form the foundation of our seas. They are integral to its health and its ability to provide us healthy, sustainable seafood.
From vast forests of kelp, to shoals of sandeels, muddy sea lochs to cold water corals, Scotland’s seas are rich in life. These species form an interwoven web of life, the marine ecosystem. Together this connected web provides the living, breathing and working sea that delivers fish to our tables, provides water, oxygen to nourish our lives, and circulates and captures carbon dioxide in a way that helps stabilise our climate.
Scotland’s seas are home to ocean giants like the basking shark, humpback whales and even killer whales. However, when thinking about our seas, it’s worth also thinking about the smaller things that are less well known, make less of a splash, but are actually just as important. Things that live on the Scottish seafloor establish the foundation of all our marine life; they form an integral part of the way the seas function, by creating habitats for fish, shellfish and other marine creatures to spawn, grow up, live and hunt in.
Here, we want to showcase just a few of these crucially important seafloor species, and in particular take a look at their history in Scotland’s seas, and what the future may hold. Native oyster, horse, fan and blue mussels, serpulid reefs, flame shells, seagrass, maerl, gravels with burrowing sea cucumbers, cold water corals and Scotland’s seafan and sponge communities each play a key role in our seas. Telling their story gives an insight into the history of our seas more generally – and hopefully inspires us to think about where we can go in the future.
We’re particularly interested in these species and habitats because they form the backbone of the Scottish Government’s current approach to managing our seas. Along with another 70 odd species, they have been identified as “Priority Marine Features”, which, put simply, are some of the most important species and habitats in Scotland’s seas. Scotland has a National Marine Plan which was designed in 2015 and sets out the way we should make use of our sea and. When it comes to protecting the environment, the Plan dictates that any use and development of the sea should not result in significant impacts on these priority features. General Policy 9 is a planning policy just like the important policies that guide sustainable development on land.
Here we look at the role of each in underpinning the health of our sea, what has happened to them in the decades leading up to now and their current status, before considering what the future holds for such Scottish marine habitats and species as we hopefully move forward towards a more sustainable future.
Although you’ll regularly see oysters on the cold slab in a supermarket, or in posh restaurants, it’s normally the case that these shellfish are Pacific oysters, grown in oyster farms around our shores. European oysters are slightly different, they’re flatter and fatter, and unfortunately now much less common than their Pacific cousin.
As well as being a food source, oysters can play an important role in the way our marine environment works. In the wild they typically live up to 10 years and spend that entire time connected to the gravelly, stony bits of the seabed where they form large masses of interwoven shells. As they grow, mature, reproduce (each female generating more than a million eggs) and die, they begin to create a solid reef structure on the seafloor – an interconnected mass of shells which adds to the complexity of that bit of the sea. By filter-feeding the passing seawater they are also filtration powerhouses and help clean up the sea. A single oyster can filter 240 litres of water every day! Combined these effects create the conditions for a range of other species to thrive and survive.
Dense beds of oysters once carpeted our Firths and shallow seas, they are unfortunately now more often found as lone individuals, holding on in remote corners of our seas.
What happened to them?
Oysters were once very very common around Scotland’s coasts, huge beds were found in our wide eastern firths and sheltered west coast sea lochs. The Firth of Forth is widely known to have been the largest such oyster bed anywhere in the world, covering more than 150 km2. They were an integral part of Scotland’s seafood and were an important food source ever since our coastlines were first populated – archaeological surveys in the Inner Forth found that, not only were they consumed in huge quantities stone age forebears, the shells were sometimes used to build their homes!
A dredge fishery developed to harvest Scottish oyster grounds in the early 1700s using heavy rakes similar to modern day scallop dredges. Unlike today’s dredgers, these were pulled by four men rowing in a boat – sometimes singing ‘interesting’ songs about the oysters whilst they did so. By the late 1700s they were hauling as many as 30,000,000 oysters a year from the Firth of Forth alone, feeding thousands and creating a booming export market with the oysters being sold to London, Europe and beyond. Unfortunately the fishery was beset by problems and never properly managed and, although the fishers, councils, governments, the Crown and others all tried their approaches to keep the catch within sustainable limits, unfortunately none succeeded.
Boats began overfishing grounds, selling small oysters that had yet to spawn to foreign traders, and overexploiting each other’s grounds. The lack of any sensible management led to a collapse of the fishery and massive clashes between fishermen as they fought for shares of a smaller and smaller stock – groups from Newhaven and Cockenzie once fought fists, oars and clubs all the way from one side of the Forth to the other! The Forth, which once provided 30 million oysters a year, reduced to 1.3 million in 1870, 0.4 million by 1880s and only 1,200 by 1894. The beds were eventually so depleted and individual oysters so distant from one another that the species stopped being able to effectively reproduce and the species was lost entirely from the area. Similar stories played out around the rest of our coasts.
Where are they now?
Today there are no known records of native oyster remaining in the Firth of Forth. The only place where a sustainable wild fishery remains is in Loch Ryan on the west coast, where the loch was restocked in the 1950s and 60s, and the Loch Ryan Oyster Fishery Co established with strict management rules. Further work, underway right now and led by the Marine Conservation Society, scientists from Heriot Watt University and whisky distillers Glenmorangie, is hoping to also recover the beds in the Dornoch Firth, just as was done successfully in Loch Ryan. Isolated pockets of oyster beds and individual oysters remain in a handful of places. However, in each case these are now isolated and very small. Records can be found in the waters around Mull, in the sea lochs of Skye, Loch Ailort, and around in Orkney and Shetland. Nearly all are very near shore areas, often less than 5m depth, restricted by the fact that many of the areas of suitable habitat do not have good enough water quality or are regularly damaged by other fishery activities. There is growing momentum behind calls for widespread restoration for oysters around our coast.
Several projects are underway seeking to reintroduce and enhance native oyster reefs in the UK. We were fortunate to visit the Solent Oyster Restoration Project, which is working to improve recruitment of native oysters in the Solent.
Horse mussel beds
Horse Mussel Beds near Port Appin, Argyll. Video from Heriot Watt University’s Scientific Divers
Horse mussels look like giant cousins of the mussels you’ll find in the fishmongers – they are a huge mollusc! In Gaelic they are known as ‘clabby dhu’ meaning black mouth, a name referring to their gaping mouth which filters the passing currents and that can look pretty disturbing when seen underwater…
Where they cluster in a dense and big enough group, the complex matt of live and dead horse mussel shells starts to form a reef amongst which other small marine life takes hold and takes advantage of this horse mussel-created-habitat. Well established reefs provide grounds for a range of species, including cod and haddock, spider crabs, whelk and scallop spats. These species spawn and feed and spend their juvenile (and highly vulnerable) years in this habitat.
Horse mussel beds off the Llyn Peninsular in North Wales. Video from Cyngor Cefn Gwlad Cymru/Countryside Council for Wales
What has happened to them?
They once lived on similar grounds to oysters, found alongside oyster reefs in places like the Forth. Unfortunately, because they are fragile and highly vulnerable to being pulled out of the seabed by bottom-towed fishing gear, the expansion of the oyster dredge fisheries, and subsequent expansion of scallop dredge fisheries on their other grounds, removed large beds and has caused a significant decline throughout recent decades. The world’s largest bed was previously found Stangford Lough in Ireland, but patchy records show their distribution extended throughout the Scottish coastline, east and west, and stretched all the way north into Shetland.
Because they were not regularly harvested for food, we have fewer historical records than for oysters and know only a little about their historic distribution. However, where records do exist, such as in Ireland, the mismanagement of other fisheries (in the Irish case, their queen scallop one) has resulted in long term, significant declines to the horse mussels species and habitat.
A horse mussel bed in Loch Creran, providing habitat for a huge number of brittle sea stars and urchins, amongst others
Where are they now?
Unfortunately, stories similar to that in Strangford Loch played out around Scotland, significant hotspots now remain in only a few areas, including a small reef in Loch Creran, Loch Alsh, a very large reef off Wick in the North East of Scotland, one in the waters between Rum and Canna and several in the waters around Shetland. Several of these areas are now within the network of Scotland’s marine protected areas and protected from potential damage from scallop dredging or other activities (salmon farming may also have an impact). In Shetland, where the horse mussels are found in clusters considered dense enough, they are protected from Shetland’s scallop dredge fishery.
Data on the distribution of horse mussels taken from NBN Atlas. Note, not all data has been quality assessed – note also, some records indicate only isolated individual records. Data collected by Scottish Natural Heritage; Joint Nature Conservation Committee; Natural England; Conchological Society of Great Britain & Ireland; Outer Hebrides Biological Recording Project; Cumbria Biodiversity Data Centre; Seasearch/Marine Conservation Society; Porcupine Marine Natural History Society; Lorn Natural History Group; Marine Biological Association; Highland Biological Recording Group
Unfortunately, however, at the time of writing, the site which covers the waters between Rum and Canna remains entirely without protection and remains at risk to more damage. The smaller, isolated horse mussels found in the upper reaches of Loch Linnhe, toward Fort William, in the upper Clyde and in the waters around Skye, also remain without any protection leaving them potentially exposed to a range of threats, and the local future of the species therefore at potential risk.
Horse mussel beds provide important nursery grounds for a range of shellfish species, like this whelk
That’s all for now… much more to come in the coming weeks!