When you think of coral reefs your mind probably pictures white sandy beaches, clear blue waters and blistering heat. What you probably don't picture is the cold and dark waters of the UK - but you would be mistaken, there are in fact corals dotted around the UK! These cold-water corals are just as important as their tropical counterparts and shouldn't be overlooked, so in this post, we will deep dive into the world of the UK's cold-water corals from how they differ from warm-water corals to the conservation threats they're facing.
How do cold-water corals differ from warm-water corals?
Corals in deep waters make up approximately half of the 5,100 species of coral alive today! However, due to the harsh environment, cold-water reefs usually comprise of just one or two different species, unlike warm-water coral reefs which can have hundreds of different species on one reef.
Cold-water corals live in deep waters with little, if any, light available. This lack of light means cold-water corals don't have light-dependent symbiotic algae, like warm-water corals. The algae on warm-water corals produce oxygen, through photosynthesis, for the coral to use and in return, the coral provides the algae with a protected environment, this mutualistic relationship helps them both to survive. Without this algae, cold-water corals have to use another technique to get the nutrients they need to survive. They do this by feeding solely on capturing suspended particles in the surrounding water by extending their stinging tentacles and catching plankton, krill and other small crustaceans. Cold-water corals grow at a much slower rate than warm-water corals, they grow at around 4-25mm/year while warm-water corals can grow up to 150mm/year. This difference in growth rates is likely due to warm-water corals living in more nutrient-rich water and their mutualistic relationship with algae.
Cold-water corals are found in water temperatures between 4 - 13 degrees celsius and at a depth range of 39 - 1,000+ meters, in comparison, warm-water corals are found between 20-29 degrees celsius and 0-100 meters. Although cold-water corals global coverage is not fully known, it is thought that their global coverage could be equal to or even exceed that of warm-water reefs, which have global coverage of 284,300km².
The distribution and habitat conditions of the UK's cold-water corals
The main species of cold-water corals found in UK waters is Lophelia pertusa. Cold-water corals have been found off the west coast of Scotland at depths of around 200 - 400m, with a shallower reef being located around 150m near Barra and Mingulay, Scotland. This shallower Scottish reef covers 100 sq km and is thought to be over 4,000 years old! Not all of the coral colonies around Scotland are from thousands of years ago, some are thought to be just 5 years old, which suggests these cold-water corals are still in active growth. Cold-water corals are also found around Ireland and a few colonies near Plymouth.
The distribution of cold-water corals around the UK.
(Freiwald A, Rogers A, Hall-Spencer J, Guinotte JM, Davies AJ, Yesson C, Martin CS, Weatherdon LV (2017). Global distribution of cold-water corals (version 5.0). Fifth update to the dataset in Freiwald et al. (2004) by UNEP-WCMC, in collaboration with Andre Freiwald and John Guinotte. Cambridge (UK): UN Environment World Conservation Monitoring Centre. URL: http://data.unep-wcmc.org/datasets/3)
Environmental Importance of cold-water corals in the UK
You may think that because cold-water corals are found at such deep depths they might not be as integral to marine ecosystems, but you'd be wrong! Lophelia pertusa plays a key role in providing cover for fish, it does this by creating a three-dimensional habitat in deep waters that can otherwise lack shelter for fish. A study found that fish species richness and abundance was greater on the reef than in surrounding areas, a whopping 92% of species and 80% of individual fish were associated with the reef. This is likely due to Lophelia providing feeding grounds, shelter from predators, breeding and nursery habitats for these fish. Not only do these reefs benefit the species abundance and richness of fish in these deep waters, but they also support commercial fish stocks - 68% of the fish species on Lophelia were of commercial importance. Cold-water corals aren't as heavily researched as their tropical counterparts, but the research that has been done suggests that they play just as an important role in deep-water ecosystems. As deep-water research technology improves and becomes more accessible it's only a matter of time before more research on these cold-water corals is carried out, we just need to make sure they are still around for when it does.
Conservation issues surrounding cold-water corals
Cold-water coral ecosystems have been around for years, with some dating back 8,000 years. These corals are slow-growing and fragile, Lophelia is recorded to only grow between 4 to 25mm per year, this slow-rate means that reefs that suffer from physical damage could take hundreds of years to recover! Trawling is a huge problem for these cold-water reefs and involves dragging large nets along the seabed, usually to fish bottom-dwelling species. This type of fishing is highly destructive as large areas are ploughed through in a short time, destroying everything including sponges, coral, fish and other marine animals, leaving behind lines known as 'trawl scars'. The damage caused by trawling was not evident for a long time due to the practice taking place in deep water, lending itself to 'out of sight out of mind'. However, it's damage to cold-water coral reefs is evident on almost every reef that has been surveyed. Once an area is trawled and the coral is disrupted recolonisation can sometimes happen, however, it would take decades or even centuries before the same level of habitat complexity in mature reefs would be achieved. Trawling is just one of the conservation issues surrounding cold-water corals; sadly, like warm-water corals, they are also negatively impacted by ocean acidification, pollution and rising sea temperatures.
Is there a future for these reefs?
Awareness surrounding cold-water corals has increased in the last couple of decades, as deep-sea surveying techniques have improved and become more accessible, the importance and the health of these reefs have been surveyed. This research has led to laws being introduced to the UK to protect are cold-water corals. In 2004, the UK banned trawling on the Darwin Mounds, Scotland to protect the reefs east of Rockall. Additionally, the reefs in East Mingulay are included in a Marine Protected Area, for being a Special Area of Conservation.
These protective laws are a great first step towards safeguarding our cold-water corals, however, no amount of laws or Marine Protected Areas can prevent these corals from feeling the effects of global warming. Corals, like nearly everything else on the planet, are suffering because of the rapidly rising temperatures. In order to protect not only cold-water corals but many other species, we have to start shifting our way of thinking towards a greener way of living and supporting companies and people that align with our environmental beliefs. We've only just started to scratch the surface on the importance of these reefs, it would be devastating if they were destroyed before we got a chance to fully discover the wonders they hold!