It is 9 years (last month) since the South Arran Marine Protected Area was established, and COAST brought news of NatureScot’s recent research into the MPA (conducted from the RV COAST Explorer in 2023). The summarised results report that “Although no signs of increases in maerl bed extent, distribution, and live maerl coverage was detected, this was expected, given the slow recovery of maerl*. No deterioration in maerl bed condition was noted, and although further statistical analysis is needed, the initial results of this survey suggest that the biodiversity of the maerl beds may have increased since 2014. Overall, the results are positive, indicating that protection has prevented further deterioration of the maerl habitats around Arran.”
*Did you know – it takes maerl 10 years to grow just 1cm! Meaning maerl that has been growing since COAST started has only grown 3cm!
The following blog by NatureScot explains more. Featured image: Dense live maerl with bivalve shells at South Arran MPA, ©NatureScot/Lisa Kamphausen.
A living seabed: monitoring maerl in the South Arran MPA
Western Scotland’s famous white beaches are made not of coral but of fragments of dead maerl, crushed by the waves and bleached by the sun. Living maerl is a purple-pink hard seaweed that forms spiky underwater ‘carpets’ on the seabed, known as maerl beds. These beds provide vital shelter to many and varied marine creatures. Their protection is crucial to managing our seas wisely. Maerl is an extremely slow-growing species and beds can take many decades to recover from damage, Rie Pors, from NatureScot’s Marine Survey & Monitoring team, looks at the research taking place at one of Scotland’s Marine Protected Areas (MPAs) to assess changes in this important habitat.
What are maerl beds?
Maerl is a type of red algae, which forms pink coral-like fine branches, lives unattached and forms extensive beds that are full of life. Different species of maerl are found all over the world – from the equator to the Arctic. In Scotland, we predominantly have three species of maerl: Phymatolithon calcareum, Lithothamnion glaciale and Lithothamnion corallioides (NatureScot CR 406: Descriptions of Scottish PMFs). Maerl is long-lived and slow growing – Scottish maerl has been found to grow less than < 1 mm per year, with individual pieces older than 100 years, and beds that can be over 4000 years old! Maerl beds provide many important functions for nature, including essential habitats for fish and other species (as nurseries and spawning grounds) and long-term storage of organic material to support blue carbon storage.
Due to its slow growth, maerl beds recover very slowly if disturbed or damaged. Each bed recovers at different speeds – this is dependent on the species composition and environmental factors of the individual beds, and the extent and type of impact the bed has experienced. Recovery is expected to take decades, if recovery occurs at all. Detecting growth and recovery of maerl in the field is difficult: it has been suggested that detection is only possible over periods of more than 20 years. Current and future survey work aims to trial other ways to detect changes in the short to medium term. Find out more about maerl on our website.
South Arran Marine Protected Area
South Arran MPA was designated in 2014 and encompasses the Lamlash Bay No Take Zone (NTZ), which was previously designated in 2008 following a campaign led by the Community of Arran Seabed Trust (COAST). Various levels of fishing restrictions were put in place in 2015, ranging from the area of the original NTZ, where all fishing activity is prohibited, to areas where trawling and dredging are restricted or prohibited.
Map showing the extent of the South Arran Marine Protected Area (MPA) together with fisheries management zones and 2023 survey site locations.
South Arran MPA was designated for the protection of maerl beds, along with seagrass beds and five other seabed habitats and species. Survey work at this site has focused on assessing the condition of maerl beds, which are in ‘unfavourable condition’. The conservation objective or aim for maerl beds in the South Arran MPA is to ‘recover’ maerl beds to ‘favourable condition’. The maerl habitats around South Arran include maerl beds, as well as areas of maerl gravel, which make up part of another protected feature, ‘Kelp and seaweed communities on sublittoral sediment’.
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