(Read part 2 here)

To mark World Seagrass Day, today’s blog is from marine ecologist, Isabel Key. Issy is working with NatureScot until the spring on a PhD Internship. She is contributing to guidance on monitoring for ongoing SMEEF-funded seagrass restoration projects and to the upcoming update of NatureScot’s seagrass restoration handbook. Her PhD, at the University of Edinburgh, explored visual and acoustic approaches to assessing ecosystem health of seagrass meadows in Scotland; she talks us through her key findings in this blog.

Hidden beneath the waves in Scotland’s shallow waters underwater flowering plants form lush meadows that are every bit as important as forests on land. Seagrass meadows are home to a great diversity of marine life, protect coastlines from erosion, improve water quality by trapping sediment and absorbing nutrients, and store carbon, helping to slow climate change.

Unfortunately, across the UK seagrass has declined by at least 44% since the 1930s. Nutrient pollution, dredging and coastal development, as well as disease, have all taken their toll. For decades, these underwater meadows were out of sight and largely out of mind.

But the tide is turning. In Scotland, seagrass is recognised as a Priority Marine Feature and there is growing momentum to protect and restore it. Multiple restoration projects are trialing ways to replant seagrass and more areas are being proposed for protection from activities such as bottom-towed fishing gear. Communities, charities, policymakers, researchers and the private sector are all working together to bring seagrass back.

Protecting and restoring seagrass effectively isn’t easy, but improving our understanding of the current health of meadows is one thing that can help: it can help us understand why meadows declined in the first place, inform how and where to restore and protect, and measure the success of projects so that methods can be improved.

An intertidal meadow at Montrose Basin with a mixture of Zostera marina and Zostera noltii seagrass. (C)Isabel Key A subtidal meadow on the Isle of Skye featuring a juvenile pollack, two-spotted gobies and mermaids tresses seaweed. (C)Isabel Key Filling the evidence gap

When I began my PhD, there was limited information on seagrass meadow health across Scotland. Ideally, we need data across a range of geographic regions and aspects of ecosystem health. To achieve this, we need monitoring approaches that are scalable and accessible to a range of users, including community groups.

To help fill the evidence gap, I surveyed six seagrass meadows in the summers of 2022 and 2023 — three subtidal meadows (always underwater) and three intertidal meadows (exposed at low tide). With the help of wonderful field assistants, I used underwater cameras, shore-based cameras and sound recorders to build a picture of life in these bustling ecosystems.

A remarkably rich meadow

One result stood out immediately. A subtidal meadow on the Isle of Skye supported an exceptionally diverse fish community. Using baited underwater video cameras, we recorded around twice as many fish species and three times as many individual fish there compared to the other subtidal sites. In fact, fish diversity at this meadow was higher than has been recorded elsewhere in the UK using the same method. This highlights the importance of studying a range of meadows, including in more isolated areas, so that we don’t underestimate the life that Scottish seagrass is capable of supporting.

Gadoids and wrasse were significantly more abundant in seagrass than in sand-macroalgae mosaic control plots. The opposite was true for decapods (e.g. shore crabs) and demersal fish (e.g. gobies and flatfish) – this may partly reflect species’ preferences but may also be due to seagrass hiding these ground-dwelling creatures from view. Illustration (C)Isabel Key

Across sites, subtidal seagrass also supported significantly greater numbers of wrasse and juvenile gadoid fish (e.g. cod, pollack and saithe), compared to neighbouring sandy seabed. This suggests that the meadows are succeeding in their role as a nursery, providing food and shelter for young fish before they move into deeper waters. Gadoids are commercially important species, so this means that healthy seagrass today could mean healthier fisheries for the future.

Tomorrow, in part 2 of this World Seagrass Day blog, I’ll look at the importance of seagrass beds for wildlife above the surface. I’ll also reveal what I heard when listening to these underwater meadows and consider some of the emerging technologies that are helping us to monitor and collect data about this vital habitat.