(Read part 1 here)

In the second part of our World Seagrass Day blog marine ecologist, Isabel Key, looks at the importance of seagrass beds for wildlife above the surface. She reveals what she heard when listening to these underwater meadows and considers some of the emerging technologies helping us to monitor and collect data about this vital habitat. Issy is working with NatureScot until the spring on a PhD Internship.

Birds above the blades

Seagrass doesn’t just support life underwater. Some birds feed on the seagrass itself; many others feed on invertebrates — worms, crustaceans and molluscs — that live among the leaves and sediment. Across the intertidal sites we recorded 20 bird species feeding within the meadows. There was evidence for wading birds, dabbling ducks/geese, and gulls preferring to feed in the seagrass compared to the neighbouring muddy areas. This evidence was especially strong for oystercatcher and curlew. Recognising the importance of seagrass as a feeding ground for birds could help strengthen management strategies to support struggling bird populations.

Twenty bird species were documented feeding in intertidal meadows – this included curlew that feed on invertebrates in the sediment, and wigeon that feast on the seagrass itself. The snails are Hydrobia which are very common in some intertidal meadows, and food for some birds. Illustration (C)Isabel Key.

Birds visit subtidal seagrass less often than they do the intertidal, so to study this interaction I set up cameras on the shore looking over the water surface. These cameras captured hunting activity of birds, otters and seals over the seagrass. At Skye, otters visited on average once every 24 hours, whilst shags were more frequent, arriving roughly once every two hours, with each visit lasting an average of two minutes. These charismatic predators are important members of the seagrass food web – understanding more about their feeding behaviour could give a great insight into the resilience of the ecosystem as a whole.

Shag hunting in seagrass, diving down vertically before swimming along the canopy (C)Isabel Key Remote camera set-up for spying on birds, otters and seals diving over seagrass meadows, (C)Isabel Key Listening to the meadows

Most of this monitoring relied on sight. But what if we could also listen?

Many marine animals produce sound — to communicate, defend territories or simply as a by-product of feeding and movement. By placing underwater sound recorders in seagrass, we can eavesdrop on this hidden world.

Acoustic monitoring has exciting advantages. It can detect animals that are camouflaged or hidden; it works at night; and recorders can be left in place for long periods, allowing continuous monitoring with relatively little effort or disturbance.

In my study, I detected sounds likely associated with fish, crabs and other invertebrates. Interestingly, the number of different types of potential fish sounds (i.e. phonic richness) was linked to the fish diversity observed on video. This suggests that phonic richness could be used as a proxy for fish biodiversity. Fantastic!

However, we need to be cautious in our interpretation of sound recordings. Vegetation absorbs sound, so when animals are in a denser seagrass area, it may be more difficult to hear their vocalisations. Moreover, non-target sounds like boat traffic and wave noise can mask animal sounds, preventing them from being detected.

A surprise problem was noise from oxygen bubbles! During photosynthesis, seagrass releases oxygen, forming bubbles on the leaf surface. When these bubbles detach, they make ‘clicking’ sounds. These overlap with the low-pitched sounds produced by many fish, making it harder to detect fish calls during the day when photosynthesis is in full swing. This doesn’t undermine the promise of acoustic monitoring, but it does show that we must attempt to account for the effects of natural background sounds on any measurements we take.

A shore crab perched atop a HydroMoth (C)Isabel Key Bubbles of oxygen on a seagrass blade, with a snakelocks anemone (C)Isabel Key Looking ahead

Emerging technologies offer opportunities to make data collection more efficient. Advances in machine learning are making it easier to analyse large volumes of video and audio data; in the future, automated systems could help detect key species and track changes over time.

Interest in protecting and restoring Scottish seagrass is growing rapidly. Alongside this comes an increasing need for effective, coordinated monitoring. There is momentum in Scotland and across Europe to align monitoring approaches, ensuring that data collected by different groups can be compared, leading to more reliable conclusions overall. As guidance develops, it will be crucial to prioritise methods that are robust but also accessible. A coordinated and collaborative approach will help maximise the effectiveness of protection and restoration efforts, and help us collectively become better guardians of our seagrass meadows.