It's 8am on a misty, murky day in Scilly and I'm sat in the stern of the rib, bombing out across the water from St Mary's towards Great Ganinnick. Tom and Ricky from the Inshore Fisheries Conservation Authority (IFCA) are heading up the bow and we are all eagerly looking forward to the day ahead. Why's that I hear you ask? (If you didn't, then never mind as I'm excited and you're getting the answer anyway!) Well today, we're off to learn all about the green stuff that grows in the blue stuff...

No I've not entirely lost it (yet).  I'm talking seagrass!  Seagrass is a flowering plant which grows in marine environments, and is incredibly important ecologically for a whole host of reasons!  Seagrasses provide important habitat for wildlife, act as a vital carbon sink, and may even hold a role as a natural coastal defence...and Scilly is home to the largest unbroken expanse of Eelgrass (a species of seagrass) in England and Wales, making our little island home the perfect spot to study this ecological wonder!

Seagrasses underpin vital ecosystem services, providing blue carbon capture, coastal stabilisation and important sheltered areas for juvenile fish.

Photo: Natalie Rance

So that's exactly what we're dramatically jetting off across the water to find out more about.  We're en route to meet scientists from the University of Plymouth at their survey site just off the island of Great Ganinnick, who are working to quantify the role of seagrass as a natural coastal defence.  Seagrasses extract energy from the waves and currents that wash over them, thereby promoting the deposition of sediment, creating sandbanks and lessening the force of the waves reaching our beaches...in turn protecting them.  However, exactly how the moving seagrass fronds affect the waves, currents and sediment transportation and to what extent seagrass meadows help to protect our coastline is largely unknown...but these are the important questions that the core team of researchers and technicians from the NERC-funded BLUEcoast project are hoping to answer.  Their research aims to gain a better understanding of the interactions between seagrass and the water in which it resides, in order to inform and significantly increase the success rate of seagrass restoration and seeding projects, which currently is only estimated at a 30% success rate.

View of the University of Plymouth scientists temporary research vessel Seaquest from IFCA's rib.  The team had just removed a hydrodynamic rig from their survey site, as can be seen on the bow of Seaquest.  

Photo: Natalie Rance

The team delved in to their research, executing an extensive four-part approach:

1. Meadow mapping with YellowPig!

The study area was extensively mapped both from the air by drone, as well as from the sea surface using a USV (uncrewed surface vessel) called YellowPig!  YellowPig has an echosounder, as used in boats to emit a signal downwards towards the seabed, which is then bounced back to the USV and analysed to assess channel depth and composition of the seabed itself.  Using both a drone and YellowPig provided not only an incredibly accurate map of seagrass presence, but information of abundance and length of seagrass fronds beneath the surface!  The data collected suggested that regions of dense seagrass are associated with local areas of shallower water, supporting seagrass' sediment trapping ability!        

2. Sediment Sampling

The team collected over a whopping 100 sediment samples from both within and outside of seagrass meadows, as well as from the beach on St Martin's.  These samples will be analysed for both sediment texture and carbonate content to assess whether the sediments support the team's hypothesis that regions of seagrass represent relatively calm areas and areas of deposition, and as such sediment should be finer inside than outside seagrass meadows.

University of Plymouth's Coastal Research team at their temporary Research Station examining the project's main instrument rig. 

Photo: Peter Ganderton

3. Self-logging Sensors

A number of self-logging wave and current sensors were deployed around the large seagrass meadow north of Great Ganinnick.  The pressure sensors were deployed for two whole months in order to assess whether or not seagrasses filter waves and currents!  By comparing the waves and currents entering the seagrass meadow with those exiting it, the ability of the seagrass to extract energy from the waves and currents can be evaluated.  Thanks to the beautiful clarity of our waters here in Scilly it was relatively easy for the team to deploy and retrieve these clever little sensors!

Pressure sensors which record both waves and currents entering and exiting the seagrass meadow were deployed for a period of two months.

Photo: Peter Ganderton

4. A big old rig!

The team used a large rig equipped with a range of acoustic, electro-magnetic and optical instruments to collect incredibly detailed hydro- (water) and sediment-dynamic (how they move) measurements within the seagrass canopy.  The instrument rig was carefully prepared on Par Beach and carried into the water to be installed within a small seagrass patch just 100m from the low tide line.  The rig was connected to the team's tecchy mobile field laboratory by a 240m-long cable running from the beach to the field behind the dunes that the makeshift station was set up in!  Amongst others, the instruments measured detailed flow characteristics of the water right down at the sea bed, as well as the amount of sediment in the water column...and even seemed to prove pretty popular with the local bass!

On our trip out to meet the team we watched as they removed the vast rig from the water, diving in and manually hoisting the equipment up out of the water and onto the bow of Seaquest, the boat which became their research vessel for the duration of the trip.  This gave us a chance to get a better look at how the rig works.  Dr Gerd Masselink and Dr Daniel Conley, both researchers on the project gave us a quick brief on how the rig records both water and sediment movement within the seagrass meadow.

"So they have these three prongs at the bottom," explains Gerd as Daniel points out the branched three metal prongs at the base of the rig.  "I call them a bat underwater because they work on sound," Gerd continues.  

"It sends out a sound that gets bounced back," says Daniel.

"So it gives us wave currents and tidal currents.  The idea of the deployment is that one of them is on the upstream end of the seagrass meadow and the other is on the downstream end, and the idea is that you can record the slowing down of the current as it goes through the seagrass meadow," finishes Gerd.  

Very clever stuff indeed...to find out more about the team and their invaluable work check out our Instagram on @ScillyWildlife and look for the highlight titled 'UoP'.

A massive thank you to both the Coastal Processes Research Group and Coastal Marine Applied Research Consultancy Group of the University of Plymouth for having us along and giving such an amazing insight into your wonderful work!  Stay tuned for more coming soon...

Hydrodynamic rig deployed at one survey site to measure waves and currents. 

Photo: Peter Ganderton