Usually summer allows me to keep in touch with the practicalities of working in the challenging marine environment, as well as a very welcome opportunity to escape the office for some fresh air.
So here are my memories of an annual expedition to CCW’s monitoring site on the extensive Horse Mussel Reef off the Llyn Peninsula. This reef forms part of the Pen Llyn a’r Sarnau Special Area of Conservation (designated under the EC Habitats Directive) which requires regular monitoring to report its environmental condition.
The journey
It was an early morning start as we rendezvoused at Fellinheli marina where Pedryn our survey vessel was moored. There was a lot of hustle and bustle as the crew gathered and the kit was organised on board.
After a safety briefing, we set off, heading south down the glacially carved Menai Strait. Tides and timing are crucial on these expeditions. We needed adequate water to get us over the lip of the marina and across the sand banks at Caernarfon, to arrive at the dive site and catch the slack tide.
And it was a glorious morning. The glassy water of the Menai Strait carried perfect mirror-like reflections of the marginal trees and flimsy wisps of mist hung over the green fields of Ynys Mon. We sneaked over the treacherous Caernarfon Bar with everyone focused on the shallow water depth readings on the echo sounder.
Paul, our Skipper, said “there’s no turning back now”, as we stared into the open water of Caernarfon Bay and the oncoming tumbling waves. He went on to describe how, on the previous day, the waves broke over the roof of the cabin at this point in the journey. Thanks Captain.
Dragonet fish at Horse Mussel Reef
Pedryn picked up speed and skipped over the wave tops, just like the Storm Petrel after which she was named. On board we followed the silhouette of the Llyn against the rising sun and as we approached our objective, the divers struggled into their dry suits in the small cabin.
Sauntering onto the deck, they donned their external armour of additional equipment (weight belts, dive cylinders, regulators, goggles, snorkel, monitoring quadrats, camera’s) and lumbered to perches on the inflated sides of the boat.
The arrival
We had arrived at the correct GPS coordinates for the monitoring site. A button was pressed on board and the inflated orange automatic site marker buoy emerged on the brilliant blue sea surface. The installation of these markers at our monitoring sites saves a lot of precious dive time as the buoy line leads directly to the monitoring station on the seabed.
A monitoring 'quadrat' is used to estimate the abundance of species within a 1-metre area
Scientific diving is a strictly regulated activity carefully planned in advance, over seen by a dive supervisor, with each diver carrying wrist watch-like dive computers. These record the duration and conditions of the dive. At this site it is an intensive exercise as each diver has a short amount of time to carry out a specific task at a relatively deep depth, around 30m. Absolute concentration is crucial.
Ready to go, our crew finally readied themselves for the plunge. In an instant, six divers plop heels over head backwards into the welcoming water – and with an upward flip of their black fins, they are gone.
The boat suddenly felt more spacious, and we could chat in comfort without the noise of the revving engine. Being left to bob around on the undulating wild blue sea surface, even for a seasoned sailor, can be a challenge to the senses. It is always wise to have a few chocolate or ginger biscuits at hand, as an antidote to nausea. So we made a cup of tea, and waited.
About 30 minutes later the bubbles of the surfacing divers were being located by all on board. From the glassy waters fins were suddenly thrown on board, and our diving team ambled up the ladder at the rear of the boat.
“Mission accomplished.” “No problems”. “Visibility was good.” “I would like to do that again!”
But what did they see?
The living reef
A horse mussel reef is a splendid and ancient underwater environment.
The living reef is formed from large wave-like mounds of shells up to 1-metre deep, and it is credible that this reef has survived off the Llyn for at least the last 150-years but more likely much longer.
Individual mussels on this reef can live for around 40 years. Each shell is attached to its neighbour by threads, and together these carpets of horse mussel shells play an important role in stabilising the sediment on the seabed and filtering the water – thereby helping to keep our seas clean.
A wandering Octopus wants in on the action
Lots of other animals are crammed into the nooks and crannies created by the horse mussel shells, creating a true biodiversity hot spot. The arms of brittle stars wave above the reef surface, while fluffy white Deadman’s Fingers poke through the crust.
Looking closer still, you can spot the breathing tubes of sea squirts while squat lobsters, hermit crabs and spider crabs scuttle about and dog whelks and starfish prey on their neighbours.
One of our team, Rohan, remarked on an octopus that seemed determined to make monitoring history. He replayed the video recording on the camera so we could see it, crawling out of the gloom into the monitoring quadrat – which is used to estimate the abundance of species within a 1-metre area.
The monitoring images and the data derived from them allow us to understand the structure and functioning of this living reef, and advise on its future management.
Once the divers were relieved of their dive cylinders and the kit was safely stored, we turned for home. It had been a rewarding expedition.
However, while the mental cobwebs were totally blown away by the invigorating ride back to Fellinheli, it was something of a struggle to settle in front of a computer for the afternoon!
