Sunday, 24 February 2013

Freediving at the Menai suspension bridge


I had been to try and dive by the suspension bridge in the Menai Strait before with little success. I went at low water but the current was extremely strong and the area I was in composed of thousands of tennis ball sized rocks covered in barnacles with little else. This video shows that dive (http://www.youtube.com/watch?v=3At4Eq6CH1s).

However during Friday lunch break I went there again with Ryan Mowat with much more success. Part of that success was working out when slack water was, which is not the same as time of high or low water in the Menai Strait. To over simplify it the time of lowest current velocity is roughly 2 – 1 ½ hours before the time of High or Low water. This video shows some clips from that trip.



Going at slack water is important for a safe dive where you’re not drifting away, visability is likely to be better and it means less fining against the current potentially giving longer dive times. Ryan suggested diving down a subtidal cliff on the South side of the bridge and it was a great spot. The vis was about 3 m but we had lots of amazing sessile epifaunal to look including incrusting and branching sponges, large and abundant Dahlia anemones and deadman’s finger colonies. Motile organisms included lots of common starfish, edible crabs, velvet swimming crabs and small spider crabs amongst the sponges. There were no doubt many other species which I did not observe. I always regret not staying in one post and looking for smaller organisms, I so often pass over areas looking more generally at what is there.  It was 5 – 6 degrees C probably and I reached a max depth of 7 metres during my dives but depth was not the objective of the dives. 

Dahlia anemones in the Menai Strait

Common starfish foraging among breadcrumb sponge in the Menai Strait

Common starfish, sponges and an edible crab in the Menai Strait

Dahlia anemones in the Menai Strait

Common starfish feeding amongst breadcrumb sponge with a velvet swimming crab at the bottom. Menai Strait

The finger like structure is either the sponge Haliclona oculata or the bryozoan Alcyonidium diaphanum.   

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