Last Wednesday I went for a sneaky worktime dive across the Fal estuary on the Maerl beds between St Just in Roseland and St Mawes. Maerl is a slow growing, calcified type of seaweed (looks more like coral) which forms a unique and quite rare habitat, see these older posts. The water was 17°C so nice and comfortable and it was probably the shallowest dive I’ve ever done, no deeper than 3 meters. I took my new Canon G16 in a Fantasea housing and went all semi-pro by adjusting the white balance first (not that I had a go at any other settings…). I was really pleased with the results, a world of difference to the Canon D30. The beds are an expanse of maerl nodules with very little to break it up, no rocks, no sand, just the occasional old bottle and so it is hard to get any exciting angles. Still there is always something to see. In order: a baby Smallspotted catshark Scyliorhinus canicula, a Spiny starfish Marthasterias glacialis, a (breadcrumb?) sponge, a closed-up Snakelocks anemone Anemonia viridis (a rare sight), a Parasitic anemone Calliactis parasitica, a Fan worm Myxicola infundibulum, a Harbour crab Liocarcinus depurator, a Velvet swimming crab Necora puber and a very well-camouflaged Spider crab Maja squinado.
The weather was not great last weekend and we were too late at the diveshop on Saturday to be back in time to get the tanks refilled for a dive on Sunday but the one dive was (as always) worth the effort! We took dive buddy Chris’s boat from Loe Beach in Feock over to the other side of the Fal Estuary (between St. Just and St. Mawes) to explore the Maerl beds. See an earlier post on a snorkel trip to see this bed of ‘Cornish coral’ for some more background information. After the usual faffing about with equipment on board we plunged in the water. I took a single photo of the boat which turned out quite dramatic:Although we were diving 1-2 hours before high water (the best time, as clear seawater is pushed in the estuary), the visibility was quite bad. After going just a couple of meters down, fields of maerl loomed into view (the dive was really shallow, 5.9 meters max I think!). There were quite a lot of Thornback ray Raya clavata egg cases (foreground first picture) but we did not see the rays themselves. There are two main Maerl genera around here, Phymatolithon and Lithothamnion but their growth forms are varied and there are other encrusting Pink paint weeds that could look similar. We saw a number of golf balls that were completely covered in coralline algae, quite cool.We saw a couple of *very well* camouflaged crabs sitting about. They were completely covered by sponges, coralline algae and seaweeds. There are a number of crab species shaped like this but most of them seem too small. Best guess is th
e Toad crab Hyas coarctatus the Europan spidercrab Maja squinado in a particular extravagant mood. There are lots of little things hiding in the Maerl; gobies (rock gobies I think), squat lobsters, swimming crabs, hooded prawns and things that hide faster than I can identify them. I noticed a dainty little prawn sitting about which is probably Thoralus cranchii, although it could also be Eualus occultus (second picture is cropped). Swimming crabs were common and probably mostly were the Harbour crab Liocarcinus depurator. The first picture was the only one with flash and shows the Maerl colours a bit better. The second photo shows a Velvet swimming crab Necora puber under a snakelocks anemone sitting on top of a bottle. This species can be very commonly seen rockpooling. Lastly an empty shell of the largest European sting winkle Ocenebra erinaceus I have seen so far and probably the largest sponge I have seen so far too (with a human head for scale).