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.
Tag Archives: Calliactis parasitica
aquarium update 12
It has been a while since I last posted an aquarium update; I have been a bit busy and have not done much with the tank recently. I have not done any water changes, never use the skimmer but have had zero algae because I have kept the light level low. I have experimented a bit with various seaweeds but nothing thrived. The Chrysemenia was doing well growing on the Tunze pump but disappeared overnight. Kelp always does well when attached to the pump. The tank is still a bit bare so no ‘full tank shot’ but some inhabitants below. I collected some Parasitic anemones Calliactis parasitica attached to an empty shell figuring that a not so pretty species might be actually quite hardy. Turns out they just stayed a bit limp and I therefore returned them to the sea.
The Tompot blenny is a real character, very alert and always hungry. If you stick your finger in the water he immediately comes and nips it. The small scallop remarkably survived over the summer (remarkably because there is almost nothing to filter from the water) but the hungry Tompot ate it in the end (like most other snails). As the snails were not going to last long anyway, I introduced two small Common starfish Asterias rubens and two small Spiny starfish Marthasterias glacialis. They are usually hidden but that makes it extra fun when you spot one. The Cushion star Asterina gibbosa of course remain unperturbed and are always on the prowl. I noticed a tiny offspring (<2 mm).
Cornish Coral
A couple of weeks back I went for a boat trip and snorkel over Maerl beds with friends on the other side of the Fal Estuary, just north of St. Mawes. I did not post about it at the time, as my photographs were quite crap and I reckoned I could go back to try and come home with something better. However, there hasn’t been any time for that, nor will there be in the near future, and as it was such a cool experience I reckoned it would be nice to write a little post about it for now anyway. The beach was fringed with sea grass, but the Maerl beds started very near the coast, at around two meters depth at low tide. Maerl is something special; it must have taken early biologists a while to figure out whether it was mineral, animal or plant. It is actually a calcareous alga that (very slowly) grows in fist-sized nodules or thalli. The Fal and Helford estuaries are one of the few places in the country where it occurs, and the Maerl beds here are under threat of dredging. Although Falmouth has the third deepest natural harbour in the world, big cruise ships cannot land close to the town centre which makes it unattractive for ships to stop. Falmouth would be a very pretty last port of call sailing west and cruise ships are of course good for business, hence the dredging plans. I will save the debate on economy versus conservation for a future post, as it will require a lot more text. I was able to take some pictures of the Maerl with my old Canon Powershot in plastic housing before the new batteries decided to quit on me prematurely:
As you can see the Maerl really looks more like a coral than a seaweed (and dead pieces of Maerl form a type of coral sand, see here and here). It provides an ideal structured habitat for all kinds of organisms to live in and on (for instance fine seaweeds and snakelocks anemones). Besides various fish, crabs and sponges and small things darting to safety in general, we saw a big hermit crab in a Buccinum undatum shell with the large anemone Calliactis parasitica on top. Very cool, and apparently not very commonly encountered (this was of course after my batteries had run out). What was striking as well, were the very large (one of them measured half a meter across), very fat and very pale Spiny starfish Marthasterias glacialis:
Maerl with a sponge growing through it (or possibly the other way around):
Maerl is protected, so not an option for the aquarium, although I am sure it would make for a fantastic looking display (moreover potentially a very stable display as Maerl is not seasonal but grows for centuries). Hopefully more and better pictures later this year!
An Bollenessor 