The Underside of Rocks

Yesterday I went rockpooling at Ob Lusa as previously arranged with Neil. Finding Stephen and Wilma already inside Neil's car was a very pleasant surprise. I clambered in and we set off on our 'family outing' as I called it, though I'm not entirely convinced Wilma appreciated me calling her 'mum'.

Ob Lusa is a site I've driven past umpteen times but never visited before. It wasn't the most exhilarating rockpooling session we've ever undertaken, but it turned up a few decent bits and bobs. I could see rock ledges a little further out, mostly hidden beneath the waves. I may well visit again, but I think it would need a proper super-low tide to reveal its full potential. Or I could try snorkelling. My boss has a wetsuit that he will never use again, he probably has flippers somewhere too. On the other hand I might not, my one and only panic attack happened during my first (and last) attempt at snorkelling in the sea.

We found a few biggish things, but mostly it was time spent turning rocks to see what was hiding beneath. Fish included a couple of Eelpout, several nicely marked Worm Pipefish, a few Butterfish and this sizeable Rock Goby.

We're gonna need a bigger pot...

Neil has a keen eye when it comes to spotting tiny things on the underside of rocks, but in all fairness you'd have to be heavily visually impaired to have overlooked the Sea Gherkin that he found, it probably being the largest specimen I've ever seen.

Sea Gherkin with a lovely colour morph Harmothoe imbricata

I casually quipped that somebody must have been desperately hungry to have discovered that these slimy white blobs taste just like a gherkin. Judging by their look of mild horror, I think I convinced at least one person that I was being serious.

The tunicate (sea squirt) Ascidiella scabra. They aren't often as beautifully red as this one

A Long-clawed Porcelain-crab. We didn't find any Broad-claweds at all - very odd!

Neil, true to form, found something I'd never heard of before. He called out a name and I just stared back blankly. Say what? This is his discovery, a brand new species for my PSL.

It's the white rounded structures amongst the Spirobranchus tubes

Each structure is a colony of Plagioecia patina, a species of cyclostome bryozoan. They form these calcified structures and the underside of this particular boulder had maybe twenty or thirty individual colonies. Despite searching for a couple more hours, these remained the only ones found. Why just that one boulder, why not others nearby? The Spirobranchus were commonplace beneath many rocks, so why not the bryozoan? It's a mystery to me. As are the species in the following two images

I see this (sponge?) often, but I've never nailed the ID

A transparent solitary sea-squirt, species unknown

Sometimes it's difficult to even know what family something belongs to; is it a bryozoan, a tunicate, a sponge, or something else entirely? You'd think I'd be getting better at this by now, but it seems that every day at the shore really is a school day. Happily I can recognise a scallop when I see one.

Chlamys varia the Variegated Scallop attached to the underside of a rock

This gorgeous thing is a Tortoiseshell Limpet Testudinalia testudinalis

Note the green-coloured mantle around the inside rim of the shell

Neil told me about the green colour of these Tortoiseshell Limpets then flipped this one over to show me. Yup, no denying it. He really does hold the weirdest knowledge inside that head of his!

Starfish regeneration in action! 

But not everything was attached to the underside of a rock, some of it was attached to weed in the water column.

These are Colpomenia peregrina aka the Oyster Thief

This beautiful thing is Diplosoma listerianum, a colonial sea-squirt

Colonies of Obelia dichotoma, a hydrozoan (the jellyfish family)

I took these back to examine beneath the microscope. The branching pattern, side branches forming in the axils, petiole lengths and the shape of the bell housing the medusoids all helped separate it from the far commoner Obelia geniculata. This was my second lifer of the day, found without the aid of eagle-eyed Neil for once. Nobody else on the PSL site has recorded this species, but I suspect this is simply because nobody is keying these tiny wispy things out rather than it truly being a rare find.

Bit of an underwater chase going on whilst trying to take pics of this Hyas coarctatus

Eventually the tide turned and we were pushed off of the rocks and back onto the sandy beach. Masses of empty Sea potato husks were rolling in the surf and an occasional squirt of water at our feet revealed the location of razor clams. I tried to dig one up by hand, but they are fast and dig deep. No joy, I shall need to bring a spade one day and add a razor clam (any species will do!) to my PSL . 

I had a quick tot up, it seems that so far this year I have recorded a total of 128 species during my rockpooling sessions. That's not including any plants, mammals, birds or lichens seen whilst at the shore, just the actual rockpool denizens themselves. Broken down it consists of one species of cyanobacteria, 21 'seaweeds' and 106 species of marine animals. Cool, I'm happy with that!