Sunday, August 14, 2011

Sex and the Single Gastropod

I adore the seaside. I love collecting bags of shells, seaweed, driftwood, broken bits of crabs and feathers. Anything really.

Brancaster in North Norfolk has a wide expanse of sandy beach, perfect for beach-combing. The Brancaster Estate is owned and managed by the National Trust. We serendipitously met, and had an interesting and informative chat with the local NT coastal warden, Keith Miller. What a great place to work.

Parking was £3.50 all day in the private car-park (there is no NT car park here) next to the famous Royal West Norfolk Golf Club, right by the beach (and next to public toilets and an ice cream shop; all you need really). 

I was a bit non-plussed as to what to do. Brancaster has some fabulous habitats to explore; salt marsh, dunes, dune slacks and beach. Too much choice! But the beach looked inviting, despite the fierce wind and patchy drizzle. 
From the beach, the wreck of the SS Vina is clearly visible (at full zoom) on a sand bar with its black spheres, the marker for isolated danger at sea.
SS Vina was a coaster working the Baltic trade routes from the East coast, until the war when she was requestioned and eventually ended up, in 1944, rather ignominiously being used for target practice. She now lies rusting off the Norfolk Coast, too expensive to do anything about now.

So time for some serious beach-combing. Trouble is I'm a bit out of my depth when it comes to identifying what I find. I can do the basics like limpets and cockles, but then things get a rather hazy. Here's a selection of finds.

I managed razor shell, tentatively identified here as Ensis siliquia, the pod razor shell. The live animal lives under the sand and has a hydraulic foot which anchors it in place.

What I believe is, another sand-burrower, the blunt gaper, Mya truncata...
...with its spoon-shaped process (a chrondrophore) on which the internal ligament attaches, visible in the photo below.
The European oyster, Ostrea edulis. Here the lower, saucer-shaped valve...
...and here the flatter upper valve.
The spiral shell of the common whelk or buckie, Buccinum undatum
The whelk is a fearsome predator, if you are a cockle, anyway. It attaches to a cockle shell, then either asphyxiates it or just forces the valves apart, in order to dine.

Near the water's edge were hundreds of worm casts, most likely from the lugworm, Arenicola marina.

Don't let these little sand casts or the fact that lugworms rarely leave their burrows fool you into thinking they lead dull, lugubrious lives. Lugworms are hermaphrodites. More specifically they are simultaneous or synchronous hermaphrodites: individuals have both male and female sex organs at the same time. In the case of the lugworm the eggs are fertilised by sperm from another individual. How? Lugworms have an annual sex jamboree in October, called a genital crisis. So they must be starting to get a bit excited about now, it being mid-August; only 2 months to go. They all release their eggs and sperm at the same time, into the water above, where the eggs are fertilised. Amazing.

Staying with the sex and hermaphrodite theme, here is a blue mussel (Mytilus edulis) carrying an entire habitat on its back, including a most interesting hitch-hiker. Mussels are not sand-dwellers, they attach to firm substrates and are filter feeders. This one must once have been anchored off the coast on rocks. 

On this empty mussel shell are barnacles, brown, red and green seaweeds, bryozoans (the white encrustations) and......slipper limpets (Crepidula fornicata).
Slipper limpets are gastropods. The name Crepidula fornicata might raise a few eyebrows in Victorian sitting rooms. Crepidula is from the Latin for a small boot, from the shape of the inside of the shell (see photo below).  Fornicata is from the Latin fornix, an arch or vaulted chamber. Roman prostitutes plied their trade under arches. Hence the word fornication, which essentially means, I suppose, sex under the arches. Crepidula fornicata is a small arched boot. Which sounds a bit dull.
Not a bit of it. These little gastropods actually have gripping sex-lives. They are hermaphrodites but with a difference: they're sequential hermaphrodites: born one sex and change to another. They are gregarious and tend to form stacks, with shells piled one on top of the other. The largest animal, at the base of the stack is female. The smaller ones on top are male. In my photo (above) a small (probably male) shell is on the back of the larger (probably female) shell. All on the back of that poor old mussel. If the large female dies, the largest male will become female. They are thus protandrous; they start male, and become female. Enthralling little creatures.

The tide was coming in fast and I was getting into very choppy waters with my shell id. I'll only venture a few more. The common cockle Cerastoderma eduli, which must live in fear of those carnivorous whelks.
This is, I think, a piddock shell, possibly Pholas dactylisa creature that incredibly emits a luminescent green light in its burrow!
Hornwrack, Flustra foliacea.
And what may be a battered cat-shark (Scyliorhinus spp) eggcase.
All the while the wind was blowing relentlessly across the beach. 
I feel the need for something a little more botanical to finish, as this is primarily a botany blog. It's a tenuous link, but here is the fishing vessel Speedwell, painted appropriately blue, temporarily grounded as she heads home on the rising tide.
Any corrections to my tentative identifications above, will be most graciously and gratefully received.

Bibliography and Sources of Information
Campbell AC (1988) The Country Life Guide to the Seashore and Shallow Seas of Britain and Europe. Country Life Books.
I found this amazing website about British bryozoans, a much neglected group of minute but intriguing organisms.

The Field Studies Council has a website here, for identifying organisms found on the seashore.
***The National Museum of Wales website here is a fantastic resource for identifying marine bivalve molluscs. It looks good, is easy to use and is comprehensive, covering not only identification but ecology***  
The Natural History Museum has a website that deals with British seaweeds here. There are also details of the Big Seaweed Search on the site as well, downloadable recording forms and an id guide. 

2 comments:

  1. Thanks for leaving a comment Mel and I thought I'd come and have a look at your postings, great posting and love the seaside exploration, not often seen on blogs. I'll be back and if you're interested Malham will be broadcast this Sunday 21st Radio 4 at 06.35am.... I know, the i-player is better :-) Andrew

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  2. Hi Andrew. Thanks. I've noticed not many bloggers go beach-combing, yet such a goldmine of fascinating things to find and stories to tell. I will listen to the Malham broadcast with great interest...and yes, I do prefer to use iPlayer ;-) Mel

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