Digging for clams

On Saturday we worked a very lovely shore at Rochers de Dranguet.  Nick and I discovered this shore 2 weeks ago and had fun raking in a rather random fashion for whatever clams we might find.  On this visit, with a larger group of us, I wanted to try and refine this technique and also look more closely at the rocks and take a sample of the fine red seaweeds which grow on the rocks at low water.

Myriads of tiny organisms live in the fronds of these weeds and if we are to learn how diverse these weed faunas are and how their diversity varies from place to place and shore to shore we need to take a bag full of the weeds, soak them in fresh water for a few hours then sieve over a 0.3mm sieve to catch all the molluscs, crustaceans, and single-celled shelled foraminiferans that fall out of the seaweeds………….. and identify them.  To stare at these tiny, intricately structured animals through a microscope is to see the world at the level of a grain of sand.

Unlike hunting for shrimps, prawns, crabs and lobsters on the shore – which requires cunning and stealth – bivalve molluscs, otherwise known as clams are sessile which means they just sit quietly in the sediments hoping not to be noticed.  Inside the two shells is a body consisting of a foot, a mantle to lay down shelly material at the growing edge of the shell, some metabolising organs and two siphons to take in water carrying food particles and to eject waste products.

All you need to dig for clams is the ability to look and learn.  Bas and I had lugged a large garden sieve, a fork, spade and rake to the shore.  In the event the mesh on our sieve was too fine for the gravels so we had to dig a hole then search it.  We started digging rather randomly and occasionally struck lucky.

After a while we noticed siphon holes developing in the sands and gravels as the water drained away and the sediments dried out a bit.  The siphon holes are the means by which the clam maintains contact with the outside world.  What we noticed on the shore is that not all the siphon holes were the same size or shape and that we could recognise, perhaps, six different types.  With experience we learnt to recognise the siphon holes for the different species of clam we were finding and then I got really cocky and would announce before I put spade to sand how many and what species I would collect!

Some species were more abundant than others: Dosinia clams (which are somewhat less tasty than some other types) were very plentiful but another species, Gari depressa, was very sparse.  This latter clam has a rather lovely common name.  It is known as the Sunset Shell.  Once the tide had turned at the end of the afternoon and the light was beginning to sink we hauled ourselves back up the shore to go home.  On the way up through the channel through the rocks I made a delightful find.  Sitting in the gravels with the light shining through was a Sunset shell.  Look at the picture below and you will see how apt its common name is.

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