Head for rocks... time to nab a crab
It wasn’t the first time I found them on coastal cliffs when they were nowhere present in the fields inland. Could it be the slightly higher coastal temperature or the relatively warm coastal fogs bring them on? In any case, these specimens have always been especially stocky, firm and unwormed, delicious on toast.
It was 16C that evening, and the fog was beginning to roll in. The water in the rock pools was warmish but there were no shrimps — which was most unusual — and just one rock pool fish, a somewhat dazed-looking two-inch long shanny that let me capture it in my cupped hands, much to the glee of my small grandson and his pal from the Czech Republic.
We had already captured a number of shore crabs, which we carried about in clear plastic bags full of water. The bags made excellent, miniature marine aquariums, with all round visibility.
The Czech children were mightily excited at the opportunity to hunt for crabs. They have none at home, of course, no sea or seaweed, no rock pools. The great thing is that crabs can be found on every rock platform along the coast. The green shore crab is an aggressive little fellow, and can pinch quite painfully. The children thought it was a hoot when an inch-wide specimen gripped my finger with its sharp pinchers, especially as I made suitable cries of distress.
Rock-pool hunts almost always absorb children, and crabs are great fun to watch as they scuttle sideways with upraised claws for the cover of rocks or seaweed. One can make a game of trying to find a ‘red’ shore crab (most are green but rare individuals are rust-coloured) or a crab with one claw (approximately one in 20 will have lost a claw in scraps with neighbours).
When we came to release our captives, the children were intrigued to see that two had “stuck together”. While in the case of frogs, the smaller male frogs piggy-back on the females for days at a time, waiting for them to emit spawn which they will then fertilise, male crabs, always bigger than the females (they mate only with females with a carapace 10mm smaller than their own) carry the female around until she moults.
That moulting is signalled by pheromones she releases. To ensure that he will be her sole partner, the male holds her in a tight, amplexus embrace until she has cast her shell: he even helps her undress. He then gently turns her over and deposits his sperm packets in her oviduct.
For days afterwards, he protects the soft-shelled and vulnerable mother-to-be, the pair hiding in a rock crevice, the entrance guarded by him.
After their copulation, the female’s shell gradually hardens. In late autumn, she spawns, carrying the eggs in the ‘purse’, the curved tail like a flap under her body (the female’s tail is broader than the male’s).
Yellow and sponge-like at first, these eggs, called berries, become dark as the larvae develop eyes as the sea warms. In summertime, they hatch and join the ocean-borne larval soup of dozens of marine species. A female can lay over 180,000 eggs but only a very small percentage survive to become tiny crabs.
Shore crabs are tenacious and adaptable creatures and, in the last two centuries, have spread from the North Atlantic and Baltic to other oceans, endangering native species on both coasts of the Americas, and in South Africa and Australia. They probably arrived in ship’s ballast, via migration of larvae on ocean currents or by rafting on flotsam or jetsam.
Shore crabs, enjoyed in soups by the French, are eaten by any predator with a mouth large enough to swallow them. This includes grey herons, although our heron is, apparently, too fussy. Ron, as he is called, still visits daily and clacks and cawks at me when I appear in the yard, begging for food. However, when I drop a few fish in the garden stream (say three small flatfish, dragonets or gurnard) he will generally leave one uneaten. Clearly, he is feeding himself, and the ‘begging’ is simply a sort of reflex response.
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