CRITTER CONFIDENTIAL
Lobster lairs
and lives
Homarus gammarus
Paul Naylor reflects on the home-making habits of his local lobbies , and the richness of their environment
I
recently had the privilege of meeting two of these impressive crustaceans in quick succession on the same dive in Plymouth Sound . Both encounters showed me aspects of the animals ’ lives , and highlighted the amazing biodiversity of the place in which they resided .
We were only a few minutes into the dive when we met the first lobster , a large old-timer with its armour well covered in barnacles and the calcareous tubes of small worms , which showed that it had not moulted for some considerable time . Its imposing claws followed the standard format for this species , a heavy ‘ crusher ’ on one side ( the left , with this individual ) and a more slender ‘ cutter ’ on the other . The lobster had excavated a home beneath a large boulder and the resulting small cave was festooned with several different species of sponge , plus hydroids and large tubeworms . Although it was in very shallow water , the shade under the boulder meant there was insufficient light for seaweeds , thus allowing the sponges and other animals space to thrive .
When we initially encountered our second lobster , in slightly deeper water , it was occupying the central cavity of a long-ago discarded traffic cone ! Only the overall shape made this item of litter recognisable , as it had been colonised by a remarkable variety of creatures . There was now a rich cover of feather stars plus sea cucumbers , sea squirts
Rare sight of a wandering lobster in very shallow water in the daytime
and a scallop as well as sponges , hydroids and tubeworms , all benefitting from the plankton-rich waters sweeping in with Plymouth Sound ’ s strong currents .
The lobster itself was smaller than the first , with clean armour indicating a recent moult . It had a full-size ‘ cutter ’ on the left but its claw on the right , while shaped like a ‘ crusher ’, was much smaller than the expected heavyweight version . It had presumably lost its right claw in a fight , very possibly with another lobster ( maybe the bruiser we had just met !), as these animals are well known for cannibalism .
It was now going through the usual crustacean limb replacement process facilitated by the moulting cycle but I was interested to see that it was taking a different approach to many crabs . When shore crabs , for example , lose the heavier claw of their pair , they convert the remaining claw to the sturdier shape and develop a new lighter weight claw on the other side . Perhaps the lobster ’ s strategy is determined by the fact that the ‘ cutter ’ claw is actually more essential in terms of feeding ?
Our next surprise , and the highlight of the dive , was that this lobster emerged from its traffic cone and set out on a trek across the seabed . From the way it kept stopping and adjusting its course before proceeding , we got the definite impression that navigation was involved . Sure enough , on an otherwise fairly flat seabed , it found a shelter and walked in ! This time it was a cavity beneath a discarded lobster pot which , fortunately , was now too damaged to ‘ ghost fish ’ in any way . Sadly , this is often not the case with lost fishing gear , so here ’ s a big thank you to all those divers who get involved in removing ghost gear , and preventing a serious hazard to marine life , including this relocating friend ! �
A smaller lobster was occupying a discarded traffic cone .
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