Wednesday, August 22, 2012

Crab species

(originally published 23 May, 2012)
A trip to Ballycotton some weeks ago allowed for some rock pooling, the searching of rock pools for interesting life. What turned up amongst other things where several of Irelands crab species. It is suprising just how many species of crab you can find, even by turning just a few rocks on the shore line.

First off, my favourite of the irish species, this is a velvet swimming crab (Necora puber), part of a family of crabs with specially adapted back legs for swimming in the water. As you can imagine this gives them a great advantage over other crabs that are limited to living on or near the sea floor since they can swim up to the surface. Velvet swimmers are particularly evil looking with those red eyes and are quite aggressive. This one was not full grown and unfortunately I didn’t actually get a chance to photograph its adapted legs. Anyway, it gets its name because hairs give it a soft velvety feel.
Note the purple/blue tinges and red eyes that give this crab a colourful and quite evil apearance,

The shore crab (Carcinus maenas) is Ireland’s most common crab and is probably one of the planets most widespread and invasive species. Adults are quite large (size of your hand) and are always green with an orangy tinge whilst the young come in an array of different colours and patterns, presumably to blend in with multicoloured sediment. If you’re near any shore line with rocks (or even sand) you are bound to find them under almost every stone below the tide line. Adults can be harder to find but become more common closer to the sea’s edge at low tide.
Handle with care, those claws can draw blood
A female, the triangular area on its belly is wide to allow her to carry eggs, the male has a narrow strip

The edible crab (Cancer pagurus) is amongst the largest Irish species. Full grown adults are rarely found in rock pools and prefer deeper water but young ones are quite common. When approached they tend to play dead by curling their legs inwards and staying motionless but this tactic is often abandoned in favour of aggression. As their name suggests these crabs are edible and are often caught by fishermen.
Not a friendly crab by any means
Playing dead behaviour

Montagu’s crab (Lophozozymus incises) is a small species of crab quite commonly found in rock pools, as this picture shows it has some impressive claw strength going on. It refused to let go of that rock, which was bigger then its body and could easily hold on to it. Like the edible crabs they play dead.
Body builder crab

The broad clawed porcelein crab (Porcellana platycheles) despite its tiny size has some impressive claw strength and can actually give quite a potent nip. It’s a very common rock pool species that often goes unnoticed because of its small size and great camouflage.
This crab has lost a claw, usually this happens when they fight with other crabs, luckily for the crab, they grow back.

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