As a child I was delighted by sea anemones, and no doubt caused absolute havoc among the rock pools, sticking my chubby fingers into every hapless anemone who happened to cross my path. As a grown-up scuba diver, I am still delighted by them, and have realised that they look much prettier – and are much happier – without the interference of my digits.
As a novice underwater photographer, sea anemones are the ideal photographic subject. They are stationary, usually located on the sand so that I can lie right down next to them and get some solid purchase, come in a variety of pretty colours, and when there’s surge they offer just enough movement of tentacles to provide a little but not insurmountable challenge.
While they are rarely spotted on the move, they do have some element of mobility. While I was doing my volunteer training at the Two Oceans Aquarium, we were told of a specimen living in the tanks located in the classrooms upstairs who mounted a daring escape attempt and in the process completely blocked the filtering system for his tank. During the rescue/unblocking process he had to be cut in half (horizontally), and both halves survived for about two weeks before slipping this life’s mortal coil.
During our training we learned that anemones have a hydrostatic skeleton – they draw water into their bodies, and contract their muscles against the water in order to hold their shape. This is why it’s not kind or nice to touch an anemone in the centre, or to stick your finger into its mouth (the central opening). The pressure you exert can force the water out of his body, and while it is possible to recover from this, it takes a while. At the touch pool at the aquarium we encourage the kids to touch the anemones on the side, below the tentacles, and very gently.
Anemones are radially symmetric (i.e. their body structure radiates from a central point) and use their stinging tentacles to capture small shrimps, plankton and other unsuspecting prey in the water. The prey is paralysed by the stinging cells, and then the anemone draws it inwards towards its mouth.
A lot of the time they seem to get sand over their mouths – I always worry that it feels uncomfortable, and I wonder how they get rid of it to eat… But I guess they are accustomed to it, living where they do! I have tried purging my octo gently over one of them to blow away the sand, but it didn’t work.
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