O’behave Part 1

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Barkley Sound is home to a great many species of nudibranchs in equal amount of sizes and colours. It
strikes me sometimes that divers who do find these beautiful creatures give them a quick glance, maybe
take a photograph and then move on to larger and more exiting species such as octopus, wolf eel etc. In
doing so they miss a chance to see some of the weirdest and yet more interesting hunters at work.
Particularly the Giant Nudibranch (Dendronotus iris) who is a lover of sandy areas between rocks is
worth observing for a while. In winter and early spring vast numbers of this nudibranch can be seen in
shallow water hunting for food or laying eggs. The Giant Nudibranch is a lover of the tube dwelling
anemone (Pachycerianthus torreyi) who is an inhabitant of the sandy areas too. Since nudibranchs have
no eyes the detection of its favourite snack takes place via its sensory organs, the so-called rhinophores,
which are basically chemical detectors. Once the prey is located by means of the rhinophores or
sometimes by running into the stinging cells of the anemone, an interesting spectacle takes place. In
slow motion the Giant Nudibranch prepares itself for the attack by coming closer to the anemone and
slowly rearing itself up, thus exposing its head with the radulae, a series of file like extensions with
teeth on it. It then literally dives down into the anemone’s tube with amazing speed. The anemone
sometimes detects the attack in time and retreats into the tube. But if it is a split second too late, the
nudibranch will grab a hold of the tentacles and try to tear them out of the tube. This whole act can take
a minute or 2 and on occasion the nudibranch will completely miss its target and end up in the sand.
Other times, the nudibranch is pulled into the tube only to emerge, eventually, with a few tentacles. In
any case it is a great thing to observe. Another cool fact is that the stinging cells of the anemone are
“absorbed”by the nudibranch and are thus used for its defence. Incidentally this nudibranch has a dual
relationship with the tube dwelling anemone as it is both food and a safe haven for the nudibranch to
lay its eggs on or next to the anemone. Its stinging cells most likely keep other predators who like the
nudibranch eggs at bay. The egg mass, which is laid in spiralling white ribbons, looks like an old
telephone cord.

And just as you thought that this was strange behaviour, this nudibranch has another trick up its sleeve.
If the nudibranch is disturbed it can take off and swim. In an undulating motion its propels itself
through the water (mostly up and down) and it has earned itself the nickname of Spanish dancer after
its famous colleague in the Red Sea. So next time you see the Giant Nudibranch, give yourself a bit
more time and you may observe this spectacle yourself.

Peter Mieras

Peter Mieras

Peter Mieras and his wife Kathy own and run Rendezvous Dive Adventures, a small diving resort in the heart of Barkley Sound, Vancouver Island, Canada. Peter has dived all over the world and is an accomplished underwater filmmaker. Along with Rendezvous Dive Adventures and his film work, Peter keeps busy with various research and conservation projects. For more information on Peter visit www.rendezvousdiving.com

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