Sunday, February 24, 2008

Snorkeling on the North Cottesloe Reef

Yesterday's great conditions at the South Cottesloe Beach have encouraged me to go to Cottesloe again today. But instead of heading for the South Cottesloe Reef, I went to the North Cottesloe Beach. The water was still calm and reasonably clear like yesterday's.

I was in the water for about an hour. I didn't see as many types of fishes as yesterday. But I saw two spotted jellyfishes about 15 cm across. The jellyfishes were a bit orangish with lots of white spots on the medusa (their umbrella-like structure). They had no tentacles around the edge of the medusa. They did have some oral arms or mouth arms. Beneath these, there were some translucent tentacles with white roundish tips. These seem to fit the textbook description of a spotted jellyfish (Phyllorhiza punctata).


A spotted jellyfish that I spotted in the Swan River.

Anyway, what's really amazing is that one of them was 'covered' in maybe a hundred (?) small fishes, whose name is again I-don't-know. These small fishes remained close to the surface of the jellyfish whichever way it swam. Obviously a case of symbiosis, or rather commensalism. It benefits the small fishes to hang around the jellyfish - for safety reasons, but the jellyfish is neither harmed nor helped by the fishes. A case of a marine creature being generous and helping the needy? Well, these fishes must be immune to the stings of this jellyfish, too.

And I also saw a comb jellyfish and a box jellyfish!

The comb jellyfish had some bands of cilia (tiny hair-like structures) along the length of its body. When these were beating, you would see some luminescent rainbow colours moving down its body. Very nice.

The box jellyfish, well, it was on its own this time. I actually ran into a group of them the first time I snorkeled at North Cottesloe. Still, the sight of a transparent jellyfish with a box-like medusa and only four tentacles hanging from fours corners is enough to make me run for my life. I don't like stingers - deadly or not.

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