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Reef Report for Friday, March 21, 2003

Cephalopods; Interesting Residents of the Reef

This week I have been reading some fact sheets on Molluscs provided to me by Paddy from Reef Teach. It is thought that there are over 100,000 known species of molluscs in the world, which make mollusks one of the most diverse groups in the animal kingdom. © Undersea Explorer Although they take many different forms they all share certain characteristics, the most prominient being soft bodies and a muscular foot. Most mollusks possess a shell, but there a few do without one altogether.

The Cephalopods are one of the four groups of Molluscs. Examples of Cephalopods found on the Great Barrier Reef are the cuttlefish, squid, octopus and the nautilus. I was fortunate enough to see a Nautilus while on a recent dive trip with Undersea Explorer. Nautilus are rarely sighted by scuba divers, as they live at depths of up to 800 metres during the day, then rise at night to depths of 200 metres for feeding. Undersea Explorer conducts regular research into the nautilus. Known as the ‘head-foot’ molluscs I read they are the brainiest of all the invertebrates.

Unlike it's close relatives, nautilus have an external shell and belong to the ancient family which evolved over 550 million years ago. The cuttlefish has an internal shell (the chalky cuttlebone you will see in birdcages and lying on the beach) and similar to the Nautilus both use their shells for controlling bouyancy. The nautilus only occupies the shell closest to the opening while the rest of the shell is a series of empty chambers which they fill with gas or water, depending on how buoyant they want to be. The Nautilus’s molluscan foot has evolved into 60-90 arms which it uses to grasp food, mainly crustaceans.

On the reef this week the weather conditions did not produce the best diving or snorkeling conditions. Still, people who did travel to the reef still came back with some good stories.

At Paradise Reef certified divers on Passions of Paradise reported seeing an impressive school of hump-headed parrotfish feeding. They saw at least sixty of these huge colourful sea creatures. Lots of Moorish idols and Blue lined surgeonfish were also spotted. Introductory divers saw crown squirrelfish, a Honeycomb Moray Eel and even a Blue-spotted stingray resting on the ocean bottom. One lucky snorkeler saw a Black-tipped Reef Shark cruising in 8m of water.

Reef Magic Cruises went to Hastings Reef where "Wally" the giant Maori Wrasse came in for a play along with some turtles and a few small white tip reef sharks. The crew reported winds at around the 15 to 20 knots with the sun shinning all day. At Saxon Reef certified divers spotted a Lionfish hunting small Chromis fish amongst the corals. Onboard Scubapro at Flynn Reef divers witnessed turtles eating jellyfish at Gordon’s dive site. Despite the poor visibility everyone got to see “Brian” the large table-sized Green Turtle.

With the threat of the recent cyclones now well and truly gone the winds are starting to ease and this coming weekend should be producing much better conditions. On all reports we should experience 10 to 15 knots and hopefully more form the SE direction. As always, safe diving! Steve Brady

(C) Pro Dive Cairns This weekly reef report was written by Steve Brady of Pro Dive Cairns, who compiles them from the dive trips he takes, as well as the many conversations he has with divers, dive instructors, captains, and others in the Cairns dive community. The report is published weekly in the Cairn Post, the local daily paper and appears here thanks to the courtesy of Pro Dive Cairns.

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