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| It is a misconception that temperate reefs are any less spectacular than tropical ones, especially if you carry a light. The first 10-15m has big kelp underwater forests, then the next 15-20m has colourful sponge habitat. Sponges and other sessile animals move in their larval stages but as adults they grow stuck to rocks. The bright colours are meant as warnings (don't eat me, I taste bad) as animals stuck to rocks can't run away.
Colourful sponges growing in Sydney Harbour region (J Turnbull)
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Sponges have other defence mechanisms. They have tiny glass shards through their flesh and produce chemicals that are unpleasant or even toxic.
Diving does have different depth bands. When you first learn to dive you can go down to 18m which is where most of the interesting stuff is. John is certified to go to 40m but there are limitations to going deeper. A diver has less time because air is consumed quickly at depth and there is also less and less life to see. In Sydney Harbour there is less to see past 40m, apart from wrecks, there being four to five in the harbour. One steam-driven wreck between North and South Head has its old boiler and a big flywheel. Wreck dives can use a different mixture of gases, having more oxygen and less nitrogen to stay down longer. Divers have to come up slowly to let the gas out of their tissues rather than forming bubbles. A deep dive is often followed by a shallower one to counteract those effects.
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| Left: Kelp fronds Sydney Harbour (J Turnbull)
At deep levels fish have very big eyes which let them capture more light. They are often red-coloured which effectively makes them invisible as red light doesn't penetrate as deep down as other colours. Fish with swim bladders (a lot of them) know when they are deep since they have to inflate those swim bladders to maintain buoyancy under the greater water pressure. Some fish at those depths do make their own light using bioluminescence.
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Pineapple fish, which can be seen at Shiprock in Port Hacking, have headlights underneath their eyes. These headlights are filled with bioluminescent algae which glow red, lighting up the bottom of their caves and the shrimps they eat. Divers do have to be careful of weather, even though the weather below water is very different. While they don't have to worry about rain, days of rain does make the water murky. Wind, however, makes quite a difference. Above the waves wind creates chop on the surface which agitates the layers of water, making it murky and challenging to get in and out. The most powerful and disruptive weather is a deep swell. This refers to how long a wave is from peak to peak, not its height. The longer a wave is the deeper it goes underwater. A 2m high wave of short peak length is not noticed 5-6m below the surface whereas 2m swell with a long period between peaks (like 12-15 seconds) creates a lot of surge on the bottom like a washing machine. Such surges take the divers and sediments with it, very unlike the peace and weightlessness of other dives. Some divers even get seasick!
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Above: Grey nurse shark off Clovelly (J Turnbull)
There is quite a lot of sound underwater but that is often muffled in temperate waters as divers wear hoods. Sound is really noticeable in tropical waters and tropical reefs are quite noisy with a lot of animals using sound for various purposes. Tropical reefs have a background hum, with of clicks, scratches, snaps, pops and bubbles. Temperate waters get deeper and booming sounds. Divers there really notice ships and outboard motors. In one spectacular dive off Shark Point near Clovelly, John recorded a humpback whale singing as the whales travelled past. He could feel it as much as hear it, as the sound literally went through his body. John is excited about other creatures he encounters, sharks being one. Most sharks are not dangerous and he has never felt threatened by one. They are amazing creatures to watch, like the powerful, graceful grey nurse sharks URG spotted off North Bondi.
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Above: Sydney Harbour Cuttlefish (J Turnbull)
He also enjoys cuttlefish which, like with octopus, are among the most intelligent invertebrates on the planet. Cuttlefish have an amazing ability to change colour and texture. The giant cuttlefish, endemic to Australia, are very effective stealth hunters. A giant cuttlefish has two tentacles that shoot out, like harpoons, to catch its prey. It will investigate divers, putting up two arms as a warning first. It might even put on a display of coloured stripes running down its body, stripes that change from white to yellow to red to brown in a flash.
Such a rippling flow of neon flashing display is one of the many astonishing features of deep space, except this deep space is all under water.
John Turnbull was interviewed for A Question of Balance by Ruby Vincent. Images from John Turnbull. Summary text by Victor Barry, October 2017.
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