Dr Scott Bennett is a surfer and marine ecologist at the University of Tasmania. His work has taken him from Townsville to WA, South Africa and now Spain, where he’s studying the Mediterranean and the Arctic. According to Bennett, “oceanographic processes like the poleward flow of the East Australian Current down the east coast, and the Leeuwin Current that wraps down the west coast and along the south coast” are vital in distributing larvae and ‘propagules’ (like spores in the wind) throughout the GSR. Thanks to those flows, the GSR is more or less defined everywhere by one humble organism: the habitat-forming species of kelp Ecklonia radiata (“common kelp”).
Bennett says kelp forests are the GSR’s “biological engine”, supporting an abundance of temperate marine species. But his research shows that the forests are dying in the north and growing in the south. You’re not imagining it when you feel that winter dips aren’t as cold as they used to be – isotherms (lines of temperature) are shifting poleward at a rate of 20 to 50km per decade. Because of the east-to-west alignment of Australia’s southern coast, he says, there will come a point when continued warming means “there is no more southerly habitat to which (the kelps) can retreat.”
As the East Australian Current pushes warm, nutrient-poor water southward into eastern Tasmania, we’re seeing dramatic losses of giant kelp (Macrocystis pyrifera) forests. These beautiful structures have been habitat and hiding place for everything from fur seals to lobsters and whelks. Their destruction is a silent and unseen disaster. Eight years ago, the Australian giant kelp forests became the first marine community to be listed as endangered under the Environment Protection and Biodiversity Conservation Act. But the losses continue unabated.
One of the causes of kelp loss is the southward march of a large purple menace; the Longspine or “black” sea urchin (Centrostephanus rodgersii), resulting in bare patches called “urchin barrens”, and reduced fisheries productivity. They’re native to New South Wales, but temperature changes have enabled them to get a foothold in Tassie. At up to 30 centimetres in diameter, and with an appetite to match, they’re a serious threat to Tasmania’s kelp forests. Once they've destroyed the larger marine plants, they'll scrape micro-algae off the rocks and live quite happily in their own barrens. Studies have shown that large crayfish predate on the urchins, and help maintain healthy kelp forests; in a sense, keeping marauders out of their own homes. Trouble is, southern rock lobsters are themselves under significant pressure from overfishing.