The waters around the Tasman Peninsula are one of the last Australian bastions of giant kelp, Macrocystis pyrifera. Kelp beds are the foundation for a submarine ecosystem as diverse and productive as a land-based forest. Charles Darwin first encountered kelp-beds in South America and was impressed enough to comment ‘a great volume might be written, describing the inhabitants of one of these beds of sea-weed’. In Tasmania, kelp holdfasts shelter abalone and sea-stars; the stems are encrusted with bryozoans and hydrozoans; and the buoyant, bladdered leaf blades are grazed by tiny crustaceans – food for weedy seadragons and many other fish. more...
Kelp can grow 60 cm a day through the winter, reaching lengths of up to 50 m by late spring. It once grew so densely as to be an impediment to shipping. But as whales and seals were slaughtered, the kelp retreated, no longer able to benefit from the fertilising effect of the sea-mammals’ poo.
Today, kelp beds in eastern Tasmania face a further threat. Stressed by the warmer, nutrient-poor waters of the strengthening East Australian Current, kelp struggles to survive being eaten by newly invading long-spined sea urchins. On settling out after their planktonic larval stage, urchins graze on baby kelp plants, leaving desolate ‘urchin barrens’ in their wake. Things might be easier for the kelp if populations of southern rock lobsters – the urchins’ main predators – were not under such intense pressure from fishing: old lobsters of a size necessary to manhandle adult urchins are now rare.
Regrettably, the future for Tasmania’s iconic kelp forests looks bleak, despite their recent federal listing as an endangered ecological community. As Darwin noted ‘if in any country a forest was destroyed, I do not believe nearly so many species of animals would perish as would here, from the destruction of the kelp’.
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