Tuesday, 15 August 2006

Snail trails

When I go beachcombing, I usually head south-west to Barwon Heads or Apollo Bay or occasionally as far as Portland. But every now and then, I visit the other side.

Flinders lies at the southern end of the Mornington Peninsula, about an hour and a half from Melbourne. The platforms of black basalt from the Older Volcanics (laid down in the Eocene, between 36 and 53 million years ago) are home to a high diversity of molluscs.

Perhaps the most abundant snails are Nerita atramentosa. At low tide, they cling to rocks, holding on tight to avoid desiccation. When the waves roll in, they emerge to graze on the veneer of algae laid down by the sea. Nerita atramentosa is the modest cousin of more exuberant tropical species, many of which are reknowned for their patterned shells. But what it lacks in colour, it makes up for in persistence. This species is the only temperate nerite in the world. Although its main distribution is southern Australia and New Zealand, it has also colonised Easter Island. Now that's impressive.

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