The Intertidal Wilderness

A Photographic Journey through Pacific Coast Tidepools

Anne Wertheim Rosenfeld

The introduction of nonnative species amounts to biological pollution of native genes, species, communities, and ecosystems. Every species introduction surely has some impact on its new community; impacts run the gamut from the barely measurable to the ecologically and economically destructive.

The native red abalone is the basis of a large-scale, economically valuable shellfish farming industry on the Pacific coast of North America. This industry has suffered from the accidental introduction of a nonnative sabellid (fan worm) that hitchhiked with abalone shipments from South Africa to California. Through subsequent shellfish transfers, this pest has spread along the Pacific coast to farms from Mexico to Oregon. The tiny sabellid does not kill the abalone directly but interferes with the hostÕs shell growth. Juvenile worms settle at the edge of the abalone shell, causing the host to interrupt its normal growth and manufacture a nacreous shell layer, resembling mother of pearl, over the worm. As this layer hardens, it does not kill the worm: it simply creates a sturdy home for the parasite, which grows to reproduce and incubate more larvae. If the sabellid infestation is heavy, the abalone stops growing normally altogether; instead it repeatedly makes shell layers stacked vertically on each new crop of worms and eventually may occlude its own respiratory pores. These domed, stunted abalone never reach market size, and their shells, riddled with fan worm tubes, grow weak and brittle. Like most species introductions, the sabellid plague is difficult and expensive to eradicate; if it spreads into wild populations of other bivalves and snails, it may be impossible to control.

Copyright 2002 by Anne Wertheim Rosenfeld. Not to be reproduced without written permission of the publisher.

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