The Intertidal Wilderness

A Photographic Journey through Pacific Coast Tidepools

Anne Wertheim Rosenfeld

The distribution of every species on the rocky shore is determined by a combination of the organismÕs physiological tolerances, its dispersal ability, and the prey, competitors, and predators it encounters. Range extensions occur when a species disperses naturally, often with winds or currents, beyond its usual distributional limits to colonize a new location. Such range extensions may be precipitated by fluctuations in ocean circulation patterns or by shifts in temperature regime caused by glaciation cycles or global climate change. When a species moves to a new location under human agency, we witness the introduction of a nonnative species to a new community. The bat star, Asterina (formally Patiria) miniata, is native to and common in California, where it is unusual among sea stars in consuming plant as well as animal matter. Extremely rare in Oregon and Washington, it appears again abundantly in British Columbia along the outer coast of Vancouver Island. At some point, apparently, the bat star extended its range northward from California to reach British Columbia, skipping the hundreds of kilometers in between. It is unknown what factors limit its abundance, even presence, in Washington and Oregon.

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

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