Sea urchin barrens as alternative stable states of collapsed kelp ecosystems
Sea urchin barrens are expansive rocky reefs dominated by coralline algae; in the absence of sea urchin grazing, they support luxuriant seaweed communities such as kelp beds. Filbee-Dexter & Scheibling examine the global distribution of urchin barrens along temperate and polar coasts, and document the drivers and thresholds of phase shifts between barrens and kelp beds as evidence of alternative stable-state dynamics. Anthropogenic impacts play an important role in triggering the collapse of kelp-based ecosystems and the resulting phase shifts to barrens. Negative interactions between kelp and sea urchins stabilize both ecosystem states, making these phase shifts difficult to reverse.
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