Kelp Forests versus Urchin Barrens: Alternate Stable States and Their Effect on Sea Otter Prey Quality in the Aleutian Islands

Abstract EN

Macroalgal and urchin barren communities are alternately stable and persist in the Aleutians due to sea otter presence and absence.

In the early 1990s a rapid otter population decline released urchins from predation and caused a shift to the urchin-dominated state.

Despite increases in urchin abundance, otter numbers continued to decline.

Although debated, prey quality changes have been implicated in current otter population status.

This study examined otter prey abundance, size, biomass, and potential energy density in remnant kelp forest and urchin-dominated communities to determine if alternate stable states affect prey quality.

Findings suggest that although urchin barrens provide more abundant urchin prey, individual urchins are smaller and provide lower biomass and potential energy density compared to kelp forests.

Shifts to urchin barrens do affect prey quality but changes are likely compensated by increased prey densities and are insufficient in explaining current otter population status in the Aleutians.