Wednesday, August 8, 2007

PS 45-86: Possible alternate stable states in an soft-sediment benthic marine habitat

Christy M. Bowles, UC Davis and Edwin D. Grosholz, University of California, Davis.

Ecological systems can be modified by many factors including habitat modification, eutriphication, introduction of species and fishing. Alternate stable state theory may be important for understanding dynamics and managing ecological systems, but experimental evidence for the existence of a true alternate stable states (A.S.S.) is limited and controversial. I experimentally examine the potential for A.S.S. in a soft-sediment benthic marine habitat in Bodega Harbor, CA. Here a native polychaete worm, Boccardia proboscidea, has recently formed large, dense patches on mudflats adjacent to habitat dominated by venerid clams and phoronids. These dense patches have been observed for more than five years and given the nearly annual life cycle of most of the species, these states may represent alternate stable states. To test this idea, I examined the biological, physical and chemical characteristics of the Boccardia and clam-phoronid communities. I experimentally manipulated Boccardia and clam-phoronid communities using transplants and disturbances to study community structure, stability and recovery. Data show Boccardia and clam-phoronid patches are distinct communities with different physical properties. Boccardia, phoronids and clams can survive in transplants after four months. I found strong support for alternate states, but stability determination awaits final sampling.  These results and the potential existence of alternate stable states have important implications for the management of benthic marine systems. In the face of habitat alteration, eutrophication, species invasions and overfishing, these stressors may be able to shift communities beyond the threshold for recovery and potentially to less desirable community state with compromised diversity or ecosystem function.

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