A Landscape Disturbance Process in the Marine Environment: Revising Expectations of Climate Change Impacts.
Carlos Robles, California State University Los Angeles, Los Angeles, CA, United States, Patricia M Halpin, Marine Science Institute, University of California, Santa Barbara, CA, United States, Rebecca Schrecengost, Experium Science Academy, Torrence, CA, United States, Daniel Orr, California State University, Monterey Bay, CA, United States and Jennifer Aleman-Zometa, University of California, Los Angeles, CA, United States
Abstract:
Episodic disturbance is a ubiquitous feature of natural communities. An archetype for theory in the marine environment is wave-torn gaps in the cover of intertidal mussel beds. We mapped gap formation in eight mussel beds over eight successive years in Barkley Sound, British Columbia. We constructed a GIS database integrating small-scale measurements of topography, wave force, the 3-D structure of the mussel aggregations, and photo-mosaics of the mussel covers. Photographic analysis showed that gaps recurred predominantly in the center of the beds. The more stable peripheral regions of the beds are continually thinned by physical and biotic stresses, while the center region thickens and differentiates into layers. The mussels comprising the superficial layer attach to each other and have no direct attachment to the rock. Furthermore, the superficial layer suppresses mussels in the interior, weakening their attachment. Spatial analyses showed that it is these structural differences, rather than the spatial distribution of wave force, that account for landscape patterns of gap formation. Thus, sub-regions of disturbance arise from processes intrinsic to the community, including self-organization of the mussel aggregation, which interact with the external forcing of waves in a stochastic but coherent landscape process. This view differs from published models, which assume wave force alone generates gaps randomly across the mussel beds. Long-term records of seismographic activity and indicate the wave beat on the shore is increasing with global warming. We may fail to accurately anticipate the consequences of the elevated wave forcing, unless we also take into consideration changes in ocean production and other factors affecting mussel bed structure.
