Artificial armored shorelines: Introduction of open coast communities into a southern California Bay
Jana L.D. Davis
Lisa A. Levin
Shelly M. Walther
Artificial hard substrates like riprap and bulkhead have been used to stabilize naturally soft bay shorelines for centuries. Despite the fact that many bays have lost more than half of their natural shoreline, very little attention has been paid to the communities that inhabit armored shorelines and to the ecological implications of armoring. The goal of this study was to examine factors affecting spatial and temporal variation of theintertidal riprap biota (emergent species,fishes, and birds), with emphasis on the influence of exposure, distance from the mouth and similarity toopen coast, hard substrate communities. We examined community composition at 8 San Diego Bay (California, USA) riprap sites (an exposed and a protected site at each of 4 Bay areas) in June and December 2000 and at 2 open coast sites in August 2000. Community structure was more variable spatially than temporally on the scales we studied, affected more by distance away from the Bay mouth and by level of exposure to wave energy than by seasonality. Exposed sites close to the Bay mouth were more similar to natural open coast sites, sharing about 45% of the same species, than protected sites and sites farther from the mouth, which shared as few as 8% of their species. In general, exposed sites had less bare space, higher species richness, and usually higher percent cover of individual species than protected sites. Species tended to occur higher in the intertidal zone at exposed than protected sites, and higher in November, when sea level was higher, than in June. Results such as these will become increasingly more useful as shoreline managers are forced to examine the ecological implications of hardening long stretches of bay coastline and address ways to incorporate artificial hard structures into ecosystems in a more meaningful way.
Manuscript submitted to Marine Biology.
September 7, 2006
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