Artificial armored shorelines: sites for open-coast species in a southern California bay

Abstract

Artificial hard substrates have been used to stabilize naturally soft bay shorelines for centuries. Despite the loss of over half of the natural shoreline in many bays, little attention has been paid to the communities inhabiting armored shorelines and to the ecological implications of armoring. The goal of the present study was to examine factors affecting spatial and temporal variation of intertidal, hard-substrate biota (emergent species and fishes), with emphases on the influence of exposure, distance from the open ocean, and similarity to open-coast, hard-substrate communities. We examined community composition at eight San Diego Bay (California, USA) sites (an exposed and a protected site at four bay locations) in June and November 2000 and two open-coast sites in August 2000. At all bay sites, the shore was armored with granite boulders, a form of shoreline stabilization referred to as "riprap." Community structure was more variable spatially than temporally on the scales we studied, affected more by distance from the bay mouth and exposure to wave energy than by differences between June and November. Exposed sites near the bay mouth were more similar to natural open-coast sites, sharing about 45% of their species, than protected sites and sites farther from the mouth, which shared as few as 8%. Species richness was generally higher in exposed than protected bay 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. Such results will be useful to shoreline managers who examine the ecological implications of hardening long stretches of coastline and may suggest ways to incorporate artificial structures into ecosystems in a more meaningful way.