Abstract
Hydrodynamic forces associated with waves influence the structure and function of rocky intertidal communities, but their effects on species composition and morphology within other marine communities have not been well studied. We measured wave characteristics and current speeds with acoustic Doppler velocimeters (ADVs) at oyster (Crassostrea virginica) reefs in St Charles and Aransas Bays, Texas. We investigated wave effects on communities at these reefs by comparing species composition, relative abundance, and species morphology on windward versus leeward sides. In addition, acorn barnacles Amphibalanus eburneus were used as biological indicators of flow because they develop larger basal diameters and shorter feeding appendages in faster flows. Waves were higher and current speed was faster on the windward sides of oyster reefs. Leeward sites had a greater abundance and diversity of species. Brachyuran crabs were significantly larger and more abundant when shielded from waves. Porcelain crabs Petrolisthes armatus were smaller and, in contrast to brachyuran crabs, more abundant at windward sites. Windward sites had fewer fish species though there was no difference in the size of fish found on either side of the reef. Barnacles settling in late spring had larger basal diameters but relatively shorter feeding appendages in windward areas, compared to leeward areas; these morphological differences mirrored ADV measurements, verified long-term differences in flow and were indicative of bigger waves and higher flow velocities in windward locations. Thus, oyster reefs can reduce wave height and slow current velocity and influence the diversity, abundance, and morphology of associated species. The decrease in wave height can provide shoreline protection, an ecosystem service of oyster reefs often mentioned but rarely measured.