ABSTRACT: The effects of commercial culture of oysters, Crassostrea gigas, on submerged aquatic vegetation (SAV), Zostera marina, were examined with replicated field experiments in the South Slough estuary, Oregon, USA. Both stake and rack methods of oyster culture resulted in significant decreases in the abundance of SAV compared to undisturbed reference areas. SAV cover in both stake and rack treatments was less than 25% of that in reference plots after 1 yr of culture, and was absent from rack treatments after 17 mo of culture. Field experiments using marked plants revealed no difference in growth between plants in stake and reference plots. Comparisons of sediment surface topography demonstrated that oyster culture resulted in significantly greater sediment deposition in stake plots and greater erosion in rack plots. Silt-clay fractions and carbon content of sediments tended to increase with stake culture and decrease with rack culture, but only for carbon content at racks were the differences significant between culture and reference plots. Stake culture likely affected SAV via increased sedimentation and direct physical disturbance during placement and harvest, while increased erosion and perhaps shading resulted in the marked decrease in SAV coincident with rack culture. These results indicate the potential for significant loss of SAV from estuarine ecosystems where these methods of oyster culture and SAV coincide.

KEY WORDS: Eelgrass . Zostera marina . Oysters . Crassostrea gigas . Mariculture

Published in MEPS Vol. 125 (1995) on September 14
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1995