Submitted to: Hydrobiologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2007
Publication Date: 8/24/2007
Citation: Richardson, N.F., Ruesink, J.L., Naeem, S., Hacker, S.D., Tallis, H.M., Dumbauld, B.R., Wisehart, L.M. 2007. Bacterial abundance and aerobic microbial activity across natural and oyster aquaculture habitats during summer conditions in a northeastern Pacific estuary. Hydrobiologia.596:269-278.
Interpretive Summary: Intertidal aquaculture of oysters is an important industry along the west coast of the United States. Oyster aquaculture is conducted on broad intertidal mudflats in estuaries where the presence of oysters creates a new habitat that may influence the composition of the sediment microbial community. We sampled the sediment in six different habitat types in Willapa Bay, Washington including eelgrass, unstructured mud/sand, oyster hummocks (reefs) long-line oyster aquaculture, hand picked on-bottom oyster aquaculture, and dredge harvested on-bottom oyster aquaculture. We found that sediments generally became siltier (more fine particles) and more organically enriched the further away one sampled from the estuary mouth, but found no consistent differences in sediment properties amongst the various habitats. The total number of bacteria or benthic microbes followed the same trend as sediment organic content, but activity and diversity of aerobic benthic microbes (as judged by Biolog plates) was different amongst habitats. Aerobic bacterial metabolism was lower in microbes from on-bottom oyster aquaculture areas than those in eelgrass habitat. Although humans clearly alter microbial activity by conducting oyster aquaculture, we found changes to be smaller and distinct from those that normally occur along the gradient from estuary mouth to the head of the estuary near the river mouths.
Technical Abstract: We measured sediment properties and the abundance and functional diversity of microbes in Willapa Bay, Washington, USA, to test the response of sediment microbes to oyster aquaculture. Sites spanned the estuary gradient (salinity 24-30) and six different habitat types: eelgrass (Zostera marina), unstructured tideflat, oyster hummocks (reefs of Crassostrea gigas), longline oyster aquaculture, hand-picked on-bottom oyster aquaculture, and dredged on-bottom oyster aquaculture. Sediments generally became siltier and more organically-enriched into the estuary, but no consistent differences in sediment properties occurred across habitat types. Bacterial cell density tracked organic content. However, total activity and functional diversity of aerobic microbes, as judged by carbon source utilization (Biolog plates), differed significantly across habitat types. Aerobic metabolism was generally lower in sediment microbes from on-bottom aquaculture than from eelgrass. Humans indirectly alter microbial activity through biogenic habitats created during aquaculture, but these changes appear smaller than (and distinct from) sediment changes along estuarine gradients.