SS3.15 Physical Forcing and Pelagic-Benthic Interactions in Aquatic Systems
Date: Thursday, June 13, 2002
Time: 10:00:00 AM
Location: Oak Bay
 
MacrellisHM, Department of Zoology, University of Washington, Seattle, USA, bulan@u.washington.edu
Wing, S, R, Department of Marine Sciences, University of Otago, Dunedin, New Zealand, 
Frew, R, D, Chemistry Department, University of Otago, Dunedin, New Zealand, 
 
LINKING WATERSHED-SCALE ALTERATION OF HYDROLOGY TO ESTUARINE HABITAT CONVERSION AND LOCAL BIODIVERSITY DECLINE
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The New Zealand littleneck clam, Austrovenus stutchburyi, has undergone local extinction events in the inner reaches of Doubtful Sound, New Zealand. The operation of a hydropower plant in the upstream watershed has doubled freshwater flow into the fjord. The objective of this study was to determine whether changes in the salinity regime induced by power plant operations are linked to clam extinction events. Oxygen isotope analyses of remnant clam shells showed that clams lived in the inner fjord under pre-powerplant salinity conditions. Natural variation in dissolved sulphide (as an indicator of anoxia), sediment type, and shore height did not covary with clam distribution. A laboratory experiment found that extended low salinity exposures do cause mortality in A. stutchburyi from Doubtful Sound (37 day LC50 = 2.5). In situ transplant experiments demonstrated that conditions in the inner fjord are still lethal to this species. Our data suggest that the increased freshwater input from the power plant converted habitat in the inner reaches of Doubtful Sound to one with sustained low salinity that served as the mechanism for the extirpation of A. stutchburyi.