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Seminar Abstract

Alan C. Trimble - March 18, 2003


Post-invasion shifts in recruitment timing and magnitude of Pacific oysters (Crassostrea gigas)

Pacific oysters (Crassostrea gigas) were originally introduced to Washington in 1919 and have since established persistent populations in Willapa Bay and Hood Canal. In both areas, records of spawning and recruitment have been kept since the 1930’s. I have examined these long-term records for evidence of shifts in the timing and magnitude of recruitment. Since 1947 in Willapa Bay, recruitment has occurred on average 4.5 days earlier per decade, consistent with phenological changes observed in hundreds of terrestrial species. In contrast, no trend was observed in the frequency of large recruitment events: about half the years between 1940 and 1980 had sufficiently high recruitment for use by aquaculture. Two alternative mechanisms, not mutually exclusive, could have caused earlier recruitment since the initial introduction. First, oysters may be responding to warmer water due to global climate change. Second, oysters may be adapting to local conditions, if earlier-spawning individuals have higher reproductive success. Correlations with long term temperature records and comparison to the recruitment timing of the native “Olympia” oyster (Ostreola conchaphila) for the same period were used to determine the mechanisms for significant changes in reproductive timing of this introduced species.

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