FACTORS PREVENTING THE RECOVERY OF A HISTORICALLY OVEREXPLOITED SHELLFISH SPECIES, OSTREA LURIDA CARPENTER 1864

The Olympia oyster, Ostrea lurida Carpenter 1864,dagger in estuaries along the Pacific coast of North America, experienced overexploitation throughout its range in the late 1800s, resulting in commercial extinction before 1930. Significant harvest restrictions and marine reserves were established in Washington State by 1897 to protect new recruits, and harvest pressure has been negligible for the past 80 y. Nevertheless, O. lurida remains locally rare. This study focuses on the contemporary dynamics of the remnant population of O. lurida in Willapa Bay, Washington, historically home to the largest native oyster fishery oil the coast, with a broad focus on factors preventing recovery. Failed recovery could be because of reproductive limitation, or to poor post recruitment performance. In this case, reproductive limitation Seems unlikely, because historical (1947 to 1983) and modern (2002 to 2006) records reveal 5-fold higher annual spatfall for O. lurida than introduced Pacific oysters (Crassostrea gigas.) However, O. lurida remains rare and C. g gas is commercially exploited from natural recruitment. To evaluate the effects of abundant C. g gas in intertidal areas on O. lurida settlement patterns, strings of C. gigas shell were placed at two tidal elevations in three habitat types-open mud, eelgrass beds of Zostera marina, and C. g gas reefs. Settlement of O. lurida was significantly higher on the shell strings placed in the C. g gas reefs at both tidal heights. To evaluate postrecruitment demography, juvenile O. lurida were outplanted at three tidal elevations at five sites, and fouling organisms were manipulated to test for competition. Short emersion times (8% greater exposure) reduced survival by 80% relative to subtidal treatments, but did not affect growth rates of survivors. Naturally-setting competitors, mostly nonindigenous, depressed survival by 50% and growth by 20%. In a third experiment, manipulating the density and stability of shell Substrate, O. lurida was easily moved or buried when outplanted in a thin, unconsolidated layer. These results indicate that recovery has been hampered by the removal of dense subtidal native oyster shell accumulations during exploitation, by direct competition from exotic species, and by the appearance of novel introduced oyster shell settlement substrate in the intertidal zone. This altered web of interactions influencing O. lurida serves as a model for beginning to explore the failed recovery of overfished species in rapidly changing coastal systems.