COS 115-2
Intraspecific diversity affects ecological functions of a habitat building species
As populations decline, their intraspecific diversity may diminish. Population decline may be exacerbated if a decrease in intraspecific diversity also reduces important ecological functions that maintain population numbers. Oyster reefs are severely overharvested, declining by ~85% worldwide. We tested how increasing within species diversity of eastern oysters (Crassostrea virginica) using transplants would affect recruitment of oyster larvae, a key function necessary to maintain future populations. If harvesting reduces population numbers, within species diversity, and connectivity, then oysters may lose the ability to adapt to changing environmental conditions as well as incur lower levels of recruitment that may hasten their decline. We performed a series of manipulative experiments to ascertain the effects of adult oyster diversity on oyster recruitment. First, we compared recruitment to living oysters vs. dead oyster shells to determine if chemical cues from adult oysters mediated oyster settlement under both lab and field conditions. We then manipulated intraspecific diversity using transplant experiments. Oysters were collected from three estuaries in Texas, USA: San Antonio Bay, Matagorda Bay, and Carancahua Bay. We placed oysters into St. Charles Bay, near Rockport, TX, USA in one of four treatments trays: a high diversity treatment containing 20 oysters from each bay and one of three low diversity treatments containing 60 oysters from a single collection location. Sets of trays were placed in the field in a block design. Oyster recruitment was measured in each treatment in 2010, 2011, and 2012 and compared using ANOVA.
Results/Conclusions
Results from lab and field studies indicated that oyster larvae use chemical cues from adult oysters to select settlement sites, and we found significantly increased recruitment to living oysters in the field (p < 0.05). Significantly greater recruitment (p< 0.01) of ~30% occurred in higher diversity treatments in 2010, 2011, and 2012 despite variation in oyster recruitment by an order of magnitude during the study. The net biodiversity effect ranged from three in 2010 to 15 in 2011, but was positive in all three years, indicating that increased recruitment in mixed treatments can be greater than the additive effect of the single bay treatments. Losing intraspecific diversity may reduce recruitment and lead to further declines in populations of exploited species, illustrating the need for understanding how intraspecific diversity influences ecological functions.