Intraspecific variation influences natural settlement of Eastern Oysters

Background/Question/Methods

Intraspecific variation can significantly affect populations and communities in ecological time by increasing stability and productivity.  Most studies examining intraspecific diversity have focused on clonal organisms and manipulated numbers of genotypes. We tested how intraspecific diversity affected the ecological function of a habitat-forming, non-clonal species by examining how increasing diversity of adult oysters (Crassostrea virginica) influenced natural settlement of oyster larvae We collected oysters from three distinct bay systems in Texas, USA and compared natural settlement in treatments where all oysters were from a single bay to a mixture of all three bays.

Results/Conclusions

In the field, oyster larvae preferentially settled when living oysters were present vs. dead oyster shells.  Significantly greater recruitment occurred in mixed treatments in 2010 and in 2011, and oyster recruitment was an order of magnitude greater in 2011. The net biodiversity effect was significantly positive in both years, indicating that increased recruitment in mixed treatments was greater than an additive effect of the single bay treatments and suggesting some form of facilitation is involved. However, we cannot determine whether differences in cues among the adult oysters, biofilms, or oyster-biofilm interactions are the direct cause of this pattern. Neutral genetic differences among populations were not found, but neutral markers may not be good predictors of genome-wide variation or the importance of intraspecific effects. This system can serve as a model for studying intraspecific effects in non-clonal habitat-building species.