Recruitment of the eastern oyster, Crassostrea virginica, in response to settlement cues and predation in North Carolina

• The settlement cue Glycyl-Glycyl-Arginine (GGR) enhances larval settlement in the lab.
• We assessed the ability of settlement cue GGR to enhance oyster settlement in the field.
• GGR presence actually reduced oyster recruitment in the field.
• Caging experiments suggested high predatory mortality regardless of cue treatment.
• Chemical inducers are ineffective in the face of predation under field conditions.

We conducted two field experiments to test the hypothesis that recruitment of the eastern oyster, Crassostrea virginica, could be enhanced through the selective deployment of artificial settlement cues. For both experiments, either dead shell or live oysters were cemented to patio blocks. In the first experiment, half of the blocks received discs that diffused the tri-peptide Glycyl-Glycyl-Arginine (GGR), a potent analog for natural settlement inducers, and only blocks with dead shell received GGR in the second experiment. Recruitment was therefore monitored on substrata with settlement cues (live oyster or shell with GGR) and no settlement cues (dead shell only). In our preliminary experiment (Experiment 1), recruitment of oysters was lower to blocks with live oyster or GGR, counter to our expectation. We repeated the experiment with the addition of anti-predation cage treatments (with partial cage controls). Again, we found no enhancement of recruitment to blocks with live oysters or with cue added. However, recruitment was significantly higher on blocks shielded from predation. These results suggest both a strong predator control in this system and that adding chemical cues are not likely to be an effective restoration strategy.