Applicability of the valve gape monitor to assist with oysters bed (Ostrea edulis) restoration projects

Samenvatting

To monitor flat oyster reef restoration projects in offshore pilots innovative techniques with a focus on remote monitoring are needed. This will reduce the frequency with which offshore pilot study locations have to be visited. The valve gape monitor can potentially be used as an effective method to monitor survival and behaviour of the European flat oyster Ostrea edulis. This is an in situ device that continuously measures the opening and closing of the shell of live bivalves (valves) equipped with sensors. It has been successfully used in combination with other bivalve species. In this study, eight oysters Ostrea edulis from two different regions (Norway and the Netherlands (Grevelingen)) were fitted with valve gape sensors. Valve gape activity was monitored during different experimental conditions (tide simulation and starvation) under controlled conditions to test the applicability of the valve gape monitor to assist with monitoring of O. edulis reef restoration projects. No significant differences in valve gape activity of Norwegian oysters and oysters from the Grevelingen were detected under controlled conditions. Tide simulation did not appear to affect valve gape activity. However, the oysters were responsive to disturbances such as daily maintenance as well as starvation. Size frequency distribution of gape class clearly shows that fed individuals show longer periods of open valves and percentage closure is significantly higher in the starved oysters. Gape width is larger in fed conditions then in starved conditions. In addition, starved oysters open less wide when they open. These results indicate that food availability affects valve gape activity and the valve gape monitor can provide information on the behaviour and stress response of Ostrea edulis. In situ monitoring of flat oyster gape activity should incorporate environmental parameters such as Chl a, temperature, salinity, current speed and oxygen to provide insight into the environmental stressors on and/or the behavioural patterns of flat oysters.