Community ecology and population dynamics of the European native oyster (Ostrea edulis) in Essex, UK: A baseline for the management of the Blackwater, Crouch, Roach and Colne Estuaries Marine Conservation Zone

Following the designation of the Blackwater Crouch Roach and Colne Estuaries Marine Conservation Zone (hereafter BCRC.MCZ) in 2013, there is now a legal obligation to “protect and enhance” remaining stock of the European native oyster, Ostrea edulis. Despite this, little is known about the current distribution, abundance and status of the O. edulis populations within this protected area, with no studies documenting epibenthic species associations with naturally occurring native oyster densities. Widescale dredge surveys were used to assess the current status O. edulis over a 5-year period between 2014 and 2018 and associated species between 2016 and 2018 across the BCRC.MCZ. Between 2016 and 2018 surveys were completed biannually in post-winter (February/Post-winter) and post-summer (September/October) to assess seasonal variation in these distributions. Associations between increasing natural densities of native oyster and increasing epibenthic species richness have been observed across the BCRC.MCZ, however, these associations are suppressed and even reversed in areas which also support high densities of the non-native Crepidula fornicata. In addition, a novel experiment was designed to monitor the growth rates and survival of O. edulis with individual oysters monitored for a maximum of 18 months across three sites within the BCRC.MCZ and four sites within areas designated for the mariculture of native oysters. Data from both studies was then used to create an Integral Projection Model to assess the current status of native oyster populations, assess limiting factors to population growth, and make future projections of these populations to drive management and restoration decisions. Site-dependent restoration techniques are recommended with strategies to increase adult oyster survival and juvenile recruitment recommended.