LB 20-177 - Effects of a non-native Watersipora on the abundance and percent cover of native Olympia oyster, Ostrea lurida

Non-native fouling organisms settling onto natural hard substrata in estuaries can harm native species via mechanisms like space competition and predation. Understanding how non-native foulers influence native species recruitment is critical in predicting future native species composition. The effects of the non-native bryozoan, Watersipora subtorquata, and other foulers on Ostrea lurida recruitment were studied to determine whether their percent cover affects native oyster abundance and cover. Terracotta tiles were deployed in Newport Bay, California at tidal elevations between -0.5 and -1.0 feet MLLW during oyster’s spawning and recruitment season. Four treatment groups (n=10 per treatment) were established to examine the effects of foulers on O. lurida recruitment: unmanipulated controls, W. subtorquata removal, other fouler removal, and all fouler removal. Treatments were maintained by monthly removal of W. subtorquata and other foulers as appropriate per treatment. Oysters recruiting to the tiles were measured for length and width, identified, and quantified. Point contact technique was used to record cover of species recruiting to tiles. We hypothesized that presence of W. subtorquata and other foulers would lead to low abundance and cover of O. lurida recruits. Surprisingly, W. subtorquata and other foulers had no significant effect on abundance or cover of O. lurida. Fouling species, including ubiquitous non-natives like W. subtorquata, may not be as harmful to native species in local estuarine habitats as predicted.