Restoration potential of Asian oysters on heavily developed coastlines

Abstract

Reef-building oysters historically provided the main structural and ecological component of temperate and subtropical coastal waters globally. While the loss of oyster reefs is documented in most regions globally, assessments of the status of Asian oyster reefs are limited. The feasibility of restoration within the regional biological and societal contexts needs to be assessed before implementation. Here, we quantified the current distribution of natural oyster reefs (Crassostrea spp.) in the shallow coastal waters of Hong Kong, assessed the biological feasibility of reestablishing reefs using natural recruitment, and examined their current and potential water filtration capacity as a key ecosystem service provided by restoration. We found natural low-relief oyster beds in the low intertidal coastal areas at a subset of the locations surveyed. These areas are, however, degraded and have sparse densities of oysters generally <2 years old. Recruitment was high in some areas (>500,000 indiv./m2) and while survival to maturity varied across sites there was adequate larval supply and survival for restoration. Filtration rates for a 1-year-old recruit (90 mm length, approximately 30 L/hour per individual) at summer temperatures (30°C) meant that even the small remnant populations are able to provide some filtration services (up to 31.7 ML/hour). High natural recruitment means that oyster reef restoration can be achieved with the addition of hard substrate for recruitment, increased protection of restoration sites, and would not only increase the ecological value of reefs regionally but also serve as a model for future restoration in Asia.