Widespread global declines in shellfish reefs (ecosystem-forming bivalves such as oysters and mussels) have led to growing interest in their restoration and protection. With restoration projects now occurring on four continents and in at least seven countries, global restoration guidelines for these ecosystems have been developed based on experience over the past two decades. The following key elements of the guidelines are outlined: (a) the case for shellfish reef restoration and securing financial resources; (b) planning, feasibility, and goal setting; (c) biosecurity and permitting; (d) restoration in practice; (e) scaling up from pilot to larger scale restoration, (f) monitoring, (g) restoration beyond oyster reefs (specifically mussels), and (h) successful communication for shellfish reef restoration projects.

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./m 2) 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.

Oyster reefs are structurally complex habitats which are increasingly recognized for their importance in estuarine systems. With over 85% of oyster reefs lost to human activities globally, there is increasing interest in aquaculture to not only meet the growing need for food worldwide, but also enhance ecological functions and services. Prime among these services is the provision of habitat for marine biodiversity. We assessed the biodiversity associated with an abandoned benthic oyster farm to investigate the potential ecological benefits of benthic farming techniques used in traditional oyster farms. In addition, we made note of any invasive species which may use these abandoned structures as habitat. The macrobenthic assemblage in the oyster habitat formed by the farm was different from the surrounding mudflats, containing 61 and 26 species, respectively. Density of invertebrates was similar in both habitats (~ 5,777 ± 981 indiv·m−2), but biomass in the oyster farm over ten times greater than the mudflat substrate, which had a fauna dominated by small polychaetes (&lt;5 mm long). Molluscs and crustaceans were especially abundant in the oyster habitat and contributed to 90% of the enhanced biomass associated with oyster habitat (excluding oyster biomass). Only one invasive species was documented, the mussel Xenostrobus secures, but at densities lower than nearby artificial substrates (e.g., concrete shorelines). Oyster development on this abandoned farm appears to be self-sustaining, provide habitat and trophic support for associated benthic macrofauna. In addition to supporting higher biodiversity and biomass of associated species, traditional oyster aquaculture could improve the restoration potential of oyster reefs by supporting broodstock of native oysters, thus maintaining larval supply.

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