Shellfish Reefs at Risk: A Global Analysis of Problems and Solutions

This is the first global assessment of the distribution and condition of bivalve shellfish reefs that occur in temperate and subtropical estuaries. The assessment is focused primarily on biogenic reefs formed by oysters within their native ranges, but also includes observations aboutmussels that formbeds and provide other ecosystemservices.We compiled quantitative and qualitative data about these reefforming species frompublished literature as well as expert surveys and direct observations and derived condition estimates for oyster reefs in 144 estuaries and 40 ecoregions around the world. Based on these data, we conclude that oyster reefs are one of, and likely themost, imperiledmarine habitat on earth: oyster reefs are in poor condition, defined as having declined >90%fromhistoric levels, in 70%of bays and 63%ofmarine ecoregions. Even more troubling, oyster reefs are functionally extinct (>99% loss of reefs) in 37%of estuaries and 28%of ecoregions. Globally, we estimate that 85% of oyster reefs have been lost—even greater than the losses reported for other important habitats including coral reefs,mangroves, and seagrasses. Although oyster reefs are beginning to receive some conservation attention, they remain an obscure ecosystemcomponent and still are vanishing at sometimes alarming rates. Many threats that have contributed to the profound loss of reefs around the world continue largely unabated today. Destructive fishing practices that directly alter the physical structure of reefs have been implicated in rapid declines in both fisheries productivity and overall reef condition in many estuaries. Fishing practices involving translocation and introduction of non-native shellfish within and between bays has increased the incidence and severity of disease and parasite outbreaks that have all but eliminated fisheries in many coastal areas. Coastal development activities including filling (“land-reclamation”) and dredging of shipping channels have also taken a toll on reefs. Likewise, activities occurring upstreamcontinue to cause problems as human populations increase in coastal watersheds. Altered river flows, construction of dams, poorlymanaged agriculture, and urban development can all impact the quality and quantity of water and sediments that affect whether shellfish reefs persist or perish. There are many things that can and should be done to address this glaring gap inmarine conservation.We identify a series of cost-effective strategies that can help turn the tide. No one strategy will be right for each area or threat and it is assumed thatmultiple strategies will be needed inmost places. The strategies are grouped into five themes: • Improve Protection for reefs of native shellfish; • Restore and Recover Reefs back to functioning ecosystems that providemultiple services to humans; • Manage Fisheries Sustainably for ecosystems and livelihoods; • Stop the Intentional Introduction and Spread of Nonnative Shellfish; and • ImproveWaterQuality