Post-settlement survival and growth of the Suminoe oyster, Crassostrea ariskensis, exposed to simulated emersion regimes

In high salinity habitats along the Middle and South Atlantic coasts of the United States the Eastern oyster, Crassostrea virginica occupies an intertidal refuge from predation, facilitated by its tolerance of aerial exposure and associated desiccation and temperature stress. Observations of the Suminoe oyster, C. ariakensis in its native environments in Asia reveal that this species is most commonly found subtidally or in the very low intertidal zone, suggesting that it may be less tolerant of aerial exposure. With serious consideration being given to introducing C. ariakensis to the mid-Atlantic region, it is important to understand the ability of this non-native species to invade and become established in the intertidal zone. We conducted experiments in an outdoor quarantined facility to compare the tolerances of C. virginica and C. ariakensis to varying levels of aerial exposure. Diploid C. virginica and C. ariakensis were set on 10 cm x 10 cm PVC tiles, held in a flow-though quarantine system exposed to ambient weather conditions, and subjected for eight weeks to four simulated tidal emersion regimes-(1) high intertidal (3.5 h emersion), (2) mid intertidal (2 h emersion), (3) low intertidal (1 h emersion), and (4) subtidal (constant immersion)-and four exposure orientations-(1,2) vertical north- and south-facing, and (3,4) horizontal up- and down-facing. Complete mortality of both species occurred in the high intertidal treatment by the end of week 1. No C. ariakensis had survived in the mid intertidal treatment by week 2 and very few remained alive in the low intertidal treatment. By the end of week 5, only 1.25% of the C. ariakensis had survived in the low intertidal treatment, whereas survival of C. ariakensis in the subtidal treatment was 36.88%. Significantly, C. virginica survival was 80.63% in the subtidal treatment and 67.50% and 28.13% on the vertically-oriented tiles (north- and south-facing treatments combined) in the low intertidal and mid intertidal treatments, respectively. Growth rates of C. virginica across tidal treatments were greatest in the subtidal treatment and C. ariakensis grew faster in the subtidal treatment than C. virginica. These results indicate that even with modest aerial exposure, under climatic conditions characteristic of summers in the mid-Atlantic region of the United States, C. ariakensis would suffer high rates of early post-settlement mortality, effectively restricting this non-native oyster species to subtidal environments if introduced to the region

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\u2014even 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 (\u201cland-reclamation\u201d) 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: \u2022 Improve Protection for reefs of native shellfish; \u2022 Restore and Recover Reefs back to functioning ecosystems that providemultiple services to humans; \u2022 Manage Fisheries Sustainably for ecosystems and livelihoods; \u2022 Stop the Intentional Introduction and Spread of Nonnative Shellfish; and \u2022 ImproveWaterQualit

Oyster reefs at risk and recommendations for conservation, restoration, and management

Native oyster reefs once dominated many estuaries, ecologically and economically. Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide. We examined the condition of oyster reefs across 144 bays and 44 ecoregions; our comparisons of past with present abundances indicate that more than 90% of them have been lost in bays (70%) and eco regions (63%). In many bays, more than 99% of oyster reefs have been lost and are functionally extinct. Overall, we estimate that 85% of oyster reefs have been lost globally. Most of the world's remaining wild capture of native oysters (> 75%) comes from just five ecoregions in North America, yet the condition of reefs. in these ecoregions is poor at best, except in the Gulf of Mexico. We identify many cost-effective solutions for conservation, restoration, and the management of fisheries and nonnative species that could reverse these oyster losses and restore reef ecosystem services