The importance of restoring filter-feeders, such as the Eastern oyster Crassostrea virginica, to mitigate the effects of eutrophication (e.g. in Chesapeake Bay) is currently under debate. The argument that bivalve molluscs alone cannot control phytoplankton blooms and reduce hypoxia oversimplifies a more complex issue, namely that ecosystem engineering species make manifold contributions to ecosystem services. Although further discussion and research leading to a more complete understanding is required, oysters and other molluscs (e.g. mussels) in estuarine ecosystems provide services far beyond the mere top-down control of phytoplankton blooms, such as (1) seston filtration, (2) benthic-pelagic coupling, (3) creation of refugia from predation, (4) creation of feeding habitat for juveniles and adults of mobile species, and for sessile stages of species that attach to molluscan shells, and (5) provision of nesting habitat.

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Restoration of degraded ecosystems is an important societal goal, yet inadequate monitoring and the absence of clear performance metrics are common criticisms of many habitat restoration projects. Funding limitations can prevent adequate monitoring, but we suggest that the lack of accepted metrics to address the diversity of restoration objectives also presents a serious challenge to the monitoring of restoration projects. A working group with experience in designing and monitoring oyster reef projects was used to develop standardized monitoring metrics, units, and performance criteria that would allow for comparison among restoration sites and projects of various construction types. A set of four universal metrics (reef areal dimensions, reef height, oyster density, and oyster size-frequency distribution) and a set of three universal environmental variables (water temperature, salinity, and dissolved oxygen) are recommended to be monitored for all oyster habitat restoration projects regardless of their goal(s). In addition, restoration goal-based metrics specific to four commonly cited ecosystem service-based restoration goals are recommended, along with an optional set of seven supplemental ancillary metrics that could provide information useful to the interpretation of prerestoration and postrestoration monitoring data. Widespread adoption of a common set of metrics with standardized techniques and units to assess well-defined goals not only allows practitioners to gauge the performance of their own projects but also allows for comparison among projects, which is both essential to the advancement of the field of oyster restoration and can provide new knowledge about the structure and ecological function of oyster reef ecosystems. Implications for Practice• Requests from restoration practitioners for a set of specific monitoring guidelines tiered to account for limitations in budgets and expertise in oyster restoration projects have been fulfilled by a panel of scientific experts and restoration practitioners. • Oyster restoration projects should monitor established universal metrics primarily focusing on structural attributes (vertical relief of oyster reefs, oyster density, and spatial footprint over time); specific minimum requirements for timing of monitoring are essential. • Measurement of broader ecosystem-based metrics would allow for more thorough examination of specific ecological benefits of restoration projects. • Detailed methodology provided publicly through a workshop report gives restoration practitioners access to training material and reporting information.

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ABSTRACT. The protozoan oyster parasite Perklnsus marinus causes extensive mortality in eastern oyster (Crassostrea vlrglnica) populations during summer and fall across much of the oyster's distnbution. Despite more than 40 yr of research on thls particular parasite, no study has unequivocally demonstrated a genetic basis for host resistance to P marinus nor has it been determined whether or not there are races of P mannus that vary in virulence. Using recently developed techniques to culture P mannus In vitro, we examined the resistance of 4 genetically distinct oyster populations that had different natural histories of exposure to l? marinus and the virulence of 4 geographically distlnct isolates of P marinus. Offspring were produced from each oyster population and reared in a common environment, then exposed to each isolate of P ~narininus. Oysters showed levels of resistance roughly corresponding to the duration parental populations had been exposed to P marinus (Texas > Virginia > New Jersey = Maine), indicating that those populations which have been exposed to P mannus for more than 40 yr have developed some resistance. Parasites isolated from the Atlantic coast (Mobjack Bay, VA and Delaware Bay, NJ, USA) produced heavier infections than those lsolated from the Gulf of Mexico coast (Barataria Bay, LA and South Bay Laguna Madre, TX, USA), indicating that Atlantic isolates were more virulent than Gulf isolates. These data indicate that resistant races of the eastern oyster exist, and imply the existence of virulent parasite races. No statistically significant interaction was detected between oyster populations and parasite isolates. Relative infection intensities among oyster populations remained more or less constant across parasite isolates and vice versa. The lack of a significant interaction between host populat~ons and parasite isolates Indicated that mechanisms of resistance and virulence were general, not race-specific.