Abstract or Summary
Oyster reefs or beds are a globally imperiled marine habitat, with degradation primarily driven by anthropogenic factors such as overharvest, changes to hydrology and salinity regimens, pollution and introduced disease. While oyster restoration efforts have historically focused on improving harvests, in recent decades there has been an increasing recognition and better quantitative description of a broader array of ecological services provided by oysters. This has prompted many agencies and conservation organizations to re-focus their attention on restoring oyster habitat for these broader ecological functions and societal benefits. Benefits include production of fish and invertebrates of commercial, recreational and ecological significance, water quality improvement, removal of excess nutrients from coastal ecosystems, and stabilization and/or creation of adjacent habitats such as seagrass beds and salt marshes. Increasingly, these ecosystem services are cited as the principal or exclusive goal(s) of oyster restoration projects.
Despite increased restoration the restored reefs have often not been monitored to an extent that allows for comparison. A recent meta-analysis of oyster restoration projects in the Chesapeake Bay examined the available datasets from 1990 to 2007, analyzing over 78,0000 records from 1035 sites (Kramer and Sellner 2009, Kennedy et al. 2011). The analysis found that relatively few of the restoration activities were monitored, and that the restoration goals of many of the projects were not well-defined, with only 43% of the datasets including both a restoration and monitoring component. The authors concluded that the monitoring of this large body of work was inadequate, and they were unable to assess changes in oyster populations on the constructed reefs. Their recommendations were to implement all oyster restoration projects using experimental designs with robust sample size replication and quantitative pre- and post-restoration monitoring. Sufficient monitoring would allow for adaptive management during the post-construction phase, for assessing whether the project met its goals and related performance criteria or to determine whether restored reefs are achieving the stated ecosystem-based restoration goals.
To address this critical gap, a working group was formed that consisted of restoration scientists and practitioners from the Atlantic, Pacific, and Gulf coasts of the US. The aim of the group was to recommend monitoring techniques and performance criteria for both the eastern oyster (Crassostrea virginica) and the Olympia oyster (Ostrea lurida) that would allow for more extensive and consistent post-restoration assessment between projects on varying geographic scales. With additional expert input, the working group developed recommendations for a set of Universal Metrics that should be monitored for all oyster restoration projects. The working group also developed guidelines for assessing optional Restoration Goal-based Metrics. The Goal-based Metrics were not meant to be monitored for all projects, but could be monitored as needed to measure project performance and to advance the science of oyster habitat restoration depending on the availability of the necessary funding, capacity, and expertise. The Universal Metrics allow for the systematic assessment of the basic performance of restoration projects, whereas the Restoration Goal-based Metrics would allow practitioners to assess the performance of the restored reefs in meeting the ecosystem service-based restoration goal(s) associated with a project. Together, these metrics allow for the comparison of projects across a variety of scales and restoration approaches. Monitoring of the Universal Environmental Variables will also aid in the interpretation of Universal and Restoration Goal-based Metrics data collected through both pre- and post-restoration monitoring.
The Universal Metrics that should be monitored for every oyster restoration project include: (1) reef areal dimension; (2) reef height; (3) oyster density; and, (4) oyster size-frequency distributions. Performance criteria for the Universal Metrics are based on emergent structure (assessed as reef height), successful recruitment, and oyster density present at both short and mid-term post-construction time frames. The following Universal Environmental Variables should also be monitored for every oyster restoration project to aid with interpretation of Universal Metrics data: (1) water temperature; (2) salinity; and, (3) dissolved oxygen (for subtidal reefs). Restoration practitioners that lack the equipment or capacity to conduct the minimum required monitoring should collaborate with others able to provide this capability such as local researchers from academic institutions and local, state or federal agencies.
Along with the Universal Metrics, the Restoration Goal-based Metrics are an optional set of monitoring guidelines provided to enable project managers to assess the following ecosystem service-based restoration goals: (1) brood stock and oyster population enhancement; (2) habitat enhancement for resident and transient species; (3) enhancement of adjacent habitats; and (4) water clarity improvement. This handbook is meant to be a living document that allows for future updates as monitoring methodologies and the state of the science evolve, and as meta-analyses of comparable data are undertaken. Restoration practitioners and other interested parties may at any time submit their comments and any suggestions for improvement to the handbook to ormetrics@gmail.com for consideration in future editions.