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How to Monitor Sites using Oyster Restoration Metrics
Restoration of subtidal and intertidal oyster reef habitat is ongoing in most U.S. coastal states. Determining the success of restoration efforts is critical both for the cost-effective use of resources and maintenance of best management practices. Assessing success depends on the identified goals of a restoration project. Different measures or metrics will be suitable and ⁄ or unsuitable for assessing whether a restoration project’s goals are attained.
Click on each of the following reef restoration goals identified in the May 2004 Metrics Workshop to view its associated metrics:
Habitat
Shoreline
Water Quality
Harvesting
Broodstock
Education
Habitat: Oyster reefs provide habitat for fish and invertebrates that require structural complexity for foraging, nesting and refuge from predators. Fish associated with oyster reefs range from residents that use the reef as a primary habitat to transient species that are wide ranging and may forage on or near the reef. Some fish species, such as oyster toad fish, gobies, and blennies, attach eggs to the undersides of oyster shells, relying on reef architecture or microhabitat for reproductive success. Crabs commonly are found in greater densities on oyster reefs than on surrounding open-bottom habitat where vulnerability to predation is greater and prey resources are less abundant. Bivalves including clams and mussels also may utilize reefs as a refuge from predators enabling populations within reefs to act as a source for mudflat and marsh populations that may be depleted more easily by predators.
Appropriate metrics: reef density; size frequency; associated fauna; reef size; reef architecture; fragmentation; salinity; dissolved oxygen; temperature.
Shoreline: Oyster reefs are hard structures on typically unconsolidated or mobile bottom sediments that can extend above the sediment surface in subtidal areas or fringe marshes in the low intertidal zone. In subtidal systems, reefs provide vertical relief in otherwise featureless benthic environments that can reduce fetch and the wind-driven resuspension of particulate matter. Oyster reefs near salt marshes absorb wave energy and promote colonization and persistence of the salt marsh habitat. The reduction in sediment input from shoreline erosion and subtidal resuspension can increase light penetration and promote growth of submerged aquatic vegetation (SAV) or benthic microalgae that further stabilize unconsolidated sediments. Restored reefs can be placed near SAV and⁄or intertidal marshes to enhance the value of the vegetated habitat and control erosion (e.g., mediating boat wake effects that can cause marsh banks to erode into tidal creeks).
Appropriate metrics: reef density; size frequency; reef size; reef architecture; fragmentation.
Water Quality: Filter feeding bivalves can affect significantly water quality and phytoplankton dynamics. Extensive oyster populations have a substantial filtering capacity and may remove significant phytoplankton biomass from the water column. The result is a reduction in the biological oxygen demand from the microbial decomposition of algal cells that otherwise would settle to the sediment. Bivalve filtration may have improved the water quality in several basin-wide ecosystems, but bivalve control of phytoplankton has been questioned. Ecosystem rehabilitation typically relies on a reduction of nutrient inputs (e.g., nitrogen, phosphorus) that result in eutrophication, but filter feeding bivalves such as oysters may be equally important for improving water clarity and quality by removing algae and sediments suspended in the water column.
Appropriate metrics: reef density; size frequency; associated fauna; reef size; salinity; dissolved oxygen; chlorophyll; turbidity; temperature.
Harvesting: Fisheries enhancement often is the goal of many restoration projects, especially in states experiencing a decline in the oyster fishery. Economic incentives to maintain an oyster fishery remain even in states with drastically reduced yields. Oyster reef restoration often is undertaken to create marketable-size oysters that are available to both recreational and commercial harvesters. An unanticipated conflict to creating reefs for harvesting is the frequent observation that harvesting can affect negatively the ecological success of the reef (e.g., breaking up clusters to retrieve marketable oysters)
Appropriate metrics: reef density; size frequency; reef size; reef architecture; fragmentation; salinity; dissolved oxygen.
Broodstock: Creating oyster reefs in refuge areas where oyster harvesting is not allowed can protect brood stock and larger individuals with disease resistance. Creation of oyster reefs off limits to harvesting can enhance oyster populations in surrounding harvested areas that are many times the size of the refuge itself. Off limit reefs provide protection for larger individuals that have the greatest fecundity and some resistance to disease potentially increasing the fitness and survival of recruits to the harvestable population. Oyster reef sanctuaries develop into mature and structurally complex habitats with many associated benefits for fish and decapod crustaceans.
Appropriate metrics: reef density; size frequency; reef size; fragmentation; salinity; dissolved oxygen; temperature.
Education: Community-based restoration projects provide educational benefits through programs that foster a more scientifically and environmentally informed public. In some areas, coastal residents of all ages become involved in the construction and monitoring of local reefs (e.g., SCORE). Waterfront property owners are informed about the ecological benefits of filter feeding bivalves to water quality and overall coastal ecosystem health. Small scale reef restoration projects may be implemented successfully with private citizen involvement.
Appropriate metrics: reef density; associated fauna; reef architecture; salinity; dissolved oxygen; turbidity.