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Research: Ecosystem approaches to aquatic health assessment: linking subtidal habitat quality, shoreline condition and estuarine fish communities
 Final Report
Project goals
1) Estimate levels of development stressors at the land-water interface that elicit fish community responses
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Amount of Developed Upland Land Use
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Shoreline Modification (Bulkhead, Riprap, Natural)
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Developed lands and Shoreline modification combinations
2) Link habitat condition monitoring datasets to support nearshore ecosystem models.
Coastal development impacts estuarine resources by severing terrestrial-aquatic linkages, reducing shallow-water habitats, and degrading ecosystem services. We assessed the effects of landscape features on nearshore habitats and biological communities, relating subtidal habitat, shoreline condition, upland land use and nearshore fish communities in a Chesapeake Bay tributary, the James River, Virginia. Both upland development and the placement of erosion control structures on the shoreline were associated with reduced fish community integrity, and shoreline alterations were linked with the amount of subtidal structural habitat in the nearshore. Ecological thresholds in nekton community integrity were evident at ≥ 23% developed land use within 200 and 1000 m buffer increments. Nekton assemblages at sites with low development (≤ 23%) and natural or riprap shorelines were different from all other combinations of altered conditions (low development with bulkhead, and high development with riprap or bulkhead). Species composition along natural or riprap revetment shorelines with low upland development tended to be diverse and inclusive of tidal marsh species, while highly developed sites or bulkhead shorelines were dominated by a few generalist species. The complex interaction between watershed (both nearshore and inland) and shoreline development presents a unique challenge for coastal planning. Alternate moderating approaches for coastal development may include preservation of riparian buffers, the placement of living shorelines for erosion control where appropriate, and development of targeting tools to identify landscapes near an ecological threshold.
Figure 1. Fish Community Survey Locations and land use on the James River, 2005 (National Land Cover Database).
Amount of structural benthic habitat (such as oyster reefs, clam beds or woody debris) was highest at sites with natural shoreline (30%), as opposed to hardened shoreline (riprap or bulkhead; 6 %) indicating a potential land-water nexus
Fish Community index lowest for bulkhead sites—the most altered shorelines. Natural and riprap revetment sites similar
Established a threshold of fish community response to gradients of developed lands. Significant negative fish community response occurred at ≥23% developed lands 95% probability a threshold occurred
Species composition along natural or riprap revetment shorelines with low upland development tended to be diverse and inclusive of tidal marsh species, while highly developed sites or bulkhead shorelines were dominated by a few generalist species.
Conclusions
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Both upland development and the placement of erosion control structures on the shoreline were associated with reduced fish community integrity.
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Evident ecological thresholds, or breakpoints at which the fish community notably responded to a disturbance, occurred at relatively low levels of development (>23%) indicating that comprehensive shoreline and watershed land use plans are imperative to minimize impacts
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Fish community integrity was lowest along bulkheaded shorelines, and indistinguishable between natural and riprap revetment sites, which may mimic natural shorelines.
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The preservation of riparian zones and natural shoreline conditions, may help mitigate the stress from upland watershed development below the threshold---HOWEVER, additional research is necessary to establish what shoreline type, and/or riparian buffer type & width may be most effective in high development scenarios.
Associated Publications:
Bilkovic, D.M. and M. Roggero. Effects of coastal development on nearshore estuarine nekton communities. Marine Ecology Progress Series.
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