Carl Hershner

Sustainable aquaculture: developing the promise of aquaculture

As experience with aquaculture grows worldwide, the concept of sustainable aquaculture is increasingly recognized to incorporate both spatial and temporal dimensions of environmental, economic, and social parameters. Practitioners have discovered that sustainable aquaculture must not only maximize benefits, but also minimize accumulation of detriments, as well as other types of negative impacts on natural and social environment. Therefore, sustainable aquaculture development must be advanced in a manner that is environmentally sustainable and that protects the quality of the environment for other users, while it is equally important for society to protect the quality of the environment for aquaculture. This paper provides a brief review of the worldwide aquaculture development in the last decade, and gives a few examples of sustainable aquaculture activities in the coastal areas that are using natural coastal habitats and ecosystems. Based on already existing national and international efforts to promote sustainable aquaculture, key recommendations are provided, including what should be the next proactive steps.

Influence of land use on macrobenthic communities in nearshore estuarine habitats

Macrobenthic community indices were examined for their ability to characterize the influence of shoreline alteration and watershed land use in nearshore estuarine environments of the Chesapeake Bay, U.S.A. Twenty-three watersheds were surveyed in 2002 and 2003 for nearshore macrobenthic assemblages, environmental parameters (i.e., dissolved oxygen, pH, total suspended solids, salinity, and sediment composition), shoreline condition, and land use. Two indices of macrobenthic biological integrity, benthic index of biological integrity in the nearshore (B-IBIN) and abundance biomass comparison (W-value), were evaluated for associations with environmental and shoreline condition, and riparian and watershed land use. Comparisons between nearshore measures of the B-IBI with offshore values (>2 m; Chesapeake Bay benthic index of biological integrity [B-IBICB]) were conducted to assess the ability of the index to reflect land use patterns at near and far proximities to shore. Nearshore macrobenthic communities were represented by a total of 94 species (mean number of species =9.2 ± 0.4 sample−1), and were dominated by the phyla Arthropoda, Annelida, and Mollusca. Temporal variability in environmental conditions and macrobenthic abundance and biomass may be attributable to the notable increase in precipitation in 2003 that led to nutrient influxes and algal blooms. For the biotic indices applied in the nearshore, the highest scores were associated with forested watersheds (W-value, B-IBIN). Ecological thresholds were identified with nonparametric change-point analysis, which indicated a significant reduction in B-IBIN and W-value scores when the amount of developed shoreline exceeded 10% and developed watershed exceeded 12%, respectively.

Managing Invasive Aquatic Plants in a Changing System : Strategic Consideration of Ecosystem Services

Climate change is projected to increase stress for many coastal plant communities. Along large portions of the North American coast, habitat degradation from anthropogenic changes to the environment already threaten the community structure of tidal marshes and submerged aquatic grass beds. The potential loss of ecological services historically provided by these communities has been a long-standing rationale for aggressive control of invading plants such as Phragmites australis and Hydrilla verticillata. Increasing evidence of ecological services provided by invasive species such as P. australis and H. verticillata suggest that, in the face of increasing stress, it may be prudent to take a more pragmatic approach regarding the effect of these species on coastal ecosystems. The notable resilience of these species to control efforts and their competitive success and comparative vigor in stressed systems and capacity to provide at least some beneficial services combine to suggest some invasive species may have a useful role in managed coastal ecosystems.

Temporal changes in the vegetation pattern in a tidal freshwater marsh

Temporal changes in vegetation patterns of Chesapeake Bay wetlands have been poorly documented. Data from a 1987 vegetation analysis of a Chesapeake Bay tidal freshwater marsh were compared to those of a vegetation study completed in 1974. Changes in the vegetation pattern were calculated using species importance values and a species diversity index. Comparison of the 1987 and 1974 results shows no significant difference in species diversity index. However, there was a significant difference in species contribution to the index.Spartina cynosuroides, an oligohaline species that was not among the dominant species listed in the 1974 study, had the fourth highest importance value in this study. The change in dominant species composition of the marsh may reflect a directional shift from tidal freshwater toward oligohaline conditions.

Macroscale Assessment of American Shad Spawning and Nursery Habitat in the Mattaponi and Pamunkey Rivers, Virginia

Abstract Variation in habitat suitability can alter the growth and mortality of early life stages of fishes but is often difficult to measure, quantify, and apply to the entire system. We designed and tested habitat suitability index (HSI) models incorporating both proximate riverine parameters and surrounding landscape features as determinates of optimal spawning and nursery areas for American shad Alosa sapidissima. American shad eggs and larvae were collected in the Mattaponi and Pamunkey rivers, Virginia, during 1997–1999 as direct evidence of nursery habitat use and indirect evidence of spawning reaches. Hydrographic, physical habitat, shoreline, and land use features were examined for associations with the presence of eggs and larvae. Principal components analyses and logistic regressions indicated the importance of hydrographic parameters (current velocity, dissolved oxygen, and depth), physical habitat features (sediment type and woody debris), forested shoreline, and land use features to the pres...

The Effects of Derelict Blue Crab Traps on Marine Organisms in the Lower York River, Virginia

Abstract Derelict (abandoned or lost) traps targeting blue crab Callinectes sapidus have the potential to affect the blue crab fishery and other marine-oriented species. We used side-scan sonar to locate derelict traps and assess their extent and accumulation rate. Experimental traps were monitored at four locations to calculate catch rates of marine organisms and trap degradation rates. In 2006, 635–676 derelict traps were identified in a 33.5-km2 area of the lower York River in Virginias portion of the Chesapeake Bay. Trap loss rates are estimated at 30%, resulting in the potential addition of over 100,000 traps annually to the Chesapeake Bay derelict trap population in Virginia. The top four species captured in the experimental traps were blue crab, Atlantic croaker Micropogonias undulates, oyster toadfish Opsanus tau, and white perch Morone americana. Experimental derelict traps captured 50.6 blue crabs·trap−1·season−1 during April–November 2006 and 13.6 Atlantic croakers·trap−1·season−1 during May–A...

DISAPPEARANCE OF THE NATURAL EMERGENT 3-DIMENSIONAL OYSTER REEF SYSTEM OF THE JAMES RIVER, VIRGINIA, 1871–1948

Abstract Anecdotal reports have long indicated that oysters, Crassostrea virginica (Gmelin), in the Chesapeake Bay once grew in large 3-dimensional reef structures. However, hard evidence of widespread 3-dimensional oyster reefs in the Chesapeake Bay has been scarce. This study uses data collected from historic charts of the James River, one of the most productive oyster producing tributaries of the Chesapeake Bay, to examine the natural occurrence of these reefs as well as their destruction. An early series of charts from the 1870s clearly documents widespread emergent oyster reefs in the James River from Burwells Bay to Newport News Point. They were long, fairly wide, and shoal-like and oriented at right angles to the current. A 1940s series of charts indicates that by this time nearly all of these reefs had become submerged. Paired t-tests indicate a significant decrease in reef height and volume but not in reef area. This suggests that oysters and shell have been physically removed from the reefs. This likely had a major impact on water circulation patterns over and around the reefs, which may also have further adversely affected oyster populations.

Daily variability in abundance and population characteristics of tidal salt-marsh fauna

Nekton and macrocrustacean population levels and characteristics were studied in two similar tidal marsh creeks. Absolute and area-adjusted data were analyzed to determine variability resulting from daily population fluctuations. Two sampling schemes—intensive 3-d seasonal and periodic 1-d—were examined by constructing probability matrices to compare the accuracy of data comparisons resulting from each scheme. The probability of inaccuracies in comparisons of abundance using nonreplicated sampling schemes ranged from 0% to 100%. Significant differences between consecutive day data were observed for population characteristics such as blue crab (Callinectes sapidus) sex ratios, spot (Leiostomus xanthurus) length-weights, killifish: sciaenid ratios, and killifish: blue crab ratios. These data support the need to account for short-term variability when assessing mobile aquatic fauna abundance in estuarine wetlands.

Developing and Communicating a Taxonomy of Ecological Indicators: A Case Study from the Mid-Atlantic

To ensure indicators of ecosystem health are integrated into environmental decision-making, it is imperative to provide a comprehensive framework for indicator selection and use. The same framework can also be used to evaluate the utility of any given indicator. The Atlantic Slope Consortium (ASC) has developed such a framework, based upon three primary elements: 1) The specific questions to be answered (the type of indicator), recognizing the following types of questions/indicators: Condition assessment: snapshot of the current state of the system; Stressor diagnosis: identification of causative factors of condition; Communication to the public: encouraging comprehension of condition in its most elementary or integrated form; Futures assessment: estimating the probable trajectory of condition, or assessing the vulnerability of any system to a stochastic event; Evaluation: a subset of condition indicators that evaluate the effectiveness of management actions. 2) The spatial and/or temporal scale of the issue being addressed (the spatial/temporal scale over which the indicator is valid). 3) The context of the question, using categories of surrounding land use as surrogates for social choices. A Fish Community Index (FCI) developed for the ASC will provide an example of utilizing the framework to select an indicator, as well as using the framework to judge the utility of the indicator.

Analysis of wetland total phosphorus retention and watershed structure

The relationship between total phosphorus retention, landscape position of wetlands, and surrounding land-use patterns was explored with the goal of identifying easily determined landscape parameters as indicators of a wetland’s role in water quality maintenance. Sediment cores were collected from 14 wetland sites chosen to represent a range of wetland types, wetland position, and surrounding land-use patterns in a small coastal Virginia watershed. Sediment accumulation rates and total phosphorus retention rates were analyzed using137Cs dating and acid extraction techniques. Both sediment accumulation rates and total phosphorus retention rates were found to be comparable to previously reported values for similar wetland types. The landscape analysis did not support the hypothesis that total phosphorus retention would vary with landscape setting and/or wetland type. The wetlands sampled may represent landscape parameters too similar to detect any significant differences. Alternatively, the findings may indicate that in small coastal watersheds, most wetlands perform total phosphorus retention functions to the same level. The management implications of this latter conclusion may be that headwater wetlands are particularly important for water quality functions.