Charles J. Keppler

Water Quality Variation and Clam Growth: Is pH Really a Non-issue in Estuaries?

A tandem deployment system was used to critically evaluate relationships between important water chemistry parameters (pH, salinity, dissolved oxygen) and biotic performance based on clam growth. The effects of environmental conditions on growth of juvenile clams,Mercenaria mercenaria, were determined after 7-day field deployments in cages at reference sites from 1998 to 2000. Continuous measurements of the overlying water chemistry parameters were monitored by deploying an in situ water quality instrument (Hydrolab Datasonde) at the same time. While salinity was identified as an important determinant of clam growth over wide salinity ranges (10–35‰), pH was also found to be a very important parameter, especially in low-salinity regimes (<25‰). Average pH measurements ranged from 7.2 to 7.8; minimal pHs ranged from 6.9 to 7.6. The results indicated that when average pH levels fell below 7.5 or minimum pH levels fell below 7.2, growth rates were <50% that of clams deployed under higher pH conditions. Estuarine systems are generally perceived as being well-buffered so pH is frequently assumed to be unimportant, but our results suggest that pH levels can decline in estuarine systems to levels that can adversely affect biological responses. The potential impacts on biological resources of even moderate decreases in pH, particularly in systems that naturally tend to have lower pH conditions, may be more important than previously realized.

Harmful algal blooms in South Carolina residential and golf course ponds

The South Carolina coastal zone is among the fastest growing areas in the U.S., and population epicenters are marked by dense brackish water pond (lagoon) coverage associated with housing complexes and golf courses. Surveillance efforts in 2001–2002 documented the widespread occurrence of several types of potentially or measurably toxic harmful algal blooms (HABs) in these ponds. These man-made retention ponds were constructed in order to serve as a buffer between developed areas and open estuaries or for aesthetic reasons. However, the combination of restricted tidal flow and nutrient and/or contaminant deposition creates a stimulatory environment for potential HAB formation. These discoveries introduce the need to consider mitigation measures to existing ponds and HAB preventive strategies for future pond construction.

Biomarker studies with juvenile oysters (Crassostrea virginica) deployed in-situ

Hatchery-reared juvenile oysters (Crassostrea virginica) were deployed in situ for approximately 1 month from mid-May to mid-June of 1996 at sites that were classified as reference, agricultural, suburban, or urban/industrial. Cellular responses (lysosomal destabilization, glutathione concentrations, lipid peroxidation, heat shock proteins, metallothioneins, and multi-xenobiotic resistance proteins) were analysed, and their efficacy as biomarkers of stress was evaluated. Increased lysosomal destabilization, glutathione depletion, increased lipid peroxidation, and induction of heat shock proteins and metallothioneins were observed at many of the polluted sites, but increases in multixenobiotic resistance proteins were not. Significant correlations between sediment contaminants and lysosomal destabilization or glutathione concentrations were observed. Similarly, there were significant correlations between sediment cadmium and copper levels and metallothioneins. Although elevated lipid peroxidation products and heat shock proteins were observed at some of the contaminated sites, there were no significant correlations with contaminants. These studies suggest that lysosomal destabilization and glutathione depletion are sensitive, robust indicators of contaminant stress. Although lipid peroxidation and heat shock protein responses were not correlated with contaminants, they are still regarded as valuable indicators of stress. These studies demonstrate the value of using a suite of cellular biomarkers to identify and characterize stress responses related to anthropogenic perturbations.

Expression of P-glycoprotein in the gills of oysters, Crassostrea virginica: seasonal and pollutant related effects

The expression of p-glycoprotein (p-gp) in aquatic organisms has been proposed as a biomarker of pollution exposure. Previous research has provided evidence that p-gp is inducible by organic xenobiotics and that p-gp is overexpressed in mussels from degraded areas. However, seasonal changes in expression at polluted sites has not been described previously. The purposes of these studies were to evaluate the expression of p-gp in polluted and unpolluted sites in oysters (Crassostrea virginica) and to determine if there were seasonal differences. P-gp expression and total protein concentrations were measured seasonally in the gills of southeastern oysters, Crassostrea virginica, at degraded and undegraded sites in Charleston Harbor, South Carolina, USA. At all sites, p-gp expression was generally higher during the warmer months and lower in the colder months. Polluted sites tended to show a decrease in p-gp expression in June and September, suggesting that p-gp inhibition may have occurred. P-gp expression was not significantly related to specific classes of sediment contaminants or to overall sediment contaminant loading. Total gill protein concentrations at all sites were lower during the warmer months and higher during the colder months. In general, all sites tended to show decreased total gill protein concentrations when compared to the control site. Total protein concentrations were significantly related to water temperature, specific classes of sediment contaminants and overall sediment contaminant loads, but there was no relationship with salinity.

Comparison of methods for evaluating acute and chronic toxicity in marine sediments

Sublethal test methods are being used with increasing frequency to measure sediment toxicity, but little is known about the relative sensitivity of these tests compared to the more commonly used acute tests. The present study was conducted to compare the sensitivity of several acute and sublethal methods and to investigate their correlations with sediment chemistry and benthic community condition. Six sublethal methods (amphipod: Leptocheirus plumulosus survival, growth, and reproduction; polychaete: Neanthes arenaceodentata survival and growth; benthic copepod: Amphiascus tenuiremis life cycle; seed clam: Mercenaria mercenaria growth; oyster: Crassostrea virginica lysosome destabilization; and sediment-water interface testing with mussel embryos, Mytilus galloprovincialis) and two acute methods (amphipod survival with Eohaustorius estuarius and L. plumulosus) were used to test split sediment samples from stations in California. The test with Amphiascus proved to be the most sensitive sublethal test and the most sensitive overall, identifying 90% of the stations as toxic. The Leptocheirus 10-d test was the most sensitive of the acute tests, identifying 60% of the stations as toxic. In general, the sublethal tests were not more sensitive to sediments than the acute tests, with the sublethal tests finding an average of 35% of the stations to be toxic while the acute found 44%. Of the sublethal tests, only the Amphiascus endpoints and Neanthes growth significantly (p <or= 0.05) correlated with sediment chemical concentrations. Poor correspondence occurred between the toxicity endpoints and the indicators of benthic community condition. Differences in test characteristics such as mode of exposure, species-specific contaminant sensitivity, changes in contaminant bioavailability, and influence of noncontaminant stressors on the benthos may have been responsible for variation in response among the tests and low correspondence with benthic community condition. The influence of these factors cannot be easily predicted, underscoring the need to use multiple toxicity methods, in combination with other lines of evidence, to provide an accurate and confident assessment of sediment toxicity.

Seasonal variation in lysosomal destabilization in oysters, Crassostrea virginica.

Lysosomal destabilization assays have been used as valuable biomarkers of pollutant exposures in a variety of bivalve and fish species. The responses of oysters, Crassostrea virginica, deployed at and native to various reference and degraded sites were evaluated for lysosomal destabilization during both summer and winter seasons. In both native and deployed oysters, lysosomal destabilization rates tended to be higher during the winter at both reference and polluted sites. There are at least two hypothetical explanations. Greater lysosomal destabilization rates may be related to physiological changes associated with mobilization of nutrient reserves during the winter and gametogenesis. However, lysosomal destabilization in deployed oysters was correlated with tissue metal concentrations. These data also support a second hypothesis that seasonal differences in physico-chemical factors (such as reduced levels of acid volatile sulfides) may increase the bioavailability of metals during the winter so that adverse effects are more pronounced.

Cellular responses of oysters, Crassostrea virginica, to metal-contaminated sediments

Abstract Elevation of metal concentrations in coastal environments associated with anthropogenic enrichment pose a significant threat to estuarine organisms. The purpose of this study was to evaluate the relationships between cellular responses that may be potentially valuable as indicators of chronic stress and metal-contaminated sediments. For these studies, hatchery-reared juvenile oysters were deployed in situ at 15 sites for approximately 1 month around Charleston Harbor, SC. The effects on lysosomal destabilization and glutathione concentrations were determined; and the relationships between the cellular responses and sediment metal concentrations were described. Both single metal and multiple metal parameters (based on total metal concentrations, aluminum normalizations, and summed sediment quality guidelines) were considered. Generally, significant correlations were observed for individual metal analytes and multiple metal parameters. Since many of the individual metal analytes covary, the responses may reflect overall contaminant loading rather than responses to individual metals. Methods for estimating overall contaminant loading based on multiple analytes provide a more realistic estimate of potential adverse effects.

A spatial assessment of baseline nutrient and water quality values in the Ashepoo-Combahee-Edisto (ACE) Basin, South Carolina, USA.

The Ashepoo-Combahee-Edisto (ACE) Basin (South Carolina, USA) National Estuarine Research Reserve System (NERRS) encompasses some of the least developed USA coastline. Yet, periodic sampling showed that certain regions have higher nutrient, fecal coliform, and chlorophyll a levels, often with lower dissolved oxygen, than other South Carolina estuaries. To evaluate the spatial extent of these issues, a summer (2008) baseline study was conducted. Physical water quality, total nitrogen and phosphorus, chlorophyll a, dissolved organic carbon, and suspended solids were measured from surface waters of 67 stations (30 tidal creek, 37 open water). Nutrient and chlorophyll a levels were significantly (p<0.01) and negatively correlated with the extent of open water (% land cover), and chlorophyll a and nitrogen levels were, at times, elevated relative to concentrations typical of other estuaries in the state, reinforcing previous findings. This survey also identified several creeks not previously monitored that exhibited elevated nutrients.