Awantha Dissanayake

A multibiomarker approach to environmental assessment.

Incorporation of ecologically relevant biomarkers into routine environmental management programs has been advocated as a pragmatic means of linking environmental degradation with its causes. Here, suites of biomarkers, devised to measure molecular damage, developmental abnormality and physiological impairment, were combined with chemical analysis to determine exposure to and the effects of pollution at sites within Southampton Water (UK). Test species included a filter feeder, a grazer, and an omnivore to determine the sensitivity of organisms occupying different trophic levels. Linear regression confirmed a significant association between incidence of intersex in Littorina littorea and tributyltin (TBT) concentrations (R2 = 0.954) and between PAH metabolites in Carcinus maenas urine and PAHs in sediments (R2 = 0.754). Principal component analysis revealed a gradient of detrimental impact to biota from the head to the mouth of the estuary, coincident with high sediment concentrations of heavy metals, PAHs, and biocides. Multidimensional scaling identified C. maenas as the organism most sensitive to contamination. Carboxylesterase activity, metallothionein and total haemolymph protein were the most discriminating biomarkers among sites. This holistic approach to environmental assessment is encouraged as it helps to identify the integrated impact of chemical contamination on organisms and to provide a realistic measure of environmental quality.

The influence of seasonality on biomarker responses in Mytilus edulis.

The utility of some biomarkers in environmental monitoring may be limited due to the lack of knowledge that exists on how they respond to extrinsic abiotic and intrinsic biotic factors. During the present study we investigated the seasonal responses of three biomarkers, Neutral Red Retention, clearance/filtration rate and heart rate in the common blue mussel Mytilus edulis located in the Exe Estuary, UK during September 2006–September 2007. During the current study, a significant decrease in feeding rate was observed in mussels during June, July and August 2007, coinciding with the period following spawning when the mussels lay down nutrient reserves. Heart rate also increased between April and September 2007 and corresponded with times when mussels were spawning and laying down nutrient reserves. By integrating the individual biomarker responses into a Biomarker Response Index (BRI) we were able to identify times of the year when environmental impact was highest and hence when the timing of monitoring programmes using biomarkers should be carried out. For many years the lack of knowledge of normal physiological ranges of biomarkers has impeded their applied use, however by integrating biomarker responses into the BRI and creating an index of health, we have shown that we can limit the natural variability of individual responses; and thus we are better able to make informed judgements on the overall health status of these populations of mussels.

Physiological responses of juvenile and adult shore crabs Carcinus maenas (Crustacea: Decapoda) to pyrene exposure

This study measured aspects of the physiology of juvenile [(<35mm carapace width (CW)] and adult (>60mm CW) Carcinus maenas to test the hypothesis that these different life-history stages exhibit different sensitivities to environmental contamination. Newly-collected juveniles had significantly (P<0.05) lower immunocompetence (phagocytosis and cellular integrity), lower metabolic energy (haemolymph glucose) and increased scope for growth compared with adults. Seven day exposure to a sub-lethal concentration (200microgL(-1)) of pyrene significantly (P<0.01) reduced immunocompetence, elevated basal heart rate and decreased respiration (at rest) for juveniles but had no overall impact on adult crab physiology. Results confirm that physiological differences exist between juvenile and adult shore crabs, and cause juveniles to be more susceptible to the effects of pyrene exposure than adults. Such differences in sensitivity to contamination between life-cycle stages of the same species have to be taken into account during the risk assessment process.

Nutritional status of Carcinus maenas (Crustacea: Decapoda) influences susceptibility to contaminant exposure.

Using the shore crab Carcinus maenas as a model, this study tested the hypothesis that nutritional status influences susceptibility of adult crabs (>60mm carapace width (CW)) to environmental contamination. In the laboratory, crabs were either starved, given a restricted diet (fed on alternate days) or fully fed (fed each day). In addition, crabs under each feeding regime were exposed to a sublethal concentration (200microgl(-1)) of pyrene (PYR) as a model organic (PAH (polyaromatic hydrocarbon)) contaminant. Various physiological end points were measured after 7 and 14 days. Results indicated that adult shore crab physiology was relatively robust to short-term (7 days) nutritional changes as multivariate analysis (ANOSIM) showed no significant difference in shore crab physiological condition between control and pyrene-exposed crabs, irrespective of dietary feeding regime [Global R=0.018, P (%)=19.2]. After 14 days, however, starved crabs showed significant impacts to physiological condition (as revealed by multivariate analysis) [Global R=0.134, P (%)=0.1], [R=0.209, P (%)=0.1]; starved individuals had significantly lower antioxidant status (F(2,48)=5.35, P<0.01) compared to crabs under both types of feeding regime. Exposure to pyrene resulted in significantly elevated pyrene metabolite concentrations in the urine at 7 and 14 days compared with control individuals (P<0.001), validating contaminant bioavailability, and this was found for all dietary treatments. Also, exposed crabs had significantly increased protein levels (proteinuria) than controls (P<0.001) in their urine after 7 and 14 days, irrespective of dietary regime. After 7 days, pyrene-exposed crabs showed significantly increased antioxidant status (P<0.001) and cellular functioning (increased cellular viability and decreased phagocytosis) (P<0.001) compared to control crabs; however, after 14 days, antioxidant status (P<0.01) and cellular viability (P<0.001) were significantly decreased in pyrene-exposed compared to unexposed crabs. Results indicate that differences in nutritional status of adult crabs result in shore crabs being robust to short-term sublethal (7 days) pyrene exposure. Susceptibility to contaminant exposure, however, was measured after prolonged exposure (14 days) as indicated by reduced ability to combat oxidative stress. These results indicate that ecotoxicological studies need to take into account the nutritional state of the test organism to achieve the full assessment of contaminant impact. In addition, the results highlight that subtle seasonal biotic features of an organism can influence biomarker responses, and these need to be considered when interpreting field data and during the routine application of biological-effects tools in environmental monitoring.

Evaluation of the Genotoxic and Physiological Effects of Decabromodiphenyl Ether (BDE-209) and Dechlorane Plus (DP) Flame Retardants in Marine Mussels (Mytilus galloprovincialis).

Dechlorane Plus (DP) is a proposed alternative to the legacy flame retardant decabromodiphenyl ether (BDE-209), a major component of Deca-BDE formulations. In contrast to BDE-209, toxicity data for DP are scarce and often focused on mice. Validated dietary in vivo exposure of the marine bivalve (Mytilus galloprovincialis) to both flame retardants did not induce effects at the physiological level (algal clearance rate), but induced DNA damage, as determined by the comet assay, at all concentrations tested. Micronuclei formation was induced by both DP and BDE-209 at the highest exposure concentrations (100 and 200 μg/L, respectively, at 18% above controls). DP caused effects similar to those by BDE-209 but at lower exposure concentrations (5.6, 56, and 100 μg/L for DP and 56, 100, and 200 μg/L for BDE-209). Moreover, bioaccumulation of DP was shown to be concentration dependent, in contrast to BDE-209. The results described suggest that DP poses a greater genotoxic potential than BDE-209.

Behavioral, physiological, and cellular responses following trophic transfer of toxic monoaromatic hydrocarbons.

The trophic transfer of monoaromatic hydrocarbons to predatory organisms feeding upon contaminated marine animals is not well reported within the scientific literature. Branched alkylbenzenes (BABs) unresolved by gas chromatography have been reported to be principal toxic components of bioaccumulated hydrocarbons in the tissues of some wild mussel, Mytilus edulis, populations with poor health status. Mussels, M. edulis, contaminated with a commercial mixture of BABs were fed to shore crabs, Carcinus maenas, for 7 d, and effects upon the behavior, heart rate, hemolymph cellular viability, and immune response of the crabs were assessed. Accumulation of BABs in crab midgut gland tissue was quantified by gas chromatography-mass spectrometry, and the presence of BABs in crab urine was detected spectrophotometrically using ultraviolet fluorescence spectroscopy. Analysis of crab tissues and urine revealed a proportion of the BABs was transferred from the mussel tissues to the crabs, but the majority was not present 3 d after consumption of the mussels and may have been metabolized, excreted, or both. The results do not support the hypothesis that BABs are likely to be biomagnified, at least by crabs, in the marine environment. Alterations to measured cellular and physiological responses of crabs fed BAB-exposed mussels were not significant. Consumption of contaminated mussels was shown to cause highly significant abnormal behavior that, in the wild, may affect the feeding ability of crabs and make them more vulnerable to predation.

Ocean Acidification and Warming Effects on Crustacea: Possible Future Scenarios

Continuously-increasing concentrations of atmospheric carbon dioxide CO2, primarily through the burning of fossil fuels, are rapidly increasing the oceanic concentrations of CO2 and leading to the phenomenon of ocean acidification. Evidence to date on the effects of altered seawater chemistry on the biota is growing, yet is in its infancy. Evidence of effects is limited mostly to fish, molluscs and echinoderms, yet there is a growing body of evidence of effects of ocean acidification on the Crustacea. Our predictive ability on physiological effects and the potential ecosystem level effects is currently limited. By posing fundamental questions, the answers may lie in implementing mechanistic-level studies in order to elucidate organism physiological limits and species’ potential to adapt to future oceanic conditions.