Blue mussel (Mytilus edulis)-A bioindicator of marine water contamination by protozoa: Laboratory and in situ approaches.

AIMS: The protozoan parasites Cryptosporidium spp., Giardia duodenalis and Toxoplasma gondii are identified as public health priorities and are present in a wide variety of environments including the marine ecosystem. The objective of this study was to demonstrate that the marine bivalve blue mussel (Mytilus edulis) can be used as a tool to monitor the contamination of marine waters by the three protozoa over time. METHODS AND RESULTS: In order to achieve a proof of concept, mussels were exposed to three concentrations of G. duodenalis cysts and Cryptosporidium parvum/T. gondii oocysts for 21 days, followed by 21 days of depuration in clear water. Then, natural contamination by these protozoa was sought for in wild marine blue mussels along the northwest coast of France to validate their relevance as bioindicators in the field. Our results highlighted that: (a) blue mussels bioaccumulated the parasites for 21 days, according to the conditions of exposure, and parasites could still be detected during the depuration period (until 21 days); (b) the percentage of protozoa-positive M. edulis varied under the degree of protozoan contamination in water; (c) mussel samples from eight out of nine in situ sites were positive for at least one of the protozoa. CONCLUSIONS: The blue mussel M. edulis can bioaccumulate protozoan parasites over long time periods, according to the degree of contamination of waters they are inhabiting, and can highlight recent but also past contaminations (at least 21 days). SIGNIFICANCE AND IMPACT OF THE STUDY: Mytilus edulis is a relevant bioaccumulators of protozoan (oo)cysts in laboratory and field conditions, hence its potential use for monitoring parasite contamination in marine waters.

Occurrence, sources and effects of polycyclic aromatic hydrocarbons in the Tunis lagoon, Tunisia: an integrated approach using multi-level biological responses in Ruditapes decussatus.

Coastal lagoons are critical ecosystems presenting a strategic economic importance, but they are subjected to potential anthropogenic impact. As part of the Tunis lagoon (Tunisia) biomonitoring study, levels, composition pattern and sources of polycyclic aromatic hydrocarbons (PAHs) in surface sediments along with their bioavailability in clam Ruditapes decussatus were investigated in polluted (S2-S4) and reference (S1) sites. In order to investigate the contamination effects at different biological levels in clams, a wide set of biomarkers, including gene expression changes, enzymatic activities disruption and histopathological alterations, was analysed. Biomarkers were integrated in a biomarker index (IBR index) to allow a global assessment of the biological response. Principal component analysis (PCA) was used for chemical and biological data integration to rank the sampling sites according to their global environmental quality. Sediment PAHs levels ranged between 144.5 and 3887.0 ng g-1 dw in the Tunis lagoon sites versus 92.6 ng g-1 dw in the reference site. The high PAH concentrations are due to anthropogenic activities around the lagoon. PAH composition profiles and diagnostic isomer ratios analysis indicated that PAHs were of both pyrolitic and petrogenic origins. Clams sampled from S2 and S3 exhibited the highest PAH contents with 2192.6 ng g-1 dw and 2371.4 ng g-1 dw, respectively. Elevated levels of tissue PAHs were associated to an increase in biotransformation and antioxidant activities, and lipid peroxidation levels along with an overexpression of different genes encoding for general stress response, mitochondrial metabolism and antioxidant defence, in addition to the emergence of severe and diverse histopathological alterations in the clams' digestive glands. IBR index was suitable for sampling sites ranking (S1 = 0 < S4 = 0.4 < S3 = 1.15 < S2 = 1.27) based on the level of PAH-induced stress in clams. PCA approach produced two components (PC1, 83.8% and PC2, 12.2%) that describe 96% of the variance in the data and thus highlighted the importance of integrating contaminants in sediments, their bioaccumulation and a battery of biomarkers of different dimensions for the assessment of global health status of coastal and lagoon areas.

Combined effects of metal contamination and abiotic parameters on biomarker responses in clam Ruditapes decussatus gills: an integrated approach in biomonitoring of Tunis lagoon.

The spatial and seasonal alteration in a battery of biomarkers responses (enzymatic activity of glutathione-S-transferase, catalase and acetylcholinesterase and lipid peroxidation) were investigated to assess the metal derived effects in clam (Ruditapes decussatus) gills, collected from Tunis lagoon (Tunisia). Trace metals (Ag, As, Cd, Cu, Hg, Mn, Ni, Pb, V and Zn) concentrations were assessed seasonally in sediments and tissues of R. decussatus from three different sites (S1, S2 and S3). Bioaccumulation factor (BAF) analysis showed a spatio-temporal variation of metal uptake rates in clams through sediments. Likewise, the multibiomarker approach enabled a time-site trend differentiation between sites with distinctive degrees of anthropogenic contamination. Site S2 was identified as the most impacted region due to the presence of different contamination sources (shipping and industrial activities). The results suggest that biomarker's seasonal variation arises from a complex interaction between environmental conditions (e.g. temperature, salinity) and probably biological factors (mainly the reproduction process) along with anthropogenic pressure. The general biological response measured with the IBR index at all the sampling sites revealed the highest metabolic stress in summer. The combined effects of metal contamination and increased temperature and salinity in summer appear to induce the highest metabolic adaptation response. The selected biomarkers provided an integrated response, which is useful for the assessment of the combined effects of metal contamination and abiotic parameters in clams and the environmental status of coastal lagoon ecosystem.

Transcriptomic, Biochemical, and Histopathological Responses of the Clam Ruditapes decussatus from a Metal-Contaminated Tunis Lagoon.

This study was designed to investigate the molecular (transcriptional expression), biochemical (oxidative stress and neurotoxicity), and histopathological effects of metal contamination in the gill of clams (Ruditapes decussatus) sampled from the Tunis lagoon. The concentrations of five heavy metals (Cd, Pb, Hg, Cu, and Zn) in surface sediments and their accumulation in soft tissues of R. decussatus were evaluated in three sites (Z1, Z2, and Z3). A metal contamination state of Tunis lagoon sediments was noted with spatial variations with relatively high levels at Z2. Biomarker analyses showed an increase in glutathione S-transferase and catalase activities and lipid peroxidation levels and a decrease in acetylcholinesterase activity in the studied sites. Molecular investigation showed a significant overexpression of: cytochrome c oxidase subunit I, ribosomal RNA 16S, Cu/Zn superoxide dismutase, heat shock protein 70, and metallothioneins in the three sampling sites. Moreover, our data were correlated to severe and diverse histopathological alterations in the clam gills. The principal component analysis showed that the Z2 region is more affected by metal contamination than Z1 and Z3 regions. Current field results suggest the use of several combined biomarkers at different cell levels instead of individual ones in monitoring programs.