Methylmercury and selenium in vitro effects on harbor seal (Phoca vitulina) lymphocytes : a multidisciplinary approach

Methylmercury (MeHg) bioaccumulates along the food web, leading to the highest levels in tissues of predatory species. It constitutes the predominant form present in the blood of marine mammals. The blood cells, including the immune cells, are therefore exposed to the toxic properties of that chemical. Nevertheless, selenium (Se) is an essential element absorbed concomitantly to MeHg which seems to modulate this toxicity. The goal of this study is to evaluate the immunotoxicity of MeHg on the harbor seal (Phoca vitulina) T lymphocytes, highly important in the adaptive immune response, and to investigate the modulating effect of Se on that toxicity. In parallel, the concentrations of MeHg, total mercury (T-Hg) and Se are determined in free-ranging harbour seal blood in order to follow their contamination levels. The T lymphocytes were isolated from the whole blood, exposed to various MeHg and Se concentrations and the exposure effects were estimated by functional tests including the evaluation of viability, proliferation, metabolic activity, DNA and protein synthesis, and by morphological analysis by transmission electron microscopy. The mean T-Hg concentration was 172 ± 143 µg/l of whole blood. The T lymphocytes cultures in vitro displayed a decreasing number of viable cells with increasing concentrations of MeHg, and numerous ultrastructural defects. The cells exposed to MeHg notably displayed distortion of the plasmic membrane, nucleus fragmentations, chromatin compaction, swelling mitochondrias and cytoplasmic vacuolisations. Those results highlighted various immunotoxic effects of MeHg, both at the functional and ultrastructural levels. The antagonistic role of Se on MeHg immunotoxicity is discussed

Posidonia oceanica meadow: a low nutrient high chlorophyll (LNHC) system?

BACKGROUND: In spite of very low nutrient concentrations in its vicinity – both column and pore waters-, the Posidonia oceanica of the Revellata Bay displays high biomass and productivity. We measured the nutrient fluxes from the sediment into the water enclosed among the leaf shoots ("canopy water") to determine if it is possible source of nutrients for P. oceanica leaves. RESULTS: During the summer, the canopy water appears to act as a nutrient reservoir for the plant. During that period, the canopy water layer displays both a temperature 0.5°C cooler than the upper water column, and a much higher nutrient content, as shown in this work using a very simple original technique permitting to sample water with a minimal disturbance of the water column's vertical structure. Despite low nutrient concentrations in pore water, mean net fluxes were measured from the sediment to the canopy water. These fluxes are sufficient to provide 20% of the mean daily nitrogen and phosphorus requirement of the P. oceanica shoots. CONCLUSION: An internal cycling of nutrients from P. oceanica senescent leaves was previously noted as an efficient strategy to help face low nutrient availability. The present study points out a second strategy which consists in holding back, in the canopy, the nutrients released at the water-sediment interface. This process occurs when long leaves, during poor nutrient periods in the water column, providing, to P. oceanica, the possibility to develop, high biomass, high chlorophyll quantities in low nutrient environment (a Low Nutrients High Chlorophyll system)

Fish farm impacts on Posidonia oceanica meadows: interest of the microbenthic loop.

Posidonia oceanica, the seagrass endemic to the Mediterranean Sea, is a valuable tool to assess the environmental quality in coastal zones. However, only few studies have attempted to use characteristics of its sediment compartment as an indicator of environmental perturbations. In this study, the impact of a fish farm on the microbenthic loop (organic matter, bacteria, microphytobenthos and meiofauna) of P. oceanica meadows will be described. Samples were taken under an aquaculture situated in Calvi Bay (Corsica, France) at a depth of 22 m, in March and June 2008. The control site was the meadow situated in front of the research station STARESO (Calvi Bay, Corsica, France), sampled at the same periods and depth. Results concerning bacteria, microphytobenthos and organic matter will be presented here. For both seasons, differences between sites exist. For example, biomasses of organic matter, microphytobenthos and bacteria are higher in the fish farm than in the control site, indicating that the microbenthic loop has potential to be a good early indicator of pollution in this sea.Utilisation de l'exergie pour mesurer et détecter les effets des perturbations affectant les herbiers à Posidonia oceanica (L.) Delile: caractérisation au sein du compartiment sédimentaire

Potential early indicators of anthropogenically derived nutrients : a multiscale stable isotope analysis

Increasing human pressure along Mediterranean coastlines raises the need to define sensitive bioindicators that provide an early response to nutrient enrichment. We performed multiscale carbon and nitrogen stable isotope analyses on the limpet Patella caerulea, the snail Monodonta turbinata, epilithic biofilms, and the macroalga Rissoella verruculosa inhabiting the rocky midlittoral zone. Samples were seasonally collected in 2006 from 5 sites exposed to a range of anthropogenic discharges in the Revellata Bay area and in Marseille harbour (France). All bioindicators exhibited strongly elevated δ15N values at impacted sites compared to pristine ones, which revealed the biological availability of anthropogenically derived nutrients. Only epilithic biofilms tended to show both the occurrence of nutrient pulses during the tourist season and a δ13C response at impacted sites. In contrast to macroalgae, which exhibited a somewhat equivocal signal, gastropods and especially M. turbinata provided the best time-integrated picture of the graduated exposure of the 5 sites to anthropogenic impact. Results also showed first evidence of large isotopic variability at a scale of tens of metres, close to that found at the kilometre scale. The intra- and interspecific isotopic variability in gastropods may be explained by the patchiness of resources and specific morphological and behavioural features, but these factors do not greatly hamper their potential as early bioindicators of wastewater disturbances.Peer reviewe

Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter

The coexistence of three idoteid species in Posidonia oceanica litter raises the question of trophic diversity and their role in the litter degradation process. Hence, diet composition of Idotea balthica, Idotea hectica and Cleantis prismatica was studied using a combination of gut contents and stable isotopes analysis. Gut content observations indicate that P. oceanica dead leaves are an important part of the ingested food for the three species, although their tissues are constituted of only a small to medium fraction of P. oceanica carbon. Our results also underlined the potential role of these species in the degradation of P. oceanica litter by mechanically fragmenting the litter and by assimilating a small to medium fraction of carbon. Moreover, we showed that there were considerable inter- and intra-specific differences in diet composition. Diet differed between juveniles and adults for I. balthica. Crustaceans are an important food source for adults of I. balthica, while I. hectica indicated a major contribution of algal material. C. prismatica showed an intermediate diet. This trophic diversity is probably one of the factors allowing these species to coexist in the same biotope

Small scale variations in the microbenthic loop of Posidonia oceanica meadows: an experimental interpolation design.

In the sediment compartment of Posidonia oceanica meadows, there is a severe lack of information on small scale variations. In an attempt to understand spatial variations of the microbenthic loop (bacteria, organic matter, microphytobenthos and meiofauna), an experiment based on interpolation methods was led in Calvi Bay (Corsica, France), in March 2008, at 10 m depth. Twelve points were sampled randomly in a 125 x 125 cm square, divided into twenty-five 25 x 25 cm squares, to assess and describe the spatial distribution and variations of different parameters of the sediment. Those parameters are granulometry, density of P. oceanica, concentration in nutrients in the pore water, bacteria (biomass, abundance, morphotypes), organic matter (biomass), microphytobenthos (biomass), roots and rhizomes (biomass) and meiofauna (biomass). Results and distribution maps of the respective sediment parameters will be presented for the first time.Utilisation de l'exergie pour mesurer et détecter les effets des perturbations affectant les herbiers à Posidonia oceanica (L.) Delile: caractérisation au sein du compartiment sédimentaire

Importance of the microbenthic loop of Posidonia oceanica meadows to detect anthropogenic perturbations early: first results

It was demonstrated that Posidonia oceanica, the marine magnoliophyte endemic to the Mediterranean Sea, is a valuable tool to assess environmental qualities of the coastal zones. However, only few studies have attempted to use characteristics of its sediment compartment as an indicator of the environment state of health. Yet, organisms living in this compartment have a turnover which is faster than for canopy-organisms which makes them useful as valid early descriptors of pollution. The study described here takes place in a project which aims to find an early holistic indicator of anthropogenic perturbations in the Mediterranean coastal zones. The investigation is based on the microbenthic loop (organic matter, bacteria, microphytobenthos and meiofauna) and was led in two different sites of Calvi Bay (Corsica, France), at 10 m depth, in March and June 2007. Only results about bacteria (abundance, biomass, morphotypes), microphytobenthos (biomass) and organic matter (biomass) will be presented. For both seasons, significant differences between sites are found, irrespective on whether variables are treated separately or together, thus indicating that the microbenthic loop has potential to be a good early indicator of pollution.Utilisation de l'exergie pour mesurer et détecter les effets des perturbations affectant les herbiers à Posidonia oceanica (L.) Delile: caractérisation au sein du compartiment sédimentaire

Harbour porpoise thyroids: Histological investigations and potential interactions with environmental factors

The thyroid plays an important role in development and is of primary importance in metabolism and heat loss for cetaceans, including the harbor porpoise (Phocoena phocoena). Several studies have demonstrated that environmental contaminants can alter various aspects of thyroid function in mammals and may contribute to various histologic changes. The present study completes the data set of a 2006 study by Das et al., by performing histological and immunohistologic investigations on thyroids of 36 harbor porpoises from Belgian and United Kingdom waters. The number and mean diameter of follicles (µm) and the relative proportion of follicular, connective, and vascular tissue (%) were quantified in the thyroid gland of each individual. Interfollicular fibrosis has been observed in these thyroid glands, and the collective findings support the hypothesis of an endocrine disruption of thyroid function through organochlorinated compounds. Our study aimed also to reveal potential relationships between thyroid morphometric data and metal levels (Cd, Fe, Zn, Cu, Se, and Hg) using multivariate statistical analysis. The multiple regressions revealed statistically significant relationships between trace elements (cadmium, selenium, and copper) and thyroid fibrosis. The largely negative relationships are interesting findings but do not support the hypothesis that these elements have an adverse effect on thyroid morphometry. Further research is needed to understand the nature of any relationship between organochlorine and trace element exposure and thyroid gland morphology and function in harbor porpoises.Peer reviewe

Trace metal concentrations in Posidonia oceanica of North Corsica (northwestern Mediterranean Sea): use as a biological monitor?

BACKGROUND: Within semi-closed areas like the Mediterranean Sea, anthropic wastes tend to concentrate in the environment. Metals, in particular, are known to persist in the environment and can affect human health due to accumulation in the food chain. The seagrass Posidonia oceanica, widely found in Mediterranean coastal waters, has been chosen as a "sentinel" to quantify the distribution of such pollutants within the marine environment. Using a technique similar to dendrochronology in trees, it can act as an indicator of pollutant levels over a timeframe of several months to years. In the present study, we measured and compared the levels of eight trace metals (Cr, Ni, Cu, Zn, As, Se, Cd, and Pb) in sheaths dated by lepidochronology and in leaves of shoots sampled from P. oceanica meadows collected from six offshore sites in northern Corsica between 1988 and 2004; in the aim to determine 1) the spatial and 2) temporal variations of these metals in these areas and 3) to compared these two types of tissues. RESULTS: We found low trace metal concentrations with no increase over the last decade, confirming the potential use of Corsican seagrass beds as reference sites for the Mediterranean Sea. Temporal trends of trace metal concentrations in sheaths were not significant for Cr, Ni, Cu, As or Se, but Zn, Cd, and Pb levels decreased, probably due to the reduced anthropic use of these metals. Similar temporal trends between Cu levels in leaves (living tissue) and in sheaths (dead tissue) demonstrated that lepidochronology linked with Cu monitoring is effective for surveying the temporal variability of this metal. CONCLUSION: Leaves of P. oceanica can give an indication of the metal concentration in the environment over a short time period (months) with good accuracy. On the contrary, sheaths, which gave an indication of changes over long time periods (decades), seem to be less sensitive to variations in the metal concentration in the environment. Changes in human consumption of metals (e.g., the reduction of Pb in fuel) are clearly reflected in both organs. These results confirm that P. oceanica is a good bioindicator of metals and a good biomonitor species for assessing Cu in the environment

Long-term feeding ecology and habitat use in harbour porpoises Phocoena phocoena from Scandinavian waters inferred from trace elements and stable isotopes

BACKGROUND: We investigated the feeding ecology and habitat use of 32 harbour porpoises by-caught in 4 localities along the Scandinavian coast from the North Sea to the Barents Sea using time-integrative markers: stable isotopes (δ(13)C, δ(15)N) and trace elements (Zn, Cu, Fe, Se, total Hg and Cd), in relation to habitat characteristics (bathymetry) and geographic position (latitude). RESULTS: Among the trace elements analysed, only Cd, with an oceanic specific food origin, was found to be useful as an ecological tracer. All other trace elements studied were not useful, most likely because of physiological regulation and/or few specific sources in the food web. The δ(13)C, δ(15)N signatures and Cd levels were highly correlated with each other, as well as with local bathymetry and geographic position (latitude). Variation in the isotopic ratios indicated a shift in harbour porpoise's feeding habits from pelagic prey species in deep northern waters to more coastal and/or demersal prey in the relatively shallow North Sea and Skagerrak waters. This result is consistent with stomach content analyses found in the literature. This shift was associated with a northward Cd-enrichment which provides further support to the Cd 'anomaly' previously reported in polar waters and suggests that porpoises in deep northern waters include Cd-contaminated prey in their diet, such as oceanic cephalopods. CONCLUSION: As stable isotopes and Cd provide information in the medium and the long term respectively, the spatial variation found, shows that harbour porpoises experience different ecological regimes during the year along the Scandinavian coasts, adapting their feeding habits to local oceanographic conditions, without performing extensive migration