Seasonality of bioaccumulation of trace organics and lysosomal integrity in green-lipped mussel Perna viridis

The long-lived deep-sea bivalve Acesta excavata is sensitive to the dual stressors of sediment and warming

Human influence in the deep-sea is increasing as mining and drilling operations expand, and waters warm because of climate change. Here, we investigate how the long-lived deep-sea bivalve, Acesta excavata responds to sediment pollution and/or acute elevated temperatures. A. excavata were exposed to suspended sediment, acute warming, and a combination of the two treatments for 40 days. We measured O2 consumption, NH4+ release, Total Organic Carbon (TOC), and lysosomal membrane stability (LMS). We found suspended sediment and warming interacted to decrease O:N ratios, while sediment as a single stressor increased the release of TOC and warming increased NH4+ release in A. excavata. Warming also increased levels of LMS. We found A. excavata used protein catabolism to meet elevated energetic demands indicating a low tolerance to stress. A. excavata has limited capacity for physiological responses to the stressors of warming and sediment which may lead to decreased fitness of A. excavata.

Effects of temperature and particle concentration on aggregation of nanoplastics in freshwater and seawater

Microplastics have become a significant environmental problem worldwide. Compared with microplastics, nanoplastics are apparently more abundant and harmful but their environmental processes are less well understood. The fate and ecological impacts of nanoplastics in aquatic environments are largely determined by their aggregation properties, which were investigated here using pure water and artificial seawater prepared in the laboratory, as well as river water and coastal seawater collected from subtropical Hong Kong. The tests were carried out at an environmentally realistic temperature range (15-35 °C) with particle concentrations over four orders of magnitude (0.1-100 mg L^-1). Under these experimental conditions, parameters of dynamic light scattering were used to determine the extent of aggregation and colloidal stability of polystyrene nanospheres (nPS), a common test model of nanoplastics. Our results showed that aggregation of nPS was minimal in pure water and river water, but became strong under the ionic strength of artificial seawater and coastal seawater, in which 70 nm nPS could aggregate to > 2000 nm, and this aggregation clearly increased with increase in temperature and particle concentration. The aggregates with increasing size and decreasing colloidal stability were deposited more quickly. Findings from this study imply an increased risk of nanoplastics to marine benthic organisms through the aggregation and deposition processes, particularly in warmer waters.

Differential gene responses in the embryo of the green mussel Perna viridis exposed to dichlorodiphenyltrichloroethane (DDT)

The green-lipped mussel, Perna viridis, is considered to be an ideal indicator for marine environmental pollution. Dichlorodiphenyltrichloroethane (DDT), a typical persistent organic pollutant, is extensively distributed in marine environments. However, little is known about the toxic effects of DDT on the embryo of marine animals, particularly in marine bivalves. Using next-generation sequencing technology, we studied P. viridis embryo after DDT stress at the transcriptome level. A total of 99 202 unigenes were obtained based on the 2383 bp of unigene N50. These differentially expressed genes (DEGs) participated in the various molecular pathways of biological effects, including oxidative stress, detoxification, innate immunity and neurobehavioral disease. Quantitative real-time PCR was performed to verify the mRNA expression of several genes identified by differential gene expression (DGE) analysis. The results indicated that DDT was in induced a dose-dependent manner in the embryo of P. viridis, and most genes involved in oxidative stress and detoxification were up-regulated by DDT exposure; however, the immunity-related genes were down-regulated, except the genes involved in phagocytosis. Gene expression changes in embryo from P. viridis provide a preliminary basis to better understand the molecular toxic response mechanisms of embryo to DDT.

Application of a weight of evidence approach utilising biological effects, histopathology and contaminant levels to assess the health and pollution status of Irish blue mussels (Mytilus edulis)

A weight of evidence (WOE) approach, integrating biological effects, mussel histopathology and tissue contaminant levels is proposed to evaluate mussel health and pollution status. Contaminant levels, histopathology and several biological effects (BEs) including Lysosomal membrane stability (LMS), acetylcholinesterase (AChe), metallothionein proteins (MT) and alkali labile phosphate (ALP), in Mytilus edulis are presented, improving the current knowledge base for these data. Potential links between histopathology, BEs and contaminants and ranking of sites are investigated with an integrated response (IR) indexing technique. Histopathological condition indices (Ih) in mussel digestive gland are used to calculate health indices. A spatial and temporal assessment is conducted at Irish coastal locations. Linear mixed effects modelling revealed effects of confounding factors such as reproductive condition on NRRT (gonad stage (p < 0.001)). Higher prevalence of inflammation, brown cells and epithelial thinning of the digestive gland was evident at Dublin and Wexford and this linked well with the Ih. Levels of contaminants were generally found to be low with few exceptions as were BE responses. Using the IR approach, Dublin was ranked as being most impacted while Shannon ranked the least impacted, this being consistent with the BE ranking.

The brown mussel Perna perna (L., 1758) as a sentinel species for chlorinated pesticide and dioxin-like compounds

To contribute to the use of the tropical brown mussel Perna perna as a sentinel species for organochlorine pesticides (OCP) and polychlorinated biphenyls (PCB), the present study reports data on the toxicokinetics of these compounds in P. perna. Specifically, the authors present data on OCP and PCB bioaccumulation for eight sampling months from three bays (SE Brazil) and two transplant experiments (each 1 month long). Although seasonality is observed in the total lipid content of the whole soft tissue, with summer samples showing higher values, no such seasonality is observed in the OCP and PCB concentrations bioaccumulated by the mussel P. perna. Because no seasonal effect is observed in the annual OCP and PCB concentrations bioaccumulated by P. perna, the use of this species as a sentinel organism to monitor organochlorinated compounds is encouraged. One month of transplantation is not enough to allow the transplanted specimens to reach the concentrations observed in animals reared at the destination site. Nevertheless, P. perna showed a clear tendency to depurate the DDT metabolites p,p'-DDD and p,p'-DDE after 1 month of transplantation.

Assessing potential risks of wastewater discharges to benthic biota: an integrated approach to biomarker responses in clams (Ruditapes philippinarum) exposed under controlled conditions

Marine clams Ruditapes philippinarum were exposed under laboratory conditions to sediments sampled at five sites affected by wastewater effluents at the Bay of Cádiz (SW, Spain). Contamination and early biological stress were determined. Metabolism and antioxidant system differed according to seasons. Health status diminished in summer. Metabolism of detoxification, and oxidative effect were related to concentration of metals, PAH, secondary alkane sulfonates (SAS) and antibiotics in winter. Antioxidant system and DNA damage were linked to metals and pharmaceutical products. Phase I and antioxidant system were associated to PAH and SAS in summer. Oxidative stress and effects were related to pharmaceuticals. Phase II was linked to metals and pharmaceuticals. Seasonality of sediment contamination by organic compounds and biological responses was determined. Clams were useful bioindicators, since the set of biomarkers applied was validated as potential tools for sediment quality assessment of wastewater discharges areas.

De novo transcriptome analysis of Perna viridis highlights tissue-specific patterns for environmental studies

BACKGROUND

The tropical green-lipped mussel Perna viridis is a common biomonitor throughout the Indo-Pacific region that is used for environmental monitoring and ecotoxicological investigations. However, there is limited molecular data available regarding this species. We sought to establish a global transcriptome database from the tissues of adductor muscle, gills and the hepatopancreas of P. viridis in an effort to advance our understanding of the molecular aspects involved during specific toxicity responses in this sentinel species.

RESULTS

Illumina sequencing results yielded 544,272,542 high-quality filtered reads. After de novo assembly using Trinity, 233,257 contigs were generated with an average length of 1,264 bp and an N50 length of 2,868 bp; 192,879 assembled transcripts and 150,111 assembled unigenes were obtained after clustering. A total of 93,668 assembled transcripts (66,692 assembled genes) with putative functions for protein domains were predicted based on InterProScan analysis. Based on similarity searches, 44,713 assembled transcripts and 25,319 assembled unigenes were annotated with at least one BLAST hit. A total of 21,262 assembled transcripts (11,947 assembled genes) were annotated with at least one well-defined Gene Ontology (GO) and 5,131 assembled transcripts (3,181 assembled unigenes) were assigned to 329 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The quantity of assembled unigenes and transcripts obtained from male and female mussels were similar but varied among the three studied tissues, with the highest numbers recorded in the gills, followed by the hepatopancreas, and then the adductor muscle. Multivariate analyses revealed strong tissue-specific patterns among the three different tissues, but not between sexes in terms of expression profiles for annotated genes in various GO terms, and genes associated with stress responses and degradation of xenobiotics. The expression profiles of certain selected genes in each tissue type were further validated using real-time quantitative polymerase chain reaction assays and a similar tissue-specific trend was seen.

CONCLUSIONS

The extensive sequence data generated from this study will provide a valuable molecular resource for facilitating environmental studies with P. viridis, and highlight the importance of tissue-specific approaches in the future.

Effects of contaminant exposure and food restriction on hepatic autophagic lysosomal parameters in Herring Gull (Larus argentatus) chicks

Lysosomal autophagic responses, such as lysosomal membrane stability, neutral lipids (NL), lipofuscin (LF), and malondialdehyde (MDA) levels, are valuable measures of cellular early-onset effects induced by environmental stress factors, such as contaminant exposure and fasting. In this study, these parameters were analysed and related to levels of halogenated organic contaminants (HOCs) in 40 Herring Gull (Larus argentatus) chicks. Chicks were experimentally exposed to HOCs through diet and went through a period of nutrient deprivation at the end of the experiment. HOC exposure and fasting were conducted separately and in combination. NL storages were depleted, and lysosomal membranes were destabilised after HOC exposure and nutrient deprivation. These responses were not related specifically to one type of stress or the extent of the treatment. No synergistic or additive effects from the combination of HOC exposure and fasting were observed. LF accumulated, and MDA levels increased as a result of fasting, but were unaffected by HOC exposure. LF accumulation was strongly associated with the percent weight change in the chicks. Large weight loss was associated with high LF levels, and slight weight gain was associated with low LF levels. Hence, food deprivation affected all the measured parameters, and HOC exposure decreased NL levels and lysosomal membrane stability in HG chick liver. Furthermore, autophagic lysosomal parameters have frequently been applied as biomarkers of cellular health status in previous studies of marine and terrestrial invertebrates, and this study suggests that these parameters may be good candidates for biomarkers of cellular health status in seabirds as well.

Application of neutral red retention assay to caged clams (Ruditapes decussatus) and crabs (Carcinus maenas) in the assessment of dredged material

Dredged material management is a key issue for the protection of aquatic environments. The in situ approach using caged bioindicator species has been chosen lately as a new methodology for the assessment of dredged material. In a tier testing approach, neutral red retention (NRR) assay has been applied as a screening tool to detect adverse changes in health status associated with contamination. Nevertheless, to authors' knowledge, little is known about the application and validation of this technique in sediment bioindicator species and under field conditions. Caged Ruditapes decussatus and Carcinus maenas were exposed during 28 days to potentially contaminated sediments at three sites in Algeciras Bay (SW Spain) and one site in Cádiz Bay (SW Spain). Lysosomal membrane stability was measured over time in haemolymph samples of exposed clams and crabs using the NRR assay. Sediment characterization of the study sites was performed in parallel. NRR time did not vary significantly (p > 0.05) over time in organisms from Cádiz Bay. Conversely, significant differences (p < 0.05) in NRR time were found in clams and crabs exposed to sediments from Algeciras Bay, which exhibited a 30-70% decrease in haemocyte lysosome membrane stability compared to day 0. Statistical analysis showed a strong correlation between the drop of haemocyte lysosome membrane stability, in both crabs and clams, and the presence of metals (p < 0.05) and PAHs (p < 0.01) in the studied sediments. The results obtained confirmed the use of NRR assay as a suitable and sensitive method to be used in the assessment of sediment quality using as bioindicator species the clam R. philippinarum and the crab C. maenas.

Functional and metabolic characterization of hemocytes of the green mussel, Perna viridis: in vitro impacts of temperature

The green mussel, Perna viridis, is a bivalve mollusk native to Asia and was recently introduced to Florida, USA. Since its first observation in 1999 in Tampa Bay, Florida, green mussel population has expanded considerably, to reach the Atlantic coast of Florida, Georgia and South Carolina. Most of currently available studies about the ecology and biology of green mussels were performed in the Indian and Pacific oceans. Very recently, it has been suggested that due to a weak low temperature resistance, green mussels might have already reached the Northern edge of their distribution in the USA. However, there is currently an obvious lack of data about the adaptation capacities of Perna viridis to environmental conditions in Florida, especially at the physiological and cellular levels. In the present work, we determined and characterized the populations of circulating hemocytes, and the cellular components of hemolymph involved in various physiological functions, including immunity. Two main populations were characterized, hyalinocytes and granulocytes. Granulocytes accounted for 60% of circulating cells, and displayed higher phagocytic capacities, lysosomal content and basal oxidative metabolism than hyalinocytes. Hemocyte parameters were not influenced by the size of green mussels. In addition, hemocytes were subjected to acute temperature challenges (10, 20 and 30 °C) and their immune-related functions and metabolism analyzed. Our results showed that 10 °C represent a stressful condition for the Floridian green mussels, as depicted by a low phagocytosis capacity and an increase of oxidative metabolism.

Lysosomal and lipid-associated parameters in the livers of three species of arctic seabird chicks: species differences and relationships with contaminant levels

Lysosomal membrane stability, lipofuscin (LF), malondialdehyde (MDA), neutral lipid (NL) levels, as well as halogenated organic compounds (HOCs), Cr, Cd, Pb and Fe concentrations were analyzed in liver of black-legged kittiwake (BK), herring gull (HG), and northern fulmar (NF) chicks. There were significant species differences in the levels of NL, LF and lysosomal membrane stability. These parameters were not associated with the respective HOC concentrations. LF accumulation was associated with increasing Cr, Cd and Pb concentrations. HG presented the lowest lysosomal membrane stability and the highest. LF and NL levels, which indicated impaired lysosomes in HG compared to NF and BK. Lipid peroxidation was associated with HOC and Fe2+ levels. Specific HOCs showed positive and significant correlations with MDA levels in HG. The study indicates that contaminant exposure can affect lysosomal and lipid associated parameters in seabird chicks even at low exposure levels. These parameters may be suitable markers of contaminant induced stress in arctic seabirds.

Integrated biomarker assessment of the effects exerted by treated produced water from an onshore natural gas processing plant in the North Sea on the mussel Mytilus edulis

The biological impact of a treated produced water (PW) was investigated under controlled laboratory conditions in the blue mussel, Mytilus edulis. Mussel health status was assessed using an integrated biomarker approach in combination with chemical analysis of both water (with SPMDs), and mussel tissues. Acyl-CoA oxidase activity, neutral lipid accumulation, catalase activity, micronuclei formation, lysosomal membrane stability in digestive cells and haemocytes, cell-type composition in digestive gland epithelium, and the integrity of the digestive gland tissue were measured after 5 week exposure to 0%, 0.01%, 0.1%, 0.5% and 1% PW. The suite of biomarkers employed were sensitive to treated PW exposure with significant sublethal responses found at 0.01-0.5% PW, even though individual chemical compounds of PW were at extremely low concentrations in both water and mussel tissues. The study highlights the benefits of an integrated biomarker approach for determining the potential effects of exposure to complex mixtures at low concentrations. Biomarkers were integrated in the Integrative Biological Response (IBR/n) index.

Ethoxyresorufin-O-deethylase enzyme activities and accumulation of secondary/tertiary lysosomes in rabbitfish Siganus oramin as biomarkers for xenobiotic exposures

The sensitivities of using hepatic and intestinal ethoxyresorufin-O-deethylase (EROD) activities and hepatic accumulation of secondary/tertiary (2 degrees/3 degrees) lysosomes to detect xenobiotic exposures were assessed in the rabbitfish Siganus oramin in a metropolitan harbour, subtropical Hong Kong, over a complete seasonal cycle of one year. Additional information on the body-burden pollutants and physiological indices in S. oramin, and seasonal variables in seawater quality, were extracted from published data and re-analyzed. Under the influences of pollutant cocktail and seasonal factors, neither the hepatic nor intestinal EROD activity was indicative of total polycyclic aromatic hydrocarbons (Sigma PAH), total polychlorinated biphenyls, condition factor and hepatosomatic index (HSI) in S. oramin. However, the relative ratio of hepatic to intestinal EROD activities provided an indication to differentiate the xenobiotic intake route in the fish through diffusion via gills/skin or consumption of contaminated food. In addition, the elevated hepatic accumulation of 2 degrees/3 degrees lysosomes was closely associated with the dominant temporal trends of zinc and Sigma PAH, as well as reduced HSI, in S. oramin. Being minimally influenced by any investigated seasonal factors, the hepatic 2 degrees/3 degrees lysosomes in S. oramin was recommended as an effective biomarker of xenobiotic exposures and toxic effects for use in coastal pollution monitoring programmes.