Metaplasia of respiratory and digestive tissues in the eastern oyster Crassostrea virginica associated with the Deepwater Horizon oil spill

Metaplasia is a well documented and deleterious effect of crude oil components on oysters. This reversible transformation of one cell type to another is a common response to petroleum-product exposure in molluscs. It has been shown experimentally in previous work that eastern oysters (Crassostrea virginica) exposed to petroleum products will exhibit metaplasia of digestive tissues. Here we document for the first time that wild adult oysters inhabiting coastal waters in the northern Gulf of Mexico during and in the aftermath of the Deepwater Horizon oil spill (2010) exhibited metaplasia in both ctenidial (respiratory and suspension feeding) and digestive tract tissues at significantly higher frequencies than geographic controls of C. virginica from Chesapeake Bay. Metaplasia included the loss of epithelial cilia, transformations of columnar epithelia, hyperplasia and reduction of ctenidial branches, and vacuolization of digestive tissues. Evidence for a reduction of metaplasia following the oil spill (2010-2013) is suggestive but equivocal.

The mysterious mass death of marine organisms on the Kamchatka Peninsula: A consequence of a technogenic impact on the environment or a natural phenomenon?

The increased incidence of environmental disasters in recent years is a matter of serious concern. The reasons for the disaster on the Kamchatka Peninsula (Russia), which occurred in September 2020 and caused the mass death of marine organisms, have not yet been established. This is the first study of the environmental disaster on Kamchatka and should shed light on the possible impact of two main man-made factors associated with an oil spill and a rocket fuel spill. The traces of oil products found in marine organisms could not have led to their death, as they indicate old oil pollution, heavy metals concentrations did not exceed the average values for the studied objects. The propellant and its transformation products were not found in the samples. Thus, having excluding the two main technogenic factors of the death of marine organisms, we can conclude that it was probably caused by a natural phenomenon.

Combined exposure to pyrene and fluoranthene and their molecular effects on the Sydney rock oyster, Saccostrea glomerata

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously detected in the water column, associated with particulate matter or in the tissue of marine organisms such as molluscs. PAH exposure and their resultant bioaccumulation in molluscs can cause a range of serious physiological effects in the affected animals. To examine the molecular response of these xenobiotics in bivalves, Sydney rock oysters (Saccostrea glomerata) were exposed to pyrene and fluoranthene for seven days. Chemical analysis of the soft-tissue of PAH stressed S. glomerata confirmed that pyrene and fluoranthene could be bioaccumulated by these oysters. RNA-Seq analysis of PAH-exposed S. glomerata showed a total of 765 transcripts differentially expressed between control and PAH-stressed oysters. Closer examination of the transcripts revealed a range genes encoding enzymes involved in PAH detoxification (e.g. cytochrome P450), innate immune responses (e.g. pathogen recognition, phagocytosis) and protein synthesis. Overall, pyrene and fluoranthene exposure appears to have resulted in a suppression of pathogen recognition and some protein synthesis processes, whereas transcripts of genes encoding proteins involved in clearance of cell debris and some transcripts of genes involved in PAH detoxification were induced in response to the stressors. Pyrene and fluoranthene exposure thus invoked a complex molecular response in S. glomerata, with results suggesting that oysters focus on removing the stressors from their system and dealing with the downstream effects of PAH exposure, potentially at the exclusion of other, less immediate concerns (e.g. protection from infection).

Diseases of the Chilean flounder Paralichthys adspersus (Steindachner, 1867) as biomarkers of marine coastal pollution near the Itata River (Chile). Part I: in situ macroscopic lesions

This study evaluated the health of the Chilean flounder Paralichthys adspersus inhabiting the marine coastal area influenced by the Itata River. Flounder were also sampled at two reference sites during the course of 1 year. The pathological examination was done following the ICES protocol: external and internal lesions, condition factor, hepatosomatic and spleen indexes, and number of erythrocytes, lymphocytes, and thrombocytes. The prevalence of fish with lesions differed significantly among sites. The flounder sampled in the Itata area were the most affected. The evaluation of the macroscopic lesions observed on the flounder caught in the Itata area revealed (1) seven different types of macroscopic lesions, (2) a high prevalence of epidermal irritation lesions, and (3) a normal K factor, hepatosomatic index, and blood cell count. Significant differences were found in epidermal irritation lesions between stages and sites and between sexes and sites. Juveniles and adults as well as males and females were affected. A seasonal analysis of the macroscopic lesions on the flounder caught in the Itata area showed significant differences for only the epidermal irritation lesions between the sampled seasons of the year; the flounder caught in winter 2006 had the highest prevalence (77%) of such lesions. These results are discussed in relation to the hydrographic conditions, the contents of inorganic, nutrient and other organic compounds in the water column, and the contents of organic compounds and metals in the sediments of the subtidal environment in the Itata area.

Immunomodulation the marine green mussel Perna viridis exposed to sub-lethal concentrations of Cu and Hg

Environmental pollution is a growing concern and, more importantly, pollution of the aquatic ecosystem is alarming. Marine pollution may be one of the reasons for disease incidence in marine organisms, which is caused due to adverse effects of pollutants on the immune system. Bivalves are commonly used as bio-indicators of marine pollution, and immunomodulation due to toxicants is one of the important bio-markers used. Perna viridis too have been used as a bio-indicator, but this study is, to our knowledge, a first report on immunomodulation produced by metals, in P. viridis. Animals were exposed to copper and mercury at their sub-lethal concentrations of 20 microg L(-1) and 10 microg L(-1), respectively. Immune parameters including phenoloxidase, reactive oxygen species generation, and phagocytosis were monitored. The study period was for 25 days (chronic long-term exposure) and objectives established whether metals produced immunomodulation and to understand the effects of long-term exposure on immunomodulation. Results showed that both metals adversely affected immune parameters studied and, interestingly, there appears to be some level of recovery (depuration) from the toxic effects of metals.

Assessment of stress-related bioindicators in winter flounder (Pleuronectes americanus) exposed to discharges from a pulp and paper mill in Newfoundland: a 5-year field study

This study assessed the effects of discharges from a sulphite-bleaching paper mill on winter flounder (Pleuronectes americanus) sampled each spring over a 5-year period in St. George's Bay, Newfoundland, prior to foraging activity. The fish were captured by SCUBA divers near the mill and at a reference site 10 km up current. Several bioindicators were used to assess fish health. Larger and older flounder exhibiting gross and microscopic tissue lesions, lower condition factor, and elevated hepatosomatic index but lower gonadosomatic index that was associated with delayed development, were observed in samples caught near the mill compared to those at the reference site. Additionally, fish examined near the mill were infested with an ectoparasite, Cryptocotyle lingua, that causes black spot disease but harbored fewer numbers of a digene, Steringophorus furciger, in the digestive tract than samples taken at the reference site. These results suggest that abnormal size distribution, interruption of growth, high prevalence of lesions, lower condition factor, enlarged liver, delayed gonadal development, and differences in parasitic levels were indicative of stress in winter flounder caused by discharges from the mill compared to samples from a reference site. There was no evidence of a population decline in the inlet because of annual recruitment possibly from St. George's Bay into which it opens.

Uptake and elimination of naphthalene from liver, lung, and muscle tissue in the leopard frog (Rana pipiens)

The effects of a 0-12-hour naphthalene exposure on pulmonary CO(2) excretion and bioaccumulation in the leopard frog, Rana pipiens, were investigated. The data showed that naphthalene transport occurred from the aqueous phase into the frog tissue. The first-order rate constant (k in day-1) for the entry of naphthalene from the water into the frog was 0.079 +/- 0.007 (k +/- 95% C.I.). Bioaccumulation of naphthalene was measured in liver, lung, and thigh muscle tissue. Exposure to naphthalene caused a significant reduction in pulmonary CO(2) excretion, particularly following the first 30 minutes of exposure. Pulmonary CO(2) excretion returned to baseline levels after 8 hours of exposure, indicating that some degree of acclimation had occurred. Depuration experiments were used to monitor recovery from naphthalene exposure. Recovery of CO(2) excretion was evident following 2 hours of depuration and complete elimination of naphthalene from tissues occurred after 3 hours. The data indicate that accumulated polycyclic aromatic hydrocarbons (PAHs) may alter normal physiologic functions such as gas exchange. Since amphibians, such as frogs, are one of the first organisms to come into contact with contaminated water and sediments, the information in this study suggests that this species may be used to assess bioaccumulation and toxicity of PAHs in ecosystems.

Influence of pollution on parasites of aquatic animals

We have tried to draw attention to an increasing body of evidence (from several publications) that parasites of fish might be useful indicators of pollution. Several types of pollutants, including domestic sewage, pesticides, polychlorinated biphenyls, heavy metals, pulp and paper effluents, petroleum aromatic hydrocarbons, acid rain, and others, are known to affect aquatic animals. Many of the latter are parasitized and, under natural environmental conditions, most fish parasites are believed to cause little or no harm. However, chronic exposure to pollutants over a period of time causes biochemical, physiological and behavioural host changes that ultimately can influence the prevalence and intensity of parasitism. Some of these changes include host nutrition, growth and reproduction. Macroscopic lesions might not always be apparent, but subtle disorders in several specific tissues and organs might occur. Pollutants might promote increased parasitism in aquatic animals, especially fish, by impairing the host's immune response or favouring the survival and reproduction of the intermediate hosts. Alternatively, decreased parasitism might ensue through toxicity of the pollutant to free-living stages and intermediate hosts or by alteration of the host's physiology. Experimental studies indicate that the numbers of ectoparasites such as trichodinid ciliates and monogeneans increase significantly on the gills following exposure to a pollutant, and this is supported by field data on other ciliates and monogeneans where evidence of pollution has been clearly demonstrated. There is also evidence that endoparasitic protozoons, such as myxozoons, microsporans and haematozoons, all of which are capable of proliferating in their hosts, increase substantially in prevalence and intensity when interacting with pollutants. The period of patency might also be prolonged in haematozoan infections. Most reports of pollution effects on endoparasites suggest increased parasitism in fish hosts. This also applies to fish living in areas which receive thermal effluents. Parasites might in turn enhance their hosts' susceptibility to pollutants, and information in support of this view is accumulating. Finally, immunosuppression represents one of the underlying mechanisms influencing increased parasitism. Thus, while published information suggests more than a casual connection between fish parasites and pollution, further research is needed to establish the cause-and-effect relationship and at the same time take cognizance of histopathological effects of the toxic agents and their concentrations in water. Areas for future research are recommended.