In light of the current rising mean temperatures and fluctuations in temperature extremes involved in global climate change, a cause-and-effect understanding of the temperature- dependent impacts of additional environmental stressors on marine life is crucial for the elaboration of how marine ecosystems will shape in the future. The thermal environment plays a direct role in the distribution and survival of marine ectotherms through the temperature-dependent effects on their physiology, as well as indirectly by affecting the organism's susceptibility to other biotic and abiotic stressors. We review studies that have investigated the effects of temperature and anthropogenic pol- lution by trace metals, with a focus on metabolic regulation as a major mechanism that underlies the interactive effects of temperature and metals on the physiology and survival of ectotherms. These studies suggest that impairment of energy metabolism plays a key role in the synergistic effects of these stressors, and we elaborate a mechanistic framework for understanding these interactions. Fur- thermore, the present study seeks to provide an impetus for future investigations in order to define more precisely the physiological mechanisms and functional properties of temperature-pollution interactions.

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Interactive effects of metal pollution and temperature on metabolism in aquatic ectotherms: implications of global climate change

Polychaetes are usually the most abundant taxon in benthic communities and have been most often utilized as indicator species of environmental conditions. This review finds that, while the use of indicator species for a particular pollutant is not simple, polychaetes can provide a useful means of assessing the effects of poor environmental conditions. Polychaetes may be used as sensitive monitors of water quality especially in terms of the effects of pollutants on life history characteristics. They may also be utilized as general indicators of community diversity but those species indicative of lower diversity may differ geographically and temporally. While sewage is often a mixture of high organic material and other pollutants such as heavy metals and pesticides, high organic situations associated with aquaculture facilities indicates that members of the Capitella capitata species complex and the dorvilleid genus Ophryotrocha are often dominant. Some species of polychaetes are able to live in sediments very high in trace metal content and body burden of these metals often does not reflect sediment concentrations due to regulation by these species. Many species seem relatively resistant to organic contaminants and pesticides and the effects of these pollutants on life history characteristics of these species may provide a more sensitive assay method. Recent studies using biomarkers in polychaetes to indicate general heavy metal or pesticide contamination has shown some success. Polychaete species known to occur in appreciable densities in the Gulf of Nicoya, Costa Rica, and which have been most often used as indicator species of pollution, are listed as potential taxa for environmental monitoring in this tropical estuary. Rev. Biol. Trop. 56 (Suppl. 4): 11-38. Epub 2009 June 30.

https://revista-ciencia-tecnologia.ucr.ac.cr/index.php/rbt/article/download/27162/27262

The use of polychaetes (Annelida) as indicator species of marine pollution: a review

Heavy metals are an important class of pollutants with both lethal and sublethal effects on organisms. The latter are receiving increased attention, as these may have harmful ecological outcomes. For example, recent explorations of heavy metals in freshwater habitats reveal that they can modify chemical communication between individuals, resulting in “info-disruption” that can impact ecological relationships within and between species. Info-disruption can affect animal behavior and social structure, which in turn can modify both intraspecies and interspecies interactions. In terrestrial habitats, info-disruption by metals is not well studied, but recent demonstrations of chemical signaling between plants via both roots and volatile organic molecules provide potential opportunities for info-disruption. Metals in terrestrial habitats also can form elemental plant defenses, in which they can defend a plant against natural enemies. For example, hyperaccumulation of metals by terrestrial plants has been shown to provide defensive benefits, although in almost all known cases the metals are not anthropogenic pollutants but are naturally present in soils inhabited by these plants. Info-disruption among microbes is another arena in which metal pollutants may have ecological effects, as recent discoveries regarding quorum sensing in bacteria provide an avenue for metals to affect interactions among bacteria or between bacteria and other organisms. Metal pollutants also may influence immune responses of organisms, and thus affect pathogen/host relationships. Immunomodulation (modification of immune system function) has been tied to some metal pollutants, although specific metals may boost or reduce immune system function depending on dose. Finally, the study of metal pollutants is complicated by their frequent occurrence as mixtures, either with other metals or with organic pollutants. Most studies of metal pollutants focus on single metals and therefore oversimplify complex field conditions. Study of pollutant impacts on chemical ecology also are difficult due to the necessity of studying effects at varying ecological scales: “dynamic scaling” of chemical ecology studies is rarely done completely. It is clear that much remains to be learned about how heavy metal pollution impacts organisms, and that exciting new research frontiers are available for experimental exploration.

https://www.auburn.edu/academic/cosam/faculty/biology/boyd/lab/Boyd_JCE_review_2010.pdf

Heavy Metal Pollutants and Chemical Ecology: Exploring New Frontiers

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review.

MicroRNAs and their role on fish oxidative stress during xenobiotic environmental exposures

Comparison of heavy metal toxicity in life stages (spermiotoxicity, egg toxicity, embryotoxicity and larval toxicity) of Hydroides elegans

Environmental contaminants can interfere with hormonal regulation in both vertebrates and invertebrates, and these contaminants may disrupt the endocrine system of human and other organisms. Evidence is growing that contaminants may be partly responsible for the observed increase of disease in marine organisms by adversely affecting their immunity. Fish are commonly used as sentinel organisms in vertebrate immunotoxicology; however, to date, studies have been undertaken only on a single size group of fish (juvenile/adult) and for acute exposure. In the present study, Lateolabrax japonicus fingerlings and juveniles were exposed to two sublethal concentrations (200 and 2,000 ng/L) of 17beta-estradiol (E2) for 30 d under laboratory conditions, and alterations in immune parameters comprising differential leukocyte count, respiratory burst, myeloperoxidase, immunoglobulin levels, serum lysozyme, and bactericidal activity were investigated to establish whether estrogen produced immunomodulation and to understand the effects of long-term exposure on these immune parameters in fish fingerlings and juveniles. The results revealed a significant elevation of respiratory burst activity, myeloperoxidase, immunoglobulin levels, and differential leukocyte counts of the fish exposed to estrogen compared to the control. The remaining parameters were significantly reduced in the experimental groups when compared to the control. The results indicated that sublethal E(2) exposure induced immunomodulation in both fingerling and juvenile L. japonicus, and the changes caused by estrogen might affect the function of immune system in fish.

Effect of 17β‐estradiol on the immunocompetence of japanese sea bass (Lateolabrax Japonicus)

Sublethal effect of silver and chromium in the green mussel Perna viridis with reference to alterations in oxygen uptake, filtration rate and membrane bound ATPase system as biomarkers.

Immunotoxic effects of nickel in the mud crab Scylla serrata.

The toxicity of heavy metals to marine invertebrates has been widely investigated; however, the effects on marine sedentary polychaetes have largely been ignored. The toxicity of copper, aluminium, lead, nickel, and zinc on fertilization, embryogenesis, and larvae of Hydroides elegans was examined in laboratory acute-toxicity tests. Exposure to metal during fertilization or early developmental stages leads to fertilization block and arrested development, which resulted in morphologic abnormalities in embryo and larvae. Fertilization rate showed a drastic decrease at the highest metal concentration tested. Embryos of H. elegans showed a differential response to metals, and the responses were stage-specific. The different morphologic effects of heavy metals reflect differentiation of the early embryonic cells. For individual metals, the toxicity ranking for 24−hour trochophore larvae was Cu > Al > Pb > Ni > Zn, with EC50 values of 0.122, 0.210, 0.231, 0.316, and 0.391 mg l−1, respectively. Rate of larval development and embryogenesis were the most sensitive end points, although the latter is more advisable for routine assessment of seawater quality because of its greater simplicity. In addition to bivalves and sea urchins, polychaete embryos can provide biologic criteria for seawater quality taking into account the sensitivity of a polychaete and contributing to the detection of harmful chemicals with no marked effect on the species currently in use in seawater quality bioassays.

Singaram Gopalakrishnan

Papers

Comparison of heavy metal toxicity in life stages (spermiotoxicity, egg toxicity, embryotoxicity and larval toxicity) of Hydroides elegans

Effect of 17β‐estradiol on the immunocompetence of japanese sea bass (Lateolabrax Japonicus)

Sublethal effect of silver and chromium in the green mussel Perna viridis with reference to alterations in oxygen uptake, filtration rate and membrane bound ATPase system as biomarkers.

Immunotoxic effects of nickel in the mud crab Scylla serrata.

Toxicity of Heavy Metals on Embryogenesis and Larvae of the Marine Sedentary Polychaete Hydroides elegans