Interactive effects of copper exposure and environmental hypercapnia on immune functions of marine bivalves Crassostrea virginica and Mercenaria mercenaria

Abstract

Estuarine organisms such as bivalves are commonly exposed to trace metals such as copper (Cu) and hypercapnia (elevated CO2 levels) in their habitats, which may affect their physiology and immune function. This study investigated the combined effects of elevated CO2 levels (∼800-2000 μatm PCO2, such as predicted by the near-future scenarios of global climate change) and Cu (50 μg l(-1)) on immune functions of the sediment dwelling hard clams Mercenaria mercenaria and an epifaunal bivalve, the eastern oyster Crassostrea virginica. Clams and oysters were exposed for 4 weeks to different CO2 and Cu levels, and tissue Cu burdens and immune parameters were assessed to test the hypothesis that hypercapnia will enhance Cu uptake due to the higher bioavailability of free Cu(2+) and increase the immunomodulatory effects of Cu. Exposure to Cu stimulated key immune parameters of clams and oysters leading to increased number of circulating hemocytes, higher phagocytosis and adhesion ability of hemocytes, as well as enhanced antiparasitic and antibacterial properties of the hemolymph reflected in higher activities of lysozyme and inhibitors of cysteine proteases. Lysozyme activation by Cu exposure was most prominent in normocapnia (∼400 μatm PCO2) and an increase in the levels of the protease inhibitors was strongest in hypercapnia (∼800-2000 μatm PCO2), but other immunostimulatory effects of Cu were evident in all PCO2 exposures. Metabolic activity of hemocytes of clams and oysters (measured as routine and mitochondrial oxygen consumption rates) was suppressed by Cu exposure likely reflecting lower rates of ATP synthesis and/or turnover. However, this metabolic suppression had no negative effects of the studied immune functions of hemocytes such as phagocytosis or adhesion capacity. Hypercapnia (∼800-2000 μatm PCO2) slightly but significantly enhanced accumulation of Cu in hemocytes, consistent with higher Cu(2+) bioavailability in CO2-acidified water, but had little effect on cellular and humoral immune traits of clams and oysters. These findings indicate that low levels of Cu contamination may enhance immunity of estuarine bivalves while moderate hypercapnia (such as predicted by the near future scenarios of the global climate change) does not strongly affect their immune parameters.

Changes in the biochemical and nutrient composition of seafood due to ocean acidification and warming

“…Since bivalves are filter feeders, they readily accumulate metals present in the surrounding waters into their edible tissue (Lu et al, 2017;Raposo et al, 2009). This process can be modulated by ocean acidification, for instance enhancing the bioaccumulation of Cu in oysters (Belivermiş et al, 2015;Götze et al, 2014;Hawkins & Sokolova, 2017;Ivanina et al, 2015;Ivanina et al, 2016). While Cu accumulation under ocean acidification and warming can come at metabolic costs to organisms (Hawkins & Sokolova, 2017) emissions.…”

Environmental behaviors and toxicity of heavy metals and metallic nanoparticles to marine organisms under ocean acidification

“…缓解毒性 [45] (图2中过程⑥). 长期暴露时, 在OA条件 下金属硫蛋白和铁蛋白表达上调, 增强了血细胞的金 属结合能力 [47] , 通过蛋白与金属螯合缓解毒性 [46,52,53] (图2中过程⑦).…”

Effect of Electroplating Waste water on Immune Function in Kunming Mice

“…For instance, very low copper intake may impair immune function in human [18]. However, low levels of copper contamination may enhance immunity of estuarine bivalves [19]. Zinc is an essential trace element which is important for maintenance and development of immune cells of both the innate and adaptive immune system [20].…”