Abstract
Combined effects of reduced pH, as predicted under climate change scenarios, and the most popular and widely used stimulant caffeine were assessed in hemocyte parameters of the mussel Mytilus galloprovincialis, being hemocytes involved in immune defense. Bivalves were exposed for one week to natural pH (8.1) and two reduced pH values (pH −0.4 units and pH −0.7 units). Exposure continued for additional two weeks, both in the absence and in the presence of environmentally relevant concentrations of caffeine (0.05 and 0.5 µg/L). Hemocyte parameters (total hemocyte count, hemocyte volume and diameter, neutral red uptake and hemocyte proliferation) were measured after 7 days of exposure to pH only, and after 14 (T1) and 21 (T2) days of exposure to the various pH*caffeine combinations. At all sampling times, pH significantly affected all the biological variables considered, whereas caffeine exhibited a significant influence at T2 only. Among the various hemocyte parameters, caffeine caused a significant increase in total hemocyte count at T2, and in hemocyte volume and diameter at both T1 and T2, when a significant interaction between pH and caffeine was also found. Overall, results demonstrated that hemocyte functionality was strongly influenced by the experimental conditions tested. Further studies are needed to assess combined effects of climate changes and emerging contaminants on bivalve immune system when challenged with environmental pathogens.
Highlights
Organic wastewater contaminants, such as pharmaceuticals, occurring in fluvial, estuarine and coastal environments have produced increasing concern on their potential ecotoxicological effects to aquatic species [1,2,3]
Combined effects of reduced pH, as predicted under climate change scenarios, and the most popular and widely used stimulant caffeine were assessed in hemocyte parameters of the mussel Mytilus galloprovincialis, being hemocytes involved in immune defense
Despite that the high consumption and environmental occurrence of caffeine are well documented, the effects of caffeine to aquatic organisms need to be more fully investigated, especially in marine species living in estuarine and coastal environments, which are mostly affected by human activities
Summary
Organic wastewater contaminants, such as pharmaceuticals, occurring in fluvial, estuarine and coastal environments have produced increasing concern on their potential ecotoxicological effects to aquatic species [1,2,3]. Despite that the high consumption and environmental occurrence of caffeine are well documented, the effects of caffeine to aquatic organisms need to be more fully investigated, especially in marine species living in estuarine and coastal environments, which are mostly affected by human activities. Eng. 2020, 8, 238 change scenarios) and caffeine (a widely used substance in many formulations) on some hemocyte parameters, such as THC, hemocyte diameter and volume, neutral red (NR) uptake and hemocyte proliferation were investigated for the first time in the Mediterranean mussel M. galloprovincialis This species is widespread in marine coastal areas and is extensively used as model organism in ecotoxicological studies [33]. We choose to evaluate the combined effects of lowered pH and caffeine on mussel hemocytes, as such cells are involved in immune responses in bivalves [24,25,26] and hemocyte parameters (or immunomarkers) are widely used to evaluate the effects of environmental contaminants in molluscs [34]
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