Abstract
Water acidification, temperature increases and changes in seawater salinity are predicted to occur in the near future. In such a global climate change (GCC) scenario, there is growing concern for the health status of both wild and farmed organisms. Bivalve molluscs, an important component of coastal marine ecosystems, are at risk. At the immunological level, the ability of an organism to maintain its immunosurveillance unaltered under adverse environmental conditions may enhance its survival capability. To our knowledge, only a few studies have investigated the effects of changing environmental parameters (as predicted in a GCC scenario) on the immune responses of bivalves. In the present study, the effects of both decreased pH values and increased temperature on the important immune parameters of two bivalve species were evaluated for the first time. The clam Chamelea gallina and the mussel Mytilus galloprovincialis, widespread along the coast of the Northwestern Adriatic Sea, were chosen as model organisms. Bivalves were exposed for 7 days to three pH values (8.1, 7.7 and 7.4) at two temperatures (22 and 28°C). Three independent experiments were carried out at salinities of 28, 34 and 40 PSU. The total haemocyte count, Neutral Red uptake, haemolymph lysozyme activity and total protein levels were measured. The results obtained demonstrated that tested experimental conditions affected significantly most of the immune parameters measured in bivalves, even if the variation pattern of haemocyte responses was not always linear. Between the two species, C. gallina appeared more vulnerable to changing pH and temperature than M. galloprovincialis. Overall, this study demonstrated that climate changes can strongly affect haemocyte functionality in bivalves. However, further studies are needed to clarify better the mechanisms of action of changing environmental parameters, both individually and in combination, on bivalve haemocytes.
Highlights
Global climate changes (GCCs) are occurring presently and are predicted to continue in the coming decades through changes in abiotic environmental factors, such as temperature increases, water acidification, and changes in precipitation and seawater salinity [1]
At 28 and 34 PSU, pair-wise comparisons demonstrated that Neutral Red (NR) uptake by haemocytes from clams kept at 8.1 pH and 22uC was significantly lower than animals from the other experimental conditions, except for clams held at 7.7 pH and 22uC and at 8.1 pH and 28uC, both at 34 PSU (Figures 3A, 3B)
An opposite pattern of variation in NR uptake was observed at 40 PSU, with dye levels being significantly higher in animals kept at 8.1 pH and 22uC compared with animals from the other experimental conditions (Figure 3C)
Summary
Global climate changes (GCCs) are occurring presently and are predicted to continue in the coming decades through changes in abiotic environmental factors, such as temperature increases, water acidification, and changes in precipitation and seawater salinity [1]. Pre-industrial atmospheric CO2 levels were approximately 280 ppm, whereas at present, they have increased to more than 380 ppm, mainly due to anthropogenic activities [2]. Several reports have implied that the continued release of CO2 into the atmosphere has already caused a reduction in ocean pH values of approximately 0.1 pH units with respect to the preindustrial levels and that reductions from 0.3 to 0.5 pH units are predicted to occur before the end of the 21st century [1,4,5,6]. Increasing atmospheric CO2 levels may cause a pH reduction of 0.7 units by 2300 [7]
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