First Evidence of Immunomodulation in Bivalves under Seawater Acidification and Increased Temperature

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.

Pathogenic challenge reveals immune trade-off in mussels exposed to reduced seawater pH and increased temperature

“…In showing immune system maintenance to be compromised by exposure to a reduced seawater pH of 6.50, this study would appear to support previous research on the impact of elevated seawater pCO 2 on the invertebrate immune response (Bibby et al, 2008;Matozzo et al, 2012). Bibby et al (2008) found that a 32 day exposure to OA reduced the ability of impacted mussels to increase phagocytic activity when compared to controls, suggesting that an increased haemolymph calcium concentration interfered with cellular signalling pathways, and thus immunocompetence.…”

“…Hernroth et al (2011) also demonstrated a suppression of phagocytic activity, as well as a reduction in coelomocyte counts and an inhibition of p38 MAPkinase activity, in Asterias rubens exposed to pH 7.7. Similarly Matozzo et al (2012) demonstrated a reduction in host defence in mussels exposed to reduced seawater pH, with the lysozyme-like activity of cell free haemolymph reduced in Mytilus galloprovincialis exposed to pH 7.7 and 7.4 for 7 days.…”

“…Yet, in this species phagocytic capacity was only impacted by reduced seawater pH. Matozzo et al (2012), in exposing M. galloprovincialis and Chamelea gallina to reduced seawater pH, also maintained these bivalves at two different temperatures, 22°C and 28°C. However, despite demonstrating a significant impact of a combined temperature and reduced pH exposure on a number of immune parameters (including total haemocyte counts, lysozyme like activity of cell-free haemolymph and neutral red retention) these authors highlight the lack of clear response of bivalve host defence.…”

“…If this is the case then an OA/ temperature induced trade-off in host defence should reduce immunocompetence, and increase pathogen susceptibility, as was hypothesised by both Bibby et al (2008) and Matozzo et al (2012). However, it is important to note that these two studies were undertaken in the absence of a pathogen.…”

Effects of ocean acidification on immune responses of the Pacific oyster Crassostrea gigas

“…Recently, it has been found that OA stress has the potential to promote pathogen development and survival, disease transmission and host susceptibility [33]. However, only few studies have investigated the immune responses of mollusks under OA stress so far [18,19,34].…”