BLUE MUSSEL HAEMOCYTE FUNCTION UNDER ENVIRONMENTAL STRESS
Blue mussels (Mytilus spp.) are economically and ecologically significant, they are the most farmed bivalves in Europe representing 35% of total aquaculture production. Climate change is increasing the frequency of extreme rainfall events, causing hyposalinity stress in sea loch aquaculture sites. Mussel immunity depends on haemocyte phagocytosis, but the effects of salinity stress on this critical immune function remain poorly understood. Haemocytes were extracted from Scottish rope-grown Mytilus spp. and exposed to salinities of 33, 20 and 13 parts per thousand (ppt) representing standard marine conditions, moderate hyposalinity and severe hyposalinity. Phagocytic activity was quantified using pHrodo™ fluorescent beads conjugated with Staphylococcus aureus, Escherichia coli, and Zymosan particles over 3-hour live imaging sessions. Additional experiments examined combined salinity and heat shock effects. Cells incubated at marine salinity (33 ppt) sustained stronger long-term phagocytic responses than those at 20 ppt or 13 ppt; severe hyposalinity uniformly suppressed phagocytosis. While mild hyposalinity produced a transient increase in phagocytic activity, likely representing a change between immune function and osmotic stress tolerance. Optimal survival conditions were modelled at 28.4 ppt and 10.4°C. Severe hyposalinity combined with heat stress severely compromised haemocyte function. These findings highlight the vulnerability of mussel aquaculture to climate driven multi-stressor events and suggest that extended observation periods are essential for accurate assessment of phagocytic capacity.
Figure 1: Graphical abstract: Combined salinity and thermal stress from climate change impairs haemocyte health and pathogen phagocytosis in blue mussels (Mytilus spp.).
References
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