Salt in the wound: consequences of changing salinities on marine disease.

Salinity plays an important role in the physiology of marine organisms and their pathogens. As the climate continues to change, marine and estuarine salinities may become more extreme and irregular, potentially altering host-pathogen interactions. In this review, we explore and highlight the role of salinity on a range of pathosystems, outlining impacts to the host, pathogen and their interactions. We present fisheries and aquaculture-focused case studies, including behavioural preferences for freshwater in sea louse-infested trout and the use of freshwater as a delouser in salmon aquaculture, the effects of rainfall and drought on prevalence of a lethal parasitic infection of crustaceans, as well as low saline environments as refugia from oyster disease. We also present a case study of human health risks examining how changing coastal salinities can affect seafood-associated illnesses, and a conservation-directed case study examining the role of salinity and disease in defining the distribution of a habitat-forming species. Changing climatic conditions drive diverse salinity-altered epidemiological outcomes in these pathosystems. As salinities become more variable and less predictable, and fisheries management and marine conservation require increasing priority, future studies investigating multiple stressors, salinity included, on pathosystems will provide insights into organism and ecosystem resilience under future climate scenarios. This article is part of the theme issue 'Managing infectious marine diseases in wild populations'.