Quantifying the influence of salinity and temperature on the population dynamics of a marine ectoparasite

Abstract

Sea lice are common ectoparasites of farmed and wild salmonids and can cause substantial morbidity and mortality in their hosts. While sea lice infections are common in estuarine areas with variable salinity, the effects of salinity on population dynamics are poorly understood. We used existing literature to parameterize salinity-dependent logistic mortality curves for different life stages of sea lice. We then used population matrix models to characterize the effects of temperature and salinity on sea louse population growth. Our models showed that low salinity decreases survival, while low temperature retards sea louse development. In contrast with the linear effects of temperature on sea louse development, salinity has a nonlinear effect on sea louse survival; values below 20 psu cause mortality, while values above 20 psu have little effect on survival. Simulations showed that sea louse population growth can be greatest in zones that are intermediate between estuarine and oceanic. In these cases population growth is not limited by the low salinities found in more estuarine sites or the low temperatures found in more oceanic sites.