Does infectious disease influence the efficacy of marine protected areas? A theoretical framework.
Marine protected areas are increasingly being recommended as an essential component of the management of exploited marine species, but virtually no attention has been given to the influence of parasites. This may be substantial, as a primary effect of marine reserves is to increase the density of an exploited population within the reserve relative to outside the reserve, which may facilitate parasite transmission. We used a simple deterministic model of microparasitic infection in a fishery with a reserve to investigate equilibrium yield and parasite prevalence inside and outside the reserve as a function of three control variables: the proportion of habitat inside the reserve, fishing mortality and the rate of interchange between the stock and the reserve. While our model is generic, we parameterized it with values that may be appropriate to the interaction between abalone and Rickettsia. The presence of a pathogen does not necessarily decrease yield when a reserve is present, particularly if the rate of movement of adult hosts between stock and reserve is low. Synthesis and applications. Pathogens have important implications for the design of marine reserves. Our modelling identifies two key considerations. First, 'fishing out' a pathogen by reducing the host population density to a level below the threshold for disease maintenance is a potential management strategy that is made more difficult by establishing a reserve. Secondly, the effect of a highly transmissible pathogen without a reserve is to cause a rapid decline in equilibrium yield for efforts beyond those that produce maximum sustainable yield, making the fishery prone to collapse. Introducing a reserve decreases yield in this case, but makes the fishery much more resistant to collapse.