Towards an eco-epidemiological framework for managing freshwater crayfish communities confronted with crayfish plague

Wildlife diseases figure prominently among the main causes of biodiversity loss worldwide. Especially fungal and fungus-like pathogens are on the rise, wreaking havoc across the tree of life by threatening species persistence and destabilizing ecosystems. A worrisome example are freshwater crayfish species in Eurasia and Oceania, facing the dual challenge of introduced competitive crayfish species and an introduced water mold ( Aphanomyces astaci ) causing crayfish plague. A. astaci locally extinguishes susceptible native crayfish populations, while non-native individuals (mostly from North America) remain largely unaffected. Despite its significant impact and its ∼150 years of presence in Europe, studies and disease management recommendations for crayfish plague that are firmly rooted in epidemiological theory are scarce. Here, we present a practical eco-epidemiological framework to understand how multi-species crayfish communities react to crayfish plague introductions. The framework is based on the observation that the dynamics of crayfish communities are mainly determined by life-history characteristics, within- and among-species competition, effects of generalist predators (including fishing), and host-pathogen interactions. From this ecological and epidemiological context, we derive fundamental epidemiological metrics, single-host species and community-level basic reproduction numbers ( R ₀ ). We investigate how host species densities affect the likelihood of a disease outbreak in a crayfish community, and we demonstrate that a community’s R ₀ value is simply the sum of the community’s single-host species R ₀ values, adjusted for competition and predation. We further demonstrate how R ₀ can be used to guide preventative and mitigation actions for crayfish communities. For example, we show how R ₀ expressions – even without a detailed parametrization – can be used to construct regional risk rankings for different crayfish communities, for an effective allocation of resources to local conservation plans. Our eco-epidemiological framework will also be of interest to the management of other aquatic host-pathogen systems with water-borne pathogen transmission as the main route of pathogen spread.