Acanthocephalan parasites in sea otters: Why we need to look beyond associated mortality…

The acanthocephalan parasite, Corynosoma enhydri, uses sea otters (Enhydra lutris) as definitive host. Despite high prevalence and abundance in southern sea otters (E. l. nereis), sublethal impacts of infection on otter health are unknown. Parasites are an integral part of ecosystem structure and functioning. Many affect host behavior, reproduction, predation, or prey preference. Parasites can suppress host immune response, facilitate secondary bacterial, viral, or parasitic infections, and influence concurrent microbial infection. Acanthocephalan infections can have significant effects on host metabolism, digestion, nutrient absorption, and energetics. Because high metabolic expenditures and resource limitations are known to affect southern sea otter populations, even subtle effects of infection could negatively impact individual health and population recovery. In this review we summarize reports of host-parasite-environmental interactions for helminth infections and discuss how these same attributes could manifest in southern sea otters and coastal food web dynamics. Based on these data, investigation of potential sublethal impacts of C. enhydri is warranted. We recommend expanding understanding of the significance of parasites in marine ecosystems beyond associated mortality. Future investigation into the ecological implications of sublethal effects are essential to fully grasp parasite impacts on host populations, and predict potential additive effects with climate change in ecosystem functioning.