Sea star populations of multiple species in western North America have been degrading and dying from an outbreak of an epidemic Sea Star Wasting Syndrome. Infected individuals develop white skin lesions which spread until the whole body decays. The Sea Star-associated Densovirus (SSaDV) discovered in symptomatic individuals was implicated as a potential initiator of the disease, although the mechanisms of defense and tissue disintegration are unknown. Echinoderm innate immune reactions include an organismic response (increasing numbers of coelomocytes (immune cells)), and a cellular response (e.g. increasing phagocytic activity, clumping cells, and the expression of defensive proteins). We examined the bat star coelomic fluid before and throughout disease progression to determine differences in the coelomocytes of healthy and wasting bat stars, and after exposure to isolated virus. We identified several coelomocyte types and increases in the concentration, aggregation, and phagocytic activity of coelomocytes throughout disease progression. The increase in phagocytosis and cell death before the symptoms appear suggests the beginnings of an immune response before the appearance of wasting symptoms. Our analysis of the coelomic fluid proteome shows an increase in signaling, adhesion, and immune response proteins before and after symptoms appear. The increase in cell signaling, phagocytosis, and death is suggests the bat stars do have an immune response to the wasting syndrome, and the pathogens that may be associated with the epidemic.