COS 234-4 - Toward an ecological understanding of Dermo disease in Eastern oysters: investigating variation in infection patterns and virulence across the landscape

Abstract: Perkinsus marinus, the protozoan pathogen responsible for causing Dermo disease, infects Eastern oysters (Crassostrea virginica) along the American East coast and the Gulf of Mexico. Because of its associations with large-scale oyster die-offs, research on P. marinus is often focused on understanding its impacts on fisheries. However, this pathogen offers additional opportunities for understanding geographic variation in pathogen transmission and virulence. Through conducting a literature review and analyzing long-term data on P. marinus infection of Eastern oysters collected from the Gulf of Mexico, we highlight differences in patterns of infection, discuss gaps in the literature, and present new ecological questions on the system.

First, we find that infection dynamics between oysters and P. marinus are different in the Gulf of Mexico than they are in the Northeastern United States. For instance, we find that prevalence of P. marinus is relatively high (approximately 50%) and constant over the annual cycle. This is in stark contrast to infection dynamics in the Chesapeake Bay, where prevalence undergoes annual cycles, oscillating between as high as 100% in late summer and near zero in the winter. Second, we find limited associations between P. marinus abundance and metrics of host mortality in gulf coast oysters. This again contrasts with the Chesapeake Bay patterns, where Dermo disease causes oyster mass mortalities, and raises questions on the virulence of gulf coast P. marinus. Third, our literature review revealed substantial geographic disparities in field research on P. marinus. While this pathogen has been well-studied in the Northeastern United States, populations from the American Gulf of Mexico have been less studied, and studies are virtually absent from the Mexican Gulf. These geographic data gaps make it challenging to contextualize the observed differences in infection patterns and virulence. One potential driver of these differences is environmental conditions. There is strong evidence to suggest that P. marinus infections vary with temperature, salinity, and large climate oscillations. By examining disease data alongside environmental data, we explore how regional differences in environmental parameters covary with differences in infection and virulence. These findings raise important questions about how host tolerance and parasite virulence may change in different environmental contexts and motivate future ecological study of this system.