Award: OCE-0929086

Terrestrial epidemiology is different from that in marine ecosystems, a crucial difference being the more rapid spread of diseases in the ocean due to the presumed absence of barriers to waterborne dispersal. Yet, the movement of pathogens in the sea and its importance to disease dynamics in marine metapopulations remains little studied. Marine pathogens can certainly spread among distant host populations, as demonstrated by expanding epizootics, but nearly all studies of marine diseases treat such events as transitory, focusing instead on local disease dynamics. This approach suggests that small-scale phenomena have a great influence on pathogen connectivity or that long-distance dispersal of marine pathogens is simply too intractable for empirical investigation.  However, dispersal by infected larvae could be an important mechanism linking outbreaks over long distances. Most marine animals have life histories that include planktonic larvae, many of which are highly dispersive.  If infected by pathogens, such larval vectors would provide an efficient mechanism for distributing pathogens at high concentrations directly into habitats where uninfected hosts dwell. Long-distance pathogen dispersal in the sea could be possible via infected meroplanktonic larvae, an analogy much like how arboviruses use insects for dispersal in terrestrial systems.

            We examined dispersal pathways for a pathogenic virus (PaV1; Panulirus argus virus 1) that infects the Caribbean spiny lobster, Panulirus argus – a commercially important species broadly distributed throughout the Caribbean. Previous work indicated that the virus was present in different regions of the Caribbean; regions demographically linked only by dispersing larvae that spend >6 mos. in the open ocean. Our initial data indicated that lobster postlarvae recruiting to coastal nurseries in Florida were infected with PaV1, providing novel evidence for pathogen connectivity among distant host populations. Thus, our objectives were (1) to investigate the dynamics and mechanisms of PaV1 infection of larvae and the effect of infection on larval behavior and mortality, which influence dispersal and demographic connectivity; (2) to examine the importance of large-scale connectivity by PaV1-infected postlarvae on the maintenance of local disease dynamics and patterns of disease prevalence at local scales; and (3) to explore the ramifications of planktonic pathogens and the hydrodynamic environment on large-scale patterns of disease connectivity. These objectives were tackled by a team of scientists from ODU, VIMS, RSMAS, and University of Florida. The VIMS portion of the research focused on the development and use of diagnostic assays for detection of PaV1. Additional findings are given in the Project Outcomes Report from the other participating institutions.

PaV1 had a high strain diversity with many unique strains from around the Caribbean. Several strains supported the connectivity model for lobster populations. For example, PaV1 from Puerto Rico shared strains with the virus from Florida and Cuba. However, PaV1 in lobsters from the Bahamas had several unique strains, supporting regional endemicity perhaps based on prevailing current patterns.  Indeed, viral sequence variation was not a feature of hypermutation but representative of a very large effective population size. The extraordinary genetic diversity of the virus in the Caribbean and the existence of multiple strains in the same regions (e.g., countries), suggests that virus-host dynamics are local-scale phenomena, but many strains are shared between areas with high connectivity. Nonetheless, field studies demonstrated the patchiness of viral prevalence. It is constrained to hard-bottom areas.&nbs...