Award: OCE-1658466

Diseases of marine animals have important ecological and economic consequences, yet are hard to predict because the movement of disease agents in marine systems is complex. We sought to understand the factors that promote the movement of a virus (CsRV1) that infects the American blue crab (Callinectes sapidus). Across the range from New England to Uruguay, we identified crabs with virus infections, and sequenced the genetic material of both crab and virus. We investigated how overwintering affected crab – virus interactions, and collaborated with an oceanographer to examine models of how ocean currents influence where crab larvae would be dispersed. The ultimate goal was to understand how viruses and crabs interact across time and space, including whether the virus adapts its infection strategy depending on latitude. 

Though the virus is common along the US mid-Atlantic coast, we found that CsRV1 prevalence was lower in semi-tropical areas and dropped to nearly zero in the tropics. An accompanying image of the prevalence is included with this Project Outcomes Report. In temperate areas, the prevalence of virus is lower in overwintering crabs, but does not drop to zero, which shows that the virus has a winter reservoir (Zhao et al. 2023; Zhao et al. 2020). The work involved dozens of collaborators, many of whom are co-authors. This included international researchers and even a Baltimore City high school student. 

We saw that the genetic relatedness of the virus across the Atlantic coasts of the Americas was consistent with geographic distance. There was one notable exception, however: the genetic relatedness of CsRV1 from crabs on the coast of Louisiana was unusually similar to CsRV1 found in the Chesapeake Bay (see accompanying figure). This could not be explained by oceanographic models or by what we know about crab movement. There is intense commerce of live blue crabs between Louisiana and the Chesapeake, mainly to meet winter demand for blue crabs when crabs are dormant in the cold months. The potential for human-mediated movement of a crab pathogen between states was communicated with fishery managers in Maryland. It also led to a Maryland Sea Grant-funded project to investigate whether there are other crab viruses with potential to be transported by interstate commerce shipments. That project has discovered nearly 100 new viruses associated with blue crabs (Herrera, J., 2025. Identification and Characterization of Viruses Associated With the Atlantic Blue Crab, Callinectes sapidus, Across Its United States Geographic Range (Master's thesis, University of Maryland, College Park)). 

The puzzle of why the prevalence of CsRV1 drops in the Caribbean was investigated by leveraging funding from NOAA Educational Partnerships Program to look in detail at the ecology of blue crabs in an estuary in Puerto Rico. In this study, PhD student Olivia Pares collected blue crabs over a 1-year period. The study revealed that in the tropics, C. sapidus was not the dominant crab species. Instead, it was one of five species of Callinectes in the estuary; only 81 of 259 crabs were C. sapidus. In the year of sampling, we failed to detect CsRV1 in any crabs. One possible reason for this is that in a habitat where C. sapidus is infrequent, and other species of Callinectes are not hosts for CsRV1, there would be little transmission and the virus would not persist in the population. In support of this, our attempts to infect other species of Callinectes with CsRV1 were not successful (Pares et al., in preparation). Field work engaged students from high schools in San Juan, and two teachers from the Park School, in Baltimore County (see accompanying figure). 

The genetic analysis of the relatedness of blue crabs from across the study range is nearly complete. The method used identifies thousands of genetic differences between crabs from every location and draws a network of relationships between each population (ref: Plough 2017). Genetic data is being analyzed in parallel with the oceanographic models that create predictions about where crab larvae will disperse over time. This will show whether predictions based on oceanographic currents and geography agree with the genetic data. If the two sets of data do not align, it would be evidence that there are things we don’t know about movement or history of crabs or their larvae.   

Overall, the project created new knowledge about the host and geographic range of the most common virus pathogen of blue crabs, with implications for protection of fishery resources. It generated several other funded projects, engaged k-12 students in Maryland and Puerto Rico, and produced information that is useful for crab fishery managers. The collaborative work (not part of this report) on crab behavior and models of dispersal will add to the significance of the disease work described here. 

Last Modified: 11/28/2025
Modified by: Eric J Schott