Award: OCE-1658396

The Atlantic blue crab (Callinectes sapidus) is an iconic crustacean living in estuaries and coastal marine habitats along the US Atlantic and Gulf coasts but it has a remarkable home-range that extends from Maine to Argentina. It supports fisheries and fishing communities across this range but is also an important member of the marine community, serving as predator, prey, and scavenger. Its life history, as with many marine organisms, is shaped by its environment, thus it can vary with latitude and environmental conditions. For the blue crab, life history includes such things as the time spent in the plankton as a larvae, the location and type of juvenile habitat available, salinity of the mating and spawning habitats, and in regions where the water temperature drops below 10? C in the winter, it means winter hibernation or dormancy. Marine organisms are also affected by parasites across their life history stages and across their geographic ranges but we know little about how these factors interact to drive disease. We used the Atlantic blue crab and its viral parasite, Callinectes sapidus Reo-like VIrus 1 (CsRV1), to study how the crab host and parasite are connected across their broad range, and how latitude intersects with life history to drive differences in disease. Our project had three main objectives: 1) Determine how life history variation in the blue crab affects patterns of CsRV1 prevalence, virulence and host susceptibility. 2) Determine the genetic structure of the blue crab and CsRV1 populations from temperate to tropical regions. 3) Characterize the population connectivity of the blue crab across its entire geographic range and compare this to host and pathogen population genetic structure. Intellectual Merit We collected blue crab samples across their range and found that in the part of their range where blue crabs are dormant in the winter (far north and south Atlantic), the prevalence of the CsRV1 virus is much higher than in the central part of their range where they are active year-round. This could be due to a difference in temperature preference of the virus for cooler warmer waters but could also be affected by the lower density of blue crabs in the Caribbean that limits transmission of the virus between crabs. We also found that prevalence of CsRV1 appears much lower during the winter in regions where the crabs experience dormancy; however, laboratory experiments show that the virus remains present at much lower levels in dormant crabs and begins to multiply rapidly in the spring when the water warms. Hence, our results showing lower prevalence in the winter could actually be a result of the virus also going dormant and being less easily detected. Our genetic studies show that the Atlantic blue crab is the same species across its range but the populations we sampled show genetic differences consistent with different oceanographic regions and distances separating those populations. The genetic population of CsRV1 virus was consistent with the host geographic origins and was only found affecting the blue crab Callinectes sapidus, not any of the other species of Callinectes (e.g., C. danae, C. bocourti, C. similus, C. ornatus, C. marginatus) found within the range of the blue crab. The connectivity of blue crabs and the CsRV1 virus across their range are driven by different factors. Blue crabs are transported across long distances as pelagic larvae and to a lesser degree by bottom-dwelling adult crabs moving between estuaries. The CsRV1 virus, on the contrary, is only transported by adult crabs moving it along the coast since it does not infect crab larvae and is unlikely to remain viable for long outside the host crab. Although healthy adult crabs can travel long distances outside of estuaries, when infected with CsRV1 their activity rapidly declines, which reduces the likelihood of an infected crab moving from one coastal estuary to the next before dying. Broader Impacts We worked directly with local fishers, fishery managers, and scientists to collect all of the blue crab data from across their range. At many of these locations we also gave presentations on the research project and ongoing results. Where appropriate, our partners were engaged in the publication of the results and included as co-authors. The project also involved the training of enumerable graduate and undergraduate students with diverse backgrounds from the University of Florida and University of Maryland. We continue to give presentations stemming from the project to scientific and agency personnel, the latter of whom are using our results in their directives to manage fishery stocks and aquaculture operations. Last Modified: 09/05/2023 Submitted by: Donald Behringer