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1. Coastal Vegetation and Bathymetry Influence Blue Crab Abundance Across Spatial Scales

   https://doi.org/10.1007/s12237-021-01039-5  

   Cheng, Selina L.; Tedford, Kinsey N.; Smith, Rachel S.; Hardison, Sean; Cornish, Michael R.; Castorani, Max C. (September 2022, Estuaries and Coasts)

   Abstract Blue crabs ( Callinectes sapidus ) are highly mobile, ecologically-important mesopredators that support multimillion-dollar fisheries along the western Atlantic Ocean. Understanding how blue crabs respond to coastal landscape change is integral to conservation and management, but such insights have been limited to a narrow range of habitats and spatial scales. We examined how local-scale to landscape-scale habitat characteristics and bathymetric features (channels and oceanic inlets) affect the relative abundance (catch per unit effort, CPUE) of adult blue crabs across a > 33 km 2 seagrass landscape in coastal Virginia, USA. We found that crab CPUE was 1.7 × higher in sparse (versus dense) seagrass, 2.4 × higher at sites farther from (versus nearer to) salt marshes, and unaffected by proximity to oyster reefs. The probability that a trapped crab was female was 5.1 × higher in sparse seagrass and 8 × higher near deep channels. The probability of a female crab being gravid was 2.8 × higher near seagrass meadow edges and 3.3 × higher near deep channels. Moreover, the likelihood of a gravid female having mature eggs was 16 × greater in sparse seagrass and 32 × greater near oceanic inlets. Overall, we discovered that adult blue crab CPUE is influenced by seagrass, salt marsh, and bathymetric features on scales from meters to kilometers, and that habitat associations depend on sex and reproductive stage. Hence, accelerating changes to coastal geomorphology and vegetation will likely alter the abundance and distribution of adult blue crabs, challenging marine spatial planning and ecosystem-based fisheries management. 

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2. Investigating conspecific CsRV1 transmission in Callinectes sapidus

   https://doi.org/10.1016/j.jip.2023.107987  

   Lively, Julie A; Spitznagel, Matthew I; Schott, Eric J; Small, Hamish J (November 2023, Journal of Invertebrate Pathology)

   A reo-like virus, CsRV1, is found in blue crabs, Callinectes sapidus, from every North American location assessed, including Chesapeake Bay and the Atlantic and Gulf coasts, USA and associated with blue crabs in softshell production. CsRV1-associated crab mortality is prevalent in captive crabs, but it is still unknown how CsRV1 is transmitted. The purpose of this study was to examine the role that conspecific predation or scavenging may play in per os transmission in single exposure and repeated exposure experiments. For viruses without cell culture propagation, repeated exposure experiments have the challenge of presenting the virus consistently during the experiment and across time replicates. In a single-exposure experiment, none of the crabs fed muscle tissue of crabs carrying intense infections of CsRV1 developed CsRV1 infections. In a repeated-exposure trial, using infected muscle tissue prepared in alginate blocks, CsRV1 was detected in 11% of the crabs fed infected tissue but was not significantly different from the control group fed alginate lacking CsRV1. For repeated per os exposure experiments, the study demonstrated the utility of using alginate to present the same homogenous sample of virus, both injected and per os, over time for oral challenge experiments. Conspecific predation and scavenging could be a transmission route, but future work into this and other possible routes of transmission for CsRV1 is important to better understand the role this virus plays in wild crab populations and the soft-shell crab industry. 

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3. Tracing exploitation of egg boons: an experimental study using fatty acids and stable isotopes

   https://doi.org/10.1242/jeb.246247  

   Nair, Parvathi; Miller, Cambria M.; Fuiman, Lee A. (November 2023, Journal of Experimental Biology)

   ABSTRACT Coordinated spawning of marine animals releases millions of planktonic eggs into the environment, known as egg boons. Eggs are rich in essential fatty acids and may be an important lipid subsidy to egg consumers. Our aim was to validate the application of fatty acid and stable isotope tracers of egg consumption to potential egg consumers and to confirm egg consumption by the selected species. We conducted feeding experiments with ctenophores, crustaceans and fishes. We fed these animals a common diet of Artemia or a commercial feed (Otohime) and simulated egg boons for half of them by intermittently supplementing the common diet with red drum (Sciaenops ocellatus) eggs for 10–94 days. Controls did not receive eggs. Fatty acid profiles of consumers fed eggs were significantly different from those of controls 24 h after the last egg-feeding event. Consumers took on fatty acid characteristics of eggs. In fishes and ctenophores, fatty acid markers of egg consumption did not persist 2–5 days after the last egg-feeding event, but markers of egg consumption persisted in crustaceans for at least 5–10 days. Additionally, consumption of eggs, which had high values of δ15N, led to δ15N enrichment in crustaceans and a fish. We conclude that fatty acids and nitrogen stable isotope can be used as biomarkers of recent egg consumption in marine animals, validating their use for assessing exploitation of egg boons in nature. 

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4. Blue crab Callinectes sapidus dietary habits and predation on juvenile winter flounder Pseudopleuronectes americanus in southern New England tidal rivers

   https://doi.org/10.3354/meps13909  

   Taylor, DL; Fehon, MM; Cribari, KJ; Scro, AK (January 2022, Marine Ecology Progress Series)

   Blue crabs Callinectes sapidus have expanded their geographic range northward in the NW Atlantic with possible trophodynamic effects on benthic communities. In this study, we examined the blue crab’s diet in 2 southern New England tidal rivers (USA) and expounded on their predator-prey interaction with juvenile winter flounder Pseudopleuronectes americanus . Blue crabs (8-185 mm carapace width [CW]; n = 1835) were collected from the Seekonk River, Rhode Island, and Taunton River, Massachusetts, between May and August 2012 to 2016, and their feeding habits were assessed via stomach content, stable isotope, and molecular genetic analyses. Blue crabs were found to be generalist carnivores-omnivores with diets varying throughout ontogeny, yet shifts in prey composition had no effect on size-based nitrogen isotope signatures and trophic position (3.50 ± 0.35, mean ± SD). Carbon isotope values indicated that detritus-macroalgae were the dominant carbon source to the food web, with additional contributions from terrestrially derived organic matter and phytoplankton in oligohaline and polyhaline waters, respectively. The main prey of blue crabs ≤49 mm CW were amphipods, shrimp, and unidentified crustaceans, and larger conspecifics fed on bivalves, crabs, and fish. Winter flounder remains, e.g. sagittal otoliths, were identified in the diet of 2.5% of field-collected blue crabs, whereas PCR-based assays detected winter flounder DNA in 17.7% of crab stomachs. Blue crabs 23 to 160 mm CW preyed on winter flounder ranging from 26 to 66 mm total length, with occurrences of predation most closely associated with increases in crab size. Blue crab predation on winter flounder also varied spatially in the rivers, reflecting site-specific differences in flounder densities, abundances of other preferred prey, and dissolved oxygen concentrations that altered predator-prey dynamics. Lastly, the current predatory impact of blue crabs on juvenile winter flounder is nearly equivalent to other portunid crab species. Anticipated temperature-mediated increases in blue crab densities at northern latitudes, however, will intensify the predator-induced mortality of winter flounder and likely hinder their recovery in southern New England. 

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5. Plasticity, not Genetics, Shapes Individual Responses to Thermal Stress in Non-Native Populations of the European Green Crab ( Carcinus maenas )

   https://doi.org/10.1093/icb/icaf131  

   Venkataraman, Yaamini_R; Kelso, Julia_C; Payne, Catlin; Freitas, Heidi_L; Kohler, Jasmine; Tepolt, Carolyn_K (July 2025, Integrative And Comparative Biology)

   Synopsis Temperature is a major driver of individual performance in ectotherms, with this impact depending on stressor intensity and duration. Differences in individual response across temperature, time, and populations are shaped by the interplay between evolutionary adaptation and phenotypic plasticity. Some populations are able to thrive in novel and changing environments despite limited genetic diversity, raising the question of how plasticity and adaptation interact after significant genetic diversity loss. The European green crab (Carcinus maenas) is a textbook example of this phenomenon: invasive populations boast a broad thermal tolerance and exceptional thermal flexibility even after repeated genetic bottlenecks. Despite this loss of diversity overall, prior work has found a strong population-level association between variation at a specific extended genomic region (supergene), cold tolerance, and sea surface temperature. We conducted a series of three experiments using righting response to characterize sublethal thermal tolerance and plasticity in introduced green crab populations, then determined if these factors were associated with supergene genotype for individual adult crabs. Crabs showed signs of stress after exposure to a 30°C heat shock in one experiment. Interestingly, a second experiment exposing C. maenas to repeated 24-h heat shocks showed that prior heat shock conferred beneficial plasticity during a subsequent event. The third experiment examined cold acclimation over multiple timepoints up to 94 h. At 5°C, certain crabs exhibited an acclimatory response where righting slowed dramatically at first, and then gradually sped up after a longer period of cold exposure. Several crabs failed to right at 1.5°C, which could be indicative of dormancy employed to reduce energy consumption in colder conditions. There were no significant relationships between individual plasticity and supergene genotype in any experiment. Linking population-level genetic associations with individual-level physiology is complex, and reflects the impact of environmental conditions such as temperature throughout life history in shaping adult phenotype. Our results highlight the robust thermal tolerance and plasticity that adult green crabs maintain despite a substantial reduction in genetic diversity, and underscore the importance of probing population-level genotype-phenotype associations at the individual level. 

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