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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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Testing the Ontogenetic Migration Hypothesis in the emerging Rhode Island Jonah crab (Cancer borealis) fishery using stable isotope analysis
In southern New England, rapid ocean warming over the past two decades has caused substantial redistributions of fishes, invertebrates, and the fisheries they support. The rapid emergence of the warm water-tolerant Jonah crab (Cancer borealis) fishery, once discarded as bycatch from the now declining lobster fishery, illustrates a prime example of climate-adaptive shifts in southern New England fisheries. However, limited data exist on the basic life history of Jonah crabs, despite their growing economic and societal value. This hinders ocean management capacity to meet multiple ecological, economic, and socio-cultural goals of sustainable harvest. Off the southern coast of Rhode Island, Jonah crabs are currently harvested in two fishery zones (inshore and offshore) delineated as holdovers from the lobster management zones. Jonah crabs landed in the offshore fishing zone are significantly larger, on average, than those landed in the inshore fishing zone. This presentation gives an overview of a study developed to test the hypothesis that these size differences reflect ontogenetic migration of Jonah crabs from the inshore to offshore fishing zones. To do this, we developed seasonally resolved isoscapes (isotope maps) of the region, which revealed distinct geospatial gradients in environmental stable isotope values between inshore and offshore necessary to track potential movement of Jonah crabs between fishing zones. We then used stable isotope analysis of three Jonah crab tissues with differential metabolic turnover times: the carapace (reflecting residence one year ago), muscle (reflecting residence averaged over the last ~4 months), and hepatopancreas (reflecting residence averaged over the last ~4 weeks) to construct an “isotopic clock” of residence throughout the regional isoscapes. This work provides key data on critical life history characteristics of the Jonah crab through a collaborative effort by scientists at the University of Rhode Island and the Rhode Island Department of Environmental Management to inform management decisions on this emerging climate-adaptive fishery.
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- Award ID(s):
- 2049307
- PAR ID:
- 10501402
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Ocean Sciences Meeting
- Format(s):
- Medium: X
- Location:
- New Orleans, LA
- Sponsoring Org:
- National Science Foundation
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