Blue crabs are crucial to Delaware as they account for $15 million of the annual state’s economy. Evaluating the feeding habits of commercially important aquatic species such as blue crabs is necessary to manage and conserve them. C and N isotopes are used as tracers of nutrient flow in food webs. The carbon isotope δ13C is used primarily to trace the food source from primary producers, while the nitrogen isotope δ15N indicates the trophic level of species and dietary shifts. In this study, stable Carbon (C) and Nitrogen (N) isotope ratios were compared in blue crabs collected from various sites along Blackbird Creek, Delaware, to provide insight on their feeding habits.
Blue crab sampling was conducted in 2017, 2020 and 2021. Sampling sites were distinguished by the existent dominant vegetation along the creek: Sporobolus alterniflorus dominant, Phragmites australis dominant or mixed vegetation (Fig 1). Blue crab tissue samples were obtained from the walking legs and used in C and N isotope analysis. Based on our preliminary results from 2017, we found no significant difference for the δ13C among blue crabs collected from different sites with a reported average range of -19.47 ‰ to -21.28 ‰. In contrast, there was a significant difference in the δ15N values, which ranged from 9.32 ‰ to 13.44 ‰ (Fig 2). The preliminary results from δ15 N suggest a difference in feeding habits of blue crabs at different sites. Complementary gut analysis will be conducted to draw conclusive results on availability and type of prey.