Carbon and nitrogen isotopes of lizardfish provide insight into regional patterns of ocean biogeochemistry across the eastern continental United States

Abstract

Mapping spatial variation in stable isotope values (isoscapes) of primary producers and consumers can provide insight into regional patterns of biogeochemistry and be used to trace the movements of mobile animals. Here we present carbon (δ¹³C) and nitrogen (δ¹⁵N) isoscapes for an expansive region of the continental United States (Mid Atlantic Bight to the NW Gulf of Mexico) derived from inshore lizardfish (Synodus foetens) and explore temporal stability and environmental drivers of observed isotopic variation. We observed significant spatial variation in lizardfish δ¹³C and δ¹⁵N values throughout much of the Atlantic and Gulf coasts, reflecting local biogeochemistry regimes. Extensive sampling throughout the northern Gulf of Mexico (NGOM) revealed positive relationships between lizardfish δ¹³C values and bottom temperature, likely reflecting lower carbon isotope discrimination between CO₂ and phytoplankton in highly productive, warm, inshore environments. Conversely, δ¹⁵N values were not well explained by environmental parameters, but appeared higher in nearshore environments of the NGOM, which are heavily influenced by nitrogenous run-off from land. An isotopically unique region of high δ¹³C values and low δ¹⁵N values were observed for lizardfish sampled in the Eastern NGOM off the southwest coast of Florida, reflecting a potential influence of seagrass and/or macroalgal productivity supporting the base of the food web. Overall, these findings underscore the utility of benthic lizardfish stable isotopes for inferring local patterns of ocean biogeochemistry throughout expansive ocean environments. In application, these data can be used to define migratory histories of mobile taxa and support contemporary critical habitat assessments.