title: Stable isotopes in bivalves as indicators of nutrient source in coastal waters in the Bocas del Toro Archipelago, Panama.
abstract: To examine N-isotope ratios ((15)N/(14)N) in tissues and shell organic matrix of bivalves as a proxy for natural and anthropogenic nutrient fluxes in coastal environments, Pinctada imbricata, Isognomon alatus, and Brachidontes exustusbivalves were live-collected and analyzed from eight sites in Bocas del Toro, Panama. Sites represent a variety of coastal environments, including more urbanized, uninhabited, riverine, and oceanic sites. Growth under differing environmental conditions is confirmed by δ (18)O values, with open ocean Escudo de Veraguas shells yielding the highest average δ (18)O (-1.0‰) value and freshwater endmember Rio Guarumo the lowest (-1.7‰). At all sites there is no single dominant source of organic matter contributing to bivalve δ (15)N and δ (13)C values. Bivalve δ (15)N and δ (13)C values likely represent a mixture of mangrove and seagrass N and C, although terrestrial sources cannot be ruled out. Despite hydrographic differences between end-members, we see minimal δ (15)N and δ (13)C difference between bivalves from the river-influenced Rio Guarumo site and those from the oceanic Escudo de Veraguas site, with no evidence for N from open-ocean phytoplankton in the latter. Populated sites yield relative (15)N enrichments suggestive of anthropogenic nutrient input, but low δ (15)N values overall make this interpretation equivocal. Lastly, δ (15)N values of tissue and shell organic matrix correlate significantly for pterioideans P. imbricata and I. alatus. Thus for these species, N isotope studies of historical and fossil shells should provide records of ecology of past environments.
authors.affiliation: Department of Geology and Geophysics, Texas A&M University , College Station , TX , USA.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Graniero
authors.affiliation: Department of Geology and Geophysics, Texas A&M University , College Station , TX , USA.
authors.forename: Ethan L
authors.initials: EL
authors.lastname: Grossman
authors.affiliation: Smithsonian Tropical Research Institute , Balboa , Republic of Panama.
authors.forename: Aaron
authors.initials: A
authors.lastname: O'Dea
keywords: Anthropocene; Carbon isotopes; Caribbean; Eutrophication; Molluscs; Nitrogen isotopes