A comparison of blue crab and bivalve delta15N tissue enrichment in two North Carolina estuaries

Stable isotope analyses (delta(15)N) were used to examine invertebrate tissue enrichment in two North Carolina estuaries with differing amounts of nutrient loading. Bivalves collected from a nutrient sensitive estuary yielded a significant difference in mean nitrogen isotopic composition of tissue (10.4 per thousand+/-0.82; N=66) compared to bivalves collected from a less nutrient sensitive estuary (6.4 per thousand+/-0.63; N=45). Similarly, blue crabs from nutrient sensitive sites had a nitrogen isotopic composition of 11.4 per thousand (+/-1.3, N=77), which was significantly different (P<0.001) than the tissue of less nutrient sensitive blue crabs (9.6 per thousand+/-0.6; N=77). The results showed that an inverse relationship exists between invertebrate tissue enrichment and indicators of water quality across estuarine sites. This study suggests that a relationship may exist between nutrient sources and subsequent energy transfer to estuarine consumers in two North Carolina estuaries.