Spatial variation in the delta C-13 signature of Ruppia megacarpa (Mason) in coastal lagoons of southwestern Australia and its implication for isotopic studies

Ruppia megacarpa was collected from three coastal lagoons in southwestern A ustralia: Nornalup Inlet, Peel Inlet and Oyster Harbour. In each case, plan ts were sampled from four sites and delta C-13 values were determined for l eaves, rhizomes and roots of replicate plants to assess the variability bet ween lagoons, between sites in lagoons and between plant parts at sites. Th e delta C-13 values of tissue ranged from -6.6 to - 17.8 parts per thousand with a mean of - 11.15 parts per thousand. In Nornalup Inlet, there were s ignificant differences in the delta C-13 values of different plant parts, b ut there was also a significant interaction between plant part and site. In Peel Inlet significant differences were found between plant parts and betw een sites. Oyster Harbour displayed no significant differences in delta C-1 3 values between any of these factors. The delta C-13 values of R. megacarp a were highly variable, with only one other marine angiosperm having a high er recorded range in values. Significant differences in delta C-13 values o ccurred between sites within lagoons and between plant parts, and the patte rn of spatial variability was different in each lagoon. The spatial differe nces within lagoons appear to relate to differences in water quality result ing from proximity to river and ocean inputs. Differences between plant par ts may be related to the storage of biochemical products with distinct isot ope ratios. Trophic studies, therefore, need to be conducted in a way that explicitly identifies the spatial scales that capture the variability in de lta C-13 values relevant to the aims of the study. (C) 2001 Elsevier Scienc e B.V. All rights reserved.