Stable carbon isotopes in seagrasses:variability in ratios and use in ecological studies

Abstract

Seagrass 611C values reported in the literature show variation over a range of approximately 20XtJ. A frequency histogram constructed on the basis of the collected data set shows a unimodal distribution, with values between -10 and -11'::., (relative to the PDB standard) found with the highest frequency. Seagrasses thus have stable carbon ~sotope signatures which are typically lcis depleted In '.'C than those of other groups of aquatic prlnlary producers. Thls points to a characteristic set of phvsiological, anatoniical and perhaps environmental features shared by all seagrasses. A significant negdtive correlation exists between seagrass 6I3C values and geographical latitude of the sampling location, indicating that from tropical to temperate regions seagrasses tend to become more ''C depleted. The physiological and environmental causes of variability are discussed. The most relevant environmental factors inducing vanation in seagrass &'"C values appear to be, in order of decreasing importance, source carbon, irradiance and temperature. The integrated ~nformation reflected in the natural 6C values of seagrasses can be used in support of the reconstrucl~on of environmentally related growth dynamics on the scale of individual shoots and that of entire populations. In addition, '% may be used experimentally as a tracer of carbon flow in short term, carbon allocation and production studies.