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

Seagrass delta(13)C values reported in the Literature show variation over a range of approximately 20 parts per thousand. A frequency histogram constructed on the basis of the collected data set shows a unimodal distribution, with values between -10 and -11 parts per thousand (relative to the PDB standard) found with the highest frequency. Seagrasses thus have stable carbon isotope signatures which are typically less depleted in C-13 than those of other groups of aquatic primary producers. This points to a characteristic set of physiological, anatomical and perhaps environmental features shared by all seagrasses. A significant negative correlation exists between seagrass delta(13)C values and geographical latitude of the sampling location, indicating that from tropical to temperate regions seagrasses tend to become more C-13 depleted. The physiological and environmental causes of variability are discussed. The most relevant environmental factors inducing variation in seagrass delta(13)C values appear to be, in order of decreasing importance, source carbon, irradiance and temperature. The integrated information reflected in the natural delta(13)C values of seagrasses can be used in support of the reconstruction of environmentally related growth dynamics on the scale of individual shoots and that of entire populations. In addition, C-13 may be used experimentally as a tracer of carbon flow in short term carbon allocation and production studies.