STABLE CARBON ISOTOPES IN SEAGRASSES - VARIABILITY IN RATIOS AND USE IN ECOLOGICAL-STUDIES

Seagrass delta(13)C values reported in the Literature show variation o ver a range of approximately 20 parts per thousand. A frequency histog ram constructed on the basis of the collected data set shows a unimoda l distribution, with values between -10 and -11 parts per thousand (re lative to the PDB standard) found with the highest frequency. Seagrass es thus have stable carbon isotope signatures which are typically less depleted in C-13 than those of other groups of aquatic primary produc ers. This points to a characteristic set of physiological, anatomical and perhaps environmental features shared by all seagrasses. A signifi cant negative correlation exists between seagrass delta(13)C values an d geographical latitude of the sampling location, indicating that from tropical to temperate regions seagrasses tend to become more C-13 dep leted. The physiological and environmental causes of variability are d iscussed. The most relevant environmental factors inducing variation i n seagrass delta(13)C values appear to be, in order of decreasing impo rtance, source carbon, irradiance and temperature. The integrated info rmation reflected in the natural delta(13)C values of seagrasses can b e used in support of the reconstruction of environmentally related gro wth dynamics on the scale of individual shoots and that of entire popu lations. In addition, C-13 may be used experimentally as a tracer of c arbon flow in short term carbon allocation and production studies.