SKELETAL GROWTH IN THE ECHINODERM ASTERIAS-RUBENS L (ASTEROIDEA, ECHINODERMATA) ESTIMATED BY CA-45-LABELLING

The skeletal dry weight of the 4.4 ± 0.2 cm size class of Asterias rubens L. from Kiel Bay in the western Baltic is 0.34 ± 0.08 g. The sum of calcium and magnesium carbonates in the skeleton amounts to 94.0 ± 1.3% while the individual concentrations are 86.9 ± 1.3% CaCO3 and 7.1 ± 0.7% MgCO3. The MgCO3 is 4% lower than expected for a magnesium calcite precipitated under Baltic temperature conditions (8°C). Strontium was not determined but strontium carbonate is known to be in the region of 0.4%. The remainder is organic matter and this gives rise to 2.9 ± 1.3% organic carbon. Animals studied were at the 'waiting stage' and their actual growth was minimal. Uptake of 45Ca in the skeleton consists of a fast step followed by a slow step. The fast step is attributed to saturation of exchangeable skeletal pools while the slow step is due to net deposition of CaCO3. Skeletal growth at the waiting stage calculated from the second rate constant was found to be 0.76 μg CaCO3j-mg skeleton-1 · day-1 or 0.09% · day-1 compared with 9.3 μg CaCO3 · mg skeletont1̄ · day-1 or 1.1% · day-1 at log phase. The isotope method is considered superior to size-frequency analysis in that it is capable of detecting differences in growth rate in individuals of the same size class and thus provides an insight into asteroid population structure. © 1979.