Fractionation of the stable isotopes of carbon and oxygen in marine calcareous organisms - the Echinoidea. Part II. Environmental and genetic factors
The carbon and oxygen isotopic composition of the calcite skeletons of recent sea urchins and sand dollars has been determined for representatives of all major taxonomic groups. The specimens comprise a world-wide sampling of the class Echinoidea in which polar to tropical and littoral to abyssal dwellers are included. Although the spines differ relatively little in isotopic composition, large variations in δC13 (up to 13 per mil) and δO18 for the tests and parts of the echinoid lantern are apparent. C 13/C 12 and O 18/O 16 for individuals of a single species from a given locality, for different species from the same locality, and for the same species from different localities, in conjunction with depth and temperature data, show that the degree of isotope fractionation is largely genetically controlled, although the effect of temperature is detectable, especially in the case of O 18/O 16. Carbon and oxygen isotope ratios are correlated with crystallographic data and the application of this information to phylogenetic problems is discussed with two examples: the question of a polyphyletic ancestry of the order Echinoida, and inhomogeneity in the order Cidaroida.