MEPS 275:139-151 (2004)  -  doi:10.3354/meps275139

ABSTRACT: Natural abundances of ¹³C were measured in bulk biomass and in individual lipids isolated from 2 species of sea urchins, Heliocidaris erythrogramma and H. tuberculata, and from calcareous and green benthic algae on which they were feeding. Planktonic larvae of H. erythrogramma are lecithotrophic whereas those of H. tuberculata are planktotrophic. The organisms were collected from a subtidal environment in Botany Bay, Sydney, Australia. The biomass of both consumers was enriched in ¹³C relative to their diets by up to 1.8”. The carbon skeletons of sterols from the urchins derive at least in part from de novo biosynthesis by the urchins. Depending on chain length and degree of unsaturation, carboxylic acids from the urchins derive from de novo biosynthesis (14:0, unsaturated acids), from the diet (18:0), or from both these sources (16:0). H. tuberculata synthesizes a greater distribution and proportion of unsaturated carboxylic acids. Odd-C and branched-chain carboxylic acids derive in part from bacterial sources and are enriched in ¹³C relative to algal lipids and depleted relative to those in urchins. Only H. erythrogramma, which uses wax esters as storage lipids in its relatively large and buoyant eggs, produces significant quantities of n-alkanols; n-alkanols in H. tuberculata derive from the diet. In terms of molecular distributions and isotopic compositions, the lipids in fecal matter from both heterotrophs resemble those of the diet rather than those of the urchins.

KEY WORDS: ¹³C · Heterotrophy · Isotope effect · Biosynthesis · Urchin · Sterol · Alcohol · Fatty acid