Ontogenetic changes in the feeding habits of the abalone Haliotis discus hannai: field verification by stable isotope analyses

The ontogenetic changes in the feeding habits of the abalone Haliotis discus hannai were elucidated for the first time in natural habitats using stable isotope analyses. Abalone individuals were grouped into three developmental stages: small juveniles (<10 mm shell length (SL)), large juveniles (10–50 mm SL), and adults (>50 mm SL). The inferences of natural diets indicated that benthic diatoms, small red macroalgae and (or) juvenile brown macroalgae, and adult brown macroalgae were the primary food sources for small juveniles (6.5 ± 1.0 mm SL), large juveniles (23.7 ± 6.1 mm SL), and adults (81.8 ± 14.3 mm SL), respectively. The changes of δ13C in abalone were similar among three sampling stations and were explained by ontogenetic changes in feeding habits. The decrease of δ13C in abalone (≤20 mm SL) indicated a transition from diatom feeding to juvenile brown macroalgae and (or) small red macroalgae feeding, whereas the subsequent increase of δ13C (>20 mm SL) represented a feeding transition to adult brown macroalgae. These results prove the hypothesis of the ontogenetic changes in the feeding habits of the abalone H. discus hannai.