Energetic changes throughout early ontogeny of the brooding Antarctic sea star Rhopiella hirsuta (Koehler, 1920)

Abstract

An unusually high proportion of Antarctic echinoderms brood their young. Protection, reproductive constraints, low temperatures and limited food supply are all suggested motives for this reproductive pattern. This study looks at the reproductive energetics of the Antarctic asteroid Rhopiella hirsuta, and to establish the dynamics of feeding and elemental composition throughout its early juvenile development. Brooding females were analysed in terms of adult size, brood size and juvenile size with non-significant trends occurring with depth. Four brooding females were frozen straight after sampling and enabled the study of changes in elemental composition throughout embryo and early juvenile development with regard to their feeding mode. Morphological and elemental analyses indicate aseasonality of reproduction and lecithotrophic early ontogeny in this species. The most advanced juveniles found were significantly different from all earlier stages, with an increase in dry weight (DW) to 5.87 (± 1.08) mg suggesting growth, but a high C:N ratio of 8.60 (± 0.59) that would indicate lecithotrophy. However, as the increase in DW was attributed to an increase in carbon, but not to an increase in nitrogen, it was not possible for the food source to be of organic origin.