Metabolism and development in pelagic larvae of Antarctic gastropods with mixed reproductive strategies

The Antarctic gastropods Marseniopsis mollis (Smith, 1902) and Torellia mirabilis (Smith, 1907) lay eggs in the late austral summer and autumn; these hatch the following late winter and early summer. Field observations indicate that M. mollis lays eggs in the tests of ascidians in January to March. Ascidians with M. mollis broods were collected in April and held in culture. Larvae hatched between mid-October and mid-December, a brooding period of 8 to 11 mo. T. mirabilis egg masses laid in aquaria in April took 6 to 7 mo to hatch. Both species released large veliger larvae (presumably planktotrophic). Natural phytoplankton were provided, but feeding was not confirmed. These larvae were maintained in culture for 25 to 50 d, during which period they were regularly offered a range of substrata, but no settlement behaviour was observed. Metabolism was estimated in individual larvae using microrespirometers of 30 to 45 μl volume, and a couloximeter system to measure water oxygen-content. Average M. mollis veligers contained 14.1 μg ash-free dry mass (AFDM) and consumed 310 pmol O2 h–1. Corresponding values for T. mirabilis veligers were 17.6 μg AFDM and 221 pmol O2 h–1. The periods of protected development here were shorter than those previously reported for Antarctic gastropods, including T. mirabilis, by a factor of ×4, although previous reports were for species hatching as juveniles. The protected periods here were, however, around 5 time longer than for temperate gastropods. The oxygen-consumption rates for M. mollis and T. mirabilis veligers were around ×10 less than those for comparable temperate gastropod and bivalve veligers.