MEPS 215:191-200 (2001)  -  doi:10.3354/meps215191

ABSTRACT: Sperm concentration and sperm ageing effects on fertilisation success were evaluated in the laboratory in the free-spawning Antarctic soft-shelled clam Laternula elliptica and Antarctic limpet Nacella concinna. Fertilisation success was highly dependent on sperm concentration. Highest levels of fertilisation success were consistently replicated at ~10⁷ sperm ml^-1 for L. elliptica, and ~10⁶ to 10⁸ sperm ml^-1 for N. concinna. However, both species exhibited extremely low fertilisation rates at concentrations <10⁶ sperm ml^-1. At sperm concentrations >10⁶ sperm ml^-1 N. concinna displayed a rapid increase in abnormally developing larvae which, along with only a small decline in total fertilisation success above 10⁸ sperm ml^-1, was taken to indicate polyspermy. A small increase in abnormal development followed by a rapid decline in fertilisation success at high sperm concentrations (>10⁷ sperm ml^-1) for L. elliptica was attributed to oxygen depletion. Using the optimum sperm concentration found for fertilisation success, spermatozoa were capable of fertilising fresh ova for >90 h in L. elliptica, and ~65 h in N. concinna. The sperm concentrations required for fertilisation success and sperm longevities reported here are at least an order of magnitude greater than those reported for nearshore temperate molluscs. Our data strongly suggest that the specific reproductive behaviour and timing of spawning activities displayed by these Antarctic molluscs is vital to enhance fertilisation success in the polar marine environment.

KEY WORDS: Fertilisation success · Antarctica · Reproduction · Free-spawning · Sperm concentration · Sperm age · Laternula elliptica · Nacella concinna