FERTILIZATION EFFICIENCY AND GAMETE VIABILITY OF A SESSILE, FREE-SPAWNING BIVALVE, CERASTODERMA-EDULE

The fertilization biology of the free-spawning bivalve Cerastoderma ed ule was studied in the laboratory. Fertilization success declined dras tically with decreasing sperm concentration. Viability of both eggs an d sperm decreased with age so that no fertilization took place after 4 -8 hours. A dilution model suggests that in the field sperm is rapidly diluted to concentrations that would result in very low fertilization efficiencies. The dilution process thus operates on a much smaller ti me scale than gamete ageing, indicating that most eggs are fertilized close to spawning males. However, it is also shown that under certain circumstances high concentrations of sperm may accumulate over dense p opulations of bivalves.