Fertilization efficiency and gamete viability of a sessile, free-spawning bivalve, Cerastoderma edule

The fertilization biology of the free-spawning bivalve Cerastoderma edule was studied in the laboratory. Fertilization success declined drastically with decreasing sperm concentration. Viability of both eggs and 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 time 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 populations of bivalves.