Sperm swarm around the egg, jostling it and each other in the race to be the first to fertilise it.
Interference microscopy gives good contrast between the egg and sperm.
Such is the power of the scent that within seconds of the first sniff, thousands of sperm can descend on an egg, swarming in a seething mass and causing the egg to spin and bump around. The scent, however, is not a 'specific' attractant. Eggs of the serrated wrack attract sperm not just of the serrated wrack but also of related seaweeds, like the bladder wrack and egg wrack.