The majority of sessile marine invertebrates reproduce by releasing eggs and sperm (gametes) into the water column where they come into contact and fertilization occurs. This method is called free spawning. Each resulting embryo develops rapidly in the plankton, giving rise to a free-swimming larva. Depending on the species, this larva swims in the plankton for a few minutes up to several months before settling onto a substratum and metamorphosing into the adult form.