Jellyfish

Areas which have been seriously affected by jellyfish blooms include the northern Gulf of Mexico, about which, Graham states, "Moon jellies have formed a kind of gelatinous net that stretches from end to end across the gulf."
Life cycle
Jellyfish are usually either male or female (occasionally hermaphroditic specimens are found). In most cases, both release sperm and eggs into the surrounding water, where the (unprotected) eggs are fertilized and mature into new organisms. In a few species, the sperm swim into the female's mouth fertilizing the eggs within the female's body where they remain for the early stages of development. In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber for the developing planula larvae.