OCTOPUS REPRODUCTION

Octopus reproduction is fairly similar from species to species. This description will focus mainly on the Giant Pacific Octopus (Enteroctopus dofleini) because it has one of the longest life spans. Most octopuses live shorter lives with shorter egg development, etc.

Biologists believe that when a female octopus is ready to mate, she releases a chemical attractant which is distributed by ocean currents. Males are drawn to the female by following the scent along the current. The female may attract more than one male, who sometimes fight for the opportunity to mate. In some cases, the female will mate with more than one male. In the case of the Giant Pacific Octopus we don't how many males the female will accept, but current theory favours just one mate.

The chemical attractant also prevents the larger male from attacking and eating the sometimes-smaller female. Cannibalism is common in octopuses - a smaller octopus will not usually allow a bigger octopus to approach it.

Once the male has been accepted by the female, he will transfer packages of sperm (usually two) - these are called spermatophores. A male octopus has no suckers on the end of his third right arm. Instead it is modified into a structure called a hectocotylus that is used to pass the spermatophore to the female.

The female accepts the spermatophore and stores the sperm for later use. Once the male has left, the female spends some time (up to a month or so in the case of the Giant Pacific Octopus) looking for a den in which to lay her eggs. The den she selects is usually in water deeper than 15 metres and under a large rock. She gathers rocks from the surrounding area and seals off all but one entrance to the den. Then she crawls into the den, reaches out for the remaining rocks and pulls them in to seal off the entrance.

Now the female begins laying eggs. She crawls up to the roof of the den and lays them one at a time, fertilizing each as it is produced then passing it through her reproductive tract and out her siphon to the suckers near her mouth. Each egg looks like a raindrop with a long string coming off the narrow end. The eggs of the Giant Pacific Octopus are about 5 mm long with an 11-mm-long string attached. Using her saliva and some of the small suckers near her mouth, the female weaves about 200 eggs into a string and glues it to the roof of the den. In about three weeks she will lay about 57,000 eggs.

For approximately six and a half months, the female Giant Pacific Octopus will constantly groom the eggs to prevent bacteria, algae and colonial animals such as hydroids from growing on the eggs and killing them. The female also blows water across the eggs ensuring a constant oxygen supply. During this time, the foetal octopuses develop inside their eggs, using the yolk for food. As the yolk is used up and the baby octopus becomes larger, it moves from the small end of the egg to the large end. By now the baby octopuses have large dark eyes that can be seen through the egg.

Eventually the big night arrives. After the sun has gone down and many of the fish predators are asleep, the nest of eggs will hatch. The female blows strongly on the eggs and thrashes them around to help the babies break free of their eggs. When they hatch, the babies, now called paralarvae, begin swimming towards the surface of the ocean. This is a very long trip for the tiny paralarvae (only 6 mm long) because the surface may be 30 metres or more away. The babies will never see their mother again. Very shortly after the eggs hatch, the female will move some of the rocks away from the den's entrance, crawl out and die. Marine scavengers such as crabs and sea stars, will dispose of her remains quickly.

jellyfish

The paralarvae spend many weeks near the surface of the ocean. They cling to the underside of the water surface and drop off to feed on small planktonic animals, such as copepods, and the larvae of crabs and sea stars. Larger animals, such as jellyfish and the largest of the plankton feeders, the baleen whales, feed on the paralarvae.

When the paralarvae gets too large to stay in the plankton layer, it descends to the bottom of the ocean where it will spend the rest of its life. As the octopus grows, feeds on many different animals, progressing to large crabs and clams. At the same time may predators will try and eat the octopus. Eventually, only the largest fishes (such as halibut and lingcod) and marine mammals such as seals, sea lions and dolphins will be able to feed on adult octopuses.

An octopus becomes sexually mature in about three years. They will have grown from 0.028 grams as a paralarva to an adult weighing about 18 kilograms. Now the whole process starts over again.

PART 1: Introduction
PART 3: Jim Cosgrove's Octopus Adventures