Octopus reproduction is a one-shot affair. After mating, a female giant Pacific octopus finds a den, attaches strings of eggs to its ceiling, and remains with them. Recorded clutches run into the tens of thousands of eggs, and brooding periods of five to seven months are typical in the wild, longer in colder water.
Through that period she jets water over the eggs to oxygenate them and grooms them to keep fouling organisms off. She feeds little or not at all. By the time the paralarvae hatch and drift away as plankton, she is emaciated, and she dies soon after. Males also die within months of mating.
The mechanism behind this decline is partly hormonal rather than simple starvation: the optic glands, a pair of structures behind the eyes, drive the post-reproductive changes. Removing them in a related octopus extended life and restored feeding, in classic work by Jerome Wodinsky. What remains debated is how far that single laboratory result generalises across octopus species.