Giant Pacific octopus
The giant Pacific octopus, also known as the North Pacific giant octopus, is a large marine cephalopod belonging to the genus Enteroctopus and Enteroctopodidae family. Its spatial distribution encompasses much of the coastal North Pacific, from the Mexican state of Baja California, north along the United States' West Coast, and British Columbia, Canada; across the northern Pacific to the Russian Far East, south to the East China Sea, the Yellow Sea, the Sea of Japan, Japan's Pacific east coast, and around the Korean Peninsula. It can be found from the intertidal zone down to, and is best-adapted to colder, oxygen- and nutrient-rich waters. It is the largest octopus species on earth and can often be found in aquariums and research facilities in addition to the ocean. E. dofleini play an important role in maintaining the health and biodiversity of deep sea ecosystems, cognitive research, and the fishing industry.
Etymology
The giant Pacific octopus was first described in 1910 by Gerhard Wülker of Leipzig University in Über Japanische ''Cephalopoden. He describes the species' morphology in detail, and mentions that there seems to be much variation within the species. The specific name dofleini was chosen by Gerhard Wülker in honor of German scientist Franz Theodor Doflein. It was moved to genus Enteroctopus'' by Eric Hochberg in 1998.Description
Size
E. dofleini is distinguished from other species by its large size. It is the largest octopus species. Adults usually weigh around, with an arm span up to. The largest individual weighed in at, with a radial span of. American zoologist G. H. Parker found that the largest suckers on a giant Pacific octopus are about and can support each.Ecology
Diet
E. dofleini preys on shrimp, crabs, scallops, abalones, cockles, snails, clams, lobsters, fish, squid, and other octopuses. Food is procured with its suckers and then bitten using its tough beak of chitin. It has also been observed to catch spiny dogfish up to in length while in captivity. Additionally, consumed carcasses of this same shark species have been found in giant Pacific octopus middens in the wild, providing strong evidence of these octopuses preying on small sharks in their natural habitat. In May 2012, amateur photographer Ginger Morneau was widely reported to have photographed a wild giant Pacific octopus attacking and drowning a seagull, demonstrating that this species is not above eating any available source of food within its size range, even birds.Predators
Scavengers and other organisms often attempt to eat octopus eggs, even when the female is present to protect them. Giant Pacific octopus paralarvae are preyed upon by many other zooplankton and filter feeders. Marine mammals, such as harbor seals, sea otters, and sperm whales depend upon the giant Pacific octopus as a source of food. Pacific sleeper sharks are also confirmed predators of this species. In addition, the octopus is a significant source of protein for human consumption. About are commercially fished, worth $6 billion annually. Over thousands of years, humans have caught them using lures, spears, pot traps, nets, and bare hands. The octopus is parasitized by the mesozoan, which lives in its renal appendages.Movement patterns
E. dofleini move through the open water using jet propulsion, which is achieved by drawing water into its body cavity and then forcefully expelling it through a siphon, creating a powerful thrust and propelling the octopus through the water at a high speed. When moving on the seafloor, however, the octopus crawls using its arms.E. dofleini remain stationary or in hiding 94% of the time, usually concealed within dens, kelp, or camouflaged in their environment. Otherwise, they exhibit activity throughout the day, increasingly so from midnight to the early morning. While stationary, E. dofleini hide, groom, eat, sleep, and maintain dens. E. dofleini are capable of moving vast distances to occupy new areas or habitats, with large octopuses moving further than smaller ones. Their movements are not random; they demonstrate a preference for habitats with dense kelp cover and rocky terrain suggesting a sophisticated level of habitat selection, likely optimizing foraging efficiency and minimizing exposure to predators. Furthermore, their movement patterns include direct relocations to new areas and central-tendency movements to return to familiar habitats. This navigation behavior is influenced by the use of familiar cliff edges, substrates, and topography as well as visual navigation.
E. dofleini migration patterns vary depending on the population. In the eastern Pacific waters off the coast of Japan, migration coincides with seasonal temperature changes in the winter and summer. Here, E. dofleini migrate to shallower waters in the early summer and winter and offshore in the late summer and winter. There is no evidence of these migration patterns in the Alaskan and northeast Pacific populations of ''E. dofleini.''
Shelter
E. dofleini are den dwellers, which serve as a central point from which they forage while also providing protection, shelter, and privacy. After hunting, they bring food back to the den to feed in a safer environment and avoid predators. Shells, bones, and other feeding debris pile up outside of the den, creating "den litter" that is commonly used by scientists and divers to find E. dofleini.Dens range across depth and substratum type including caves, holes dug beneath rock, and even trash on the ocean floor such as bottles, tires, pipes, and barrels. Den selection is greatly influenced by foraging behavior and preferred prey. Dens made of soft substrata may be preferred in areas where bivalves are abundant while dens near rocky areas might be chosen in areas with higher crab populations. The size of the den is small, usually being just large enough for the octopus to fit inside and turn around. E. dofleini beak size determines the size of the space it can fit inside, with its body being able to compress through tiny spaces as small as. E. dofleini prefer to occupy same shelter for at least one month, often longer if possible. It is common for these octopus to leave their den for short periods of time and eventually return to re-use the same den. However, over longer periods of time, E. dofleini relocate to new dens situated relatively nearby, within an average distance of 13.2 meters.
Lifespan and reproduction
Unlike most other octopus species, whose lifespans normally span only one year, the giant Pacific octopus has a lifespan of three to five years. They reach sexual maturity at one to two years of age. Gonadal maturation has been linked to the optic gland of octopuses which has been compared functionally to the vertebrate pituitary gland. These optic glands are the only endocrine glands identified in octopuses, and their secretions have been found to contribute to behaviors linked with reproduction and senescence. When removed, females no longer brood their eggs, resume feeding, increase in weight, and experience longer lifespans compared to sexually mature, brooding females who still retain their optic glands.To help compensate for its relatively short lifespan, the octopus is extremely prolific. It can lay between 120,000 and 400,000 eggs which are coated in chorion, and attached to a hard surface by the female. The spawn is intensively cared for exclusively by the female, who continuously blows water over it and grooms it to remove algae and other growths. While she fulfills her duty of parental care the female stays close to her spawn, never leaving to feed, leading to her death soon after the young have hatched. The female's death is the result of starvation, as she subsists on her own body fats during this period of approximately 6 months. Hatchlings are about the size of a grain of rice, and very few survive to adulthood. Their growth rate is quite rapid: starting from and growing to at adulthood, which is an increase of around 0.9% per day. The giant Pacific octopus' growth over the course of a year has two sections: a faster section, from July to December, and a slower section, from January to June. Because they are cool-blooded, they are able to use most of their consumed energy for body mass, respiration, physical activity, and reproduction. During reproduction, the male octopus deposits a spermatophore more than long using his hectocotylus in the female's mantle. The hectocotylus is found on the third arm of male octopuses and occupies the last four inches of the arm. This part of the male arm anatomy contains no suckers. Large spermatophores are characteristic of octopuses in this genus. The female stores the spermatophore in her spermatheca until she is ready to fertilize her eggs. One female at the Seattle Aquarium was observed to retain a spermatophore for seven months before laying fertilized eggs.
Both male and female giant Pacific octopuses are semelparous, meaning they only go through one breeding cycle in their life. Analysis of egg clutches has shown evidence of polygyny and polyandry in giant Pacific octopuses, where males and females mate with multiple partners. This multiple paternity potentially allows females to increase the odds of at least one of the males she mates with producing fit offspring. After mating, both the males and females stop eating and ultimately die. After reproduction, they enter senescence, which involves obvious changes in behavior and appearance, including a reduced appetite, retraction of skin around the eyes giving them a more pronounced appearance, increased activity in uncoordinated patterns, and white lesions all over the body. While the duration of this stage is variable, it typically lasts about one to two months. Despite active senescence primarily occurring over this period immediately following reproduction, research has shown that changes related to senescence may begin as early as the onset of reproductive behavior. In early stages of senescence, which begins as the octopus enters the stage of reproduction, hyper-sensitivity is noted where individuals overreact to both noxious and non-noxious touch. As they enter late senescence, insensitivity is observed along with the dramatic physical changes described above. Changes in sensitivity to touch are attributed to decreasing cellular density in nerve and epithelial cells as the nervous system degrades. Death is typically attributed to starvation, as the females have stopped hunting in order to protect their eggs; males often spend more time in the open, making them more likely to be preyed upon.