- Giant Pacific octopus the largest known octopus species in the world.
- A recent study suggests that deep-dwelling giant Pacific octopus are positively correlated with urbanization intensity.
- This may be due to the large amount of junk that ends up on the seafloor in urban areas.
In 1955, Columbia Pictures released the thriller It Came From Beneath The Sea, in which an enormous octopus begins terrorizing the good citizens of San Francisco. Though lacking in certain factual details (for instance, the octopus possesses only six legs in some shots) and decidedly biased against the octopus, the film alludes to one phenomenon that is not entirely fictitious.
It turns out there are giant octopodes lurking in the depths of urban waterfronts in coastal cities on the West Coast of North America. They are giant Pacific octopus (Enteroctopus dofleini), the largest known octopus species in the world. Reaching over 20 feet in length from one tentacle tip to the other, they are veracious predators of crabs, clams, and other invertebrate prey.
In a 2018 study in Urban Ecosystems, Eliza Heery and colleagues at the University of Washington, Seattle Aquarium, and NOAA set out to determine whether giant Pacific octopus distribution and habitat-use patterns were related to urbanization intensity, and if so how and why.
Because of the large size and expansive home range of giant Pacific octopus, characterizing their distribution patterns using traditional ecological survey techniques is not an easy feat. Instead, Heery et al. relied upon citizen-contributed data from the REEF program (www.reef.org). These data provided information about octopus presence/absence over a much larger spatial scale and a much longer time period than would otherwise have been available. Heery et al. used the REEF data in a series of statistical models, which you can read more about here, to ultimately conclude that urban effects varied with depth. In deep habitats (> 24 m), the probability of encountering octopus increased with adjacent land-based urbanization intensity.
Why might this be? They conducted additional field surveys to explore two potential explanations – giant Pacific octopus are considered to be a mesopredator, meaning they are medium sized predators that are at a middle point in the food chain, with some prey and some predators of their own. Past studies in terrestrial urban ecology have demonstrated that urbanization facilitates mesopredators such as raccoons, in part by providing food and shelter resources. To determine whether the increased occurrence of octopus at depth in urban areas was associated with food resources, Heery et al. collected middens – piles of shells leftover from past meals of octopus – from octopus dens throughout Puget Sound. These data indicated there were no differences in the diets of urban octopus and more rural octopus, suggesting that food resources are not the driver of urban-related distribution patterns. Secondly, Heery et al. conducted a series of video surveys in adjacent areas where there was a lot of versus very little anthropogenic debris (junk). Results from these surveys indicated that octopus are far more common where there is a lot of junk on the seafloor, suggesting that this may be one of the mechanisms driving urban-related distribution patterns in giant Pacific octopus.