The authors, Eliza Heery and colleagues at the Seattle Aquarium, NOAA, and the University of Washington, used REEF sightings data on Giant Pacific Octopus (Enteroctopus dofleini) in Washington State to evaluate patterns of occurrence with urbanization. The species is the largest known octopus in the world, and they can reach over 20 feet in length from one tentacle tip to the other. The study objectives were to determine whether the distribution and habitat-use patterns of Giant Pacific Octopus were correlated with urbanization intensity on nearby shorelines in Puget Sound. REEF was instrumental in the study, providing data for a much larger spatial area and longer time period than would otherwise have been available. Heery et al. used REEF data in a series of statistical models and found that urban effects varied with depth. On deeper dives (> 24 m), REEF divers had a higher probability of encountering octopus in more urban locations.
Why might this be? The study's authors conducted additional field surveys to explore two potential explanations. To determine whether food resources played a role, Heery et al. collected middens – piles of shells leftover from past meals of octopus – from octopus dens throughout Puget Sound. Midden piles indicated there were no differences in the diets of urban octopus and rural octopus, suggesting that food resources were not the driver of urban-related distribution patterns. Secondly, they conducted a series of video surveys in sets of adjacent sites where there was a lot versus very little anthropogenic debris (junk). As many recreational divers might have predicted, they found more octopus in locations where there was a lot of junk.
How is this important for science? Past studies in urban ecology have suggested that mesopredators (mid-sized consumers) benefit from urbanization because of the food and shelter resources city environments provide, but those studies have focused exclusively on terrestrial mesopredators (like racoons and coyotes). This is the first study to examine whether marine mesopredators exhibit comparable patterns. It concludes that within certain habitats (deeper zones), octopus are indeed positively correlated with urbanization. Yet it is likely that shelter resources (from junk) rather than food are the driver.