Novel interaction between an octopus and an introduced macroalgae

Abstract

Numerous macroalgae facilitate other species, modifying the diversity patterns, reducing the environmental stress, or providing non-trophic resources. In the sandy–pebbly bottoms of San Antonio Bay (north Patagonia, Argentina), where shelters are an important but limiting resource for the small Patagonian octopus (Octopus tehuelchus), the recently introduced macroalgae Undaria pinnatifida has shown a rapid increase in abundance. Herein, we documented the use of U. pinnatifida as shelter for octopuses and describe the size and maturity condition of individuals using the macroalgae. Our results suggest that U. pinnatifida facilitates octopuses by providing shelter in an environment where these are scarce and there is competition for high-quality shelters. The presence of small octopuses and brooding females under U. pinnatifida suggest that the structure of the macroalgae constitute an adequate shelter for brooding and may facilitate a portion of the population that usually lose the competition for traditional shelters. Indeed, the holdfast of U. pinnatifida, full of potential food sources, may provide a larger positive effect on octopuses. The effects of U. pinnatifida in north Patagonia should be tested on the different components of the community since there seem to be no similar native macroalgae providing structural complexity in these sandy–pebbly bottom ecosystems.