Thousands of octopus (Muusoctopus robustus) discovered recently at the base of Davidson Seamount migrate to deep-sea hydrothermal springs to breed. In what is the largest known aggregation of octopus on Earth, 6000 to as many as 25000 M. robustus gather at this “Octopus Garden” on a small hillock at a depth of 3200 m (2 miles) to mate, brood clutches of eggs, and die. What about these hydrothermal springs has led to these breeding aggregations? Is it easier to find a mate, or is the benefit from the warm (~5-10 ^oC; 40-50^oF)?

Deep-sea octopuses are ectotherms (cold-blooded) and the cold waters of the deep-sea slow their metabolism as well as the rate of embryonic development. Thus, most deep-sea octopuses have very slow incubation periods compared to their relatives inhabiting shallow warmer waters. At the near freezing temperatures of the abyss, warmth from hydrothermal springs will increase their metabolism and may shorten incubation times, to some advantage for the brooding octopus moms.

We’ve been studying the behavior of octopus at the Octopus Garden in relation to the conditions found in the nests. Over repeated visits, we’ve identified individual females sitting on nests for years at a time. Many questions remain, from what advantage individuals breeding in these hydrothermal springs have over those that breed elsewhere, to how common such hydrothermal springs are in deep waters. Many ectotherms could benefit from elevated metabolism near localized deep-sea heat sources like these hydrothermal springs.