Warming up the underwater brood period

Octopuses may be congregating near warm-water vents to improve their reproductive success.

Enormous numbers of deep-sea octopus are congregating around the base of certain seamounts, scientists say.

There are so many, in fact, that a team led by James Barry of the Monterey Bay Aquarium Research Institute, US, counted 7,242 nesting females in a single 2.5 hectare “Octopus Garden,” about 120 kilometres offshore from central California.

The octopuses – all of the species Muusoctopus robustus

– appear to be drawn to warmwater springs at the base of the seamount, which Ann Hartwell, a PHD candidate at the University of New Hampshire, US, says were only discovered in the last 10 years and appear to be very different from the geothermal vents that have long fascinated ocean scientists.

Those vents are super-hot, while the newly discovered ones are merely warm, raising the water temperature by at most 10°C, according to Hartwell.

Why octopuses are drawn to these warm springs was initially a mystery. But Barry thinks it’s because the warmth helps them reproduce more effectively.

At the depths of the Octopus Garden, 3200m below sea level, the normal temperature is

1.6°C, he says. That’s an issue for octopus reproduction, because studies have shown that the time needed for octopus eggs to develop and hatch is extremely long. It is also dramatically affected by water temperature. At 5°C their brood period is around 600 days. At 1.6°C it is likely be pushing close to 14 years.

Barry’s team studied 26 nesting females. The water temperature averaged 5.1°C, and brood periods averaged 576 days; no wonder they were drawn to the warmer waters.

A massive colony of octopuses (Muusoctopus robustus) observed near Davidson Seamount in the Monterey Bay National Marine Sanctuary. These octopuses are likely brooding their eggs: protecting them by inverting their arms and covering them with their body.