Thousands of octopus mothers lay and tend their eggs at a deep-sea site with warm hydrothermal vents because it dramatically reduces hatching times, from more than 14 years to under two years.
鈥淭hey have about a 90 per cent reduction in brood period because, I think, they are brooding in warm water,鈥� said at the Monterey Bay Aquarium Research Institute in California, during a virtual talk at .
In 2018, other researchers found thousands of abyssal octopuses (Muusoctopus robustus) clustered together at a site 3200 metres deep near the base of the Davidson Seamount off California. The site was dubbed the octopus garden after the 1969 Beatles song.
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The water temperature in this part of the ocean is usually around 1.6掳C, but at this particular site, hydrothermal vents raise it to around 5掳C. As the octopuses are all females caring for eggs, the leading suggestion for why they gather here has been to speed the development of their eggs. Barry鈥檚 team has now directly measured egg development times.
Female octopuses stay with their eggs to protect and tend them. They stop feeding during brooding and die around the time the eggs hatch. In warm tropical waters, this process lasts only a few weeks. But in cold waters the egg development time increases dramatically.
One brooding octopus found 1300 metres down in the Monterey Canyon, also off the California coast and with a water temperature around 3掳C, by a remotely operated vehicle. It took more than four years for her eggs to hatch, by far the longest egg-brooding period known for any animal. The condition of the 鈥渙ctomom鈥�, as the animal was dubbed, steadily deteriorated over this time.
Based on the strong link between temperature and octopus brood time, Barry and his team predicted the brood period at 1.6掳C would be an astonishing 5188 days 鈥� over 14 years. But the 5掳C waters at the octopus garden should reduce this to around 620 days, they predicted.
The researchers then monitored 26 brooding females at the site over several years, gently moving them aside so they could see how developed their eggs were. They found the actual brood period was around 590 days, very close to that predicted.
Barry thinks many other deep-sea animals might take advantage of hydrothermal vents for similar reasons. In fact, it is already known that some skates deposit eggs in hydrothermal vent areas. As well as being warmer, some of these places may be rich in minerals that could be extracted.
鈥淭here are probably many such aggregations of animals breeding in odd areas that we need to start thinking about before we go out and starting mining,鈥� Barry said.
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