The garden can hold 20,000 octopuses on the seabed

US Researchers have discovered a garden of tens of thousands of octopuses gathered around a hydrothermal vent off the coast of California.

The garden can hold 20,000 octopuses on the seabed — Octopus gardens cluster around hydrothermal vents. Video: *MBARI*

The discovery of thousands of octopuses about 2 miles below the ocean’s surface in 2018 left marine scientists equally excited and puzzled, according to IFL Science . The octopuses were clustered around hydrothermal vents, openings in the seafloor where warm, mineral-rich water erupts in the midnight darkness. The octopus garden, located on a small hill near the base of Mount Davidson, an extinct underwater volcano 80 miles southwest of Monterey, California, was filled with Muusoctopus robustus , or pearl octopuses, because they curl up upside down to protect their eggs.

This is the largest octopus colony on the planet. Researchers counted more than 6,000 octopuses in just one area. "We think there could be as many as 20,000 octopuses there. The question is why are they there and why are they congregating together? It seems that the warm water coming from the geyser is the key to that," said Jim Barry, a scientist at the Monterey Bay Aquarium Research Institute.

The researchers believe that the octopuses migrate to the hot springs in such large numbers to mate and nest, according to the study published in the journal Science Advances. After laying their eggs, expectant mothers cradle their eggs and protect them from predators. Warmer temperatures speed up the embryonic development. Barry explains that the long incubation period increases the chances that the eggs will not survive. By nesting next to a hot spring, the mother octopus can support her young.

The ambient water temperature at a depth of 3,200 m is 1.6 degrees Celsius. However, the water temperature in the fissure in the octopus garden is up to 11 degrees Celsius. A team of experts at the Monterey Bay Aquarium Research Institute and colleagues at many other institutions used advanced underwater technology to study the octopus garden.

The institute’s remotely operated vehicle Don Ricketts dived multiple times over a 14-day period between 2019 and 2022, capturing high-definition video of the octopuses and mapping the garden at meter-level resolution. The sub also left behind a time-lapse camera and sensors to measure temperature and oxygen levels for long-term observations of octopus behavior. The camera took pictures every 20 minutes and collected about 12,200 images between March 2022 and August 2022.

With this information, the scientists deduced why the octopuses were attracted to the area. The scars and other distinctive features allowed the team to track individual octopuses and the development of their offspring. The presence of adult male and female octopuses, developing eggs, and newly hatched octopuses suggested that the area was used specifically for incubation and raising young.

The eggs hatched in less than two years, much faster than expected, the study found. Another deep-sea octopus incubates its eggs for 4.5 years. In areas far from the vents, in the near-freezing temperatures of the deep sea, incubation typically takes several years. The researchers believe that the vents increase the metabolic rate of the female octopus and her eggs, reducing the time needed to incubate and making the eggs less likely to be eaten by predators. However, the team will continue to survey Mount Davidson for similar geological sites that might support octopus gardens.

After laying eggs, octopuses often fast to look after their young and often die around the time the eggs hatch. The bodies of the mother octopus and her hatchlings provide food for invertebrates such as starfish and sea anemones that live nearby. Researchers have recorded a total of four octopus gardens to date, two off the coast of Central California on the Davidson Mountains and two off the coast of Costa Rica.

An Khang (According to IFL Science/CNN )

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