In recent years, various seabeds have been located where large numbers of octopuses are concentrated for reproductive purposes. The largest of these hatcheries or nurseries (the young are more protected in these areas) was discovered in 2018 on the central coast of California, at about 3,200 meters below sea level.
Researchers at the NOAA Monterey Bay National Marine Sanctuary and Nautilus Live dubbed this area the “Garden of the Octopus,” estimating that it was home to more than 20,000 adult octopuses.
Scientists from the Monterey Bay Aquarium Research Institute (MBARI) have studied this pulp nursery species for three years, the one with the largest population known to date, and have been able to determine the reasons for this location of specimens of the Muusoctopus species. robustus. In short, as explained in an article published this week in the journal Science Advances, the Octopus Garden is located near an underwater volcano where several hydrothermal springs are active; octopuses take advantage of these funds to mate, nest and end their days peacefully. “The heat of the springs plays a key role in increasing metabolic rates, accelerating embryonic development, and presumably increasing reproductive success,” the authors note in the abstract of their results presentation paper.
The Octopus Garden is one of the few deep-sea octopus hatcheries known. In this hatchery, the heat from deep-sea hot springs accelerates the development of octopus eggs. Scientists believe that the shorter rearing period increases the newborn octopus’ chances of survival.
“Thanks to MBARI’s advanced marine technology and our partnership with other local researchers, we were able to observe Jarín del Pulpo in great detail, which helped us figure out why so many deep-sea octopuses congregate there. These findings may help us understand and protect other unique deep-sea habitats from climate impacts and other threats,” said MBARI scientist Jim Barry, lead author of the new study.
The Octopus Garden is located 3,200 meters on a small hill near the base of Seamount Davidson, an extinct underwater volcano 130 kilometers southwest of Monterey, California. The area hosts large concentrations of Muusoctopus robustus, a species nicknamed pearl octopus by MBARI researchers because, from a distance, nesting individuals look like opalescent pearls on the seafloor.
Over the course of 14 dives with MBARI’s Doc Ricketts remotely operated vehicle (ROV), the research team discovered why such large numbers of pearl octopuses are attracted to this location. The presence of adult male and female octopuses, developing eggs, and baby octopuses indicated that the site is used exclusively for reproduction. The team did not observe any intermediate-sized individuals or any evidence of feeding. Pearl octopuses gather at this site solely to mate and nest.
When NOAA and Nautilus Live researchers first discovered the Octopus Garden, they observed “shimmering” waters. This phenomenon occurs when warm and cold waters mix, suggesting that the region had hitherto unknown hot springs. Additional investigations by MBARI researchers and their collaborators confirmed that octopus nests are clustered in crevices bathed by hydrothermal springs where warmer waters flow from the seafloor.
The ambient temperature of the water at a depth of 3,200 meters is 1.6° Celsius. However, the temperature of the water inside the cracks and crevices of the Octopus Garden reaches almost 11°C.
Octopuses are ectothermic, or cold-blooded animals. The frigid temperatures of the deep sea slow down their metabolism and their rate of embryonic development. Most deep-sea octopuses have very long incubation periods compared to their relatives that inhabit warmer, shallower seas.
Previous experiments have measured the incubation time of the eggs of various octopus species in habitats and locations around the world. Comparison of egg incubation times clearly demonstrates how temperature affects the rate of embryo development: the colder the water, the slower the embryos grow.
At the near-freezing temperatures of the abyss, researchers expected pearl octopus eggs to take five to eight years, if not longer, to hatch. A 4K camera on MBARI’s Doc Ricketts ROV provided an up-close look at nesting mothers.
The MBARI researchers and their collaborators used the scars and other distinguishing features of individual mother octopuses to monitor the development of their young. Amazingly, the eggs hatched in less than two years. The heat from the hot springs increased the metabolism of female octopus and their young, reducing the time needed for incubation.
The researchers believe that the shorter nursery period in warmer waters greatly reduces the risk of predators damaging or eating developing octopus embryos. Nesting in warmer waters increases the reproductive success of the pearl octopus, better ensuring the survival of the offspring.
“The deep sea is one of the most challenging environments on Earth, yet animals have evolved clever ways to cope with frigid temperatures, perpetual darkness, and extreme pressure. Very long rearing periods increase the likelihood that the mother’s eggs don’t survive. By nesting in hydrothermal vents, mother octopuses give their young an advantage,” Barry said.
The enormous number of octopuses in an area attracts both predators and scavengers. Like most other cephalopods, the pearl octopus dies after reproducing. Dead octopuses in the Octopus Garden provide a feast for scavengers. A rich community of invertebrates lives alongside nesting females, no doubt benefiting from unhatched eggs, vulnerable hatchlings, or adult octopuses that have died.
Davidson Seamount and its octopus garden are protected as part of the Monterey Bay National Marine Sanctuary. Previous MBARI expeditions to Davidson Seamount in 2002 and 2006 revealed the impressive community of life on its rocky slopes.
“Essential biological hotspots like this deep-sea nursery need to be protected,” Barry said. “Climate change, fishing and mining threaten the deep sea. Protecting the unique environments where deep-sea animals gather to feed or breed is critical, and MBARI’s research provides the information resource managers need for decision making”.
