A group of MBARI researchers under the direction of Bruce Robison have been conducting surveys of deep-sea species at a study location they refer to as "Midwater 1" for the past 25 years. During one of these surveys in May 2007, the scientists came across a female octopus clinging to a rocky outcrop just above the canyon's floor, some 1,400 meters (4,600 feet) below the water's surface. Graneledone boreopacifica, a species of octopus, was not present during their previous dive at this site in April.
The researchers underwent 18 dives at this location over the course of the following four and a half years. They consistently discovered the same octopus in the same location, which they could recognize because to her recognizable scars. Her translucent eggs expanded in size over the years, and the scientists could observe the development of little octopuses inside. The female steadily lost weight over this time, and her skin become slack and pallid.
The female never left her eggs or consumed anything, according to the researchers. As long as they did not disrupt her eggs, she did not even show interest in the small crabs and shrimp that crawled or swam by.
The brooding octopus was last observed by the scientists in September 2011. One month later, they came back and discovered the female had vanished. The rock face she had colonized contained the ragged remains of empty egg capsules, the researchers noted in a recent publication published in the Public Library of Science (PLOS ONE).
The researchers calculated that the female octopus had been brooding roughly 160 eggs after counting the egg capsule fragments.
The majority of female octopuses only produce one clutch of eggs before passing away right before the eggs hatch. Graneledone boreopacifica's eggs are little olive-sized teardrop-shaped capsules. They need a lot of oxygen while they grow inside the eggs. To prevent the eggs from getting coated with silt or debris, the female octopus must regularly wash them in fresh, oxygenated seawater. To keep predators from eating her eggs, the female must vigilantly protect them.
The juvenile octopus spends a lot of time in its eggs, so by the time it hatches, it is completely prepared to live independently and search for little prey. In contrast to the hatchlings of other octopuses or squid, G. boreopacifica's young are bigger and more developed.
In their most recent study, the researchers note that octopus eggs develop more slowly in cold water, just like those of other invertebrates. At the Midwater 1 site, the seawater is around three degrees Celsius (37 degrees Fahrenheit) below the ocean's surface, which is normal for Monterey Canyon's depths.
It is not unexpected that octopuses are not the only deep-sea creatures that spend a lot of time tending to their offspring given this frigid habitat. One species of mysid, a shrimp-related animal that is common in Monterey Canyon's depths, carries its eggs for 20 months while fasting. The young of this shrimp hatch from their eggs as completely formed miniature adults, just like octopus hatchlings do.
The juvenile octopus spends a lot of time in its eggs, so by the time it hatches, it is completely prepared to live independently and search for little prey. In contrast to the hatchlings of other octopuses or squid, G. boreopacifica's young are bigger and more developed.
In their most recent study, the researchers note that octopus eggs develop more slowly in cold water, just like those of other invertebrates. At the Midwater 1 site, the seawater is around three degrees Celsius (37 degrees Fahrenheit) below the ocean's surface, which is normal for Monterey Canyon's depths.
It is not unexpected that octopuses are not the only deep-sea creatures that spend a lot of time tending to their offspring given this frigid habitat. One species of mysid, a shrimp-related animal that is common in Monterey Canyon's depths, carries its eggs for 20 months while fasting. The young of this shrimp hatch from their eggs as completely formed miniature adults, just like octopus hatchlings do.
An evolutionary difficulty is posed by such prolonged brooding periods, particularly for creatures with short lifespans like octopuses. The ability of the mother to tolerate a protracted time of brooding and the competitiveness of her hatchlings are trade-offs within the reproductive strategy of deep-living octopods, as the authors emphasized in their research. Graneledone boreopacifica breeds hatchlings that are exceptionally well-developed, giving them the benefit of a high chance of surviving.
According to this study, Graneledone boreopacifica may also be one of the longest-living cephalopods in addition to breaking records for the longest animal brooding periods (a group that includes octopuses, squids, and their relatives). Most octopuses and squids in shallow water only live for a year or two.
However, in this first example from the deep water, brooding also confers an extension of adult life that significantly exceeds most forecasts of mollusk lifespan, according to the researchers. "The ultimate fate of a brooding female octopus is inevitably death," they said.
Long-term studies of deep-sea species are uncommon, but the researchers suggest that prolonged brooding periods may be prevalent there. When evaluating how human activities affect deep-sea species, these longer life phases would need to be taken into consideration. In any case, Graneledone boreopacifica, one of the most prevalent deep-sea octopuses in the Northeastern Pacific, appears to have benefited from this tactic.
