Thursday, September 7, 2023

An Octopus Behavior in the Deep Ocean

Environmental & Science Education, STEM, Earth Systems, Earth & Space Science, Nature, Wildlife, Nature of Science, History of Science

Ed Hessler

Science Advances reports (23 August 2023, v. 934, # 34) on a paper by 18 authors titled "Abyssal hydrothermal springs—Cryptic incubators for brooding octopus."

The introduction notes that "of all the hurdles faced by animals in the deep sea, cold may be the most challenging. Metabolism slows as temperature drops. ... Consequently, growth, locomotion, reproduction, and similar integrative physiological processes are typically slow in deep- or cold-water species, often lead to delayed (embryonic) development, low birth rates and long lives. Rates of embryonic development...for species inhabiting waters near  0 degrees C can be 4 to 33 times slower than related taxa from waters 10 degrees C warmer.

In deep waters "off central California, thousands of octopus (Muusoctopus robustus) migrates through cold dark waters to hydrothermal springs near an extinct volcano to mate, nest, and die, forming the largest known aggregation of octopus on Earth. Warmth from the springs plays a key role by raising metabolic rates, speeding embryonic development, and presumably increasing reproductive success (the authors) call attention that brood times for females are ~1.8 years, far faster than expected for abyssal octopods.

The Octopus Garden as it is known, is found in waters 3175- to 3300-m depth (~10417 ft to ~10827 ft) "to which male and female M. robust migrate to these hydrothermal springs.  ... The remarkable aggregation of ~ 6000 M. Robustus nesting at (these depths)... at the Octopus Garden suggests strongly that this breeding behavior provides a reproductive advantage." 

The authors also discuss this as an adaptation. "Deep-sea octopuses that nest on the seafloor require exposed rock surfaces for egg laying. M. robustus, after spending much of its life foraging over the muddy abyssal landscape, finds its way to relatively rare rocky habitat on seamounts to reproduce, resulting in localized breeding groups. Aggregation in rocky areas, with or without thermal springs have influenced reproductive success by enhancing made finding. However, not all rock surfaces are suitable.... Currents sweeping over the knoll housing the Octopus Garden, weak flow from hydrothermal springs, and perhaps also the nesting behavior of M. robustus act to resuspend and sweep away fine sediments to maintain open space. .... Whether the use of thermal springs by M. robustus arose in part from the availability of suitable nesting space or ... ancestral affinity...for warm brooding sites is unknown."

The authors wonder whether such thermal springs are common or just hard to find (cryptic) and make some suggestions on selecting possible sites for future research.

The paper includes graphs, illustrations and photographs.  There is much more in this paper if you want a deeper "dive," e.g., the materials and methods section. Remotely operated underwater vehicles (ROV) are a relatively new tool which is changing deep water research practices as well as its nature, extending the history of science.

Evolutionary biologist Richard Dawkins wrote a book, "The Extended Phenotype."  I don't see it mentioned very often, if at all any more and it isn't in this paper, but at one time, as this Wiki entry notes "the concept of extended phenotype has provided a useful frame for subsequent scientific work.  Dawkins himself asserted, 'Extended phenotypes are worthy of the name only if they are candidate adaptations for the benefit of alleles responsible for variations in them," illustrating the idea with a possible candidate construction: "a beaver's dam."
PubMed has a report published in 2018 which is about the revival of the extended phenotype. The author ends the paper by writing "What is beyond doubt then is that the original EP concept is alive and well and has become a seed corn for research into evolution and coexistence within ecosystems of varying complexities. On the practical side, it is timely as a better understanding of the co‐evolution of species in complex ecosystems has great potential for agricultural applications and for conservation and mitigating climate change."

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