You Ask, I Answer

A great response from the readers to last week's Pose a Question post. Here are some answers.

• Jim inquires, "What's the current take on a deep sea origin of life?" A great question that I addressed as part of the ongoing 25 Things You Should Know Series.

• Mustafa ponders, "Does an octopus have a medulla oblongata?" No.  The medulla oblongata, although fun to say, is part of the brain stem, which is not found in invertebrates.  Yet, the octopus central nervous system is more like the vertebrate brain than 'brains' of its relatives, snails and clams.  Consider that the common seaslug, Aplysia, has a mere 20,000 neurons and the typical octopus has 500 million.  The octopus CNS is divided into three parts the central brain, optic lobes, and arm nervous system.  The later two reside outside the central ganglia cluster.  The arm nervous system is autonomous and "In this hierarchical organization, the brain only has to send a command to the arm to do the action--the entire recipe of how to do it is embedded in the arm itself." That's right, the arms have a mind of their own.  The optic lobes have a three cortical layers that mimic those of the vertebrates.  The central brain lies in a cartilaginous brain case and is composed of 40 lobes! Everything else you would ever want to know can be found in the wonderful paper of Hochner et al. (2006).

• Mustafa also wonders, "Will you perish as a mere desire-ridden terrestrial, or will you endure the rite of 365 points and sublimate yourself as a creature of the ocean?" The answer should be obvious.  Bring on the 365 points...hell bring on all 400.

• Chris asks, "There have been several terrestrial mass extinction events. Did those same events cause similar results in the deep sea, or does the deep sea has its own such events." Unfortunately, little explicit research for a majority of the deep-sea fauna addressing this question has ever been conducted, except possible for forams and ostracods.  Obviously this reflects the lack of fossil record for these other groups.  Because a majority of deep-sea systems are reliant on ocean surface production for food, one can envisage any disruption of phytoplankton production during an extinction event being detrimental to deep-sea fauna.  This is one of reasons why hydrothermal vent communities, not dependent on this process, are thought to be buffered against these events.  In addition from McClain et al. (2006)...

  The current understanding of the deep sea is that much of its fauna died out in the mid-Cenozoic Era and was replaced by shallow-water immigrants (Gage, 2004). During the period of 30-40 Ma, bottom temperatures throughout much of the deep sea decreased by up to 10 C concurrent with an ocean-wide disoxyia/anoxia event. The mass extinction was followed by a colonization of species from coastal sources. Hypothesized shallow-water origins include polar regions; the Mediterranean Ocean, other regions where the water column is isothermal; or multiple shallow-water areas (Wilson, 1999; Gage, 2004). [For example] Gastropoda, is proposed to have only recently (c. 30 Ma) immigrated to the deep sea from multiple coastal centres (Clarke, 1962). Although...some deep-sea taxa appear to be ancient with high levels of in situ speciation (Wilson, 1999), the predominant direction of migration for many organisms is into deeper water (Jacobs & Lindberg, 1998)

• Ellie queries, "Is "tell me a bunch more about Nudibranchs" too general?" Yes, but I will say Nudibranchs are commonly found in the deep sea, often in deep coral meadows.  Only a single species is described from a hydrothermal vent.

• Ellie also proposes, "And if it is, how about info on how deep deep is. What's the deepest point and have we touched down there yet? What's the deepest a human has gone. An unmanned submersible? And a compare those to scale with layers of the earth and the atmosphere." For the purpose of DSN, I define the deep sea as those environments below 200m.  The deepest part of the ocean, and deepest part in the earth's crust, is Marianas Trench at 10,911m (6.78 miles).  In 1960, Picard and Walsh reached this spot in the Trieste.  JAMSTECS's Kaiko, an unmanned ROV, repeatedly has visited the deepest part of the trench.  Surprisingly, because of the equatorial bulge you are closer to the earth's core when you in the Artic abyssal plain (~4,500m; 3,947 miles from the core) than in the Marianas Trench (3,955,9 miles).

• Ellie also requests, "Are deep seeps located in the deep sea? I don't know at what depths they're usually found, but if they are I have plenty more questions about them."  Methane seeps are also found in shallow water, but are a common feature of deep-sea systems.