Cumberland Times-News

Bob Doyle - Astronomy

November 30, 2013

What life is found on the deep ocean floor?

I recently purchased “Oceans: A Visual Guide” by S. Hutchinson and L. E. Hawkins. “Oceans” is a Firefly book, published in 2008 with ISBN 13-978-1-55407-427-3 (paperback).

What I found most fascinating were the ghastly appearances and dynamics of the deep sea creatures that dwell in the darkness (living deeper than 300 meters or 1,000 feet).

The only light that breaks the blackness is the light emitted by the creatures themselves that live in or below this level. There is little mixing between the surface levels and the depths below.

Because water is densest at 4 C or 39 F, this is the temperature of the deep ocean. The pressures are enormous; roughly, for every 10 meters below the ocean surface, there is an increase of 1 atmosphere or 14.7 pounds per square inch.

So at 1,000 meters below, the pressure is 100 times our air pressure or 1,470 pounds per inch. The oceans’ floors average 4,000 meters or 2.5 miles in depth; here the pressure is 400 atmospheres or nearly 6,000 pounds per square inch!

How can any organism withstand such great pressures? At each level of the ocean, the external pressure on a life form equals its internal pressure outward.

But creatures living far below the ocean’s surface have their processes adapted to these pressures; if they are brought to the lower levels (for example, put in a fish tank), they will not survive.

The key reality is that most of the food for deep sea creatures is washed from the land or from the near surface layers of the oceans.

The deeper the level, the smaller the amount of plant and animal debris that descends from the upper layers of the ocean. Predators such as sharks also contribute to this rain of materials.

The total amount of organic carbon formed near the oceans’ surface by plants is 36 billion tons each year. Only 24 per cent of this material reaches the 1,000 meter (3,280 feet) level.

Less than 1 per cent of this material reaches the abyssal plains or ocean floors at 4,000 meters or 2.5 miles down. This rain is thicker at the equator and thinner in far north or far south latitudes.

Who lives on the ocean floor? The deep sea crustaceans (includes crabs, lobsters and shrimp) are stone crabs and the goblin or armored shrimp, both about a few inches across.

Deep sea squid may be quite small (about an inch across) or large (60 feet long).

Many deep sea squid are bioluminescent with light emitting organs on their bodies. Squids have eyes very similar to our own eyes but are much more sensitive owing to the very low light environment.

Most deep sea fishes are only a few inches in size. These fishes belong to primitive groups such as sharks, eels and bony fishes.

Bristlemouths are the most numerous fish in the oceans, living between 330 and 2,500 feet down. The hacketfishes dwell between 500 and 4,000 feet down; they have eyes that are up to 30 times more sensitive than human eyes.

Deep sea worms can be up to 6 feet long. Nematodes may represent from 50 t0 90 per cent of the live weight of animals in deep sea sediments.

There may be millions of species of nematodes. Deep sea cucumbers are estimated to be 95 per cent of the total biomass of animals over large part of the deep sea floor.

The deep sea floor has an area that is 41 per cent of the world’s oceans, an area comparable to the Earth’s land area. This floor is covered by soft, fine sediments accumulated over millions of years.

Just off the continental shelves, there is 200 grams of organisms per square meter. In the deep ocean floors, there is only 1 gram per square meter. The restricted food and low temperature cause the deep sea life forms to grow very slowly.

SKY SIGHTS AHEAD:  If Comet ISON survives its close passage by the sun late Nov. 28), it may be a conspicuous object in the 6:30 a.m. eastern dawn tomorrow morning.

It’s at low altitude (a few degrees) so you need to observe it from a place with a flat eastern horizon. Binoculars will be helpful in spotting the bright center or coma from which the fainter tail sprouts upward, pointing away from the sun.

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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