Life at the Bottom of the Ocean

Cross section of mariana trench

Life at the bottom of the Marianas Trench is unlike that of life found anywhere above the earth’s surface and is uniquely interesting in every aspect. At about 6.8 mi (36,069 ft.) deep, the Marianas Trench is considered the deepest part of earth’s crust. Located in the Western Pacific off the coast of the Marianas Islands, temperatures at the lowest point of the trench, an area identified as the Challenger Deep, range anywhere from 1-4 degrees Celsius. It is at this area where water pressure easily exceeds 15,000 psi, or 1000x normal atmospheric pressure.

These interesting environmental conditions allow specific life forms to reside and even thrive at the bottom of the trench. Most recently, in 2011, famous Canadian director James Cameron, famously known for his big-budget blockbusters Titanic and Avatar, piloted a solo mission down to the Challenger Deep in a specially designed submersible craft known as the Deepsea Challenger. In his expedition, he found many unique life forms inhabiting the base of the trench.

Unidentified amphipod - journal.pone.0053590.g003-i
Amphipod
Image from Wikimedia Commons

Amphipods, a common organism found at these depths, were found to inhabit the deepest parts of the trench. These organisms range in size from 1 to 340 millimeters (0.039 to 13 in) and are mostly scavengers. Amphipods are found in almost all aquatic environments, from freshwater to seawater and most biologists regard them as an important component of aquatic ecosystems as they provide essential nutrients to their environments.

Sea cucumber holothurian
Sea Cucumber
Image from Wikimedia Commons

Another organism found to inhabit the sea floor in the trench are sea cucumbers. These organisms are known to inhabit the sea floor worldwide. They can be found in great numbers within the trench where they often make up the majority of the animal biomass. Sea cucumbers are typically 10 to 30 cm (3.9 to 12 in) in length, although the smallest known species is just 3 mm (0.12 in) long, and the largest can reach 1 meter (3.3 ft). As an echinoderm, sea cucumbers have an endoskeleton just below the skin. An interesting note is that while having no true brain, sea cucumbers communicate with each other by sending hormone signals through the water and the organism is quite capable of functioning and moving about extracting oxygen from water inside the anus, so that they breathe by drawing water in and then expelling it.

These creatures are generally scavengers, feeding on debris in the ocean. Their diets of mostly consists of plankton and decaying organic matter found in the sea. Some sea cucumbers position themselves in currents and catch food that flows by with their open tentacles. They also sift through the bottom sediments using their tentacles. A remarkable feature of these animals is the “catch” collagen that forms their body wall. If the animal wants to squeeze through a small gap, it can essentially liquefy its body and pour into the space allowing the collagen fibers to attach themselves to whatever surface the orgasms desires to reside on.


Foraminifera
Image from Wikimedia Commons

One of the largest concentration of creatures found to inhabit the bottom of the trench were Foraminifera. The “ hole bearers” are characterized both by their thin outer layer that form an external net for catching food, and they usually have an external shell made of various materials however at extreme depths, this shell is composed of mostly organic material. They are usually less than 1 mm in size, but some are much larger, the largest species reaching up to 20 cm. Four unique species have been found in the Challenger Deep, one of which is representative of an endemic genus unique to the region. They are Resigella laevis and R. bilocularis, Nodellum aculeata, and Conicotheca nigrans (the unique genus).

This is not to mention that the concentrations of bacteria found in sediment samples at the bottom of the trench are stunningly high. Because of the nutrient rich sediment found at the bottom of the trench, bacteria thrive in the Challenger Deep and are found there in even greater abundance than on the surrounding abyssal plain. The trench is mainly occupied with bacteria called Paracoccus denitificans, which are the primary producers in the system, feeding on hydrogen and methane released by seawater-induced serpentinization of the rocks on which they’re growing. The other bacteria in the trench are Paracoccussystem which benefit from the trickle-down of nutrients from other organisms.

It is true that the Marianas Trench is inhabitable for most large organism but many others find it a welcoming environment and are happy to call it home.

About Mr. Mohn

Biology Teacher

This entry was written by Nasir M. and tagged . Bookmark the permalink.

One Response to Life at the Bottom of the Ocean

  1. Andrew P says:

    Very cool blog post, Nasir. The sea cucumber is quite different than any other species I have ever heard of, and it will be very interesting to learn about the discoveries of this environment in the near and distant future.

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