Strange creatures - the deep ocean floor .

THE DEEP-SEA FLOOR

Most of the deep-ocean floor is an area of endless sameness. It is eternally dark, almost always very cold, slightly hypersaline (to 36%0, and highly pressurized. But there are 4,500 organisms per square meters. There were 798 species recorded in 21 samples in 1980s: a blind tripid fish, abyssal bentic animals such as oneirophanta, holothurian (sea cucumber), apseudes galatheria in the Kermadec trench, oneirophanta.

Marine Zoogeography, 1974, from J.C.Briggs. the ooze.
The deep-sea floor is the ocean�s most uniform habitat. It is populated by a large variety of highly specialized species.

http://en.wikipedia.org/wiki/Scotoplanes
http://animals.jrank.org/pages/1631/Sea-Cucumbers-Holothuroidea-SEA-PIG-Scotoplanes-globosa-SPECIES-ACCOUNTS.html

Smaller beasts
Foraminiferan remains from the White Cliffs of Dover, UK. The cliffs are made up of unimaginable numbers of chalky shells of long-dead marine animals. Foraminifera are very simple organisms that consist mainly of protoplasm.
Apart from when they are brought together by these food bonanzas, animals big enough to be seen with the naked eye are distributed fairly thinly on the deep-sea floor with perhaps one animal every 10 or 20m. But for every one of these big animals there are many thousands of tiny ones, no more than a few millimetres long and living hidden away in the abyssal mud. Many different animal groups are represented here, but just four or five groups dominate in terms of numbers.

First, at the lower end of the size range are the single-celled animals, the foraminiferans and their relatives. These are very simple organisms which feed by engulfing bacteria or other tiny pieces of organic matter into their protoplasm, and are extremely numerous. By secreting a chalky shell, or by sticking together mud particles or pieces of other animals'' shells into balls, tubes or multi-chambered little houses in which they live, these tiny animals produce a bewildering variety of strange shapes.

Acanthometra, a radiolarian with skeletal spicules of strontium sulphate, and foraminiferans from the Indian Ocean.
Another important group of single-celled animals are the Radiolaria. They have skeletons made of glass-like silica or strontium sulfate, often in radiating spicules--hence their name. Most of the 4,000 or so species are planktonic, but a few live on the bottom.

The second most abundant group, and among the smallest of the many-celled animals, are the nematodes or thread worms. Nematodes are found in all environments--marine, fresh-water and terrestrial--and may outnumber all other many-celled animals on Earth. In the deep sea they range in length from a few tenths of a millimetre to a centimetre or more, and include bacterial grazers (specialist predators that can puncture the prey''s cell membranes and suck out the internal juices), and active and deadly hunters.

Marine nematode worm. Nematodes or thread worms are one of the dominant groups in deep-sea muds. There are certainly thousands, possibly tens of thousands, of species still to be discovered.
The crustaceans are the next in importance. They include amphipod shrimps, which are related to, but much smaller than, the big scavenging amphipods, and several other groups specialised in producing tunnels or in pushing their way through the sediment by simply moving aside mud particles or other animals. Deep-sea isopods appear in a variety of forms--some resemble their terrestrial relatives, woodlice; others have a flattened form; some have long, thin, matchstick-like bodies ideal for ploughing through the sediment; others have long spindly legs well-suited for walking across the soft surface of the mud.

The most abundant of the mud-dwelling crustaceans, however, are the harpacticoid copepods, related to the dominant zooplankton group in the mid-water realm, but specialised for living in the sediment and feeding on bacteria or organic detritus.

Newly discovered polychaete worm, Sigambra sp., from the floor of the abyssal Atlantic. Though some polychaetes reach 10-20cm, most deep-sea species, like this one, are a few millimetres long.
Next come the polychaete worms which are found at all depths and include very mobile species, which crawl actively across the bottom, or even swim; and sedentary species, which live in tubes or burrows, and either forage over the sediment surface for pieces of food or catch floating particles with feather-like tentacles.

Only one other deep-sea, mud-dwelling group, the bivalve molluscs (relatives of the shallow-water clams and mussels with two shells, or valves, hinged together), approaches the polychaetes in abundance. Most deep-sea bivalves live buried in the sediment and send out feeding palps to gather pieces of food from the surface of the mud, while a few have become accomplished carnivorous hunters.

But most surprising of all, there are specialist deep-sea, wood-boring bivalves. Their environment is just about as far from a source of any wood as is possible. These bivalves will attack the hulls of sunken wooden ships, but they were around long before humans first sailed over the deep ocean. Unlikely as it seems, trees from coastal forests must fall into the sea and eventually sink into the abyss sufficiently often to make this strange lifestyle worthwhile.



VENT COMMUNITIES

Hydrothermal vents and their exotic fauna were first discovered on the Gal�pagos Rift in the Pacific as recently as 1977!! Vents are found on mid-ocean ridges and back-arc basins, which are deep-water volcanic chains. One of the most striking adaptations of vent animals is their association (symbiosis) with microogranisms that use the chemical energy found on the vent fluids for the production of organic matter.


1976 Scripps Institution of Oceanography
Riftia �tube worms, chemosynthetic bacteria, , giant white clam, Calyptogena magnifica

Deep-vent communities, near black smokers and atop cold seeps, depend on chemosynthesis rather than photosynthesis for energy.

Cold seep ecosystems were found for the first time as recently as 1984 in the deep Gulf of Mexico! The animals that thrive on cold seeps are similar to those found on hydrothermal vents and also depend on the production of microorganisms that use reduced chemicals as source of energy.


Lakes�650ft beneath the waves
Deep beneath the waves, far down on the ocean floor are scenes and images often associated with the stuff of nightmares - translucent fish with wide black eyes capable of seeing in the dark, shell fish with bioluminescent skeletons and colossal squid, so huge that no one has yet to picture them. All these creatures, though bizarre, are somehow quite expected but it�s doubtful whether many people when asked what else they would find strange to discover at the bottom of the ocean would picture a lake.

As unlikely as it sounds there are a handful of underwater lakes and rivers boasting their own mini ecosystems.


Abyss Greek word meaning ''bottomless''. The deep part of the oceans, between about 3,000m and 6,000m deep.

Amphipods Group of shrimp-like crustaceans ranging in length from a few millimetres to more than 10 cm.

Bacteria Tiny living organisms, neither clearly plants nor animals, which have no clear nucleus like the cells of most other creatures.

Copepods One of the most important groups of planktonic crustaceans in the oceans. Most are small, just a few millimetres long, and many feed on phytoplankton cells.

Hydrothermal vents Springs of very hot, chemically-laden water gushing through the sea floor along the mid-ocean ridge system.

Species The basic unit into which scientists divide the living world. Members of a species can interbreed with one another, but not with members of another species.