Strange animal communities survive and even proliferate in the obscurity of the ocean deeps. But where do these organisms find the energy that is necessary for all forms of life? How have ecosystems been able to develop in conditions where photosynthesis is impossible? Is it possible to fabricate organic matter without light?
A descent into the ocean deeps
For a long time, the ocean deeps were looked on as deserts. This world of the abyssal plains, 307 million km² in area, where cold, obscurity and extreme pressure reign, seemed hostile to the development of even the simplest ecosystem. Today, we know that animals perfectly adapted to these extreme surroundings evolve there in total tranquillity.
On the surface of the globe, the plants feed the herbivores, and they are eaten in their turn by the carnivores.
But beyond a depth of 150 metres there is no vegetation, the lack of light making photosynthesis impossible. Nevertheless, plants are at the base of the food chain for the majority of animals in the ocean deeps. In fact, they feed on the residues of plants and dead animals which reach them from the surface.
So in the obscurity of the oceans, the “herbivore” link in the classic food chains is replaced by the “detritivore” link, composed of animals which feed on the leftovers from the banquets on the surface and which, in their turn, present an excellent meal for the carnivorous fish of the deeps. However in certain zones at the bottom of the sea, there are life forms which play no part in this cycle. To discover them, we must go to those places where the physical features of the ocean floor are in movement …
A new type of ecosystem
In the middle of the oceans, at the frontier between tectonic plates, we discover genuine underwater mountain ranges. These features result from the outpouring of basalt lava caused by the widening of the gap between tectonic plates at that point. The mountains are known as the ocean ridges.
In 1997, whilst exploring of the Galapagos ridge, two geologists on board their submarine Alvin made a major discovery. At a depth of 2500 meters, along the crest of the ridge, a whole community of organisms of surprising shapes and sizes, proliferated around hydrothermal springs. This profusion of life left the scientists astonished. Never had they imagined finding such living organisms grouped together in such a small area, so deep below the surface of the ocean.
The discovery had the effect of a bomb in the world of oceanography. In this case, the obscure abyssal desert enclosed “oases” without access to sunlight, housing communities of living beings which had quite clearly found a food source other than organic material arriving from the surface. It was totally impossible that they relied on photosynthesis, but in that case, where did these organisms of a completely new type find their energy?
Did you know?
In 1844, the English naturalist, Edward Forbes, basing his conclusions on results from his deep trawling in the Aegean Sea, affirmed that there was no life in the seas beyond a depth of 600 meters. Nevertheless, even at that time, a lot of observations contradicted this theory.
Organisms which live at a depth of 5000 meters must support a pressure of 500 kg/cm². That is the equivalent of the weight of a horse balanced on one fingernail!
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