Only 200 meters under the surface of the sea is a fascinating, almost unknown, dark habitat: the deep sea. It is the largest habitat on our planet – the deep sea floor under 1,000 meters of water covers 62.3 per cent of the earth’s surface. By comparison, all the continents taken together account for a mere 30 per cent. Nevertheless, only a fraction of this gigantic region has been explored so far: all the explored areas of the deep sea add up to just five square kilometers. Professor Michael Türkay, Head of the Marine Zoology department and the Crustacea Section and Deputy Director of the Senckenberg Society for Natural Research, explains why deep sea research is so fascinating and challenging.
Professor Türkay, why was the exhibition so popular?
The show brought home to the public that the deep sea is one of our last horizons. People were very keen to find out about this totally unknown and mysterious world. Fascination with technology was another major success factor. We were able to show how modern technology suddenly opens the door to a whole new world: we can now go down into the deep sea and take samples and perform experiments there. Harnessing today’s transponder and location technology, we can find specific locations in the gigantic ocean again to an accuracy of a meter.
One of the most important discoveries of deep sea biology of the last few years is the existence of ecosystems that have nothing to do with light and green plants and are not reliant on the production of organic material at the water surface. Instead of this there is life at places we would never have thought possible, for instance at the hydrothermal vents, not discovered until 1977, whose energy comes from the earth’s interior. Chemosynthetic life communities have been found at these underwater geysers, for example a new group of chaetopod worms that produce their own food, as it were. The intestine of this group of animals is a closed sac in which they cultivate bacteria, feed them with hydrogen sulfide and then digest them. However, the scientists were faced with a mystery when they found that these animals have hemoglobin in their blood. After all, hemoglobin is poisoned by hydrogen sulfide! By conducting biochemical examinations, they finally found that these creatures have a special type of hemoglobin with two bonding sites, one for oxygen, the other for hydrogen sulfide. The international scientific community has only gradually discovered this and other fascinating mechanisms.
Further, it is becoming increasingly clear that the deep sea is a mega biodiversity region, that is to say it is home to many different species. There are only a few individuals of any one species per area unit, because the habitat is extremely low in nutrients – this used to make us think that the deep sea has a very low diversity of species. But this assumption was based on a methodical error: whereas three or four samples are enough to represent fauna in shallow water, you need 20 to 25 samples in the deep sea. And every sample can contain new, previously unknown animals! It’s safe to assume that 90 per cent of small animals caught are completely unknown, in meiofauna, i.e. animals smaller than 1 mm, the number could even be 99 per cent.
We still don’t understand how each of the chemo-synthetic habitats in the deep sea originate. We know their function, but we don’t understand how the individual species develop, how they maintain their population. Hydrothermal vents are found along the volcanically active mountain ranges of mid-ocean ridges in all the world’s oceans. A thin band of microhabitats extends along the ocean axis from north to south. The function of these microhabitats is always the same, but the actors are different. And these species must have originated. We now know that the springs can dry up within a period of 30 to 50 years and re-form at other places – and at the places they re-form they are very soon inhabited by the corresponding fauna. The question is: where was this fauna, how did it spread? We will not be able to solve this problem with the currently available technology.
It would have to be possible to track animals individually, i.e. fit them with a transmitter – but at present the antennae of such transmitters are much too big and the transmission range is too short. Technical miniaturization has not progressed far enough yet. No doubt we will see tremendous advances in the field of molecular biological probes or microchips in future. At the moment, all we can do is make precise observations and in situ experiments. However, these experiments are only snapshots. We don’t know what has really happened, how the flora and fauna we are observing have developed.
Another key topic is barobiology. This branch of science has been intensively researched since the eighties, particularly in the USA. But there is still no way of transferring the animals into experimental aquariums without loss of pressure. So the animals are fetched up from the sea floor in pressure vessels. Then they are put into the aquariums, being first decompressed and then immediately recompressed. Nobody knows what changes during this process, so it may well be possible that abnormal animals are examined.
I just can’t reconcile myself to the fact that half our planet is unfathomed territory. All our climate and flow models are produced on a basis that is not bad in itself but neglects many aspects. The movements of deep sea water, for example: The total volume of the water in our oceans passes through the deep sea once in a millennium. The water sinks in the Norwegian Sea, spreads southwards, towards the American and African coasts, further into the Indian and Pacific Oceans, into the Bering Sea and is then returned to the Norwegian Sea in the global system of surface currents. So what we do today influences what people will see on the sea surface in several hundreds of years. That’s why deep sea research is futurology.
Deep sea research is also basic research. We live in a biosphere that is changing fast. If we want to influence something in this biosphere we have to watch it closely. We have to find out how our systems are changing. But timescales of several hundreds or thousands of years are not available to us in experiments. We therefore need long-term observations like the ones we make in deep sea research.
Fig. 6: Animals living in the Atlantic deep sea, 5,000 meters under the surface (from top to bottom):
• Fangtooth (Anopologaster cornuta)
• Deep sea cuttlefish (Bathotauma)
• Deep sea shrimp (Aristeidae)
• Glass sponge (Hexactinellida)
Photos: M. Türkay
- The average water depth of the open sea is 3,800 meters.
- The German Research Foundation (DFG) and the Federal Ministry of Education and Research (BMBF) operate four large ships, suitable for deep sea research.
- The vast areas of the deep sea house an ecosystem that depends on surface production and lives from sinking organic matter. The situation is different at the hydrothermal vents, which have their own bacterial primary production.
- Below 1,500 meters the ocean is completely dark. Some animals therefore produce their own light. This bioluminescence is used for gender recognition or to track down prey.
- Extreme conditions prevail on the deep sea floor: at a depth of 5,000 meters, animals live under a pressure of 500 bar. By comparison: the pressure in a propane gas flask is 8.4 bar.
- The deepest point of the ocean is situated in the Mariana Trench in the Pacific Ocean and is 11,034 meters.