The deep-sea springs, of which there are both hot and cold versions, are oases in a hostile desert. So far, these biotopes have been considered to be young in terms of evolutionary biology. But a closer look reveals a "Image" established wildlife. alt="
It was the biological discovery of the 1970s: Deep down on the sea floor, which until then had been considered barren and empty, oases of flourishing life flourished. The deep-sea hydrothermal vents owe their splendor to a substance that has a rather bad reputation: hydrogen sulfide.
Those who are adapted to life in these places can indeed live very well here
(Crispin Little) Under high pressure, water several hundred degrees hot bubbles out of crevices together with the poisonous substance. But what is deadly for most organisms, others know how to use for themselves. Bacteria, for example, which oxidize the hydrogen sulphide and the methane that also escapes here and thus tap into these substances as a source of energy. And these microbes in turn feed a rich animal world that has learned to endure the poison. "If you're adapted to life in these places, you can indeed live here very well," explains Crispin Little of the University of Leeds.
In the meantime, it has become apparent that, in addition to the hydrothermal vents, there are also versions where things are not quite as hot. In the so-called cold seeps, hydrogen sulfide and methane bubble out rather unspectacularly at a temperature that corresponds to that of the surrounding seawater. But the same applies here as for its hot sisters: thriving life, built on hydrogen sulfide and methane.
The deep sea springs are not a case for eternity now. Sometimes one source can dry up, sometimes a new one emerges elsewhere. The animal world living here - according to previous assumptions - should therefore show species that are young in terms of evolutionary biology. In order to prove this, Little and his colleague Steffen Kiel were particularly interested in molluscs, which are well represented in the sea by numerous mussels, snails and beetle snails. The researchers evaluated a total of 102 genera of the animal phylum-present and fossil dating back to the Jurassic-from 125 deep-sea cold springs.
The scientists excluded genera for which there was no fossil evidence from their further analysis, as well as those that were probably only encountered by chance at the sulphide sources. 36 genera remained, seven of which are now extinct. Of the remaining cold-seep molluscs, only one mussel lived as early as the Jurassic, around 150 million years ago. A few more genera were added in the Cretaceous period, most then appearing during the Tertiary Eocene 55 to 34 million years ago.
For comparison, Kiel and Little now used the fossil evidence of the "normal" mollusc fauna outside the deep-sea sources. Here, too, the first representatives of the molluscs that are still alive today appeared in the Jura. However, the largest group of the 2366 genera studied appeared on the sea floor quite late: in the Oligocene 34 to 24 million years ago and in the subsequent Miocene.
Thus, the molluscs of the deep-sea springs prove to be at least one epoch older than the other mollusks and thus bury the theory of the young spring fauna. And another hypothesis is also shaky: Until now, whale carcasses, whose decomposition also produces hydrogen sulfide and methane, have been considered ecological "stepping stones" between the sources, enabling an exchange of species. The first precursors of whales actually appeared in the Eocene. But fossil evidence of luxuriant white oaks only comes from the Oligocene, when marine mammals experienced their first heyday - the molluscs of the deep-sea sources were already "Image" established rabbits. alt="
Now the researchers don't want to completely deny the whales their role as promoters of the source fauna, but their importance in the evolution of molluscs remains modest. But why have the molluscs survived unchanged at the poisonous springs for so long?
Kelel and Little suspect that they found a retreat here for bad times. Apart from the great extinction of species at the Cretaceous-Tertiary boundary, there have been other events in the history of the earth in which drastic changes - such as the reduction in oxygen levels - have badly affected the inhabitants of the sea. Even during these crises, the deep-sea wells "were powered by a constant source of geothermal energy," Little points out. This boring constancy created lush oases in the barren desert of the deep sea.