Citizens of the deep
This article was written by biologist Jon Copley for Beyond the Edge of the Sea,
an exhibition produced by Cindy Van Dover and artist Karen Jacobsen.
'The ocean depths,' wrote the nineteenth-century naturalist Charles Wyville Thompson, 'are wastes of utter darkness, subject to such stupendous pressures as to make any kind of life impossible'. Such was the prevailing view of that time, later disproved by Wyville Thompson himself and others who led early voyages of deep-sea discovery.
Fast-forward a century, and the prevailing view in the mid-1970s was that the ocean depths, while not completely lifeless, were like deserts. Textbooks taught that deep sea life was scarce, albeit consisting of some weird life-forms. But the discovery of deep-sea vents in the late 1970s showed that there could be rich oases of life in the otherwise sparsely-populated abyss.
Discoveries since then have continued to provide lessons in humility and wonder. Like Wyville Thompson, whenever we are tempted to make generalisations about life in the deep ocean, a new surprise challenges our understanding. And that experience, together with the beauty of this realm and its inhabitants, keeps us coming back for more.
But what is it like to be a citizen of these oases on the ocean floor, where once we thought life was impossible? The inhabitants of deep-sea vents face several apparent challenges, at least from our perspective as surface-dwellers. They need to feed, while living far from the sunlight that powers most food chains on Earth. They also need to cope with the high pressures, occasional high temperatures, and often toxic chemistry of the extreme environment where they live.
And as each deep-sea vent does not last forever, they need be able to hop from one oasis to another somehow. Finding out how life overcomes these challenges has kept biologists busy for the past thirty years - and uncovered yet more questions for future generations of explorers and scientists.
Creatures at vents generally make their living far beyond the reach of the Sun's life-giving rays. Photosynthesis - the process by which plants use sunlight to make their own food - only takes places in the upper sunlit layer of the ocean. In the dark depths below, life usually depends on the supply of food that comes from above. The deeper you go, the less food there is available, because it gets eaten on the way down. So you can imagine the surprise when biologists first saw the riot of life around a vent nearly two miles deep in the eastern Pacific.
According to the textbooks of the time, there simply shouldn't be enough food to support the lush thickets of red-lipped tubeworms and beds of large white clams at such a depth. But to understand how life at vents breaks the rules of the textbooks, take the red-tipped tubeworms. They initially posed a puzzle to biologists: as adults, they have no mouths - or indeed any apparent digestive system. Instead, their bodies contain a bag-like organ brimming with bacteria. These bacteria are the key to life in these oases on the ocean floor.