Muddled by mud

I sort a sample of abyssal mud that has just landed on the deck. It is sieved carefully with a 0.3 mm sieve. Everything alive is carefully picked out of the petri dish with tweezers under a microscope. All living things end up in four little cups that stand in a Tupperware box of ice. One for worms, one for crustaceans, one for clams and one for other groups such as moss animals and brachiopods. In total, there will be between fifty and one hundred animals in the quarter square meter sample from the mud at a depth of four kilometers. At just over 50 percent of the Earth's surface, this mud is our planet's most common habitat, but at the same time also the least studied.

We biologists are interested in who we share the planet with (taxonomy) and how all of us organisms have evolved and interact (evolution and ecology). But this research has historically been stymied by technical limitations. The foundations were laid in the 18th and 19th centuries. Linnaeus worked in the 18th century and was the founder of taxonomy, and evolutionary research got a kick-start with Darwin a century later. With the help of students' travels and their own expeditions, they collected data from all corners of the earth and their discoveries thereby gained a kind of false image of universality. For the most part they had no opportunity to study and draw any conclusions from the ocean - it was mostly just a means of transport to the next beach out in Australia or the Galapagos Islands.

Now that developments in underwater technology have made it possible to explore the ocean and map life, it turns out that the theorems constructed by Linnaeus and Darwin were strongly coloured by the narrow world view they acquired by just studying the land and shoreline. It's a bit like describing how a car works by only having knowledge of the body. Similarly, marine biologists who do research only on the narrow continental shelves are bound by dogmas built in an environment quite unlike that of the greater ocean.

Large parts of the differences between coastal areas and the oceans revolves around the availability of nutrition. In the marginal zones of the sea (and at most places on land) there is unlimited food and the evolutionary forces act based on competition for other resources than for food. In the sea, it is only in the thin, sunlit surface layer that food is found because phytoplankton produce it with the help of the little nutrition that is available in the form of trace elements such as iron.

Here it is an extreme fight for food. Most of it is used up and only a tiny fraction makes it through the thin surface layer to the bottom. The bottom of the sea, on average 3682 m down, is therefore even more poor in food than the already meagre surface, so there is a lot of room for those who can manage to live on almost nothing.

In the deep sea, the normal state is starvation. Most animals are much smaller than their distant shallow relatives. And they are significantly fewer and more spread out. A bottom sample at the shoreline contains between ten and a hundred times more animals than a corresponding sample in the deep sea.

Traditional concepts and methods in taxonomy and ecology often work poorly in the sea. For example, when new species are to be described, a type (voucher) specimen is required. No problem for Linnaeus and his students who worked on the shore where the animals are large and easy to handle, but a big problem for biologists at sea when we have to try to bring up an often gelatinous animal in decent condition through 4 km of water. In the tropics, the surface water is 28 C and if you can still see what it is when it lands on the ship's deck, it is often further damaged before it reaches any of our test tubes.

Ecologists who study life on this most representative part of the planet's surface often find it difficult to describe the environments here based on common terms such as keystone or foundation species. It’s hard to explain the astonishing richness of species found in the sediment where competition is low, barriers to dispersal are limited and where physical parameters such are stable over very long time periods compared to those on land.

As James Cook steams to next sampling station, I close the lid of the 2 ml vial and check if I can see the speckle of an animal that I just placed there. Not described in any fauna or guidebook over marine species, the small animal I just sampled will be brought back to the lab and get some of its DNA sequenced. With that data at hand, we can see where it fits in the tree of life and assign an appropriate name. If it’s a species never registered or described, as is the case for most of them, it will be described and the data on shape, color, place where it was collected, and DNA sequence will be published in the scientific literature and made available in databases for future use, perhaps as part of environmental baseline studies as requested by managing authorities to conserve deep sea biodiversity.