"Food puzzle" of the deep sea cracked

Discarded mucus nets provide organic material for seabed inhabitants

"House" of Larvaceae MBARI
Read out

In the deep sea not only high pressure and permanent dark prevail, it also does not offer its inhabitants much food. Nonetheless, many animals live in this seemingly hostile world. But what are they living on? It was exactly this question that American scientists were able to answer in a surprising way.

Marine biologist Bruce Robison and his colleagues at the Monterey Bay Aquarium Research Institute (MBARI) specifically studied the animals that live off the deep ocean floor off the coast of central California. After analyzing hundreds of hours of video recordings, the researchers identified so-called "sinkers" as food sources. These are fine mucus nets, which are released by small animals of the middle water depths, the so-called Larvaceae. The results were published in the current issue of the journal Science.

Puzzle food

The deep sea is inhabited by a wide range of swimming, burrowing and crawling animals. However, since no plants grow at this depth, most deep-sea dwellers either have to eat their own or feed on the material that sinks from above. Decades of marine biologist measurements have shown that the amount of food needed is much greater than the amount of drowning. So what do the animals eat?

Although there were several theories, only now could the scientists find one of these enigmatic food sources. Larvacea are small molluscs related to tunicates or sea squirts that feed on the smallest organic particles in the surrounding water.

The most widespread Larvacee, the giant larvacea of ​​the genus Bathochordaeu, lives inside two netlike mucus filters, their "house". The outer filter intercepts coarser particles and can reach up to one meter in width. The inner filter is denser and serves to "fish" the food. After about 24 hours of "continuous operation", the filters are closed and the Larvacee leaves her house, which has now become incapacitated, to build a new one. The deposited filters sink to the bottom of the sea, carrying with them their rich cargo of organic particles and small marine animals. display

Strapless mucus nets

Biologist Bruce Robison discovered hundreds of these abandoned webs in motion pictures taken by remote-controlled diving robots off the coast of California. He explains, "When I realized that the sinkers were transporting significant amounts of organic carbon to the deep sea, we asked other oceanographers if they had found those things in their sediment traps. It turned out that although the sinkers are very common, they rarely catch themselves in the traps. In addition, they often disintegrate upon contact with a solid object. "So far, the researchers either registered no sinkers or found only a formless lump of mucus they held for contamination and secreted.

To find out how much carbon these sinkers carry to the seabed, Robison first explored how common they were. For ten years, the researchers carried out a monthly Volksz hlung in ten different water depths. On one day, they counted an average of four sinkers per square meter or in other words: on a surface the size of a plate, around one hundred sinkers land each year.

More than enough carbon for everyone

But how much carbon does such a sinker transport? In order to find out, the scientists used remote-controlled diving robots, which captured the floating mucus nets not an easy task. Back in the lab, researchers measure the amount of organic carbon in each sinker. From these values, they found that the sinkers transport almost as much carbon to the seabed as all the detritus collected in sediment traps. With that they had found an additional source of food for the deep-sea dwellers, which is more than sufficient to feed all.

These finds have implications beyond marine biology, as they also provide important new insights for climate research. Because the oceans are part of the global carbon cycle and therefore it is essential to know how much carbon is transported within the oceans.

(Monterey Bay Aquarium Research Institute (MBARI), 13.06.2005 - NPO)