Deep-sea coral very frugal with food

Surviving together during food shortages

Detail of the coral community, including a number of sponges

Deep-sea corals live in an environment with very little food. Researchers at Utrecht University, NIOZ, the University of Gothenburg and the German GEOMAR centre reveal a new part of deep-sea corals' metabolism and show that they deal with their scarce food resources in an incredibly efficient way. Their results will be published in Nature Scientific Reports on 8 December 2015.

Corals living in shallow tropical seas get their energy from a symbiotic relationship with algae, which extract energy from sunlight and can thus convert carbon dioxide into biomass. Deep-sea corals, on the other hand, live in pitch darkness, which makes photosynthesis impossible. They are therefore forced to get their energy from the few nutrients that sink down from the sunny surface. Little is known about how deep-sea corals cope with this food shortage.

Nitrogen and carbon

Together with their team, principal researchers Jack Middelburg, earth scientist at Utrecht University and Dick van Oevelen, biologist at the Royal Netherlands Institute for Sea Research (NIOZ), collected corals from a depth of some three hundred metres from the seas of Norway and kept them alive under controlled laboratory conditions. In various experiments, they studied precisely how deep-sea corals deal with important nutrients such as nitrogen and carbon.

Stored in the corals

Van Oevelen: ‘By adding stable isotopes of the two substances to the environment of the corals we could watch what the corals did with them. The first thing we discovered was that bacteria that live with the coral could use the remaining energy from the waste product ammonium to convert inorganic carbon into biomass. This means that carbon fixation also takes place in the coral community in the dark. The deposited carbon was traced in essential fats and proteins. As a result, these bacteria fulfil a functional role that appears to be similar to the one played by symbiotic algae in tropical corals.’

Moreover, it appeared that the body of symbiotic organisms were able to convert nitrogen gas into biological forms of nitrogen within 24 hours. This is remarkable, because that process requires a lot of energy and therefore is not expected in the energy-limited deep sea. Further research is needed in order to understand the role of nitrogen fixation for the deep-sea coral community.

Detail with individual polyps of the most common cold-water coral species, Lophelia pertusa.

Extremely efficient

‘The fact that tropical corals have a strong symbiotic relationship with all organisms living in the coral-reef community was already known,’ explains Middelburg. ‘But we did not know that deep-sea coral communities are able to deal so efficiently with their nutrients, and even fixate nitrogen gas, which is an energy-consuming process. We suspect that these metabolic mechanisms are essential for survival in the nutrient-poor deep sea.’

Collaboration

In November 2014, NIOZ and Utrecht University signed a declaration of intent for intensive collaboration. The two knowledge institutes have been working together for more than 25 years in the fields of marine and climate sciences. This research emphasises their close collaboration.

The research also falls within the Netherlands Earth System Science Centre (NESSC), a cross-university research initiative that links up scientists with a background in physics, earth sciences, ecology and mathematics to help better understand climate change and to help make better predictions about climate development in the near future.

Deep-sea coral reefs are extremely rich communities with high biodiversity.

More information

Faculty of Geosciences: a sustainable Earth for future generations

More information
Faculty of Geosciences