The Secret of the Reef Engineers

Coral reefs are complex and extraordinarily species-rich ecosystems. Two groundbreaking LMU studies have now delivered new insights into these important habitats – as has the new low-impact tool for studying these fascinating underwater worlds. A group of researchers led by Dr. Christian Wild dedicated themselves to studying the scarcely investigated cold-water corals living at several hundred meters depth in the ocean. The scientists demonstrated that these reefs – like their tropical warm-water cousins – discharge enormous amounts of organic material, which can significantly influence the activity of microorganisms in their ecosystem. Another study, led by Dr. Christian Laforsch, has now closed even more knowledge gaps: he and his team have developed a method of surveying the surface area of corals which – unlike any of the other typical methods used so far – leaves the sensitive coral tissue undamaged. The surface area of coral is a critical parameter for researching and clarifying biophysical processes. Now, science has an essential tool at hand for investigating nutrient cycles, growth rates and other processes in the reef. (Coral Reefs, December issue, and Marine Ecology Progress Series, 9 December 2008)

2008 was declared the 2nd International Year of the Reef in order to raise public awareness as to just how vital coral reefs are as ecosystems of this world. Coral reefs, which can grow to gigantic size, are built by the animals of the cnidaria phylum, and in turn provide a habitat for a huge range of other species. Tropical coral reefs have frequently been referred to as the “rainforests of the sea” because they are a place in which many kinds of animal can live, including starfish, sponges, crustaceans, fish and mussels. Alongside these live a whole series of microorganisms, such as bacteria, viruses and protozoa. And yet, coral reefs are under serious threat from global warming and certain fishing techniques that can destroy the sensitive cnidarians. Several work groups at LMU are studying these vital ecosystems; habitats which we are far from understanding fully.

Cold-water corals in particular, which were practically unheard of ten years ago, are still relatively unresearched. Cold-water corals live at water temperatures of four to ten degrees Celsius, and are found living in waters a hundred to several thousand meters depth. Only a handful of laboratories worldwide have the means to sustain these deep-sea animals in an aquarium, so it is accordingly difficult to research them at all. One research group, led by Dr. Christian Wild, head of the Coral Reef Ecology Work Group (CORE) at the GeoBio Center of LMU, is now the first to have successfully unraveled the mystery of the interaction between cold-water corals and the life forms in their environment. In an aquarium at the Norwegian University of Berge, the scientists investigated the discharge of organic materials from cold-water corals. They revealed that these cnidaria continually discharge organic material in the form of slimes and sugars into the water, and in similar quantities to their relatives in tropical waters.

These substances are rich in nutrients, and serve as a basic food source for a series of microorganisms. With this finding, Wild and his team demonstrated that the activity of microorganisms is ten times higher in the direct vicinity of the coral reef than in the water column above the reef. In turn, metabolic cycles are set in motion that could influence where certain life forms settle in the reef. "You could say that cold-water corals are reef architects," explains Wild. "They determine a whole series of properties and processes of the deep reefs. That means they contribute significantly to the functions of the entire reef ecosystem."

Given climate change and the impact of humans, however, these sensitive ecosystems are in seriously jeopardy. The rising acidity of the oceans, for example, is one factor accelerating the chemical destruction of the corals’ sensitive calcium structure, and dragnet fishing and oil pipeline laying are physically smashing up ever more sections of reef. "Properly understanding the ecological processes in cold-water coral reefs is therefore a decisive factor for placing these ecosystems quickly and effectively under protection," stresses Wild.

One important parameter for clarifying the biophysical processes in these reefs is the surface area of the corals. This serves as a reference from which to determine the rate of photosynthesis, nutrient cycles or the growth rate of the corals. So far, it has only been possible to determine these using complicated methods in which coral arms were dipped in wax or wrapped in aluminum foil, which most often results in the death of the coral. While non-invasive methods in which geometric models are used to characterize the surface area avoid damaging the corals, they are relatively inaccurate by their very nature. Now, a workgroup led by biologist Dr. Christian Laforsch at the Department of Biology II has developed a method by which the coral surface area can be very accurately measured without causing any damage.

This new method, which was developed in collaboration with Christian Wild’s CORE workgroup and scientists of the Institute of Clinical Radiology of the Medical Faculty of LMU, involves using computer tomography (CT) to create cross-sectional images of the coral skeleton. Using this method, the researchers have even successfully investigated live corals. The corals were introduced into the CT scanner inside an acrylic aquarium, so that the water container would not corrupt the data. Thanks to modern computer technology, the researchers then reconstructed a 3D model of the coral structure. "The skeleton of the corals is only covered by a thin layer of tissue," explains Laforsch. "That means the surface area of the calcium skeleton can be essentially equated with the surface area of the coral."

This new technique allows even the finest of coral structures to be illustrated in three dimensions. "This method is by far the most accurate method existing at this time," states Laforsch. "It will allow us in future to calculate the surface area and growth habit of any type of coral." That means the method could be used just as successfully for future research of cold-water corals as for their tropical water relatives. Further studies by the CORE workgroup are already being planned. In a project funded by the European Science Foundation (ESF) and the Deutsche Forschungsgemeinschaft (DFG), for example, Wild and his group intend to study the biological and geochemical processes in cold-water coral reefs to greater detail than ever before. (ca/suwe)

Publications

"A precise and non-destructive method to calculate the surface area in living scleractinian corals using X-ray computed tomography and 3D modeling"
Christian Laforsch, Eva Christoph, Christian Glaser, Malik Naumann, Christian Wild und Wolfgang Niggl
Coral Reefs, Bd. 27, S. 811-820, 2008
doi: 10.1007/s00338-008-0405-4

"Organic matter release by cold water corals and its implication for fauna-microbe interaction"
Christian Wild, Christoph Mayr, Laura Wehrmann, Sandra Schöttner, Malik Naumann, Friederike Hoffmann und Hans Tore Rapp
Marine Ecology Progress Series, Bd. 372, S. 67-75, 9/12/2008
doi: 10.3354/meps07724

Contact

Dr. Christian Wild
Coral Reef Ecology Work Group (CORE)
GeoBio Center and Department of Earth and Environmental Sciences
Tel.: 0049-(0)89 / 2180 – 6706
Fax: 0049-(0)89 / 2180 – 6601
c.wild@lrz.uni-muenchen.de

Dr. Christian Laforsch
Department of Biology II and GeoBio Center
Evolutionary Ecology
Tel.: 0049-(0)89 / 2180 – 74252
laforsch@biologie.uni-muenchen.de
Web: http://sci.bio.lmu.de/ecology/evol_e/people_laforsch_g.html