Coral reefs are dying all over the world. Is it possible to artificially reproduce marine animals in order to reforest reefs? Doctoral candidate Laura Fiegel travelled to the island of Moorea in the middle of the South Pacific for three months to conduct field experiments.
Laura Fiegel snorkelling. As it gets deeper, she dives down. The water: turquoise-coloured. On the mainland behind her: volcanic mountain ranges, tropical forest, white sand. The 30-year-old has not travelled to Moorea - an island just eleven kilometres wide in the middle of the tropical South Pacific right next to Tahiti, which belongs to French Polynesia - for a three-month beach holiday. But to find out under which conditions stony corals can reproduce more easily. She carefully removes the calcareous skeletons from the seabed. She uses a hammer and chisel to help her remove individual corals from the reef as gently as possible.
What Fiegel is experimenting with on the other side of the world will be incorporated into her doctoral thesis. In the Environmental Biochemistry working group headed by Prof Dr Peter Schupp, she is working with other researchers on how baby corals can be colonised with the help of certain biochemical substances. The long-term vision is to help revitalise damaged reefs using innovative methods.
Because corals are in a bad way worldwide. Entire reefs are dying off. There are many reasons for this. In addition to overfishing and environmental pollution, the main problem is that the oceans are warming due to climate change, which is disrupting the vital symbiosis between corals and microalgae. As a result, the coral reefs bleach and eventually die. In addition, species structures and food webs can become unbalanced. The extent to which additional stress factors can have a negative impact on coral reefs is shown, for example, by the crown-of-thorns starfish. It eats corals on a large scale by covering itself over the animals. In mass outbreaks, this species can eat the corals of entire reefs in a very short time.
Settling baby corals
Fiegel can see for himself just how rampant this dreaded "reef killer" is when diving. However, the main reason she took the 30-hour flight to Moorea was to find out under real conditions whether certain coral species in the wild in the South Pacific would respond to a newly developed colonisation method. This had previously proved promising in tests in the laboratory aquarium at the Wilhelmshaven site of the Institute of Chemistry and Biology of the Marine Environment (ICBM).
The procedure is more complex than the conventional artificial propagation method of fragmentation, in which pieces of adult coral are broken off in order to grow small offshoots, or clones. Instead, Fiegel transfers the corals removed from the reef during diving to an aquarium on the island at a very specific time. This is exactly when spawning is due, i.e. the moment when corals release millions of eggs and sperm into the water - packed in small "packages". When these rise to the surface, the packets burst open. Eggs and sperm then have to find each other for fertilisation in the water. This process of sexual reproduction is triggered by environmental factors such as the lunar cycle and water temperature. This time cannot be predicted exactly, especially in the aquarium, which is why Fiegel has to check what is happening in the tank every half hour after sunset during this phase.
Making corals more resistant to climate change
As soon as the fertilised egg cells have developed into swimming coral larvae, Fiegel gives them the biochemical signalling substance cycloprodigiosin (CYPRO). This triggers colonisation, i.e. the transformation from a swimming larva to a sessile polyp. This process only occurs naturally after the larvae have been swimming through the reef for several days - and it is not always successful. At the research institute, the researchers use the chemical to trigger this process artificially under controlled conditions in the aquarium - which in some experiments was accompanied by a significantly higher success rate than in nature.
Fiegel and other researchers around the world are currently working on methods that could be used to reintroduce baby corals to the natural reef in the long term. The advantage of this propagation method: "We assume that the young corals can adapt better to changing environmental conditions than cloned offshoots," explains Fiegel. "Sexual reproduction results in new gene combinations and animals with a greater variability of characteristics." Research by other scientists has already shown that young corals propagated in this way are better able to adapt to warmer water temperatures.
"However, such research approaches will not be able to stop the worldwide extinction of corals," emphasises Fiegel. Especially as this is still basic research. Initial experimental data from Moorea that has already been analysed indicates that the biochemical substance promoted the settlement of coral larvae from the wild to a lesser extent than in the laboratory. The reason for this is still a mystery. According to Fiegel, it is striking that other colonisation methods on Moorea did not work as well as expected. "Perhaps the larvae of these colonies are not healthy or the natural settlement substrates in the reef no longer work as well as they used to," she surmises. Further experiments would be needed to assess this.
