Korallen bleiben cool

Korallen-Horrostories waren lange Zeit ein Lieblingsthema der Medien. Mittlerweile sehen Journalisten die Lage der Korallen jedoch deutlich differenzierter. Ein gutes Beispiel war 24. Oktober 2016 in Spektrum der Wissenschaft zu lesen, wo Kerstin Viering ermutigende Forschungsresultate nicht unter den Tisch fallen ließ:

Warum manche Korallenriffe allen Problemen trotzen
Klimawandel, Schadstoffe, Überfischung: Korallen haben es heutzutage nicht leicht. Einige Riffe aber trotzen den Widrigkeiten bisher erstaunlich gut. Ein Grund zum Optimismus?

Weiterlesen in Spektrum der Wissenschaft

Die Forschung macht derzeit gute Fortschritte. Nun beginnt man auch langsam zu verstehen, wie sich Korallen an veränderte Bedingungen anpassen können. Pressemitteilung der University of Texas at Austin vom 7. November 2016:

New Coral Research Exposes Genomic Underpinnings of Adaptation

Scientists at The University of Texas at Austin have observed for the first time that separate populations of the same species — in this case, coral — can diverge in their capacity to regulate genes when adapting to their local environment. The research, published today in Nature Ecology and Evolution, reveals a new way for populations to adapt that may help predict how they will fare under climate change.

The new research was based on populations of mustard hill coral, Porites astreoides, living around the Lower Florida Keys. Corals from close to shore are adapted to a more variable environment because there is greater fluctuation in temperature and water quality: imagine them as the more cosmopolitan coral, adapted to handling occasional stressful events that the offshore coral are spared. When researchers swapped corals from a close-to-shore area with a population of the same species from offshore waters, they found that the inshore-reef corals made bigger changes in their gene activity than the corals collected from an offshore reef. This enabled the inshore corals to adapt better to their new environment.

„It is exciting that populations so close together — these reefs are less than 5 miles apart — can be so different,“ says corresponding author Carly Kenkel, currently affiliated with the Australian Institute of Marine Science. „We’ve discovered another way that corals can enhance their temperature tolerance, which may be important in determining their response to climate change.“

Differences in gene regulation — the body’s ability to make specific genes more or less active — can be inherited and are pivotal for adapting to environmental change. It was already known that separate populations often develop differences in average levels of gene activity, but now scientists have found that populations can also diverge in their ability to switch genes on and off.

„We show that one population has adapted to its more variable environment by developing an enhanced ability to regulate gene activity,“ says Mikhail Matz, co-author of the study and an associate professor in the Department of Integrative Biology.

Researchers swapped 15 genetically distinct coral colonies from inshore with 15 colonies found offshore to see whether the corals would regulate their genes to match the pattern observed in the local population. After a year, the transplanted populations did show differences: Formerly inshore corals transplanted offshore changed their gene activity dramatically to closely resemble the locals, whereas offshore corals transplanted inshore were able to go only halfway toward the local gene activity levels. In short, corals that originated from the more variable, close to shore environment were more flexible in their gene regulation.

The lack of flexibility took its toll on the offshore corals, which did not fare well at the inshore reef and experienced stress-induced bleaching. Their higher bleaching levels were linked to the diminished ability to dynamically regulate activity of stress-related genes, confirming that flexibility of gene regulation was an important component of adaptation to the inshore environment.

„We saw different capacity for gene expression plasticity between coral populations because we looked at the behavior of all genes taken together instead of focusing on individual genes,“ says Kenkel. „If we hadn’t, we would have missed the reef for the coral, so to speak.“

The research was funded by the National Science Foundation’s Division of Environmental Biology.

Zehn Tage später gab dann auch das Smithsonian Tropical Research Institute eine hoffnungsfrohe Pressemitteilung heraus, dass einige Korallen wohl viel zäher sind als lange gedacht:

Corals Survived Caribbean Climate Change

Half of all coral species in the Caribbean went extinct between 1 and 2 million years ago, probably due to drastic environmental changes. Which ones survived? Scientists working at the Smithsonian Tropical Research Institute (STRI) think one group of survivors, corals in the genus Orbicella, will continue to adapt to future climate changes because of their high genetic diversity.

“Having a lot of genetic variants is like buying a lot of lottery tickets,” said Carlos Prada, lead author of the study and Earl S. Tupper Post-doctoral Fellow at STRI. “We discovered that even small numbers of individuals in three different species of the reef-building coral genus Orbicella have quite a bit of genetic variation, and therefore, are likely to adapt to big changes in their environment.”

 “The implications of these findings go beyond basic science,” said Monica Medina, research associate at STRI and the Smithsonian’s National Museum of Natural History and associate professor at Pennsylvania State University. “We can look forward to using similar approaches to predict demographic models to better manage the climate change-threatened Orbicella reefs of today.” 

To look back in time, the team of researchers working at the Smithsonian’s Bocas del Toro Research Station and Naos Molecular and Marine Laboratories collected fossils from ancient coral reefs and used high-resolution geologic dating methods to determine their ages. They compared the numbers of fossilized coral species at different time points. One of the best-represented groups in the fossil collections were species in the genus Orbicella. In addition to the fossil collections, they also used whole genome sequencing to estimate current and past numbers of several Orbicella species.

Within a single individual there are two copies of their genetic material, and in some instances, one copy is different than the other and is called a genetic variant. The authors first assembled the full genomic sequence of an individual from Florida and then, using it as an anchor, reconstructed the genetic variation contained within single individuals. Depending on the amount of the genetic variation at certain intervals across the genome, the authors were able to recover the population sizes of each species at different times in the past.

Between 3.5 to 2.5 million years ago, numbers of all coral species increased in the Caribbean. But from 2 to 1.5 million years ago, a time when glaciers moved down to cover much of the northern hemisphere and sea surface temperatures plunged, the number of coral species in the Caribbean also took a nosedive. Sea levels fell, eliminating much of the original shallow, near-shore habitat.

 “Apart from the species that exist today, all species of Orbicella that survived until 2 million years ago suddenly went extinct,” write the authors. When huge numbers of species die out, it makes room for other species to move in and for new species to develop to occupy the space the others held.

Two species that grow best in shallow water doubled in number at about the same time that their sister species and competitor, the organ pipe Orbicella (O. nancyi) disappeared.

When a species declines during an extinction event, it loses more and more genetic variation and sometimes does not have much to work with during the recovery period. Scientists call this a genetic bottleneck. Orbicella was able to recover after the bottleneck.

“It’s incredible how predictions from genetic data correlated so well with observations from the fossil and environmental record,” said Michael DeGiorgio, assistant professor of biology at Pennsylvania State University.

“We see hope in our results that Orbicella species survived a dramatic environmental variation event,” said Prada. “It is likely that surviving such difficult times made these coral populations more robust and able to persist under future climatic change.”

 “The in-depth analysis of population size in a now ESA-threatened coral, as well as the release of its genome and that of its close relatives (which are also threatened) would be of great interest to coral reef researchers addressing conservation issues,” said Nancy Knowlton, senior scientist emeritus at STRI, currently at the National Museum of Natural History.

Authors are from STRI, the National Museum of Natural History, Pennsylvania State University, University of Iowa, U.S. National Oceanic and Atmospheric Administration, Hudson Alpha Institute of Biotechnology, Universidad Nacional Autónoma, Australian Research Council Centre of Excellence for Coral Reef Studies and University of Queensland School of Biological Sciences, Florida State University, Natural History Museum and the Systems Biology Institute.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The Institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Website: http://www.stri.si.edu.

Prada, C., Hanna, B., Budd, A.F., et al. 2016. Empty niches after extinctions increase population sizes of modern corals. Current Biology.

Bereits im Juni 2015 beeindruckte Sascha Karberg in der Zeit mit einem sehr ausgewogenen Artikel:

Korallen bleiben cool
Zu warmes Wasser lässt Korallen erbleichen. Doch besondere Gene können die riffbildenden Tiere schützen. Auch mit der Versauerung scheinen sie gut zurechtzukommen.

Korallen müssen nicht auf zufällige Genmutationen warten, die sie fit für die Klimaerwärmung machen – die nötigen Genvarianten gibt es bereits. Das haben Biologen herausgefunden, indem sie Korallen aus warmen und kälteren Klimazonen miteinander kreuzten. „Um das Aussterben von Korallen zu verhindern, könnte etwas so Simples ausreichen, wie Korallen aus verschiedenen Breiten auszutauschen und damit die bereits existierenden Genvarianten zu verbreiten“, sagt Mikhail Matz von der Universität Texas in Austin.

Weiterlesen in der Zeit. Ähnliche Artikel erschienen beim ORF und Tagesspiegel

Hier die dazugehörige Pressemiteilung der University of Texas at Austin vom 25. Juni 2015:

Corals Are Already Adapting to Global Warming, Scientists Say

Some coral populations already have genetic variants necessary to tolerate warm ocean waters, and humans can help to spread these genes, a team of scientists from The University of Texas at Austin, the Australian Institute of Marine Science and Oregon State University has found.

The discovery has implications for many reefs now threatened by global warming and shows for the first time that mixing and matching corals from different latitudes may boost reef survival. The findings are published this week in the journal Science.

The researchers crossed corals from naturally warmer areas of the Great Barrier Reef in Australia with corals from a cooler latitude nearly 300 miles to the south. The scientists found that coral larvae with parents from the north, where waters were about 2 degrees Celsius warmer, were up to 10 times as likely to survive heat stress, compared with those with parents from the south. Using genomic tools, the researchers identified the biological processes responsible for heat tolerance and demonstrated that heat tolerance could evolve rapidly based on existing genetic variation.

„Our research found that corals do not have to wait for new mutations to appear. Averting coral extinction may start with something as simple as an exchange of coral immigrants to spread already existing genetic variants,“ said Mikhail Matz, an associate professor of integrative biology at The University of Texas at Austin. „Coral larvae can move across oceans naturally, but humans could also contribute, relocating adult corals to jump-start the process.“

Worldwide, coral reefs have been badly damaged by rising sea surface temperatures. Bleaching — a process that can cause widespread coral death due to loss of the symbiotic algae that corals depend on for food — has been linked to warming waters. Some corals, however, have higher tolerance for elevated temperatures, though until now no one understood why some adapted differently than others.

„This discovery adds to our understanding of the potential for coral to cope with hotter oceans,“ said Line Bay, an evolutionary ecologist with the Australian Institute of Marine Science in Townsville.

Reef-building corals from species in the northern Pacific Ocean and the Caribbean Sea are similar to those used in the study. There, too, reefs may benefit from conservation and restoration efforts that protect the most heat-tolerant corals and prioritize them for any restoration initiatives involving artificial propagation.

„This is occasion for hope and optimism about coral reefs and the marine life that thrive there,“ Matz said.

In addition to Matz and Bay, the study’s authors were Groves Dixon, Sarah Davies and Galina Aglyamova at UT Austin and Eli Meyer of Oregon State University.

This study was supported by funds from the National Science Foundation and the Australian Institute of Marine Science.

View a slideshow of images from the Great Barrier Reef.