Riffe können mit Korallenbleiche offenbar besser umgehen als gedacht

Klimaaktivisten sind einfallsreiche Gesellen. Sie können zu jeder Tag- und Nachtzeit neuen Klimaalarm erfinden. Wenn in Neuseeland ein Schaf umfällt, war es der Klimawandel, der es umgepustet hat. Fällt in Afrika ein Nilpferd in eine Schlucht, dann hat der Klimawandel das Sehvermögen des Tiers beeinträchtigt. Und wenn ein junger Eisbär in der Arktis tragisch verendet, war es ganz, ganz sicher auch wieder der Klimawandel – denn was sollte es denn sonst sein. Die Gleichschaltung aller Gedanken mit einer einzigen legitimen Lösung macht regelrecht Gänsehaut. War es nicht eine Errungenschaft des Wissenschaftszeitalters, alle Möglichkeiten zunächst einmal in Betracht zu ziehen und dann nach ausgewogener Abwägung mögliche Ursachen vorsichtig zu diskutieren? Diese Zeiten scheinen vorbei. In ihrem religiösen Eifer überbieten sich die jungen und alten Klimaaktivisten und werden vermutlich noch in eine Sternschnuppe einen Zusammenhang mit dem Klimawandel hineininterpretieren.

Die Korallenbleiche ist ein Lieblingsthema der Aktivistenzunft. Bei Hitzewellen kommt es durchaus vor, dass riesige Korallenflächen erbleichen und absterben. Wenn Aktivisten von einem solchen Ereignis Wind bekommen, setzen sie sich sogleich in den nächsten Flieger und düsen zum Tatort, um möglichst schockierende Aufnahmen zu machen und den Medien zuzuspielen. Seht her, der böse Klimawandel war der Mörder! Journalisten greifen das Thema sehr gerne auf. Schockierende Bilder und Katastrophen hat das zahlende Publikum schon immer interessiert. Wenn dann die Kameras wieder ausgeschaltet sind, die Aktivisten zurück in ihre Kommunen gekehrt sind, passiert in der Regel etwas Unerwartetes: Die Riffe erholen sich wieder. Das können sie, denn die Korallen tauschen einfach ihre Symbionten aus, eine altes Spiel (siehe hier, hier, hier).

Aktivisten drehen gerne dramatische Bilder und schnappen sich jedes offene Mikrofon, was nicht bei drei auf den Bäumen ist. Das Studium der Fachliteratur zum Thema Korallenbleiche gehört in der Regel nicht zum Tagesablauf eines Aktivisten. Dabei wäre da doch soviel zu entdecken. Hier ein paar Beispiele.

The Telegraph am 28. November 2017:

Hope for Great Barrier Reef with discovery of hardcore 100 able to withstand climate change
Australia’s Great Barrier Reef is more resilient to climate change and better able to regenerate itself than previously thought, scientists have said. A new study has revealed a collection of 100 individual reefs spread throughout the 2,000 mile-long marine ecosystem that not only withstand warming seas and attacking starfish but also protect others.

Hier die dazugehörige Pressemitteilung von PLOS (via Science Daily):

Resilience of Great Barrier Reef offers opportunities for regeneration
Regionally connected undisturbed reefs could provide larvae necessary to regenerate damaged reefs, but researchers warn that effective local protection is required.

New research has found that, despite the extensive damage to coral in recent events, there are still 100 reefs on the Great Barrier Reef that are well suited to promoting the regional recovery of the ecosystem after major disturbances. The results publishing 28 November in the open access journal PLOS Biology by Dr Karlo Hock, Prof Peter Mumby, and colleagues from the University of Queensland, CSIRO, the Australian Institute of Marine Science, and the University of Sheffield, suggest that these reefs not only appear to be less at risk of being exposed to damaging effects of bleaching and starfish predation, but are also well connected to other downstream reefs by ocean currents, and therefore possess the potential to provide coral larvae to support the recovery of other reefs.

Australia’s iconic Great Barrier Reef, a large coral ecosystem consisting of more than 3800 individual reefs, has recently been subjected to various disturbances, including unprecedented instances of coral bleaching events over the last two years, as well as ongoing and widespread outbreaks of the coral-eating crown-of-thorns starfish. This has yet again brought to public attention the current state of coral reefs worldwide and the challenges that need to be met to preserve them.

The new study identified 100 reefs that fulfil three highly desirable criteria to promote coral recovery. First, the reefs should lie in cool areas and rarely experience damage from coral bleaching themselves; this means that corals are relatively healthy on these reefs and able to supply larvae (fertilised eggs) to other reefs. Second, because larvae travel on ocean currents, reefs should be located in areas that supply larvae to as many reefs as possible. Third, while these reefs should supply coral larvae, they should not spread the larvae of the crown-of-thorns starfish. „Finding these 100 reefs is a little like revealing the cardiovascular system of the Great Barrier Reef,“ states author Professor Peter Mumby. „Although the 100 reefs only make up 3% of the entire GBR, they have the potential to supply larvae to almost half (45%) of the entire ecosystem in a single year.“

„The presence of these well-connected reefs on the Great Barrier Reef means that the whole system of coral reefs possesses a level of resilience that may help it bounce back from disturbances,“ says the paper’s lead author Dr Karlo Hock, „as the recovery of the damaged locations is supported by the influx of coral larvae from the non-exposed reefs.“ „Unfortunately, these findings by no means suggest that the Great Barrier Reef corals are safe and in great condition, and that there are no reasons for concern,“ Dr Hock cautions, „Indeed, the fact that the study only identified around a hundred of these reefs across the entire 2300km length of the massive Great Barrier Reef emphasises the need for both effective local protection of critical locations and reduction of carbon emissions in order to support this majestic ecosystem.

The research also indicates that focusing the efforts on these well-connected reefs and monitoring their health may be a step in the right direction, but the ecosystem remains vulnerable to the impacts of multiple stressors. „While more research is needed to determine to what extent the Great Barrier Reef will benefit from replenishment by these 100 reefs, given the scale of the recent disturbances, the importance of supporting such natural recovery mechanisms is likely to increase in future as climate change makes various disturbances more intense and unpredictable,“ Prof Mumby adds. „Saving the Great Barrier Reef is possible but requires serious mitigation of climate change and continued investments in local protection. We talk to management agencies frequently and our results can inform where they target on-the-ground actions.“

Paper: Karlo Hock, Nicholas H. Wolff, Juan C. Ortiz, Scott A. Condie, Kenneth R. N. Anthony, Paul G. Blackwell, Peter J. Mumby. Connectivity and systemic resilience of the Great Barrier Reef. PLOS Biology, 2017; 15 (11): e2003355 DOI: 10.1371/journal.pbio.2003355

Siehe auch Artikel bei ABC News.

Der General-Anzeiger aus Bonn berichtete zur gleichen Zeit über eine erfolgreiche Transplantation von Korallenlaich aus einem Teil des Great Barrier Reefs in einen anderen gefährdeten Teil. Das Projekt könnte helfen, beschädigte Ökosysteme weltweit wiederaufzubauen.

Gute Nachrichten auch im Juni 2017 in der südafrikanischen Times:

Global coral bleaching may be ending, US agency says
Coral reef bleaching may be easing after three years of high ocean temperatures, the longest such period since the 1980s, the National Oceanic and Atmospheric Administration said Monday. Its experts said satellite data and other analysis showed widespread bleaching was no longer occurring in all three ocean basins — Atlantic, Pacific and Indian — „indicating a likely end to the global bleaching event.“Scientists from the NOAA, an agency of the US Department of Commerce, said they will closely monitor sea surface temperatures and bleaching „over the next six months to confirm the event’s end.“

Weiterlesen in der Times.

Weitere gute Nachrichten von der israelischen Bar-Ilan University im Juni 2017:

Coral Reefs in the Gulf of Aqaba May Survive Global Warming, New Study Finds

Coral reefs in the Red Sea’s Gulf of Aqaba can resist rising water temperatures. If they survive local pollution, these corals may one day be used to re-seed parts of the world where reefs are dying. The scientists urge governments to protect the Gulf of Aqaba Reefs.

Coral reefs are dying on a massive scale around the world, and global warming is driving this extinction. The planet’s largest reef, Australia’s Great Barrier Reef, is currently experiencing enormous coral bleaching for the second year in a row, while last year left only a third of its 2300-km ecosystem unbleached. The demise of coral reefs heralds the loss of some of the planet’s most diverse ecosystems.

Now, scientists at EPFL (Ecole polytechnique fédérale de Lausanne) and UNIL (Université de Lausanne) in Switzerland, and the Mina and Everard Goodman Faculty of Life Sciences at Bar-Ilan University and the InterUniversity Institute of Marine Sciences in Israel, have shown that corals in the Gulf of Aqaba in the Northern Red Sea are particularly resistant to the effects of global warming and ocean acidification. The results were recently published in the journal Royal Society Open Science.

The implications are important, as the Gulf of Aqaba is a unique coral refuge. The corals may provide the key to understanding the biological mechanism that leads to thermal resistance, or the weakness that underlies massive bleaching. There is also the hope that the Gulf of Aqaba Reefs could be used to re-seed deteriorated reefs in the Red Sea and perhaps even around the world.

The Scientists performed the very first detailed physiological assessment of corals taken from the Gulf of Aqaba after exposure to stressful conditions over a six-week period. They found that the corals did not bleach.

“[Under these conditions,] most corals around the world would probably bleach and have a high degree of mortality,” says EPFL scientist Thomas Krueger. “Most of the variables that we measured actually improved, suggesting that these corals are living under suboptimal temperatures right now and might be better prepared for future ocean warming.”

At the InterUniversity Institute for Marine Sciences in Eilat, scientists exposed corals of the species Stylophora pistillata, collected from the Gulf of Aqaba, to water temperatures and acidification. The conditions resemble the summer conditions of a future ocean in this region if local ocean warming continues at its current rate of approximately 0.4-0.5°C per decade. They performed an overall health check of all the major physiological functions of the corals, measuring variables like energy metabolism, the ability to build a skeleton, and nutrient exchange at the molecular level between the coral-host and their algae symbionts. These physiological variables were mostly unaffected by the harsh experimental treatment. Still, further work on ecologically relevant variables like fertility or competitive performance is needed.

Symbiotic corals live together with an algae partner, much in the same way humans are in symbiosis with gut bacteria. Just as bacteria in the gut aid with digestion, providing valuable nutrients to the rest of the body, the algae that live within the coral-partner provide nutrients to the corals. The bacteria in our body thrive within our digestive tract, just as the algae benefit from living within the coral partner. Bleaching occurs when the colored algae are ejected by their coral-partner, and the symbiosis breaks down. If the algae do not return, the coral dies.

Pre-acclimated to thermal tolerance

The coral species Stylophora pistillata occurs in other regions of the world, and beyond the Gulf of Aqaba, does not necessarily demonstrate thermal resistance. The biological mechanism that underlies the robustness of the Gulf of Aqaba Reefs is still unknown, but the scientists have an idea of how the species evolved to become thermally resistant.

“Corals in the Gulf of Aqaba are pre-acclimated to thermal tolerance due to the special geography and recent history of the Red Sea,” says scientist Prof. Maoz Fine of Bar-Ilan University’s Mina and Everard Goodman Faculty of Life Sciences and the InterUniversity Institute of Marine Sciences.

At the end of the last ice age, corals started recolonizing the whole of the Red Sea through the southern connection to the Indian Ocean. The thermal bottleneck at the southern entrance with summer water temperatures rising to 30-32°C provided a selective barrier, allowing only highly resistant individuals to move north. Ironically, this heat-resistant founding population encountered much cooler waters once reaching the northern end, where the Gulf of Aqaba is located.

Based on this, the study hypothesized that these corals might be able to better cope with today’s ocean warming, considering that they not only descended from a heat-selected founding population, but they also started their warming trajectory from a lower temperature, compared to their counterparts in the central and southern Red Sea.

Protection of the Gulf of Aqaba Reef

Despite being resistant to global warming, the corals from the Gulf of Aqaba are still vulnerable to other stresses like pollution. “Local disturbances, such as local oil pollution, nutrients from fish farms, herbicides from gardening, may reduce the exceptionally high tolerance of the Gulf of Aqaba Reefs,” says Fine.

“This reef should receive international recognition as a natural site of great importance, because it might very well be one of the last reefs standing at the end of this century,” says Anders Meibom of EPFL and UNIL. “I would like to encourage the countries around the Gulf of Aqaba – Saudi Arabia, Egypt, Jordan and Israel – to get together and create a strong protection environmental program, because even if these corals are resistant to rising water temperatures, they are still sensitive to local pollution, overfishing etc, and they need to be protected from this now.”

Der eine oder andere Aktivist, der sich versehentlich in unser Blog verlaufen hat, mag nun bereits innerlich hoffen, dass diese Lawine an guten Nachrichten doch bitte ausreichen möge. Nein, diesen Gefallen können wir ihnen leider nicht tun es geht weiter, mit guten Nachrichten aus der Welt der Korallen. Pressemitteilung von frontiers (via Science Daily):

A super-algae to save our seas? Genetic engineering species to save corals
Foundation for genetically engineering a species of microalgae that lives in corals to stop a global coral bleaching catastrophe

Solutions to climate change, and particularly its effects on the ocean, are needed now more than ever. Coral bleaching caused by climate change is a huge threat to coral reefs. Recent extreme bleaching events have already killed corals worldwide and permanent destruction of reefs is projected within the century if immediate action is not taken. However, genetically engineering a group of microalgae found in corals may enhance their stress tolerance to ocean warming and save coral reefs.

Weiterlesen bei Science Daily

Weiter mit den guten Korallennachrichten, jetzt mit der University of Edinburgh, die im Oktober 2017 meldete:

Hardy corals make moves to build reefs from scratch

Resilient species of coral can move to inhospitable areas and lay the foundations for new reefs, a study shows. Edinburgh scientists have discovered that these tough, mobile corals can create their own stable habitats, which act as a base upon which other species can attach and build reefs. These hardy corals – known as coralliths – grow on pebbles or fragments of dead reefs, and they can survive being buffeted by waves and ocean currents.

Reef formation

The findings suggest many existing coral habitats – particularly those in areas dominated by sand and rubble – may have been created by coralliths. The ability of coralliths to establish themselves in harsh environments mean they could play a key role in efforts to conserve at risk habitats, the team says. Coralliths have previously been identified in the fossil record, and evidence suggests that they have played a role in reef formation since at least the last Ice Age, researchers say.

Tropical waters

Scientists from the Universities of Edinburgh, Glasgow and Heriot-Watt University made the discovery while carrying out fieldwork on coralliths in the tropical waters of the Maldives. They identified a variety of structures – from pea-sized balls to boulders several feet across – in places where corals would not otherwise be able to settle and survive. The study is published in the journal Scientific Reports. It was funded by the Natural Environment Research Council.

Dr Sebastian Hennige, School of GeoSciences: „For years we assumed that coral reefs, and small patches of coral in sandy habitats, needed stable ground on which to build. Now we know that corals can engineer their own stable environment from nothing, and create habitats for all sorts of species in places that we thought were unsuitable for reef formation.“

Der Standard am 5. Oktober 2017:

Superkorallen trotzen in Westaustralien der Bleiche

Artikel hier lesen.

Und abschließend noch die University of Califonia in Davis am 1. November 2017:

Can Corals Adapt to Climate Change? Corals Can Persist if Nations Control Emissions

Cool-water corals can adapt to a slightly warmer ocean, but only if global greenhouse gas emissions are reduced. That’s according to a study published Nov. 1 in the journal Science Advancesof genetic adaptation and the likely effects of future warming on tabletop corals in the Cook Islands. The study found that some corals in the normally cool waters of the Cook Islands carry genetic variants that predispose them to heat tolerance. This could help the population adapt more quickly to rising temperatures. But the preliminary results show they may not adapt quickly enough to outpace climate change. “These corals aren’t going to adapt at an unlimited rate,” said lead author Rachael Bay, a postdoctoral scholar at the University of California, Davis. “Keeping these reefs around requires curbing emissions.”

Simulating future climate

In previous work, the researchers identified genes that make some individual corals more heat tolerant than others. In the current study, they found these warm water variants in corals in the Cook Islands, at low levels. To test how well the corals could use these genes to adapt to future climate change, the scientists ran computer simulations based on projections by the U.N. Intergovernmental Panel for Climate Change. In a business-as-usual scenario, emissions continue to rise rapidly throughout the 21st century, and temperatures rise between 2 and 3.7 degrees Celsius. The least severe scenario is where warming does not exceed 1.8 degrees Celsius by 2100. In between is the moderate scenario suggested by the Paris Accord, in which emissions peak and then rapidly decline by about 2040.

In the simulations, coral could survive under the mild and moderate scenarios. But under the more severe scenarios, adaptation was not fast enough to prevent extinction. This research focused specifically on tabletop corals. Further study is needed to understand the broader implications for other coral species. “Many existing coral populations have a bank of adaptations that has been evolving for a long time,” said co-author Steve Palumbi from Stanford University. “Those existing adaptations are an asset for them to survive longer and for us humans to benefit longer.”

Helping species adapt

Reef-building corals are among the most vulnerable organisms to rising ocean temperatures. Over the past three years, coral reefs have experienced the worst bleaching and mortality events in recorded history, largely due to warmer waters. “This sort of framework could be used for any population we want to help adapt to future climate change, whether it’s corals or birds or insects,” Bay said. “It’s a way to integrate the genomic data to produce tangible, predictive outcomes.”