Gesunde Klimadiät: Ausgewogene Ernährung stärkt Korallen gegen Hitzwewellen

Den Korallen geht es ein bisschen wie dem Menschen: Eine gesunde ausgewogene Ernährung schützt am besten gegen Krankheiten und Unbill der Natur, zum Beispiel Hitzewellen. Die University of Miami Rosenstiel School of Marine & Atmospheric Science gab am 1. Oktober 2015 bekannt:

A Balanced Diet is Good for Corals Too, Study Finds

Researchers examine nutrient enrichment and bleaching resilience in Red Sea corals. A new study found that a nutrient-rich, balanced diet is beneficial to corals during stressful thermal events. The research led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science and the Centre Scientifique de Monaco concluded that the particular nutrient balance in seawater is what matters most. To test which nutrients were more beneficial to corals during elevated temperature conditions, the scientists fed them two types – inorganic nutrients of nitrogen and phosphorus commonly found in the ocean as a result of fertilizers and sewage runoff, and organic nutrients of zooplankton, tiny animals in the ocean that coral are known to feed on.

The research team placed specimens of the yellow scroll coral, Turbinaria reniformis, collected from the Red Sea in separate seawater tanks with varying temperature and nutrients. The corals were subjected to two different inorganic nutrient enrichment scenarios – increased nitrogen only or increased nitrogen and phosphorus at varying temperatures – 25 degrees Celsius to represent normal temperature conditions and 30 degrees Celsius to represent thermal stress conditions. Some of the corals also received organic nutrient enrichment of tiny ocean animals called zooplankton during the laboratory experiment. All of the corals were then returned to normal temperature conditions to examine their recovery.

“We found that the coral’s resilience to thermal stress totally depends on the kind of inorganic enrichment – if it’s ‘balanced’ or not,” said Erica Towle, an alumna of the UM Rosenstiel School. The researchers found that excess nitrogen alone and zooplankton made high-temperature bleaching events worse. While excess nitrogen in combination with extra phosphorus and zooplankton afford the coral resilience to bleaching. This study is one of the first to assess the three-way interaction between the two types of nutrients enrichment and thermal stress on coral health.  

The UM Rosenstiel School research team published a previous study in 2015 that showed the critically endangered Staghorn coral may benefit from supplemental nutrition to mitigate the adverse impacts of global climate change. The results revealed that temperature, CO2 and feeding each had significant effects on the coral’s growth rate. That study was the first to document that an endangered coral species, which was once found widely throughout South Florida and the Caribbean, can buffer the effects of increased CO2 in the ocean by increasing feeding rates. “Excess nutrients from land sources and thermal stress will likely occur in concert in the future so it’s important to assess them together,” said Towle. “Incorporating nutrient levels in thermal bleaching models will likely be very important for coral reef managers in the future as ocean waters warm.”

The study, titled “The relationship between heterotrophic feeding and inorganic nutrient availability in the scleractinian coral T. reniformis under a short-term temperature increase,” was published in the early online version of the journal Limnology and Oceanography. The study co-authors include: Erica Towle and Chris Langdon of the UM Rosenstiel School; Leila Ezzat and Christine Ferrier-Pagès of the Centre Scientifique de Monaco; and Jean-Olivier Irisson of the Sorbonne Universités Laboratoire d’Océanographie de Villefranche. Funding was provided by MOTE grant #POR-2012-22 and support from the Centre Scientifique de Monaco (CSM)

WUWT berichtete über ein Korallenriff in der Südsee zwischen Hawaii und Fidji, dass 2003 für tot erklärt wurde. Im ‚Totenschein‘ wurde damals Hitzetot eingetragen. Gut zehn Jahre später schaute man nocheinmal nach und stellte überraschenderweise fest, dass sich das Riff bester Gesundheit erfreute. Offenbar hatte man die Widerstandsfähigkeit der Natur unterschätzt, den Patienten zu früh für tot erklärt. Peinlich. Eine ähnliche Panne ereignte sich kürzlich am Great Barrier Reef. Wissenschaftler erklärten den Medien, dass es fünf vor zwölf stünde und es schlecht um die Korallen stünde. Taucher hingegen fanden, dasss lediglich 5% aller Korallen von den Problemen betroffen waren. So bauscht man Alarm künstlich auf.

Die Wildlife Conservation Society (WCS) sieht die Zukunft der Korallen realistisch: Einige Korallenarten kommen mit dem Hitzestress besser zurecht als andere, wie sie am 2. Mai 2017 per Pressemitteilung bekanntgab:

Some – But Not All – Corals Adapting to Warming Climate

A new WCS study reveals evidence that some corals are adapting to warming ocean waters – potentially good news in the face of recent reports of global coral die offs due to extreme warm temperatures in 2016. The study appears in the latest issue of Marine Ecology Progress Series.

The study looked at responses to extreme temperature exposures in the same reefs over time, and found less coral bleaching in 11 of the 21 coral species studied. WCS Senior Conservation Zoologist Tim McClanahan, who has been studying coral responses to climate change since the extreme temperatures of the1998 El Nino, authored the study.

The study took place in two marine national parks of Kenya. Looking at two similarly severe warming events in 1998 and 2016, McClanahan found that the number of pale and bleached coral colonies declined from 73 to 27 percent, and 96 to 60 percent in the two parks with different background temperatures. Most of this change was due to about half of the most common species that did not bleach strongly in 2016.  One rare species was, however, more sensitive than in 1998.

Bleaching takes place when stressed corals discharge beneficial algae that supply energy to corals causing them to turn pale or white and often starve. Worldwide, an estimated 60 percent of corals and 90 percent of coral species experienced bleaching due to unusually warm ocean water in 2016.

McClanahan says: “This was a rare chance to study bleaching responses during two separate times with very similar conditions. Adaptation is evident for some of the more important reef building corals but, sadly, many species are not adapting, so this is a good news-bad news story.”

But McClanahan warns: “Evidence for adaptation in the past is not evidence for adaptation in the future. Nevertheless, I suspect this adaptation to hot water started before my 1998 work and could have begun during the 1983 and 1988 El Niños, when coral bleaching was first observed in the region.”

Said Tim McClanahan: “Despite the many caveats and interpretation of these results, this study provides one of the first response-rate estimates for many common corals at the population level.  It therefore provides a basis for future studies and improving model predictions and the types of evaluations needed to address the future health of coral reefs.”

Global awareness continues to grow about the immediate threats facing coral reef ecosystems, and a global commitment to address those threats. In February, at the Economist World Ocean Summit in Bali, Indonesia, the ‘50 Reefs’ initiative was launched by the Global Change Institute of the University of Queensland and the Ocean Agency. The initiative brings together leading ocean, climate and marine scientists to develop a list of the 50 most critical coral reefs to protect, while leading conservation practitioners are working together to establish the best practices to protect these reefs.

Abschließend sei noch auf eine neue Datenbank zur Korallenbleiche hingewiesen, die eine wichtige statistische Basis für Studien bildet.