Neues zur Korallenbleiche

Immer wieder kommt es in den Korallenriffen der Welt zu Bleichereignissen. Dann sterben große Teil der Korallen ab und sehen ganz fahl aus. Zum Glück erholen sich die Riffe davon wieder, denn die Korallenbleiche ist so alt wie die Korallen selber, viele Millionen Jahre. Heute schauen wir im Schnelldurchlauf auf neue Forschungsresultate zum Thema Korallenbleiche. Interessierte Leser können sich in den verlinkten Arbeiten, Pressemitteilungen (PM) und anderen Berichten ein Bild zur Lage machen. Wem die englische Sprache etwas schwer fällt, dem sei das kostenlose Übersetzungstool DeepL empfohlen. Einfach den englischen Text in die linke Box kopieren und dann auf der rechten Seite auf deutsch lesen.

PM der Florida Institute of Technology von 2017. El Nino bringt den Korallen Krankheit und Bleiche:

Coral disease outbreaks fluctuate with El Niño years, new research finds

Study analyzes 18 years of data from 2,100 sites

Disease outbreaks in corals have followed El Niño-fueled coral bleaching events in the past, leading to speculation about the connection between the diseases and the El Niño cycles. This new study confirms the speculation. Occurrences of three common diseases affecting Caribbean corals spike during El Niño years, an alarming association given how climate change may boost the intensity of El Niños.

The findings from Florida Institute of Technology research associate Carly Randall and biology professor Rob van Woesik, published earlier this month in the journal Scientific Reports, are based on an analysis of 18 years of coral-disease data, at nearly 2,100 sites collected by the Atlantic and Gulf Rapid Reef Assessment Program. Those data were compared with 18 years of coinciding climate data to see if the disease cycles matched the climate cycles.

„We found that three coral diseases — white-band disease, yellow-band disease and dark-spot syndrome — peak every 2-4 years, and that they share common periodicities with El Niño cycles,“ Randall said. „Our results indicate that coral diseases cycle predictably and that they often correspond with El Niño.“ And because of the potential increase in the intensity of El Niño weather patterns associated with climate change, „our findings suggest that we might see diseases in corals ramping up in the coming decades,“ Randall added.

Because disease outbreaks in corals have followed El Niño-fueled coral bleaching events in the past, there was speculation about the connection between the diseases and the El Niño cycles, which are associated with warmer than usual weather in the Caribbean. This study, titled „Some coral diseases track climate oscillations in the Caribbean,“ confirms the speculation. Such climate-driven patterns in the ocean are similar to patterns described for malaria and dengue fever on the land, which are reported to track climate cycles.

Paper: C. J. Randall, R. van Woesik. Some coral diseases track climate oscillations in the Caribbean. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-05763-6

El Nino-Effekte auf Korallen erden auch von anderen Autoren beschrieben, z.B. von Tortolero-Langarica et al. 2017:

Historical insights on growth rates of the reef-building corals Pavona gigantea and Porites panamensis from the Northeastern tropical Pacific

Historical coral growth assessed by sclerochronology records provides an environmental retrospective and future perspective on the maintenance of coral-reef ecosystems. Three growth parameters, extension rate, skeletal density, and calcification rate were evaluated over the past two decade’s interval (1988–2013) in different gender of two massive corals Pavona gigantea and Porites panamensis. The species P. gigantea calcified two-times faster (0.84 ± 0.29 g cm−2 yr−1) than P. panamensis (0.36 ± 0.15 g cm−2 yr−1); and male colonies presents13-58% higher calcification rates than females. Annual growth parameters do not show significant trends over the period 1988–2013, but significant, growth disruption associated with ENSO events. The data presented here suggest that P.gigantea and P.panamensis from the area have developed phenotypic plasticity to a wide range of environmental condition; the life history of both species is reflected in their calcification rates during both optimal and non-optimal conditions over the last two decades. Massive species develop denser structures that provide a permanent habitat to many marine species and contributes to the long-term maintenance of coral reef communities in the eastern tropical Pacific.

Oder von McGowan & Theobald 2017:

ENSO Weather and Coral Bleaching on the Great Barrier Reef, Australia

The most devastating mass coral bleaching has occurred during El Niño events, with bleaching reported to be a direct result of increased sea surface temperatures (SSTs). However, El Niño itself does not cause SSTs to rise in all regions that experience bleaching. Nor is the upper ocean warming trend of 0.11°C per decade since 1971, attributed to global warming, sufficient alone to exceed the thermal tolerance of corals. Here we show that weather patterns during El Niño that result in reduced cloud cover, higher than average air temperatures and higher than average atmospheric pressures, play a crucial role in determining the extent and location of coral bleaching on the world’s largest coral reef system, the World Heritage Great Barrier Reef (GBR), Australia. Accordingly, synoptic‐scale weather patterns and local atmosphere‐ocean feedbacks related to El Niño–Southern Oscillation (ENSO) and not large‐scale SST warming due to El Niño alone and/or global warming are often the cause of coral bleaching on the GBR.

Oder von Lisboa et al. 2018:

El Niño, Sea Surface Temperature Anomaly and Coral Bleaching in the South Atlantic: A Chain of Events Modeled With a Bayesian Approach

Coral bleaching represents one of the main climate‐change related threats to reef ecosystems. This research represents a methodological alternative for modeling this phenomenon, focused on assessing uncertainties and complexities with a low number of observations. To develop this model, intermittent reef monitoring data from the largest reef complex in the South Atlantic collected over nine summers between 2000 and 2014 were used with remote sensing data to construct and train a bleaching seasonal prediction model. The Bayesian approach was used to construct the network as it is suitable for hierarchically organizing local thermal variables and combining them with El Niño indicators from the preceding winter to generate accurate bleaching predictions for the coming season. Network count information from six environmental indicators was used to calculate the probability of bleaching, which is mainly influenced by the combined information of two thermal indices; one thermal index is designed to track short period anomalies in the early summer that are capable of triggering bleaching (SST of five consecutive days), and the other index is responsible for tracking the accumulation of thermal stress over time, an index called degree heating trimester (DHT). In addition to developing the network, this study conducted the three tests of applicability proposed for model: 1‐ Perform the forecast of coral bleaching for the summer of 2016; 2‐ Investigate the role of turbidity during the bleaching episodes; and 3‐ Use the model information to identify areas with a lower predisposition to bleaching events.

Auch in vorindustrieller Zeit hat es Korallenbleichen am Great Barrier Reef gegeben, wie der Evening Express 2018 berichtete:

Coral bleaching dates back 400 years – study

[…] Dr Nick Kamenos from Glasgow’s School of Geographical and Earth Sciences said: “It’s clear in the core data we examined that bleaching has been occurring on the Great Barrier Reef for at least 400 years, but the frequency of bleaching events has increased markedly since the early 1800s and those events have affected 10% more corals since the late 1700s. “We can see that corals have been able to acclimate and recover from past bleaching events. […]

Aber steigt die Häufigkeit der Bleichereignisse wirklich an? Paul Homewood zeigt Daten, die ein anderes Bild erlauben.

Paper von Kamenos & Hennige 2018:

Reconstructing Four Centuries of Temperature-Induced Coral Bleaching on the Great Barrier Reef

Mass coral bleaching events during the last 20 years have caused major concern over the future of coral reefs worldwide. Despite damage to key ecosystem engineers, little is known about bleaching frequency prior to 1979 when regular modern systematic scientific observations began on the Great Barrier Reef (GBR). To understand the longer-term relevance of current bleaching trajectories, the likelihood of future coral acclimatization and adaptation, and thus persistence of corals, records, and drivers of natural pre-industrial bleaching frequency and prevalence are needed. Here, we use linear extensions from 44 overlapping GBR coral cores to extend the observational bleaching record by reconstructing temperature-induced bleaching patterns over 381 years spanning 1620–2001. Porites spp. corals exhibited variable bleaching patterns with bleaching frequency (number of bleaching years per decade) increasing (1620–1753), decreasing (1754–1820), and increasing (1821–2001) again. Bleaching prevalence (the proportion of cores exhibiting bleaching) fell (1670–1774) before increasing by 10% since the late 1790s concurrent with positive temperature anomalies, placing recently observed increases in GBR coral bleaching into a wider context. Spatial inconsistency along with historically diverging patterns of bleaching frequency and prevalence provide queries over the capacity for holobiont (the coral host, the symbiotic microalgae and associated microorganisms) acclimatization and adaptation via bleaching, but reconstructed increases in bleaching frequency and prevalence, may suggest coral populations are reaching an upper bleaching threshold, a “tipping point” beyond which coral survival is uncertain.

Siehe auch Bericht der GWPF zum Paper.

PM der Wildlife Conservation Society aus dem Oktober 2019:

Besides hot water, coral bleaching also about location, location, location

A new study revealed a more complex view than current standard predictions of coral bleaching events caused primarily by heat stress; rather, the scientists found that bleaching is driven by a variety of stressors, and each region responds differently.

As conservationists grapple with unprecedented levels of coral reef bleaching in the world’s warming oceans, scientists in the Indian and Pacific Oceans used the most recent El Niño of 2016 (the warmest year on record) to evaluate the role of excess heat as the leading driver of coral bleaching. The findings were, in a word, complicated, according to marine researchers from WCS (Wildlife Conservation Society) and other groups. Specifically, the WCS-led study revealed a more complex view than current standard predictions of coral bleaching events caused primarily by heat stress; rather, the scientists found that bleaching is driven by a variety of stressors, and each region responds differently. The authors note that any good predictions of the future will need to consider these complexities, specifically because they are important for effective policies, management, and conservation plans.

The new study titled „Temperature patterns and mechanisms influencing coral bleaching during the 2016 El Niño“ appears in the latest edition of Nature Climate Change. „Our results suggest that coral responses to global climate change may be changing as corals have different past experiences and tolerances to heat and stress,“ said Dr. Tim McClanahan, WCS Senior Conservation Zoologist and co-author of the study. „The consequence is that management and policies need to be aligned with the locations and types of stresses if we are to identify potential refugia and other priority actions for coral reefs.“

The widespread coral bleaching in the Indo-Pacific during the most recent El Niño event (2014-2017) was the latest in a series of thermal stresses to impact corals in the region, preceded by events in 1983, 1988, 1998, 2005, 2010, and 2013. The year 2016 brought about the most severe bleaching episodes, including extensive mortality in the Great Barrier Reef. Coral communities are symbiotic relationships between animals (corals) and algae that give their hosts color and sustenance. According to previous studies and field observations, coral bleaching generally occurs when corals expel their algae while under stress from water temperatures significantly above normal. Reefs closer to the warmer equator have also bleached more in the past and expected to degrade further in 2016.

But assessments made from the field during the study — with data collected from 226 sites stretching from East Africa to Fiji — found that coral bleaching patterns did not neatly align with past predictors of excess temperature and distance from the equator. Instead, bleached corals were highly variable in terms of warm water temperatures and location, with some reefs suffering bleaching levels of up to 60 percent and others surviving with no impact. To determine what other mechanisms are at work in coral bleaching events, the scientists evaluated 26 variables and more than 2000 models that were solved by a supercomputer to test the effects of factors such as thermal exposure, depth, habitat, coral community composition, and the types of management used in reef systems.

In terms of geography, the researchers found that bleaching depended greatly on where the corals lived along the longitudinal gradient from East Africa to Fiji, with the strongest bleaching observed in East Africa. Consequently, some regions, it seems, will be affected earliest and worse than other regions. Examining seawater temperatures 90 days before the bleaching, the researchers found that the best predictors of coral bleaching were highest average temperatures, how long cool water endured prior to peak temperatures, and the existence of two peaks in temperature. However, this depended on where the reefs were located, and East African reefs were found to be more stressed than reefs in Indonesia and Fiji. Thus, it was general stress rather than just warm water that affected corals the most, and some coral locations responded to stress better than others did.

Paper: Tim R. McClanahan, Emily S. Darling, Joseph M. Maina, Nyawira A. Muthiga, Stéphanie D ’agata, Stacy D. Jupiter, Rohan Arthur, Shaun K. Wilson, Sangeeta Mangubhai, Yashika Nand, Ali M. Ussi, Austin T. Humphries, Vardhan J. Patankar, Mireille M. M. Guillaume, Sally A. Keith, George Shedrawi, Pagu Julius, Gabriel Grimsditch, January Ndagala, Julien Leblond. Temperature patterns and mechanisms influencing coral bleaching during the 2016 El Niño. Nature Climate Change, 2019; DOI: 10.1038/s41558-019-0576-8

PM des Florida Institute of Technology aus dem März 2019:

Coral reefs near equator less affected by ocean warming

Research based on analysis of field observations from 20-year global coral survey

Ocean warming is threatening coral reefs globally, with persistent thermal stress events degrading coral reefs worldwide, but a new study has found that corals at or near the equator are affected less than corals elsewhere. The findings from Florida Institute of Technology Ph.D. student Shannon Sully and professor Rob van Woesik, along with colleagues at the University of California at Santa Barbara and Reef Check, were published March 20 in the journal Nature Communications.

The work, which was supported by the National Science Foundation and the Zegar Family Foundation, was based on analysis of field observations from a 20-year global survey of over 3,500 coral study sites led by Reef Check founder and former director Gregor Hodgson. As expected, coral bleaching was most common in localities experiencing high-temperature stress, but it was significantly less common in those places with high monthly variation in temperatures. „We found that it took higher temperatures to bleach corals this past decade than it did 20 years ago,“ Florida Tech’s Shannon Sully said.

The authors suggest that bleaching at higher temperatures this decade is likely a consequence of the decline in temperature-sensitive corals during previous bleaching events and that the remaining populations now have a higher thermal threshold for bleaching. „We found that the reefs near the Equator were less affected by bleaching than elsewhere, despite similar thermal-stress levels at equatorial sites,“ said Deron Burkepile, a co-author from UCSB. Rob van Woesik, professor and director of the Institute for Global Ecology at Florida Tech, said even with the new analysis, some questions remain.

„We are uncertain why equatorial reefs are more tolerant of recent temperature stress, but we do know that we must protect these equatorial reefs — and reefs everywhere — from other disturbances, lest we lose coral reefs that protect coastal inhabitants from storm waves and help feed millions of people worldwide,“ he said. Jan Freiwald, Reef Check’s executive director, added that he was glad to see Reef Check’s data put to good use. „Reef Check’s citizen science divers work hard to survey reefs all over the world so that we have the data we need to understand our reefs and make effective management decisions in a changing planet,“ he said.

Paper: S. Sully, D. E. Burkepile, M. K. Donovan, G. Hodgson, R. van Woesik. A global analysis of coral bleaching over the past two decades. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-09238-2

PM von PLOS aus dem April 2018:

Great Barrier Reef coral predicted to last at least 100 years before extinction from climate change

Model predicts rapid adaptation of corals despite increasingly severe bleaching events, but corals‘ more distant future remains uncertain

A common Great Barrier Reef coral species has enough genetic diversity to survive at least 100 years before succumbing to global warming predicts Mikhail Matz of the University of Texas at Austin and colleagues. They report these findings in a new study published April 19th, 2018 in PLOS Genetics.

A warming climate, ocean acidification and destruction of coral habitats have all taken a significant toll on coral populations along the Great Barrier Reef. Previous studies offered hope that corals can adapt to warming conditions but no one knows if they can outpace climate change. Matz and his colleagues developed a model to estimate the ability of the common coral species Acropora millepora to evolve by redistributing existing heat-tolerance genes, taking into account the coral’s present-day genetic diversity and how far its larvae migrate before settling down. The model predicts that the coral will become more sensitive to temperature swings, which will cause occasional die-offs, but that coral populations will successfully adapt to temperatures along the Great Barrier Reef and survive at least another century. Whether corals will be able to adapt any further is uncertain and depends on several currently unknown parameters of coral genetics.

This study of a common inhabitant of the Great Barrier Reef is a rare optimistic contribution to our understanding of how a species can adapt to changing climate conditions. The findings show that recent catastrophic coral bleaching events do not necessary signal imminent coral demise and can also inform reef management strategies, suggesting that interventions that help reshuffle coral genetic diversity among reefs will likely increase the coral’s odds for survival in the near future.

Paper: Mikhail V. Matz, Eric A. Treml, Galina V. Aglyamova, Line K. Bay. Potential and limits for rapid genetic adaptation to warming in a Great Barrier Reef coral. PLOS Genetics, 2018; 14 (4): e1007220 DOI: 10.1371/journal.pgen.1007220

Siehe auch Bericht auf WUWT.

PM der University of California – Irvine aus dem April 2018:

Bleaching of coral reefs reduced where daily temperature changes are large

By taking a closer look, scientists find resilience in face of heat stress

Coral reef bleaching is stark evidence of the damage being inflicted by global climate change on marine ecosystems, but a research team led by scientists at the University of California, Irvine has found some cause for hope. While many corals are dying, others are showing resilience to increased sea surface temperatures, pointing to possible clues to the survival and recovery of these vitally important aquatic habitats.

„Field observations have shown a heterogeneity or patchiness of the bleaching process at the reef scale, which means that some corals are responding differently to heat stress,“ said Aryan Safaie, lead author of a study published today in Nature Communications. „We know that some species are more thermally tolerant than others,“ he added. „But our study shows additionally that certain locations within a reef might be more amenable to allowing corals to persist in the face of increasing water temperature.“

To reach this conclusion, Safaie, a Ph.D. student in UCI’s Department of Civil & Environmental Engineering, said it was necessary to examine reefs more closely in terms of both space and time, versus relying solely on satellite remote-sensing products. He and his collaborators analyzed decades‘ worth of field data collected at 118 locations spanning five coral reef regions around the world, including the Great Barrier Reef near Australia and sites in the Indian Ocean, Pacific Ocean, Caribbean Sea and the Red Sea.

„Satellite images are indispensable in giving us the big picture and providing tools for long term projections of ocean health,“ he said. „But, these spacecraft collect data only once or twice weekly, there just isn’t enough to provide a clear understanding of the daily and hourly variability of ocean conditions unless you’re looking at more frequently reported field observations.“ The team found that in reef locations with more high-frequency temperature variability — water temperature spiking during the day and dropping at night, day in and day out — severe bleaching was less likely to occur.

„We think of corals as these thermally sensitive organisms, and that temperature variability would mean they would have a harder time all the time,“ said coauthor Kristen Davis, UCI assistant professor of civil & environmental engineering and Earth system science. „Instead, what we found is that higher daily temperature variability made corals stronger and more resilient when a thermal stress event came along.“

The upshot of this work, according to Davis, is that scientists now have a better way to predict the outcome of coral reef bleaching events, which can lead to better conservation strategies. „As we move into a time when corals are threatened by global warming, if there are some living corals remaining on a reef after a bleaching event, there will be some genetic material to repopulate the reef with corals that are more thermally resilient,“ she said. Davis said further work is needed to identify where these super corals live, so that those areas can be protected from over fishing and development.

Paper: Aryan Safaie, Nyssa J. Silbiger, Timothy R. McClanahan, Geno Pawlak, Daniel J. Barshis, James L. Hench, Justin S. Rogers, Gareth J. Williams, Kristen A. Davis. High frequency temperature variability reduces the risk of coral bleaching. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-04074-2

PM der Duke University aus dem Juni 2018:

Local interventions boost coral’s resilience to bleaching

Corals fared better after researchers picked off some snails

Local conservation actions, like rounding up predatory snails, can significantly boost the resilience of corals to climate-induced bleaching, according to a study led by Duke University researchers.

The study, published June 18 in Nature Ecology & Evolution, comes at a time when scientists are deeply divided over whether local efforts to protect and manage coral reefs are enough to help stem the global tide of thermal bleaching that’s decimating corals worldwide as ocean temperatures continue to warm. To test whether local actions can make a difference, the Duke-led team focused on one threat to reefs that is often controlled by local managers — populations of coral-eating animals like snails and starfish that have become too abundant.

„At high densities, these coral-eating animals, or ‚corallivores‘, can cause low-grade but chronic stress to corals. Some of them are like Dracula, constantly sucking the energetic reserves out of corals and leaving them less equipped to deal with harsh environmental conditions like extreme warm temperatures and bleaching,“ said Elizabeth Shaver, a 2018 doctoral graduate of Duke’s Nicholas School of the Environment, who is now a coral restoration scientist with The Nature Conservancy’s Reef Resilience Program.

To get a global sense of how managers deal with this threat, the researchers surveyed more than 30 coral reef management agencies worldwide, finding that many agencies reduce local corallivore populations in their sites. The researchers then mimicked managers by manually removing a voracious and common coral-eating snail from corals in the Florida Keys during a three-month spike in ocean temperatures in 2014. That warmup caused widespread coral bleaching across much of the eastern Caribbean and Gulf of Mexico.

The researchers focused their efforts on brain corals, which were found in a survey of six corals reefs in the Florida Keys to be particularly susceptible to predation by the snail. „The idea was to see if removing these snails helped corals withstand and recover from warm temperatures and bleaching compared with corals that had average or naturally high densities of snails. And it did,“ said Shaver. „When snails were removed, corals experienced only 50 percent bleaching. Corals that still had high snail densities experienced near 100 percent,“ Shaver said.

In November 2014, they returned to the reefs after water temperatures cooled down and measured the extent of dead tissue on the corals. „We found that if a coral experienced only mild to moderate bleaching, as they did when snails were removed, it recovered almost completely,“ said Brian Silliman, Rachel Carson Associate Professor of Marine Conservation Biology at Duke’s Nicholas School of the Environment. „But if it experienced severe bleaching like the corals with high snail densities, tissue recovery was reduced by more than 80 percent,“ Silliman said. „Some of these corals completely died, turning into algae-covered underwater basketballs. Removing or reducing the populations of snails played an important role in determining these outcomes.“

The new findings challenge several recent large-scale analyses arguing that local impacts and management have little effect in protecting reefs from climate-induced bleaching, Silliman said. „Tens of millions of dollars have been invested in local coral reef conservation over the last 40 years. But more and more people are now saying we should end this approach and instead put most of our money into global efforts to reduce greenhouse gas emissions because there’s no evidence that local actions are making enough of a difference,“ he said.

„These new findings reopen the discussion and provide a ray of hope for corals by showing that local interventions do make a difference.“ „Very few local interventions have been tested for their ability to enhance coral reef resilience,“ Shaver said. „We found one simple solution by reducing coral predation stress, which can be done through removals or possibly in marine protected areas where studies show coral-eating invertebrates are naturally less abundant.“ The findings may also be important because the world’s climate is projected to continue changing even if carbon emissions were drastically reduced today. „We need conservation dollars for both global and local efforts,“ said Shaver, „so we can identify other resilience-enhancing approaches and arm local managers with tools to protect their reefs and resources.“

Paper: Elizabeth C. Shaver, Deron E. Burkepile and Brian R. Silliman. Local Management Actions Can Increase Coral Resilience to Thermally Induced Bleaching. Nature Ecology & Evolution, 2018 DOI: http://dx.doi.org/10.1038/s41559-OT80589-0

PM der University of Plymouth vom Juli 2018:

Immunity could be key to addressing coral crisis

Coral reefs support a quarter of all marine life, feed hundreds of millions of people and contribute vastly to the global economy. But they are dying in mass bleaching events, as climate change warms our oceans and breaks down vital relationships between corals and energy-providing algae.

A new commentary, published in Nature’s Communications Biology, provides hope that a shift in research focus towards coral immunity will support reef conservation and restoration efforts.

Dr Caroline Palmer, Visiting Research Fellow at the University of Plymouth, has spent more than a decade examining coral health from an immunological perspective. In particular, she has identified coral immune mechanisms and sought to understand what enables some corals to survive while others die. This led Dr Palmer to discover that corals with higher immune defences are less likely to become diseased or to bleach.

In her latest work, she expands on this observation, drawing on a theory from insects that explains how corals might coexist with specific microorganisms, as a ‚holobiont‘, while resisting infection or other disturbances. Dr Palmer also presents a model of coral susceptibility, whereby investing in immunity enables coral, with its microorganisms, to tolerate more damage before initiating an immune response. This model describes how coral tolerance may vary among corals indicating their susceptibility to disturbances, such as bleaching events.

„There is no question that climate change is devastating coral reef systems. But if we are to conserve or restore them, we need to understand coral health — what drives tolerance and how can we promote it,“ Dr Palmer says. „If you have a strong immune system, and the energy to support it, you are more likely to be healthy and to survive adverse conditions.“

Dr Palmer first started examining the immune systems of reef-building corals more than a decade ago, and her PhD was the first research to look at the subject in depth. But she says that coral immunity remains an under-studied area of research. Coral bleaching, on the other hand, has been a research focus for decades, though is often considered distinct from immunity — Dr Palmer, however, suggests it is a component of coral holobiont immunity.

Dr Palmer also proposes an immunological model by which corals may increase their tolerance to adverse conditions — suggesting a way coral may adapt to new, more extreme, conditions. Dr Palmer, who is currently Lead Scientist on the Seeking Survivors project examining coral health in Costa Rica, added: „Coral biologists are racing to conserve coral reefs before it’s too late. There is currently a lot of interest in creating more tolerant corals through genetic engineering and of restoring reefs by targeting more resilient corals. I fully support these approaches, but believe understanding what drives coral health will be key to their success.“

Paper: Caroline V. Palmer. Immunity and the coral crisis. Communications Biology, 2018; 1 (1) DOI: 10.1038/s42003-018-0097-4

PM der University of Miami Rosenstiel School of Marine & Atmospheric Science aus dem August 2018:

Some corals might adapt to climate changes

Study exposes two threatened corals to future climate change conditions

New research shows that not all corals respond the same to changes in climate. The University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science-led study looked at the sensitivity of two types of corals found in Florida and the Caribbean and found that one of them — mountainous star coral — possesses an adaptation that allows it to survive under high temperatures and acidity conditions.

„Stressful periods of high temperature and increasingly acidic conditions are becoming more frequent and longer lasting in Florida waters,“ said Chris Langdon, marine biology and ecology professor and lead author on the new study. „However, we found that not all coral species are equally sensitive to climate change and there’s hope that some species that seemed doomed may yet develop adaptations that will allow them to survive as well.“

The researchers exposed two threatened Caribbean reef-building coral species, staghorn coral (Acropora cervicornis) and mountainous star coral (Orbicella faveolata), were exposed to combinations of normal (26 degrees Celsius) and elevated temperature (32 degrees Celsius) and increased carbon dioxide levels (pH 7.8/800 ppm) for nine weeks. Genetic and physiological data such as skeletal growth was then collected on the corals to determine if stress events are recorded in a coral’s skeletal history.

At the end of the nine weeks any corals that were still surviving were recovered at the cool temperature and normal pH to determine the capacity of these corals to bounce back once environmental conditions became more hospitable as naturally occurs as summer transitions into fall.

The researchers found that the staghorn coral was more sensitive to heat stress. It experienced 100 percent mortality after 25 days at the elevated temperature of 1.5 degrees Celsius above the historical maximum monthly mean temperature for the Florida Keys. South Florida waters could begin to experience hot spells of this intensity and duration once every five years by 2035, which according to the researchers suggests that the species could become increasingly rare within 20 years.

The mountainous star coral survived 62 days at the elevated temperature and quickly recovered when temperature was reduced at the end of the experiment. Reduced pH did not affect survival but did significantly impact growth under normal temperatures.

„Based on these results we predict that mountainous star coral will very conservatively be able to tolerate any warming the Florida Keys is likely to experience now until 2060 and very possibly to the end of the century,“ said Langdon. „This optimistic prediction needs to be qualified by the fact that decreasing pH will impact the reproductive potential of this species. While the decreasing pH won’t kill the corals outright it will mean that fewer baby corals will be produced to replace adult corals that die of natural or unnatural causes.“

Coral reefs are especially vulnerable to climate change because they are easily affected by warm water. When ocean temperatures rise, the algae that give coral its bright colors leave their host, causing it to look white, a condition known as ‚coral bleaching‘. The loss of algae, which provide coral with much of its energy, make corals vulnerable to starvation and disease.

The mountainous star coral had special algae, called D symbionts, which the researchers believe made it able to adapt to the experimental climate change conditions.

Rapidly warming oceans are resulting in more frequent and severe mass bleaching events, while the uptake of CO2 by the surface ocean is driving down the pH making it more difficult for corals and other organisms to build their skeleton and shells.

The study allows researchers to better understand how corals respond to heat stress and ocean acidification, which is important since these conditions are expected to affect corals in coming decades and to understand how these stressors are recorded in coral skeletons.

Paper: Chris Langdon et al. Two threatened Caribbean coral species have contrasting responses to combined temperature and acidification stress. Limnology and Oceanography, July 31, 2018 DOI: 10.1002/Ino.10952

PM der Penn State aus dem August 2018:

Diverse symbionts of reef corals have endured since ‚age of dinosaurs‘

Coral-algal partnerships have endured numerous climate change events in their long history, and at least some are likely to survive modern-day global warming as well, suggests an international team of scientists.

The team’s conclusion is based on the finding that the relationship between corals and the mutualistic micro-algae that enable them to build reefs is considerably older and more diverse than previously assumed. „Past estimates placed the initiation of these symbiotic relationships at 50 to 65 million years ago,“ said Todd LaJeunesse, associate professor of biology, Penn State. „Our research indicates that modern corals and their algal partners have been entwined with each other for much longer — since the time of the dinosaurs, approximately 160 million years ago. During their long existence, they have faced severe episodes of environmental change, but have managed to bounce back after each one.“

According to LaJeunesse, the micro-algae, commonly called zooxanthellae — of the dinoflagellate family Symbiodiniaceae — live inside the cells of corals, allowing them to acquire energy from sunlight and to build the massive, economically valuable reef formations upon which countless marine organisms rely for habitat. „The fossil record shows that today’s reef-building corals exploded in diversity around 160 million years ago,“ said LaJeunesse. „Finding that the origin of the algal symbionts corresponds to major increases in the abundance and diversity of reef-building corals implies that the partnership with Symbiodiniaceae was one of the major reasons for the success of modern corals.“

The team used genetic evidence — including DNA sequences, phylogenetic analyses and genome comparisons — to calculate the micro-algae’s approximate age of origin. They also used classical morphological techniques in which they compared visual characteristics of these symbionts using light and electron microscopy, along with computer modeling and other methods, to discover that in addition to being older, the algae family is far more diverse than previously perceived. The results appear online today (Aug. 9) in Current Biology.

„Presently, numerous algal lineages, called clades, are lumped into just one genus,“ said John Parkinson, postdoctoral researcher, Oregon State University. „Using genetic techniques, we provide evidence that the family actually comprises at least 15 genera, including hundreds and possibly thousands of species worldwide.“ This is important, he explained, because some micro-algal symbionts have characteristics that make them more resilient to changes in the environment than other symbionts.

„The updated naming scheme offers a clear framework to identify different symbionts,“ said Parkinson. „Accurate taxonomy (the identification and naming of species) is a critical step in any biological research. This is especially true for studies attempting to understand how the partnership between reef corals and their micro-algae, which are needed for survival and growth, may adapt to climate change. For example, when many corals are exposed to high temperatures they lose their symbiotic algae and die. Others are far more tolerant of heat, and some of this resilience is based on the species of algae they have.“ Parkinson noted that the team has been working for close to a decade to modernize coral symbiont taxonomy in order to improve communication among scientists and advance future research on reef corals.

„Until now, studies on the physiology and ecology of these algae attempted to compare apples to apples,“ said Parkinson. „Considering how different some of them are, we now recognize that often we were comparing apples to oranges. These changes will help researchers to think more accurately about the comparisons they are making in experiments.“

Paper: Todd C. LaJeunesse, John Everett Parkinson, Paul W. Gabrielson, Hae Jin Jeong, James Davis Reimer, Christian R. Voolstra, Scott R. Santos. Systematic Revision of Symbiodiniaceae Highlights the Antiquity and Diversity of Coral Endosymbionts. Current Biology, 2018; DOI: 10.1016/j.cub.2018.07.008

PM von PeerJ aus dem August 2018:

Corals are becoming more tolerant of rising ocean temperatures

Scientists replicate landmark study to determine changes in coral sea temperature tolerance over time. In the three species of Hawaiian corals retested, bleaching occurred later, with higher survivorship and growth rates than the same species of corals in 1970. However, scientists warn that temperatures are rising faster than corals can change.

The existence and causes of coral bleaching are recognized as an increasing world-wide environmental concern related to climate change. A number of experiments have been conducted since the early 1970s at the Hawai’i Institute of Marine Biology’s (HIMB) Coral Reef Ecology Laboratory in Kane’ohe Bay, Hawai’i and the Mid-Pacific Marine Laboratory (MPL) at Enewetak, Marshall Islands to determine the long-term temperature thresholds inducing coral bleaching. A new study published in PeerJ — the Journal of Life & Environmental Sciences replicates 1970s experiments and provides encouraging evidence to suggest corals today are adapting at an unexpectedly rapid rate. Still, these rates are being outpaced by rising ocean temperatures.

Coral bleaching is a process wherein corals lose their symbiotic algae, zooxanthellae, which provide a significant food source and color to their coral host. The white coral skeleton is then visible through the transparent tissues giving the characteristic „bleached“ appearance. Mortality will occur if the coral and symbiont relationship is not reestablished shortly.

The 1970s experiments were the first to simulate elevated temperature stress in a flow-through seawater system, and the results duplicated the effects of high temperature events that have become increasingly wide-spread, frequent and severe in coral habitats worldwide in the last 35 years. Results determined temperature tolerances of corals were very low, only +1-2ºC above the normal maximum temperatures. Although temperatures varied geographically, most coral species began to bleach within this range.

The identical system, methodology, and location of the initial 1970s experiment was replicated in 2017 with one of the original researchers, Dr. Steve Coles. This provided an unique opportunity to evaluate whether coral bleaching thresholds have changed in nearly half a century. Corals were held at ambient and elevated temperatures comparable to the 1970 experiment for a one-month exposure, followed by a 28 days recovery period.

„To better understand coral acclimatization and adaptation, most studies compare corals from different reef locations, whereas this is the first study to compare the same coral species from the same location over time. Re-running a 48-year old experiment using the same coral species, same experimental setup, and same observer allows us to directly test changes in coral temperature tolerance over the last half century,“ according to Dr. Keisha Bahr.

Differences between the two experiments were dramatic. Results show a substantial increase in temperature tolerance within the tested corals. In the three species of Hawaiian corals retested, bleaching occurred later, with higher survivorship and growth rates than corals in 1970. In 2017, survivorship was significantly higher (60-92%) as compared to 1970 (0-40%). Under elevated temperatures, calcification growth rates were reduced by an average of 26-63%, whereas in 1970, average calcification reductions ranged between 99-173%.

Such dramatic differences in coral bleaching temperature thresholds indicate a capacity for adjustment in temperature tolerance, either by changes in physiological process or shifts in symbiotic zooxanthellae types (acclimatization), or natural selection for the survival of more temperature tolerant corals (adaptation). Until now, it had not been determined how long these processes take or if this change can occur at a pace rapid enough to adjust to the frequency and severity of current elevated temperature events.

„Although these results are encouraging in their indication that acclimatization/adaptation of corals and their symbionts can occur at an unexpectedly rapid rate, increased bleaching tolerance may not be enough for widespread coral survival“ Dr. Ku’ulei Rodgers said.

„A possible influence on the results may be the substantially higher water quality in the Kane’ohe Bay in 2017 as compared to 1970 due to nearby secondary treated sewage release at the time. Elevated levels of dissolved nitrogen have been implicated in stimulating coral bleaching. When verified, this will support the importance of reducing land-based source nutrients to assist management in limiting coral bleaching and mortality,“ according to Dr. Steve Coles.

The slow growth and recruitment of many species of corals, combined with repetitive bleaching events of increasing severity and duration, may lead to catastrophic regional reductions in coral diversity and abundance. To prevent or even mitigate, this will require reduction in use of fossil fuels and lower emissions of CO2 and other greenhouse gases that are increasing air and seawater temperatures worldwide at an alarming rate.

Paper: Steve L. Coles, Keisha D. Bahr, Ku’ulei S. Rodgers, Stacie L. May, Ashley E. McGowan, Anita Tsang, Josh Bumgarner, Ji Hoon Han. Evidence of acclimatization or adaptation in Hawaiian corals to higher ocean temperatures. PeerJ, 2018; 6: e5347 DOI: 10.7717/peerj.5347

PM der University of California – Davis aus dem September 2018:

Large stretches of coral reefs can be rehabilitated

New ’spider‘ technique found to help coral reefs. Coral reefs can be rehabilitated over large scales using a relatively inexpensive technique.

Even after being severely damaged by blast fishing and coral mining, coral reefs can be rehabilitated over large scales using a relatively inexpensive technique, according to a study led by the University of California, Davis, in partnership with Mars Symbioscience.

For the study, published this week in the journal Restoration Ecology, researchers installed 11,000 small, hexagonal structures called „spiders“ across 5 acres of reef in the center of Indonesia’s Coral Triangle. Coral diversity is the highest on Earth in that region but is threatened by human activity, including overfishing, pollution and climate change.

Between 2013 and 2015, researchers attached coral fragments to the structures, which also stabilized rubble and allowed for water to flow through freely.

A CORAL SUCCESS STORY

Live coral cover on the structures increased from less than 10 percent to more than 60 percent. This was more than what was reported for reefs in many other areas of the Coral Triangle, at a cost of about $25 per square meter.

„Coral reef rehabilitation and restoration efforts are rapidly increasing around the world, but there are few large-scale examples of successful projects,“ said corresponding author Christine Sur, who was a UC Davis graduate student at the time of the study. „Our study demonstrates a cost-effective, scalable method that can inform other coral reef restoration efforts aimed at reducing the global decline of these valuable and unique ecosystems.“

Of particular surprise, while massive coral bleaching decimated other parts of the world between 2014 and 2016, bleaching in the rehabilitation area was less than 5 percent, despite warm water conditions known to stress corals.

A SCIENTIST’S LEGACY

The study is one of the last publications led by Susan Williams, a professor and marine biologist with the UC Davis Bodega Marine Laboratory and Department of Evolution and Ecology who passed away in April 2018.

„Collaboration played a key role in the study’s outcome,“ said corresponding author Jordan Hollarsmith, a doctoral candidate in the UC Davis Graduate Group in Ecology at Bodega Marine Laboratory. „Dr. Williams‘ dedication to building true partnerships between industry, local scientists and the people who live by the reefs she worked to rebuild was critical to this project’s success.“

Mars Symbioscience, a business segment of Mars, Incorporated, initiated the project in 2013 in collaboration with local residents on the islands.

„This research is an important step in demonstrating how coral can be restored to a higher degree of cover quite quickly and at a relatively low cost,“ said Frank Mars, vice president of Mars Sustainable Solutions. „Healthy coral reef ecosystems provide natural coastal protection and are the foundation for many local fisheries, as well as jobs for tourism. They also play a critical role in the Mars supply chain as they provide food security and work for the families and communities we rely on to grow the raw materials we use in our brands around the world. For Mars, helping restore coral reefs is not only a business issue, it’s also the right thing to do to ensure the planet, people, and communities that rely on them are healthy and thriving.“

BUYING TIME TO REVERSE THE DECLINE

Coral reefs are declining worldwide. Reversing their decline will require fully addressing climate change and other human impacts, the study said. For instance, illegal fishing, lack of island sanitation systems, threatened seagrass communities and marine debris such as plastic pollution are common issues in Indonesia and many tropical environments. People living in small island communities in this region also have few alternatives to fishing livelihoods and often lack access to education about the ocean environment.

In the meantime, the „spider“ technique and restoration projects offer a way to rehabilitate large swaths of coral reefs and the communities that depend on them, giving the reefs a chance to adapt or acclimate to worsening ocean conditions.

Paper: Susan L. Williams, Christine Sur, Noel Janetski, Jordan A. Hollarsmith, Saipul Rapi, Luke Barron, Siobhan J. Heatwole, Andi M. Yusuf, Syafyudin Yusuf, Jamaluddin Jompa, Frank Mars. Large-scale coral reef rehabilitation after blast fishing in Indonesia. Restoration Ecology, 2018; DOI: 10.1111/rec.12866

PM der Oxford University Press USA aus dem Oktober 2018:

Higher temperatures could help protect coral reefs

A new study in the journal Behavioral Ecology, published by Oxford University Press, suggests that higher water temperature, which increases the aggressiveness of some fish, could lead to better protection of some coral.

In the face of global warming, recent years have seen an increasing number of studies predicting the future of corals. It is well established that higher water temperatures lead many corals to die. Over the past century, global temperature has increased by 1°F. Meanwhile, research has shown that coral recovery can be significantly influenced by the behavior of species living around coral reefs.

Researchers here evaluated the relationship between fish behavior and coral performance using a farmerfish-coral system. Farmerfish (stegastes nigricans) are aggressive damselfish found around coral reefs in tropical climates that defend gardens of algae from intrusion by other fish. This study tested the relationship between coral recovery rates and the level of aggression exhibited by farmerfish groups when defending their gardens. The researchers did so by planting small coral fragments into farmerfish territories with different levels of aggressiveness.

The researchers collected data from 29 farmerfish colonies in French Polynesia from 2016 and 2017. They evaluated the average aggressiveness of each farmerfish group as well as the group’s reaction when intruders entered the farmerfish group’s territory.

Researchers found that more branching corals resided in the territories of aggressive farmerfish groups. In addition, corals experimentally planted into the territories of non-aggressive farmerfish suffered 80 percent more damage than the corals planted into the territories of aggressive groups.

Researchers also found that farmerfish groups composed of larger animals were more aggressive. However, follow-up analyses showed that group aggressiveness mattered more than group member size in determining coral success. Fish aggressiveness is therefore likely to be an important part of how coral reefs will grow and survive in future environments.

While warming oceans negatively impacts a variety of biological processes, this study hints that warmer temperatures, which often increase fish aggressiveness, could enhance the protective function of farmerfish for nearby corals.

„Predicting the future of corals will require a systems approach. Failing to account for broader ecological processes, such as species interactions, could lead us to issue the wrong predictions about how some corals will fare in future environments,“ said the paper’s author, Jonathan Pruitt. „Heating up many corals even mildly can negatively impact a variety of physiological processes. However, this study shows that small increases could provide greater protection by resident fishes. Obviously this can’t go on for forever, though. At some point, all the protection in the world won’t matter anything if the corals can’t feed themselves.“

Paper: Pruitt et al. 2018

PM der Woods Hole Oceanographic Institution aus dem November 2018:

Study tracks severe bleaching events on a Pacific coral reef over past century

A new study has uncovered the history of bleaching on a reef in the epicenter of El Nino, revealing how some corals have been able to return after facing extreme conditions

As climate change causes ocean temperatures to rise, coral reefs worldwide are experiencing mass bleaching events and die-offs. For many, this is their first encounter with extreme heat. However for some reefs in the central Pacific, heatwaves caused by El Nino are a way of life. Exactly how these reefs deal with repeated episodes of extreme heat has been unclear. A new study from the Woods Hole Oceanographic Institution (WHOI), has uncovered the history of bleaching on a reef in the epicenter of El Nino, revealing how some corals have been able to return after facing extreme conditions. The study was published Nov. 8, 2018, in the journal Communications Biology.

„These huge marine heatwaves, which are being exacerbated by global warming, are equivalent to an atomic bomb in terms of impact on coral reefs — they kill millions of corals across huge areas of ocean in a very short time“ says WHOI scientist Anne Cohen, who was principal investigator on the work. „We’ve seen this play out now globally for the past 30-40 years, and bleaching events have become more frequent and more severe.“

When water temperatures rise even slightly, symbiotic algae that live inside the cells of the live coral start to create toxic substances and are ejected by the corals. The algae normally provide the corals with food and energy, as well as their bright colors. Without them, the corals appear to be „bleached“ white, then starve and die.

In their study, Cohen’s team traveled to Jarvis Island, a tiny, unpopulated coral reef island 1,400 miles south of Hawaii, to study the effects of extreme climate on the corals there. Because Jarvis is both remote and part of a marine protected area, it has been home to stunningly rich coral reefs — but with its location in the middle of the Pacific, it also experiences more extreme heat waves caused by periodic El Nino events than coral reefs elsewhere.

„The fact that it’s placed right at the equator in the central Pacific puts it at epicenter of El Niño dynamics.“ says NOAA researcher Hannah Barkley, who was a graduate student and later a postdoctoral fellow in Cohen’s lab at the time of the study, and is the paper’s lead author. „It’s subject to incredible variability and extremes in temperature..“

Because there is no observational record of bleaching on the reef at Jarvis before 2015, Cohen and Barkley turned to massive old corals that had lived on the reef for more than 100 years. They took core samples from the corals, creating a sort of skeletal biopsy that records the history of the reef. After running the cores through a CT scanner, they found for the first time evidence of multiple bleaching events preserved in the physical structure of the reef. The longest cores revealed bleaching as far back as 1912.

„We found that when the reef bleaches, these big old corals lay down „stress bands,“ or a dense layer of calcium carbonate, the bonelike material that make up the structure of corals. Those bands appear clearly in the CT scan, and correspond with historical heat waves,“ says Cohen. The memory of past bleaching events on Jarvis is locked into these corals — they can tell us what has been going even though we weren’t there to see it for ourselves.“

Jarvis has experienced above-average temperatures every four to seven years, going back decades or even centuries. The team discovered that with each heat wave, the reef experienced severe bleaching, yet seems to have bounced back fairly quickly each time.

Based on their samples, the group thinks that one major reason for the reef’s recovery is the currents nearby. The topography of the ocean floor, combined with the force of trade winds on the surface, brings cold, nutrient-rich water up from the deep. That upwelling feeds a dense array of fish and other aquatic life around the reef, which in turn eat away grassy algae that compete with the corals. In the process, they leave room for new, young coral polyps to eventually settle.

„These reefs are resilient, having bleached and recovered many times, “ says Dan Thornhill, program director in the National Science Foundation’s Division of Ocean Sciences, which funded the research. „But the 2015-2016 bleaching event was particularly severe, so the island is providing us with new insights into how some of the world’s most resilient corals are faring in the face of severe bleaching stress.“

Understanding how coral reefs like Jarvis are able to recover after extensive bleaching will be essential for understanding how other reef ecosystems may grow back in the future, says Barkley.

But the 2015 Super El Nino caused Jarvis to heat up more than it ever did before, and the bleaching that ensued was the worst on record. 95 percent of island’s corals died.

„The big question for us is whether the reef can bounce back at all this time,“ says Barkley. „Even reefs like Jarvis that have regrown in the past have a threshold beyond which they may not recover. What happens over next few years will really help us understand severe bleaching.“

Still, she’s guardedly optimistic. „It’s easy to look at a place like Jarvis after the 2015 bleaching event and feel depressed. But the historical record we got from our core samples says we’re not beyond hope. Jarvis is just one example: even though we are seeing signs of accelerated bleaching and mortality worldwide, we have a narrow window to address the effects of climate change on corals. Some reefs may be able to persist through huge stress events.“

„The initial signs of recovery are there,“ says Cohen. „Now we wait, watch and learn.“

Also collaborating on the study was Kathryn R. Pietro and Pat Lohmann of WHOI, Cohen Lab graduate students Nathaniel R. Mollica, Hanny E. Rivera, Thomas M. DeCarlo, Elizabeth J. Drenkard, and Alice E. Alpert of the MIT-WHOI Joint Program in Oceanography; Russell E. Brainard and Thomas A. Oliver of the NOAA Pacific Islands Fisheries Science Center; Charles W. Young, Bernardo Vargas-Angel, and Kevin C. Lino of NOAA and the University of Hawaii at Manoa; and Victoria H. Luu of Princeton University. Funding for the study was provided by National Science Foundation awards OCE 1537338, OCE 1605365, and OCE 1031971 to A.L. Cohen, and the Robertson Foundation to A.L. Cohen; National Science Foundation Graduate Research Fellowships to T.M DeCarlo and A.E. Alpert; and a National Defense Science and Engineering Graduate Fellowship to H.E. Rivera.

Paper: Hannah C. Barkley, Anne L. Cohen, Nathaniel R. Mollica, Russell E. Brainard, Hanny E. Rivera, Thomas M. DeCarlo, George P. Lohmann, Elizabeth J. Drenkard, Alice E. Alpert, Charles W. Young, Bernardo Vargas-Ángel, Kevin C. Lino, Thomas A. Oliver, Kathryn R. Pietro, Victoria H. Luu. Repeat bleaching of a central Pacific coral reef over the past six decades (1960–2016). Communications Biology, 2018; 1 (1) DOI: 10.1038/s42003-018-0183-7

PM der Lancaster University aus dem November 2018:

Thriving reef fisheries continue to provide food despite coral bleaching

Reef fisheries can continue to provide food and income despite corals being lost to climate change, according to new research conducted in the Seychelles.

The unexpected results of a 20-year study into reef fisheries published in the journal Nature Ecology and Evolution this week showed fisheries being maintained despite extreme coral bleaching. Remarkably, rapid proliferation of fishes with low dependence on corals led to catches remaining stable or even increasing.

But the results also showed fishing success was ‚patchy‘ and more dependent on fewer species.

Around six million people fish on coral reefs. Each year their catch — estimated to be between 1.4 and 4.2 million tonnes — provides a critical source of food and income for many millions more. But climate change-driven coral bleaching events, caused by warming seas, are damaging coral habitat and depleting fish biodiversity, which has sparked fears that these vibrant ecosystems will no longer support productive fisheries.

A Lancaster University-led study set out to test this, using 20 years of fish abundance, catch and habitat data to assess the long-term impacts of climate-driven coral mass mortality and changes in artisanal coral reef fisheries in the Seychelles.

As part of their study they looked at more than 45,000 daily fishery landing records from 41 different sites. They also conducted 960 underwater surveys at 12 locations.

After the mass coral bleaching event in 1998, which caused substantial loss of coral habitat across Seychelles, reef fish catches have either remained the same and even increased. Although many reefs became overgrown with seaweeds, increases in algal-feeding fish communities such as rabbitfish are enabling local fishers to continue harvesting food.

Dr James Robinson of Lancaster University’s Environment Centre said:

„Bleaching in 1998 caused mass coral mortality, habitat collapse, and shifts to seaweed dominance on some reefs, and so we expected the fishery to be in decline. But we overlooked the potential for algal-feeding fish to benefit from higher algal productivity.“

„With coral bleaching events becoming more frequent and more intense as the climate warms, the unexpected news was that these fisheries continued to provide benefits for people.“

Calvin Gerry of the Seychelles Fishing Authority, a co-author of the study, said: „We focussed on the inshore trap fishery in this study, as it is an important sector in Seychelles, and a common gear on coral reefs globally.“

„Most of the fish from the trap fishery are sold and consumed locally, rather than exported internationally. Therefore, changes to this fishery have potential to influence both fishers and consumers domestically.“

The study focused on short- and medium-term impacts of climate change. But the researchers have warned that these fisheries may be more unpredictable and variable than before because the fishes contributing to catches were much more patchily distributed.

Declines in healthy coral habitat reduced the diversity of species in catches, and fishers were more reliant on a few highly productive rabbitfish species.

Professor Nicholas Graham of Lancaster University, a co-author of the study, added: „Although we saw that after coral bleaching the average fish catch rose or remained stable, fishing success was patchy. After bleaching, catches became either much larger or much smaller than the average.“

„These data from the Seychelles forewarn of changes likely for coral reef fisheries in other countries. While the news for fishers is better than we might expect, the algal-covered reefs are in marked contrast to the complex coral habitats which once hosted myriad and diverse coral reef fishes.“

While the rabbitfish boost was shown to give fishers a few years of respite from the effects of widespread coral bleaching, the authors caution that the longer-term outlook for reef fisheries remains uncertain.

Paper: James P. W. Robinson, Shaun K. Wilson, Jan Robinson, Calvin Gerry, Juliette Lucas, Cindy Assan, Rodney Govinden, Simon Jennings, Nicholas A. J. Graham. Productive instability of coral reef fisheries after climate-driven regime shifts. Nature Ecology & Evolution, 2018; DOI: 10.1038/s41559-018-0715-z

Huffpost 2018:

‚Glimmer Of Hope‘ For Great Barrier Reef As Study Shows Tolerance To Climate Change

Last year’s oceanic heat wave wasn’t as destructive as one the year before, scientists said.

Peter Ridd in The Australian am 26.12.2018 (via GWPF):

Coral Reefs Can Take The Heat, Unlike Experts Crying Wolf

Weiterlesen bei der GWPF

Sully et al. 2019 in nature communications:

A global analysis of coral bleaching over the past two decades

Thermal-stress events associated with climate change cause coral bleaching and mortality that threatens coral reefs globally. Yet coral bleaching patterns vary spatially and temporally. Here we synthesize field observations of coral bleaching at 3351 sites in 81 countries from 1998 to 2017 and use a suite of environmental covariates and temperature metrics to analyze bleaching patterns. Coral bleaching was most common in localities experiencing high intensity and high frequency thermal-stress anomalies. However, coral bleaching was significantly less common in localities with a high variance in sea-surface temperature (SST) anomalies. Geographically, the highest probability of coral bleaching occurred at tropical mid-latitude sites (15–20 degrees north and south of the Equator), despite similar thermal stress levels at equatorial sites. In the last decade, the onset of coral bleaching has occurred at significantly higher SSTs (∼0.5 °C) than in the previous decade, suggesting that thermally susceptible genotypes may have declined and/or adapted such that the remaining coral populations now have a higher thermal threshold for bleaching.

Sciscep.com im April 2019:

Coral Bleaching Update; It’s Not As Bad As We Thought

In 2018, the Woods Hole Oceanographic Institution revealed that, during the 2015/16 El Nino, 95% of corals bleached through heat stress around Jarvis Island in the equatorial Pacific. Upon investigating the reef further, they also found that the reef recovered from past severe bleaching events, though the 2015/16 event was the severest on record, which is unsurprising, because the last El Nino comparable to 2015/16 was way back in 1876/78 and their study only documented bleaching events since 1960. The research team were optimistic that there would be a similar recovery from the latest severe bleaching event, due entirely to a temporary spike in water temperature induced by a very powerful super El Nino, not climate change™.

Now the Scripps Institution of Oceanography and engineers at UC San Diego tell us that another coral reef in the central Pacific north east of Australia, located at Palmyra Atoll, not a million miles from Jarvis Island, which also suffered the same fate in 2015/16, has indeed largely recovered from severe thermal bleaching during the 2015/16 El Nino.

Weiterlesen auf Sciscep.com

JoNova im Juli 2019:

Coral reef totally recovers (for 400th time) and researchers surprised

If only coral researchers read skeptic blogs, they’d know that corals have been getting bleached and wrecked by cyclones for millions of years. They have adaptable genes, honed by 500 million years of natural selection, plus epigenetic tricks, and with safe zones to seed recovery. The Great Barrier Reef spans 2,000 kilometers and five degrees Celsius from 27 to 32°C and we’re still finding reefs we didn’t even know about. The pH swings on a daily basis, and fish do better when it does. One coral has adapted to ocean “acidification” in 6 months. Other fish remarkably adapted from salt to freshwater in just fifty years. As Peter Ridd says: Of all the ecosystems in the world, the reef is one that’s best at adapting to climate change.

So once again, corals have recovered — and yet the “experts” who wear their dogma covered glasses didn’t see it coming.

University of Barcelona im Oktober 2019:

Researchers describe a survival strategy in living corals which was only seen in fossil records

Some corals can recover after massive mortality episodes caused by the water temperature rise. This survival mechanism in the marine environment -known as rejuvenation- had only been described in some fossil corals so far. A new study published in the journal Science Advances reveals the first scientific evidence of the rejuvenation phenomenon in vivo in Cladocora caespitosa coral colonies, in the marine reserve in Columbrets, in the coast of Castellón (Spain).

The authors of the study are the experts Diego Kersting and Cristina Linares, from the Department of Evolutionary Biology, Ecology and Environmental Sciences from the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona.

Heatwaves, more and more common in the Mediterranean

The Mediterranean Sea is one of the most affected areas by the climate change and the increase of heatwaves. „We are used to hear and read on the general impacts related to the climate change, but we rarely get news on the life recovery after impacts related to global warming“, says Diego Kersting, first author of the article and researcher at the Free University of Berlin (Germany).

Since 2002, Kersting and Linares have been monitoring 250 coral colonies of Cladocora caespitosa in the marine reserve in Columbrets, an area for studies on the effects of climate change on the marine environment. This coral -the only one able to create reefs in the Mediterranean Sea- is listed as an endangered species, mainly because of the mortalities associated with global warming.

Experts had described that the unusual rise of water temperature in summer was killing many of these Mediterranean coral colonies. For instance, during the summer of 2003, one of the hottest ones, „the 25% of the surface occupied by these corals in Columbrets disappeared due a loss of the colonies“, says the authors of the study.

Some coral polyps survive under extreme conditions

In a Mediterranean Sea with higher and higher temperatures and frequent heatwaves, the survival alarms for these species had already rang. However, the long-run monitoring of the coral in Columbrets revealed a surprising result: some coral colonies that were considered lost years ago show some living parts.

According to the experts, this kind of recuperation was possible thanks to a procedure named rejuvenation. In particular, under stress conditions -for instance, excessive water warming-, some polyps in the coral colonies which are dying are able to become smaller until they can abandon their calcareous skeleton.

In this reduced state, these polyps can survive under extreme conditions which cause the death of the other polyps in the colony. When conditions improve, polyps recover its common size and form a new calcareous skeleton. Afterwards, they reproduce by budding until they can recover the dead colony again.

A hidden survival strategy

According to the authors, this survival strategy had been unnoticed until now due the external good image the colonies show once they have recovered, which masks the mortality that had taken place before. „The real story of these colonies can only be found if controlled every year, over the years, or if we study the skeleton, since the process leaves characteristic features!, warn Kersting and Linares.

So far, researchers had found signs of this rejuvenation only in Paleozoic corals, which lived hundreds of millions of years ago. Therefore, the results of this study will enable making comparisons between the in vivo observations and the description through the fossils, and therefore knowing the implication of these kinds of survival processes and adaptation in corals.

This discovery provides new perspectives for the survival of the only reef coral in the Mediterranean, which has a slow growth -about 3 mm per year- and a limited ability to create new colonies. „However, it is hard for these mechanisms to balance the serious increase of the frequency and severity of the heatwaves in the Mediterranean, so it is necessary to act urgently in order to slow the causes of climate change, and dedicate enough resources to maintain these monitoring procedures in the long run“, warn the authors.

Brown et al. 2019:

Long-term impacts of rising sea temperature and sea level on shallow water coral communities over a ~40 year period

Effects of combined rising sea temperature and increasing sea level on coral reefs, both factors associated with global warming, have rarely been addressed. In this ~40 y study of shallow reefs in the eastern Indian Ocean, we show that a rising relative sea level, currently estimated at ~11 mm y−1, has not only promoted coral cover but also has potential to limit damaging effects of thermally-induced bleaching. In 2010 the region experienced the most severe bleaching on record with corals subject to sea temperatures of >31 °C for 7 weeks. While the reef flats studied have a common aspect and are dominated by a similar suite of coral species, there was considerable spatial variation in their bleaching response which corresponded with reef-flat depth. Greatest loss of coral cover and community structure disruption occurred on the shallowest reef flats. Damage was less severe on the deepest reef flat where corals were subject to less aerial exposure, rapid flushing and longer submergence in turbid waters. Recovery of the most damaged sites took only ~8 y. While future trajectories of these resilient reefs will depend on sea-level anomalies, and frequency of extreme bleaching the positive role of rising sea level should not be under-estimated.

The Australian 2016: Great Barrier Reef: scientists ‘exaggerated’ coral bleaching

JoNova: Great Barrier Reef scare: exaggerated threats says head of GBR Authority

Spektrum.de 2018:

Warum Ratten Korallenriffe bedrohen

Nein, die Nager knabbern nicht etwa die Unterwasserstrukturen an. Wie sie die empfindlichen Ökosysteme schädigen, wird erst auf den zweiten Blick deutlich.

PM der Cornell University aus dem Januar 2018:

A ‚marine motorhome for microbes‘: Oceanic plastic trash conveys disease to coral reefs

For coral reefs, the threat of climate change and bleaching are bad enough. An international research group led by Cornell University has found that plastic trash — ubiquitous throughout the world’s oceans — intensifies disease for coral, adding to reef peril, according to a new study in the journal Science.

„Plastic debris acts like a marine motorhome for microbes,“ said the study’s lead author, Joleah Lamb, a postdoctoral research fellow at Cornell. She began collecting this data as a doctoral candidate at James Cook University in Australia.

„Plastics make ideal vessels for colonizing microscopic organisms that could trigger disease if they come into contact with corals,“ Lamb said. „Plastic items — commonly made of polypropylene, such as bottle caps and toothbrushes — have been shown to become heavily inhabited by bacteria. This is associated with the globally devastating group of coral diseases known as white syndromes.“

When plastic debris meets coral, the authors say, the likelihood of disease increases from 4 to 89 percent — a 20-fold change. The scientists estimate that about 11.1 billion plastic items are entangled on reefs across the Asia-Pacific region, and that this will likely increase 40 percent over the next seven years.

Coral are tiny animals with living tissue that cling to and build upon one another to form „apartments,“ or reefs. Bacterial pathogens ride aboard the plastics, disturbing delicate coral tissues and their microbiome.

„What’s troubling about coral disease is that once the coral tissue loss occurs, it’s not coming back,“ said Lamb. „It’s like getting gangrene on your foot and there is nothing you can do to stop it from affecting your whole body.“

Lamb and colleagues surveyed 159 coral reefs from Indonesia, Australia, Myanmar and Thailand, visually examining nearly 125,000 reef-building corals for tissue loss and disease lesions. The number of plastic items varied widely, from 0.4 items per 100 square meters (about the size of a two-bedroom Manhattan flat), in Australia, to 25.6 items per 100 square meters in Indonesia. This is significant given that 4.8 to 12.7 million metric tons of plastic waste are estimated to enter the ocean in a single year, Lamb said.

The scientists forecast that by 2025, plastic going into the marine environment will increase to roughly 15.7 billion plastic items on coral reefs, which could lead to skeletal eroding band disease, white syndromes and black band disease.

„Our work shows that plastic pollution is killing corals. Our goal is to focus less on measuring things dying and more on finding solutions,“ said senior author Drew Harvell, professor of ecology and evolutionary biology. „While we can’t stop the huge impact of global warming on coral health in the short term, this new work should drive policy toward reducing plastic pollution.“

Coral reefs are productive habitats in the middle of nutrient-poor waters, Harvell said. Thanks to the symbiotic relationship between corals and their solar-powered algae, „this miracle of construction creates the foundation for the greatest biodiversity in our oceans,“ she said. „Corals are creating a habitat for other species, and reefs are critical to fisheries.“

Said Lamb: „This study demonstrates that reductions in the amount of plastic waste entering the ocean will have direct benefits to coral reefs by reducing disease-associated mortality.“

Paper: Joleah B. Lamb, Bette L. Willis, Evan A. Fiorenza, Courtney S. Couch, Robert Howard, Douglas N. Rader, James D. True, Lisa A. Kelly, Awaludinnoer Ahmad, Jamaluddin Jompa, C. Drew Harvell. Plastic waste associated with disease on coral reefs. Science, 2018 DOI: 10.1126/science.aar3320

Soweit unsere Übersicht zu den neuesten Forschungsresultaten zu Korallenbleiche und verwandten Themen. Hoffentlich ist irgendwer ganz unten in diesem Blogpost angekommen – es ist in der Tat ein sehr aktiver Forschungszweig. Umso seltsamer, dass man in der deutschen Presse kaum eine der Pressemitteilungen aufgegriffen hat. Ob es nur an mangelnden Englischkenntnissen der Redakteure liegt, oder passen die Ergebnisse nicht ins Konzept?

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