Die gerne verdrängten Korallenkiller: Sonnenmilch, Mückenspray & Co.

Immer wieder lesen wir von schlimmen Korallenbleichen, wobei der Schuldige schnell ausgemacht ist: Der Klimawandel. Oft unerwähnt bleibt dabei, dass es eine ganze Reihe von anderen Gefahren für Korallen gibt. Der Lieblingstäter CO2 muss also nicht an allem und jedem Schuld sein.

Fallender Meeresspiegel

Sie haben richtig gelesen. Der Meeresspiegel ist keine Einbahnstrasse. Insgesamt auf globalem Maßstab steigt er, aber regional gibt es auch mehrmonatige und -jährige Phasen, in denen der Meeresspiegel sinkt. Das mögen die Korallen natürlich überhaupt nicht, denn dann liegen die obersten Teile trocken und sterben ab. Nachzulesen zum Beispiel in einer Arbeit von Eghbert Elvan Ampou und Kollegen, die am 24. Februar 2017 in Biogeosciences erschien:

Coral mortality induced by the 2015–2016 El-Niño in Indonesia: the effect of rapid sea level fall
The 2015–2016 El-Niño and related ocean warming has generated significant coral bleaching and mortality worldwide. In Indonesia, the first signs of bleaching were reported in April 2016. However, this El Niño has impacted Indonesian coral reefs since 2015 through a different process than temperature-induced bleaching. In September 2015, altimetry data show that sea level was at its lowest in the past 12 years, affecting corals living in the bathymetric range exposed to unusual emersion. In March 2016, Bunaken Island (North Sulawesi) displayed up to 85 % mortality on reef flats dominated by Porites, Heliopora and Goniastrea corals with differential mortality rates by coral genus. Almost all reef flats showed evidence of mortality, representing 30 % of Bunaken reefs. For reef flat communities which were living at a depth close to the pre-El Niño mean low sea level, the fall induced substantial mortality likely by higher daily aerial exposure, at least during low tide periods. Altimetry data were used to map sea level fall throughout Indonesia, suggesting that similar mortality could be widespread for shallow reef flat communities, which accounts for a vast percent of the total extent of coral reefs in Indonesia. The altimetry historical records also suggest that such an event was not unique in the past two decades, therefore rapid sea level fall could be more important in the dynamics and resilience of Indonesian reef flat communities than previously thought. The clear link between mortality and sea level fall also calls for a refinement of the hierarchy of El Niño impacts and their consequences on coral reefs.

Siehe auch Beitrag von Jim Steele hierzu auf WUWT.

 

Pestizide

Die University of North Florida beschrieb in einer Pressemitteilung vom 20. Januar 2015 einen weiteren Korallenkiller: Pestizide. Die Forscher fanden lediglich eine mittlere Resistenz gegen die untersuchten Mückenpestizide. Oder anders ausgedrückt: Unter gewissen Umständen können diese Pestizide Korallenlarven abtöten.

Pioneer Study Examines Declining Coral Reef Health Due to Pesticides/Sea Surface Temperatures

The declining health of coral reefs is intensifying worldwide at an alarming rate, due to the combined effects of land-based sources of pollution and climate change. Despite the persistent use of mosquito-control pesticides in populated coastal areas, studies examining the survival and physiological impacts on the early life stages of foundation species, like corals, are limited. In order to better understand the combined effects of mosquito pesticides and rising sea-surface temperatures, Dr. Cliff Ross, an associate professor of biology at the University of North Florida, along with scientists from Mote Marine Laboratory, exposed larvae from the coral, Porites astreoides, to selected concentrations of pesticides and temperatures.

In this pioneer study, recently published in Ecotoxicology, Ross and his colleagues—Kevin Olsen, Michael Henry and Dr. Richard Pierce—uncovered that this particular coral larvae were shown to have a moderate degree of resistance against short-term exposure to ecologically relevant concentrations of pesticides, even in the presence of elevated temperature.

“The significance of this work is that coral reefs across the globe are declining at an alarming rate due to climate change (warming ocean temperatures) and pollution. If baby corals don’t survive exposure to these stressors, then you won’t have adults, which are needed to reproduce and maintain the populations,” said Ross, who is focusing his current research at UNF on understanding the effects of climate change and environmental stressors on marine organisms, such as corals and sea grasses.

One big issue in the Florida Keys and many other coastal environments, Ross noted, is the use of mosquito-control pesticides. The Florida Keys relies heavily upon tourism. Unfortunately, the same beautiful habitat is conducive towards mosquito growth. According to Ross, the Florida Keys Mosquito Control district does an excellent job controlling mosquito populations by applying pesticides. Unfortunately, he said, some of these pesticides can inadvertently end up in the ocean and have a negative effect on marine life.

What kind of possible negative effects? In order to better understand the combined effects of mosquito pesticides and rising sea-surface temperatures, Ross collected and exposed coral larvae to selected concentrations of two major mosquito pesticide ingredients, naled and permethrin, and seawater elevated to +3.5 degrees Celsius. After 18 to 20 hours of exposure, larvae subjected to high naled concentrations had significantly reduced survivorship compared to controls. These effects weren’t detected in the presence of permethrin or elevated temperature.

Additionally, larval settlement, post-settlement survival and bleaching weren’t impacted by any treatment. To evaluate the sub-lethal stress response of larvae, several cellular and molecular assays were run. These assays determine if the larvae are stressed, much like a human blood test. The molecular responses to pesticide exposure were variable and contingent upon pesticide type, as well as the specific biomarker being employed.

In some cases, such as with the protein carbonylation and catalase gene expression, the effects of naled exposure and temperature were interactive. In other cases, pesticide exposure failed to induce any sub-lethal stress response.

Overall, these results demonstrate that Porites astreoides larvae have a moderate degree of resistance against short-term exposure to ecologically relevant concentrations of pesticides, even in the presence of elevated temperature. However, Ross notes much more work is needed on this topic, since there are many different types of environmental stressors that can interact with pesticides to cause damage to corals.

“With the onset of increasing stress to coral reefs, via direct human activities, or indirectly through effects associated with climate change, a more complete understanding of how stress impacts corals is essential,” said Ross. “In particular, as the use of pesticides increases in coastal communities there is a need to investigate the negative effects on early life stages of foundation species like corals.”

The full study, to be published in the February 2015 issue, can be found at http://link.springer.com/article/10.1007/s10646-014-1402-8.

 

Sonnencreme

Sogar Sonnencreme von badenden Strandgästen kann den Korallen gefährlich werden wie National Geographic bereits 2008 meldete:

Swimmer’s sunscreen killing off coral
The sunscreen that you dutifully slather on before a swim on the beach may be protecting your body—but a new study finds that the chemicals are also killing coral reefs worldwide. Four commonly found sunscreen ingredients can awaken dormant viruses in the symbiotic algae called zooxanthellae that live inside reef-building coral species.

Weiterlesen in National Geographic

Die Universität Tel Aviv gab 2015 im Rahmen einer Pressemitteilung weitere Forschungsergebnisse zur Problematik bekannt:

Sunscreen is proven toxic to coral reefs

Tel Aviv University researchers discover chemical found in most sunscreen lotions poses an existential threat to young corals

The daily use of sunscreen bearing an SPF of 15 or higher is widely acknowledged as essential to skin cancer prevention, not to mention skin damage associated with aging. Though this sunscreen may be very good for us, it may be very bad for the environment, a new Tel Aviv University study finds.

New research published in Archives of Environmental Contamination and Toxicology finds that a common chemical in sunscreen lotions and other cosmetic products poses an existential threat — even in miniscule concentrations — to the planet’s corals and coral reefs. „The chemical, oxybenzone (benzophenone-3), is found in more than 3,500 sunscreen products worldwide. It pollutes coral reefs via swimmers who wear sunscreen or wastewater discharges from municipal sewage outfalls and coastal septic systems,“ said Dr. Omri Bronstein of TAU’s Department of Zoology, one of the principal researchers.

The study was conducted by a team of marine scientists from TAU, including Prof. Yossi Loya, also of the Department of Zoology, the Haereticus Environmental Laboratory in Virginia, the National Aquarium (US), the US. National Oceanic & Atmospheric Administration, Ben Gurion University of the Negev, and other labs in the US.

A deadly day at the beach

A person spending the day at the beach might use between two to four ounces of sunblock if reapplied every two hours after swimming, towelling off, or sweating a significant amount. Multiply this by the number of swimmers in the water, and a serious risk to the environment emerges.

„Oxybenzone pollution predominantly occurs in swimming areas, but it also occurs on reefs 5-20 miles from the coastline as a result of submarine freshwater seeps that can be contaminated with sewage,“ said Dr. Bronstein, who conducted exposure experiments on coral embryos at the Inter University Institute in Eilat together with Dr. Craig Downs of the Heretics Environmental Laboratories. „The chemical is highly toxic to juvenile corals. We found four major forms of toxicity associated with exposure of baby corals to this chemical.“

Forms of toxicity include coral bleaching, a phenomenon associated with high sea-surface temperature events like El Niño — and with global mass mortalities of coral reefs. The researchers found oxybenzone made the corals more susceptible to this bleaching at lower temperatures, rendering them less resilient to climate change. They also found that oxybenzone damaged the DNA of the corals, neutering their ability to reproduce and setting off a widespread decline in coral populations.

The study also pointed to oxybenzone as an „endocrine disruptor,“ causing young coral to encase itself in its own skeleton, causing death. Lastly, the researchers saw evidence of gross deformities caused by oxybenzone — i.e., coral mouths that expand to five times their healthy, normal size.

It only takes a drop

„We found the lowest concentration to see a toxicity effect was 62 parts per trillion — equivalent to a drop of water in six and a half Olympic-sized swimming pools,“ said Dr. Bronstein. The researchers found concentrations of oxybenzone in the US Virgin Islands to be 23 times higher than the minimum considered toxic to corals.

„Current concentrations of oxybenzone in these coral reef areas pose a significant ecological threat,“ said Dr. Bronstein. „Although the use of sunscreen is recognized as important for protection from the harmful effects of sunlight, there are alternatives — including other chemical sunscreens, as well as wearing sun clothing on the beach and in the water.“

The researchers hope their study will draw awareness of the dangers posed by sunscreen to the marine environment and promote the alternative use of sun-protective swimwear.

 

Fischerei

Die Fischerei bedroht wichtige Fischarten in den Korallenriffen, so dass die Artenvielfalt hier stark gefährdet ist. Siehe Meldungen der University of Queensland und des ARC Centre of Excellence in Coral Reef Studies. Die Wildlife Conservation Society schlug 2015 sogar vor, bestimmte Fischarten gezielt in beschädigten Korallenriffen auszusetzen, die dann bei der Reparatur des Ökosystems und der Korallen mithelfen.

 

Seesterne

Böse Buben sind auch die Seesterne, wie die Augsburger Allgemeine am 17. Dezember 2015 berichtete:

Great Barrier Reef in Gefahr: Killer-Seesterne fressen Korallen
Für seine in allen Farben schillernde Unterwasserwelt ist das Great Barrier Reef vor der Küste Australiens weltbekannt. Doch ihm droht Gefahr durch einen Killer-Seestern.

Weiterlesen in der Augsburger Allgemeinen

 

Sauerstoffarmut

Das Smithsonian Tropical Research Institute wies am 21. März 2017 auf einen viel zu wenig berücksichtigten Korallenkiller hin: Sauerstoffarme Zonen im Meer, sogenannte Dead Zones. Etliche Korallenbleichen die man vormals der Ozeanerwärmung und Ozeanversauerung zugeordnet hatte, sind wohl in Wahrheit eher eine Folge von Sauerstoffarmut. Dabei wird der Sauerstoffgehalt nicht einmal routinemäßig von allen Ozeanmonitorstationen erfasst. Eine große Forschungslücke.

Dead zones may threaten coral reefs worldwide

Dead zones affect dozens of coral reefs around the world and threaten hundreds more according to a new study by Smithsonian scientists published in Proceedings of the National Academy of Sciences. Watching a massive coral reef die-off on the Caribbean coast of Panama, they suspected it was caused by a dead zone — a low-oxygen area that snuffs out marine life — rather than by ocean warming or acidification.

„Ocean warming and acidification are recognized global threats to reefs and require large-scale solutions, whereas the newly recognized threats to coral reefs caused by dead zones are more localized, said Andrew Altieri, staff scientist at the Smithsonian Tropical Research Institute and first author of the study. Fortunately dead zones can be reduced by controlling sewage and agricultural runoff into the ocean.“ In September, 2010, coral reefs in Almirante Bay, Bocas del Toro Province, showed severe signs of stress. In addition to corals turning white and dying, which is typical during coral bleaching associated with warming events, there were other clues suggesting that more was involved than high temperatures. Many unusual observations pointed to something else as the culprit. There were thick mats of bacterial slime, and the dead bodies of crabs, sea urchins and sponges lay scattered on the ocean floor. Even more odd, there was a clear depth line above which the reefs looked OK, and below which, something had gone terribly wrong. Even single colonies of corals that straddled the line were fine above and dying below.

Scientists went to work, measuring several aspects of water quality. One set of measurements came back as a shock. Extremely low oxygen levels in deeper waters contrasted with high oxygen levels in shallow waters where corals were still healthy. This is the hallmark of a dead zone. The team thinks that such dead zones may be common in the tropics but have gone largely unreported, simply because scientists never looked. „The number of dead zones currently on our map of the world is 10 times higher in temperate areas than it is in the tropics, but many marine biologists work out of universities in Europe and North America and are more likely to find dead zones close to home,“ Altieri said. „We were lucky that there was already a reef monitoring program in place at STRI’s Bocas del Toro Research Station as part of the Smithsonian’s Marine Global Earth Observatory Network,“ said Rachel Collin, station director.

„Based on our analyses, we think dead zones may be underreported by an order of magnitude.“ said Nancy Knowlton, coauthor and Sant Chair for Marine Science at the Smithsonian’s National Museum of Natural History. „For every one dead zone in the tropics, there are probably 10 — nine of which have yet to be identified.“ The researchers found 20 instances when dead zones were implicated in the mass mortality of coral reefs worldwide. „Hypoxia (low oxygen) isn’t even mentioned in several of the most important academic reviews of threats to coral reefs and is rarely discussed at scientific meetings,“ Altieri said, „Even worse, many coral-reef monitoring efforts do not include measurement of oxygen levels, making it nearly impossible to identify low oxygen as the cause of mass coral mortality after the fact.“ For example, the cause of a 2016 mass mortality at the Flower Garden Reefs in the Gulf of Mexico remains unclear, but some of the photographs look strikingly similar to what was observed in Panama.

The authors argue that building capacity to monitor oxygen on reefs will help people to improve coral reef health and understand how dead zones might interact with other forces such as global warming in a one-two punch, which put reefs in even greater danger.

 

 Die Korallenkillerbande

Die Oregon State University fasste am 7. Juni 2016 die vielfältigen Gefahren für die Korallenriffe in einer Pressemitteilung zusammen:

Coral reefs fall victim to overfishing, pollution aggravated by ocean warming

Coral reefs are declining  around the world because a combination of factors – overfishing, nutrient pollution, and pathogenic disease – ultimately become deadly in the face of higher ocean temperatures, researchers have concluded. A study published today in Nature Communications, based on one of the largest and longest field experiments done on this topic, suggests that the widespread coral deaths observed in recent decades are being caused by this combination of multiple local stressors and global warming. These forces greatly weaken corals, and allow opportunistic pathogens to build to such levels that corals cannot survive.

The findings were made by researchers from six institutions following a three-year experiment that simulated both overfishing and nutrient pollution on a coral reef in the Florida Keys. The large body of field data collected over an extended period of time helped resolve some of the fundamental questions about the cause of coral reef declines, scientists said. “This is grim news, but at least it will help settle the argument over why corals are dying,” said Rebecca Vega Thurber, an assistant professor in the College of Science at Oregon State University and corresponding author on the study. “This makes it clear there’s no single force that’s causing such widespread coral deaths. Loss of fish that help remove algae, or the addition of excess nutrients like those in fertilizers, can cause algal growth on reefs. This changes the normal microbiota of corals to become more pathogenic, and all of these problems reach critical levels as ocean temperatures warm.”

The end result, scientists say, is a global decline of coral reefs that is now reaching catastrophic proportions. “We need to know how human activities are affecting coral reef ecosystems,” says David Garrison, program director in the National Science Foundation’s Division of Ocean Sciences, which funded the research.  “Coral reefs are among the most sensitive indicators of the health of the oceans. This report is a major contribution toward understanding how reefs will fare in the future.” Scientists say the problems caused by bacterial infections due to local stressors and warm temperatures are in addition to damage from mass coral bleaching events already under way. Only in the early 1980’s did researchers observe the first mass bleaching event in recorded history. There have now been three such events just in the past 20 years.

“About 25-35 percent of the corals on the Great Barrier Reef are dying right now,” Vega-Thurber said. “In 2014-16 large portions of tropical reef across the planet experienced bleaching, and this past April, 90 percent of the Great Barrier Reef bleached as part of a massive El Nino event. Corals everywhere seem to be dying.” In addition to helping to sort out the effects of known stressors like overfishing and nutrient pollution, the researchers made one bizarre and totally unexpected finding.

In normal conditions, parrotfish, like many other species, are essential to the health of coral reefs, nibbling at them to remove algae and causing no permanent damage. But in one part of the experiment corals were so weakened by nitrogen and phosphorus pollution that when parrot fish would bite them, 62 percent of the corals would die. A normally healthy fish-coral interaction had been turned into a deadly one. “Normally benign predation by the parrotfish turned into coral murder,” said Deron Burkepile, also a corresponding author on the study at the University of California – Santa Barbara. “But it’s not the parrotfishes, they’re like the reef janitors, keeping it clean. Those extra nutrients — nutrient pollution — turn parrotfishes into an actual source of mortality by facilitating pathogens in the wounds left by their bites. Excess nutrients turn a coral accomplice into a coral killer.”

The researchers said they want to make it clear that parrotfish are not the problem, they are an essential part of healthy reef ecosystems. “The problem is when corals are so weakened they cannot withstand normal impacts,” Vega-Thurber said. “And the solution will be to help those corals recover their health, by ensuring that their local environment is free of nutrient pollution and that fish stocks are not depleted.” Among the findings of the study:

• Overfishing, nutrient pollution and increased temperature all lead to an increase in pathogens;
• The sheer abundance of pathogens is more important than what particular type or species they are;
• Coral reef mortality mirrors the abundance of pathogens;
• Heat exacerbates these problems, with 80 percent of coral deaths coming in the summer or fall, but only when fish are removed or nutrient pollution is present;
• While high thermal stress has received the most attention, even modest temperature increases make corals more vulnerable to bacteria;
• Loss of fish can increase algal cover up to six times;
• In a distressed system with many algae, coral disease levels double and coral mortality increases eight times;
• Increased algal cover or elevated temperature can reduce levels of naturally-secreted antibiotics that help protect corals from harmful bacteria;
• Direct algal contact driven by overfishing and nutrient pollution destabilizes the coral microbiome, in some cases leading to a 6- to 9-time increase in mortality.

The findings, researchers say, make it clear that in the face of global warming, some of the best opportunities to protect coral reefs lie in careful management of fishing and protection of water quality. This would give corals their best chance to have a healthy microbiome and resist warmer conditions without dying.

 

Nun da die Korallenkiller identifiziert sind, können zeitnahe Maßnahmen ergriffen werden, die die Korallenriffe effektiv schützen und stärken würden. Das ARC Centre of Excellence in Coral Reef Studies stellte 2015 einen Maßnahmenkatalog vor (via ScienceDaily):

We can fix the Great Barrier Reef

Leading coral reef scientists say Australia could restore the Great Barrier Reef to its former glory through better policies that focus on science, protection and conservation. In a paper published in the journal Nature Climate Change, the authors argue that all the stressors on the Reef need to be reduced for it to recover.