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Coral Reefs will be Unable to Keep Pace with Sea-Level Rise

NOAA contributed to a study published today in the journal Nature that compares the upward growth rates of coral reefs with predicted rates of sea-level rise and found many reefs would be submerged in water so deep it will hamper their growth and survival. The study was done by an international team of scientists led by the University of Exeter in the United Kingdom. 

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Coral Bleaching Study Offers Clues about the Future of the Florida Keys Reef Ecosystem

A recent study by AOML and partners identified coral communities at Cheeca Rocks in the Florida Keys National Marine Sanctuary that appear to be more resilient than other nearby reefs to coral bleaching after back to back record breaking hot summers in 2014 and 2015 and increasingly warmer waters. This local case study provides a small, tempered degree of optimism that some Caribbean coral communities may be able to acclimate to warming waters.

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AOML Leads Research Efforts Across Caribbean to Improve Bleaching Predictions

For the third time in recorded history, a massive coral bleaching event is unfolding throughout the world’s oceans, stretching from the Indian Ocean to the Caribbean. Above average sea surface temperatures exacerbated by a strong El Niño could result in the planet losing up to 4,500 square miles of coral this year alone, according to NOAA. The global event is predicted to continue to impact reefs into the spring of 2016.

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Study Provides Local-scale Projections of Coral Bleaching Over the Next 100 Years

In a new study published April 1 in Global Change Biology, NOAA oceanographers and colleagues have developed a new method to produce high-resolution projections of the range and onset of severe annual coral bleaching for reefs in the Gulf of Mexico and Caribbean. The scientists built on a previous study that used global climate models from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change that produced projections at a very coarse resolution of about 70 miles or 100 kilometers. By using a regional oceanic model and an approach called statistical downscaling, the scientists calculated when increasingly warmer waters would cause severe bleaching on an annual basis. The resulting local-scale projections of bleaching conditions, at a resolution of about 6 miles or 10 kilometers, will help managers include climate change as a consideration in planning and conservation decisions.

Coral bleaching is a major threat to coral ecosystems and primarily occurs when ocean temperatures are warmer than has been normal in the past. Temperature stress disrupts the relationship between corals and the algae that live within their tissues; a relationship that usually benefits both parties. The algae are expelled as they cannot photosynthesize under the extreme conditions. The white limestone coral skeleton becomes visible through tissue that is now transparent since the expelled algae give corals their vibrant colors. Extensive coral bleaching events, called ‘mass bleaching’, have increased in frequency and severity over the past two decades and have contributed to overall reef loss globally.

The loss of coral reefs results in significant ecological, social and economic loss. Coral reefs provide rich habitat for valuable fisheries that people depend on for food. They also serve as protective buffers to coastlines by absorbing wave energy from storms, and they boost local economies by attracting tourists who fish, dive and explore these underwater treasures.

A main conclusion of the study is that almost all coral reef locations in the Gulf of Mexico and Caribbean are projected to experience bleaching conditions every yearby mid-century. This result applies to the past coarse-resolution projections as well as the new high-resolution projections. However, the high-resolution projections show there is great within-country variation in the projected timing of extreme conditions. There are locations within many countries where some reefs are projected to experience annual bleaching conditions 15 or more years later than other locations. This applies to reefs in Florida, the Bahamas, Cuba, Puerto Rico, the Dominican Republic, Turks and Caicos, and Mexico. Reefs projected to experience bleaching conditions later are conservation priorities. These locations are a type of refuge, and are among the locations most likely to persist as the climate changes.

“At these locations, referred to in the study as ‘relative refugia’, lower rates of temperature increase and fewer extreme events mean reefs have more time to acclimate and adapt to climate change,” says study lead Dr. Ruben van Hooidonk, a coral and climate researcher with the Cooperative Institute for Marine and Atmospheric Studies at the University of Miami’s Rosenstiel School and NOAA’s Atlantic Oceanographic and Meteorological Laboratory.

Coastal and environmental managers, as well as conservation staff, throughout southern Florida, the Gulf of Mexico and Caribbean can now use the projections to identify local conservation priorities. Managers may decide to preferentially protect these locations within marine protected area networks or may target a range of other actions to these relative refugia to reduce stress caused by human activities.

Bob Glazer of Florida’s Fish and Wildlife Conservation Commission said he welcomed the new research. “Coral bleaching poses a grave threat to coral reefs and these high-resolution projections provide vitally needed spatial information about the degree of threat and inform opportunities to make better management decisions.”

The study authors also compare the two approaches they used to produce the high-resolution projections. Using the regional ocean model represents dynamical downscaling, which is state-of-art but is expensive in time, money and effort. The regional ocean model was developed by the Geophysical Fluid Dynamics Laboratory at NOAA and has been set up for use in the Gulf of Mexico and Caribbean by oceanographers at AOML.

In contrast, the statistical downscaling method the authors developed uses observed relationships between historical temperatures and current conditions to modify the outputs from the global climate models. This method has the advantage of being far less resource-intensive than dynamical downscaling. The study authors found that the results from the two very different approaches were very similar. This gives the team confidence that statistical downscaling should be applied for all of the world’s coral reefs, which the team plans to undertake over the coming year.

NOAA’s Reef Manager’s Guide, which provides information on the causes and consequences of coral bleaching, outlines some of the management strategies and tools that can help reef managers address the coral bleaching threat. Find out more here.This study was funded by NOAA’s Coral Reef Conservation Program and supported by NOAA AOML. The Open Access paper can be downloaded by clicking the thumbnail to the left.

Originally published April 1st, 2015 by Edward Pritchard

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The Science Behind Coral Bleaching in the Florida Keys

 

bleached pillar coral

Photograph of bleached pillar coral on November 13, 2014 at Sand Key. Image credit: NOAA’s Florida Keys National Marine Sanctuary.

2014 was a relatively warm summer in South Florida, and local divers noticed the effects of this sustained weather pattern. Below the ocean surface, corals were bleaching. In the month of August, the Coral Bleaching Early Warning Network, jointly supported by Mote Marine Lab and NOAA’s Florida Keys National Marine Sanctuary, received 34 reports describing paling or partial bleaching and an additional 19 reports indicating significant bleaching. Scientists continue to monitor the impact of this severe bleaching event to determine the extent of coral mortality.

This image, taken on November 13, 2014 by the Florida Keys National Marine Sanctuary, shows a severely bleached pillar coral at Sand Key in the Florida Keys. Images like this one indicate that some regions and species will definitely be affected. Pillar coral is one of the species of coral listed as threatened under the Endangered Species Act.

AOML Coral Ecologists Derek Manzello and Jim Hendee provide insight as to how the environmental conditions they are tracking indicate that a mass bleaching event is possible and even likely in the Florida Keys.

 

What is coral bleaching?

Coral colonies are made up of hundreds or even thousands of genetically identical individuals called polyps. These polyps have microscopic colorful algae called zooxanthellae living within their tissues. The zooxanthellae work like an internal symbiotic vegetable garden, carrying out photosynthesis and providing energy to their coral hosts, which helps reef-building corals create reef structures. When a coral bleaches, it expels its zooxanthellae, and can die within a matter of weeks unless the zooxanthellae populations are able to recover. The term bleaching is used because the dazzling colors of living corals are due to the zooxanthellae in coral tissue, and when zooxanthellae are lost, corals appear white, or “bleached.”

 

 

Extensive bleaching of the soft coral Palythoa caribaeorum on Emerald Reef, Key Biscayne, FL.

Extensive bleaching of the soft coral Palythoa caribaeorum on Emerald Reef, Key Biscayne, Fl. (Credit:NOAA)

What causes coral bleaching?

 

It is well established that elevated sea temperatures cause widespread coral bleaching. Warmer waters “stress” corals and trigger coral bleaching.

There are two types of heat stress that can trigger bleaching:  (1) short-term, acute temperature stress (several days of very high water temperatures) and, (2) cumulative temperature stress (weeks of consistent moderately elevated water temperatures). Scientists have documented that coral communities around the world have different heat stress thresholds that typically trigger bleaching in response to heat stress. Scientists rely on long-term observing stations co-located with coral reefs to identify the specific conditions that correlate to bleaching within different regions.

What specifically triggers bleaching of coral found in the FL Keys?

Using long-term in situ datasets such as the Coastal-Marine Automated Network, or C-MAN, stations in the Florida Keys, AOML scientists identified specific patterns of warm waters on coral reefs that tend to precede bleaching

events.  The indices that proved to be the most reliable indicators for bleaching for the Florida Reef Tract are maximum monthly sea surface temperature and the number of days >30.5 C (86.9 F).

What patterns have scientists noticed leading up to this most recent bleaching event?

Data from the Molasses Reef C-MAN station showed that the winter of 2014 was the warmest on record since these stations began recording data in 1988.  The second warmest winter on record was the winter of 1996/97, which preceded back-to-back bleaching years in the Keys (1997/98) and was the worst bleaching event ever documented in the Florida Keys.  The most recent significant bleaching event in the Florida Keys occurred in 2005, and there have been mild localized bleaching events since then.

The image on the left shows a coral colony at Cheeca Rocks from July 2013. The image at the right shows the same coral colony in August 2014, with the colony now bleached.

The images above were taken from a coral colony at Cheeca Rocks in the Florida Keys. On the left shows the coral colony from July 2013. The image at the right shows the same coral colony in August 2014, with the colony now bleached. (Credit: NOAA)

The warm winter and warm water temperatures this spring caused scientists to start watching the long-term average water temperatures at these stations to see if the average daily temp was regularly reaching or exceeding 30.4 C, the trigger point for previous bleaching in the FL Keys. The Molasses Reef C-MAN site quickly approached this temperature threshold in July and August. Average temperatures were also warmer than normal at the Fowey Rocks C-MAN station and the Cheeca Rocks Atlantic Ocean Acidification Testbed in the northern Keys. With water temperatures now exceeding this threshold for more than thirty days, and reports of bleaching beginning to pour in, there are concerns about widespread bleaching throughout the region.  To assess the extent of the bleaching event, Florida Keys National Marine Sanctuary has been working with its partners to monitor the current state of corals along the reef tract.

Jim Hendee is the acting division director of AOML’s Ocean Chemistry and Ecosystems Division. Jim leads the coral group at AOML and studies the environmental conditions that cause ecosystem-wide changes on coral reefs using in situ observing stations. Derek Manzello is a coral ecologist at AOML and leads research of the impacts of ocean acidification on coral reefs. Derek also studies the impact of other changes in environmental conditions on reefs such as temperature and tropical storm impacts.

Originally Published September 2014 by Shannon Jones

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Volcanic Island of Maug Provides Natural Lab for Ocean Acidification

diver swimming at maug reefs 

CIMAS researcher Ian Enochs “diving in champagne” at the Maug reefs Photo credit: Open Boat Films/NOAA

 

Ian Enochs, a scientist with NOAA’s Cooperative Institute for Marine and Atmospheric Studies at the University of Miami, traveled in May to the Island of Maug in the Pacific Ocean as part of a NOAA expedition aboard NOAA Ship Hi’ialakai to study coral reef ecosystems. The expedition was led by NOAA’s Pacific Island Fisheries Science Center Coral Reef Ecosystem Division and the Pacific Marine Environmental Lab’s Earth-Ocean Interaction group. Enochs focused his research on underwater vents that seep carbon dioxide into the Pacific.

Why journey to the Island of Maug to study ocean acidification?

Maug is a unique natural laboratory that allows us to study how ocean acidificationaffects coral reef ecosystems. We know of no other area like this in U.S. waters. Increasing carbon dioxide in seawater is a global issue because it makes it harder for animals like corals to build skeletons.

What is the Island of Maug like?

Maug is an uninhabited volcanic island in the Commonwealth of the Northern Mariana Islands about 450 miles north of Guam. The volcano breaks through the ocean surface in three areas to form islands and the relatively shallow water surrounding these islands is full of coral reefs. The underwater vents that seep carbon dioxide are found on the side of the caldera or crater formed by the volcano. Usually when I scuba dive, the moment I enter the water, air bubbles surround me and fade away quickly. On Maug, the bubbles never ceased and it felt like I was swimming in a glass of champagne.

collecting underwater gas samples
A funel is used to collect carbon
dioxide gas bubbles from the
seeps near the coral reefs.
Photo credit: Open Boat Films/NOAA 

What are your goals for studying the carbon dioxide vents?

We’re mapping carbonate chemistry over time and space to examine the extent of carbon dioxide at the site. We’re looking at how that chemistry changes over this area as you get farther from the vents and what corresponding changes there are in the coral community. We hope to learn more about which coral species are especially sensitive to elevated carbon dioxide and which may be resilient. Finally, we will look at how elevated carbon dioxide levels in seawater may influence the response of various organisms over time, including their growth rate.

What does your sampling show so far?

The carbon dioxide appears to be strongly influencing the growth of corals and algae in a small area around the vents. While there is weedy algae near the vent due to high levels of carbon dioxide, this gives way to healthier coral reefs as you get farther away from the site.

How do you measure these effects over time?

This first trip has allowed us to begin measuring the effects of carbon dioxide and to place instruments in the area that will continuously measure temperature, light, the partial pressure of carbon dioxide, seawater pH, and water currents. When we return in August, we’ll have three months of data on how this special environment has been changing day to day. Additionally, we are able to measure coral growth over time by taking core samples and by using a special dye to measure new growth.

 

diver drilling for coral core samples

CIMAS researcher Ian Enochs uses a drill to take coral core samples to measure changes in growth. Photo credit: Open Boat Films/NOAA
 

How can this research help our understanding of this and other areas of the ocean?

Research at the Maug site will help us determine the effects of elevated carbon dioxide on an entire natural ecosystem. Using this information, we’ll have a better understanding of how the rest of the ocean’s coral reefs may react to global increases in carbon dioxide and acidification. If the predictions of the Intergovernmental Panel on Climate Change remain the same, by the end of the century, the impact of ocean acidification on coral reefs around the world will be comparable to what we see on the reefs near Maug’s carbon dioxide seeps today.

Note: Ian Enochs’ research is part of a much larger research mission involving NOAA Fisheries, NOAA’s Coral Program, NOAA Research’s Pacific Marine Environmental Lab, the National Institute of Standards and Technology and other partners, including Scripps Institution of Oceanography, the University of Guam, and Open Boat Films. NOAA worked closely with CNMI coral management and monitoring experts at the Division of Coastal Resource Management and the Department of Environmental Quality. More information on the research mission is posted online.

 

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