Thirty years of unique data reveal what's really killing coral reefs

Thirty years of unique data reveal what's really killing coral reefs
A snorkeler swims among healthy Elkhorn corals off Key Largo in the Florida Keys in the early 1980s. Named for its antler-like shape for its colonies, the Elkhorn coral is one of the most important corals in the Caribbean. Current populations are struggling to recover from coral disease and bleaching. Elkhorn coral once dominated coral reefs in the Florida Keys. Today, less than 5 percent of these corals remain in the Florida Keys. Credit: Larry Lipsky

Coral reefs are considered one of the most threatened ecosystems on the planet and are dying at alarming rates around the world. Scientists attribute coral bleaching and ultimately massive coral death to a number of environmental stressors, in particular, warming water temperatures due to climate change.

A study published in the international journal Marine Biology, reveals what's really killing coral reefs. With 30 years of unique data from Looe Key Reef in the lower Florida Keys, researchers from Florida Atlantic University's Harbor Branch Oceanographic Institute and collaborators have discovered that the problem of is not just due to a warming planet, but also a planet that is simultaneously being enriched with reactive from multiple sources.

Improperly treated sewage, fertilizers and top soil are elevating , which are causing phosphorus starvation in the corals, reducing their temperature threshold for "bleaching." These coral reefs were dying off long before they were impacted by rising . This study represents the longest record of reactive nutrients and algae concentrations for coral reefs anywhere in the world.

"Our results provide compelling evidence that loading from the Florida Keys and greater Everglades ecosystem caused by humans, rather than warming temperatures, is the primary driver of coral degradation at Looe Key Sanctuary Preservation Area during our long-term study," said Brian Lapointe, Ph.D., senior author and a research professor at FAU's Harbor Branch.

A key finding from the study is that land-based nutrient runoff has increased the nitrogen:phosphorus ratio (N:P) in reef algae, which indicates an increasing degree of phosphorus limitation known to cause metabolic stress and eventually starvation in corals. Concentrations of are above critical ecosystem threshold levels previously established for the Florida Keys as are phytoplankton levels for offshore reefs as evidenced by the presence of macroalgae and other harmful algal blooms due to excessive levels of nutrients.

Thirty years of unique data reveal what's really killing coral reefs
As can be seen by this bleached coral in Looe Key in the lower Florida Keys in 1987, these coral reefs were dying off long before they were impacted by rising water temperatures. Credit: Brian Lapointe, Ph.D., Florida Atlantic University's Harbor Branch Oceanographic Institute

Researchers gathered data from 1984 to 2014 and collected seawater samples during wet and dry seasons. Lapointe and collaborators from the University of Georgia and the University of South Florida also monitored the living coral and collected abundant species of seaweed (macroalgae) for tissue nutrient analysis. They monitored seawater salinity, temperature and nutrient gradients between the Everglades and Looe Key. They wanted to better understand how nitrogen traveled from the Everglades downstream to the coral reefs of the Florida Keys National Marine Sanctuary, which now has the lowest amount of coral cover of any reefs in the wider Caribbean region.

Data revealed that living coral cover at Looe Key Sanctuary Preservation Area declined from nearly 33 percent in 1984 to less than 6 percent in 2008. The annual rate of coral loss varied during the study, but increased from 1985 to 1987 and 1996 to 1999 following periods of heavy rainfall and increased water deliveries from the Everglades. Between 1991 to 1995, significant increases in Everglades runoff and heavy rainfall resulted in increases of and phytoplankton levels at Looe Key above levels known to stress and cause die-off of coral reefs. Despite reduced Everglades flows, the water quality has not yet recovered to the levels of the 1980s.

Nitrogen loading to the coast is predicted to increase by 19 percent globally simply as a result of changes in rainfall due to climate change, which suggests the need for urgent management actions to prevent further degradation.

"The future success of the Comprehensive Everglades Restoration Plan will rely on recognizing the hydrological and nitrogen linkages between the Everglades, Florida Bay and the Florida Keys," said Lapointe. "The good news is that we can do something about the nitrogen problem such as better sewage treatment, reducing fertilizer inputs, and increasing storage and treatment of stormwater on the Florida mainland."

The impact of local land-based nitrogen contributions from that service 76,000 year-round residents and an estimated 3.8 million tourists annually is currently being mitigated by completion of centralized wastewater collection and advanced wastewater treatment plants and nutrient removal facilities throughout the Florida Keys.

Underwater video at Looe Key in the lower Florida Keys shows the degradation of these once pristine corals reefs over the course of more than 30 years from 1988 to 2019 (Longer video b-roll and additional photos are available). Credit: Brian Lapointe, Ph.D., Florida Atlantic University's Harbor Branch Oceanographic Institute

According to the Florida Keys National Marine Sanctuary, ocean-related activities associated with coral reefs add more than $8.5 billion each year and 70,400 jobs to the local economy in southeast Florida.

"The Bonaire coral reefs in the Caribbean Netherlands is a great example of effective nitrogen pollution mitigation. These coral reefs are beginning to recover following the construction of a new sewage treatment plant in 2011, which has significantly reduced nitrogen loading from septic tanks," said Lapointe.

The study's co-authors are Rachel A. Brewton and Laura W. Herren of FAU's Harbor Branch; James W. Porter, Ph.D., emeritus professor of ecology at the University of Georgia; and Chuanmin Hu, Ph.D., of the College of Marine Science at the University of South Florida.

"Citing climate change as the exclusive cause of coral demise worldwide misses the critical point that water quality plays a role, too," said Porter. "While there is little that communities living near can do to stop global warming, there is a lot they can do to reduce nitrogen runoff. Our study shows that the fight to preserve requires local, not just global, action."


Explore further

Menu change for corals in warming reefs

More information: floridakeys.noaa.gov/corals/economy.html

Brian E. Lapointe et al. Nitrogen enrichment, altered stoichiometry, and coral reef decline at Looe Key, Florida Keys, USA: a 3-decade study, Marine Biology (2019). DOI: 10.1007/s00227-019-3538-9

Journal information: Marine Biology

Citation: Thirty years of unique data reveal what's really killing coral reefs (2019, July 15) retrieved 22 August 2019 from https://phys.org/news/2019-07-years-unique-reveal-coral-reefs.html
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Jul 15, 2019
Brian Lapointe. The originan Reef Relief stood behind Brian we took our hits from Big Industry and the government they support. Facts are facts and truth is truth. Flood the Bay Kill the reef. NOAA and Billy Causey had ought to hide under a rock for allowing the Killing of coral. We knew this 30 years ago! Brian ...you the man!

Jul 16, 2019
This study was credible, until they brayed "climate change".

Jul 16, 2019
Gee, the climate is changing, regardless of cause it is warming.
The study specifically said it is NOT the warming that is the problem in this particular case.

Knowing they will get a mighty overreaction, some folks poke just for their own amusement.

Jul 16, 2019
This does not mean there is no global warming, or that it's not killing reefs. Just that people get confused by multifactorial causation.

There's no doubt the best coral reef is farthest from population. Most pristine I ever saw was off Peleliu Island waaay out off Palau. Only 600 people there.

Florida reef diving has been bad for decades, and Australia's is starting to go. Belize is not far behind.

It you want to see pure nitrogen effect, try the Gulf of Mexico. A third of it is totally dead due to Mississippi runoff.

Jul 16, 2019
So predictably, the liar deniers jump on this as #buttbuttbutttheresnoglobulwaruming!!!111!!oneoneeleventyone!!!11 when really it's a combination of nitrogen runoff from antiquated sewage treatment, and topsoil erosion, and agricultural fertilizer runoff, **AND** AGCC. They can't keep two factors in their itty bitty minds at the same time, too stupid.

And BTW the reason for the antiquated sewage treatment is because the liar deniers refuse to raise taxes to pay for modern sewage treatment and refuse to allow laws to be made regarding excess unused fertilizers creating unnecessary agricultural runoff. Again, too stupid. Floriduh is destroying its own economy by this very act; they'll lose billions in revenue and tens of thousands of jobs, but the liar deniers wanna "win." Looks more to me like they wanna lose.

Jul 16, 2019
This does not mean there is no global warming, or that it's not killing reefs. Just that people get confused by multifactorial causation.

There's no doubt the best coral reef is farthest from population. Most pristine I ever saw was off Peleliu Island waaay out off Palau. Only 600 people there.

Florida reef diving has been bad for decades, and Australia's is starting to go. Belize is not far behind.

It you want to see pure nitrogen effect, try the Gulf of Mexico. A third of it is totally dead due to Mississippi runoff.

Uh huh. That's because Palau is out of this world, so gloBULL warming can't reach it.
Unfortunately, you can.

Jul 16, 2019
Not really wanting to read more posts on how to do geigh seks, /me declines to read @tehgeighalgore's post.

Jul 16, 2019
"Uh huh. That's because Palau is out of this world, so gloBULL warming can't reach it. Unfortunately, you can."

Yes, and likewise I've also been to the Kenai in S. Alaska where all the glaciers are melting like a snowcone in a Florida July.

Nobody can make a man believe what he doesn't want to, no matter the data. I've debated smokers who don't believe smoking causes lung cancer since not all smokers get it (just 20 %). Duh.

I used to debate HIV deniers in the early 90s who said it didn't exist or didn't cause AIDS (10% never got AIDS— duh). That was right before the first really good HIV treatment. Now the infected deniers (who wouldn't take antivirals) are over 90% dead. Science progresses, as Planck said, funeral by funeral.

The problem with climate change is the believers suffer right along with the deniers. We're all in this one together.

Jul 16, 2019
Yes, and likewise I've also been to the Kenai in S. Alaska where all the glaciers are melting like a snowcone in a Florida July.

Nobody can make a man believe what he doesn't want to, NO MATTER THE DATA.


So true.
Linear trends through the whole period provide a very misleading interpretation. Except for the Arctic region, all of the warming in Alaska occurred in the two-year period of – 1976 - 1978. The temperature trend was decreasing prior to the 1976 climate shift and since then has also not been warming.

http://appinsys.c...aska.htm

Jul 16, 2019
Gee, the climate is changing, regardless of cause it is warming.
The study specifically said it is NOT the warming that is the problem in this particular case.

Knowing they will get a mighty overreaction, some folks poke just for their own amusement.


Why didn't you read the article, dumb ass?

Jul 16, 2019
The temperature trend was decreasing prior to the 1976 climate shift and since then has also not been warming.
You mean other than the record-shattering 90 degree heatwave in Anchorage?

So, lie much, @tehgeighalgore?

Just askin'.

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