What’s really killing the Coral Reefs?

From ScienceAlert!

There’s Another Thing Killing The Coral Reefs, And We Can Actually Fix This Problem


17 JUL 2019

Coral reefs are one of the most threatened ecosystems on our planet, and in the past two decades alone, half of the coral in Florida has died off completely. Global warming is known to be a deadly factor, but rising ocean temperatures are only part of the story.

Thirty years of research in the Looe Key Sanctuary Preservation Area (LKSPA) on the southern tip of the Florida Keys has now revealed the cost of a devastating threat to coral that rivals even climate change: direct human pollution.

For years, agricultural run-off and improperly treated sewage have flowed into Florida’s ocean waters from the northern Everglades, elevating the sanctuary’s nitrogen levels and lowering the reef’s temperature threshold for bleaching, researchers say.

As a result of this deadly combination, coral cover in the region has declined from nearly 33 percent in 1984 to less than 6 percent in 2008.

In their analysis, the authors found that three mass bleaching events that occurred during these years only happened after heavy rainfall and increased land-based runoffs. In other words, if we can reduce the amount of local pollution that makes its way into our oceans, we might be able to reduce the worst of the damage.

“Citing climate change as the exclusive cause of coral reef demise worldwide misses the critical point that water quality plays a role, too,” says ecologist James Porter from the University of Georgia.

“While there is little that communities living near coral reefs 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 coral reefs requires local, not just global, action.”

227 2019 3538 Fig1 HTML(Klein & Orlando, Bulletin of Marine Science, 1994)

Elevated nitrogen levels are known to cause corals metabolic stress, increasing their susceptibility to disease and boosting algal blooms that reduce light and accelerate coral reef decline. Nevertheless, scientists are still not sure how these changes relate to the growing problem of mass coral bleaching, disease, and mortality.

Previous studies have shown that between 1992 and 1996 – when Florida’s freshwater flows were directed south against scientific advice – there was a 404 percent increase in coral diseases throughout the Florida Keys National Marine Sanctuary (FKNMS), which, like the LKSPA, also sits downstream from the Everglades.

Full article here.

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Al Miller
July 20, 2019 10:18 pm

As a non-scientist I can safely say the first paragraph of this article is complete twaddle. The world, including corals has endured many eons of climate change quite nicely thank you. Following that the rest of the piece is quite logical and likely the case that at least it is a major factor in Florida.

Willem Jan Goossen
Reply to  Al Miller
July 21, 2019 1:10 am

Well..(hitting the SARC Button), as thing go the way Solar Cycle 25 is shaping up to be, the problem of the Pyhtons will be solved by mother nature herself. Floriada’s native species can handle cold spells. Invasive can not. Remember the falling Iguanas…, I hadn’t heard of that till 2 years ago. How many “cold snapes” has Florida had the past years.

Reply to  Al Miller
July 21, 2019 8:04 pm

We spent two months diving from our boat in Bonaire this last winter season. This is one of the premier destinations for diving water is clear enough for un-aided photography at over 100 feet using only natural light. The entire island is a national managed park out to the 200 foot depth. We happened to be moored very near the out flow of a tiny stream in the main town, Kralendijk. This stream happens to be where the town’s treatment facility discharges. Oddly, the reef below our boat shows higher than normal algae concentration and dead or stressed corals unlike elsewhere on Bonaire. My cousin happens to be a naturalist with the park service and confirmed this. Unfortunately, the local take on this is that boats on the 40 moorings are the cause due to pumping out rather than the effluent of the town’s 17000 population.

In other places throughout the Caribbean we see similar stress where people are concentrated. I don’t buy for a moment any nonsense about water temperature. We see the same corals and fish through the entire Caribbean with north – south variations in the tens of degrees and seasonal variations of several degrees in any given location. We observed in June between Grenada and Trinidad yearly swings in open water 31.5C to 34C (spa temperatures) while temperatures in Puerto Rico last season required a wet suit top for more than a short dip. In previous years, we never wore the tops.

Reply to  Al Miller
July 29, 2019 4:59 am

“coral cover in the region has declined from nearly 33 percent in 1984 to less than 6 percent in 2008”

You’ll excuse me if, when I read something like this, that I ask, “Why did you stop at 2008?” I can’t help but feel that I’m being lied to through cherry-picking.

John F. Hultquist
July 20, 2019 10:28 pm

While they are cleaning up the water, perhaps they can do something to get rid of the Burmese pythons in the Everglades.
Both are serious issues that can be addressed.
Climate change — not so much.

Reply to  John F. Hultquist
July 21, 2019 8:42 am

They’ve got few colorful snaggle-toothed local ‘snake hunters’ out on the case. Cable TV loves this stuff.

re the water: IIRC this has been commented on before.

…cannot possibly be overpopulation and land use changes flowing down from an amusement park larger than Manhattan, nah… global warming for sure.

Louis Hooffstetter
Reply to  John F. Hultquist
July 21, 2019 1:25 pm

Adult alligators love the taste of tender, young Burmese Python…
and visa-versa.

July 20, 2019 10:29 pm

This hypothesis sounds a bit whiffy to me.
Here in Great Barrier Reef country we’re always being told how awful our banana and sugar cane farmers are for “polluting” a reef system forty-odd kilometres off-shore when the currents and winds work continually to prevent terrestrial run-off ever reaching the GBR.
Similarly for the southern tip of Florida, it seems, if the Nullschool current maps are correct – https://earth.nullschool.net/#current/ocean/surface/currents/orthographic=-83.67,26.72,3000

Reply to  Cardimona
July 21, 2019 3:09 am

its whiffy
in Aus our farms are on low inputs and all been forced to have berms and barriers for many years
the input of nitrogen is sydney and brisbanes shitfarm effluent we dump into the sea
all the land chem from parks gardens stormwater and the toxic brew from laundry toilet shanpoos etc

July 20, 2019 10:34 pm

This hypothesis sounds a bit whiffy to me.
Here in Great Barrier Reef country we’re always being told how awful our sugar cane and banana farmers are for “polluting” the reef, even though it’s 40-odd kilometres off-shore and the prevailing winds and currents work continually to keep terrestrial run-off close to the mainland.
Similarly with south Florida if Nullschool is correct – https://earth.nullschool.net/#current/ocean/surface/currents/orthographic=-83.67,26.72,3000

Reply to  Cardimona
July 21, 2019 8:44 am
July 20, 2019 10:50 pm

This isn’t anything new. I have done a fair bit of snorkelling and diving in SE Asia. Off of Phuket, Thailand, in close vicinity to the island and drainage, 80%+ of the corals are damaged and dead. Lots of influence from human development including reducing the numbers of beaked coral eaters like Parrot Fish. Along with increased run off pollution from development and agriculture, sand harvesting, algae growth and human/tourist meddling with the coral and habitat. The islands off shore like the Phi Phi Islands are in much better shape, even with a lot of tourists diving and snorkelling. I imagine this is the case with the GBR close in to land, as well as a lot of other coral reef locations around the world. I would heartily agree that we need to clean up pollution as best we can, since at the end of day, I think this is the metaphor that people interchange with ‘carbon pollution’, and everyday pollution of every kind. This everyday pollution should be cleaned up as well as we can, before we throw the kitchen sink at CO2 abatement policies to try and fix every other weather problem under the Sun.

Walter J Horsting
Reply to  Earthling2
July 21, 2019 6:13 am

Let’s not forget the toxic suntan lotion….worn by the snorkling tourists.

Julian Flood
July 20, 2019 11:19 pm

This problem is only part of the puzzle.

1. Is run-off pollution of dissolved silica maintaining spring diatom blooms for longer than before large-scale powered farming became common?

2. Humanity’s power to fix nitrogen is immense. Is fertiliser run-off altering phytoplankton populations? Are dymethyl-sulphide-producing phyto populations being damaged?

3. The annual run-off from a major city includes the sort of pollution impact of a tanker disaster. Does the reduction in wave action from oil smoothing – fewer salt aerosols, lower albedo, less nutrient stirring — alter the temperature in the polluted area?

It would be sensible to answer these questions before closing down our power grids and hence our civilisation.



Reply to  Julian Flood
July 21, 2019 3:50 am

Great points. Add to that – anti-fouling paints on most ships now. Outboard motors that put the exhaust through the water. Drug run off – those drugs that get people high end up passing through the sewage system. Changed to fish populations (eg parrot fish) etc etc. There are SO MANY things that we are doing that each have small effects, that when combined, make it impossible to blame one thing or the other on it’s own.

Ewin Barnett
Reply to  Julian Flood
July 22, 2019 3:21 am

The elephant dung in the room, so to speak, is the effect on the biosphere of the estrogen in water from oral contraceptives.

Reply to  Julian Flood
July 22, 2019 2:13 pm

Every thunderbolt fixates enough nitrogen to fill a 55 gallon drum. An active lightning thunderstorm is the equivalent of an overturned railroad car tanker, dumping it’s contents into the rivers.
100% natural fertilizer indistinguishable from man-made fertilizer.

Julian Flood
Reply to  Max
July 22, 2019 2:35 pm

One of the few things that humanity does that matches Nature — so I have read — is nitrogen fixation. Doubling the input of fertiliser to an ecology will change the ecology.


July 20, 2019 11:24 pm

I wonder how long until the sugar cane industry in florida has these people taken out and shot…

it’s that bad.

Michael Jankowski
Reply to  Prjindigo
July 21, 2019 4:21 am


July 20, 2019 11:38 pm

Perhaps another hazard to the reef would be Antifouling systems… coating, paint, and surface treatment used on a solid (e.g., ship hull) to control or prevent the attachment of unwanted organisms. The main components of these compositions are biocides, which slowly “leach out” into the seawater, killing barnacles and other marine life that have attached to the solid surface. However, studies have shown that these compounds persist in the water, threaten sea life, harm the environment, and possibly enter the food chain.

A full study would include many factors before jumping to any conclusions about the dreaded myth of Climate that has not eliminated the coral through millenia.

July 20, 2019 11:44 pm

“Human pollution” is hurting the reefs.
Let me break this down for everybody. “Human pollution” = municipal sewerage.
Sewerage feeds algae blooms which in turn causes oxygen depletion which stresses the whole local ecosystem. This has been well known since approximately *forever*. This is a process the Field Biology types call “eutrophication”. There is a solution to the problem, which is simple and effective. Obtain a biology textbook suitable for any university freshman Biology 101 course, the heavier, the better. Next, grab the “journalist” who has attempted to pass off eutrophication as “new”, or “research” and beat them with the textbook. Beat them severely and without mercy about the head and shoulders. Use the textbook to slam then in the face repeatedly. Leave them bloody and battered. Threaten them with a textbook in Marine Ecology if they ever do it again.

These press releases are so dumbed down they are insulting, even without the obligatory whining about global warming. Of course, she has to throw global warming in there somewhere.

“I write about science, the environment and feminism. | published in @ausgeo @huffpost @sciencealert”

Feminist coral reef studies, anybody?

Reply to  TonyL
July 21, 2019 1:58 am

Yes: I’m a feminist so that I can tell people what to do and think. I’m an enviro activist so that I can tell people what to do and think. I “write about science” to give a pretense that I’m objective and not an ignorant regressive progressive/ illiberal liberal.

I’m sure she has some great “science based” articles about gender neutral bathrooms too.

Reply to  TonyL
July 21, 2019 2:26 pm

30 years of research ?
I was aware of the problem in Kaneohe Bay ~ 1972
Are things supposed to be different around FL ?
But, you can’t say Florida without the duh.

July 21, 2019 12:16 am

“Coral reefs are one of the most threatened ecosystems on our planet”. Nonsense.
Yes there is some damage occurring with reefs near the shore where pollution occurs or there is significant agricultural runoff and sediment. As Peter Ridd says, coral reefs are one of the most robust ecosystems on the planet. The GBR (~60km from my place) is doing fine. The do-gooders weren’t much in evidence when the real work of protecting the reef was done by the Landcare consortiums creating buffering of agricultural land to prevent runoff etc. As there is longshore drift, there needs to be some runoff of sediment to replenish the beaches.

Chauncey Chapman
July 21, 2019 2:29 am

These alarmists miss the root cause of the loss of stony coral in the western Atlantic coral reefs, the almost total extinction of the keystone species in a mass mortality event in 1983. Diadema Antilarum, the long spine black sea urchin saw 98% of the billions in the western Atlantic coral reefs die in one year. These guys are algae eaters with a voracious appetite. They prevented algae from successfully competing with the symbiotic corals for sunlight. Without Diadema the zoozanthalae algae was deprived of sunlight and died, so died the corals. A very good overview is available here: http://alertdiver.com/diadema. If we still had the population of Diadema, they would keep the algae in check.

July 21, 2019 3:02 am

One other thing is that heavy rainfall and flood plume events have both been cited as causes of coral bleaching, all by themselves.

Michael Jankowski
July 21, 2019 4:23 am

From tbe link about half of FL’s coral being dead is a tidbit about the Pacific:

…Much of the early damage to near pristine Pacific and Indian ocean reefs may have been done in the 1980s when overfishing peaked in tropical and subtropical seas. Shark fishing and the use of cyanide and explosives to supply fish to Hong Kong, Singapore, and mainland China has wiped out whole fish populations…

Cyanide for fishing?

A C Osborn
July 21, 2019 4:25 am
July 21, 2019 4:50 am

A quick search turned up factors which can cause bleaching.
A change in ocean currents, which relates to changes in phytoplankton and zooplankton populations, as well the number of other nutrients present in the water.
Increase/decrease in water temperatures.
Increase/decrease in water salinity.
Increase/decrease in air temperatures.
A build-up of carbon dioxide and methane gasses.
Exposure to increased ultraviolet radiation.
Exposure to high light levels.
Increased or high water turbulence.
Decreased levels of light.
Sedimentation, which relates to a decrease in light levels, as well as suffocation of sessile marine life.
Pollution, which is not limited to the depositing of sediment from soil erosion, chemicals such as nitrite, nitrate, ammonia, phosphate, as well as other detrimental contaminants into the sea via river run-off and drain pipes.

Note that changes in salinity can cause bleaching, and the four sampling locations are in the outflow from the everglades which have had freshwater diverted into them. If freshwater is the problem than perhaps not much can be done other than wait to see if the coral recovers.

My suggestion would be to establish a healthy control colony and then to closely monitor conditions at other locations so that the important factors can be determined. Guesswork can be very expensive.

July 21, 2019 5:52 am

‘Global warming is known to be a deadly factor’

Known by whom?

Fact: no organism, any, never ever, has been killed by ‘global warming.’ Organisms respond to local conditions. They couldn’t care less about a rise in global mean temperature, which is in fact a human calculated value – it doesn’t actually exist anywhere. No organism is exposed to GMT.

jack morrow
July 21, 2019 6:44 am

Speaking of pollution-I wish everyone could fly over NYC and watch the garbage barges inline traveling out to the dump area in the ocean. The mess in the ocean off shore is visable for miles. I have no solution for the city’s problem.

Brooks Hurd
Reply to  jack morrow
July 21, 2019 7:54 am

It is ironic that the folks who work at GISS (Columbia University) are fouling the ocean with their own trash. I am certain that Gavin would enjoy being reminded about this inescapable fact.

A C Osborn
Reply to  jack morrow
July 21, 2019 8:47 am

Burn it and generate Electricity and heat if needed.

HD Hoese
Reply to  jack morrow
July 21, 2019 10:49 am

I was unaware that this offshore barge dumping was still going on, one of the earliest US ocean pollution problems. The Gulf Stream is far offshore and there is an inshore current going S, brought interesting things as far as Virginia along with critters in winter. Google Earth and their skeletons show one for the New York Bight, with this comment. “As much as 987 square kilometers of the bottom environment of the New York Bight was affected by a one-time hypoxic event in 1976.” Their overall skeleton homework is not very good as in their Long Island Bay pollution starting in 1990. Old story there about duck farms. Old, now recycled, belief was never to trust anybody over 30, now nobody under (pick a year)???

Mark Broderick
Reply to  jack morrow
July 21, 2019 11:08 am

How is that even legal ?

Tom Abbott
July 21, 2019 6:58 am

From the article: ““Citing climate change as the exclusive cause of coral reef demise worldwide misses the critical point that water quality plays a role, too,” says ecologist James Porter from the University of Georgia.”

Citing Climate Change (CAGW) as the exclusive cause of coral reef demise should be discouraged because CAGW is not an established fact, and therefore any coral reef destruction ascribed to CAGW is also not an established fact, so it is a good thing that Mr. Porter is discouraging its use, although he doesn’t go far enough. There is no evidence CAGW is real or affecting coral reefs. No evidence whatsoever. People who think there is are seeing what they want to see, not what is there or not there.

July 21, 2019 7:12 am

Oh, Lord! Now we’ll be treated to a whole bevy of pointless no-phosphates-in-dishwasher-detergent type of regulation where it only inconveniences consumers and does nothing to effect actual impacts to the environment! But what was that about redirecting runoff to the south? That will never change! Just like the Mississippi River should have naturally rerouted itself through the Atchafalaya Basin 60 years ago, we will spend $ millions/year fighting Mother Nature, while constantly beating the average Joe over the head with guilt and more of these studies!

HD Hoese
July 21, 2019 7:27 am

Well over two decades ago I went to a seminar about western Atlantic coral bleaching blamed on high temperature. Some of us wondered how the heat could be enough to get so deep on some of them. Have not read the papers below, but the automatic attempt seems to be to find a human cause, especially nutrients. Maybe so, but that’s not science.

https://www.gainesville.com/news/20190716/florida-keys-coral-demise-linked-to-mainland-runoff-study-says/1 “LaPointe tied higher coral die offs to three periods of time — the mid 1980s, 1996 to 1999, and 2013 — all years of heavy rainfall or increased releases of water to Everglades National Park, where it naturally flows through sloughs into Florida Bay.” “Bruckner praised LaPointe’s research, but said the primary cause of coral bleaching events is temperature and increased ultraviolet radiation. He noted that mass coral die offs have occurred in remote areas not influenced by artificial nutrients.” Heavy rainfall periods like these have also produced large populations (not in coral reef areas) of blue crabs, like sargassum?

https://www.palmbeachpost.com/news/20190709/worlds-largest-sargassum-bloom-why-its-probably-here-to-stay “Last year, the bloom contained more than 20 million tons of seaweed….“It can alter food chains,” he said. “I’m kind of looking at sargassum as another canary in the coal mine for our planet.”.”

National Geographic TV has excess nutrients causing shark attacks. I was taught to look at all hypothetical possibilities which they claim to do. I do wonder though how much the environmental movement has corrupted the finding of real answers, a much more satisfying operation.

Reply to  HD Hoese
July 21, 2019 6:28 pm

“… He noted that mass coral die offs have occurred in remote areas not influenced by artificial nutrients. …”

I find this sort of language innately biased and misanthropic.

Humans are a completely natural feature on this planet, and so is every law of nature used to employ natural high-technology produced by this natural animal to aid its natural adaptation and survival.

The very concept that natural humans produce “artificial” nutrients is what’s really contrived, prejudiced, biased and “artificial”.

We are part of the environment, we’re not going away soon, and we’re not apologizing or feeling ‘guilty’ about our allegedly automatically presumed ‘sinful’ place within it, nor feeling bad about adapting to our world to make our own niche in it a better and more favorable place to live for us.

Coral grows wild like a weed both within the brown-water littorals and the open blue-water tropical oceans. That’s not changed. The coral just grows and dies-back in cycles like every other part of Earth’s biology.

No known species losses due to alleged CAGW is the truth (some crisis!).

And a greening a very healthy planet, via our kind gift of CO2 addition, and extra natural nutrients, is what we do. We’re humanity, we don’t feel bad about it, we’re good for the environment of this planet. Apparently the Earth’s environment really likes the NET effects of what we do. Ever heard of “creative destruction”? It’s what the entire environment and all species naturally do. Humans are particularly creative.

I’m proud of what human do. We should never be faux ‘guilted’ by imaginary myths into a political control trap set to snare and limit our unique creativity.

Mark S Jordon
July 21, 2019 9:34 am

If you have visited or lived in the Keys for years one can see the increased pollution. I have traveled to the Keys since the 70’s and the change in water quality is remarkable, the visibility has decreased markedly. Many species used to be found right off the beach and are no longer seen there. I suspect much of the problem is due to local development and pollution rather than fertilizer flow from Southern Florida.

July 21, 2019 9:49 am

comment image

Corals in some areas are doing very well, no evidence of ‘Global Warming’ killing them off …

William Haas
July 21, 2019 1:05 pm

The previous interglacial period, the Eemian, was warmer than this one with more ice cap melting and higher sea levels yet the coral survived so we know that it is not the modern warm period that is killing them. The reality is that the climate change we have been experiencing is caused by the sun and the oceans over which mankind has no control. There is no real evidence that CO2 has any effect on climate and there is plenty of scientific rationale to support the idea that the climate sensitivity of CO2 is zero.

Pamela Gray
July 21, 2019 2:25 pm

Years ago I was in Ensenada, Mexico. And before that Jamaica. I was shocked at the sheer number of open sewer and rain water runoff ditches going right into the ocean. The smell was horrendous and the ditch areas covered in slimy mold. Locals walked about as if nothing was amiss. It was so disgusting I have not been back there since.

Bruce of Newcastle
July 21, 2019 4:28 pm

The main thing killing coral reefs is dynamite. Literally.
Blast fishing is blowing reefs apart in several countries’ littorals. I suspect the practice is more widespread and more damaging than is typically reported, since that is a story not so convenient to the climateers.

July 21, 2019 4:34 pm

Just you wait, “for every action, there is a reaction, and a corals reaction is quite a f’n thing”.

Stolen from the movie Snatch.

July 21, 2019 9:07 pm

Saw a documentary on Cuba’s reefs and they mentioned that the coral shows signs that it started getting much healthier in’92 when the USSR collapsed and hence the factory farms were forced to shut down. Might be one factor for sure.

July 21, 2019 9:26 pm

Friends of the coral unless you’ve overfished them in the past for their collectable shells as spiny coral predator becomes another COT case-

July 22, 2019 5:09 am

These articles about Coral are ridiculous – Climate change is not the problem other wise it would effect coral in the following areas-
Where coral is Protected- 5% – Coral is in good condition.
Where man does not go – Bikini Atoll- Coral is in pristine condition and growing like a forest..
Where pesticides and fertilisers are not used- Cuba- Coral is in pristine condition and growing like a forest.

There are other reasons, flagged up above, Dynamite, but also drag nets, use in building- now stopped in the Maldives, fish- Species are now spreading across the world- Take Lionfish- “Native to the Indo-Pacific oceanic region, lionfish are quickly spreading throughout the coasts and coral reefs of the East Coast of the United States” Lionfish devastate coral reefs”

and on and on and on.

michael hart
July 22, 2019 12:13 pm

“While there is little that communities living near coral reefs 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 coral reefs requires local, not just global, action.”

The concept of “local” needs to expanded in many people’s minds.

In an ideal world we would have developed nuclear power to the point where it globally supplies so much ultra-cheap energy that we can all afford to take the expensive industrial options that reduce local pollution.That is one of the great things that wealth does for us.

Currently, that ‘pollution’ expense is just off-shored to China et al. Net result is that genuinely polluting industries simply move out of town and ill-educated greens get to think they have done something useful for the world and so scream even louder at their next protest. In reality they have probably achieved less than nothing.

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