Florida Atlantic University's first student-run news source.


Florida Atlantic University's first student-run news source.


Florida Atlantic University's first student-run news source.


A new perspective: Chemical changes in water causes coral bleaching

Brian LaPointe’s research shows that coral bleaching is caused by a change in the chemistry of waters worldwide, not just rising temperatures.
This image depicts coral bleaching. Courtesy of Brian LaPointe.

Growing up in South Florida, Brian LaPointe has always loved the water — leading him to a lifelong career in marine studies.

Many people believe that global warming and rising temperatures cause coral bleaching but Florida Atlantic Unversity’s Harbor Branch Oceanographic Institute Research Professor Brian LaPointe says otherwise. His research leads him to believe that chemical changes in the water cause an abundance of nitrogen and a lack of phosphorus, causing water color to change and the mortality of reefs.

Editor’s Note: This Q&A has been edited for brevity and clarity.

Why is this topic important to you?

I ended up going down to Woods Hole Oceanographic Institution in Cape Cod, as part of an independent study in conservation biology. I had read a paper by a very famous scientist at Woods Hall by the name of John Ryder, who had written several papers. His paper was a game changer in oceanography because it showed that while a lot of freshwater systems like Lake Okeechobee and the Great Lakes, you hear all about phosphorus being the key to limiting nutrients to algal blooms in the marine environment. It was nitrogen, not phosphorus. With all the population growth and all the tourism that we were beginning to see in Florida, the increasing nitrogen from humans, particularly wastewater, is what everyone was thinking about sewage and wastewater back then, not as much as about fertilizers.

Is the decaying of coral caused by a lack of phosphorus in the water?

Yeah… I personally believe this is the most important topic right now in the global coral reef crisis. Most coral reef scientists are biologists, and they don’t study or measure the chemistry of the water, particularly nutrients. It takes a lot of effort to measure nutrients accurately. When they see more algae growing on the reef, they immediately think, ‘Oh, this reef needs more grazers, more sea urchins or more parrot fish to eat the algae,’ not realizing that increased algae biomass, that upper limit of that biomass is really set by nutrient availability. So it’s been, I think, a missing element to a broad understanding of what’s really killing coral reefs all around the Caribbean… We’ve seen the decline of reefs in the Caribbean, including the Florida Keys. It began in the 1970s and really by the year 2000 we have lost over 90% of the living coral in the Florida Keys.

What causes the chemistry of the water to change?

Because the nutrients in that runoff from the mainland of Florida, had a lot of nitrogen in it. That exacerbated the algae blooms and bleaching and coral die-off. When that happened in the 1990s, a lot of water went south. All these big algae blooms developed in Florida Bay and were carried by currents to the reefs offshore the keys and we lost about 50% of the living coral. It was primarily coral diseases that killed the corals and of course algae blooms. So we realized and I kind of warned our water manufacturers that this might not be a good idea upfront. It was the opinion of a lot of the scientists with agencies that this would be a good thing, but there was no data to support it. So it ended up being a catastrophe sadly, and no one really wants to talk about it anymore. 

Do you think there’s anything that humans have done to cause the chemical change in the water? Is there anything that we can do to prevent it from worsening?

Well, it’s only going to get worse. The planet is warming. That’s indisputable. I think what’s being argued is the human contribution to the warming trend. I think some people are in denial that humans have a role in climate change. A lot of people want to blame this whole problem on CO2 increase in our atmosphere and it’s driving the global warming that we’re witnessing. It’s become kind of a catch all for all these problems that we’re seeing, including algal blooms. 

There’s this phenomenon called global change, which is about how humans are altering the nutrients on our planet, particularly nitrogen. We have more than doubled the amount of reactive nitrogen on our planet. This is not to be confused with climate change, which is a whole different phenomenon. However, global change and human alteration of the nitrogen cycle can interact simultaneously with climate change. You can have more than one thing going on… A lot of things that are really being driven more by global change and nitrogen increase are being attributed to climate change… [During] lobster mini season, people that paid 1000s of dollars to come down for two days to get their share of the lobsters, but they couldn’t even see the lobsters on the bottom because the water was so dirty. Everyone’s just talking about the high temperatures. But this other phenomena is happening simultaneously… We’ve never seen an algae bloom like this before…

When all these chemicals enter the waterways, does it lead to low phosphorus levels? Does it lead to nutrient starvation?

It’s more a question of nutrient balance. Laboratory studies have shown that corals exposed to high nitrogen low phosphorus conditions become stressed due to the low phosphorus relative to nitrogen and it causes an imbalance and it results in them substituting sulfur, which is in seawater, for phosphorus in their photosynthetic membranes, which becomes very stressful to the photosynthetic mechanism… The symbiosis of the coral kind of breaks down and can lead eventually to bleaching and, ultimately, mortality.

Is this phenomenon being seen around the world or just in Florida?

Yes, to varying degrees this is global. This is not restricted to South Florida. However, we are like the ground zero in the world in terms of population growth, water management, I mean, there is no other place in the world… Even on the open ocean, we’re seeing high nitrogen, low phosphorus conditions. 

Jessica Abramsky is the Editor-in-Chief of the University Press. For more information on this article or others, you can reach Jessica at [email protected] or DM her on Instagram @jessabramsky.

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About the Contributor
Jessica Abramsky
Jessica Abramsky, Editor-in-Chief
Jessica Abramsky is a staff writer for the University Press. She previously served as the Editor-in-Chief during the 2023-2024 school year and as News Editor during the Spring 2023 semester. She is a junior majoring in multimedia journalism who hopes to be a respected editor at a major news organization. You can reach Jessica at [email protected] or DM her on Instagram @jessabramsky.

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