JUL 15, 2019 5:21 PM PDT

What's Really Killing Coral Reefs?

WRITTEN BY: Tiffany Dazet

A variety of environmental stressors threaten the world's coral reefs, most notably increases in water temperature due to climate change. Changes in water temperature change the waters' chemistry causing coral bleaching events, in which the corals' symbiotic microalgae purge from the coral's living tissues causing the polyps to die. The corals' calcium carbonate skeleton structure remains, a lifeless symbol of the changing ocean.

Scientists from Florida Atlantic University Harbor Branch Oceanographic Institute and partner organizations recently discovered another critical reason for coral bleaching events—the presence of excess nitrogen in coastal waters from multiple land-based sources. Their study, published this week in Marine Biology, used 30 years of data from Looe Key Reef in the lower Florida Keys, representing the longest record of reactive nutrient and algae concentration data for coral reefs worldwide. 

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

Reactive nitrogen levels elevated in this region because of improperly treated sewage, fertilizers, and topsoil runoff which enters the coral ecosystem during periods of heavy rainfall. The increased nitrogen to phosphorus ratio in corals leads to metabolic stress, starvation, and lowers their temperature threshold for bleaching events. According to the study, water temperatures at Looe Key did exceed the bleaching threshold during the study period, but the bleaching events only occurred when the nitrogen to phosphorus ratios increased after heavy rainfall and increases in Everglades runoff.

Coastal regions worldwide are predicted to experience a 19% increase in nitrogen loading, which is a result of increasing rainfall due to climate change. Lapointe is hopeful that the problem of nitrogen loading can be addressed, whereas climate change issues present more of a challenge. In the FAU statement, he said, "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."

Sources: Marine Biology, PHYS
 

About the Author
  • Tiffany grew up in Southern California, where she attended San Diego State University. She graduated with a degree in Biology with a marine emphasis, thanks to her love of the ocean and wildlife. With 13 years of science writing under her belt, she now works as a freelance writer in the Pacific Northwest.
You May Also Like
DEC 05, 2019
Earth & The Environment
DEC 05, 2019
Scientists Get a Closer Look at "The Plastisphere"
Plastic litter is a global problem, and some of the tiniest culprits are not visible to the naked eye. These microplastics have infiltrated the world's...
DEC 23, 2019
Plants & Animals
DEC 23, 2019
Brave Ant Explorers Engage a Termite Colony
Ants and termites have known their place as bitter rivals in the animal kingdom for more than 150 million years. Even today, as populations peak at some of...
JAN 06, 2020
Plants & Animals
JAN 06, 2020
Every River Leap a Proboscis Monkey Makes Could be its Last
Leaves are one of the most essential components of a proboscis monkey’s diet, and in some cases, getting to the tastiest leaves means taking an enorm...
JAN 28, 2020
Plants & Animals
JAN 28, 2020
A Slug Does All it Can to Defend Against Hungry Ants
Slugs are slow, and this makes them easy targets for predators however big or small they might be. Here, we see that a slug has been spotted by a hungry co...
FEB 03, 2020
Plants & Animals
FEB 03, 2020
Watch a Polar Bear Mom Scare Off a Bully So Her Cubs Can Eat
Polar bears realize that food can be scarce at times, and that’s a problem considering just how much they like to eat. In many cases, they find food ...
FEB 12, 2020
Earth & The Environment
FEB 12, 2020
Urban Heat-Islands Mistakenly Signal Spring to Trees
Have you noticed trees and other vegetation in your city turning green earlier than usual? A new study from Iowa State University has shown that urban land...
Loading Comments...