Coral reefs are some of the most vulnerable ecosystems in the world, and environmental stressors such as climate change lead to their bleaching and eventual death.

Although the warming planet is, in particular, seen as the major stressor affecting coral reefs, researchers of a new study found another driver of coral degradation that can actually be dealt with.

Coral Cover In Florida

Florida Keys National Marine Sanctuary now has the lowest coral cover in the wider Caribbean region, and researchers of a new study wanted to understand how nitrogen travels from the Everglades to the coral reefs. Armed with 30 years’ worth of Florida Keys and Looe Key Reef data, researchers collected seawater samples during wet and dry seasons as well as seaweed samples for tissue analysis, and also monitored the living corals as well as the seawater salinity, temperature, and nutrient gradients in the area.

Interestingly, the data showed that coral cover at Looe Key Sanctuary Preservation Area significantly dropped from 33 percent in 1984 to less than 6 percent in 2008, with varying rates of decrease in the period. Specifically, from 1985 to 1987 and 1996 to 1999, significant coral decline was observed due to heavy rainfall that increased water flow from the Everglades and resulted in the increase of phytoplankton and reactive nitrogen to levels that cause stress and eventual coral-reef death.

Nutrient Runoff Killing Coral Reefs

So where is the nutrient runoff killing coral reefs coming from? According to researchers, the land-based nutrient runoff that is resulting in increased nitrogen-phosphorus ratio is coming from improperly treated sewage, fertilizers, and top soil. With increased nitrogen levels from such sources, corals are subjected to phosphorus starvation and their temperature threshold for bleaching decreases.

“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,” said senior author Brian Lapointe Ph.D. “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.”

Local Action To Save Coral Reefs

While climate change is a main player in coral reef death, the study shows that water quality plays a significant part as well. This means that preventing further coral reef death can be achieved by reducing nitrogen runoff through simple steps such as creating proper treatment plants and reducing the use of fertilizers.

Simply put, even if coral reef death is a global problem that requires global action, concrete local steps can also be taken to preserve coral reefs.

The study is published in Marine Biology.