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 coral bleaching is not just due to a warming planet, but also a planet that is simultaneously being enriched with reactive nitrogen from multiple sources.
"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 Brian Lapointe, Ph.D., senior author and a research professor at FAU's Harbor Branch.
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.
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.
Between 1991 to 1995, significant increases in Everglades runoff and heavy rainfall resulted in increases of reactive nitrogen and phytoplankton levels at Looe Key above levels known to stress and cause die-off of coral reefs.
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.