Global warming not the sole cause of coral reef bleaching

Researchers have looked at three decades of data and have found that there is another significant cause of coral reef bleaching in addition to warming waters due to global temperature increases. The study data looked at the Looe Key Reef in the lower Florida Keys and was conducted by Florida Atlantic University’s Harbor Branch Oceanographic Institute. The research shows that a warming planet isn’t the only issue.

Scientists say that another issue that is contributing to coral reef bleaching is a planet that is being enriched with reactive nitrogen from multiple sources. Nitrogen levels are increasing from improperly treated sewage, fertilizers, and topsoils. The increase in nitrogen is causing phosphorus starvation in corals, reducing the temperature threshold for bleaching.

The new research shows that the coral reefs were dying off long before rising water temperatures impacted them. This study is the longest record of reactive nutrients and algae concentrations for coral reefs anywhere in the world. Scientist and senior author of the study, Brian Lapointe Ph. D. says that the results in the study his team conducted provides “compelling evidence” that nitrogen loading from the Florida Keys and greater Everglades ecosystem, caused by humans, rather than warming temperatures, is the primary driver for coral reef degradation at the Looe Key Sanctuary Preservation Area during its long term study.

One key finding in the study is that land-based nutrient runoff has increased the nitrogen:phosphorus ratio in reef algae. That indicates an increasing degree of phosphorus limitation known to cause metabolic stress and eventually starvation in corals. Concentrations of reactive nitrogen are said to be above critical ecosystem threshold levels established by the Florida Keys.

The scientists also note that Phytoplankton levels for offshore reefs as evidenced by the presence of macroalgae and other harmful algae blooms due to excessive nutrients. Data for this study was gathered from 1984 to 2014.