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Global Environment Change Causes Extension of Coral Reefs

Coral reefs and beaches are considered one of the most threatened ecosystems on the planet and are dying at alarming rates around the globe. Scientists attribute coral bleaching and ultimately massive species of coral dying to quite a few environmental stressors, in particular, warming water temperatures due to climate change.

A study revealed in the worldwide journal Marine Biology, explains what’s killing coral reefs and their habitat. With 30 years of data from Looe Key Reef, researchers from Florida Atlantic University’s Harbor Department Oceanographic Institute and collaborators have discovered that the problem of coral bleaching is not just resulting from a warming planet, but also a world that simultaneously enriched with reactive nitrogen from multiple sources.

Improperly treated sewage, fertilizers, and topsoil are elevating nitrogen levels, which are causing phosphorus starvation in the corals, reducing their temperature threshold for bleaching. These coral reefs are dying off long before rising water temperatures impacted them. This study represents the most extended report of reactive nutrients and algae concentrations for coral reefs anyplace on the planet.

A key discovering from the research is that land-based nutrient runoff has increased the nitrogen: phosphorus ratio (N: P) in reef algae, which indicates an increasing degree of phosphorus limitation known to cause metabolic stress and eventually starvation in corals. Concentrations of reactive nitrogen are above basic ecosystem threshold levels previously established for the Florida Keys as are phytoplankton levels for offshore reefs as evidenced by the presence of microalgae and other harmful algal blooms as a result of maximum in nutrients.

Researchers collected data from 1984 to 2014 and collected seawater samples during wet and dry seasons. Lapointe and collaborators from the University of Georgia and the University of South Florida also monitored the residing coral and collected abundant species of seaweed (microalgae) for tissue nutrient analysis. They monitored seawater salinity, temperature, and nutrient gradients between the Everglades and Looe Key. They needed to understand higher how nitrogen travelled from the Everglades downstream to the coral reefs of the Florida Keys National Marine Sanctuary, which now has the bottom amount of coral cover of any beaches in the wider Caribbean region.

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