Coral reefs are among the ecosystems most threatened by human beings, responsible for climate change – the increase in water temperature is behind the bleaching of corals, a process that can ultimately lead to their death massive -, intensive agriculture – which involves the use of pesticides and fertilizers that end up reaching aquatic ecosystems – and aggressive fishing practices. Reducing human impact, both globally and locally, is imperative if we want these reefs and the fisheries that depend on them to survive for decades to come.
The rise in water temperatures is often pointed to as the main culprit for this threat, but a recent study published in the journal Marine Biology also points to another important factor. After collecting data from the Looe Key reef for thirty years, located in the National Marine Sanctuary of the Florida Keys (USA), these researchers from the Harbor Branch Oceanographic Institute, Florida Atlantic University, have discovered that the problem of Coral bleaching is not only due to the warming of the planet, but also to an increase in reactive nitrogen, which we generate through the production, for example, of fertilizers and wastewater that we then treat improperly.
The corals were already dying
Those elevated nitrogen levels cause the corals to starve for phosphorus, lowering their temperature threshold for bleaching. In fact, they point out, these coral reefs were dying long before they were hit by increased water temperatures. “Our results provide clear evidence that human-caused nitrogen loading of the Florida Keys and the greater Everglades ecosystem (subtropical natural park), rather than rising temperatures, is the main driver of degradation. coral reefs in the Looe Key Sanctuary Preservation Area, “says Brian Lapointe, lead author of this study and research professor at Harbor Branch.
Two nutrients that can give life or death
The presence of nitrogen and phosphorus is essential for life, and in aquatic ecosystems they play a fundamental role as nutrients for animals and plants. However, an excessive concentration of these elements, or an inappropriate proportion, can pose a risk to these ecosystems.
And precisely one of the key findings of this study is that nutrient runoff on land has increased the nitrogen / phosphorus ratio in reef algae, with increased phosphorus limitation, which is known to cause stress. metabolic rate and famine in corals. According to these researchers, reactive nitrogen concentrations are above the critical threshold of the ecosystem previously established for the Florida Keys, as well as levels of phytoplankton for marine reefs, as confirmed by the presence of macroalgae and other blooms. of harmful algae due to excessive levels of nutrients.
“The good news is that we can do something to solve the nitrogen problem ,” says Lapointe. In this sense, he points out that it is possible to improve wastewater treatment, reduce the use of fertilizers and increase the storage and treatment of rainwater in Florida.
According to another of the study’s co-authors, James W. Porter, Professor of Ecology at the University of Georgia, “citing climate change as the sole cause of the disappearance of coral reefs around the world loses sight of another critical point is that the quality of the water also plays a role ”. “While communities living near coral reefs can do little to stop global warming, they can instead help reduce nitrogen runoff. Our study shows that the fight to preserve these coral reefs also requires local action, and not just global, ”concludes Porter.
Image: Larry Lipsky
