image: Bleached coral in the lagoon of Moorea, French Polynesia, during a marine heatwave in 2016. Coral bleaching is when corals lose the beneficial algae living within their tissues, and occurs when corals are stressed. view more
Credit: Image courtesy of Kelly E. Speare
When coupled with even relatively mild heat stress, nitrogen pollution can increase the severity of coral bleaching, according to a study. Rising ocean temperatures due to climate change affect links between corals and beneficial algae living within their tissues, destroying reef systems. However, not all reef sections are equally affected by marine heat waves. Mary Donovan, Deron Burkepile, and colleagues examined the reef system surrounding Moorea, French Polynesia to determine how rising ocean temperatures and excess nitrogen from nutrient pollution interact. During a moderate heat stress event in 2016, the authors measured bleaching indicators for more than 10,000 coral colonies at 167 sites. The authors also quantified nitrogen distribution patterns across the reef system. The authors found that for the two predominant types of branching coral surveyed, heat stress primarily drove the proportion of colonies affected. However, the severity of the bleaching for a colony was associated with both heat and increased nitrogen levels. Even when heat stress was relatively low, high nitrogen increased the severity of bleaching up to two-fold. According to the authors, while the ultimate survival of coral reefs depends on lowering global carbon emissions, mitigating nitrogen pollution at the local level could increase coral reef resilience.
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Article #19-15395: "Nitrogen pollution interacts with heat stress to increase coral bleaching across the seascape," by Mary K. Donovan et al.
MEDIA CONTACTS: Mary Donovan, University of California, Santa Barbara, CA; tel: 808-373-6922; e-mail: donovan.maryk@gmail.com; Deron Burkepile, University of California, Santa Barbara, CA?; e-mail: dburkepile@ucsb.edu
Journal
Proceedings of the National Academy of Sciences