Climate change and human action threaten coral reef growth, UNC researchers find

Humans’ use of resources, land management and lifestyles can have significant impacts on the planet — and the ocean's coral reefs are at risk, UNC researchers said.  

Justin Baumann, a postdoctoral researcher in marine sciences and biology at UNC, along with several other researchers, examined coral in the world’s second-largest reef system and concluded that climate change and human activity pose a serious threat to coral growth. 

Researchers specifically compared the growth of nearshore and offshore corals of the same reef system. They found that the nearshore corals, which have historically grown faster, have experienced slowing growth rates while rates for offshore coral — 30 to 60 kilometers from the coast in this study — have remained stable.

“Corals can adapt and they can acclimate, so basically as long as they are not dead, there’s still hope,” Baumann said. “It’s not irreversible damage but we are sitting in a pretty precarious situation where, if we are not careful and we do not act quickly, it could become a lot more permanent.”

Baumann said coral reefs are vital to the world because they prevent coastal erosion, provide storm protection, act as a nursery for juvenile fish, boost the economy through tourism and serve as a food source. 

To understand how coral growth rates have been impacted by climate change and other stressors, scuba divers collected 124 coral core samples from 19 sites along a 300-kilometer stretch of the Belize portion of the Mesoamerican Barrier Reef System in 2009, 2011 and 2015. 

The coral's core acts like the rings of a tree, showing the coral's growth over the years.

Researchers considered the impact of coral bleaching, a process caused by environmental stressors that turns coral white. They determined that while coral bleaching does kill coral, it was not driving the long-term growth rate decline of nearshore coral.

Due to its proximity to land, nearshore coral is more heavily impacted by human activity that leads to runoff, erosion and pollution.

Since both nearshore and offshore corals are exposed to the rising ocean temperatures associated with climate change, and only nearshore coral’s growth rate is slowing, the research suggests that the combination of climate change and human activity together can cause the most damage to coral. 

“We have to be really careful about how we change the land upstream,” Baumann said. “We also have to be careful about our wastewater and how we interact with our environment."

Belize has made efforts to protect its coral reefs. The country's entire coast is lined with marine-protected areas that are co-managed by the government and a local nongovernmental organization, said Karl Castillo, a marine sciences professor from Belize who contributed to the study.

Additionally, Fragments of Hope, a nonprofit in Belize, works to replant coral in order to regenerate coral populations. Baumann has worked collaboratively with Fragments of Hope to plant coral. Agencies from other countries are using the organization’s work as a model for their own action, Castillo said.

“From this information, they will be able to use that to make management recommendations to help mitigate the local impacts,” Castillo said. “Yes, you can educate in terms of global impacts, but you will see a much quicker impact if local impacts are addressed as quickly as possible.” 

The researchers recommended scientists continue to monitor coral reefs and the ability of coral to adapt to various stressors, including ocean warming, eutrophication, sedimentation and coastal development.

Sydney Gallek, a senior global studies major and founder of the new organization Citizens Climate Lobby of UNC Chapel Hill, said she is concerned about the global impact of climate change.

“It is something we need to be acting on right now,” Gallek said. "It is something we needed to be acting on yesterday, years ago, but right now what we have to do is mitigate it the best we can.”

If the current trend of nearshore coral growth rate slowing continues, the study suggests the structure and function of worldwide coral reefs will likely be severely impaired.  

“If we do not do something about our local and global stressors that we are causing, we are going to see coral reefs degrade and a lot of corals are going to decline in growth, if not stop growing altogether," Baumann said. "And that lays our future out as a pretty bleak place."

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