Predicting the future of coral reefs is complicated by human impacts

Reviewing: Ford, A. K., Jouffray, J., Norström, A. V., Moore, B. R., Nugues, M. M., Williams, G. J., Bejarano, S., Magron, F., Wild, C. and Ferse, S. C. A. Local Human Impacts Disrupt Relationships Between Benthic Reef Assemblages and Environmental Predictors (2020). Frontiers of Marine Science, 7, 794.


A vibrant coral reef from Fiji. Photo by Jayne Jenkins, Coral Reef Image Bank

Did you know that about a quarter to third of all known marine life live on coral reefs, even though coral reefs only cover about a thousandth of the global ocean? Coral reefs are of immense value to us, by providing habitat for fish, protecting coastlines from floods and storms, providing food for over a billion people globally and supporting local economies via tourism and recreation. In fact, coral reefs worldwide are valued at up to 30 billion per year. But unfortunately, more than half of the reefs are seriously damaged due to warmer seawater temperature caused by global warming, overfishing and destructive fishing, waste runoff and sewage pollution and coral harvesting. As human impacts are increasingly threatening coral reef health, predicting the future of coral reef ecosystems is becoming more important. However, according to a recent research by a team of scientists, making a reliable projection of future reef conditions may be much more challenging in areas with higher human activities.


The research team identified 62 outer reefs (offshore, opposed to inner reefs which are closer to land) in the tropical Pacific Ocean that are close to human populated areas and classified these reefs into two categories – one with low exposure to human impact, and the other with high exposure to human impact. If there were more than 25 people living next to or fishing within the reef area per square kilometers of the reef area (or 10 people per 1 square mile of reef area), the reef was considered to be exposed to high local human impact, such as higher fish catch and shorter distance to cities and ports.


About 3% of the world’s coral reefs are located in the Maldives, and these reefs are vital to the Maldives economy. Fishing is the second largest industry in the Maldives after tourism. Photo from ADB

Then the research team built a model that can predict coral reef health (specifically the community of organisms that live on reefs) from environmental conditions including latitude, coral reef depths and frequency of exposure to storms, and used the environmental conditions of the 62 outer reefs they selected to test how well their model can predict coral reef communities on each reef. From this, the researchers found the model to be much more accurate in estimating the ecological communities on coral reefs with low human impact than those with high human impact. This happens because higher human population density leads to increase in sewage and agricultural runoff, which lower water quality and affect the organisms living in water. In addition, because increased fishing activity also removes specific fish species more quickly from the reef ecosystem, the reef loses its biodiversity and sustainability, and these changes in ecological communities cannot be accurately predicted with geographical factors alone.


American Samoa coral reefs, before and after bleaching (caused by high ocean temperature).

The results of this study show that high local human impacts can significantly impact tropical coral reef communities and affect their relationship with natural environmental conditions, which makes predicting future reef conditions especially difficult in reefs exposed to high human activities. Yet the collapse of coral reefs is disastrous to both the host of marine organisms on the reef and humans who live on the coastal communities and are supported by food and jobs provided by the reefs. Therefore, better understanding the impacts of local human activities on these precious colorful islands will be crucial to making accurate projections of future reefs, and to planning mitigation and restoration efforts.




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