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Access to sunlight is critical for the survival of coral reefs

According to a new study led by Pennsylvania State University, when it comes to preserving coral reefs, what is going on above the water surface is as important as what is going on below it. By analyzing the productivity and biodiversity of the world’s symbiotic coral communities, the experts found that the maintenance of water optical quality in coral reefs is crucial to protect them and prevent reef degradation.

“Coral reefs are one of the most biodiverse ecosystems on Earth,” said study lead author Tomás López-Londoño, a postdoctoral fellow in Marine Sciences at Penn State. “To better understand that diversity, we looked at the role sunlight plays in the symbiotic relationship between coral and the algae that provide the oxygen for its survival. We found that underwater light intensity plays a critical role in the energy expended by the coral’s symbiotic algae to maintain its photosynthetic activity.”

Scientists have long known that sunlight is a major source of energy for basically all biochemical reactions that sustain life on our planet. Yet, sunlight’s impact on corals has often been overlooked. “What’s new here is we developed a model that provides a mechanistic explanation for the biodiversity patterns in coral,” López-Londoño explained. 

“Central to that explanation is water clarity, meaning that preserving the underwater light climate should be a priority for coral reef conservation. It’s as vital as pollution mitigation, limiting ocean acidification, and reducing thermal stress.”

By studying coral grown in an aquarium at different depths and gradations of sunlight, the researchers developed a mathematical model describing the connection between the depth-dependent variation in photosynthetic energy to corals and gradients of species diversity. Then, they tested this model on existent data about reefs in contrasting water clarity, and discovered that much of the variation in species richness with depth is driven by changes in exposure to sunlight.

“The model is very elegant in that it takes into consideration only two things,” said study senior author Roberto Iglesias-Prieto, a professor of Biology at Penn State. “It looks at productivity, the potential that an alga has to extract energy from the sun, and the cost of living, the cost of the repair of the photosynthetic machinery. It’s a very simple notion and we found it explains the existing empirical data.”

The results suggest that highly productive underwater environments with plentiful access to sunlight may be a vital safeguard against the risk of species extinction. Moreover, the findings offer a new strategy for reef conservation: preserving the clarity of water. Local communities could be actively involved in this by reducing the sedimentation and pollution associated with human development. 

“Unlike so much of the environmental threats that corals face, this is something that can and should be managed locally,” Iglesias-Prieto concluded.

The study is published in the journal Nature Scientific Reports.

By Andrei Ionescu, Staff Writer

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