Just a few genes let corals build skeletons

(Credit: iStockphoto)

A new study shows how stony corals create their hard skeletons.

In addition, researchers have conducted the world’s most comprehensive analysis of coral genes, focusing on how their evolution has allowed corals to interact with and adapt to the environment.

“I think one of the more interesting aspects of these data will be to understand which coral species may become winners or losers in the face of anthropogenic climate change–what makes them tougher and what makes them susceptible to changes in temperature, changes in ocean acidification,” says Paul Falkowski, a professor who leads the Environmental Biophysics and Molecular Ecology Laboratory at Rutgers University.

The coral gene database study, led by Professor Debashish Bhattacharya and Falkowski, appears in the journal eLife. The stony coral study appears in the Proceedings of the Royal Society B: Biological Sciences.

Our 4 threats to corals

Nearly all corals are colonial organisms that consist of as many as hundreds of thousands of animals called polyps. Types of corals include stony, shallow-water species that build reefs, soft corals, and deep-water corals that live in dark cold waters, according to the National Oceanic and Atmospheric Administration.

According to Folkowski, corals face four major threats from humans:

  • Destruction of reefs by grenades and poison used to kill fish for food;
  • nutrient pollution, usually from sewage or agricultural runoff, which over-stimulates harmful algae;
  • increased heat in the upper ocean, which causes most coral bleaching that can kill reefs;
  • and acidification of the ocean.

“Corals are the most diverse marine ecosystems on the planet,” he says. “But their value to marine ecosystems—and to our own use of marine resources—is very underappreciated.”

Recent aerial and underwater surveys have found that 93 percent of the Great Barrier Reef off Queensland in Australia has endured very severe, moderate or at least some coral bleaching this year, according to the ARC Centre of Excellence for Coral Reef Studies in Australia. The reef, a world-renowned tourist attraction, is about 1,430 miles long.

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Elevated sea temperatures from global warming can cause corals to expel tiny, colorful algae, according to the center. Corals turn translucent and white when they lose the algae. Mildly bleached corals can recover if the temperature drops and algae can recolonize them. If not, corals may die.

Building skeletons

At Rutgers two years ago, leaders in the field of coral biology and genomics met to plan an analysis of 20 coral genomic datasets. The goal was to provide a comprehensive understanding of coral evolution since the organisms appeared on Earth 525 million years ago. The coral database, which includes corals in tropical waters, has been posted on the ReefGenomics website to foster growth in this important area of research.

This study’s major advances include explaining the origin and evolution of the unique genes involved in the creation of hard skeletons by corals. The study also serves as a novel toolkit compared with the genes of humans, shellfish, and other animals with hard skeletons.

[Exoskeletons let these shrimp live in very hot water]

Bhattacharya and coauthors found dozens of genes that allow corals to coordinate their response to changes in temperature, light, and pH (acidity vs. alkalinity) and deal with stress triggered by the algae that live with them and exposure to high levels of light.

Surprisingly, some of these stress-related genes are of bacterial origin and were acquired to help corals survive. An intriguing theory that arose from the study is that the vast genetic repertoire of corals may help them adapt to changing ocean conditions.

The study in the Proceedings of the Royal Society B: Biological Sciences explains how stony corals make their hard, calcium carbonate skeletons. It also explains how this process might be affected as the oceans become more acidic due to climate change. Acidity increases as oceans are exposed to higher concentrations of carbon dioxide, the main greenhouse gas and cause of climate change, in the atmosphere.

“The aragonite (hard skeleton) is not just minerals,” Bhattacharya says. “The proteins are very important for giving it shape and making it stable.”

Falkowski says the study serves as a model for understanding how we can regenerate bone. “There are amazing parallels between the production of the skeleton of coral and production of bone,” he says.

Source: Rutgers University

DOI: http://dx.doi.org/10.7554/eLife.13288