Complexity of Coral Reefs

Researcher studies bond between corals and algae.


By Marlene Cimons, National Science Foundation

Tropical coral reefs live in a close relationship with single-celled algae called dinoflagellates.  The algae offer nutrients to the coral as a byproduct of photosynthesis, while the reefs provide the algae with shelter, protection from other sea life seeking to eat them, and a home that is close to light.

The bond fascinates scientist Monica Medina, who has been studying how corals respond to natural and stressful conditions such as global warming, and coastal development, as well as their response to shifts in the microbial community both in the corals themselves and in the surrounding environments. 

“Coral reefs are threatened ecosystems,” says Medina, associate professor in the School of Natural Sciences at the University of California, Merced. “I think society is not paying enough attention. Reefs are disappearing fast, and the mounting pressure is only going up.”

In recent years she has focused her attention on the host coral, using a variety of genomic tools, believing that deciphering the genetic basis of how corals react to such pressures ultimately will lead to ways to improve management and/or inspire mitigation strategies.

She will spend the next academic year, however, trying to better understand the algae, including the dynamics of its codependence.  “We already know a lot about how the host responds, but less about the algae,” she says. “Understanding the relationship between corals and their symbiotic algae is very relevant to climate change research.”  

The algae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis, which the coral uses to make proteins, fats, and carbohydrates, and to produce calcium carbonate, which forms the reef structure.  Without the algae, the coral would have “a very nutrient poor environment, without much in terms of food,” Medina says.

Interestingly, corals cannot live without the algae for very long, but the reverse is not true.  “The algae can jump ship whenever they want and live in the water column until they find a new host,” she says.  “If they live in a cranky host, under a lot of stress, the algae can leave the host, but the host really can’t live without the algae for a prolonged period of time.” 

Medina will be conducting research at the Observatoire Océanologique de Banyuls research station in the Catalan region of France, near the Spanish border, under a Fulbright Scholar grant.  She will be working with researcher Gwenael Piganeau, a member of the Evolutionary and Environmental Genomics of Phytoplankton research group at the station. 

“I will be doing similar experiments to what I have done so far, but now focusing on the algae,” she says.  “I want to immerse myself in a group that thinks exclusively about algae.”

Medina’s award came from the J. William Fulbright Foreign Scholarship Board’s Franco-American Commission, which aims to develop understanding between France and the U.S. through educational and cultural exchanges. The commission grants only about five such awards per year.

Medina, 43, also is finishing the sixth and final year of a National Science Foundation (NSF) Faculty Early Career Development (CAREER) award, which she received in 2007.  The award supports junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organization. She has received $1 million for her work over the six years.

Medina, now a U.S. citizen, grew up in Cali, a large city in the south of Colombia, where she first developed her love for the ocean. “I was an avid admirer of nature documentaries, especially marine sciences,” she says. “Cali is two hours away from the ocean and we would go some weekends to the Pacific, but I think my interest for the ocean grew after I saw the beautiful waters of the Caribbean Sea in the north of the country when I was about ten or 12 years old.”