Coral CSI: Foster Scholar Andrea Kealoha analyzes water chemistry for clues about invertebrate mortality events

By Yaamini Venkataraman

May 2018

Swimming through hazy, green waters in the Gulf of Mexico in 2016, divers knew something was off at Flower Garden Banks National Marine Sanctuary. That’s when they noticed the vast quantities of dead marine organisms around them, and curious white mats covering the corals. One area of this pristine sanctuary was no longer teeming with life. When marine organisms die suddenly and no one knows why, that’s when you need a dedicated group of scientists for a special episode of Coral CSI.

Dr. Nancy Foster Scholar Andrea Kealoha is one of those scientists. A chemical oceanography Ph.D. student at Texas A&M, Kealoha’s penchant for coral reefs emerged from her master’s work in Papahānaumokuākea Marine National Monument in the Northwestern Hawaiian Islands. The monument protects colorful and bountiful coral reefs that are home to numerous fish species, many of which are important for native Hawaiian fishing practices.

“After visiting Papahānaumokuākea — which is one of the most beautiful places I have ever been — I was inspired to learn more about how coral reefs were affected by climate change. That’s why I wanted to get a Ph.D.,” Kealoha says.

Once she found out that researchers at Texas A&M were working at Flower Garden Banks National Marine Sanctuary, she was sold. This national marine sanctuary protects some of the healthiest reefs in the Gulf of Mexico — something Kealoha found surprising.

“I had never been to the Gulf of Mexico, but I imagined the water to be brown and murky from all the river discharge,” Kealoha says, speaking about the common misconception that the Gulf of Mexico is not a prime destination dive location. “But offshore, the water can be crystal clear, and here you have this beautiful, pristine coral reef ecosystem in the middle of nowhere,” Kealoha says.

The health of these reefs is important for local fishing communities and ecotourism. Even though the sanctuary is about 70 to 115 miles off the coasts of Texas and Louisiana, it is still subject to human impacts like climate change, overfishing, and pollution. When the localized mortality event hit in 2016, scientists worried about how it would affect the sanctuary and marine life.

Kealoha and a team of scientists from diverse disciplines participated in a rapid response cruise to figure out why the corals and other reef associated animals died so suddenly. While biologists took samples of the microscopic organisms living in the water, corals, and those mysterious white mats, Kealoha collected water to measure the oxygen content, salinity, and other important chemical properties such as pH and carbon dioxide content.

Based on the samples they collected, Kealoha believes fresh water, primarily from the Mississippi River, and an influx of deeper ocean waters led to the localized mortality event. Water that flows from the Mississippi River into the Gulf of Mexico usually stays close to the coast. But sometimes, winds can push the fresh water offshore and into the national marine sanctuary. This fresh water is hazy, so it blocks sunlight and prevents any photosynthesis — oxygen formation — by corals. And because fresh water is lighter than salty ocean waters, it sits at the top of the ocean, forming a cap that prevents oxygen from entering the ocean. Like life on land, corals and marine invertebrates need oxygen to breathe. With fresh water blocking oxygen from entering the water, the corals start to suffocate. When Kealoha looked at the water samples she collected, they had low salt content, pointing to the presence of Mississippi River water in the sanctuary.

Kealoha also believes upwelling, or the movement of deep water to the surface, also played a part in the mortality event. Because deep water is farther from the surface, it does not get to exchange oxygen with the air. These deep waters are naturally less oxygenated — a characteristic that is not good for organisms that require oxygen to survive. The combination of the hazy, freshwater cap and dense, low-oxygen deep water caused respiration to increase and photosynthesis to decrease, leading to less oxygen in the water and what Kealoha calls upwelling-induced hypoxia. The corals suffocated and died, while other animals that can tolerate low-oxygen conditions, like the creatures that formed the white mats, started to move in.

Kealoha and her team discussed these theories at a symposium organized by the national marine sanctuary, Integrated Ocean Observing System, and Gulf of Mexico Coastal Ocean Observing System in February 2018 with other groups working on piecing together data from the event. While there was no “smoking gun,” all groups agreed that both low oxygen content, as well as high water temperatures, could have contributed to the mortality event.

“One thing we did agree on is that there is a real need for a long-term oceanographic monitoring system that can detect threats such as hypoxia and ocean acidification,” Kealoha says. “Climate change is at the top of everyone's list as a major threat to this ecosystem, and its very possible that more events like this will occur in the future.”

The Coral CSI team may need to work more frequently in the future. With the potential of more extreme weather events, increased rainfall bringing Mississippi River water into the sanctuary, and ocean acidification threatening the sanctuary, Kealoha is worried. “If we can develop an understanding for current threats to the ecosystem, we can prevent these threats from causing damage in the future,” she says.

Kealoha remains optimistic about the ocean’s future. When she teaches oceanography to undergraduates at Texas A&M, she can see her students changing their actions after learning about an environment they have never seen before. Even Kealoha, who grew up in Hawai‘i subsistence fishing with her dad, had no idea she could turn a passion for the ocean into a career.

“I did not actually realize there was an oceanography degree and a huge diversity of jobs dedicated to studying the ocean,” Kealoha says. “I went to get my bachelor’s and I was like, ‘Oh my gosh, that is what I need to do!’ Because I have this cultural connection, I knew that I would never lose my drive.” When she’s at home in Hawai‘i, she works with Hawaiian youth so they know of all the career options open to them.

From undergraduate classrooms in Texas to community engagement in Hawai’i, Kealoha is inspiring the next generation of ocean stewards. Kealoha is ensuring they have the tools to protect and cherish the marine environment, so they can spread ocean optimism to the generation that follows them.

Yaamini Venkataraman is a volunteer social media intern for NOAA’s Office of National Marine Sanctuaries and a graduate student at the University of Washington.