Experts: Coral bleaching also affects Marianas reefs

Marine experts talk about the plight of CNMI corals reefs in the environmental class at Northern Marianas Trade Institute last Tuesday. (Bea Cabrera)

Reefs in the CNMI, from Rota all the way up to the northern island of Uracas, have not been spared from that worldwide phenomenon called “coral bleaching,” when coral reefs die and turn white.

Experts from the National Oceanic and Atmospheric Administration and Bureau of Environmental Coastal Quality, who have been monitoring the health of local coral reefs, blamed warming ocean temperatures for this.

“Everyone is probably aware that the Earth and our oceans have been getting warmer. …Corals are living very near their temperature maximum so warmer oceans is bad news for corals,” said Steve McKagan, a NOAA fisheries biologist, told students at the Northern Marianas Trade Institute last Tuesday.

Coral bleaching happens when corals are stressed by changes in conditions such as temperature, light, or nutrients; they expel the symbiotic algae called zooxanthellae that live in their tissue, causing them to turn completely white. In the process, corals die.

Dr. Doug Fenner, a private consultant for NOAA, explained that the amazing thing about corals reefs “is that it’s an animal but it’s got little plants in it. Once the sunlight hits them, they make food, just like any tree. They also build a skeleton and that’s what we usually call the hard stuff. Everything on Saipan is built on the rock, built by those tiny animals.”

“If you see little brown dots on them, they are individual cells of algae …They help give color to them but that is just a side effect and they basically provide food and some leaks out into to coral polyp and so the coral polyp depends on it and that’s where the trouble starts with hot water,” he added.

With sea warming, the zooxnathellae, the symbiotic algae that lives inside the coral polyp, starts to produce things that the coral perceives as poisonous. The coral ejects them, turning white in the process. When the water becomes cooler, there is a chance of recovery but if it doesn’t, the corals eventually die.

Saipan and the other Northern Islands were particularly badly hit by coral bleaching in 2013 and 2014, according to BECQ marine biologist and technical adviser Dr. Lyza Johnston.

She pointed out that bleaching events are a natural phenomenon as they happened in the past “but because of ocean warming, they are starting to happen more frequently and more severely than they ever have been before.

She said scientists saw the first major bleaching in the CNMI in 2013. She said coral reefs in the Saipan lagoon were hit particularly hard because the water is shallower.

They found out the next year, in 2014, that corals in the Northern Islands also got hit.

“There were a lot of spatial variation in bleaching throughout the island chain. So the lagoon on Saipan and Sarigan, Guguan, and Pagan had a lot of recent mortality and a lot of coral assemblages but they were all dead. In June of the same year, corals were still alive in Uracas and Maug but we started to see very severe bleaching events in the same islands after a month of going across the island chain,” she added.

According to McKagan, the state of the corals in the Northern Islands shows that bleaching does not only occur in places where the are a lot of people.

“The islands Dr. Johnston mentioned are sites that don’t have people. A lot of times we think we are going to do worse around Saipan and Guam where we have lots of people and stressors, sedatives, nutrients, and fishing pressures. But the real issue is thermal stress and it doesn’t matter where you are, how many people are there, they can still hit you,” he said.

Seas around the CNMI experienced the hottest it has ever been in 2015 since scientists started keeping track. The same thing happened in 2016 and 2017 again, “so the last three years were exceedingly hot for our oceans… Historically, there might be a bleaching event and there might be 10 years before we see another so the corals recover but it’s happening so often that it’s hard for the corals to recover now,” he added.

McKagan said that BECQ samples about 10 to 15 sites around Saipan semi-annually.

It’s possible for corals to recover but it takes a long time, according to Fenner. “They have 20 years and the hot temperature of water that is killing them.”

The community is being encouraged to take part in the recovery period of the islands’ corals as this is important because the CNMI is surrounded by corals.

“What you can do is go snorkel, spend time in the water, take advantage of the beautiful resources out there. There’s a decent chance that 10 years from now, it’s going to look very different so enjoy what you still have. …Support local initiatives like beach cleanups and, if you are certified diver, there are opportunities to help,” McKagan said. “All of us can do better in handling our carbon footprint. Our island is small and if everybody starts to take action at home and at work, we can slow down this train.”