By Elizabeth McCarthy Lukehart
Charlie Davidson and Heather Page, students at Scripps Institution of Oceanography, clean out tanks for an experiment gathering data on the effects of ocean acidification on coral reefs. The experiment involves hours of tedious work, their backs bent to the high Hawaiian sun preparing mesocosms, which are tanks in which scientists simulate the ocean environment, filling them with seawater and organisms such as coral. The experiment will give the team clues about whether an increasingly acidic ocean, caused by unprecedented levels of carbon dioxide in the atmosphere, will threaten the growth and survival of coral.
Located on Moku o Lo’e, or Coconut Island, less than a quarter mile off Oahu in Kaneohe Bay, the Hawaii Institute of Marine Biology is part of the University of Hawaii. It is home to numerous marine research projects. Sitting atop 64 acres of coral reef, it makes an excellent location for this research.
Page collects what the scientists call macroalgae, or seaweed to the rest of us, which will go into the mesocosms along with coral and other organisms collected from the reefs surrounding Coconut Island. “We’re trying to understand how biological organisms affect the seawater chemistry,” Page says. They will first make observations in unaltered seawater pumped in from the bay. Then they will simulate ocean acidification by pumping carbon dioxide into the tanks, bringing the pH of the water down, so they can observe the organisms in the acidified seawater.
Mario Lebrato, a post-doctoral fellow at Scripps Oceanography, measures flow rates, the speed at which the seawater is flowing through the mesocosms. The flow of the water mimics ocean currents, giving them data that more accurately reflect a natural coral reef ecosystem.
Davidson and Page adjust tubes to different heights, which controls the flow of water in the tanks. They tinker with these for some time until they get the flow rates just right.
Lebrato places a sensor, which detects temperature and salinity, in the water tower through which the seawater is pumped from the bay into the mesocosms. Paul Jokiel, a researcher at the Hawaii Institute of Marine Biology, spent years developing this outdoor mesocosm system with colleagues.
Kiley Yeakel, a PhD student at Scripps Oceanography, talks with Ku’ulei Rodgers, a researcher at the Hawaii Institute of Marine Biology, who provided guidance to the team throughout the experiment. Rodgers studies how human activity has contributed to coral reef decline in Hawaii.
Yeakel and Davidson calibrate an instrument that measures pH by putting the sensor in beakers containing solutions with different pH levels – one acidic, one neutral, and one basic. The pH scale ranges from 0 to 14. A pH of 7 is neutral, anything below that is acidic, and anything above is basic.
With the first experiment under way, Lebrato tests the water’s pH while Davidson and Page collect water samples.
Coconut Island, home to the Hawaii Institute of Marine Biology, was once owned by a billionaire. It is now dotted with ruins from a more glamorous age. An old white building crumbles, the flaking paint forming lines of gray stretching across its façade like spider veins. It is overgrown with hibiscus and other tropical plants.
The team works in shifts through the night, taking samples and collecting data. Both experiments run from 10 a.m. to noon the following day. Here, Page uses her headlamp to see her instrumentation. The lights of Kaneohe sparkle in the distance behind her.
By sunrise, exhaustion has set in. Davidson and Lebrato continue collecting data for several more hours before the experiment is finally finished.
Coconut Island is close to the Marine Corps Air Station in Kaneohe Bay. Planes and helicopters roar over the island regularly, as training exercises take place on a near-daily basis.
Yeakel is the team’s instruments guru. Here, she prepares a sensor to be placed in one of the tanks.
Paul Jokiel shows Page and Davidson how to work the carbon dioxide tank so they can pump it into the mesocosms for the second experiment. Jokiel, an expert in coral reef ecology, has been one of Page’s mentors. Originally from Chicago, he completed his PhD in 1985 at the University of Hawaii, where he has remained since.
A cloudburst sends Lebrato and Yeakel running inside with a computer and other electronic equipment.
Yeakel places a sensor into one of the tanks. This instrument was designed at Scripps Oceanography, and measures pH, dissolved oxygen, and temperature – key data for the team’s experiment.
No stranger to manual labor, Page hauls a container of glass bottles into the lab.
Page, Lebrato and Yeakel collect data during the second experiment. The pH of the seawater in the mesocoms has dropped by 0.4 because the carbon dioxide bubbled into it has made it more acidic. This may not seem like much, but it makes a big difference. The pH scale is logarithmic, meaning an increase or decrease by one integer changes the pH tenfold. The team targeted a 0.4 decrease because scientists project that if humans continue to emit carbon dioxide at the current rate, by 2100 the ocean’s pH will have dropped by this much. To put it in perspective, the ocean’s pH is dropping at a rate and to levels not seen for over 50 million years, which could spell disaster for many marine organisms that have evolved over millions of years to live in seawater with a specific pH. A more acidic ocean could create an environment in which coral and other organisms can’t survive.
Davidson sits down, conserving energy, while Page reads off data. With two hours down, and twenty-four to go, the team faces another long day. It’ll take them months to analyze the data. They’ll be comparing it to data Page collected over the summer. They want to see how the biological and chemical processes differ between seasons, and if the organisms fare better in the acidified seawater in winter or in summer. For the coral reefs this is a race against time, as humans continue to spew carbon dioxide in the air and the ocean grows ever more acidic.