Unseasonably warm ocean temperatures are known to cause coral bleaching events, which is why the National Oceanic and Atmospheric Administration tries to predict mass bleaching events by studying changes in water temperatures using satellites and in situ sensors. NOAA’s coral reef watch program has proven successful, but it is becoming clear that other environmental stressors should be incorporated into the bleaching prediction algorithms to improve their accuracy.
Scientists at the Scripps Institution of Oceanography studying the Heron Island coral reef near Australia’s Great Barrier Reef are zeroing in on stressors affecting the shallow-water flat. Their results, published in the journal PLOS ONE, could help incorporate multiple stressors into bleaching forecasts to improve its accuracy in a high-carbon-dioxide future.
“Coral reef flats in general are very understudied with respect to climate change,” said David Kline, associate project scientist at Scripps and lead author of the investigation. “Conditions are too shallow to put a mooring buoy and they’re challenging environments with large swings in environmental conditions.”
To get around those issues, he and others built a custom monitoring platform to take measurements around the reef flat. It was equipped with sensors to track pH, conductivity, temperature, depth, water flow, tidal salinity and light levels. The sensors interfaced with a data logger with integrated radio telemetry to broadcast findings to scientists in real time.
In addition to the measurements collected remotely, scientists gathered water samples with bottles to take back to the lab for analysis. The discrete samples were analyzed to measure water chemistry such as dissolved inorganic carbon levels, alkalinity and nutrient levels which tell researchers how much carbon dioxide the water is taking in, and the water’s saturation state.
“That (saturation state) tells us how energetically favorable it is for organisms to build shells or skeletons,” said Kline. “There’s no sensor for dissolved inorganic carbon or saturation state yet.”
All of the measurements offered useful insights for researchers, but one key finding they uncovered was the wide variability of conditions on reef flats.
“We were surprised by the daily, monthly and seasonal variability in data sets,” said Kline. “The six-month investigation really let us see how conditions changed over time.”
Periods of low pH and higher water temperatures didn’t always come at the same times on the flat, which means that corals there could be stressed more often than has been previously thought.
Kline says he expected that the conditions would overlap more, but adds that the find will be very informative for those at NOAA who develop the coral bleaching forecasts.
“We hope data from sensor networks will be integrated into the NOAA forecasts so that policymakers and reef managers have the best possible data in efforts to protect reefs during these most challenging times,” said Kline. “As climate change is a global phenomenon, advanced warning could help them further reduce local stressors, like pollution or overfishing, during these stressful periods.”
Up next for Kline’s group is to continue working to develop custom sensor networks to monitor coral reef flats and other challenging marine environments for multiple years. With the data from these integrated sensor networks, his group plans to improve experimental studies by making the controls mimic these dynamic conditions and perform the treatments as an offset from these conditions.
“A lot of the experiments to date have done control and treatment as a flatline,” said Kline. “But it’s important to incorporate variability because it affects organisms’ physiology.”
Featured Image: The sensor network deployed on the Heron Island coral reef flat. (Credit: David Kline)