A survey of the seas by the King Abdullah University of Science and Technology (KAUST), Saudi Arabia, has enabled scientists to come up with a predictive model of how planktonic heterotrophic prokaryotes – simple marine organisms that process most organic matter in the ocean – are affected by global warming.
Although small, plankton populations make up the largest living biomass in the ocean.
During an expedition in 2010, the scientists looked at plankton across subtropical and tropical waters of the Atlantic, Indian and Pacific Oceans. They scrutinized three factors: resource availability, mortality rates and temperature. They also looked at the viruses and microbes that either live off or kill off plankton.
Team leader Xose Anxelu G. Moran, associate professor of marine science at KAUST, and his peers from Saudi Arabia, Spain and Sweden, wanted to know what influenced plankton abundance and metabolism, and how this can help researchers predict the future role of the microbial populations in a changing ocean plagued by warmer temperatures and diminishing nutrients – thanks to climate change.
They found out that the effect of rising temperature on plankton is not uniform – populations living near the equator, for instance, are not as affected as those near the poles. The impact of global warming on marine microbes is more intense at higher latitudes, according to the study.
When there’s an abundance of viruses that eventually diminish the organism’s populations, temperature’s role becomes limited, the study adds. The same happens when there’s a decrease in nutrients; the water’s rising temperature almost becomes irrelevant. It’s why the scientists conclude that temperature only becomes a dominant factor when plankton are neither controlled by poor resources nor viral attacks.
As well, the study notes that a 1°C ocean warming will increase the biomass of plankton only in waters with more than 26°C of mean annual surface temperature.