Microscopic phytoplankton that form the foundation of the marine food chain are declining, according to a new Canadian study that indicates that the ocean's ecosystem and fisheries could be changing.
Researchers at Dalhousie University conducted the first global study of the populations of these microscopic organisms in the past century and found the declines - averaging about 1 per cent a year, and approximately 40 per cent since 1950 - are correlated with increases in sea surface temperatures. The study, a three-year analysis, is being published Thursday in the journal Nature.
"What we're looking at is the planet changing, and I think it's always hard to figure out a cause and effect of that, and what those implications are," said Curtis Suttle, a professor of earth and ocean sciences at the University of British Columbia. "Undoubtedly, that does have implications in terms of how oceanic food webs are structured, and that could have impacts on fisheries."
Phytoplankton act as the grass of the ocean and form the base of the aquatic food chain. The organisms live at the surface of the water, and are the main source of food for zooplankton, which in turn form the diet of fish and other sea creatures that are eaten by the bigger fish, large whales and humans that occupy the top of the food chain.
Phytoplankton are also major sources of oxygen to the atmosphere.
"This is a definite wake-up call that our oceans are becoming increasingly stressed and this is another indicator of that," said lead author Daniel Boyce, a marine ecologist and doctoral student at Dalhousie. "It's quite shocking to think that there's been a 40-per-cent decline at the base of the food chain over the past 50 years. I think it's absolutely cause for concern."
Using satellite measurements and historical records, the researchers set out to discover whether the oceans are becoming less green with algae. The organisms need sunlight and nutrients to grow. Upwellings of cold water bring to the surface the nutrients that phytoplankton require for their growth. But when temperatures rise, oceans become more stable and that limits the amount of nutrients that is delivered to phytoplankton in surface waters.
The study found phytoplankton populations fell in eight of 10 regions globally. These declines were occurring more rapidly in polar and tropical regions since 1950, the study found. Only in the southern Indian Ocean did the researchers see an increase in phytoplankton, while in the northern Indian Ocean, the organisms were stable. Mr. Boyce said further research is needed to understand what's driving that trend.
Prof. Suttle said the observations made in the paper should give scientists pause in trying to understand the direct cause of these population declines. When the basic food is taken away, then there's going to be less animal material to fuel our fisheries, he said.Report Typo/Error