Phytoplankton and pollution pushed by the ocean across the planet
In less than a decade, billions of single-celled marine organisms known as phytoplankton can drift from one oceanic to almost any other place on the globe, Princeton University researchers have found.
The same happens with plastic debris, radioactive particles and virtually any other man-made flotsam and jetsam that litter the sea, the researchers found. Pollution can migrate and cause problems for its new home.
This finding suggests that ocean biodiversity may be more resilient to climate change than we thought, according to a study published this week. Phytoplankton forms the basis of the marine food chain; their rapid spread enables them to repopulate areas where climate change has decimated them quickly.
“Our study shows that the ocean is quite efficient in moving things around,” said Bror Fredrik Jönsson, an associate research scholar in Princeton”s Department of Geosciences, who conducted the study with co-author James R. Watson, a former Princeton postdoctoral researcher who is now a researcher at Stockholm University.
“This comes as a surprise to a lot of people, and in fact, we spent about two years confirming this work to make sure we got it right,” Jönsson said.
One of the strengths of the model is its approach of the following phytoplankton wherever they go throughout the world rather than focusing on their behavior in one region, Jönsson said. Because most marine organisms are mobile, this tracking approach can offer a more complete insight.
The resulting model works for objects lacking the ability to control their movements such as phytoplankton, bacteria, and human-made debris.
The team used a computer algorithm to calculate the fastest route an object can travel via ocean currents between various points on the globe.
The researchers confirmed that the travel times calculated by their model were similar to the time it took real objects accidentally dumped into the ocean to be carried by currents. For instance, 29,000 rubber ducks and other plastic bath toys toppled off a Chinese freighter in 1992 and have since been tracked as a method of understanding ocean currents.
The researchers” model also matched the amount of time it took radioactive particles to reach the West Coast of the United States from Japan”s Fukushima I Nuclear Power Plant, which released large amounts of radioactive materials into the Pacific Ocean following massive damage from a tsunami in March 2011. The actual travel time of the materials was 3.6 years; the model calculated it would take 3.5 years.
Because phytoplankton reproduces asexually only one individual needs to reach a new area to colonize it. This fact led the team to look at the shortest time it takes to get around the world rather than the average time. “The rule for our phytoplankton was “drive at fast as possible,” Jönsson said.
To cut down the computing resources needed to track the particles, the researchers calculated the fastest way to get from one place to another using the “Dijkstra”s algorithm” after the late Dutch computer scientist Edsger Dijkstra who developed it in the 1950s.
“Dijkstra”s algorithm is a way of optimizing for the shortest path between two positions when you have a network of possible locations, and we used it to find pathways when there was no direct link from one region to another,” Watson said.
Professor of Marine Sciences Per Jonsson at the University of Gothenburg Center for Sea and Society in Sweden said. “This is the first attempt to identify timescales of connectivity and possible dispersal barriers for plankton across all oceans,” said Jonsson, who had no role in the research and is not related to study author Bror Jönsson. “The general message is that all parts of the ocean surface are connected on surprisingly short time scales.
“This implies that regional declines in plankton fitness due to climate change may be buffered by relatively rapid immigration coupled with community sorting or evolutionary change,” Jonsson continued. “The authors also offer a practical and predictive tool for a range of studies regarding global ocean dispersal, including the spread of contaminants and marine litter.”
The paper, “The timescales of global surface ocean connectivity,” was published online in-advance-of-print April 19 in the journal Nature Communications.