Research yacht Tara leaves San Diego on her last leg of a 30-month expedition. Credit: Yann Chavance/Tara
The 118-foot (36-meter) sailing vessel Tara left San Diego this weekend, heading back to her homeport of Lorient, France following a successful two-year research expedition by Tara Oceans.
Her voyage – begun September 2009 – took the famous schooner around the globe, from the Mediterranean to the Atlantic, Indian, Pacific and Southern Oceans, studying plankton in marine ecosystems.
Foundation of the Food Web
The term ‘plankton’ (from the Greek word meaning ‘drifters’) embraces the vast array of microscopic animals (zooplankton) and plants/protists (phytoplankton) plus bacteria (bacterioplankton) and viruses (virioplankton) that float throughout the world’s large bodies of water.
Dr Eric Karsenti, lead scientist and overseer of the plankton research. Credit: Tara
“Plankton is at the base of the food web, and regulates oxygen and carbon dioxide in the atmosphere,” explained Dr. Eric Karsenti, of the European Molecular Biology Laboratory (EMBL), and one of Tara Oceans’ lead scientists.
Phytoplankton employ photosynthesis to make their own food using the energy of the sun to produce nutrition, and creating oxygen as a byproduct. Zooplankton – either animals that are planktonic temporarily (like larvae) or perpetually – feed on microscopic organisms.
This combined array forms the foundation of the food web, on which all marine life depends. Equally important is that phytoplankton are the top producers of oxygen on the planet. But plankton may be threatened by global warming, acidification, variations in winds and ocean currents, and changes in the levels of nutrients, salinity, oxygen, and CO2.
Earlier reports by NOAA noted a decline in phytoplankton levels in the northern oceans over the last 20-30 years; scientists pointed their fingers at warmer waters, and changes in wind patterns.
A Global Effort
Biologists from around the world carried out research aboard the schooner Tara. Credit: A. Peyrot/Tara
As part of their ongoing research, Tara Oceans amassed an international team of oceanographers, ecologists, biologists, geneticists, and physicists, sampling water around the globe and visiting 30 sites, including Antarctica. Dr. Karsenti expressed a hope to complete the comprehensive study by sampling around the North Pole in the future.
Tara Oceans also studied currents and their effects, as a major element regulating Earth’s climate. The Agulhas Eddies, for instance – deep, wide spirals of warm, salty water from the Mozambique Channel and East Madagascar Current – travel along the eastern edge of South Africa to the Southern and Atlantic Oceans. These eddies are responsible for transporting, “enormous masses of water in the Southern Hemisphere, like the Gulf Stream does in the Northern Atlantic,” said Dr. Karsenti. “It is therefore part of the world-wide ocean water recirculation, that redistributes water masses with different temperatures around the world.” The resultant changes in salinity, temperature, and oxygen can significantly alter the ocean habitat, and affect the sea life in various ways: as the currents force upwelling which carries to the surface nutrients that feed plankton and fish.
Radiolaires are protozoa which have remained unchanged for 600-million years. Credit: J. Capoulade/EMBL/Tara
Dr. Eric Karsenti added that plankton and their ecosystems contain ancient organisms which help scientists study evolution. “The discovery that most of the genes we find are unknown, was not a real surprise, but really impressive to see how much we don’t know about the microscopic marine life.”
“Since this has never been done really at the world level, there is no possible comparison yet,” Dr. Karsenti continued. “If this type of expedition is redone in, let’s say 10 years, it might be possible to see some changes. But changes usually become visible over longer period of times for these world-wide systems.”
Predicting the Effects of Change
In much of the sampling, photodegraded plastic was gathered alongside the plankton. Credit: J. Capoulade/EMBL/Tara
For now, Dr. Karsenti, who is also co-director of Tara Expeditions, is eager to return and scrutinize information collected over the 30-month expedition. “First we need to analyze the data, and afterwards, go back to specific zones suggested by the results of the analysis, for more extensive local sampling over various seasons.”
The expedition was charged with exploring marine ecosystem adaptations, in the hopes of predicting the effects of climate change, and the resultant variations in oxygen and CO2 levels, on the marine environment. “The most important outcome for the future is that this will open the possibility to build models integrating the evolution of pelagic ecosystems with environmental changes,” said Dr. Karsenti.
Tara's 60,000-mile expedition included a stop in Moorea. Credit: L. Colchide/Tara
Tara Oceans mission is supported by the Centre National de la Recherche Scientifique, (CNRS – National Center for Scientific Research), Commissariat à l’énergie atomique et aux énergies alternatives (CEA – French Alternative Energies and Atomic Energy Commission), Pierre et Marie Curie Université, and EMBL.
