Maria-Luiza Pedrotti is one of the scientists involved in Tara’s 10th expedition. Trained in oceanography in Rio Grande, Brazil, she is a CNRS researcher and works at the Oceanographic Observatory of Villefranche-sur-Mer.
Before boarding the schooner to study the micro and macro fauna attached to plastic and focus on the characterization of plastic collected aboard Tara, the scientist described the techniques and the planned areas for sampling, as well as the first observations after 5 months of navigation:
“Since the beginning of the Tara Mediterranean mission in May we have already made 150 Manta and about 40 Bongo net tows. The plastic fragments collected in the nets were sorted and stored on board for future analysis. We are currently in the sampling phase, and Tara is criss-crossing Mediterranean ecosystems for a comprehensive analysis of the situation.
The Tara Mediterranean strategy involves sampling in the open sea, but also near coastal cities, in the mouths of rivers, and in harbors to study the effects of anthropogenic activities* and the impacts coming from land.
Our interests in coastal areas and open ocean include: studying the influence of the current in the dispersion of micro-plastics, the presence of eddies and meanders which temporarily form and can accumulate fragments. There are also the effects of surface winds in the mixing of the superficial layer and the distribution of fragments in the water column. This is why the Bongo net is employed to sample below the surface in bad weather, instead of the Manta net, which recovers micro-plastics in the neustonic layer (surface layer) in calm seas. We also sample at night when plankton migrates to the surface to feed, thereby coming into contact with plastics. It was a surprise to find plastic fragments mixed with these sometimes luminescent organisms. We want to know the role of micro-plastics in the food web*. These micro-plastics have the same size range as the plankton and can be ingested by filter feeders, for example, certain fish, and whales.
Our main concern at the beginning of Tara Mediterranean was to cover as much as possible the Mediterranean basin and the different physical structures that characterize it. To do this, during the planning stage, scientists prepared map routes and sampling areas using satellite images and ocean circulation models. These tools are provided by the Mercator Ocean Company to determine areas of interest for sampling at sea. For weather reports we use the website Sea-Seek; for currents, winds and surface waves, we use the site My Ocean, which provides information based on satellite imaging and in situ observations. The route maps are updated daily depending on meteorological and hydrological conditions.
The Mediterranean Sea does not have permanent structures such as gyres* observed in the oceans and formed under the influence of the earth’s rotation (Coriolis force). In these zones, plastics are transported by the swirling currents and are concentrated over thousands of kilometers in the middle of the Atlantic or Pacific. Studies conducted since 2011 in the north-western Mediterranean show that the amount of plastic here is the same order of magnitude as that detected in the turbulent ocean zones, which is extremely worrisome. The first results of Tara’s research are alarming! Plastic fragments were found in every net-tow, from west to east of ’Mare Nostrum.’
M. L. Pedrotti
Anthropogenic: human origin; caused by man.
Food web: a set of interconnected food chains within an ecosystem
Oceanic gyre: gigantic whirlpool formed in the ocean by a set of currents. Gyres are caused by the Coriolis force.