While studying samples of communal marine organisms, biologist/ecologist Giuseppe Suaria for the first time began wondering about the presence of plastics at sea. In 2013 this Italian researcher at the Marine Science Institute (ISMAR) undertook a study on the movement of larvae and their diffusion through Marine Protected Areas in the Mediterranean. In his net hauls, he found a large concentration of micro-plastics.
He then decided to undertake work that might seem long and tedious: identification of floating debris. Between 2013 and 2014, Giuseppe navigated in the Adriatic and the Mediterranean, but also in the Black Sea. Regardless of location, the conclusion was the same: plastic waste is everywhere! Through his observations, the first large-scale report on the abundance and distribution of macro-floating debris in the Mediterranean has been published.
What observations have you made about the presence of macro-waste in the sea?
We started working in the Adriatic Sea with a Neuston net, similar to the Manta net used aboard Tara during the last expedition. Our samples contained many plastic fragments, but we also observed a lot of macro-waste on the water’s surface while navigating, so I started counting.
We then conducted a census of macro-waste in the central and western parts of the Mediterranean, and we confirmed high levels of plastic with density variations and important spatial heterogeneity. We also found a surprising accumulation in the region of Algeria.
Why do you say “surprising”?
Because this accumulation is very far from the coast, hundreds of kilometers away, and we weren’t expecting this so far from the mainland. It’s difficult to understand where these objects come from. Several hypotheses are possible. This is the main shipping lane of the Mediterranean — all vessels enter or leave via Gibraltar. Despite the ban on throwing garbage into the sea, some commercial vessels are probably still doing it. Another possible explanation: a surface current is carrying waste along the North African coast. It should be noted that financial constraints in these countries often lead to waste mismanagement.
What census technique did you use?
We did a visual count using binoculars and GPS. We followed the position of visible objects, estimated their sizes, their distance from the boat, and determined what type of object. Then, using mathematical tools we extrapolated a density — a number of objects per square kilometer. Of course, our observations depend on navigation conditions, and we used methods that take into account the position of the sun, the height of the observer above the sea, the size and color of the object, and the speed of the boat. We can thus distinguish detritus measuring only 2 cm.
According to our calculations, in 2013 about 62 million macro-waste objects were drifting on the surface of the Mediterranean. And these were only the floating objects! According to some estimates, the waste present on the surface represents only a small percentage of existing pollution; the rest lies on the sea-bed or on beaches.
We counted an average of 25 floating objects per square kilometer throughout the basin, with high points of 162 debris per km2. The most polluted areas were found in the Adriatic Sea and in the Algerian Basin, with an average of 50 objects per km2.
We have begun the same research in the Black Sea, where we found the same concentration. 90 to 95% of the identified waste was plastic at the time of our study! In the past, the only debris floating off-shore were natural (wood, algae). Now we see 3 to 4 times more plastic than natural objects. This ratio means that marine organisms are 3 or 4 times more likely to encounter them, leading to strangulation, ingestion, or entanglement in this type of waste.
Interview by Noëlie Pansiot