Speaking to the Lusa agency, Marcos Rubal, a researcher at the University of Porto centre, explained that initially the team's aim was to study sargassum, understand its ecological importance and how this resource, a result of the natural deposition of seaweed and algae on beaches, could be valued.
However, when they began to analyse this natural resource in five beaches of the North region - Praia de Moledo, Vila Praia de Âncora, Praia do Cabedelo, Praia de São Pedro de Paramos and Barrinha de Esmoriz - they were "shocked by the amount of rubbish that appeared mixed in with the seaweed".
"We always found an enormous amount of rubbish, so we decided to add this component of rubbish to the study, and from then on, besides quantifying the sargassum and the species of algae that appeared in the sargassum, we began to quantify the rubbish in order to be able to compare", said Marcos Rubal.
During the study, which began in 2017, the team of researchers chose "undeveloped" beaches and collect sargassum, seaweed and rubbish at two different times, one during the summer and the other during the winter.
"The result of our work is that both the amount of sargassum and the amount of rubbish vary a lot, both between beaches and between dates," he said, adding, however, that the amount of trash can be "up to four times the total weight of sargassum," especially in winter.
During that time of the year, rubbish disposal, such as remains of rope, tangled nets, fishing lines, plastic stoppers for mussel culture and a variety of plastics, was higher, mainly due to "storms and rising water levels, for example from the Minho River.
"The type of rubbish changed a lot between winter and summer," Marcos Rubal added, saying that in the hottest season the rubbish found was cigarette butts, leftover food, small plastics, water bottles, juice boxes, and other pollutants.
To Lusa, Marcos Rubal said that the team's next step is to understand how rubbish changes the role of sargassum, which includes important ecological services on sandy beaches, such as maintaining the nutrient cycle or the marine food chains in the coastal ecosystem.
The study, entitled "Spatio-Temporal Variability of Anthropogenic and Natural Wrack Accumulations along the Driftline: Marine Litter Overcomes Wrack in the Northern Sandy Beaches of Portugal", was published in the international journal Journal of Marine Science and Engineering.