As part of the study, published in Frontiers in Marine Science, the research team modelled the pathways and accumulation patterns of micro- and macro-plastics in the Mediterranean. They found that most of the Mediterranean countries included in the study had at least one MPA in which over half the plastic particles came from elsewhere.
Plastic pollution is one of the biggest issues of our time and not much is known about the full effects it can have on the oceans and the species living in it. Dr. Yannis Hatzonikolakis who led the research team behind the study explains: “Our study shows that specific sites, important for the conservation of biodiversity, concentrate high amounts of plastics. Although marine protected areas are protected by restrictions from other threats, for example fishing and tourism, plastic acts like an ‘invisible’ enemy, potentially threatening the native marine organisms.”
Between 2016 and 2018, the research team used a basin-scale particle drift model to take a look at the plastic particle distribution in the Mediterranean Sea. By looking at three land-based sources of plastic particles (rivers, wastewater discharge and cities) abd taking into account important processes such as advection, stokes drift, vertical and horizontal mixing, sinking, wind drag, and beaching, the simulation was able to predict plastic accumulation zones in the region. The findings included that coastal zones were heavily impacted by micro- and macroplastics, thus arguing that national MPAs and Natura 2000 sites which tend to be closer to coastal zones accumulated more plastic pollution than offshore sites.
According to the study, “for both micro- and macroplastics, distributions at sea surface were closely related to the adopted sources. The microplastics concentration was drastically reduced away from source areas, due to biofouling induced sinking, with their size distribution dominated by larger (>1 mm) size classes in open sea areas, in agreement with observations.” Furthermore, “the distribution of macroplastics on beaches followed the predominant southeastward wind/wave direction. In the water column, a sub-surface maximum in microplastics abundance was simulated, with increasing contribution of smaller particles in deeper layers.”
The findings also reveal that land-based sources bring the majority of micro- and macroplastics into the ocean. However, floating plastic particles are also an issue and macroplastics tend to travel further from their sources than microplastics, according to the study.
The findings are an important asset for the future management of MPAs in regards to plastic pollution. It shows that a more international collaborative approach might be useful. “Most of the studied Mediterranean countries (13 out of 15) had at least one national marine protected area with over 55% of macroplastics originating from sources beyond their borders,” says Hatzonikolakis. “Our study provides results based on which stakeholders can move forward to international collaborations to deal with plastic pollution. This is a challenging task for the Mediterranean Sea, which is shared by numerous countries with great differences in socioeconomic status, political regimes, languages, governance, and cultures.”
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