As stated in Directive 2008/56 /EC of the European Parliament and the Council of June 17, 2008, the marine environment is a precious heritage that must be protected, preserved and, where practicable, restored. In Spain Law 41/2010, of December 29, on the protection of the marine environment, regulates it. The National Parks Autonomous Agency (OAPN) is also committed to this goal, since one of its responsibilities is to coordinate the MaB Program, and to promote and support the Spanish Network of Biosphere Reserves, which currently encompasses 52 territories, and 15 of them have the marine environment as part of it. All of them face common challenges, as the increasingly abundant presence of marine litter in the seas and oceans. While the vast majority of it, it is generated on land, a significant part ends up within the marine environment. Plastics, and in particular microplastics, are a typology of marine litter. Their small size facilitates their ingestion by marine fauna, which poses a risk for human health. This communication focuses on the human activities that are taking place in the Spanish Island and Coastal Biosphere Reserves, and on the potential plastic waste that they can generate. The responsible of these territories are aware of the danger that this constitutes for the maintenance of marine ecosystems. For this reason, diverse research and collaboration initiatives are ongoing. The objective pursued with them is three-fold: (i) learning about the effects of microplastics on the marine environment, and on human health; (ii) raising awareness between all productive sectors, which are potential generators of plastics; (iii) understanding the importance of taking measures to reduce them, while promoting circular economy. These initiatives are described within this communication, so that they provide an overview of the work being carried out, and the main results achieved so far.