Microplastics abundance in the coastal zones varies not only over space but also over time. Concerning the periodicity of the sampling, many studies frequently develop a single sampling while others develop a long-term evaluation, in many cases once a month. In order to accomplish this, it is important to know how the abundance of microplastics varies on small temporal scales; of particular interest is also the monitoring during a moon cycle, in order to study the possible influence of the tides on microplastics arrival. To the best of our knowledge, microplastics monitoring during a complete moon cycle has only been developed in very few occasions [1,2]. In this work, the occurrence and composition of meso- (5-25 mm) and microplastics (1-5 mm) in Playa Grande beach was monitored during a complete moon cycle on the different moon phases between 17th June and 16th July 2019 [3]. A total of 10 points were sampled each day finding an average content of mesoplastics of 18 g/m2 (0.36 g/L) and of microplastics of 78 g/m2 (1277 items/m2 or 1.6 g/L). Polypropylene and polyethylene were the most abundant types of plastics. Among the analysed particles, fragments accounted for 83 % of the total. The obtained results revealed that microplastics presence could not be related in this case with the tides but with the orientation and strength of the wind. References 1 A. R. A. Lima, M. Barletta, M. F. Costa, J. A. A. Ramos, D. V Dantas, P. A. M. C. Melo, A. K. S. Justino and G. V. B. Ferreira, J. Fish Biol., 2016, 89, 619–640. 2 J. A. A. Ramos and W. V. N. Pessoa, Mar. Pollut. Bull., 2019, 142, 428–432. 3 M. González-Hernández, C. Hernández-Sánchez, J. González-Sálamo, J. López-Darias, J. Hernández-Borges, Mar. Pollut. Bull., 2020, 150, 110757.