## 4 Discussion and Conclusions
This topic is considered, according to ISPRA and the Marine Strategy Framework Directive, one of the main indicators to be monitored in order to define the \"Environmental Status\" of our seas and coastal areas. Early results have shown that marine litter has a strong dependence on wind rather than on surface sea currents, depending on its shape [9]. This also implies a considerable dispersion of anthropogenic objects transported by rivers once they are released into the sea, and this must be taken into account in the design of Smart Drifter Clusters dedicated to this specific study. The MARTA drifter modular shape (Figure 1) meets these requirements, allowing different configurations: from the classic donut shape (similar to the CARTHE drifters [7]) to other shapes (e.g., catamaran type), with which to simulate the transport of different floating objects. Moreover, again with regard to the study of marine litter, the smart drifters can also be equipped with an innovative sensor (also low-cost and developed within the MARTA project by the CNR-ICCOM) that can count and discern the polymeric type of micro-plastics present on the water surface. This sensor, currently a prototype [18], is being tested in various aquatic environments in order to assess its potential and the reliability of the data obtained. The combination of the Smart Drifter Cluster and the microplastic sensor would introduce a genuinely low-cost monitoring solution in the field of marine monitoring. This approach would bring undeniable advantages, especially when considering the labor-intensive nature of current procedures. However, we believe that the Smart Drifter Cluster cannot replace the current standard drifters, each equipped with satellite communication, used for studying large ocean currents. The scale of interest for these currents, such as the Gulf Stream or other basin-scale gyres, is extensive, and the related meso and submesoscale dynamics are highly turbulent, resulting in a high probability of fragmentation of the initial cluster into disconnected sub-clusters. This would require the use of many primary elements (which are more expensive compared to secondaries), negating the overall cost-effectiveness of the system. In the field of marine current studies, the most suitable application for the Smart Drifter Cluster lies in monitoring coastal dynamics. In fact, this project originated from previous campaigns aimed at monitoring the dynamics of marine litter discharged into the sea by rivers. Our current efforts are focused on expanding and optimizing the communication capabilities of Smart Drifter Clusters. Specifically, we are exploring the use of different high-gain antennas and temporarily increasing the transmission power in LoRa communication. These optimization efforts are focused on expanding the linear cluster size to achieve two main objectives: to decrease the chances of subcluster division and to enhance the likelihood of the cluster boundary being in close proximity to the coast. This proximity enables the utilization of GSM/4G communication, eliminating the need for satellite communication. Conceptualization, S.M. and M.B. ; methodology, S.M., M.B., V.C., L.M., M.P., C.G. and L.S. ; software, V.C., C.G. and L.S. ; formal analysis, V.C., L.M. and M.P. ; investigation, S.M., M.B., V.C., L.M., M.P. and L.S. ; resources, S.M., M.B., V.C., L.M., M.P., C.G. and L.S. ; data curation, V.C., L.M., M.P. and L.S. ; writing--original draft preparation, S.M., M.B. ; writing--review and editing, S.M., M.B., V.C., L.M., M.P., C.G. and L.S. ; visualization, M.B., V.C., L.M. and M.P. ; supervision, S.M. ; project administration, S.M., M.B. and L.M. ; funding acquisition S.M., M.B. and L.M. All authors have read and agreed to the published version of the manuscript. This research was funded by the European Union through the project M.A.R.T.A. : SVILUPPO DI UNA INNOVATIVA MULTIPIATTAFORMA SMART DRIFTER-UMV-SAPR PER INDAGINI MARINE, POR CreO FESR Toscana 2014-2020, Call Rd5 2020, Activity 1.1.5.a1.