Citizen and scientists work together to monitor marine alien macrophytes

The introduction of non-indigenous species (NIS) is an ongoing phenomenon which has been pointed out as a major threat to biodiversity at different levels (Wallentinus, Nyberg 2007, Katsanevakis et al. 2014, Vergés et al. 2016). NIS may in time become invasive (Invasive Alien Species “IAS”) and may cause biodiversity loss and ecosystem service changes (Brunel et al. 2013, Giakoumi 2014, Vergés et al. 2016). The Mediterranean Sea is an important hotspot for marine NIS (ca. 1,000 such species recorded to date, Zenetos et al. 2012, Galil et al. 2015, Verlaque et al. 2015). To reduce the risk of future IAS introduction and to better understand their invasive po- tential and spread dynamics, monitoring and surveillance plans are required. The creation of permanent alarm systems and public awareness campaigns are crucial for reducing the risk of IAS introduction. Since intensive monitoring programs could be very expensive, citizen science, involving citizens (e.g. tourists, ishermen, divers) in the collection of data, could be a useful tool for providing data on IAS, that would otherwise be impossible to collect because of limitations on time and resources. Citizen science is having an increasing success worldwide. Citizen science projects has rapidly and enormously increased in recent years (Conrad, Hilchey 2011), also thanks to the wide availability of mobile technologies and internet access that enable an easy and cheap way to communicate, share and interchange data. The value of citizen science has been widely recognized. Of course, in order to be used for scientiic purposes and management decisions, the collected data need appropriate quality assurance measures such as validation and veriication by taxonomic experts. We report on the experi- ence of two citizen science projects: the Project “Caulerpa cylindracea – Egadi Islands” and the Project “Invasive Algae”, included within the “Seawatchers” platform.