Citizen science derived data of microplastic distribution and composition on two Galápagos Island beaches, Ecuador.

Citizen science represents a promising option for monitoring visible microplastic (> 1mm) contamination on sandy beaches across space and time. Here, high school and university students undertook supervised sampling surveys on two island beaches in the Galápagos Archipelago, Ecuador (Tortuga Bay, Santa Cruz and Punta Pitt, San Cristóbal) between 2019 and 2020. We employed a simple citizen science methodology using a standard unit (50 x 50 cm quadrat) sampled to a standardised depth (5 cm) and then sieved to 1 mm, to support microplastic monitoring efforts in the region. All suspected microplastics collected by citizen scientists from Tortuga Bay at known locations and times (n = 1,713) were analysed using FTIR spectroscopy. Due to COVID-19 travel restrictions, only ~10% of particles from Punta Pitt (n = 500; a random subsample across pooled particles, total n = 5,118) were submitted to researchers for polymer analysis. Consequently, exact coordinates and dates for each particle analysed from Punta Pitt cannot be specified, however space and time ranges are provided, along with the spatiotemporal data from all surveys. FTIR spectroscopy verified that 93% of particles collected by citizen scientists were plastic or rubber. These data revealed the highest abundance of microplastic contamination reported in the Galápagos of 0-2,524 particles m^-2, with strong accumulation gradients measured on the two beaches. The gradients observed were parallel to the strandline at Punta Pitt, but perpendicular to the strandline at Tortuga Bay, where four-fold higher concentrations were recorded at the sea turtle nesting habitat on the back-beach dune. No significant seasonal trends were measured over the course of one year.