Microplastic data derived from seawater using two sampling techniques, 1L whole water grab methodology and plankton tow (200 μm mesh) methodology, from specific locations surrounding San Cristobal Island, Galapagos, Ecuador.

Our current understanding of the threat of plastic pollution to marine fauna in the Galapagos is based upon one-year of sampling efforts using traditional net-based methodology. This research aimed to further characterise and quantify sea surface microplastics around San Cristobal Island, enabling particles smaller than 200 µm to be included at target locations. In April 2019, researchers from the University of Exeter undertook traditional 200 µm plankton net samples at 7 sites around San Cristobal Island, Galapagos (Montones, Rosa Blanca, Harbour, Carola, Puerto Grande, Cerro Brujo and Punta Pitt D). Additionally, a targeted sampling campaign utilising grab methodology (1L whole water) was employed at 4 sites in the harbour area and coastline of the town of Puerto Baquerizo Moreno, where microplastics, especially fibres, were expected to be more abundant. Grab sites (Harbour, Playa Mann, Carola and the Outflow Pipe) represented the start and end of 2 tows (Harbour and Carola). Grab and Tow sea surface samples were performed in triplicate at all sites, 0.2 m and 0-0.33 m below the surface, respectively. Grab samples were vacuum filtered through 1.2 µm GF/C filters and sealed in Petri dishes. Tow samples underwent 1-2 chemical digestions using 10% KOH at 50 °C for 72 hours to eliminate organic material, and were vacuum filtered through numerous 70 µm nylon mesh discs due to high undigested organic material remaining. Filtered from the grab samples and seawater tow samples were systematically inspected using an Olympus MVX10 microscope. Any suspected microplastic particles were quantified and characterised according to shape and colour. Particles were imaged and measured using Image J, Olympus cellSens Standard Software and the attached camera (D474). Particles were analysed using FTIR spectroscopy. Polymer composition was determined of 100% of particles identified in grab samples (n=308). Due to the vast quantity of particles isolated from the seawater tow samples (n=4,744), a stratified and randomized approach was developed; 10% or a minimum of 3 particles (highest value) within each combined colour and shape category were imaged, measured and polymer composition determined; this resulted in 26.7% of particles analysed (n=1,265). Plastic additives were included in the plastic counts due to the degraded nature of the environmental samples resulting in the anthropogenic synthetic polymer to be identified instead of the petrochemical polymer. These data revealed high average abundances of 11,500 ± 1,484.77 microplastics m^-3 in the coastal waters of the Galapagos. There was a 7,770-fold higher abundance of microplastics observed using grab sampling compared with 200 µm plankton nets (12,783-fold higher abundance when anthropogenic cellulose particles were included). The average abundance of 19,750± 1,855.07 microplastic and anthropogenic cellulose particles m^-3 is 2.8 times that found in the Pacific Ocean highlighting the high levels of plastic pollution recorded. Particles smaller than 200 µm comprised 44% of microplastic and anthropogenic cellulose particles in grab samples indicating previous estimations based on plankton nets have missed this smaller fraction of particles and consequently underestimated plastic sea surface abundances and threats to marine fauna. Tow data around San Cristobal Island reported a significant difference of microplastic abundance between sites, notable higher concentrations of microplastics (and anthropogenic cellulose particles) at Montones.