Spatial variation of plastic debris on important turtle nesting beaches of the remote Chagos Archipelago, Indian Ocean

We report Anthropogenic Marine Debris (AMD) in Chagos Archipelago in the Indian Ocean, globally amongst the most isolated island groups. AMD on 14 island beaches in five atolls were surveyed in 2019 using two techniques: Marine Debris Tracker (MDT) along littoral vegetation and photoquadrats in open beach. Over 60 % of AMD in both beach zones was composed of plastics, especially bottles and fragments (mean = 44.9 %, 27.2 %, range = 16.5–73.2 %, 4.8–55.9 % respectively in vegetation; mean = 28.7 %, 31.5 %, range = 17.7–40.7 %, 11.6–60.0 % respectively in open beach). The density of plastic debris in littoral vegetation (MDT data: 1995 bottles, 3328 fragments per 100 m2) was 10-fold greater than in open beach (photoquadrat data: 184 bottles, 106 fragments per 100 m2). Significant latitudinal variation in vegetation AMD occurred (8-fold greater in southern atolls, p = 0.006). AMD varied within island zones: most debris observed on oceanside beaches (oceanside vs lagoon, W = 365, p 60% debris was plastic bottles or fragments in open beach areas (28.7%, 31.5%) and littoral vegetation (44.9%, 27.2%).•Plastic debris density in littoral vegetation was over ten-fold more than open beaches (1995 bottles, 3328 fragments 100 m−2).•Marine debris density varied latitudinally and between beach zones (oceanside, lagoon-side, island tips).•Debris hotspots overlap with critical turtle nesting habitat, informing beach clean-up prioritisation.