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Distribution of microplastics on remote, isolated islands of the Chagos Archipelago; globally and regionally significant nesting sites of green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) sea turtle populations / KATHERINE WHITEHEAD

Swansea University Author: KATHERINE WHITEHEAD

Abstract

Microplastic concentration, composition, spatial distribution, and sediment characteristics are reported from green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtle rookeries in the Chagos Archipelago, Western Indian Ocean. Between March and July 2019, 25 sediment cores (60 cm depth by...

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Published: Swansea 2022
Institution: Swansea University
Degree level: Master of Research
Degree name: MRes
Supervisor: Esteban, Nicole ; Stokes, Kimberley ; Esteban, Peter
URI: https://cronfa.swan.ac.uk/Record/cronfa60411
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Abstract: Microplastic concentration, composition, spatial distribution, and sediment characteristics are reported from green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtle rookeries in the Chagos Archipelago, Western Indian Ocean. Between March and July 2019, 25 sediment cores (60 cm depth by 10 cm diameter) were extracted from the turtle nesting line on five beaches. This study reports the highest beach microplastic concentration recorded in the literature to date (0 – 2 cm depth; mean 371,000 particles/m3 ± 114,000 s.e.). Furthermore, with microplastic concentrations, orders of magnitude higher in both the surface layers and at turtle nesting depth than global reports; Chagos may have the highest microplastic concentrations in beach sand yet recorded. Boddam and Egmont beaches accounted for 91% of the total concentration recorded and very few microplastics were found on Nelson and Parasol Islands (5 particles). High variability was observed between stations with concentrations differing by an order of magnitude on Diego Garcia Island. Smaller microplastics were discovered in higher proportions (68%; 0.15 – 0.49 mm) than larger size classes (32%; 1 – 4.99 mm). Fragments were most prevalent accounting for 86.6%of the shapes recorded and polyethylene and polypropylene were the most frequently recorded polymers (46.3% and 20.6%). Beach sediment particle size varied from medium grained coarse skewed (Parasol, mean 0.47 mm; Nelson, stations 30 – 90, 0.46 mm; Diego Garcia, 0.40 mm) to symmetrical and fine skewed sediment (Egmont, mean 0.37 mm; Boddam, 0.31 mm). With the exception of Nelson Island (station 10) which is highly heterogenous, Chagos sediment is moderate to well sorted and the sediment particle size distribution is homogenous across the shoreline. This provides favourable conditions for high turtle nesting densities. The high microplastic concentrations discovered at turtle nesting depth however may be deleterious for this highly successful nesting site.
Keywords: Plastic pollution, marine pollution, marine turtle, endangered species, beach sediment composition
College: Faculty of Science and Engineering