Table S1.

Mean density and mass of microdebris (<5 mm) and macrodebris (≥5 mm) items (±SD) recorded in transects and quadrats on Henderson Island

Site	Density recorded, items/m2				Mass recorded, kg/m2
	Surface		Buried		Surface		Buried
	Micro	Macro	Micro	Macro	Micro	Macro	Micro	Macro
North Beach	28.4 ± 2.4	22.8 ± 1.1	156.3 ± 78.4	53.1 ± 25.8	0.001 ± 0.001	0.138 ± 0.050	0.001 ± 0.001	0.002 ± 0.001
East Beach	198.8 ± 309.8	237.0 ± 358.7	1675.0 ± 1725.0	898.4 ± 893.7	0.003 ± 0.004	0.891 ± 0.668	0.022 ± 0.025	0.080 ± 0.087

Data include surface items on the beach and items buried to a depth of 10 cm.