Classification of marine microdebris: A review and case study on fish from the Great Barrier Reef, Australia

Abstract

Marine debris, and in particular plastic pollution, is ubiquitous throughout global marine environments. Here, we present a classification of marine microdebris (i.e. debris between 0.1 μm and <5 mm) tailored to represent synthetic, semi-synthetic and naturally-derived items. The specific aim of this classification is to introduce a level of consistency in the higher-level characterisation of marine microdebris, thereby improving the overall reporting on marine microdebris contamination. We first conducted an extensive literature review on the accumulation of ingested debris in fish to identify discrepancies in marine microdebris reporting as a basis for the new classification. The review reveals the diverse nature of ingested marine microdebris, including items that are non-plastic but often incorrectly reported on as microplastics. We then applied our classification to a case study on wild-caught juvenile coral trout, Plectropomus spp., from the Great Barrier Reef World Heritage Area, Australia. This first report on accumulation of ingested marine debris in commercial fish on the reef demonstrates a high frequency of occurrence and a prevalence of semi-synthetic and naturally-derived fibres. Based on our findings, we offer recommendations on potential improvements for the classification presented, ultimately contributing to a more realistic assessment of the ecological risks of marine microdebris.

Figure 1

Photographs of representative marine microdebris in juvenile coral trout. Marine microdebris was detected in the gastrointestinal tract of 20 individual juvenile coral trout (Plectropomus leopardus and P. maculatus) collected on reefs around (a) Lizard Island, (b) Orpheus Island, (c) Heron Island, and (d) One Tree Island, in the Great Barrier Reef World Heritage Area, Australia, in 2011. Examples of chemical type assignments for marine microdebris include: (a) semi-synthetic: cellulose-derived (4), NFPC: nylon (5); naturally-derived: cellulose-natural (1, 6, 7); (b) semi-synthetic: cellulose-derived (1, 2, 3, 5, 6), NFPC: nylon (8); naturally-derived: cellulose-natural (7), keratin (4); (c) synthetic: polyester (8); semi-synthetic: NFPC: nylon (5, 6), NFPC: polyester (1); naturally-derived: cellulose-natural (2, 3, 9); (d) semi-synthetic: cellulose-derived (6), NFPC: nylon (5), NFPC: polyurethane (1); naturally-derived: cellulose-natural (4, 7), keratin (3). For the following items, natural origin (a2, a3, a8) or contamination (b9, c4) could not be ruled out. Chemical type was not assigned to fibre c7 (fibre was missing) and d2 (<60% match). NFPC = natural fibre reinforced polymer composites.

Figure 2

ATR-FTIR spectral matches of representative marine microdebris in juvenile coral trout. Marine microdebris, including fibres consisting of (a) polyester, (b) cotton, (c) polypropylene, and (d) keratin, were detected in the gastrointestinal tract of 20 individual juvenile coral trout (Plectropomus leopardus and P. maculatus), collected on reefs around four reef islands in the Great Barrier Reef World Heritage Area, Australia, in 2011.

Figure 3

Frequency of marine microdebris items in juvenile coral trout. The number of juvenile coral trout (Plectropomus leopardus and P. maculatus) against the total number of marine microdebris items detected in the 20 individual gastrointestinal tracts. Fish were collected on reefs around four reef islands in the Great Barrier Reef World Heritage Area, Australia, in 2011.

Figure 4

Condition of juvenile coral trout. The condition (Fulton’s condition index, K) of individual juvenile coral trout (Plectropomus leopardus and P. maculatus) plotted against the total number of marine microdebris items detected in each of the 20 gastrointestinal tract. Fish were collected on reefs around four reef islands in the Great Barrier Reef World Heritage Area, Australia, in 2011. Linear regression fit and bands (95% confidence level) are presented.

Figure 5

Mean number of marine microdebris items in juvenile coral trout per reef island. The average number (±s.e.m.) of marine microdebris items detected in the gastrointestinal tracts of five juvenile coral trout (Plectropomus leopardus and P. maculatus) at each of the four reef islands in the Great Barrier Reef World Heritage Area, Australia. Fish were collected in 2011.

Figure 6

Size-frequency distribution of marine microdebris items in juvenile coral trout. Marine microdebris items were detected in the gastrointestinal tracts dissected from 19 out of the 20 individual juvenile coral trout (Plectropomus leopardus and P. maculatus), collected on reefs around four reef islands in the Great Barrier Reef World Heritage Area, Australia, in 2011.