Microplastic ingestion ubiquitous in marine turtles

Abstract

Despite concerns regarding the environmental impacts of microplastics, knowledge of the incidence and levels of synthetic particles in large marine vertebrates is lacking. Here, we utilize an optimized enzymatic digestion methodology, previously developed for zooplankton, to explore whether synthetic particles could be isolated from marine turtle ingesta. We report the presence of synthetic particles in every turtle subjected to investigation (n = 102) which included individuals from all seven species of marine turtle, sampled from three ocean basins (Atlantic [ATL]: n = 30, four species; Mediterranean (MED): n = 56, two species; Pacific (PAC): n = 16, five species). Most particles (n = 811) were fibres (ATL: 77.1% MED: 85.3% PAC: 64.8%) with blue and black being the dominant colours. In lesser quantities were fragments (ATL: 22.9%: MED: 14.7% PAC: 20.2%) and microbeads (4.8%; PAC only; to our knowledge the first isolation of microbeads from marine megavertebrates). Fourier transform infrared spectroscopy (FT-IR) of a subsample of particles (n = 169) showed a range of synthetic materials such as elastomers (MED: 61.2%; PAC: 3.4%), thermoplastics (ATL: 36.8%: MED: 20.7% PAC: 27.7%) and synthetic regenerated cellulosic fibres (SRCF; ATL: 63.2%: MED: 5.8% PAC: 68.9%). Synthetic particles being isolated from species occupying different trophic levels suggest the possibility of multiple ingestion pathways. These include exposure from polluted seawater and sediments and/or additional trophic transfer from contaminated prey/forage items. We assess the likelihood that microplastic ingestion presents a significant conservation problem at current levels compared to other anthropogenic threats.

Keywords: anthropogenic debris; marine debris; marine plastic; marine turtle; microplastics; plastic pollution.

Figure 1

Study sites and number of each species sampled; Embedded pie charts of proportion of individuals with macroplastic ingestion (%); white = absent, black = present. Left to right: Atlantic (North Carolina, USA), Mediterranean (Northern Cyprus), Pacific (Queensland, Australia). Species codes: CC = loggerhead turtle (Caretta caretta), CM = green turtle (Chelonia mydas), DC = leatherback turtle (Dermochelys coriacea), LK = Kemp's ridley turtle (Lepidochelys kempii). ND = flatback turtle (Natator depressus), EI = hawksbill turtle (Ertmochelys imbricata) and LO = olive ridley turtle (Lepidochelys olivacea). Sea turtle skull figures used with permission of WIDECAST; original artwork by Tom McFarland

Figure 2

Synthetic microparticle ingestion in all species of marine turtles from three ocean basins. Total number of particles identified in each 100 ml subsample per species per ocean basin. Black line = mean number of particles. Note that 100 ml was analysed per animal irrespective of size, so the number of particles per animal should not be over‐interpreted. ATL = Atlantic (North Carolina, USA) loggerhead turtle (Caretta caretta, n = 8), green turtle (Chelonia mydas, n = 10), leatherback turtle (Dermochelys coriacea, n = 2), Kemp's ridley turtle (Lepidochelys kempii, n = 10). MED = Mediterranean (Northern Cyprus) loggerhead turtle (n = 22), green turtle (n = 34). PAC = Pacific (Queensland, Australia) loggerhead turtle (n = 3), green turtle (n = 7), flatback turtle (Natator depressus, n = 4), hawksbill turtle (Eretmochelys imbricata, n = 1) and olive ridley turtle (Lepidochelys olivacea, n = 1). Sea turtle skull figures used with permission of WIDECAST; original artwork by Tom McFarland

Figure 3

Type and colour of synthetic particles including microplastics identified from marine turtle gut content. Mean (±SE) percentage make‐up of each type (fibre, fragments, beads) isolated within the gut content residue samples from stranded turtles from the Atlantic (white), Mediterranean (light grey) and Pacific (dark grey). Colours categorized for fibrous synthetic particles ATL = Atlantic, MED = Mediterranean and PAC = Pacific. X = no detections