Field evidence for microplastic interactions in marine benthic invertebrates

Abstract

Microplastics represent an important issue of concern for marine ecosystems worldwide, and closed seas, such as the Mediterranean, are among the most affected by this increasing threat. These pollutants accumulate in large quantities in benthic environments causing detrimental effects on diverse biocenoses. The main focus of this study is on the 'polychaetes-microplastics' interactions, particularly on two species of benthic polychaetes with different ecology and feeding strategies: the sessile and filter feeder Sabella spallanzanii (Gmelin, 1791) and the vagile carnivorous Hermodice carunculata (Pallas, 1766). Since not standardized protocols are proposed in literature to date, we compared efficiencies of diverse common procedures suitable for digesting organic matter of polychaetes. After the definition of an efficient digestion protocol for microplastics extraction for both polychaetes, our results showed high microplastics ingestion in both species. Microplastics were found in 42% of individuals of S. spallanzanii, with a mean of 1 (± 1.62) microplastics per individual, in almost all individuals of H. carunculata (93%), with a mean of 3.35 (± 2.60). These significant differences emerged between S. spallanzanii and H. carunculata, is probably due to the diverse feeding strategies. The susceptibility to this pollutant makes these species good bioindicators of the impact of microplastics on biota.

Figure 1

Protocol selection in Sabella spallanzanii. Box and whiskers plot of three digestion protocols (10% KOH at 60 °C, 10% KOH at room temp and 15% H₂O₂ at 50 °C, respectively from left to right protocols 1, 2 and 3). Protocols with a digestion efficiency greater than 95% are accepted. Protocols with more robust data are those with a narrow interquartile range. The figure is obtained by the software R (ver. 4.5 14,597.0, https://cloud.r-project.org).

Figure 2

Filter before (a) and after (b) treatment with HNO₃ and H₂O₂ mixture to dissolve the chaetes of Hermodice carunculata.

Figure 3

Physical characterization of ingested microplastics by Sabella spallanzanii and Hermodice carunculata. A treemap chart (Excel) with shape categories (Frag: fragments; Film: films), size classes (S1: size class 1, 90 µm–330; S2: size class 2, 330 µm–1 mm; S3: size class 3, 1–5 mm) and colour (transp: transparent; red: red; blue; green: green; black: black; white: white). The image is obtained by the software Excel (ver. 2014, https://www.microsoft.com/it-it/microsoft-365/excel) and the software PowerPoint (ver. 2014, https://www.microsoft.com/it-it/microsoft-365/powerpoint).

Figure 4

Chemical characterization of ingested microplastics by Sabella spallanzanii and Hermodice carunculata. Picture and infrared spectra of three items are reported. (a) polypropylene (PP) fragment found in Sabella spallanzanii. (b) mix polyethylene-polypropylene (mix PE-PP) fragment found in Sabella spallanzanii. (c) polystyrene (PS) fragment found in Sabella spallanzanii. The pictures are obtained by the software of image for microscope ZEN 2011 SP1 blue edition (6.1.7601) and the FT-IR spectra are obtained by the software OMNIC 9.8.286 (Thermo Fisher Scientific Inc.).

Figure 5

The investigated biological model: Sabella spallanzanii (A) and Hermodice carunculata (B). The photo images were taken by Paolo Tomassetti (a) and Fabrizio Fabroni (b).

Figure 6

Location of the sampling sites of the Mediterranean fanworm Sabella spallanzanii (Os, SM, Pi) and the bearded fireworm Hermodice carunculata (Ga and Ma). In alphabetical order: Ga = Scoglio della Galea; Ma = Secca del Mantineo; OS = Ostia; Pi = Piombino; SM = Santa Marinella. The figure is obtained by the QGIS software (ver. 3.16.7-Hannover, https://www.qgis.org/it/site/index.html).