From the estuary to the deep sea: microplastic contamination of fishes from Southwestern Tropical Atlantic

Abstract

Worldwide, microplastics (MPs; 5 < mm) have been identified in most marine ecosystems and organisms. The large availability of this contaminant has raised the concern of scientists about the impacts on biodiversity and ecosystems. However, despite being frequently reported, some regions still lack studies on the characterisation of MPs contamination. This is the case in the Southwestern Tropical Atlantic (SWTA) region. To fill this gap, this thesis aims to provide a general understanding of the distribution and patterns of MP contamination in the ichthyofauna inhabiting the SWTA region along the estuarine-oceanic gradient. Thus, a protocol for extraction of MPs for marine organisms was adapted to diminish the probability of airborne contamination in the samples, which would be practical and of low operational cost. The thesis is structured in four chapters presented as articles and a general conclusion. The first chapter explored an estuarine trophic chain, comprising a commercially important top predatory fish and two of its main prey. Both species have different feeding habits, which was also observed in the frequency of MP ingestion, which varied with feeding strategies. In the second chapter, four coastal demersal fish species were used to characterise the ingestion of MPs in reef fishes from the SWTA region. No differences were observed between the ingestion rate of MPs by coastal species; however, a wide range of polymers was identified. The ocean ecosystem is discussed in the last two chapters of the thesis, focusing on pelagic and mesopelagic oceanic species. The third chapter characterises the contamination of two abundant mesopelagic fish families in the SWTA and addresses the influence of these species on the transport of MPs in the deep ocean. In this chapter, MP contamination in deep-sea fishes in the region was identified for the first time and areas of possible accumulation of particles were discussed. Finally, in the fourth chapter, pelagic predators important for industrial and artisanal fisheries were evaluated for the presence of MPs. In addition to the characterisation of contamination, evidence of trophic transfer of MPs from prey to predators was observed. Furthermore, this chapter discusses the ingestion of larger particles (macroplastics > 5 mm) derived from the intense ocean fishing and tourism activity in the Fernando de Noronha Archipelago (FNA). Overall, it was possible through this thesis to confirm the contamination by MPs in fish from the SWTA region. The ecological patterns, such as feeding strategies and trophic level, increased MP contamination probability. Furthermore, the influence of the species’ behaviour in the water column in areas with an accumulation of MPs. In addition, it was also possible to observe that, in general, the most frequent shape of MPs ingested by fishes are fibres. However, large oceanic pelagic predators (tunas) tended to ingest pellets and foams, which was also observed in their primary prey, indicating trophic transfer. Moreover, a variety of polymers were identified, but the most frequent polymers in the coastal region were polyethylene (PE), Alkyd Varnish and styrene-butadiene rubber (SBR); for the mesopelagic fishes in the oceanic region were polyamide (PA), PE and polyethylene terephthalate (PET). However, the most frequent polymers for tuna and prey were SBR, PA, and PET. The availability of these polymers in the SWTA region indicates intense pressure from fisheries (e.g., fishing nets and ship paint) and high tourist activity. The information available here can serve as a baseline to discuss and develop measures to mitigate the impacts caused by MPs contamination and plastic pollution in the SWTA region, thus contributing to the conservation of biodiversity and marine ecosystems.