The extent and type of microplastic (MP) contamination in South African open ocean marine resources is unknown. This study aims to report on MP ingestion in seven commercially targeted fish species from the Agulhas Bank, south of South Africa. MPs were found in all seven species sampled (N = 105) (Trachurus capensis, Merluccius capensis, Merluccius paradoxus, Etrumeus whiteheadi, Scomber japonicus, Chelidonichthys capensis and Argyrozona argyrozona). MPs were recorded in 86.67% fish sampled, with abundances ranging from 2.8 to 4.6 items/fish. Most MPs were fibres (95.14%), black (38.11%) and ranged from 1000 to 500 μm (35.55%) in size. There was no difference in microplastic concentration in relation to distance from shore (p > .05). This is the first record of MPs in offshore fish from southern Africa and the results indicate that more research is required to assess the extent of MP contamination in the region.
Plastic debris is prevalent in the marine environment with 10% of all plastic produced eventually ending up in the oceans where it potentially accumulates (Güven et al., 2017; Mattsson et al., 2017). In 2010, 275 million metric tons of plastic was generated by 192 coastal countries, with 1.75% – 4.6% of this entering the surrounding oceans (Jambeck et al., 2015). By 2015, global plastic production increased to 322 million metric tons (Worm et al., 2017) and is currently estimated to be > 350 million metric tons (PlasticsEurope, 2018). A substantial portion of plastic debris in the ocean comes from land-based sources entering the marine environment through rivers (Lebreton et al., 2017), industrial and urban effluents, and run-off of coastal sediments (Barboza et al., 2018). The other part results from direct inputs, such as offshore industrial activities, nets being lost in various fishery sectors and litter released during sea activities, including ecotourism (Barboza et al., 2018).
Plastics can persist in coastal and marine environments for long periods of time (Andrady, 2011) and is generally classified as macro- (25–1000 mm), meso- (5–25 mm) – and microplastics (MPs) (< 5 mm) (GESAMP, 2019). Microfibres, pellets, films and fragments are common categories of MPs (GESAMP, 2019; Murray and Cowie, 2011). The size of microplastics is also an important category for measuring effects of MPs as the size of MPs have the potential to affect ingestion rates of marine organisms (Andrady, 2011), and hence play an important role in organism, and ultimately ecosystem health. MP sizes fall within the optimal prey size range for a variety of marine organisms such as zooplankton, which in turn may make MPs bioavailable for ingestion by zooplankton predators, resulting in MPs bioaccumulating up the marine food chain (Lusher et al., 2017).
Negative effects of MP ingestion include blockage and damage of the digestive system, biomagnification of harmful chemicals, increase in morbidity, high levels of toxins in the liver, disruption of the endocrine system and neurotoxic effects (Lusher et al., 2013). Ingestion of marine plastics by fish was first documented by Carpenter et al. (1972) who described the existence of plastic particles (MPs) in larvae and adult fish in the coastal waters of southern New England. Research on MPs in South Africa is limited. The first study on plastics in the open ocean off South Africa by Ryan (1988) recorded an average particle density of 3.64 particles m−2 at the sea surface off the South-Western Cape Province. Most of the samples were identified as plastic foam, fragments of plastic particles and manufactured pellets and fibres (Ryan, 1988). Plastic particles were found in 33% of all trawls, corresponding to a density of almost 3600 particles km−2 , with a decrease in plastic abundance with increasing distance from the coast being recorded (Ryan, 1988). More recently Naidoo et al. (2016) provided the first report on plastic ingestion by fish in South Africa by presenting results of plastic particles in the guts of Mugil cephalus (mullet) in Durban Harbour, situated along the east coast of South Africa. Given the lack of data on MPs in fish in South Africa, we report, to our knowledge, the first study to investigate the abundance, and type of MPs in South African offshore fish, to ascertain whether further research is needed to monitor MP contamination in South African marine resources such as fish.
Read full article by Stiaan Immelman on Microplastics in offshore fish