The increasing Microplastics (MPs) in the sea another big threats to marine ecosystem, says KU research study

A microplastics (MPs) emergence study in pelagic and mesopelagic species was carried out to delineate coastal degradation and ecosystem status around the Karachi metropolis. Species of high commercial and ecological worth were sampled using a gillnet of 1.5 cm knot-to-knot mesh size in November and December 2021. In total twenty-six individuals including Liza subviridis (15), Thryssa dussumieri (3), Rastrelliger kanagurta (2), and Portunus sanguinolentus (6) were used to perceive MPs. A strong linearity between body length and MPs (R2 = 0.937, SE 0.071 and R2 = 0.928, SE 0.104) were calculated for L. subviridis and P. sangiuilatus, respectively. However, the data of T. dussummeiri and R. Kanagurta showed minimization failure. The MPs in GIT were extracted using direct observation under a sophisticated binuclear microscope and chemical digestion (KOH) together with wet peroxide oxidation (H2O2+FeSO4) methods. The MP materials were categorized as foam, film, fiber, fragment, and beads of three different sizes 170, 120, 100 μm in the stomach, intestine, and esophagus. Film-type MPs appeared frequently, whereas beads were rarely seen. It is hoped that this baseline research would help to minimize industrial release, recognize critical knowledge gaps, and demonstrate MP flux being released into the aquatic environment. The results will support mitigation of this emerging threat to the living resources around the Karachi coastal area.

Overharvest of fisheries resources and climate change has already threatened marine ecosystems globally. In recent years the emergence of microplastics in aquatic systems has augmented such threats, particularly in developing countries. In Pakistan, approximately 0.2 million tons of plastic garbage has been discharged into the Arabian Sea by the coastal inhabitants and through the Indus River (Dawn News, 2019). The Indus River is considered among the most plastic-polluted rivers in the world (Mairaj et al., 2021). About 6,000 manufacturers are involved in producing 0.6 million tons of plastic in Pakistan (Dawn News, 2019). Regretfully, plastic materials account for 65% of total garbage in Pakistan, with a 15% rise predicted each year (WWF Pakistan, 2021). In the case of a developing country, it is hard to figure out future plastic load likely to be dumped into the marine environment. Dealing with urban trash, Pakistan has encountered grave problems owing to the Karachi metropolis. Nevertheless, more plastic is anticipated to be dumped in the sea by 2050 (WWF Pakistan, 2021).

The emergence of microplastic would not merely degrade aquatic habitats but would also deform food web structures. The continuous surge of pollutants can lead to livelihood risk by affecting fisheries and aquaculture activities (Plastic, 2014Barboza et al., 2019). In this context, Barboza et al. (2019) affirmed that various coastal areas receive 61∼87% of their waste comprised of different forms of plastic. Nowadays the most widespread and persistent contaminants are plastics, which enter the coastal and marine environment by multiple routes comprising riverine and atmospheric transport, beach trash, and direct entry via aquaculture, shipping, and fishing (Lebreton et al., 2017Villarrubia-Gómez et al., 2018). Gradually plastic waste is further worn into microplastics through processes of microbial degradation, extended UV exposure, and physical abrasion (Weis et al., 2015). The integration of marine litter steadily affects the coastal scenery, limiting recreational activities, causing a loss of touristic value, potentially harming the marine environment, and finally reaches the food chain. One of the primary concerns about the environmental consequences of microplastics is their interaction with the feeding of marine organisms (Botterell et al., 2019). As tiny as they are, plastics pose a problem for the environment since they are non-biodegradable and may find their way into marine food webs (Wright et al., 2013). Ingestion of microplastics, which may be mistaken for food and enter aquatic food webs, can occur by normal ventilation or swallowing them whole (Besseling et al., 2013Setälä et al., 2014Watts et al., 2014). Moreover, MPs may also cause indirect energy costs owing to their toxicity and tissue damage, and they may also be transmitted or enhanced via the food chain, presenting both ecological and human health hazards (Larue et al., 2021Sokolova, 2021). Fish, bivalves, crabs, seabirds, phytoplankton, corals, and meiofauna have all been shown in many studies to bear adverse impacts of MPs accumulation (Wright et al., 2013Mathalon and Hill, 2014Watts et al., 2014Van Cauwenberghe et al., 2015Batel et al., 2016Lusher et al., 2018).

In an aquatic ecosystem the food web plays a crucial role in energy shift among and within organisms through a series of organisms such as zooplankton to higher animals or grazers like fishes inhabiting the pelagic regimes. The entrance of MPs into the pelagic regime can shift up to the demersal organism as they prey on small organisms living around pelagic or demersal regimes.

Indigenous information on marine litter contamination is restricted to the abiotic environment (Balasubramaniam and Phillott, 2016Qaimkhani, 2018Tahira et al., 2020). Therefore, this study envisages the concentration of microplastic in the gastrointestinal tract of commercial and ecologically important species inhabiting around Karachi coastal waters. The findings will contribute to a better understanding of the propensity of microplastics to accumulate in fish and will help to fill a research gap for future evaluations of the health-related risks and food security concern in Pakistan.

Note: This article is part of Research Article, Centre of Excellence in Marine Biology, University of Karachi, Karachi, Pakistan (Mr. Najeeb Akhter & Sher Khan Panhwar)