Date

2017-12-28

Author

Gökdağ, Kerem

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Marine litter and microplastic pollution is a growing problem for the world and Turkish seas. In this study, the levels of microplastics in surface water, water column, sediment as well as in fish digestive system from the northeastern Mediterranean Sea were studied in 2015 and 2016. The impact of virgin microplastics on seabream juveniles was also investigated at the laboratory. Number of microplastics in surface water were between 16339 and 520213 particles km-2 in 2015, and, between 39559 and 1043675 particles km-2 in 2016. For watercolumn samples, microplastic abundances ranged between 0.58 and 26.37 particles m-3 in 2015. In 2016, abundances ranged between 0.17 and 13.83 particles m-3. Insediment samples, the KRDSW1 station exhibited highest microplastic abundance with 1720 particles L-1 whilst SEYSW3 station, despite highest concentrations ofmicroplastics for surface water samples, displayed the lowest sediment abundance with 80 particles L-1 in 2015. In 2016, quantities of microplastic particles rangedbetween 73.33 particles L-1 and 553.33 particles L-1 for sediment samples. Although size range of microplastic particles was various, 94% of microplastic particles were between 0.1 and 2.5 mm in size. The least variation in the repetitive samples among the sediment compared to other media (i.e. sea surface and water column) indicates that sediment sampling is better for monitoring the levels of marine litter in Turkish seas. In 2015, a total of 1337 fish individuals encompassing 28 species (14 families) and in 2016, 175 individuals encompassing 2 species (2 families) were collected. A total of 1822 microplastic particles were extracted from stomach and intestines of fish specimens in 2015. In our study, 58% (771 specimens) and 53% (92 specimens) of all individuals contained microplastic particles either in the stomach or intestine in 2015 and 2016, respectively. These are among the highest values compared to those reported in the literature. The high numbers of fish used in these analyses enable us to determine which fish species are suitable as monitoring subjects by also taking into consideration their occurrence and economic viability. Because of the high microplastic density in their digestion system in 2015 fish sampling, the red mullet Mullus barbatus from demersal fishes, and the horse mackerel Trachurus mediterraneus, from pelagic species both economically important and wide spread species were suggested to be indicator species in national monitoring studies of Turkish seas. Specimens with ingested microplastic particles (total 120 microplastic particles) were varied 30-69% for Mullus barbatus and 46-60% for Trachurus mediterraneus in different stations in 2016. Higher number of ingested microplastic particles coincided with seawater and sediment stations that contained high amount of microplastic particles (Kruskal-Wallis and multiple comparisons of mean ranks; p < 0.01) both 2015 and 2016. This indicates that sampling fish and its environment could provide more insights in evaluating microplastic levels in the sea. For all samples (seawater, sediment and biota samples in 2015 and 2016) combined, fiber and hard plastic particles were the most abundant microplastic followed by nylon, rubber and others. Share of fibers increased from surface towards the sediment. Fibers and hard plastic particles were abundant in stations close to the mouths of the three major rivers in the sampling area. Dominant colour of microplastics were blue, black, red and green. After the microplastic feeding experiment in adult gilt-head seabream (Sparus aurata), accumulation of 6 common types of microplastics in gastrointestinal organs or to translocate to liver and muscles were monitored and recorded. Results of laboratory analysis showed that 5.3 % of all analyzed livers contained at least one microplastic particle. However, ingestion of virgin microplastics did not induce stress, altered growth rate, caused pathology, or caused microplastics accumulation in gastrointestinal tract of fish. Being the first detailed study on microplastics in the northeastern Mediterranean, results obtained here will serve as a baseline for future studies. The sample size of the present study (total 1512 combining 2015 and 2016) is the highest compared to previous studies. The results obtained here indicate that microplastic pollution is an important problem for the northeastern Mediterranean coasts of Turkey.

Subject Keywords

Mediterranean, Microplastic, Marine litter, Seawater, Sediment, Fish, Stomach

URI

https://hdl.handle.net/11511/95089

Collections

Graduate School of Marine Sciences, Thesis