ABSTRACT
Microplastics, considered an emerging pollutant, are carriers for transferring various chemical substances in natural ecosystems. They contribute to overall toxicity in oceans and can adversely affect human health through their transfer along the food chain. Coral reefs, as crucial marine ecosystems, support the livelihoods of many aquatic species and serve as essential food sources for humans. Unfortunately, in recent years, coral reefs have been threatened due to the increase in various pollutants, including plastic pollutants. In this study, the accumulation of microplastics in the hard coral species Platygyra daedalea was investigated in the Kish, Kharg, Hengam, and Larak islands. Samples were collected from the selected islands, transported to the laboratory, and examined using a stereomicroscope to assess the distribution and density of microplastics on the coral surfaces. The results indicated that all examined samples contained microplastics, with approximately 47±6.1 pieces of microplastics found per colony. Regarding the types of microplastics, fragments constituted the majority at 54%. The largest piece of microplastic found had a length of 4.5 millimeters, while the smallest measured 12 micrometers. The predominant colors of the identified microplastics were blue, followed by black. Unfortunately, all investigated locations exhibited microplastic contamination. Among the islands, Hengam Island showed the least contamination, while Kharko Island displayed the highest levels of microplastic pollution.

INTRODUCTION

Due to the importance of coral habitats in marine ecosystems as one of the food reserves for aquatic organisms and humans, the investigation of threatening factors to this ecosystem is crucial (Castro and Huber, 2008). additionally, microplastics are a new pollutant (Lamb et al., 2018), and there is still limited information about them, particularly in the coral reefs of the Persian Gulf, which serve as a seafood reserve for humans. Therefore, this study examines the accumulation of microplastics on the surfaces of coral reefs in some islands of the Persian Gulf and discusses the implications of this contamination.

MATERIALS AND METHODS

Sampling was carried out around the islands of Kharg, Kharko, Hengam, and Larak in the Persian Gulf. After collection, the samples were weighed using a digital scale, coded, wrapped in foil, and transported to the research laboratory of Hormozgan University via an icebox.
For the assessment of the distribution and density of microplastics and the presence or absence of microplastics, a portion of the samples was separated and placed in a 20% KOH solution. The samples were kept in an isolated environment at a temperature of 25 degrees for 4 to 7 days. Following the complete digestion of coral tissue and the separation of microplastics present on the surface and inside the coralites (Ding et al., 2019), the resulting solution was filtered through a Wattman filter. Subsequently, filter paper was placed under the microscope, and microplastics were examined for their accumulation, density, color, and size. The recorded data were analyzed using SPSS software version 24.

RESULTS

Unfortunately, all the samples under investigation contained microplastics. In total, 190 plastic pieces were identified, fragments constituting the highest percentage at 54%; fibers accounted for 39%, films for 6%, and pellets for less than 1% of the microplastic composition. The largest microplastic piece found had a length of 4.5 millimeters at its longest point, and the smallest piece measured around 12 micrometers.
The most prevalent colors among the identified microplastics were blue, followed by black. The overall percentage distribution of different colors of microplastics is as follows: blue 43%, black 42%, brown 4%, orange 4%, white 3%, red 2%, pink 1%, yellow 1%, and gray 1%.

DISCUSSION AND CONCLUSION

The status of microplastic pollution in corals of the Middle East has remained unexplored until now, and this study represents the first published research in this field. A comparison among four islands reveals significant differences in the type and color spectrum of the found microplastics. This variation can be crucial for identifying the source of microplastics for each island in future research and even for implementing measures to mitigate it. Among the islands, Hengam Island exhibited the least contamination, while Kharko Island had the highest microplastic pollution. The higher contamination on Kharko Island and Kharg Island can be attributed to the presence of oil facilities, companies, a larger population, and significant maritime transportation activities. Additionally, the geographical positioning of these islands in a region of the Persian Gulf where water circulation is lower contributes to the accumulation of microplastics.
Various factors, such as the sampling region, analytical methods, water currents, and coral species, can influence the prevalence of reported microplastics in rocky areas (Huang et al., 2020). Therefore, further assessment is needed in future studies to better understand and account for these influencing factors.
REFERENCES:
Castro, P.andHuber, M. E., 2008. Marine biology, McGraw-Hill Education.
Ding, J., Jiang, F., Li, J., Wang, Z., Sun, C., Wang, Z., Fu, L., Ding, N. X.andHe, C., 2019. Microplastics in the coral reef systems from Xisha Islands of South China Sea. Environmental science & technology, 53, 8036-8046. DOI: 10.1021/acs.est.9b01452. 
Lamb, J. B., Willis, B. L., Fiorenza, E. A., Couch, C. S., Howard, R., Rader, D. N., True, J. D., Kelly, L. A., Ahmad, A.andJompa, J., 2018. Plastic waste associated with disease on coral reefs. Science, 359, 460-462. DOI: 10.1126/science.aar3320.