English abstract
Marine biofouling is a process of accumulation of macro and microorganisms on a submerged surface in the marine environment. Marine biofouling form on many different surfaces and change their properties and characteristics. Plastic is one of the surfaces that is submerged in the marine environment and colonized by marine biofouling. Plastic pollution is a serious problem that affects our ecosystem. Most of the plastic waste is ended in the ocean causing hazardous effects on the marine environment, for example entanglement and suffocation of marine organisms, encountering persistent organic pollutants and leaching chemical additives from the plastic. In this study our aim was to investigate plastic associated microfouling communities on different types of plastic under temporal effect (after 20 and 80 days) in benthic and pelagic zones and to assess the degradation of plastics in the marine environment under abiotic and biotic factors. The study was held in the Marina Shangri La, Muscat, Oman. Three types of plastic were deployed, OXO biodegradable polyethylene (OXO-PE), Polyethylene (PE) and Polyethylene terephthalate (PET) at 2 m depth (pelagic) and 6 m depth (benthic) for 20 and 80 days. The accumulated biofouling was sampled and analyzed. Diatoms identification was done, and the microbial communities were characterized through next generation sequencing Miseq sequencing of 16S rRNA genes. In addition, the plastic substrates were analyzed for signs of degradation with scanning electron microscopy (SEM) and fourier-transform infrared spectroscopy (FTIR). The indicated results showed that biofouling communities are affected with time, substrate and depth. While the analysis of bacterial communities by non-metric multidimensional scaling NMDS showed that bacterial communities undergo distinct temporal shifts, whereas the three substrates showed similar communities with partial segregation. OXO-PE and PE showed high similarity in their bacterial communities while PET showed some differences in the bacterial community. Moreover, specific genera were found to favor certain plastic substrate more than the others due to the difference in the surface properties of the three plastics. Not much of a difference was detected between the pelagic and benthic zones in the bacterial communities. In terms of degradation all the three plastics showed signs of degradation after 20 days regardless of depth; however, PET showed less degradation in comparison with OXO-PE and PE. FTIR results showed formation of different bands of carbon and oxygen bonds in addition to hydroxyl bands which illustrated abiotic degradation; however, peaks of proteins and polysaccharides showed the contribution biotic degradation through microbes. Alteromonas and Haliea are examples of detected genera OXO-PE and PE that showed their ability to degrade hydrocarbons based on the previous studies. In conclusion, the different properties of plastic affects in the formation of marine biofouling communities. In addition, time is the most prominent factor that would change the microbial community structure. Finally, plastic are stable substrates especially PET, therefore they need very long time to degrade in water; however, microbes could potentially play a role and enhance plastic degradation.
