The Investigation of Bioindicator Bacteria in the Supralittoral Zone Sands and Seawater in the Sea of Marmara, İstanbul Province

Abstract

Investigation of the presence of bioindicator bacteria in the seas is important in terms of detecting bacteriological marine pollution due to human activities and as an indicator of the possible presence of pathogenic bacteria in the environment. This study definitively determined bio-indicator bacteria levels in the coastal area of the Sea of Marmara, İstanbul province, over a 1-year period from June 2021 to May 2022. The study was conducted seasonally, and samples were taken from eight heavily used swimming areas and the beach sand. The measurement of the variable environmental parameters – temperature, salinity, dissolved oxygen and pH – was conducted in situ. Sea water samples collected from the supralittoral zone under aseptic conditions were taken from the surface (0-30 cm) and sand samples were taken from 0-50 cm. In bacteriological analyses, total coliform, fecal coliform and intestinal enterococci were investigated using membrane filtration methods. Heterotrophic aerobic bacteria (HAB) levels were determined by the spread plate method using marine agar. Using descriptive statistical analysis and independent samples t-tests, the variability and significance of differences in bacterial indicator levels were assessed between beach sand and seawater samples. During the study, the higher bacteria levels were detected in beach sands than in sea waters. The annual indicator bacteria levels obtained from seawater and supralittoral zone sands were recorded at a maximum of 72.540 CFU/100 ml (the SD for total coliform was ± 0.53) at Kabakoz Beach in July 2021 and 322.400 CFU/10 g (the SD for total coliform was ±0.75) at Elmas Kum and Poyraz Beaches in July and August 2021, and a minimum of 78 CFU/100 ml (the SD for intestinal enterococci was ± 0.46) in winter season (January 2022) at Güneş Beach and spring season (May 2022) at Caddebostan Beach and 234 CFU/10 g (the SD for fecal coliform was ± 0.75) in winter season (January 2022) at Büyük Liman Beach, respectively. The annual HAB levels in seawater and supralittoral zone sands reached up to 98×10¹⁵ CFU/ml in May 2022 at Menekşe Beach and 59×10¹⁷ CFU/10g in August 2021 at Çiroz Beach, with the lowest values recorded as 1×10¹² CFU/ml in winter 2022 at Çiroz Beach and 35×10¹³ CFU/g in July 2021 at Poyraz Beach, respectively. The obtained bacteriological data clearly reflect the extent of bacterial pollution. Moreover, statistically significant differences were observed between stations even within the same season. Dissolved oxygen levels decreased markedly during the summer months across all stations, while bacterial indicator levels showed a corresponding increase. This trend was particularly pronounced at Kabakoz, Elmas Kum, and Güneş beaches. Increases in sea water temperature, changes in pH and salinity, geographical location and human-induced terrestrial effects are thought to influence the degree of bacterial contamination of beaches. This situation show that beach sand may pose a higher biological risk of microbial contamination than seawater, as bacteria are less exposed to sunlight, retain moisture longer, and allow organic matter to accumulate. The high bacterial levels detected in this study indicate a potential bacterial risk to public and ecosystem health in coastal areas. These first regional data obtained from the supralittoral zone showed that the supralittoral zone creates suitable habitats for bacteria and that this humid zone, where seawater and land interact, has the potential for bacteriological risk, especially for children's activities. The study finding contributed first data on presence of bioindicator bacteria of supralittoral zone sands in the coastal areas of the Sea of Marmara İstanbul Province.

Keywords

• Indicator bacteria
• heterotrophic bacteria
• supralittoral zone
• sea water

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