Spatial heterogeneity of marine debris distribution on a tropical remote island shoreline

Abstract

BACKGROUND AND OBJECTIVES: Enggano Island is in the Indonesian Sea, bordering the Indian Ocean. Cross-border marine debris will be stranded in the coastal areas of this island. This study was carried out over a 12-month, from June 2021 to May 2022, to examine marine debris's spatial and temporal accumulation. This study intends to assess the degree of marine debris accumulation on Enggano Island's coast, given its location adjacent to the Indian Ocean. METHODS: This study employed a survey approach and was performed at 10 different stations in the southeastern part of Enggano Island. The first sampling was carried out 30 days after cleaning, during the lowest tide at the full moon phase (28 + 3 days), conducted over 12 months from June 2021 to May 2022 to represent four seasons. For each category of marine debris, the abundance was determined by evaluating both the number of items and their respective weights. The relationship between seasonal abundance and the average seasonal current speed was examined to evaluate the influence of currents on marine debris levels. FINDINGS: The total marine debris collected in this study was 16,382 items with a cumulative weight of 24,826 grams. The average density of marine debris was determined to be 0.387 + 0.006 items per square meter, and the corresponding average weight was 11.545 + 0.146 grams per square meter. Plastic has the highest percentage of all square meter's categories in all locations and seasons, namely 91.55 percent to 92.54 percent. In all categories of macro-debris, the most prevalent types of debris are Styrofoam, plastic bottles, fragments of plastic rope or small nets, thin plastic wrapping, and Plastic cups. The Marine debris found during the cleaning was plastic bottles from China, Switzerland, Sri Lanka, India, the Maldives, Myanmar, Malaysia, Singapore, Thailand, the Philippines, Australia, Seychelles, and the Middle East, with an average percentage of Indonesian-brand bottles (58.12 percent), foreign-brand bottles (19.59 percent), and unrecognized brands (22.29 percent). Moreover, substantial discrepancies in the abundance and weight of marine debris were recorded between various locations and seasonal periods throughout the sampling. CONCLUSION: The marine debris that washed ashore on Enggano Island during the 12-month observation period, from June 2021 to May 2022, showed significant spatiotemporal variations. Each season was affected by variations in marine debris accumulation across different stations, along with the direction and speed of the seasonal currents. Plastic is the category of marine debris with the highest percentage in all locations and seasons, specifically 91.55-92.54 percent. It is believed that global marine hydrodynamics significantly contributes to marine debris strandings, indicating a need for more in-depth studies to understand the impact of hydrodynamics on the sources and heights of these strandings, especially for debris outside Enggano Island.