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. The study aims to examine whether the level of marine debris accumulation on the coast of Enggano Island is very high (because it borders the Indian Ocean).METHODS: This study was conducted by using a survey method in the southeastern of Enggano Island with 10 stations. 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. The abundance data for each marine debris category was calculated both by the number of items and weight. Seasonal abundance analysis was compared with the average seasonal current speed to determine whether currents affect the abundance of marine debris.FINDINGS: The total marine debris collected in this study was 16,382 items with a cumulative weight of 24,826 grams. The average marine debris abundance was 0.387 ± 0.006 items per square meters, and the average weight was 11.545 ± 0.146 grams per square meters. Plastic has the highest percentage of all square meter's categories in all locations and seasons, namely 91.55 percent to 92.54 percent. The dominant types of debris in all macro-debris categories are Styrofoam, plastic bottles, plastic rope or small net pieces, thin plastic wrap, 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, there were significant differences in marine debris abundances and weights between sites and seasons during 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. Variations in the accumulation of marine debris between stations, as well as the direction and velocity of the seasonal currents, influenced each season. Plastic is the category of marine debris with the highest percentage in all locations and seasons, specifically 91.55–92.54 percent. Global marine hydrodynamics is thought to play an important role in marine debris strandings, therefore more comprehensive research is needed to assess the influence of hydrodynamics in determining the source and height of marine debris strandings, especially those originating from outside Enggano Island.