Assessment of seagrass coverage on Panggang Island and Karang Congkak Island: a comparison between pre and post COVID-19 pandemic using Planetscope imagery

Abstract

Seagrass beds are ecosystems that are sensitive to anthropogenic pressures. The restrictions imposed on human activities during the Covid-19 pandemic provide a unique opportunity for coastal ecosystems to recover. This situation presents a chance to monitor seagrass ecosystems on Panggang Island and Karang Congkak Island, aiming to observe any changes in the seagrass area. The method employed to ascertain the community structure involved photo transects, which were then processed using a machine learning supervised classification approach utilizing the random forest algorithm. The classification process categorized the area into five classes: seagrass, macroalgae, coral, bare substrate, and dead coral algae. Confusion Matrix Test was chosen to assess mapping accuracy, setting an accuracy threshold of ≥ 60%. The findings reveal notable alterations in seagrass areas across both islands. Panggang Island exhibited a considerable increase in seagrass coverage by 21,05 hectares. Conversely, Karang Congkak Island experienced a decrease of 2,88 hectares in seagrass coverage. These observed changes are likely not influenced by the anthropause phenomenon but rather by natural occurrences between 2019 and 2022, including the La Niña Triple Dip phenomenon and variations in sampling time during the transition season. The Overall mapping accuracy (OA) results for