Impacts of long-term freshwater benthic insect community shifts on downstream coastal ecosystems

Abstract

Background: Sungai Ijuk is a vital freshwater ecosystem, where benthic macroinvertebrates serve as key indicators of water quality and ecosystem stability. This study evaluates long-term changes in the benthic insect community structure over a 20-year period, comparing data from 2001 and 2022, to assess the ecological impacts on this aquatic system. Methods: A descriptive method was applied through direct observation at three sampling stations along the Ijuk River. Analyses included species composition, density, diversity index, evenness index, dominance index, and similarity index. Samples were collected from rocky, sandy, and litter substrates, and statistical analyses were conducted to compare changes over the two decades. Findings: The results show a significant decline in community composition, from 9 orders, 30 families, and 62 genera in 2001 to 7 orders, 22 families, and 36 genera in 2022. Insect density also decreased, with the highest recorded density dropping from 1696 ind/m² in 2001 to 1448 ind/m² in 2022. While the diversity index peaked in 2022 on leaf-litter substrates at Station I, the dominance index remained low across both years, and the similarity index among stations increased in 2022, indicating greater community uniformity. Conclusion: This article highlight a significant ecological shift likely driven by anthropogenic pressures such as pollution and substrate modification. Despite reduced species richness and density, the low dominance and increased similarity suggest a relatively stable, though simplified, ecosystem. Novelty/Originality of This Study: This research lies in its longitudinal analysis of benthic insect community structure and its demonstration of anthropogenic impacts over time. It also reinforces the utility of benthic insects as bioindicators of freshwater quality in Indonesia and underscores the urgency of conservation efforts to sustain freshwater ecosystems.