Zooplankton Diversity as a Bioindicators of Organic Pollution in the Estuary of Lhokseumawe City, Aceh, Indonesia

Abstract

Estuaries are critical interfaces linking terrestrial and marine systems, yet escalating organic pollution threatens their ecological connectivity and resilience. Despite this, biomonitoring frameworks remain heavily reliant on phytoplankton, potentially overlooking integrative responses across trophic levels. This study tests the proposition that zooplankton community structure serves as an effective bioindicator of organic pollution in tropical estuaries. Zooplankton were sampled across five stations in the Lhokseumawe Estuary (Aceh, Indonesia) during three periods (July, September, and November 2024). Community responses were evaluated using diversity indices, tolerance-based classification, functional feeding groups, Indicator Value (IndVal), and multivariate ordination. A total of 27 taxa were identified, dominated by crustacean nauplii (44%) and Oligotrichea (41%). Diversity remained moderate (H’ = 1.33–1.83) with high evenness and low dominance, masking significant underlying ecological shifts. Tolerant taxa peaked at 60.11% during periods of elevated organic loading, while sensitive taxa increased to 21.23% during recovery phases, revealing clear signatures of disturbance and resilience. Indicator species (Brachionus sp., Euplotes sp.) exhibited strong spatial structuring, and the dominance of filter feeders (63%) highlighted tight trophic coupling between primary producers and secondary consumers. By resolving ecological gradients that are weakly captured by phytoplankton alone, this study demonstrates that zooplankton-based indicators substantially improve detection of organic pollution impacts. These findings advance a multi-trophic biomonitoring framework that strengthens inference of trophic connectivity and provides a scalable tool for resilient estuarine management, supporting evidence-based management of land–sea connected systems and advancing sustainable blue economy practices in tropical coastal regions.