Flood-Driven Spatio-temporal variation of zooplankton and seasonal dynamics of macrobenthos in the Feni river, Bangladesh

Abstract

The ecological importance of zooplankton and benthic communities as freshwater bioindicators is widely recognized, but still commonly undervalued. This study examined the spatio-temporal variations of zooplankton and macrobenthic diversity in the Feni River, Bangladesh between March 2024 and February 2025. Data were collected from three sample locations (stations) of the river, and seasonal patterns were analyzed using abundance (ind./m3), composition, and diversity indices (Shannon-Wiener, H′ and Pielou’s evenness J′). A total of 30 zooplankton species were recorded, with Copepoda as the dominant group. Following the August 2024 monsoon flood, a marked restructuring of the zooplankton community was observed. Rotifera increased from 11.10% in the pre-monsoon period to 37.85% during the monsoon, whereas Copepoda declined from 52.48% to 41.42% and Cladocera from 36.42% to 20.73%. This shift suggests a rapid response of rotifers to flood-induced hydrological changes, whereas copepods and cladocerans were comparatively more susceptible to flood-related disturbance. Zooplankton abundance peaked in autumn (1,343,061 ind./m3) and was lowest in winter (735,706 ind./m3). Diversity was highest at Station 1 during autumn (H′ = 2.42), while evenness remained consistently high (J′>0.85). These findings align with the flood-pulse concept, demonstrating how seasonal flooding shapes zooplankton dynamics. Macrobenthic diversity, assessed at the family level, was highest in winter (H′ = 2.77, J′ = 0.9246) and lowest during monsoon H′ = 2.57, J′ = 0.9071), indicating a moderately diverse and ecologically balanced community throughout the year. This study implies that the zooplankton and macrobenthic communities are generally altered by periodic flooding, and highlighting their critical value as indicators for tropical river management.

Jahangirnagar University J. Biol. Sci. 14(1 & 2): 191-205, 2025 (June & December)