Characterising benthic diatom community responses to abiotic variability in a tropical Ramsar estuarine lake

Abstract Benthic diatoms are reliable indicators of estuarine ecosystem health. These communities can be used to track water quality changes in estuarine lakes that are unique, yet highly susceptible to anthropogenic perturbations due to their high accumulation potential. This study investigated the abiotic drivers of the benthic diatom community structure in the near-natural Kosi Bay Estuarine Lake, a Ramsar Wetland of International Importance in summer/spring of 2016 and 2022. A total of 159 taxa, belonging to 57 genera were recorded. The composition of benthic diatom assemblages was related to salinity variability, with marine species dominating the tidal lower estuarine reaches and freshwater taxa in the distal and oligohaline lake compartments. Taxa capable of attachment to different substrates that enable resilience to tidal disturbance, such as Amphora , Halamphora , Mastogloia , and Seminavis , were dominant in the tidally influenced lower lake compartments. Higher species diversity (H’ > 2) was observed in proximity to the estuarine mouth, with regular sediment disturbance favouring increased diversity. An increased availability of DIP (≥ 0.01 mg L −1 ) and sediment organic content (1.1–3.7%), coupled with low flow velocities, favoured the proliferation (RA > 10%) of Cocconeis spp. in the Phragmites -dominated upper lake compartments. Nutrient tolerant taxa, such as Navicula gregaria , Nitzschia frustulum, and Tabularia tabulata, were present in the estuarine lake. However, further investigations are required to determine whether their presence is due to inherent estuarine variability or a precursor to future anthropogenic change. Studies such as these that provide baseline information are essential to help inform effective management and recovery plans of rare estuarine ecosystem types.