Diatom community dynamics in a tropical brackish coastal ecosystem from an ecological and biogeochemical perspective: A size-fractionated approach

Abstract

Diatoms are a major, ubiquitous photosynthetic group representing most aquatic ecosystem’s microalgal communities. The species composition encompasses a wide range of cell sizes. Although cell size is vital in aquatic ecology and biogeochemistry, size-based diatom community studies are sparse, especially in tropical ecosystems. This study assesses the size-fractionated brackish diatom community based on the microscopic cell abundance and carbon-biomass metrics. Despite sufficient nutrient availability, the seasonal and spatial relative proportion of abundance and biomass of the three diatom size fractions declined under high turbidity. It increased under higher light and nutrient availability with lower turbidity. Turbulence was a favorable factor irrespective of the size groups. Light availability, increased nutrients, and lower temperature resulted in a higher contribution from the larger size group to the total diatom carbon biomass. The smaller size group dominance during highly turbid conditions could be attributed to the higher surface-to-volume ratios. The intermediate-size groups thrived under reduced turbidity. Seasonal intra-species size variations reflected changes induced either due to life-cycle stages or environmental stress. The size-based metrics permitted an in-depth understanding of the diatom responses at the community and species level, which could have implications on their ecological and biogeochemical roles in aquatic ecosystems.