Title : Unravelling the spatiotemporal molecular diversity of microeukaryotes in a river-to-estuary continuum using full-length 18S rDNA
Abstract:
The taxonomic composition and diversity of microeukaryotic communities in aquatic ecosystems vary across time and space. Understanding this diversity, its variations, and the effects of natural and anthropogenic factors is crucial for assessing aquatic ecosystems and informing management strategies. This study surveyed the molecular diversity of microeukaryotes in the Pampanga River and its estuary in Manila Bay, Philippines, using metabarcoding. Full-length 18S rDNA sequences from samples collected at different sites and seasons revealed 3,973 ASVs across 35 phyla. Alpha diversity indices indicated higher diversity during the wet season across all sites, with San Luis (Site 2) showing the highest diversity and Arayat (Site 1) the lowest in both seasons. Spatiotemporal patterns were observed in taxonomic abundance and community shifts, notably with a gradual shift in abundance between Cryptophyta and Arthropoda across the sites. The communities were dominated by Ciliophora, Arthropoda, Cryptophyta, and Chlorophyta, with distinct groups prevalent at specific sites. For instance, Cryptomonas sp. and Tintinnidium sp. were prevalent upstream, while Strobilidiidae and freshwater Maxillopoda were more abundant downstream. In the estuary, brackishwater Maxillopoda and Tintinnopsis sp. were the most prominent. These distribution patterns lead to three distinct community clusters along the river-estuary gradient. Although no clear link was found between the overall microeukaryotic structuring and pesticide levels, an inverse relationship between microeukaryotic diversity and pesticide concentrations was observed each season. This study represents the first molecular assessment of river and estuarine microeukaryotes in the Philippines. It highlights the country's microeukaryotic diversity, including first report taxa, while providing valuable baseline data for conservation and serving as a model for future metabarcoding studies in similar ecosystems.
