Monsoonal Variation in Singapore Labyrinthulomycetes Community

 Labyrinthulomycetes is a group of ubiquitous saprophytic protists found in marine and estuarine environments. Labyrinthulomycetes are capable of parasitism and commensalism and known as consumers of phytoplankton litter. While Labyrinthulomycetes have been mostly studied and documented in temperate regions, understanding their interactions and variability in the tropics are lacking. They have been found to be strongly associated with particulate organic matter (POM), potentially contributing to vertical export from the surface into the dark ocean. We have conducted a pilot study to access the diversity and community structure of Labyrinthulomycetes associated to suspended sediment particles in Singapore waters. Suspended sediment particles were collected monthly during a period of one year with the deployment of SedPods (flat cylindrical concrete unit with 15 cm height and 15 cm diameter) on the reef slope off Kusu Island. Labyrinthulomycetes community composition was analysed using metabarcoding of the 18S rRNA gene. Environmental parameters such as nitrates and silicates were obtained from water column samples between April 2018 and April 2019. Results indicate that diversity follows changes in nutrient availability linked to monsoon. The relative abundance of genus Aplanochytrium increased with concentrations of nitrates and silicates. The abundance of metabarcodes assigned to the Thraustochytriceae family increased during the South-West monsoon, possibly influenced by the increased availability of detritus and organic matter from riverine inputs from the Malacca Straits and Sumatran peatlands.