Latitudinal Variation, and Potential Ecological Indicator Species, in the Dinoflagellate Genus Tripos along 110°E in the South-East Indian Ocean

Variations in oceanic environmental conditions influence phytoplankton community composition, distribution, seasonality and abundance. The dinoflagellate genus Tripos is globally widespread and as a recognised key indicator has the potential for being a marker for climate-based changes in the ocean. As part of the Australian effort for the Second International Indian Ocean Expedition, 20 stations along the 110 degrees E line from 39.5 degrees to 11.5 degrees S were sampled from the RV Investigator in 2019. Oceanic conditions ranged from cold, nutrient-rich Subantarctic waters in the south to warm, oligotrophic tropical waters in the north. The Tripos assemblages along the transect were assessed relative to the changing environmental variables. We found four main Tripos groups at a 50% dissimilarity level where the assemblages were correlated with groups based on the environmental conditions observed during the voyage. A number of potential indicator species were identified for each group, specifically Tripos lineatus which was found to be a strong indicator of cold, nitrate-rich and silicate-poor Subantarctic water and Tripos muelleri var. pulchellus as an indicator of warmer, oligotrophic waters.