Predicting macroalgal species distributions along the Thai-Malay Peninsula

Abstract

The Thai-Malay Peninsula separates the tropical Western Indo-Pacific from the Central Indo-Pacific marine biogeographic realm and has been hypothesized to form a dispersal barrier between them. In this study we assessed the potential distribution of five common macroalgal species (i.e., Halimeda macroloba, Padina boryana, Padina sp., Sargassum plagiophyllum, and S. polycystum) in the region using species distribution models. Presence data was collected from field observations and literature from the last twenty years. Five presence-absence model algorithms with twenty environmental variables were used. The model ensembles were projected across the space to predict potential distributions of each species. The potential distribution of H. macroloba, P. boryana and Padina sp. approximated the observed distribution of the species with few areas of high probability of occurrence where species were not collected. The potential distributions of S. plagiophyllum and S. polycystum are clearly separated, except in Phuket Island where the two species were observed to occur in sympatry. Each species distribution model was mainly influenced by three or four environmental variables. Bathymetry and mean sea surface temperature were found to be the most important variables in, respectively, four and three species models. This study contributes towards understanding the current distribution patterns of five ecologically important seaweeds and may contribute to studies predicting the impact of climate change and coastal development on these species.