Diversity and assemblage structure of tropical marine flora on lava flows of different ages. Seaweeds from a lava flow gradient in Réunion

Recent volcanic lava flows of Piton de la Fournaise at Réunion Island (Indian Ocean) represent an ideal opportunity to study the successional development of marine floral assemblages on bare new substratum. We describe the floral assemblages of nine lava flows of different ages (prehistoric to 2007) based on the survey of 37 stations. We identified 159 species including 148 macroalgae, 1 seagrass and 10 cyanobacteria. Fifty one of those represent new records for Réunion and at least 8 taxa were identified as new to science. Recent lava flows were characterized by the dominance of ephemeral, opportunistic species, such as Pseudobryopsis hainanensis and Acrocladus dotyanus, while prehistoric lava flows were mainly characterized by perennial species, particularly Sargassum portieranum and Turbinaria ornata. CCA analysis revealed that the environmental factor most significantly correlated to the floral assemblages was the distance to the most recent lava flow (2007). This factor was also highly correlated to coral cover. The composition of the different floral assemblages is discussed in relation to abiotic and biotic factors to explain ecological succession in tropical environments.