Epibiotic communities (microalgae and meiofauna) on the pneumatophores of Avicennia officinalis (L.)

Abstract

In a mangrove environment, several groups of organisms are symbiotically associated with pneumatophores (aerial roots). But whether these organisms are exclusively found in this habitat (uniqueness) or accidentally settled here from water or sedimentary habitat, is not clearly understood. This hampers our understanding of their functional ecology. Hence the present study aimed to characterise the epibiotic microalga and meiofauna from the pneumatophores of mangrove Avicennia officinalis. To determine the habitat influence, these communities were also compared with those found in water and sedimentary habitat. Four estuarine mangrove sites represented by brackish water (salinity varying from 5 to 12) and located at different spatial scales (5-50�km distance) were chosen to determine whether these communities are consistent or vary with sites. Overall, the microalgal community was found to vary both among the habitats as well as sites. In the pneumatophore habitat, several tychoplanktons such as Coscinodiscus, Thalassionema, Cyclotella, Fragilariopsis, and Biddulphia were observed instead of benthic ones. These diatoms are planktonic genera and might have settled on pneumatophores from the water column. The observed variability in the microalgal composition among the sites is possibly due to predatory interactions or the dominance of particular species of macroalga that govern the diatom community. On the other hand, among the meiofaunal community, diptera, halacarida, tanaidacea, and foraminifera were mainly found in the pneumatophore habitat than in the sediment. Because pneumatophores either provide refugee to meiofauna against predators or are saturated with oxygen that meiofauna can utilize for respiration. Pneumatophores were also found to harbour several rare (abundance <1%) epibionts, the ecological importance of which is discussed in this paper.