Spatial and temporal variation of floral visitors and their visitation pattern on Acanthus ilicifolius L.: a case study from the mangrove ecosystem of Indian Sundarbans

Acanthus ilicifolius is a spiny semi-woody evergreen shrub which is one of the most dominant species associated with mangrove communities. Although its floral biology is well documented, there are only a few systematic and exhaustive studies of floral visitors of this species. Successful plant reproduction is highly dependent on plant-pollinator interaction. The present study aims to understand the range of floral visitors of A. ilicifolius and their spatio-temporal variation in visitation pattern from the Indian Sundarbans. This study was conducted within five islands of Sundarbans Biosphere Reserve (SBR), namely, Bali, Gosaba, Satjelia, Gangasagar and Bakkhali during 2015 and 2016. Fifteen flower foragers under five taxonomic orders, i.e., Hymenoptera, Coleoptera, Diptera, Lepidoptera and Passeriformes were identified. Seven out of these fifteen species were reported for the first time as floral visitors of A. ilicifolius. Hymenopterans constituted about 50% of the floral visitors observed. However, Micraspis discolor of the order Coleoptera, with a relative abundance of about 32%, constituted the dominant floral visitor species of A. ilicifolius. Apis mellifera, constituting about 23%, was the dominant Hymenopteran flower visitor species. Although Gangasagar and Bakkhali being tourist spots, and facing greater anthropogenic interference, they had the highest abundance of floral visitors. A significant variation in floral visitor abundance was observed across different time of the day throughout the study period. Floral visitors were most abundant in the morning between 8 am to 12 pm. This study provides the first comprehensive report of diversity and abundance of the floral visitors and their visitation pattern on A. ilicifolius.Implications for insect conservationProper documentation of the visitation pattern and foraging behaviour is important for conserving floral visitors of A. ilicifolius. Since this is the most dominant minor mangrove species, A. ilicifolius can help attract pollinators from surrounding areas, improving the pollinator abundance in other co-flowering species. Thus, conserving the entire mangrove ecosystem.