Unveiling the association of mangrove flowering phenology on the dynamics of insect abundance

Abstract

Mangroves are ecologically unique ecosystems supporting large biodiversity. Climate change and anthropogenic interferences led to continuous decline of mangroves worldwide. Simultaneously, continuous decline in pollinators, have put these primarily insect-pollinated ecosystems under threat. Therefore, to understand seasonal and interannual variation in floral-visitor population, study of insect-visitor abundance in relation to flowering phenology is critical. In this context, present study (2022–2023) was conducted in the mangrove belt of Purba Medinipur, West Bengal, India. We observed quantitative floral availability as flowering phenology of four dominant mangrove species: Avicennia marina, Avicennia officinalis, Aegiceras corniculatum, and Acanthus ilicifolius. We also examined the seasonal and interannual variation in insect abundance within the mangrove community via pan traps. To identify potential pollinator groups among insects from the pan traps, we studied foraging behaviour of these insect visitors separately. Finally, we investigated the relationship between floral availability and insect-visitor abundance.

In this study, a total 35 insect species of eight orders were collected across all pan traps, among which, 19 species were classified as potential pollinators. Hymenoptera was most abundant in pan trap captures, followed by Diptera, Lepidoptera and Coleoptera. Significantly higher insect abundance was observed during the peak flowering at community-level. There was no interannual variation in insect abundance between two years. This is the first comprehensive quantitative study identifying potential mangrove pollinators and demonstrating their positive relationship with floral availability, which affecting pollinator abundance. This also indicates that, steady supply of floral availability is required for maintaining the pollinator abundance in the community.