Identifying the real pollinators? Exotic honeybees are the dominant flower visitors and only effective pollinators of avicennia marina in Australian temperate mangroves
The literature suggests that, in the tropics, mangroves are typically pollinated by a range of generalist pollinators, whereas in temperate populations, pollination biology is largely unstudied. We predicted that, for the mangrove Avicennia marina in temperate southeast Australia, pollinator diversity would be low and its pollination system modified by the exotic honeybee Apis mellifera. Multiyear surveys and experiments were used to test these hypotheses by determining the identity and frequency of flower visitors, quantifying pollinator foraging behaviour, determining the species composition of pollen loads, and demonstrating pollen removal and deposition. We identified 38 species that visited flowers, but only A. mellifera was a significant pollinator. It was the only species to carry large amounts of pollen and forage in a manner permitting transfer of pollen to stigmas. Moreover, A. mellifera was the numerically dominant flower visitor and was effective in both pollen removal and deposition. This study demonstrates the importance of distinguishing flower visitors from pollinators and emphasises the surprisingly widespread influence of the exotic A. mellifera. Finally, our study and a worldwide review of the literature on the pollination of mangroves reveal that the pollination biology of other mangrove systems requires similar scrutiny.