Reproductive Ecology of Mangrove Flora: Conservation and Management

摘要

Mangroves are dynamic and unique inter-tidal ecosystems, common in tropical and subtropical coastal environments. They are among the world’s most productive ecosystems and are important in protecting coasts from erosion by fierce tides, in promoting the diversity of marine organisms and fisheries by contributing a quantity of food and providing favourable habitats for animals. These economic uses of mangroves indicate that they play an important role in the lives and economies in the coastal regions of different countries. Mangrove forests are under immense threat worldwide due to their multiple economic uses and alterations of freshwater inflows by various upstream activities in catchment areas. Mangrove plants with unique adaptations play a crucial role in sustaining life in mangrove forests. Their reproductive biology is central to understanding the structural and functional components of mangrove forests. The success of sexual reproduction and subsequent population expansion in mangrove plants is linked to flowering timings, pollinators and tidal currents. Viviparous and cryptoviviparous plants are true mangroves while non-viviparous ones are mangrove associates. The dispersal propagule is seedling in viviparous and non-viviparous plants while it is seed in nonviviparous plants. In this study, viviparous and crypto-viviparous species were included for study. These species are self-compatible, self-pollinating and also cross-pollinating; such a breeding system is a requirement for the success of sexual reproduction and subsequent build up and expansion of population. They are entomophilous in the study region. The viviparous plants include Ceriops tagal, C. decandra, Rhizophora apiculata, R. mucronata, Bruguiera gymnorrhiza and B. cylindrica. The non-viviparous plants include Avicennia alba, A. marina, A. officinalis, Aegiceras corniculatum and Aegialitis rotundifolia. Sexual reproduction and regeneration events are annual in these plants and are dependent on local insects, tidal currents and nutrient content in estuarine environment. In recent times, erratic and insufficient rainfall together with industrial pollutants released into rivers is causing negative effects on the growth, development and regeneration of mangrove flora. In effect, there is a gradual decrease in mangrove cover. Added to this is continuous exploitation of mangrove plants for fuel wood, creation of shelters for cattle and changes for industrial establishments and aquaculture development in estuarine regions. As a consequence, the existing mangrove cover is struggling to survive and also not in a position to support local needs and provide livelihood opportunities through fishery resources. Further, reduced mangrove cover is showing catastrophic effects on fishing communities who live along the shore line during the period of cyclonic surges and tsunami events.