Mangrove ecosystem values and functions: an interdisciplinary approach

Humanity’s survival and well-being are intricately linked to the underlying ecosystem functions around the globe. Intertidal mangrove ecosystems are associated with a host of critical ecological functions and provide ecosystem services to a substantial proportion of the coastal population particularly in developing countries. In spite of their socioeconomic importance, empirical research has demonstrated that mangrove area has been reduced by one third primarily due to anthropogenic activities in the past 50 years. Thus, urgent conservation measures are needed to stem this decline.However, there is a dearth of management relevant information for mangrove restoration and conservation. Mangroves vary in their attributes (species composition, structure, function, dynamics and ecological history) across the 123 countries where they occur. Empirical studies on mangroves are usually conducted at small spatial scales and for short durations of time. However, the results are often extrapolated to much larger scales without caution. It remains logistically challenging to identify large-scale patterns through empirical research that may be generalizable and useful for management purposes.In part one of the thesis, we harnessed interdisciplinary thought to gather a consensus on fundamental definitions and concepts of mangrove ecosystems using the Delphi technique, individual based modelling and literature review. We present the global expert based consensus definition, plant species list and ranking of the important ecological functions, faunal groups and impacts to mangroves. The results indicate that degradation due to development had the largest impact on mangroves globally in terms of spatial scale, intensity and time needed for restoration. The experts recognized wind attenuation by mangrove ecosystems as an important ecological function. We also identified six ecosystem services (viz: fodder, water bio-remediation, protection from salt intrusion, aesthetic value, pharmaceuticals and environmental risk indicator) for which there were no economic valuation exercises. Coastal protection was identified as an important ecological function and a critical ecosystem service influencing human survival.In part two of the thesis, we focused specifically on the coastal protection function of mangroves and other coastal protection structures called bioshields. Bioshields are defined as coastal vegetation used or promoted for protection of the coast from extreme events such as storms and tsunamis. We found that application of ecological criteria has been undermined during the establishment and maintenance of bioshields. There was a general lack of awareness about conservation laws relating to coastal forests. Based on these findings, we reassessed the coastal protection function of mangroves and other bioshields. We also propose a framework for evaluation of future bioshield initiatives.This research adds to the general understanding of mangrove ecosystems from a global perspective. In addition, the interdisciplinary valuation approach adopted for mangrove ecosystem services could be applicable to other ecosystems. Further research on the wind attenuation function and fungal and faunal assemblages (particularly folivorous insects and meiofauna) is recommended. We propose that research on ecosystem functioning and management should move beyond the (artificial) delineation of boundaries of ecosystems (e.g. seagrass beds, mangrove forests, beach forests) and consider the larger seascape matrix in which these intertidal systems are embedded in.Doctorat en Sciences