specific guilds effect ecological processes to project how changes in biodiversity may influence the properties of mangrove ecosystems. There have been few manipulations of mangrove guilds to test these ideas, with the exception of the role of crabs on ecological processes such as zonation and nutrient cycling (Section 13.4). There are other mutualistic interactions between mangroves and faunal guilds (such as epibionts and insects) that may be significant at the ecosystem level, particularly in oligotrophy environments. The chemical ecology of mangrove tree species was mention in several sections of this review to have an influence on the population dynamics of specific guilds, and thus potentially influence a variety of ecological processes (Sections 13.3 to 13.5). There are a few descriptions of the species-specific nature of secondary compounds in mangroves, while ecological studies of their effect on faunal and microbial processes are few. Larger-scale manipulations of biodiversity components within coastal watersheds are also lacking since these are more complicated than examples in upland ecosystems, but given the migratory nature of organisms that utilize these coastal habitats, there may be significant linkages at this scale of interaction (Section 13.6). This void in information complicates issues of fragmentation and minimum conservation size of mangroves and tropical estuaries. Figure 13.9 shows the landscape-scale modification of the intertidal zone of a southern coastal province in Ecuador for the commercial production of shrimp (1988 photograph from CLIRSEN; Twilley ei ai. 1993). Since 1981, over 40 000 ha of shrimp ponds have been constructed in this area, resulting in the loss of over 40% of the mangrove ecosystem in this specific region. This is only one of the several impacts of humans on mangrove ecosystems throughout the tropics that, along with climate change, threaten to deteriorate natural processes of tropical estuaries (Section 13.7). The challenge for the science of mangrove ecology is to integrate approaches and techniques that can evaluate the impacts of coastal landscape fragmentation, such as in Figure 13.9, to sustain the ecological properties of tropical cstuarine ecosystems.
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