TDA-IME Project Final Report June, 2013 Results from the relatively recent application of modern molecular genetic techniques in mangrove taxonomy (e.g. Ballment et al., 1988; Duke et al., 1998b; Scheue et al., 2003, 2009a, 2009b) suggest that there is still much to be learned about the taxonomy and genetic diversity of mangroves. This is important for several reasons: (1) as indicated in the paragraph above, the loss of even one species of mangrove would represent a significant loss in terms of biodiversity, and possibly also of ecosystem functioning; (2) recent studies of the biochemistry and pharmacology of mangroves have reported species-specific differences in some metabolites and biologically-active compounds that could be involved in salt tolerance and adaptation to climate change (see Parida and Jha, 2010). Some other mangrove species appear to have potential in treating a range of human ailments, including some serious diseases (Bandaranayake, 1998). Although not widely studied, there is evidence of phenotypic plasticity and perhaps of genetic diversity within some species from different localities. For example, in Avicennia germinans, A. marina, Laguncularia racemosa and Rhizophora mangle (McMillan, 1975; Markley et al., 1982); and in Kandelia candel (Maxwell, 1995, 2007). It is highly likely that there are also phenotypic and genetic differences within populations of other mangrove species growing in different localities. This represents a major gap in present knowledge because: (1) it limits our ability to ensure that the full range of mangrove species diversity is preserved; and (2) it means that conservation of genetic diversity is best done in situ where further evolution of genetic and phenotypic traits may be possible, rather than in fixed gene banks. Phenology One of the requirements for mangroves to migrate landwards in response to sea level rise is that the trees can produce sufficient propagules to fuel migration. Many, perhaps most species, begin to flower by 10 years of age, and often as early as two to three years. One study has reported an earlier onset of flowering in response to elevated ambient CO2 concentrations (Farnsworth et al., 1996). However, flowering does not necessarily translate into the production of viable propagules. Phenological studies at Ranong on the Andaman Sea coast of Thailand, and on the west coast of Malaysia, have shown that there is a very high rate of abortion during bud formation and anthesis. For R. apiculata at Ranong, it takes about 32 months from the initiation of inflorescences to the release of mature propagules (UNDP/UNESCO, 1991). The first stage, the initiation of inflorescences to the formation of young buds, accounts for about half this time (ca 18 months). For R. mucronata, it takes only about 17 months from the initiation of inflorescences to mature propagule fall, chiefly because of rapid progress of the stage involving the formation of young buds, which takes only about a month compared with the 18 months required for this stage in R. apiculata (UNDP/UNESCO, 1991; Pandey and Pandey, 2008). In southern Viet Nam, at a similar latitude but with a longer and more pronounced dry season, Clough et al. (2000) found significant propagule production only in stands of R. apiculata over 12 years of age, propagule production being 397,000 ha-1 in 21 year-old stands and 680,000 ha-1 in 36 year-old stands. There is little comparable information for other mangrove species of the Family Rhizophoraceae. Climate change is a multi-faceted process involving changes in a whole suite of factors that could potentially influence phenology. These include temperature (especially temperature extremes) and changes in seasons and rainfall patterns, as well as other potential stressors, any of which alone or in combination might alter the phenology of flowering and propagule production. These effects will not be the same on all coastlines where mangroves are now found, and different species might respond in different ways. In addition climate change could also affect the distribution and behavior of mangrove pollinators, which include bats, birds and insects (Saenger, 2002). 32
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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