Vulnerability of Fiji's mangroves and associated coral reefs to climate change. A Review. In: Global Conservation Organisation National Stakeholders Meeting , 19 March 2009, Suva Fiji.

This report was commissioned by the WWF to review and compile existing studies and other literature on the state of knowledge of the vulnerability of Fijian mangroves and adjacent coral reefs to climate change. Information is reviewed on strategies or methodologies to adapt or increase the resilience and resistance of the region to impacts of climate change. The review has found that there is little work to date on methodologies and projects that have designed an adaptation strategy to climate change effects for mangroves or coral reef systems. The majority of work to date has been focussed on assessment of impacts. Global climate change was not recognized as a major threat to coral reefs until recently, with direct anthropogenic stresses such as increased sediment loading, organic and inorganic pollution and over-exploitation being considered to be far more critical. With widespread coral mortality in the ENSO-related bleaching events of 1997-8, including pristine and remote reefs in Fiji, views on the importance of the threat of climate change to corals radically switched. This was confirmed by recent evidence that increased CO2 concentrations change the balance between carbonate and biocarbonate ions in sea-water, reducingcalcification rates (ie growth rates) of corals. Impacts of sea-level rise on reefs are thought to be insignificant, possibly even beneficial. Inshore reefs in Fiji are particularly under stress because of threats of poor water quality, sediment loading, pollution, coastal development and over-fishing. Strong links exist between healthy mangroves and healthy inshore reefs in Fiji that will provide resistance to climate change impacts. Coral reefs provide physical protection for the mangrove ad seagrass habitats, and provide sediments to these sedimentary systems. Mangroves act as filters to terrestrial run-off, facilitating near-shore oligotrophic conditions that benefit corals and limiting algal growth. Mangroves produce coloured dissolved organic matter (CDOM) that can be transported over near shore reefs affording them some sunscreen protection. Mangroves are well known in Fiji to increase fish diversity and biomass in nearshore waters, including many species of use to subsistence and commercial fisheries. Fiji has the third largest mangrove area in the Pacific Island region of 425 km2, with seven true mangrove species, and one hybrid. Largest areas are on the SE and NW Viti Levu shorelines, and the northern shore of Vanua Levu, however, on many coastlines smaller mangrove areas exist that are significant to coastal stability and community usage. Climatic variation across the larger islands in Fiji is an influence on mangrove distribution and ecology, indicating how increase or reduction in precipitation patterns may change these. Direct climate change impacts on these mangrove ecosystems are likely to be less significant than the devastating effects of associated sea-level rise. Increase in atmospheric CO2 can be expected to improve mangrove tree growth and litter production, provided mangroves are not limited by salinity or humidity. Mangroves occupy an inter-tidal habitat, and are extensively developed on sedimentary shorelines such as deltas, where sediment supply determines their ability to keep up with sea-level rise. Studies of sediment accretion rates in Fiji’s mangrove areas do not exist, hence comparison with rates of sea-level rise projected must use inferences from elsewhere. Mangroves of low relief islands lacking rivers have been shown to be the most sensitive to sea-level rise, owing to their sediment-deficit environments. However, mangroves on larger islands will also suffer disruption and retreat. Mangrove zonation patterns will retreat with sea-level rise inland, with mortality at their present locations. In Fiji these future mangrove habitats are lowland forests on the windward areas of large islands, or salt flats in the leeward areas of large islands. Unfortunately, the areas where mangroves will seek habitat with sea-level rise are those areas most favored by human development. Fiji has a well established climate monitoring service, but the tide gauge network is nor adequate to show differential rates of sea-level rise that will result from the complex tectonic settings of the region. Some areas will have higher relative sea-level rise impacts of erosion and mangrove loss due to subsidence as well as global sea-level rise. Areas known to be subsiding include the North Coast of Viti Levu, Yasa Yasa Moala and Vanuabalavu. Fiji does not have the financial resources to support coastal engineering or beach replenishment in response to coastal erosion with sea-level rise, and there is mediocre evidence of the success of these elsewhere anyway. Therefore a long-term planning approach to deal with these changes if they occur would be prudent to adopt now. A Precautionary Principle should be adopted with respect to climate change hazards that are projected, that anticipatory planning should include future plans to retreat from the coastline. Migration zones behind current mangrove swamps should be reserved for future mangrove habitats. Reef monitoring in Fiji is not systematic or designed to indicate long term changes that may result from climate change effects. Mangrove monitoring though identified as a requirement in the Regional Wetland Action Plan has not commenced. A systematic long-term monitoring program of representative or critical sites, in conjunction with existing research-based monitoring, would improve identification in Fiji of mangroves and reefs responding to climate change effects. Coastal monitoring programs are recommended to demonstrate the erosion expected with sea level rise. Rehabilitation of degraded mangrove and inshore reef areas will increase their resilience to climate change effects. Site selection should consider value for money, the level of community or stakeholder support, benefits to adjacent systems and the relative risk of sea-level rise. Any rehabilitation program should initially remove the stress that caused decline, decide on whether to use natural regeneration or active replanting techniques, in which case us of local sources of seeds or juveniles will reduce loss of genetic variation across Fiji. A monitoring should collect baseline data before rehabilitation commences, to enable demonstration of improvement in water quality, reef cover and fisheries with progression of the rehabilitation project