Vulnerability to Climate Change of Mangroves: Assessment from Cameroon, Central Africa

Abstract

Intertidal mangrove ecosystems are sensitive to climate change impacts, particularly to associated relative sea level rise. Human stressors and low tidal range add to vulnerability, both characteristics of the Doula Estuary, Cameroon. To investigate vulnerability, spatial techniques were combined with ground surveys to map distributions of mangrove zones, and compare with historical spatial records to quantify change over the last few decades. Low technology techniques were used to establish the tidal range and relative elevation of the mapped mangrove area. Stratigraphic coring and palaeobiological reconstruction were used to show the longer term biological history of mangroves and net sedimentation rate, and oral history surveys of local communities were used to provide evidence of recent change and identify possible causes. Results showed that the seaward edge of mangroves had over two thirds of the shoreline experienced dieback at up to 3 m per year over the last three decades, and an offshore mangrove island had suffered 89% loss. Results also showed low net sedimentation rates under seaward edge mangroves, and restricted intertidal elevation habitats of all mangroves, and Avicennia and Laguncularia in particular. To reduce vulnerability, adaptation planning can be improved by reducing the non-climate stressors on the mangrove area, particularly those resulting from human impacts. Other priorities for adaptation planning in mangrove areas that are located in such low tidal range regions are to plan inland migration areas and strategic protected areas for mangroves, and to undertake management activities that enhance accretion within the mangroves.

Vulnerability assessment of mangroves to climate change and sea-level rise impacts

“…Rufiji Delta was remote from tide gauge records so at all sites relative sea level trends were interpreted from mangrove palaeoecological reconstruction (Ellison and Zouh 2012;Punwong et al 2013;Ellison and Strickland 2013). All primary sites were located in deltaic or estuarine geomorphic settings, with fluvial sediment supply, which was confirmed by high inorganic content in mangrove sediments.…”

Application of remote sensing and GIS for detection of long-term mangrove shoreline changes in Mui Ca Mau, Vietnam

“…In comparison to studies at other sites, these are much higher. In the Douala Estuary, Cameroon, results showed the seaward edge of mangroves had over two thirds of the shoreline experiencing dieback, at a rate of up to 3 m yr −1 over the period 1975-2007(Ellison and Zouh, 2012. Gilman et al (2007) observed mean landward migration of American Samoa mangroves over 4 decades was from 6.39 cm yr −1 to 3.27 m yr −1 .…”

“…Recently, Hai-Hoa et al (2013) found the width of fringe mangroves had been significantly reduced on Kien Giang coast, Vietnam, with average rates of width reduction from 3 m yr −1 to 7 m yr −1 over the period [2003][2004][2005][2006][2007][2008][2009]. The causes of the changes have been proposed to be reduction in sediment supply and mangrove overexploitation (Ellison and Zouh, 2012), shrimp farm expansion (Hai-Hoa et al, 2013) and climate change, especially sea level rise (Gilman et al, 2007).…”

“…The arrows show the direction of transects from 1 to 74 for zone 4, from 1 to 16 for zone 5 and from 1 to 44 for zone 6. complexity by modifying local coastal dynamics, which can impact mangrove ecosystem permanence by altering rates of erosion or accretion (Hashimoto, 2001). Dam construction on rivers has been reported to reduce (Ellison and Zouh, 2012) or to increase (Dahdouh-Guebas et al, 2005;Koedam and Dahdouh-Guebas, 2008) the volume of water and riverine sediment supply to the sea and coastal mangroves in the affected and adjacent river basins resulting in altered mangrove extent and/or quality. The Mekong River is likely to already have lower sediment loads due to damming of the main stream and tributaries, and this will be exacerbated in the future with more dam construction.…”

Mangrove sediment core analysis of foraminiferal assemblages - a study at two sites along the western coast of India

“…In the present study also, such correlations between sediment characteristics and foraminiferal assemblages were not significant. This may be due to intense post depositional changes including post-mortem taphonomical changes (Berkeley et al 2007) or the past environmental conditions which the mangroves experienced (Ellison & Zouh 2012). In addition to this, anthropogenic activities can also disturb the post-sedimentation process and alter the physicochemical and biotic components of core samples to a greater extent (Qiu et al 2011;Lezine et al 2002).…”