Mangrove deaths in Kenya: Causes and recommended management interventions

Abstract

Mangroves are among the most productive forest ecosystems in the world. Mangroves provide various products and ecosystem services including: fuel; timber; coastal protection; breeding sites for fish; and pollution amelioration. Due to overexploitation and land conversion, mangrove cover has reduced globally by approximately one third in recent years. This reduction in mangrove cover continues at a rate of 1-2% per annum (Polgar, 2009). The main causes for this reduction include; harvesting; conversion of mangrove forests to alternative land use mainly agriculture and urban development;oil spills ; and construction of aquaculture ponds (Macintosh et al., 2002; Walton et al., 2007). Additionally, effects and impacts of climate change have further resulted to reduced mangrove forest cover. These effects and impacts of climate change include; sea level rise, flooding, erosion, sedimentation, fluctuating precipitation and temperatures regimes, and associated phenomena like hurricane and cyclones (McLeod and Salim, 2006; IPCC, 2007; Gilman et al., 2008; Bosire et al., 2013). In Kenya, mangroves occupy protected shorelines, lagoons, creeks and estuarine distributed along the 600 km coastline. The total mangrove area in Kenya is estimated at 61,271 ha; which is 3.0% of the total natural forests or 1.0 % of the country’s area (GoK, 2017). Most of the mangrove forests occur in Lamu and the surrounding islands. Smaller populations of mangroves are found in south of Tana River, Kilifi, Mombasa and Kwale counties. There are nine species of mangroves in Kenya. The dominant species are Rhizophora mucronata and Ceriops tagal that occupy more than 75% of the mangrove formation. Other common species are Avicennia marina, Bruguiera gymnorrhiza and Sonneratia alba. Less common species include: Xylocarpus granatum, Xylocarpus mollucensis, Heritiera littoralis and Lumnitzera racemosa. Kenya losses about 0.7% of its mangroves forest cover annually (Kirui et al., 2013). However, peri-urban areas have witnessed higher loss of mangrove forest areas. For instance, between 1992 and 2009, Tudor lost 86.9% of the mangrove forest while Mwache lost 45.4% representing very high degradation rates of 5.1 and 2.7% per annum, respectively (Bosire et al., 2013). Losses of mangrove forests have also been accompanied by the loss of ecosystem services such as coastal protection and provision of habitats for juvenile fish. These losses have serious repercussions to local communities (Vannucci, 2004). Death of mangroves is common especially in Lamu, Mida Creek, Tudor and Mwache. The causes of mangrove deaths have been highlighted in a number of studies. However, information related to mangrove deaths has not been well packaged to inform managers on the affected species and site-specific factors that are responsible. This technical paper presents factors driving mangrove deaths within various mangrove formations in Kenya.