Coastal aquaculture, mangrove deforestation and blue carbon emissions: Is REDD+ a solution?
Introduction
Aquaculture is one of the fastest growing food production systems in the world as the sector has expanded at an average annual rate of 8.6% over the last three decades. Global fish production reached 66.6 million tons in 2012, of which Asia accounted for 88.4%. About 41.9 million tons (63%) and 24.7 million tons (37%) of fish production were obtained from inland aquaculture and mariculture, respectively [1]. Coastal aquaculture, a part of mariculture, is the onshore and near-shore culture of brackish and saltwater fish including shellfish [2], [3]. Globally, coastal aquaculture expanded rapidly in the 1980s and 1990s. Over the last decades, coastal aquaculture including shrimp farming has undergone a revolutionary development [4], [5].
There have been considerable debate and argument on the impacts of coastal aquaculture on the environment, biodiversity, and society [3], [5]. Globally, shrimp farming has been strongly criticized because of its socioeconomic and environmental impacts [4], [6], [7], [8], [9], [10]. Rapid loss of mangroves has accelerated over the last decades, and coastal aquaculture including shrimp farming is one of the key reasons [11], [12], [13], [14]. Driven by high economic return associated with growing demand in the international market, unplanned and unregulated shrimp farming caused widespread destruction of mangroves in a number of countries, including Bangladesh, Brazil, China, India, Indonesia, Malaysia, Mexico, Myanmar, Sri Lanka, the Philippines, Thailand, and Vietnam [12], [15].
Mangroves are the most carbon-rich forests in the tropics [16], [17], [18], [19], [20]. On average, mangroves store 3–4 times more carbon than tropical forests [17]. At the same time, mangrove deforestation rates are significantly higher than average rates of global forest loss [12]. Mangrove deforestation causes carbon emission and reduces carbon sequestration1 [20]. Carbon emissions with other greenhouse gases (CH4, N2O) are likely to have been the dominant cause of climate change [21]. To tackle climate change, it is therefore crucial to stop carbon emissions from the deforestation and degradation2 of mangroves [16], [17], [20], [22].
The conservation of mangrove forests can help to reduce carbon emissions [18], [23]. It is argued that the “Reducing Emissions from Deforestation and forest Degradation (REDD)” program can help to sequester carbon in mangroves [17], [19], [24], [25], [26]. This review paper highlights key issues in reducing carbon emissions from mangroves through REDD+. The impacts of climate change on coastal aquaculture that occur with the deforestation of mangroves are also discussed. Finally, this paper offers some preliminary conclusions about the implementation of REDD+ for the restoration of mangrove forests.
Section snippets
From RED to REDD+
Although greenhouse gas emissions increase with deforestation, controversies arose over the inclusion of forest conservation under the Kyoto Protocol that was adopted at the 3rd Conference of Parties (COP) of the United Nations Framework Convention on Climate Change (UNFCCC) in 1997 [27]. In 2005, the concept of “Reduced Emissions from Deforestation (RED)” in developing countries was first emerged at the 11th COP of the UNFCCC agenda in Montreal [28]. In 2006, at the 12th COP of the UNFCCC in
Mangrove deforestation through coastal aquaculture
Total global forest area is just over 4 billion ha, about 31% of land area. Globally, the total mangrove area is 15.6 million ha4, just 0.39% of forest area. Mangroves occur in 112 countries worldwide, mainly in the tropics and sub-tropics. However, 47% of the global mangrove area is found in 5
Mangrove deforestation and blue carbon emissions
Mangroves play a significant role as blue carbon5 sinks. Blue carbon is the organic carbon stored, sequestered, and released from coastal and marine ecosystems, including mangroves, salt marshes, and seagrasses [18], [20], [23], [25], [53], [54]. Global coverage of blue carbon ecosystems are approximately 51 million ha [55], of which 15.6 million ha (31%) is mangroves
Mangrove deforestation, climate change and coastal aquaculture
Anthropogenic climate change with loss of mangroves has devastating effects on coastal aquaculture. The impacts of climate change on coastal aquaculture have been assessed with different climatic variables, including: (1) coastal flooding, (2) cyclone, (4) drought, (3) rainfall, (5) salinity, (6) sea-level rise, and (7) sea surface temperature [58], [59]. Changes in these climatic variables have severe effects on the ecosystem of fish farms (Fig. 2). Fish are highly sensitive to ecological
REDD+: mangrove restoration for adaptation to climate change
Considering extreme vulnerability to the effects of climate change on coastal aquaculture and wider coastal economies and societies, adaptation strategies are needed. Mangrove restoration can be part of a broader approach to facilitating adaptation to climate change [61]. REDD+ can address the increased risks from coastal flooding, cyclones, and sea-level rise [25], [28]. Mangrove reforestation and aforestation7
Conclusions
Globally, coastal aquaculture including shrimp farming has devastating effects on mangrove forests. At the same time, mangroves are the most carbon-rich forests in the tropics, and thus, ecologically and economically significant at the planetary level. The loss of mangroves through coastal aquaculture causes carbon emission and reduces carbon sequestration. Blue carbon emissions are being significantly enhanced due to devastating effects of shrimp culture on mangroves. The loss of mangroves by
Acknowledgments
The study was supported through the Alexander von Humboldt Foundation, Germany. The study was a part of the first author's research work under the Georg Forster Research Fellowship by the Alexander von Humboldt Foundation at the Leibniz Center for Tropical Marine Ecology (ZMT), Bremen, Germany within the research group led by the second author. Earlier draft of this paper was presented at the ZMT seminar in April 2015. We thank audience for their positive encouragement. The views and opinions
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