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Ocean Acidification and Its Potential Impacts on Marine Ecosystems

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Ocean Acidification and Its Potential Impacts on Marine Ecosystems 1 2 Reviews and Syntheses: Ocean acidification and its potential 3 impacts on marine ecosystems 4 by 5 Khan M. G. Mostofa1*,2,8, Cong-Qiang Liu2*, WeiDong Zhai3, Marco Minella4, Davide 6 Vione4, Kunshan Gao5, Daisuke Minakata6, Takemitsu Arakaki7, Takahito Yoshioka8,9, 7 Kazuhide Hayakawa10, Eiichi Konohira8,11, Eiichiro Tanoue8,12, Anirban Akhand13, 8 Abhra Chanda13, Baoli Wang2, Hiroshi Sakugawa14. 9 10 1Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, PR 11 China. 12 2State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, 13 Chinese Academy of Sciences, Guiyang 550002, China. 14 3Institute of Marine Science and Technology, Shandong University, Ji-nan 250100, 15 China. 16 4Università degli Studi di Torino, Dipartimento di Chimica, Via P. Giuria 5, 10125 17 Torino, Italy and Centro Interdipartimentale NatRisk, Via Leonardo da Vinci 44, 10095 18 Grugliasco (TO), Italy. 19 5State Key Laboratory of Marine Environmental Science (B-606), Xiamen University, 20 Daxue Rd 182, Xiamen, Fujian 361005, China 1 1 6Department of Civil and Environmental Engineering, Michigan Technological 2 University 1400 Townsend Drive, Houghton, MI. 49931, U.S.A. 3 7Department of Chemistry, Biology and Marine Science, Faculty of Science, University 4 of the Ryukyus, Senbaru, Nishihara-cho, Okinawa 903-0213, Japan. 5 8Institute for Hydrospheric–Atmospheric Sciences, Nagoya University, Nagoya, Japan. 6 Present address: 9Field Science Education and Research Center, Kyoto University, 7 KitashirakawaOiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan. 8 10Lake Biwa Environmental Research Institute, Shiga Prefecture, Ohtsu 520-0806, Japan. 9 Present address: 11DLD inc., 2435 kamiyamada, Takatomachi, Ina, Nagagano, 396-0217, 10 Japan. 11 12Hydrospheric Atmospheric Research Center, Nogoya University, Nagoya, Japan. 12 13School of Oceanographic Studies, Jadavpur University, Jadavpur, Kolkata 700032, 13 West Bengal, India. 14 14Graduate School of Biosphere Science, Department of Environmental Dynamics and 15 Management, Hiroshima University, 1-7-1, Kagamiyama, Higashi-Hiroshima 739-8521, 16 Japan. 17 *Corresponding address: Institute of Surface-Earth System Science, Tianjin University, 18 Tianjin 300072, PR China. Tel. +8615122054195; Fax: +86-22-27401797 19 E-mail: [email protected] (K.M.G. Mostofa) and [email protected] (C.Q. 20 Liu) 21 2 1 Abstract 2 Ocean acidification, a complex phenomenon that lowers seawater pH, is the net outcome 3 of several contributions. They include the dissolution of increasing atmospheric CO2 that 2 4 adds up with dissolved inorganic carbon (dissolved CO2, H2CO3, HCO3 , and CO3 ) 5 generated upon mineralization of primary producers (PP) and dissolved organic matter 6 (DOM). The aquatic processes leading to inorganic carbon are substantially affected by 7 increased DOM and nutrients via terrestrial runoff, acidic rainfall, increased PP and algal 8 blooms, nitrification, denitrification, sulfate reduction, global warming (GW), and by 9 atmospheric CO2 itself through enhanced photosynthesis. They are consecutively 10 associated with enhanced ocean acidification, hypoxia in acidified deeper seawater, 11 pathogens, algal toxins, oxidative stress by reactive oxygen species, and thermal stress 12 caused by longer stratification periods as an effect of GW. We discuss the mechanistic 13 insights into the aforementioned processes and pH changes, with particular focus on 14 processes taking place with different time scales (including the diurnal one) in surface 15 and subsurface seawater. This review also discusses these collective influences to assess 16 their potential detrimental effects to marine organisms, and of ecosystem processes and 17 services. Our review of the effects operating in synergy with ocean acidification will 18 provide a broad insight into the potential impact of acidification itself on biological 19 processes. The foreseen danger to marine organisms by acidification is in fact expected to 20 be amplified by several concurrent and interacting phenomena. 21 22 Keywords: Acidification; CO2; organic matter; biological processes; global warming; 23 photosynthesis, impacts on marine organisms. 3 1 1 Introduction 2 Ocean acidification is typically defined as a process of increasing seawater acidity or 3 lowering seawater pH, as a consequence of the dissolution of elevated atmospheric CO2. 4 Carbon dioxide from the atmosphere (Orr et al., 2005; Feely et al., 2008) adds to the 2 5 dissolved inorganic carbon (DIC: dissolved CO2, H2CO3, HCO3 and CO3 ) originated 6 from the degradation of dissolved organic matter (DOM) (Mostofa et al., 2013a), primary 7 producers (PP) (Cai et al., 2011; Mostofa et al., 2013a), CO2 seeps from sub-seabed 8 storage (Taylor et al., 2014) and volcanic vents (Lidbury et al., 2012; Hall-Spencer et al., 9 2008) in shallow submarine zones, anaerobic oxidation of methane (Haroon et al., 2013) 10 and sulphide oxidation coupled to carbonate dissolution (Torres et al., 2014) in seawater. 11 The sources of elevated atmospheric CO2 include first of all anthropogenic activities such 12 as fossil fuels combustion (such as coal, petroleum and natural gas (Le Quéré et al., 13 2009), enhanced land-use practices (Le Quéré et al., 2009), as well as deforestation (van 14 der Werf et al., 2009; Lapola et al., 2014). Additionally, there could be significant 15 contributions from natural sources such as plant litter decomposition (King et al., 2012), 16 volcanic eruptions (Hall-Spencer et al., 2008), emission of CO2 from freshwater 17 including the Amazon River basin (Sobek et al., 2005; Abril et al., 2014) and enhanced 18 respiration of soil organic matter (OM) under global warming (GW) conditions (Knorr et 19 al., 2005). 20 The emissions of CO2 by fossil fuels combustion have increased by 29% in 2000- 21 2008 (Le Quéré et al., 2009) and, as far as natural-water sources are concerned, the 22 contribution from European estuaries is for instance equivalent to approximately 5 to 23 10% of the anthropogenic CO2 emissions in Western Europe (Frankignoulle et al., 1998). 4 1 Recent studies demonstrate that ocean acidification under elevated CO2 and temperature 2 levels could increase primary productivity of specific species (Holding et al., 2015; 3 Coello-Camba et al. 2014; Li et al., 2012). Additionally, such specific species-based 4 primary productivity is also found to increase either by increasing seawater CO2 level 5 (Kim et al., 2006; Olischläger et al., 2013) or elevated temperature alone because of the 6 effects of global warming (Yvon-Durocher et al., 2015; Lewandowska et al., 2012). The 7 primary production in the oceans contributes approximately 48.5 petagrams (1 Pg = 1015 8 g) of C yr—1 (46.2% of the total), as estimated using the integrated CASA-VGPM 9 biosphere model (Field et al., 1998). As a consequence, approximately one-third to 50% 10 of the atmospheric CO2 is fixed annually worldwide by marine phytoplankton (Sabine et 11 al., 2004; Toseland et al., 2013). However, one should also consider that the 12 photoinduced and biological mineralization of organic matter (OM), including DOM and 13 dead organisms, is an important source of DIC in seawater and liberates again an 14 important fraction of the CO2 fixed by photosynthesis (Bates and Mathis, 2009; Mostofa 15 et al., 2013a). 16 Ocean acidification is responsible for changes in the oceanic carbonate system, 17 with effects on partial pressure of CO2 (PCO2), DIC, pH, alkalinity and calcium 18 carbonate saturation state (Feely et al., 2010; Beaufort et al., 2011). In the case of 19 calcifying organisms one observes a marked pattern of decreasing calcification with 2 20 increasing PCO2, which follows the corresponding decreasing concentrations of CO3 as 21 a consequence of decreasing pH (Beaufort et al., 2011). Such effects finally cause a 22 decline in calcification and growth rates of shellfish (Talmage and Gobler 2010; 23 Wittmann and Pörtner 2013), of shell-forming marine plankton and of benthic organisms 5 1 including corals (Kleypas et al., 1999; Doney et al., 2009; Beaufort et al., 2011; Pandolfi 2 et al., 2011; McCulloch et al., 2012). The latter have already been lost or are highly 3 damaged in coastal areas near many countries including Indonesia, Hawaii, Caribbean, 4 Fiji, Maldives, and Australia (Erez et al., 2011). A 30% decline or damage of coral reef 5 ecosystems has been estimated worldwide, and it is predicted that as much as 60% of the 6 world‘s coral reefs might be lost by 2030 (Hughes et al., 2003). 7 The extent and effects of ocean acidification can be exacerbated by several 8 complex processes, some of which act as stimulating factors, such as local environmental 9 impacts including terrestrial or riverine runoff (Sunda and Cai 2012; Bauer et al., 2013), 10 modified land-use practices (Lapola et al., 2014) and atmospheric acid rain (Baker et al., 11 2007). An additional effect could be represented by the enhanced mineralization of DOM 12 and PP (e.g., phytoplankton) as a consequence of global warming (Mostofa et al., 2013a). 13 Such mineralization could be biological (respiration) or abiotic via different (mainly) 14 photochemical processes. Most of the cited effects are expected to cause eutrophication 15 or algal blooms in coastal seawater, which would in turn affect the carbon cycling and the 16 carbonate chemistry and influence the overall acidification process (Beaufort et al., 2011; 17 Sunda and Cai, 2012; Bauer et al., 2013). Such acidification is responsible for changes in
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