Introduction

Aquaculture, the farming of fish, shellfish, and aquatic plants, is the fastest growing food production sector on earth. Global aquaculture production increased sixfold between 1990 and 2016, with an average annual growth rate of 5.8% during the period 2000–2016 (FAO 2018a). Excluding aquatic plants and non-food products (pearls and shells), global aquaculture production reached 80 million tons in 2016, with 54.1 million tons (68%) of finfish, 17.1 million tons (21%) of mollusks, 7.9 million tons (10%) of crustaceans, and 0.9 million tons (1%) of other aquatic animals (FAO 2018a). A total of 598 aquatic species were recorded in inland, coastal, and marine aquacultureFootnote 1. Globally, inland aquaculture produced 51.4 million tons (64%), whereas both coastal aquaculture and mariculture (i.e., aquaculture in marine environments) produced 28.7 million tons (36%) in 2016 (FAO 2018a). Asia accounted for 89% of global aquaculture production in 2016 and China was the highest producer (61.5% of total production), followed by India, Indonesia, Vietnam, Bangladesh, Egypt, Norway, Chile, Myanmar, and Thailand (FAO 2018a). Globally, aquaculture predominates in tropical and subtropical regions, but it is also practiced in temperate regions.

Aquaculture has been playing a key role in increasing food production for human nutrition and food security (Béné et al. 2016). Global per capita fish consumption reached 20.3 kg in 2016 and fish provide over 3.2 billion people worldwide with 20% of their animal protein intake (FAO 2018a). The production of carp, catfish, and tilapia has increased remarkably in Asia for local and regional consumption. Catfish and tilapia have also been exported to international markets. The culture of salmon, shrimpFootnote 2, and other high-value species for international trade has also developed. In fact, the rapid development of aquaculture has been considered part of the “blue revolution” (Simpson 2011).

Despite aquaculture growth, the challenge remains of feeding a global population that is currently increasing by 83 million per year and expected to increase from 7.6 billion in 2017 to 9.8 billion in 2050 (United Nations 2017). Thus, global food production needs to increase by 25–70% by 2050 (Hunter et al. 2017). At the same time, 5–7 million ha (0.6%) of global farmland are lost annually as a result of industrialization and urbanization (WWDR4 2012). Continuing population and food consumption growth with increased competition for land, water, and energy has already affected food production (Godfray et al. 2010).

Aquaculture production must be increased to meet the demand for food from a growing global population. It is estimated that 62% of food fish will need to be produced from aquaculture by 2030 to fill the gap between supply and demand with rapidly expanding global fish demand and relatively stable capture fisheries (World Bank 2013). Global capture fisheries have stagnated over the last two decades, reached 90.9 million tons in 2016, of which 79.3 million tons (87%) was from marine fisheries and 11.6 million tons (13%) from inland fisheries (FAO 2018a). Global capture fisheries are expected to remain stable at around 93 million tons during 2010–2030 (World Bank 2013). To meet expected demand for fish, global aquaculture production will need to increase to 109 million tons in 2030 (FAO 2018a), and 140 million tons in 2050 (Waite et al. 2014).

Aquaculture is highly dependent on the climate, and thus, climate change is a threat to increase global fish production. Climate change has already affected aquaculture ecosystems and production (Brander 2007; De Silva and Soto 2009). Water shortages in many parts of the world as a result of climate change affect food production by rising water demand and decreasing freshwater availability (Hanjra and Qureshi 2010; Turral et al. 2011). The impacts of climate change on crop productivity could affect food availability, stability, access, and utilization, and thus, undermine global food security (Schmidhuber and Tubiello 2007; Wheeler and von Braun 2013). Climate change is one of the challenges to achieving zero hungerFootnote 3 by 2030, which is one of the United Nations sustainable development goals (FAO 2018b). Considering the vulnerability of food fish production to the effects of climate change, adaptation strategies must cope with the challenges.

This article reviews environmental concerns for increasing aquaculture production in relation to climate change. The aim of this article is to highlight key issues for minimizing environmental effects and the likely impacts of climate change on aquaculture. Finally, this paper provides some adaptation options for increasing aquaculture production and climate change adaptation.

Environmental Concerns in Aquaculture

Aquaculture has been associated with a wide range of environmental concerns (Naylor et al. 2000 and 2005; Hall et al. 2011). If growth of global fish production continued at a strong pace, aquaculture could have detrimental environmental effects (Table 1). The following sections outline various environmental challenges in aquaculture.

Table 1 Major environmental challenges for increasing aquaculture production
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Resource Decline

Increased aquaculture production will result in significant resource constraints due to limited land and freshwater resources. Globally, aquaculture covered 18.8 million ha of land (12.8 million ha inland and 6 million ha coastal) in 2010, which will occupy an estimated 44 million ha in 2050 (Waite et al. 2014). Additional land use impacts will be from terrestrial feed ingredients for aquafeed (i.e., feed for aquaculture) production. In 2010, aquaculture indirectly used 26.4 million ha of land for growing aquafeeds, which will increase to 61.6 million ha in 2050 (Waite et al. 2014).

Competition for freshwater use between agriculture and aquaculture is rapidly increasing. Globally, aquaculture utilized 201 km3 of freshwater in 2010, set to increase to 469 km3 in 2050 (Mungkung et al. 2014). Although aquaculture uses non-consumptiveFootnote 4 water (Halwart and van Dam 2006), the water footprints for aquaculture include water losses through evaporation and infiltration (Verdegem and Bosma 2009). Moreover, global water footprint of commercial aquafeed production was 31–35 km3 in 2008 (Pahlow et al. 2015), which will increase due to increased aquafeed production from 29.2 million tons in 2008 to 71 million tons in 2020 (Tacon et al. 2011). Non-fed mariculture (mollusks and seaweeds) could help release pressure on increasingly scarce freshwater resources.

Habitat Destruction

Converting low-lying rice fields and wetlands to fishponds is a common practice in many Asian countries (Bangladesh, China, and Vietnam) since it is more profitable (Edwards 2015). There is irreversible habitat destruction due to the widespread conversion of rice fields and wetlands to fish farms, affecting a great variety of flora and fauna, including aquatic plants, birds, crabs, fish, frogs, mussels, snails, and turtles. Habitat alteration as a result of land use change to aquaculture is likely to have negative impacts on biodiversity (Diana 2009).

Coastal aquaculture including shrimp farming is one of the key reasons for mangrove deforestation. Globally, shrimp farming expanded rapidly in the 1980s and 1990s, mainly in the tropics and subtropics (Lebel et al. 2002; Primavera 2006). Unplanned and unregulated shrimp farming caused widespread destruction of mangroves in Bangladesh, Brazil, China, India, Indonesia, Malaysia, Mexico, Myanmar, Sri Lanka, the Philippines, Thailand, and Vietnam (FAO 2007; UNEP 2014). Globally, 1.89 million ha of mangrove forests have been lost to coastal aquaculture, of which 1.4 and 0.49 million ha is from shrimp and other forms of aquaculture, respectively (Valiela et al. 2001). Mangrove deforestation by coastal aquaculture threatens ecosystem goods and services as mangroves are ecologically and economically important forests, which provide biodiversity conservation, coastal protection, and fisheries production (FAO 2007; UNEP 2014). The conversion of ecologically sensitive mangrove forests to shrimp farms has widespread environmental impacts, which must be avoided.

Water Pollution and Eutrophication

The application of antibiotics, fertilizers, and hormones in intensive aquaculture can contribute to water pollution. Overstocking and overfeeding of fishponds can produce organic matter and fish waste that reduce water quality. The inputs of chemical fertilizers (e.g., urea and triple super phosphate) and organic manure in aquaculture implies an increase of nitrogen (N) and phosphorus (P) in effluents. In 2010, the mean water pollution for global aquaculture production was 76 kg P/ton and 273 kg N/ton edible protein (Waite et al. 2014).

Aquaculture is an increasingly impactful source of nutrient pollution, known as eutrophication. The risk of harmful algal blooms (red tide) increases through aquaculture, which may cause massive fish kills. Economic loss from a single harmful algal bloom fish-kill event was estimated at US$330 million in Japan (Furuya et al. 2010). Aquaculture is expected to increase freshwater eutrophication from 0.38 million tons in 2010 to 0.89 million tons P eq. in 2050 (Waite et al. 2014). Aquaculture-related marine eutrophication is also set to increase from 1.4 million tons in 2010 to 3.2 million tons N eq. in 2050 (Mungkung et al. 2014). According to Bouwman et al. (2013), nutrient release from mariculture will increase up to sixfold by 2050. Thus, solutions to water pollution and eutrophication are needed to increase future aquaculture production while reducing environmental degradation.

Biotic Depletion

Although aquaculture has been advocated as a solution to overfishing, it is also one of the reasons for declining wild fish populations. The capture of wild broodstock and seedstock for aquaculture has detrimental effects on wild fish populations. Hatchery operations of prawn in Bangladesh depend on high quality wild broodstock collection that can lead to biotic depletion (Ahmed and Troell 2010). Some aquaculture operations depend on wild-caught seed; for examples, eels in Europe and Japan, groupers in Southeast Asia, milkfish in Indonesia and the Philippines, shrimp in South Asia and parts of Latin America, tunas in South Australia, and yellowtails in Japan (Naylor et al. 2000; Ottolenghi et al. 2004). The use of wild-caught seed for capture-based aquaculture with high levels of bycatch has severe effects on wild fish populations (Ottolenghi et al. 2004; Primavera 2006; Ahmed and Troell 2010). It is, therefore, necessary to reduce bycatch from wild-caught seed to promote environmentally sound aquaculture practices.

One of the long-standing debates in salmon aquaculture is the use of fishmeal and fish oilFootnote 5 in aquafeeds, which is expressed as “Fish In–Fish Out (FIFO)” ratio. FIFO values for salmon aquaculture range from 2.3 to 4.9 (Tacon and Metian 2008; Jackson 2009), meaning that 2.3–4.9 kg of wild fish is required to produce 1 kg of salmon. Increased farmed salmon production has not resulted in decreased capture of wild salmon (Naylor et al. 2000; FAO 2018a), meaning that aquaculture is not an alternative but a complement to capture fisheries. FIFO values of eel, shrimp, and trout aquaculture are 3.1, 1.3, and 2, respectively (Jackson 2009). The demand for wild fish to produce fishmeal and fish oil for aquaculture will increase from 20.2 million tons in 2010 to 47.2 million tons in 2050 (Waite et al. 2014), which can lead to biotic depletion.

Ecological Effects

Aquaculture has adverse impacts on some ecosystem functions. The construction of fish farms near rivers has modified the hydrological patterns in many parts of the world with impacts on regional ecosystems (Martinez-Porchas and Martinez-Cordova 2012). Coastal aquaculture can also lead to saltwater intrusion with detrimental effects on freshwater ecosystems. Cage aquaculture releases untreated nutrients and chemicals into marine environments, with ecological effects. The escape of farmed salmon from net-pens can have genetic and ecological threats to wild salmon populations through competition and interbreeding (Naylor et al. 2005). Spawning in the wild for escaped farmed salmon has limited success as their offspring face high mortality (Hindar et al. 2006).

Reliance on exotic fish species in aquaculture has been gradually increasing over the years (Naylor et al. 2001; De Silva et al. 2009). The introduction and frequent escape of exotic fish species pose severe threats to native species due to competition for food and habitat. The escape of non-native aquaculture species can create “biological contamination” with unpredictable and irreversible ecological impacts (Naylor et al. 2001). In fact, invasive alien species in aquaculture can have negative impacts on biodiversity (De Silva et al. 2009). Most exotic species in aquaculture are considered invasive, and thus, precautionary measures must be taken to protect ecological effects.

Fish Disease and Parasite

The rapid development of aquaculture with presence of toxins and poor water quality are major causes of disease outbreaks. Disease has destroyed shrimp farming in many Asian countries because of environmental degradation (FAO 2018a). A variety of diseases are found in shrimp farming, including black spot, gill diseases, soft shell, tail rot, and white spot. Massive loss of shrimp production has been experienced with an early mortality syndrome, caused by vibrio bacteria (Boonyawiwat et al. 2017). Disease can cause huge shrimp mortality within a week, and thus, many aquaculture farms are abandoned (Primavera 2006; Bournazel et al. 2015). Epizootic ulcerative syndrome has also a great concern in aquaculture, which can cause mass mortalities. Better management practices are needed for long-term biosecurity management in aquaculture.

Intensive aquaculture can create environmental conditions for parasite growth and transmission from farmed to wild fish. Salmon aquaculture accelerates parasite growth and infestation in the seawater environment. Sea lice have the greatest impact on salmon farming and also threaten wild salmon and trout fisheries (Torrissen et al. 2013). Sea lice parasitism in salmon aquaculture caused damages of US$436 million to the Norwegian industry in 2011 (Abolofia et al. 2017). Tackling sea lice is therefore a key concern for the salmon industry.

Greenhouse Gas (GHG) Emissions

The growth of aquaculture has increased GHG emissions. Including land use change, average GHG emissions from aquaculture were estimated at 2.12 kg CO2e/kg live weight of carps in India, 1.81 kg CO2e/kg live weight of Nile tilapia in Bangladesh, and 1.61 kg CO2e/kg live weight of striped catfish in Vietnam (Robb et al. 2017). GHG emissions from aquaculture will increase from 332 million tons in 2010 to 776 million tons CO2e in 2050 (Mungkung et al. 2014). Aquafeeds are considered the largest source of GHG emissions in aquaculture because of the production and transportation of raw materials, energy use in feed mills, and high feed conversion ratio (Robb et al. 2017).

Mangrove deforestation through coastal aquaculture releases significant amounts of blue carbonFootnote 6 as mangroves are the most carbon-rich forests in the tropics (Pendleton et al. 2012; Siikamäki et al. 2012; Alongi 2014). Mangroves stock about 3–4 times more carbon than tropical forests (Donato et al. 2011). Clearing mangroves to build shrimp farms discharges considerable amounts of blue carbon and reduces storage capacities. On average, the loss of blue carbon from the transformation of mangroves to shrimp ponds is 554 tons/ha (Kauffman et al. 2017). Blue carbon storages of redundant shrimp farms are only ~11% that of mangroves (Kauffman et al. 2014). The aboveground carbon receive in shrimp farms is 91% less than that of intact mangrove forests (Kauffman et al. 2017). Carbon emissions along with other GHG (CH4, N2O) have been the leading cause of climate change (IPCC 2014). It is, therefore, vital to reduce GHG emissions from aquaculture to confront anthropogenic climate change.

Impacts of Climate Change on Aquaculture

The survival, growth, and production of fish in aquaculture is highly susceptible to environmental concern as well as climate change (Fig. 1). Aquaculture production is often at risk from a combination of climatic variables, including cyclone, drought, flood, global warming, ocean acidification, rainfall variation, salinity, and sea level rise (Brander 2007; De Silva and Soto 2009; Ahmed and Diana 2015). Changes in these climatic factors could have severe effects on future aquaculture production (Table 2). Global marine primary production will decline by 6% by 2100 due to climate change (Kwiatkowski et al. 2017), which may undermine future seafood production.

Fig. 1
figure 1

Environmental concern and climate change in aquaculture (red colors) with possible impact on aquaculture production cycle (blue colors)

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Table 2 Potential changes in climatic factors those could affect future aquaculture production
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Cyclone

Tropical cyclones are the most destructive natural hazards to coastal aquaculture in low-lying territories those are poorly protected against tidal surges. Water quality of fish farms deteriorates after cyclones because of erosion, saltwater intrusion, and pollution. A large volume of pollutants enters into shrimp farms with tidal surges. Mariculture including salmon farming is also vulnerable to cyclones because of devastating effects on net-pen and cage culture. El NiñoFootnote 7 associated cyclones in Chile often damage the salmon industry greatly, resulting in massive escape of farmed salmon to the wild (Soto et al. 2001). Cyclones may increase occurrence of aquaculture stocks escaping into open-water, threatening biodiversity and ecosystems (De Silva and Soto 2009). Intense rainfall with massive wind associated tropical cyclones are likely to increase in South and Southeast Asian countries, those are dominant in global aquaculture production (Barange and Perry 2009). The intensity of tropical cyclones will increase by 2–11% by 2100 (Knutson et al. 2010), which may undermine future aquaculture production.

Drought

Drought is one of the key constraints in inland aquaculture. The occurrence and intensity of droughts has increased due to climate change as global warming can lead monsoon to turn into dry mode, resulting in considerable declines in precipitation (Conway and Waage 2010). Over 25% of the earth will face severe drought by 2050 if global temperature increases 2 °C (Park et al. 2018). Water demand for inland aquaculture will increase due to severe drought. Prolonged drought is also concerned for freshwater aquaculture because of reducing groundwater levels. Seasonal drought as a result of low precipitation and high evaporation often causes in short aquaculture period. Year-round fish production is not feasible due to severe or prolonged droughts and fish become anxiety in low volume of water. Drought also aggravates the concentration of waste metabolites (ammonia, CO2, and nitrites) and salinity in fishponds and shrimp farms that affects aquaculture production.

Flood

Floods appear to become extreme due to climate change (Conway and Waage 2010). Intense rainfall during the monsoon as well as erratic precipitation causes a greater frequency of floods. Sudden or prolonged floods cause physical damage to aquaculture infrastructure including fish farms. Inland aquaculture is greatly susceptible to flooding as preventing escape of fish from ponds and entering predatory fish from wild is very difficult during floods. River erosion can also intensify the effects of flooding, which may threaten cage aquaculture in rivers. Water level rise during rainy season as well as sea level rise in the Mekong Delta, Vietnam seriously affect striped catfish farming (Nguyen et al. 2014). Coastal flooding could also increase due to high river discharge, low drainage capacity, and backwater effects from seas and oceans. The frequency of coastal flooding will be doubled by 2050 due to sea level rise (Vitousek et al. 2017). Coastal flooding could affect brackish water aquaculture, including shrimp cultivation.

Global Warming

Water temperature in tropical and sub-tropical regions may have increased in recent years as a result of global warming, which could have severe effects on fish production. Global mean temperature could increase 4 °C by 2100 (IPCC 2014). Increases in water temperature could exacerbate multiple effects including changes in ecosystem functioning of freshwater ponds (Woodward et al. 2010). According to Ficke et al. (2007), a little increase in water temperature (1–2 °C) can cause sub-lethal physiological effects on tropical fish. A rise of water temperature over 17 °C would be harmful for salmon aquaculture (De Silva and Soto 2009). Sea surface temperature (SST) could also increase due to the effect of GHG as well as global warming (IPCC 2014). Increase in SST could intensify the incidence of toxic algal blooms and red tides that pose a risk to seafood production (Peperzak 2003; De Silva and Soto 2009). Global warming and subsequent increase in water temperature including SST could have dramatic effects on future aquaculture production.

Ocean Acidification

Climate change causes ocean acidification that is sometimes called “climate change’s equally evil twin” due to its harmful consequence of CO2 in the atmosphere that also affect underwater lifeFootnote 8. Ocean acidification is the consequence of rising atmospheric CO2 that is absorbed by the oceans resulting in low water pH. Ocean acidification will reduce water pH of 0.3–0.4 from 8.2 to 7.8 by 2100 (Feely et al. 2009; Williamson and Turley 2012). It is predicted that ocean acidification could be doubled or tripled by 2100 (Dupont and Pӧrtner 2013), which could affect future seafood production. The impacts of ocean acidification on mariculture has received recent attention. Ocean acidification has negative effects on finfish, seaweed, and shellfish production in North America (Clements and Chopin 2017), undermining shell formation of mussels and oysters in mariculture (De Silva and Soto 2009). According to Kroeker et al. (2013), ocean acidification has adverse effects on calcification, development, and growth of a range of calcified marine organisms.

Rainfall Variation

Climate change affects rainfall intensity and variability with adverse effects on fish productivity. Annual rainfall is likely to decrease in Mediterranean Africa, the Northern Sahara, and Southern Africa (Barange and Perry 2009), which could reduce aquaculture opportunities in these regions. Water availability in fishponds varies greatly with rainfall variation that has also increased the risk of flood and drought. Early or late rainfall with sudden intense rain can cause devastation on inland and coastal aquaculture. Heavy rainfall also causes erosion and water turbidity, reducing fish productivity. By 2050, climate change may increase rainfall erosivityFootnote 9 by 17% in the USA (Nearing et al. 2004) and 18% in Europe (Panagos et al. 2017). Abnormal patterns of rainfall could affect salinity variation in brackish water aquaculture. Low rainfall could increase the concentration of salinity in coastal aquaculture with adverse effects on brackish water ecosystems. Ultimately, rainfall variation potentially undermines aquaculture production (De Silva and Soto 2009).

Salinity

Changes in water salinity have dramatic effects on aquaculture productivity. Low freshwater discharge from rivers, high evaporation, inadequate precipitation, sea level rise, and storm surges tend to play a key role in rising coastal salinity. Changes in ocean salinity indicate a number of climate change processes, including evaporation, ice melting, rainfall variation, and river runoff (Barange and Perry 2009). The biodiversity of freshwater ecosystems is sensitive to salinity, and saltwater intrusion into freshwater ponds affects soil fertility and water quality which considerably declines fish productivity. Changes in salinity with temperatures in coastal environments also influence aquaculture production (De Silva and Soto 2009). Water salinity fluctuations over a certain range could result in transmission of white spot syndrome virus to shrimp (Liu et al. 2006). Globally, sea surface salinity (SSS) will change significantly by 2050 due to climate change (Durack 2015). Increased SSS will affect seafood productivity as most marine species are stenohaline with tolerance of 30–40 ppt salinity (Kültz 2015).

Sea Level Rise

Because of global warming and glacier melting, sea level has been rising at an alarming rate of 3.7 mm/year, which will be 11 mm/year during 2081–2100 (Church et al. 2013). Global sea level could rise 0.15–0.38 m by 2050 (Sweet et al. 2017), and 0.8–1.5 m by 2100 (Kopp et al. 2017). Sea level rise has been threatening many low altitude regions, including Asian mega-deltas, the Atlantic and Gulf of Mexico coasts of the USA, the Baltic, the Caribbean, the Mediterranean, small island regions, and other low-lying coastal areas (Nicholls et al. 2007). Although global sea level rise is not geographically equal due to its relation to regional ocean circulation processes, all coastal aquaculture ecosystems are vulnerable to sea level rise (Barange and Perry 2009). Coastal aquaculture is gradually at risk from sea level rise due to increased exposure of coastal ecosystems to tidal surges. Sea level rise could have multiple impacts on biotic, ecological, and habitat (mangroves, marshes, and wetlands) changes, thereby affecting aquaculture practices (De Silva and Soto 2009). Future sea level rise could have severe impacts on global fish production.

Adaptation to Climate Change

Adaptation to climate change is needed to produce more fish without environmental impacts. Aquaculture production must increase sustainably, whereas its environmental impacts must reduce considerably. A conceptual framework has been developed for increasing aquaculture production, reducing environmental degradation, and climate change adaptation (Fig. 2). Proposed adaptation strategies to climate change seems to increase aquaculture production with environmental sustainability (Table 3).

Fig. 2
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A conceptual framework to increase aquaculture production in relation to environmental concern and climate change; red colors illustrate environmental constraint and climate change with resource competition and population growth those could affect future aquaculture production; blue colors demonstrate possible adaptation strategies to climate change for increasing aquaculture productivity, environmental sustainability, and food security

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Table 3 Strategies for increasing aquaculture production, reducing environmental degradation, and adaptation to climate change
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Integrated Aquaculture

Integrated aquaculture is an approach of integrated resource management, which enhances natural resource use efficiency for increasing productivity, profitability, and sustainability (Pant et al. 2004; Nhan et al. 2007; Dey et al. 2010). Integrated aquaculture is a form of sustainable intensification for producing more food from the same area of land and water without or less environmental impacts (Godfray et al. 2010). Sustainable intensification is vital for adapting to climate change as both are closely interlinked concepts (Campbell et al. 2014). Integrated rice-fish farming is ecologically sound due to improving soil fertility and water quality through generating N and P with integrated pest management by fish, which in turn reduces the application of fertilizers and pesticides (Halwart and Gupta 2004). Rice-fish farming also increases the rice yield by 8% due to presence of fish (Mohanty et al. 2004). Integrated prawn-rice-fish farming in Bangladesh can adapt to climate change as community-based flood control devices (dams, embankments) and the creation of higher dikes around rice fields can protect from inundation (Ahmed et al. 2014). Pumping groundwater with irrigation may alleviate water shortage and high water temperature in dry season rice-fish culture. Rainwater harvesting in small reservoirs and supplementary irrigation of rice field can play a key role in increasing food production and climate change adaptation (Wisser et al. 2010). Salt-tolerant rice varieties and rice-fish culture in Vietnam can reduce vulnerability to storm surges and sea level rise (Shelton 2014).

Integrated aquaculture–agriculture (IAA) is also efficient to produce more food due to using nutrient-rich pond mud and water to manure fruit trees (e.g., banana, coconut, guava, lemon, and papaya) and vegetables (bean, cucumber, and gourd) on pond dikes. On average, pond-based IAA is 11% more productive than non-IAA in Malawi (Dey et al. 2010). Integrated farming could also reduce risks of crop failure due to harvesting in different seasons. Moreover, modern polyculture of 6–8 carp species in China contributes to productivity increases from 12–15 tons/ha/year to 30–40 tons/ha/year (Miao and Yuan 2007). Polyculture of filter-feeding and herbivore fish species can use natural feeds (aquatic plants and planktons) to improve farm productivity and reduce feed-related water pollution. The impacts of climate change on pond-based IAA could be reduced as fruit trees on higher pond dikes could lower erosion and flood protection during the rainy season. In Bangladesh, vegetable crops on pond slopes and aquatic weeds in ponds can provide shade and shelter for fish during hot summer to reduce thermal stress (Ahmed and Diana 2016).

Integrated mangrove-shrimp farming, known as silvo-aquaculture or silvo-fisheries, is an environmentally friendly aquaculture practiced in Indonesia, Malaysia, the Philippines, Thailand, and Vietnam (Primavera et al. 2000; Ha et al. 2012; Bosma et al. 2016). One of the adaptation strategies to compensate for mangrove deforestation by shrimp cultivation in Southeast Asian countries is to develop silvo-aquaculture for the conservation and rehabilitation of mangroves (Primavera et al. 2000). Integrated mangrove-shrimp cultivation has potential to sequester blue carbon (Ahmed et al. 2018). Mangrove restoration could also plays a significant role in mitigating climate change by sequestering and storing blue carbon (Donato et al. 2011; Irving et al. 2011; Mcleod et al. 2011; Pendleton et al. 2012). Mangrove reforestation surrounding shrimp farms is suggested in Vietnam to capture and store carbon for climate change mitigation (Bui et al. 2014). Rehabilitating mangroves in abandoned shrimp ponds of Panay Island, the Philippines could help climate change mitigation and adaptation (Duncan et al. 2016). In addition to protecting shrimp farms, mangrove restoration could increase social and ecological resilience to climate change as mangroves are significant in providing protection from coastal flooding, cyclones, shoreline erosion, saltwater intrusion, sea level rise, and tidal surges (Baird et al. 2009; Duarte et al. 2013).

Integrated multi-trophic aquaculture (IMTA) is an ecosystem-based approach to culture fed-fish (finfish), organic extractive species (shellfish), and inorganic extractive species (seaweeds) from different trophic levels in an integrated farm to create balanced systems for environmental sustainability (Troell et al. 2009; Chopin 2011; Chopin et al. 2012). IMTA operates in over 40 countries on an experimental and commercial basis, including Canada, Chile, China, Japan, the USA, and many European countries (Chopin 2011). Utilizing local environmental and socioeconomic conditions, human innovations, and further technological development could help IMTA for responsible aquaculture practices in the future (Diana et al. 2013). Open-water IMTA in coastal and marine environments may not be affected by flood, drought, rainfall variation, and sea level rise. Shellfish and seaweeds tolerate a wide range of salinity, and thus, IMTA can adapt to changes in SSS. In IMTA, absorption of waste particles and nutrients by shellfish and seaweeds reduces mineralization and higher water temperature (Sreejariya et al. 2011), which can adapt to increased SST. Seaweeds in IMTA can also keep water cooler by absorbing pollutants and toxic elements. In IMTA, carbon sequestration is also possible by seaweeds through photosynthesis (Chung et al. 2013).

Recirculating Aquaculture Systems (RAS)

RAS are land-based indoor fish farms with closed containment rearing systems where biofiltration is needed to purify water and remove toxic metabolic wastes of fish (Bostock et al. 2010; Edwards 2015). RAS can be operated with fresh, brackish or marine water to filter and clean the water for recycling back to fish tanks. Reusing the water through mechanical or biological filters, RAS can be costly to install and operate but are environmentally friendly and highly productive. RAS usually produce large amounts of fish (500 tons/year) in a relatively low volume of water (4000 m3) (Bregnballe 2015). RAS generally produce high-value fish (e.g., barramundi, salmon, shrimp, trout, and tuna) at high densities and year-round. RAS are mostly practiced in developed countries (Australia, Canada, Europe, and the USA) within a controlled environment, and thus, not directly affected by climate change. Coastal aquaculture with onshore tanks has developed in Iceland, South Korea, and Spain (Bostock et al. 2010), as these are unaffected by climate change.

Aquaponics combine aquaculture and hydroponics for producing fish in a recirculation system and growing plants in nutrient water without soil (Bregnballe 2015). The fish waste in the water supplies nutrients to plants and microorganisms, which filter and clean the water that is returned to fish tanks. Aquaponics provide an interactive and mutually beneficial environment for fish and vegetable crops. Common aquaponics fish species are bass, bluegill, catfish, perch, tilapia, and trout, whereas common plant crops are basil, cucumber, lettuce, peppers, salad greens, and tomatoes (Love et al. 2015). Aquaponics has been practiced in over 43 countries around the world (Love et al. 2014). Typically, aquaponics are 10 times more productive than conventional agriculture, and use 85–90% less water than traditional irrigation (INMED 2011). Aquaponics can be practiced as greenhouse systems without climate implications.

Seafood Culture

The further expansion of coastal aquaculture can help to produce much needed extra food for a growing global population. The expansion of coastal aquaculture with environmentally sustainable practices and appropriate adaptation strategies can increase fish production. Comparatively unexploited brackish waters in Africa and Latin America could be utilized for coastal aquaculture (Bostock et al. 2010). However, coastal aquaculture is more vulnerable to climate change than inland aquaculture due to severe effects by cyclones with tidal surges, salinity variation, and sea level rise. Nevertheless, integrated coastal management with infrastructure development (basin, dam, embankment, and irrigation) and disaster preparedness can improve resilience to climate change (Shelton 2014). Wider and stronger dikes with deeper ponds and changing water can adapt high water temperature, rainfall variation, and sea level rise for shrimp farming in the Mekong Delta, Vietnam (NACA 2012). The culture of mud crab in Vietnam is also more tolerant of salinity and better respond to sea level rise (Shelton 2014).

The stagnation of capture fisheries calls for an expansion of mariculture. Ecosystem approach to aquaculture including net-pen and cage culture in marine environment is one of the most promising practices for increasing seafood production. The future contribution of the oceans to increasing seafood production must be obtained from mariculture. However, globally 0.3 million km of coastline (44% of maritime nations) are not used for seafood production (Kapetsky et al. 2013). Thus, the expansion of onshore and offshoreFootnote 10 seafood production is huge. In fact, the expansion of onshore and offshore mariculture for increasing seafood production is a possible solution to feed the growing global population (Duarte et al. 2009). Offshore mariculture can be extended within exclusive economic zone of marine nations (Kapetsky et al. 2013), which may require technological innovation for widespread adoption. Mariculture could increase resilience to climate change due to its tolerance to flood, drought, rainfall variation, and sea level rise. According to Miller et al. (2018), marine species can adapt to climate change through shifting distributions and timing of biological events. In response to increasing temperature, Pacific salmon has physiological and genetic capacity to increase its thermal tolerance (Muñoz et al. 2015).

Seafood production including mollusks and seaweeds will be predominantly sourced through mariculture by 2050 (Diana et al. 2013). The cultivation of bivalve mollusks (e.g., clams, mussels, oysters, and scallops) and seaweeds in long-line and raft methods has been rapidly growing worldwide in countries with history of mariculture (Bostock et al. 2010; FAO 2018a). Climate change can provide opportunity for mussel farming in the southern Baltic Sea (Klamt and Schernewski 2013). Ecological impacts of mollusk and seaweed farming are minimal as they can grow without external feeding. Mollusks and seaweeds in mariculture could reduce eutrophication by removing organic waste and nutrients. Chinese seaweed culture, for instance, annually removes about 75,000 tons N and 9500 tons P (Xiao et al. 2017). Seaweed culture can contribute to climate change mitigation and adaptation through carbon sequestration, reducing methane emissions, shoreline protection, and lowering ocean acidification, which in turn benefits shellfish production (Duarte et al. 2017). Seaweed farming along the southern coast of Korea can help for mitigation and adaptation against global warming (Chung et al. 2013).

Conclusions

To meet the demand for fish from a growing global population, aquaculture production must be increased due to stagnation of capture fisheries. However, aquaculture has generated a wide range of environmental challenges, and further environmental effects are likely if aquaculture production continue. Climate change is a further threat to global fish production. Higher aquaculture production is needed that is environmentally sustainable and can adapt to climate change.

Some adaptation strategies to climate change including integrated aquaculture, RAS, and the expansion of seafood production under coastal aquaculture and mariculture potentially increase fish production. Integrated rice-fish farming, pond-based IAA, and polyculture can increase fish production with reduced environmental impacts. Environmentally friendly integrated mangrove-shrimp cultivation with mangrove restoration could increase blue carbon sequestration and achieve climate change mitigation and adaptation. Moreover, IMTA, RAS, and the expansion of onshore and offshore mariculture could increase seafood production, whereas reducing environmental impacts and adaptation to climate change.

The proposed aquaculture strategies significantly contribute to global fish production, whereas positively affecting both environmental sustainability and climate change adaptability. However, institutional support with technical and financial assistance is needed for implementing these strategies. Key stakeholders including international agencies, researchers, policymakers, government and non-governmental organizations, and fish farming communities need to collaborate for implementation of these strategies. Social, economic, and ecological challenges must also be identified and addressed to facilitate the proposed adaptation strategies. Empirical research is needed to understand interlinked processes of increasing aquaculture productivity, environmental sustainability, and climate change adaptability.