By: Marc Metian, Max Troell, Villy Christensen, Jeroen Steenbeek and Simon Pouil *
Aquaculture is the world’s most diverse farming practice in terms of number of species, farming methods and environments used. While various organizations and institutions have promoted species diversification, overall species diversity within the aquaculture industry is likely not promoted nor sufficiently well quantified. This study developed by an international group of researchers maps and quantifies the present species diversity in aquaculture and also identifies trends observed since 1980. The advantages and disadvantages for quantifying species diversification as well as the factors that shape it in aquaculture are discussed.
Diversification is often presented as an option for achieving sustainable development for future aquaculture (e.g., Simard et al. 2008; Teletchea & Fontaine 2014; FAO 2016). Diversification in aquaculture can be approached in many ways including production systems, markets and reared species.
Species diversification can be addressed at different spatial levels (local, district, country, region) through several main approaches
(i) increasing the number of species being farmed;
(ii) increasing the evenness of farmed species; and
(iii) increasing the diversity within currently farmed species by developing new strains (FAO 2016).
International institutions such as the Food and Agriculture Organization of the United Nations (FAO) have recently advocated for stronger aquaculture diversification in regard to species (FAO 2016). To adequately increase species diversity in aquaculture, it is necessary first to have a solid understanding of current diversity.
An accurate assessment of the total number of farmed species and to what extent they are being farmed is a complex undertaking; reports that include such statistics are often scant and unreliable. Therefore, national or global quantification of species farmed still remains an approximation (FAO 2018).
Variations from this approximation are likely resulting from a misreporting of countries to FAO, and these could be due, for example, to the aggregation of species to genus (or nei) or to the farming of aquatic species without being registered individually to national statistics.
It is nevertheless important to obtain reliable information on the temporal and spatial diversity in order to establish a baseline on aquaculture diversification at the global level. This will permit that accurate information is available to resource managers, business people and policymakers to assess the evolution of the industry and therefore plan future businesses.
It will be important to understand how the aquaculture industry may become impacted from, for example, climate change and the role diversity can play to help the industry adapt in order to sustaining seafood production.
Quantification of species diversity: trends, maps, index and obstacles
The number of fish species increased from 32 species of fish in 1950 to 212 species of fish in 2017 (species APR –annual percentage rate for 1950–2017 = 2.9). In 2017, 332 species were reported being farmed worldwide.
Among these, 212 were fish species (including five hybrids), 65 were mollusks, 30 crustaceans and 20 aquatic plants, three amphibians and reptiles and three other invertebrate species. In addition, some other organisms have also been farmed but have not been described at the species level; FAO usually classifies these as ‘not elsewhere included’ (nei; including potentially already known cultured or new species), with the closest link to the species levels when possible.
In 2017, there were 92 nei groups (50 fish groups, 15 mollusk groups, 11 crustacean groups, nine plant groups and seven others).
In terms of production, the total volume of farmed aquatic organisms that has been specified at the species level represented 545, 511 tonnes in 1950 (92,946 tonnes for nei, 15% of the total production) and 74’157,491 tonnes in 2017 (37’789,132 tonnes for nei, 34% of the total production).
In comparison with other food production systems, aquaculture has a relatively high diversity of aquaculture production at the species level. Indeed, as indicated by Troell et al. (2014), today 95% of human energy needs originates from 30 crop species, of which only four (rice, wheat, maize and potatoes) make-up around two-thirds of the total needs.
The meat sector is comprised of around 20 terrestrial animal species, of which only a handful is dominant (e.g., cattle, poultry, swine, goat; Troell et al. 2014).
Aquaculture production, by contrast, has involved 462 identified species and 145 nei groups listed over the last decades but the production of fish and shellfish is currently dominated by only ca. 20 species that together account for 70% of the total global volume (FAO 2019b).
In comparison, the current global crop production originates from ~160 species, and only five of these, namely sugar cane, maize, wheat, rice and potatoes (FAO 2019) make-up more than 50% of production totals.
Only a handful of animal species are cultivated for food, but genetic diversity is instead provided by about 7600 different breeds (Troell et al. 2014). The direct comparison indicates that, at least at the species level, aquaculture is more diverse than agriculture even with under-evaluation due to the nei dilemma highlighted earlier.
The theory: diversity improves resilience
Enhanced diversification in aquaculture could result in improved capacity to adapt to changes – that
is, towards building resilience. A more diverse production at different scales (farms to global production) is recognized as beneficial (Lin 2011; Troell et al. 2014) as diversity is a critical aspect of resilience of a system’s performance (Holling 1973).
However, diversity can never fully prevent a system from collapse but a resilient system may more quickly recover from a disturbance. Although Downing et al. (2012) mentioned diversity in the context of ‘wild’ systems, some of the advantages related to resilience capacity may also be obtained in more diverse cultivation systems.
The application of ‘resilience thinking’ on production ecosystems has been discussed, mainly in agriculture (Naylor 2008; Lengnick 2014) but also in other production systems (Rist et al. 2014; Troell et al. 2014).
In this case, the resilience of the production system (so called ‘coerced resilience’; Rist et al. 2014) is largely determined by technological human inputs (e.g. fertilizers, feed, energy, etc.) that, for example, increasingly replace natural processes (e.g. intensive monoculture systems).
The coerced resilience implies that the system can, after a disturbance, regain its production if available human capacities are in place (economy, social, knowledge, material, etc.).
“Fostering coerced resilience may in the long run result in a stressor that has been successfully shut out generating a bigger impact on the system compared with more natural dynamics (including disturbances) being allowed (e.g. like controlled forest fires, Drever et al. 2006).”
Aquaculture, like all agriculture sectors, is vulnerable to exogenous shocks that affect production. Generally, when production is distributed more evenly between species from different groups (e.g. fish, crustaceans, mollusks and aquatic plants), one would expect that it reduces the risks related to production failure from, for example, diseases or weakening markets, at least at a national level (Elmqvist et al. 2003; Gephart et al. 2017).
Thus, a diversified production should be more resilient to future perturbations, although it depends on the type, severity and duration of disturbance (Walker et al. 2004).
Building resilience may involve building preparedness for general disturbances (general resilience) or
for a specific disturbance (specific resilience; Folke 2006). In aquaculture production, widespread outbreaks, a global drop of a specific commodity demand, or an intense competition at global market levels could, for example, put a single species production country into crisis.
This can become a larger problem (of social and economic impacts) if a region or a country is highly depended on the affected production (Gephart et al. 2017). Building resilience within the aquaculture sector would imply increasing the species diversity.
This could be facilitated by a set of policies (principles, rules and guidelines) formulated or adopted by countries or organization to reach this long-term goal. Past and current aquaculture policies indicate a willingness to push for species diversity at different spatial scales.
FAO (2011) highlighted, for example, the existence of this global political willingness: ‘incentivizing efforts on research and development and promoting aquaculture diversification programs’.
“Diversification also requires successful development and transfer of technologies to practitioners as well as educating consumers and providing them with adequate information about new species and products. National and global policies can facilitate aquaculture diversification while strengthening the consolidated species (i.e. species well established in aquaculture; Cochrane et al. 2009).”
In the context of government policy, Pingali and Rosegrant (1995) detailed the key elements of a long-term strategy to facilitate commercialization and economy-wide diversification as:
(i) research and extension in order to generate productivity and incomeenhancing technologies;
(ii) economic liberalization, including trade and macroeconomic reform and deregulation of agriculture;
(iii) development and liberalization of rural financial and general capital markets;
(iv) establishment of secure rights to scarce resources, including land and water, and development of markets in these rights;
(v) investment in rural infrastructure and markets; and
(vi) development of support services, particularly health and nutrition programs.
The practice: few species dominate production
FAO indicated a trend towards a higher diversity of farmed species (i.e. through increasing number of farmed species; FAO 2016) and this is also confirmed by the results of this study in the Shannon Diversity Index that has globally increased from 1980 to 2017 (see full version of article for details).
However, Teletchea and Fontaine (2014) highlighted two important facts:
(i) 28% of 313 species produced in 1950 were no longer being produced in 2009; and
(ii) 18% produced in negligible quantities (<100 tonnes).
The reasons explaining that a large proportion of species were reared only for a short period of time are currently unknown and would require further investigations.
Moreover, it is now well established that global aquaculture production is still dominated by just a few key species (see Troell et al. 2014) and recent statistics confirm this: 20 species represent 70% of the global production in 2016 (fish, crustaceans and mollusks; FAO, 2019b).
“As a likely explanation, we assume that a focus on one or a limited number of species allows rapid innovation and improvement of techniques and efficiency.”
Indeed, enhancing success rates of a ‘new species’ and its viability require time and market demand considerations (Muir et al. 1996; Paquotte et al. 1996; Muir & Young 1998). Extensive zootechnical research into new species is necessary before being able to farm ‘new species’ at a largescale and at low cost.
According to Paquotte et al. (1996), the best options for success in aquaculture are both
(i) fastgrowing species at low costs; and
(ii) products acceptable to consumers.
In practical terms, aquaculture output is likely to remain based on a limited number of key species and market changes stimulated to expand demand of these core species rather than to develop demand for other species (i.e. occupying other market niches; Muir & Young 1998).
There might be occasionally some exceptions but this seems to be marginal when we look at the biggest aquaculture species produced.
A concluding perspective: the right balance to strike?
Overall, aquaculture is expanding in terms of new areas and species as well as intensifying and diversifying the product range of species and product forms to respond to consumer demands and needs (FAO 2018).
Based on these results, Asian aquaculture and particularly China’s aquaculture production is the most diversified. This is not surprising considering that diversification of cultured species has been a major goal of China’s aquaculture development program (Liu & Li 2010) as well as for some surrounding countries such as Vietnam (Luu 2011) or India (Sathiadhas et al. 2006).
Increased demand for seafood and expected farreaching climate change impacts have also been suggested as main drivers of aquaculture diversification in Asia (FAO 2016). In this continent, diversity of species created local social benefits to small scale farmers, offering both biological and economic benefits in aquaculture (Liao 2000).
However, aquaculture production in many countries outside Asia is mainly driven by a handful of species reflecting market demand.
A broad and diverse aquaculture portfolio of a country may be able to mitigate potential shocks from rapid changes in markets or environmental conditions (Troell et al. 2014), but to what extent will also depend on how the farmed species differ out from a functional perspective (Elmqvist et al. 2003).
Diversification will depend on political willingness and also close partnership between research and the aquaculture industry.
According to Liao (2000), the exploitation of new native species and introduction of exotic species are two means for aquaculture diversification. Using non-native species can, however, lead to harmful environmental impacts that are difficult to reverse or mitigate.
The transfer of non-native species constitutes a risk for wild populations (e.g. Naylor et al. 2001; De Silva et al. 2006; Laikre et al. 2010) resulting in FAO and other international organizations recommending diversifying aquaculture through the use of indigenous species (Bartley & Casal 1998; De Silva et al. 2006).
Knowledge about present species diversity within the aquaculture sector, and how this has changed trough time are important for guiding its future development. This paper identifies challenges for accurate quantification of diversity and also discusses benefits and trade-offs for different diversity managements.
Global aquaculture production is dominated by a few dozen species, something that may erode resilience against future challenges such as diseases and climate change.
*This article is a summarized version from the original publication ”Mapping diversity of species in global aquaculture” by: Marc Metian , Max Troell, Villy Christensen, Jeroen Steenbeek and Simon Pouil.
The review was originally published in the Reviews in Aquaculture Journal (1-11, 2019) from Wiley Online Library and its full version can be found at: https://doi.org/10.1111/raq.12374
References cited by the authors within the text are available under previous request to our editorial team.
