Probiotics as environmental performance enhancers in the production of white shrimp (Penaeus vannamei) larvae

Highlights

• Shrimp aquaculture must grow sustainably to meet current and future global demand.

• Probiotics in shrimp larvae production reduce emission of all estimated pollutants.

• A significant reduction on energy use and costs is observed when using probiotics.

• Nitrogen and Phosphorous amounts present in the effluents were low in all groups.

• Economic and environmental effects indicate probiotics are a sustainable technology.

Introduction

Aquaculture, like any other food production process, has an environmental cost associated (Bartley et al., 2007). Of the different crops, shrimp has a particularly high environmental impact for different reasons i.e.: i) the transformation and depletion of areas of wide ecological interest (such as mangroves), ii) production of highly nutritious effluents, causing algal blooms and hypoxia and iii) the use of postlarvae from the natural environment as production seeds, reducing the recruitment of the species in the wild (Bachere, 2000; Páez-Osuna, 2001; Hatje et al., 2016).

In the same way as agriculture, aquaculture requires of support energy sources in order to provide the water supply systems, aeration and the rest of technological support. In addition, aquaculture activities tend to develop in areas far from urbanizations, making it necessary to use energy generators based on the burning of fossil fuels. This combustion will eventually result in the emission of greenhouse gases (GHG). The emission of GHGs obtained from direct energy consumption will highly depend on the control level of the production. The higher the control required, the higher the energy consumption.

Despite the environmental impact, there are benefits associated with the growth in shrimp farming, such as the reduction of the pressure suffered by the fisheries of the species to meet market demand, which is expected to grow due to population and income increase in highly consuming countries like China, or the large number of direct and indirect jobs it provides, mainly in developing countries such as Thailand, Vietnam or Indonesia in the Asian continent, or Ecuador, Colombia and Mexico in Latin America (Neiland et al., 2001). Currently, the fisheries industry provides jobs for 19.8 million people worldwide, of which 32% belong to aquaculture, and is expected to keep growing (FAO, 2018) In addition, there is evidence of the positive effect that aquaculture can have on food security and possibly also on the alleviation of poverty (Béné et al., 2016).

Due to increasing demand of shrimp worldwide, aquaculture has been pointed out by some authors as the only alternative in order to maintain or increase production and supply levels without collapsing the fisheries of the species (Páez-Osuna et al., 2003). In 2018, farmed shrimp production reached almost 4 million tonnes, that is an increase of around 4% compared to 2017, with China experiencing an increase of 10% regarding the previous year (FAO, 2019). Furthermore, in order to have a high supply of shrimp, it is necessary to ensure a continuous production of postlarvae or seed (Kumar and Engle, 2016). This seed production eliminates one of the negative effects that the industry has on the environment, but like any transformation, it can have associated new harmful environmental effects.

The production of larvae is one of the stages of aquaculture with greater intensity and control, since the continuous larval transformations make organisms more susceptible to changes in water quality, which can cause massive mortalities (Frias-Espericueta et al., 2000). In order to maintain water quality in optimum conditions for this stage of culture, it's necessary to maintain water exchange rates that range between 15 and 30% per day, producing highly nutritious (mainly Nitrogen and Phosphorus) effluents that are directly deposited in the ocean (Kesarcodi-Watson et al., 2008). Also, there is high energy consumption derived from heating, recirculating and oxygenating the water, reaching up to 9% of the total production costs (Juarez and Martinez-Cordero, 2004) and about 20% of the variable costs. Finally, this energy consumption will be translated into GHG emissions due to the burning of fossil fuels.

In order to maintain current production levels and reduce the associated environmental impact, it is necessary to rely on the use of new technologies to boost production, taking into account the three pillars of sustainability: economy, environment and society (Béné et al., 2016).

In line with objective 14 of the objectives for sustainable development proposed by the UN (UN webpage, 2015) (http://www.un.org/sustainabledevelopment/oceans), the technologies developed must be capable of improve or at least maintain the economic yields, while reducing the environmental and social impacts associated with production. One example of this type of technology is the use of probiotics, understood in its broadest sense as a group of live bacteria that added directly to water have beneficial effects on organisms in culture such as: water bioremediation, improvement of digestion, intensification of the immune response and inhibition of the growth of pathogenic bacteria (Farzanfar, 2006).

The use of probiotics allows improving larval survivals through different mechanisms (Kesarcodi-Watson et al., 2008). It also allows the recirculation of water to be eliminated or drastically reduced, thanks to the capacity of the bacteria to transform the NH₄ present in the tanks to free N, thus eliminating its toxicity, analogous to what happens in a biological filter in a system of water recirculation (RAS) (Crab et al., 2007; Zhou et al., 2009). In this way, the production of larvae can be improved by reducing the environmental effects of the emission of effluents and the energy associated with the replacement of water. By eliminating recirculation, the volume of water to be heated is also reduced, reducing the associated impacts. On the other hand, the presence of bacteria in the tank, mostly aerobic, requires a greater oxygen supply, which can translate into an increase in aeration power.

Some efforts in estimating the CO₂ equivalent of producing 1 kg of shrimp have been made in a global scale, mainly deriving of the mangrove transformation into shrimp ponds (Kauffman et al., 2017; Järviö et al., 2017). Although some models may be overestimating CO₂ emissions (Patrik JG Henriksson et al., 2018), they all agree on the importance of the impacts of shrimp production on the emission of GHG. Current estimations apply mainly to the transformation of land use and general production practices in the fattening process, disregarding the impacts of seed production. Although the difference of emissions between organically and inorganically produced shrimp have been evaluated (Jonell and Henriksson, 2015), the effect of specific technologies on emissions remain unstudied.

While the effects of probiotics on shrimp aquaculture yields has been extensively studied on several production aspects such as improving water quality, improving the survival and growth of shrimp, as well as some associated environmental benefits such as the reduction of the use of antibiotics or the reduction of effluents in the fattening processes (Kesarkodi-Watson, 2008, Crab et al., 2007, Balcázar et al., 2006, Farzanfar, 2006); to the best of our knowledge, there is scarce information regarding the impact of the use of technology on the emission of pollutants to the environment in the form of nutritious effluents in the production of larvae, as well as the production of CO₂ associated with changes in the use of energy derived from the use of the technology. Therefore, the objective of this work is to evaluate the effect of probiotics applied to the rearing water on energy consumption, GHG emissions and the amount of N and P present in the effluents, product of the production of white shrimp larvae.