World population and food

The world population is estimated to grow from over 9.7 billion to 2050, which means more than doubled in the past 50 years and represents an annual rate of 1.2 % (PRB, 2017). If we take as reference 2001 (6.1 billion) in comparison to the estimated population for 2050, we have an increase of 62.8 %; there is an unfavorable projection in the increases of the poverty indices indicating that 1.2 million people lived in extreme poverty with pessimistic expectations for 2050 (^{Ravallion, 2013}; ^{Rougoor and Marrewijk, 2015}). In addition, the expectations of growth of the rural population by 2020 are estimated at 300 million people, while the urban population could be expected at 3.4 billion. With the rapid global growth, the expectations regarding the availability of food in terms of food security are becoming more critical (^{Fedoroff et al., 2010}). In the last thirty years, concepts of food security have evolved and now takes into account not only physical and economic access (^{Thornton, 2010}), but also considered a human right and new concepts related to food availability, food access and food utilization (^{Schmidhuber and Tubiello, 2007}; ^{Wheeler and Von Braun, 2013}). However, one ofthe most constant concerns in the international development institutions is about the availability of food with nutritional quality and stability, so that this does not represent a risk in accessing food (^{Burchi and de Muro, 2016}). This is, of the 3500 kilocalories per day (kcal day^-1) recommended to be considered with food quality status, poor countries only have access to 2000 kcal day^-1, representing a deficit of 18 %. Also, the nutritional sources in poor countries derive from agriculture and are generally deficient in essential micronutrients and amino acids indicating that more than 850 million people are suffering from chronic malnutrition (^{FAO, 2002}). One of the main concerns in that while the population is focused on the immediate benefits of food security policies, current research is more focused on how to measure it (^{Webb et al., 2006}; ^{Barret, 2010}).

This review aims to address the question of whether halophytes have the potential for the development of sustainable agriculture that feeds livestock in arid and coastal areas, taking into account the sections on food security, regional economic development, poverty and social welfare. In addition, we present a case study on combined production systems for desert agricultura in arid coastal areas, where aquaponic systems with tilapia and hydroponic systems with halophytes in Sonora state and Baja California Peninsula, Mexico, stand out as a model of agricultura.

¿Could the conventional agricultural systems supply the food demand?

With the rapid growth global population, arable lands and restriction of freshwater for agricultural use have deep implications to satisfy this century's demands for food (^{Kearney, 2010}). But certainly, this growth has involved a complex interaction between anthropogenic activities, global warming, contamination risk in food, energy supplies for industry, and transportation, among other aspects (^{Van Wesenbeeck et al., 2009}). One of the alternatives contemplated in the ONU Millenium Project in 2005 is the production in small scales or farming systems focused on the sustainable production systems. One of the opportunities for this type of production units is the use of relatively salty water or poor-quality water, considering also salts, which could affect productivity. This type of agriculture, called bio-saline, could be the best sustainable production strategy for the next 50 years, the most interesting model being the use of halophytes (^{Ladeiro, 2012}).

Recently, the bioprospecting in arid, desert and coastline áreas (Antartic: 13 829.430 km²; Artic: 13 726 937 km²; Sahara: 9 065 253 km2; Arabic: 2 300 000 km2; Australia: 1371 000 km2; Gobi: 1 300 000 km2; Kalahary: 930 000 km2, Patagonic: 670 000 km2; Siria: 409 000 km2; and Sonora = Arizona: 362 600 km2) can be led no only to uncovering new desert plant species. Dry arid and deserts zones have over 20 000 native plant species, apart from animal, marine and microbial diversity, with potential for the discovery of new drugs, new chemical compounds with pharmaceutical use, in sustainable agriculture or in the market of metabolites, where it is considered an added value in desert agriculture. The concept of bioprospecting includes the exploration and investigation of indigenous knowledge related to the utilization and management of biological sources that involve three stages: collecting, analysis and commercialization (^{Quezada, 2007}; ^{Stanley, 2008}).

Halophytes as a promise

Halophytes are a group of plants that are capable to complete their life cycle in a substrate rich in NaCl or other elements at concentrations where most and conventional plants (glycophytes) are unable to tolerate. They have been grouped according to their physiological response in their tolerance to salinity in: i) halophiles, which are those that need salt like Salicornia (Salicornia spp.), suaeda (Suaeda), Limonium spp., and Atriplex spp., among others; ii) the preferential halophiles or macrophytes, that are those that prefer the salt like seaside bulrush (Scirpus maritimus); and iii) the subsistence halophiles, that is, those tolerant to the salt like as common reed (Phragmites spp., ^{Grigore and Toma, 2017}). These are classified as naturally salt-loving plants due to the ability of their leaves to excrete Na and Cl ions (^{Flowers et al., 2010}; ^{Shabala and Mackay, 2011}). Approximately 99 % of plants used in agriculture are salt sensitive species and represent at most 2 % of earth herbal variety (^{Flowers et al., 2010}); the other 98 % are plants that growths in areas richs in salts. Since centuries ago, halophytes have been utilized as food, oilseed crop, forage, fodder, biofuel and for medicinal goals (^{Davy et al., 2001}). For example, perennial saltgrass (Distichlis palmeri) as a food crop by the indigenous at South Americans, who lived along the lower Río Colorado in Mexico (^{Bermúdez, 2005}; ^{Panta et al., 2014}). Approximately 50 species are seed-bearing with high potential for edible oil and protein sources, but also being highly valued as biofuels source, mainly for biodiesel, bio-ethanol, and fuelwood (^{Qadir et al., 2008}; ^{Flowers et al., 2010}; ^{Panta et al., 2014}).

Some of the main advantages of these plants are their hight values of crude protein and contained digestible fiber (^{Master et al., 2007}). Another advantage of this type of plants is their good adaptability in the arid coastal regions and that can be used to revegetate saline lands (^{Panta et al., 2014}). Nevertheless, the provision of scientific information related to the nutritional values of some halophytes or desertic plant shrubs is still limited, whether for agricultural use or forage and livestock production (^{Masters et al., 2007}).

On the other hand, in some arid areas of the world new alternatives are required to satisfy the food needs oflivestock; due to its climatology and diminute availability of water, it is a problem for the production of quality and quantity of food for humans and forage for livestock. Evidence indicates that some halophytes could be a contribution to the livestock system. In addition, the edible Chenopodaceae have a singular importance as a source of protein, essential for feeding animals; halophytes such as Atriplex spp., Salicornia spp. and Distichlis palmeri have been identified and applied as alternative crops for forage and feed in saline lands (^{Masters et al., 2007}). In the field of medicine, Ipomoea pes-caprae has been used for treating fatigue, strain, arthritis, rheumatism, and menorrhagia (^{Panta et al., 2014}). Also, this type of plants has been used to desalinate brackish waters, and carbon sequestration (^{Korner, 2013}; ^{Gunning et al., 2016}).

Another big problem into the arid zones close to coastal areas is the saline intrusión, which is the movement of saline water into freshwater aquifers, which can lead to groundwater quality degradation, including drinking water sources, and other consequences. Saltwater intrusion can naturally occur in coastal aquifers, owing to the hydraulic connection between groundwater and seawater. As an example, Hermosillo, Sonora, Mexico is located near the coast of the Gulf of California; the area between the coast and the city of Hermosillo is called the Costa de Hermosillo. It is one of the most important agricultural districts in Mexico country. The exploitation of coastal groundwater began in 1945 with 15 wells. In 1950 there were 258 wells pumping water, and in 1955 there were 484 (^{Flores-Márquez et al., 1998}). There are currently more than 550 wells in operation. This withdrawal of water far exceeds the natural recharge and upsets the natural balance between fresh and salt water. Severe problem and seawater intrusion evidences have been seen in several wells. Near the coast there are high concentrations of salt, and the wells should be abandoned. As this aquifer represents the only source of irrigation water, the size of irrigation areas is decreasing. In this sense, due the capacity to abosorb salts and concentrate them into their tissues, the halophytes have a high potential for desalination and phytoremediation of polluted soils (^{Padmavathiamma et al., 2014}).

In another sense, and considering the accelerated growth of the population worldwide and, consequently, its greater demand for energy, the devastating effects of climate change, as well as the reduction and increasing difficulty of access to fossil fuel deposits, have raised the need for society to seek alternative sources of energy to meet their needs and reduce palpable damage to the environment. In recent years, various countries have oriented efforts and public policies in this regard, exploring alternatives for the generation of energy for self-consumption and exports with a sustainable approach. The effects of climate change require increasing the efforts of nations to generate alternative energies such as biofuels, so as to ensure a sustainable use of the great biodiversity that exists, while promoting conditions that guarantee food supply and caring for the environment. The interest of some halophytes like Salicornia bigelovii (TORR) as a bioenergetic crop arises from the need to take advantage of coastal resources such as saline soils and brackish waters to produce food or products of commercial interest. The salicornia plant was proposed as an oilseed crop due to the properties of its seed that contains up to 30 % oil, similar to compound crops such as soybeans. Different authors mention it as the most promising species for the profitable use of coastal salt flats with a bioenergetic interest (^{Gleen et al., 1998}), with the production potential of up to 230 gallons of biodiesel per hectare cultivated (^{Shahid et al., 2013}), thus considering it an alternative for the aviation industry (^{Hari et al., 2015}) and automotive transport. The oil obtained from the seed of Salicornia can be converted into biodiesel through transesterification since its properties are very similar to the oils currently used for this purpose. On the other hand, the production of this halophyte generates a high percentage of lignocellulosic biomass (90 %) that can be converted into biofuel through enzymatic hydrolysis and microbial fermentation. Fit in mention that other non-edible halophytes that could be used as oilseed trees and alternatives for bioenergy production, have extensively documented, like Calophyllum inophyllum, Azadirachta indica, Terminalia catappa, Madhuca indica, Pongamia pinnata, and Jatropha curcas, and especially because they bring a wide range of welfare benefits to rural areas (^{Gerber, 2008}).

Recently, the bioprospecting in arid, desert, and coastline areas can be led to uncovering new desert plant species. There are over 20 000 native plant species, apart from animal, marine and microbial diversity, with potential for the discovery of new drugs, new chemical compounds with pharmaceutical use, in sustainable agriculture or in the market of metabolites, where it is considered an added value in desert agriculture. The concept of bioprospecting includes the exploration and investigation of indigenous knowledge related to the utilization and management of biological sources that involve three stages: collecting, analysis and commercialization (^{Quezada, 2007}; ^{Stanley, 2008}).

As we can see, the halophytic plants have many advantages from economic, social, and environmental approaches, but in addition, the social and environmental advantages of halophyte crops are a strong support to the agribusiness economy- with high impact on regional development; thus, production of forage and oilseed on a large-scale basis can be a profitable option.

Freshwater disponibility to agriculture

The freshwater is one of the scarcest and finite resources in the world, particularly the freshwater directed for agriculture sector (^{Koehler, 2008}; ^{Pimentel et al., 2004}). Currently, there are sites in special dry arid zones where it is scarcer. Several paths and approaches have been explored, especially those related to agronomic management and considering environmental aspects to reduce water degradation (^{Sullivan, 2002}; ^{Bates et al., 2008}). Nowadays, it is known that population growth, water scarcity, and land destruction in the arid and semi-arid zones are related to causing education difficulties for populations, poverty, environmental problems, and social and environmental insecurity (^{Brown and Funk, 2008}). It is registered that freshwater is mainly available in the countries of the northern part of the world at ample amounts, while it is scarce especially in developing countries, where about 40 % of the world's population lives. Water consumption has increased by more than 600 % during the last century and over 70 % of water worldwide is consumed for irrigation (^{Koyro et al., 2011}). The area of irrigated land has increased from 1966 to 1998 from 1.5 to 2.7 million km². This means that it is increasing twice as fast as population growth. Therefore, it is expected that 50 % of humankind will experience scarcity of freshwater by the year 2025 (^{Koyro and Lieth, 2008}).

In Mexico, as in other underdeveloped countries in arid and semi-arid regions in the world (Tanzania, Sudan, Egypt), there is a growing migration due to problems of availability of water for agricultural activities (^{Webb et al., 2006}). Also, there are some products derived of the techonology where the yield estimated in some crops like maize in standard conditions in irrigated systems is 3.5 times compared with those in dryland crops (27.3 versus 7.8 metric tons per hectare) (^{Von Grebmer et al., 2012}). Still, the introduction of new irrigation systems is helping to obtain a good management of the scarce freshwater resource. However, in the arid regions (specifically those world desert rings dedicated to agricultural sector and producing 75 % of human food), farming methods and other options have proven not to be a healthy option in terms of food sacurity. For that reason, it is very important enlarge the knowledge concidering other type of natural resources like the agroindustrial halophytes, which are growing in those rings and could be incorporated into the agricultural sector.

Bio-saline agriculture as alternative

One impediment in dry arid and coastal zones where agriculture is working, is the saline intrusion and hights leves of salts in freswater from pumps (sub-soil 4-10 gr L^-1). The use of seawater or brackish water to grow crops has been applied in arid and saline areas as an alternative farming method to produce forages, human food and raw material to biofuel (^{Abideen et al., 2014}). This type of agriculture, based on plants that are capable of growing under saline conditions, can generate an economically viable market for salinity tolerant crops while expanding production to marginal lands and reducing the high pressure on the conventional water resources. Soil salinity and scarcity of freshwater resources are two of the principal threats for agriculture, and these limitations cause to reduce food production for the human population and their livestock. About more than 30 % of the irrigated agricultural lands have produced idle's lands throughout the world (^{Koyro et al., 2011}). Salinity is one of the most important abiotic stress, which severely influences agricultural crop productivity through the accumulation of poisonous Na++ and Cl^- ions (^{Yamaguchi and Blumwald, 2005}). There are several new technologies for use the seawater and brackish water for agricultural purposes that are related with arid, semi-arid and desert coastline zones and are focused mainly in three lines: i) the agriculture using halophytes or salt-tolerant (loving-salt) species, ii) the aquaculture combined with hydroponics, and iii) use of seawater in degraded soils. It is estimated that an additional 200 million hectares of new cropland will be required over the next 30 years just to feed the burgeoning populations of the tropical and subtropical regions. Although, only 93 million hectares are currently available and comfortably accessible (^{Rees and Wackernagel, 1996}).

One of the challenges related to arid and desert areas is that most of these areas are coastlines and they include 41 % of the world's land surface and have two billion residents (^{Sternberg et al., 2015}). As the greatest biome, arid zones support 44 % of worldwide agriculture, half the world's livestock and are important for their biodiversity (^{D'Odorico et al., 2013}). However, identification of arid and desert areas and their extension has been inexact due to change climate and environmental factors (^{Thornton, 2010}).

Salicornia, a promise as bioprospection

In terms of bio saline agriculture, Salicornia is one of the main halophytes with potential for commercial cultivation and is experimentally and semi-commercially grown on almost all continents (^{Jafari et al., 2012}). It is a promising plant resource in arid coastal zones due to its potential as food, fodder and as biofuel (^{Ksouri et al., 2012}). Salicornia species are the first halophyte selected for agricultural development and have been grown and harvested on demonstration plots and farms in Mexico, Egypt, The United Arab Emirates, Kuwait and Saudi Arabia (^{Rueda-Puente et al., 2017}). However, until now the potential of Salicornia seeds has been for the extraction of high-quality oils for the cosmetology and aeronautical industry.

Being able to use a plant like S. bigelovii that tolerates high salinity conditions as forage is a point of special interest, especially in desert areas where livestock feed is usually scarce several months a year until the arrival of the rainy season. It would also open up the possibility of creating new farming and livestock production systems in areas where the coastal salt flats and other areas near the sea would not previously be considered.

The potential of this species as forage has been documented for decades. ^{Riley et al. (1994)} evaluated for several years the effect of feeding sheep and goats with various percentages of inclusion of S. bigelovii, finding that it can replace 50 % of conventional forages in sheep and 100 % in goats. Saoud et al. (2007), with a similar method, found that the sheep fed Salicornia gained more weight than in the control treatment, and although it could be thought that this weight difference is due to fluid retention due to the intake of salts contained in the plant, the authors discusses that this is not the case, but rather the ingested salts help to improve the digestion sheep, thus assimilating food better.

Other studies also highlight the potential of using the seeds of S. bigelovii and the by-product of oil extraction from them to feed species of aquaculture importance such as shrimp (^{Alam et al., 2017}) and tilapia (^{Ríos-Duran et al., 2013}), demonstrating that conventional diets can be partially or totally substituted by a low-cost one with the same benefit.

On the other hand, the effect of including the by-product of salicornia oil extraction for fattening chickens was also analyzed by ^{Attia et al. (1997)}; these authors revealed by means of different percentages of inclusion of this protein-rich by-product (34 %) that it can replace the conventional chicken diet as long as cholesterol is added.

Salicornia has long been included in the diet of human beings, mainly in Mediterranean countries, where it is used as a garnish to accompany fish and seafood. In recent years, interest in its consumption has increased not only for its pleasant taste but also for its high nutritional value, as it is rich in minerals and antioxidants such as vitamin C and B-carotene (^{Ventura et al., 2011}). It is estimated that in conditions of high salinity (500 mM) the plant has a yield of 15 ton/ha per year of fresh product, which has a shelf life of six days but can be prolonged with refrigeration (^{Zerai et al., 2010}). In addition to its nutritional value as food, it is attributed medicinal and therapeutic effects. Salicornia shows positive effects for health problems like obesity, hypertension, diabetes, asthma, arthritis, sepsis and cancer. It is also important to note that the seed oil of the Salicornia plant is rich in linoleum acid (about 70 %), an essential fatty acid for health since it cannot be produced naturally by the human body, which makes it an ideal and healthy edible vegetable oil compared to other edible oils on the market as it has excellent antioxidant and anti-aging properties (Ventura et al., 2013).

The cultivated Salicornia yields 2 ton ha¹ with a content in the seeds of 28 % oil and 31 % protein, similar to soybean yield, being a common raw material for biofuel and food in depressed countries (^{Stanley, 2008}; ^{Greenlee et al., 2009}). S. bigelovii cultivation in the United States of America and Mexico, has also been successful in Pakistan, Egypt, Saudi Arabia, and the United Arab Emirates (^{Anwar et al., 2002}; ^{Lobell et al., 2008}; ^{Zerai et al., 2010}).

Commercial development of S. bigelovii in Baja California Sur (BCS), Kino Bay and Santa Ana, Sonora, reveals yields of oilseed that range from 500 to 2500 kg ha^-1 as compared to soybean that shows a minimum oilseed yield of 1000 kg ha^-1 and a maximum of 2500 kg ha^-1 (^{Rueda-Puente et al., 2017}). The best dates for cultivating Salicornia recommended in the peninsula of Baja California are the months of January to March for the seed and from September to May for the vegetable (Fig. 1), being able to obtain a production of biomass (dry matter) up to 22 000 kg ha^-1 and of seed of 1500 to 2000 kg ha^-1, with the potential to extract 600 kg of oil per hectare (^{Rueda-Puente et al., 2003}).

Figure 1 Average height (cm) of Salicornia bigelovii plants during their phenological description in the coastal area in Sonora, México. 

Halophytes, aquaponics and combined agriculture

Historically, the most relevant research in aquaponics systems in saline environments have been carried out in Australia, Israel, North America and Abu Dhabi, commonly with shrimp, marine fish, sea urchin and crustaceans, seaweed and seagrass (^{Murray et al., 2014}). However, the aquatic component has been especially problematic at the industrial level is related to the dependence of wild species used in feeding fish (^{Zanella, 2009}). This dependence can be reduced by the production of alternative resources such as leguminous grains, seagrass or other halophytes or salt-loving plants that can be produced in the same system (^{Himabindu et al., 2016}). For example, the cultivation of protein-rich marine grasses with mullet or rabbitfish in aquaponics systems can provide feed ingredients for fish species of commercial importance. In general terms, an aquaponics module can produce about 0.568 kcal L^-1 water and 0.050 g (protein)/L water (^{Enduta et al., 2011}). This implies an acceptable yield in comparison with traditional systems of aquaculture or hydroponics. In addition, other advantages besides the efficient use of water or the food, is the use of agricultural species that could have a high added value, either due to their components (fruit, leaf or root) or the use of secondary metabolites that increase the value of the product produced. Well-documented examples are the use of antioxidants, capsaicin, lycopene and other protein products derived (^{Raskin et al., 2002}). Also, the aquaponics systems may be a resource for obtaining marine products used in the pharmaceutical and biofuel industries (^{Klinger and Naylor, 2012}).

Another important challenge and a problem still unresolved in the combined aquaponics systems is the constant increase in the conductivity and the handling of phosphorus that commonly put the efficiency of the system at risk (^{Savidov et al., 2007}). There are a small number of species that have a good response in the adaptability and efficiency of the system, and the commercial exploitation with the selected plants has been very inconsistent and there are not enough data to assess their success (^{Stankus, 2013}). Some of the best-studied species are Murray cod (Maccullochella peelii) that integrated with green oak lettuce (Lactuca sativa) have had a good response in biomass gain in different hydroponic sub-systems as gravel bed, floating root and nutrient film technique (NFT), without differences in the constant of conductivity (^{Knaus and Palm 2017}). In relation to the management of organic matter in a farm of fish operating a land-based recirculating aquaculture system (RAS), it was observed that polychaete assisted sand filters (Hediste diversicolor) combined with halophyte Halimione portulacoides remediate efficiently the organic matter generated (^{Marques et al., 2017}).

In Mexico, various models of RAS or NFT type have been carried out at the experimental level. Some has climbed at commercial level with several combinations, mainly catfish, shrimp and tilapia (^{Zetina-Cordoba et al., 2006}; ^{Segovia-Quintero, 2011}) combined with Salicornia spp. and Gracilaria spp. (^{Wade et al., 2010}). There is a model which it consists mainly in aquaponics systems and other with bio-filtration (SCB), in which principally loving-salt plants as Swiss chard, Portulaca oleracea, and aromatic plants as basil (Ocimun basilicum) (^{Buhmann et al., 2015}) has been explored. Some of the most successful production system are in Puerto Peñasco in Sonora and in Baja California Sur, México (^{Mariscal-Lagarda et al., 2012}). Efficient use of water in aquaponics in the northwest region of Mexico in the RAS hydroponics systems has not been fully tested at large scale because they have the same difficulties as always, such as the lack of initial funding for acquisition of infrastructure, experience and permanent training of technical personnel, in addition to high operating cost (^{Martínez-Porchas et al., 2010}; ^{Klinger and Nailor, 2012}). Moreover, there is a consideration that the critical aspects may change in each region or country according to electricity prices, heat availability, government policies, and the geographic environment and, consequently, there is no general optimal system, since this must be adjusted to environmental conditions (^{Lambin et al., 2003}; ^{Ronzon-Ortega et al., 2012}).

Most of the aquaponics models experimented with integrated seawater in arid lands of Mexico are based on the combination of shrimp, hybrid tilapia, and Salicornia spp. (^{Rueda-Puente et al., 2017}; ^{Klim, 2012}; ^{Mbaga, 2014}; ^{Bresdin, 2015}). The crop system in Puerto Peñasco, Sonora in the north of Mexico with the seawater farm Eritrea Co. was the first integrated seawater farm in the world on a commercial scale (^{Zanella, 2009}). The basis of the success of this farm is because it combines the extensive production of shrimps with Salicornia. Other alternatives for combined production with industrial potential have been the red algae (Gracilaria algae) for the agar industry (^{Cardozo et al., 2007}; ^{Naylor et al., 2009}) or production ofhydroponic green forage (^{Neori et al., 2017}). ^{Segovia-Quintero (2011)} cited that in La Paz, at the south of the peninsula of California in Mexico, the aquaculture and hydroponic systems have shown an acceptable level of efficiency as in many places already documented in other arid regions in the world (^{Rakocy et al., 2004}; ^{Graber and Junge, 2009}), because particularly the climatic and orographic conditions of the peninsula, that could be extrapolated and serve as semi-commercial models to adapt in other arid and semi-arid regions of the world (^{Castellanos et al., 2002}; ^{Cardona et al., 2004}; ^{Geissler et al., 2014}; Rueda-Puente et al., 2017). One of the most studied models due to its productive potential is the tilapia/ basil model (^{Racoky et al., 2004}; ^{Rodríguez-González et al., 2015}; ^{Pérez-Fuentes et al., 2016}). The freshwater models, commonly consist in a bioflock model with tilapia and a variety of salt-loving plants, principally, those with high commercial value in international markets as basil, spinach (Spinacea oleracea), Swiss chard (Beta vulgaris), cebollin (Allium schoenoprasum), peppermint (Mentha spicata) and wild oregano (Lippia palmeri) (^{Bareño Rojas, 2006}; SIAP, 2015). Also, this model explores the potential to use groundwater by linking the system to open-field cultivation with salt-tolerant crops as Jalapeño pepper (Capsicum annuum), habanero pepper (Capsicum chinense) and cherry tomato (Solanum lycopersicon) (^{Satreps, 2016}). In Baja California Sur, Mexico, there are two aquaponics systems, one with bio-filtration (SCB) and another with water replacement (SRA). Both systems, have shown promising results with the combination of tilapia and acropolis lettuce. The growth time for tilapia and lettuce was 160 and 30 days, respectively, showing for tilapia the highest average growth values (364.64 ± 43.16 g), meanwhile, the lettuce grew better in SRA (11.74 ± 1.63 g) (^{Rodríguez-González et al., 2015}). Experiments with tilapia raised in a bio flock system under high density cultivation have shown that 10:1 C:N ratio provides good survival and growth of tilapia with no water exchange and seems to be a good strategy in areas where alkaline pH is a limiting factor for aquaculture activities, but the main finding was that application of biofloc technology (BFT) optimizes energy and resources during production. In the Centro de Investigaciones Biológicas del Noroeste S.C. (CIBNOR), in conjunction with the University of Tottori (Japan), are working on a project related to development of aquaponics combined with open culture adapting to arid regions for sustainable food production, in order to reduce the global impact of the food crisis by making efficient use of water resources, especially in sustainable open-field cultivation in arid zones (^{Satreps, 2016}).

The theoretical plan is undoubtedly very important and necessary in long-term strategies for the production of foods, although to arrive at the commercial exploitation it is necessary to solve some operational difficulties such as maintaining balance in each of the phases and components, the cost, and the use of biological control (^{Rakocy et al., 2004}; ^{Shi-Yang et al., 2011}; ^{Okemwa, 2015}). All of which require greater skills, knowledge and practice and, of course, evaluate the cost/benefit, integrating all possible aspects, including production, environmental and social, that contribute to securing safe water and food, countering threats to food security in the world.

About 15 years ago the University of Arizona commenced field experimental for the planting of halophyte in many desert areas of the world, such as Mexico, Gulf of California, United Arab Emirates, the Gulf of Oman, and Egypt, and different areas in the Persian Gulf (^{Nasar, 2014}). Israel has focused most seriously on desert agriculture and has been quite successful. Considering their long-term record in the field of halophyte and desert agriculture, they have invested extensively in both types of research and on the production for several years to date (^{Panta et al., 2014}).

The Integrated Seawater Agriculture System™ project (ISAS™) considers aquaponics as a viable and sustainable strategy that includes novel concepts as long-term sustainability, mineral recycling, re-use of water, and combined production of aquatic and agricultural food with an added value that allows not only self-consumption but the generation of profits (^{Murray et al., 2014}).

Critical points

It is this review, we have analyzed the numerous advantages of bio-saline agriculture as a viable option to produce food. However, there are still aspects that need to be investigated as the requirements of inputs for the production of protein. These, including the use of fossil energy, the amount of water needed to produce a kilo of protein, and energy in terms of labor. For example, the cost of producing one hectare of Salicornia spp. is around 1 300 US dollars. Although the investment of the aforementioned values is unknown, we should consider the positive effects in terms of sustainability, benefit to the environment and social benefit. In the same sense, we should consider the energy required to desalinate seawater or saline water. The elimination of salts through reversible electrodialysis or reverse osmosis methods implies a high energy cost and a high CO₂ footprint. At the global level, the economic and environmental costs of desalination are still prohibitive for extensive use in irrigated agriculture and are only recommended for high-value agricultural products. Ultimately, market prices, profit margins in producer but non-consumer regions and the cost of moving the products to distribution points or collection centers can greatly vary from one country to another due to reasons not covered in this revision, as culture, resources availability, land tenure, local food supply, profit-oriented approaches, and water quality policies (^{Tirado et al., 2010}). Finally, the political and social environment that favors all these conditions will always be important for the final benefit of the population.