**4. The salt-lover brine shrimp** *Artemia***: adapted to critical life conditions**

The brine shrimp *Artemia* is a branchiopod crustacean well adapted to the harsh conditions of hypersaline environments impose on survival and reproduction and hence is considered a model extremophile or a salt-lover sensu Wharton [39]. It displays remarkable adaptations at different domains, one of the most striking being a highly efficient osmoregulatory system to withstand high salinities (up to 340 g/L) [6]. Also, *Artemia* females can perceive when the environment becomes suboptimal, an ability that makes *Artemia* an indicator of ecosystem quality. Under suboptimal conditions, i.e., when a shallow lagoon dries up, females switch to produce encysted offspring (oviparity), in other words, cysts or diapause embryos highly resistant to extreme conditions. Instead, offspring in the form of free-swimming nauplii (ovoviviparity) allows rapid population expansion under optimal environmental conditions. The cyst shell protects from UV irradiation, large temperature fluctuations, osmotic pressure, dryness, and other stresses, so cysts remain viable practically dehydrated [40–42]. Such evolutionary solution for populations to escape extinction when conditions become unfavorable suggests that cysts contain a memory of the past [6] that can be retrieved when cyst resurrect (sensu [43]) either naturally or experimentally, i.e., resume metabolic activity and hatch once the environment returns to normal. Since cysts deposited in saline lagoons at different times accumulate at shores and all have the chance to hatch at the same time when the environment allows it, females face a critical mating decision of choosing the right male to maximize their reproductive output. They can mate either contemporary males (hatched from cysts of the same age), males from the past (hatched from older cysts), or males from the future (hatched from more recent cysts). Females tend to select contemporary males, which would be a demonstration of male-female coevolution [44]. The sophisticated mate choice behavior of *A. franciscana* would be a consequence of such coevolution [45]. The question of how females perceive in advance when conditions will become unfavorable remains unclear, but it would be reasonable to advance the hypothesis that bacterial communication (quorum sensing) to maintain their functional diversity in extreme ecosystems could be involved. This is possible as bacteria interact with all kind of life forms in a given ecosystem, and such interaction may affect the adaptation of other species. For example, the microalgae *Dunaliella salina*, commonly found in saline environments, responds to quorum sensing [46].

In Chile, two out of the six regionally endemic and highly divergent sexual species co-occur, *A. franciscana* Kellogg, 1906 and *A. persimilis* Piccinelli and Prosdocimi, 1968 [6, 24]. The latter was previously thought endemic to Argentina, though it is now clear that inhabits Chilean Patagonia lagoons [47, 48]. Both species are segregated by a latitudinal barrier coincidently with their differential ability to colonize and cope with different environments, which is the case of *A. franciscana*, the most widely distributed of all, and considered a younger species in evolutionary expansion [24]. The species inhabits lagoons of the Atacama Desert in northern Chile, which is the southern limit of a broad north-south distribution in the Americas (North, Central, South). Instead, *A. persimilis* is restricted to Patagonia, with a probable hybrid zone between both species in solar saltworks of central Chile [49, 50]. Other sexual species are restricted to the Mediterranean area (*A. salina*), Lake Urmia and some lakes in Ukraine (*A. urmiana*), China (*A. sinica*), and Tibetan Plateau

(*A. tibetiana*). The situation in Asia seems now to be a bit complex as a mix of sexual and asexual *Artemia* species, including the invasive *Artemia franciscana* coexist as shown with mitochondrial (COI) and nuclear DNA markers (ITS) [51]. The species has also invaded and even displaced local species in Europe [52]. Such evolutionary plasticity depends on the species overall high genetic variability, which is heterogeneously distributed over the populations [49, 53]. As Gajardo and Beardmore put it [6], the species gene pool is distributed over different safety baskets.

With the advent of massive sequencing and transcriptomics, new information has been reported on the genetics of sex differentiation [54–56] and stress or adaptation-related genes [41]. A transcriptomic study in *A. franciscana* identified genes responding to salt stress by experimentally comparing *Artemia* individuals reared under hypersaline and marine conditions [57]. Authors found ~100 genes differentially expressed under hypersaline conditions controlling critical biological functions such as signal transduction, gene regulation, lipid metabolism, transport, and stress response (Heat shock 70 kDa), all contributing to maintaining homeostasis-repairing mechanisms in *Artemia.*

## **4.1 The** *Artemia***-bacteria relationship**

The brine shrimp *Artemia* and bacteria coexist and interact in hypersaline lagoons, as demonstrated by Quiroz et al. [30]. One evident expression of this interaction is that *Artemia* gets energy grazing on bacteria [58–60], which also provide enzymes to digest the algae and yeasts that are also *Artemia* food items. Additionally, environmental bacteria colonize and establish in the *Artemia* gut conforming the microbiota, which is known to provide multiple functional benefits to the host such as protection against pathogens, energy balance, immunological enhancement, and behavior [61]. Thus, imbalances (i.e., reduced diversity) in the microbiota composition due to environmental or other factors such as pathogens seriously affect the performance of the host in a given environment. The *Artemia*microbiota is an example of facultative symbiosis in which mutual benefits are provided [62]. The most evident benefit for *Artemia* is fitness, which can be constrained or expanded depending on salinity in such a way that under optimum salinity, fitness should be maximized. Therefore, the *Artemia*-gut microbiota interaction influences *Artemia* abundance, which is a good predictor of waterbird presence in hypersaline wetlands. This would explain why not all hypersaline lagoons attract the same amount of waterbirds. The importance of *Artemia* in this regard was experimentally demonstrated [17] with the introduction of *A. sinica* in a Tibetan hypersaline lake where the species did not exist. Such introduction created the conditions to attract waterbirds not previously present in the lake. Another case was the introduction of *A. franciscana* in Godolphin lakes, an artificial hypersaline wetland created to attract flamingos and charadriiform birds in Dubai [63]. The flamingo species *Phoenicopterus roseus* is a regular visitor in that habitat, as well as other bird groups such as sandpipers, plovers, avocets, grebes, ducks, and gulls, and their presence is correlated with *Artemia* blooms.

The study of Quiroz et al. [30] assessed the microbial diversity of natural brines and those present in the gut microbiota of adult individuals collected in the same environment in lagoons of the Atacama Desert, solar saltworks in Central Chile, and Patagonian lagoons. The microbiota of animals collected in natural brines contains a subsample of environmental diversity, and the authors evaluated some reported functions of the bacterial communities of the gut microbiota to test the hypothesis that they should contribute to *Artemia* fitness. For example, the genus *Sphingomonas* (Alphaproteobacteria), found in the gut of wild *Artemia* individuals, contains a species (*S. wittichii*) reported to degrade polycyclic aromatic

**67**

*Hypersaline Lagoons from Chile, the Southern Edge of the World*

hydrocarbons (PAHs) that are persistent pollutants accumulated in the food chain [64]. The genus *Chromohalobacter* (Gammaproteobacteria), also identified in the gut of wild individuals collected both in northern and southern lagoons, contains the species *C. salexigens* that produce ectoine (or hydroxyectoine), a compound protecting proteins from degradation, and other environmental stressors such as salinity changes, oxidative stress, and high UV radiation [65]. Ectoine and other compatible solutes also act as osmoprotectants facilitating bacteria establishment in the saline environment. The authors were surprised to find psychrophilic bacteria known to produce antifreeze proteins in Céjar (north) and Amarga lagoons (south). Moreover, some bacteria found in the Atacama Desert are phylogenetically closer to some types found in the Antarctic, similarity that tells about convergent environmental conditions or a similar adaptive pattern despite the latitude difference. Such similarity includes the Great Salt Lake in Utah, where bacterial sequences most closely related to genera *Halomonas*, *Psychroflexus*, and *Alkalilimnicola* were found

**5. The need to monitoring hypersaline lagoons dynamics to predict** 

tolerate high salinities, particularly copepods [71, 72].

*Chloephaga melanoptera* (Anatidae) are also present in the Salar.

The food web of these lagoons is simple and sensitive to environmental conditions such as salinity changes caused by water or brine diversion. The main ecosystem components are bacteria, microalgae, and different zooplankters (Ostracoda, Copepoda, Branchiopoda); among the latter the brine shrimp *Artemia* plays a key ecological role in the ecosystem grazing on bacteria and phytoplankton (such as the halotolerant unicellular green algae *Dunaliella*) and hence modulate their biomass. Studies in the Mediterranean [67], Crimean lakes in Ukraine [17], and Dubai [63] have evidenced the *Artemia* role to predicting waterbirds presence. Besides, *Artemia* is an intermediate host for avian helminth parasites, particularly cestodes and nematodes [68–70], also providing useful information on waterbird abundance and diversity in hypersaline ecosystems. In turn, *Artemia* abundance is controlled by copepods and amphipods species that are common at lower salinities but can also

Waterbirds inhabiting hypersaline wetlands, particularly flamingos, disperse

Patagonian saline lagoons also hold a great diversity of waterbirds, including flamingos, swans, grebes, and shorebirds [77]. Among the most abundant birds in

*Artemia* by carrying cysts in their feathers or in the digestive tube which are released to the environments with their feces [52, 53]. This service provided by flamingos would favor the colonization of new suitable habitats and would explain *Artemia* distribution to some extent [73]. The knowledge on the halophilic biodiversity of hypersaline lagoons is, therefore, a first step toward understanding why local and long migratory waterbirds use them as a source of energy and as breeding sites. Lagoons in Salar de Atacama are essential habitats for flamingos and shorebirds [74–76], some of them with conservation problems according to the IUCN Red List of Endangered Species. The Chilean flamingo and the Puna flamingo are both near threatened; meanwhile, the Andean flamingo is recognized as a vulnerable species. Lagoons from Salar de Atacama (particularly Puilar) represent the most important breeding site in the world for the Andean flamingo (**Figure 5**). In addition, these lagoons are important for migrating interhemispheric species such as Baird's sandpiper *Calidris bairdii* and Wilson's phalarope *Steganopus tricolor*, among others, despite there is no quantitative data for these species in the area. Charadriiformes and Anseriformes such as the Andean gull *Larus serranus*, and the Andean Goose

*DOI: http://dx.doi.org/10.5772/intechopen.88438*

in the water [66].

**waterbird presence**
