On a worldwide level, significant biodiversity loss is occurring (Wake, 1991). In this biodiversity crisis, amphibians are the most disadvantaged group, with 41% of the species in this group considered to be under threat (IUCN, 2017).
In this sense, the delta plain of the Llobregat is not an exception and regarding the autochthonous species present in the early 20th century (Alytes obstetricans, Bufo spinosus, Epidalea calamita, Hyla meridionalis, Pelobates cultripes and Pelophylax perezi), three of them (Bufo spinosus, Epidalea calamita and Pelobates cultripes) have disappeared from the delta plain, two of them (Alytes obstetricans and Hyla meridionalis) have been reduced to a residual population and only one of them (Pelophylax perezi) is found in good condition. Moreover, in 2005, the presence of exotic species, Discoglosus pictus (Franch et al., 2007a), was detected.
This loss of amphibian richness can be explained by the fragmentation and loss of terrestrial habitats (Sinsch, 1992; Baker and Halliday, 1999) caused by the changes in land use and loss of ecological connectivity, due to loss of quality and pollution of aquatic systems that hinder the development of amphibian populations (Sadinski and Dunson, 1992; Skelly, 1996; Joly et al., 2001; Oldham, 1999) and for the increase in the presence of invasive species (Montori et al., 2009).
In the Llobregat Delta, the fragmentation and loss of habitats are explained by a significant increase in population and development over the course of the 20th century, which has led to changes in the needs of the population that have caused an increase in the surface area destined for industrial zones, for services and for the port and airport, to the detriment of natural and agricultural areas. This variation in land use, together with erroneous administrative decisions in the management of natural areas, has caused a significant loss of ecological connectivity among amphibian populations. On the other hand, the loss of quality and degradation of aquatic systems that hinder the presence of amphibians on the delta plain is clearly reflected in the salinity, the high ammonia concentrations and the wide pH range observed at different water points in the delta. Moreover, the presence of several exotic species such as Procambarus clarkii, Trachemys scripta, Gambusia holbrocki and Discoglossus pictus among others has also contributed to the decline of amphibians to the Llobregat delta for predation and competition
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