Tree frogs, Scinax quinquefasciata, were accidentally introduced to the Galapagos archipelago in imported foods and materials and became established in wetlands on Isabela Island in 1998. This is worrying because, apart from making it impossible to maintain the Galapagos Islands in their original state, in which there was no native amphibian, frogs could cause
changes by eating insects, competing with native insect-eaters or by carrying parasites affecting water birds.
However, the frogs do not occur in all wetlands of Isabela; the map shows their distribution in 2003. They are generally absent from lagoons where salinity is above 12 g sea
salt/litre (one-third sea water) and breed all year round only in pond water containing less than 3–4 g sea
salt/litre (10% sea water). Experiments showed that Scinax quinquefasciata tadpoles have poor tolerance to salinity; tadpoles begin dying after 96 hours in 19% sea water.
The salinity in the lagoons ranges widely according to locality and season, and tadpoles develop into frogs only in favored zones or at times when inflow of fresh water provides good conditions for them. Accordingly, salinity of lagoons might be cautiously increased to restrict the distribution of frogs, as a step towards eliminating them.
Source: Charles Darwin Foundation and Galapagos National Park.