Newt
Newts, as with salamanders in general and other amphibians, serve as bioindicators because of their thin, sensitive skin and evidence of their presence (or absence) can serve as an indicator of the health of the environment. Most species are highly sensitive to subtle changes in the pH level of the streams and lakes where they live. Because their skin is permeable to water, they absorb oxygen and other substances they need through their skin. Scientists study the stability of the amphibian population when studying the water quality of a particular body of water.
Italian crested newt
As an aquatic species of newt, "T. carnifex" requires areas of standing water such as ponds, lakes, farmlands, etc., for its habitat. It is very susceptible to slight changes in its environment, and is thus considered an ideal bio-indicator species. The species is thought to be on the decline due to an increase in industrialization and housing development, both of which interfere with the habitat of the newt. The greatest threats to the newt are loss of aquatic habitats (most importantly, breeding sites), agricultural pollution and intensification, and the inclusion of new predatory fish into its habitat. The intrusion of humans not only physically destroy their habitats, but introduces chemicals and pollutants that have lethal effects on amphibian populations at what is normally considered a safe amount. Due to its wide distribution, however, extinction of the species is considered to be of small concern at present, even though the populations have been decreasing.