Amphibians' Plight: Pollution's Impact On Their Survival

Amphibians are extremely vulnerable to the effects of pollution due to their thin, exposed skin and their permeable eggs, which are often laid in water or moist areas. They are also very sensitive to environmental changes, and their populations have been declining worldwide as a result of various environmental stresses. These include increases in UV-B radiation, climatic change, habitat loss and destruction, acidification caused by acid rain, and infection.

Amphibians are important indicators of water quality and are considered a sentinel species, meaning that what affects them may affect other animal species in the future. A variety of pollutants occur in natural habitats, including fertilizers, pesticides, heavy metals, and road deicers, and these are increasingly being introduced into the environment by direct application, runoff, urban and industrial sewage, and atmospheric deposition.

The impact of pollution on amphibians is largely negative, with studies showing a decrease in survival and mass and an increase in abnormality frequency. They are also affected by light pollution, as many amphibians are nocturnally active or have biological rhythms regulated by light.

How does light pollution affect amphibians?

Light pollution has been shown to have a detrimental effect on amphibian populations. As human habitation expands near and within natural habitats, fragile ecosystems are increasingly exposed to artificial night lighting. Amphibians are an important part of forest and aquatic ecosystems and are very sensitive to environmental changes. Therefore, they are important indicators of the health of ecosystems.

The impacts of artificial light on amphibians vary depending on the species and their ecology. For example, the calling behaviour of many frog species is affected, with individuals calling less frequently and moving more often. This has the potential to decrease mating opportunities and negatively impact subsequent spawning success. However, certain species, such as the cane toad (*Bufo marinus*), appear to benefit from street lights, as they can more easily forage on the insects that congregate beneath them at night. On the other hand, North American red-backed salamanders (*Plethodon cinereus*) forage less under artificial light, hiding in the leaf litter. This may negatively impact their ability to effectively feed at night.

Artificial light may impact a range of amphibian life stages, including the growth, development, and activity of larvae, juveniles, and adults. Research has shown that juvenile American toads under artificial light treatment were more active than those under dark treatments, and had growth rates 15% lower than those in dark treatments. This increased nocturnal activity by juveniles under artificial light conditions appears to result in increased energy expenditure and thus reduced growth rates. This reduced growth may result in delayed reproductive maturity, lower fertility, and reduced survival. Combined with other stressors, such as climate change, this could lead to population declines in many common amphibian species.

In addition, common toads (*Bufo bufo*) may be particularly affected by increased levels of artificial light as they have a very short breeding season and may use light to orient themselves towards ponds and aid in synchronicity in breeding. Research on common toads in France found that after 20 days of nocturnal exposure during the breeding period at 5 lux, the total time spent active by male common toads decreased by more than half; at 20 lux, activity levels dropped by 73%. This was due to male toads being less active during nocturnal periods. The authors of the study concluded that the alteration of both activity and energy metabolism could negatively impact common toad reproduction and ultimately lead to a reduction in survival.

Overall, artificial night lighting should be considered an additional factor that negatively impacts amphibian populations. More research is needed to fully understand the potential magnitude of such impacts on the biological diversity of amphibians.

How do chemicals affect amphibians?

Amphibians are very sensitive to environmental changes due to their permeable skin. They are also indicator species, meaning that what affects them may affect other animal species in the future.

Effects of pesticides

Pesticides are a major cause of amphibian decline. They can be absorbed through the skin or through food. Pesticides can cause direct mortality, as well as delayed growth and metamorphosis, increased susceptibility to diseases, and impaired fertility and fecundity.

A study on juvenile European common frogs (*Rana temporaria) found that mortality ranged from 100% after one hour to 40% after seven days at the recommended rate of currently registered products. The study concluded that terrestrial pesticide exposure is likely a large-scale negative effect on amphibian populations.

Effects of other chemical pollutants

Other chemical pollutants such as herbicides, insecticides, and fungicides also have hazardous effects on amphibians. For example, chlorpyrifos, an organophosphate insecticide, has been found to induce an intersex condition and alter testicular morphology in some animals.

Effects of light pollution

Light pollution may also contribute to the global decline of amphibians as it affects their foraging and reproduction rates. For example, tree frogs stop calling for mates in brightly-lit areas.

How does water quality degradation affect amphibians?

Amphibians are a unique group in the animal kingdom, with skin that is more permeable than that of other vertebrates. This means that water pollution can be directly toxic to them. Some amphibians lack lungs altogether and fully depend on their skin for respiration.

Water quality degradation can cause amphibians to experience a wide range of health problems, from an increased vulnerability to disease to morphological deformities that decrease their chances of survival.

For example, exposure to chemical contamination can cause a shift in the amphibian's skin microbiome, increasing their vulnerability to disease. In severe cases of water pollution, mass mortality events can occur. In 2016, 10,000 critically endangered frogs died along a 30-mile stretch of the Coata River in Peru, with researchers linking the deaths to large concentrations of heavy metals throughout the basin, caused by regional mining operations.

Water quality degradation has also been linked to physical malformations in amphibians, including missing, malformed, and extra limbs. These deformities may be caused by chemical contaminants, ultraviolet radiation, or biological factors such as parasites or infection.

Water pollutants such as road salts, pesticides, metals, and other sources of runoff from agriculture and cities can have negative effects on the overall health and reproduction of amphibians. They may also reduce their ability to fight off pathogens, leading to reduced reproduction and mortality.

Because amphibians spend at least part of their lives in the water, the quality of the water in which they live can affect their growth, development, and survival.

How does agriculture affect amphibians?

Amphibians are highly susceptible to pollution, especially agricultural pollution, due to their permeable skin, which allows toxins to invade their organs. They are also vulnerable because they breathe through their skin to a certain degree.

Agricultural pollution can cause a wide range of health problems in amphibians, including a shift in their skin microbiome, which increases their vulnerability to disease, and morphological deformities, which decrease their chances of survival. In some cases, agricultural pollution can even lead to mass mortality events. For example, in 2016, 10,000 critically endangered frogs died along a 30-mile stretch of the Coata River in Peru, with researchers linking the deaths to pollution from regional mining operations.

Additionally, certain chemicals commonly used in agriculture, such as atrazine, a common herbicide, have been linked to reproductive abnormalities in amphibians. A study by David Skelly, a professor of ecology at the Yale School of Forestry and Environmental Studies, found that 21% of male green frogs from suburban Connecticut ponds were hermaphrodites, with immature eggs growing in their testes.

Another study, led by Tyrone B. Hayes at the University of California, Berkeley, found that leopard frogs exposed to atrazine in the laboratory had retarded testicular development and, in some cases, immature eggs in their testes.

While the direct effects of agricultural pollution on amphibians can be severe, it is important to note that these pollutants can also make amphibians more susceptible to diseases and pathogens, which may ultimately be the cause of population declines or extinctions.

How does pollution affect the growth and development of amphibians?

Amphibians are very sensitive to environmental changes due to their permeable skin, which allows oxygen to pass through but also lets in unwanted chemicals. Pollution, therefore, has a significant impact on their growth and development.

A meta-analysis of various studies found that exposure to chemical pollutants at environmentally relevant concentrations has a medium to large negative impact on amphibians. There was an overall decrease in survival and mass, as well as an increase in abnormality frequency. The study also found that the type of pollutant and the developmental stage of the amphibian play a role in the effect of pollution. For example, exposure to pollutants during embryonic stages can have more severe consequences than at later stages.

Nitrogen-based fertilizers, pesticides, and wastewater contaminants are some of the most common sources of pollution affecting amphibians. These pollutants can cause a range of issues, including reduced growth and development, increased developmental abnormalities, and behavioural alterations. For instance, exposure to pesticides can affect tadpole swimming performance and activity, making them more vulnerable to predators.

In addition to chemical pollutants, light pollution also negatively impacts amphibians. Many amphibians are nocturnal or have biological rhythms regulated by light, so artificial lighting can disrupt their behaviour, reproduction, and growth. For example, salamanders that usually forage at night to avoid predators may experience reduced foraging and reproduction rates if it is never dark enough.

The effects of pollution on amphibians can also be influenced by other factors in their environment, such as the presence of pathogens and ultraviolet-B radiation. The interaction between multiple stressors can have synergistic effects, further exacerbating the negative impacts on amphibians.

Overall, pollution has a significant impact on the growth and development of amphibians, contributing to population declines and even species extinction.

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