Wetlands also play an integral role in the ecology of a watershed. Their shallow waters, nutrients, and primary productivity are ideal for organisms that form the base of the food web upon which many species of wildlife depend. Wetland habitat provides the necessary food, water and shelter for mammals and migrating birds. Other animals, such as amphibians and reptiles, collectively known as herpetofauna, or "herps," depend on wetlands for all or part of their life cycle, meaning that their survival is directly linked to the presence and condition of wetlands.
Wetlands serve as critical habitat for many species of amphibians and reptiles. Most amphibians lay gelatinous eggs under water, while others, like certain salamanders, lay their eggs on moist land. After the eggs hatch, the baby amphibians enter an aquatic larval stage, which can last from several days to many months. Once the aquatic stage is completed, the amphibians leave the water and enter the terrestrial adult stage of life. Wetlands serve as breeding sites, as a habitat for larval development and as a primary food source for adults. Insects, spiders, snails, worms and small fish are all prey for certain amphibians.
For many reptiles, wetlands also serve as primary habitat, supplying them with an ample source of food and habitat for breeding and nursing. Specially adapted reptiles that are able swimmers are likely to be found in wetlands. Some of these include the common snapping turtle, spotted turtle, northern water snake, cottonmouth snake, diamondback water snake and garter snakes.
Amphibians and reptiles depend upon a variety of wetland types. These may include marshes, swamps, bogs and fens (and their associated subclasses). Some wetlands are only wet a portion of the year and are considered “ephemeral” wetlands. These wetlands provide important habitat and breeding grounds.
There are often strong ecological connections among wetlands in a landscape. Although some may be permanent and others ephemeral, amphibian populations can depend on multiple wetlands within a given area. To protect these species over the long term, the variety and density of suitable habitat sites within the landscape must be preserved, along with terrestrial corridors that connect the wetlands.
Why are ephemeral wetlands important?
Vernal pools, one type of ephemeral wetland, are of critical importance to amphibian populations. As small, often isolated wetlands, vernal pools are only wet for a portion of the year. Periodic drying creates a fish-free environment for amphibians, many of which have adapted rapid egg and larval stages as a race against the dry season. The absence of fish predators in vernal pools benefits amphibian populations.
Threats to Herps and Wetlands
In order to maintain healthy amphibian and reptile populations, wetland habitat must be protected. A watershed contains multiple habitats, all of which are affected by changes in hydrology, land use and water quality. Since no habitat is isolated from its surroundings, protection of herps must take place at both the large-scale watershed level and at the smaller scale of individual wetlands.
Population declines and disappearances of amphibians and reptiles leading to widespread scientific and public concern have been well documented. The causes for their decline, while not fully understood, appear to be complex and numerous.
Wetland Habitat Loss
More than 220 million acres of wetlands are thought to have existed in the lower 48 states prior to 1700. Since then, extensive losses have occurred, and over half of our original wetlands have been drained and converted to other uses. Although the rate of loss has decreased in recent decades, wetlands and other aquatic resources are still threatened by activities such as ditching, draining, dredging and stream channelization; deposition of fill material for commercial and residential development, dikes, levees and dams; crop production; logging and mining. Since many amphibian species need both aquatic and terrestrial habitat, it is very important to preserve wetlands and a buffer strip of adequate upland habitat.
Due to their amphibious lifestyles, herpetofauna are very sensitive to changes in the water and surrounding land. Many synthetic organic compounds and metals adversely affect amphibians and reptiles. Sublethal effects of chemical pollutants can impair a herp’s ability to swim, catch food and reproduce successfully. Amphibians are particularly sensitive to chemical contaminants owing to their permeable eggs and skin. A recent study by the U.S. Geological Survey (USGS) showed that “organophosphorus pesticides from agricultural areas, which are transported to the Sierra Nevada on prevailing summer winds, may be affecting populations of amphibians that breed in mountain ponds and streams.” The scientists estimate that damage could be even worse for those species more closely associated with water.
Endocrine disrupting chemicals (EDC) have been of great concern in the amphibian and reptile community. Studies have shown that chemicals like polychlorinated biphenyls (PCBs) build up in turtle eggs, reduce eggshell thickness and cause reproductive failure. Other studies have shown reduced male organ size among reptiles, which results in difficult sex recognition and the subsequent lack of reproduction. Both amphibians and reptiles are very susceptible to the dangers of EDCs.
The indirect effects of excess nutrients can be very detrimental to amphibians. Nutrients such as nitrogen and phosphorous can cause dominance of algae, which is not conducive to laying eggs. Excess nutrients can also reduce the amount of oxygen available in the water for amphibian tadpoles and alter the composition and numbers of the invertebrate communities that are food for the juveniles. In Texas, playa wetlands receiving nutrient-laden feedlot effluent were devoid of amphibians found in natural wetlands. In this case, experiments indicated that the nutrient-concentrated effluent had to be reduced to less than 3% of its original strength in order to minimize adverse effects.
- On the whole, it is difficult to document reptile population trends. Many species have secretive natures which, when combined with large home ranges, low population densities and a rarity of congregational behavior, may result in a severe population decline without being noticed by people.
- Some turtles, such as the diamondback terrapin, are endangered owing to commercial harvesting, stemming primarily from the food industry.
- The pet trade also endangers many reptiles, such as the box turtle
Why are Amphibians so Vulnerable?
Some amphibians breathe through their porous skin, which makes them extremely vulnerable to pollution in the soil, air, and water. You can think of amphibians as sponges that soak up their surrounding environment. This is why you shouldn’t try to catch frogs if you have insect repellent on; the toxic repellent will seep into their skin and harm them.
Global climate change may threaten aquatic and semiaquatic life by reducing wetland acreage due to frequency and severity of storms and sea level rise. Latitudinal shifts in temperature and precipitation patterns also threaten herps.
Ozone depletion causes an increase in the amount of Ultraviolet radiation that reaches the earth’s surface and waters. Research has shown that UV-B radiation has adverse effects on some amphibians. The Montreal Protocol has reduced emissions of ozone-depleting chemicals.