Ponds, Pipes and Parasites

It seems easy to assume that the manicured, verdant lawns of suburbia are not, by virtue of their presence, doing any favours to their surrounding environment. However, though these spaces sometimes boast an almost astounding lack of diversity they interact with their surroundings in more ways than one might expect. Researchers at the Yale School of Forestry and Environmental Studies are getting to grips with these interactions and the surprising winners and losers in the suburban pond. YIBS Field Notes spoke to Meredith VanAcker who received a Masters Research Small Grant for her work.

“My basic idea was to look at whether suburbanisation has an effect on the disease prevalence in frogs. Frogs tend to be good bioindicators of environmental quality because they are so sensitive to changes in the environment, and they are particularly useful as indicators of water quality,” says Meredith VanAcker whose Master’s project traces amphibian health in Connecticut along a suburbanisation gradient.

Recent publications from other Yale researchers had already shown a relationship between an increasingly skewed sex ratio in frogs and suburbanisation, but VanAcker wanted to look at other indicators for health and wellbeing in ecosystems that increasingly being bordered by lawns and roads. Initially working with grasshoppers in a forest in northern Connecticut, she had noticed that several individuals were parasitized with nematodes, a type of parasitic roundworm. Joining two other researchers who look at amphibian populations, VanAcker switched focus from insects to frogs and started looking for evidence of how parasites affect their risk of being eaten by predators.

“We had to approach the ponds very stealthily to get the samples we needed,” she said. “You need to make sure that the pond life isn’t disturbed before you get there. So, I crept up to the ponds in waders, carrying a huge metal pipe over my shoulder. Then I would slam the pipe down into the water, creating an air lock with the sediment at the bottom, and just scoop out everything that was inside. This gives an idea of the ratio of various species within the pond and the density of each.”

The samples collected by the team were taken back to the lab, where snails had to be analyzed immediately, often in the middle of the night. The snails were able to provide a number of interesting clues about how suburbanisation could be behind the rise in frog parasites that the team has been seeing. For one, nutrient runoff from lawn care products seems to be great for snails, which are growing to much larger sizes and harbouring thriving communities of trematodes within these larger shells. This is bad news for frogs and in seven of the seventeen ponds surveyed, researchers observed a particularly nasty flatworm parasite that can cause compromised kidney function and early mortality.

“We really saw that the nastier the pond the better it was for snails. Nitrogen and phosphorus contamination seems to be really helping them to thrive and, in turn, potentially altering amphibian populations. This is a widespread threat and something we really need to know more about. Beyond the fact that I think we need to conserve these animals for their inherent value and contribution to the ecosystem, our findings have implications for human health too. Many of the parasitic lifecycles we see in animals can be easily related to the diseases we see in humans,” said VanAcker.

This growing body of evidence that the classic green lawn might be more dangerous to surrounding ecosystems than its otherwise innocuous appearance suggests, can be added to other concerns around the water-intensity of many suburban gardening practices. It seems that now would be the right time to rethink the way we design and use yard spaces in order to ensure healthier frogs and less imposing snails.