Climate change, resulting from elevated levels of greenhouse gases in the atmosphere, particularly carbon dioxide, is affecting Earth’s biota including the land snails and slugs (hereafter called snails). Two major affects of more carbon dioxide in the atmosphere are higher temperatures (including increased variability, so higher highs and lower lows) and altered precipitation patterns, both of which affect land snails. Less prominent but still important affects include more acidic water (carbon dioxide reacts with water to form carbonic acid) and altered plants that become less nutritious and more defended.
With higher temperatures, snails living near the maximum temperature they can tolerate must move to higher elevations or toward the pole, or northward in our area. For snails that are already confined to mountaintops, there is no higher elevation, so they might become extirpated from those areas (Pearce & Paustian 2013).
Water is very important to land snails, which are like leaking bags of water trying to survive on dry land. Therefore, changes in precipitation can directly affect where snails are able to survive. The first species of any organism thought to have become extinct due to climate change is a land snail, Rhachistia aldabrae, although it was decreased rainfall, not climate warming that was blamed for the extinction (Gerlach 2007). Happily, a living population of the snail was found on the other side of the island in 2014, so it is not extinct (although it loses the title of being the first climate change related extinction).
More acidic water is certainly affecting marine mollusks, which find it more difficult to grow and maintain their shells in the more acidic water, which tends to dissolve calcium carbonate shells more. In freshwater, more acidic water affects snail’s sense of smell, suggesting that they might be less able to detect predators. On land, acid rain or acid precipitation results from calcium carbonate and nitrogen oxides reacting with water vapor in the atmosphere, and the resulting acid precipitation has affected many species of terrestrial organisms. Ongoing research suggests that acid precipitation has contributed to the decline of some land snail species in the northeastern North America (T.A. Pearce unpublished).
Plants absorb carbon dioxide from the air, so it makes sense that plants should grow better in air with more carbon dioxide. In many cases that appears to be true. However, plants use carbon dioxide to make carbohydrates including sugars that contain energy. Carbohydrates are just one of the four major groups of chemicals needed by living organisms. To make proteins, another important class of chemicals, the plant requires nitrogen. So, increased carbon dioxide can lead to larger plants with more carbohydrates (energy), but less protein. Creatures that need more protein will perform more poorly if they consume many plants grown in elevated carbon dioxide (i.e., C3 plants in contrast to C4 plants, which are less susceptible to being perturbed by elevated carbon dioxide). Furthermore, many plants produce defensive chemicals. Plants whose defensive chemicals containing nitrogen (i.e., to make protein) might produce less of the chemical, while those producing defensive chemicals without nitrogen might be able to produce more of the chemical (e.g., Ng et al. 2023).
Climate change affects in northeastern North America might be slightly less than in other parts of the continent, although there will be climate warming and drying in the Mid-Atlantic and southern part of New England.
As the climate changes, snail populations will likely need to disperse to areas with more favorable habitat or perish. However, snails are the quintessential slow-moving organism, so we expect their dispersal into new areas to be slow. Furthermore, crossing inhospitable habitat, such as an agricultural field for a forest
snail, or even crossing a road (Baur & Baur 1990) can be difficult or impossible for snails. Some conservation biologists are considering the use of assisted dispersal to help land snails reach new areas of suitable habitat (Örstan 2009).
References
Baur, A. & Baur, B. 1990. Are roads barriers to dispersal in the land snail Arianta arbustorum? Canadian Journal of Zoology 68(3): 613-617.
Gerlach, J. 2007. Short-term climate change and the extinction of the snail Rhachistia aldabrae (Gastropoda: Pulmonata). Biology Letters 3(5): 581–584. doi:10.1098/rsbl.2007.0316. Ng, M., McCormick, A., Utz, R.M. & Heberling, J.M. 2023. Herbarium specimens reveal century-long trait shifts in poison ivy due to anthropogenic CO2 emissions. Applications in Plant Sciences 110(9): e16225. https://doi.org/10.1002/ajb2.16225
Örstan, A. 2009. Will assisted colonization be a viable option to save terrestrial gastropods threatened by climate change? Tentacle 17: 14-16.
Pearce, T.A. & Paustian, M.E. 2013. Are temperate land snails susceptible to climate change through reduced altitudinal ranges? A Pennsylvania example. American Malacological Bulletin 31(2): 213-224.