MNN - Mother Nature Network

Have you ever wondered about the amazing, extraordinary creatures that slide under rocks or burrow deep down in river banks? Truth be told, I never really paid any mind to the small gastropods and bivalves that live in the streams and ponds around Upstate New York. But you'd be surprised about how small, but powerful freshwater snails and mussels are for the survival of aquatic ecosystems. Forgive me, but since I am a Tolkien nerd, think of mollusks as the hobbits of the Middle Stream/Lake/Pond...you get my drift.

 
Freshwater snails come in two main groups-the subclass Prosobranchia (gill-breathing) and Pulmonata (lung-breathing). The above snail is a pulmonate, and has a funky name, Pseudosuccinea columella. I found this guy in the above photo sliding around on a large rock on the edge of Irondequoit Creek in Rochester, NY. Since this particular species, and all of the members of the Pulmonate subclass, can breathe air and water, they can withstand a variety of water quality conditions. That's not to say that the Prosobranchs are wimps, but because they can breathe only water, they are more susceptible to poor dissolved oxygen levels in water.
 
Before I introduce you to the Prosobranchs, there is something pretty neat, or at least that I find pretty amazing, about the pulmonates. If you have a seashell or random conch laying around your house, hold it upright so that the pointy spire end is facing up-I will bet that your mollusk has its opening (aperture) on the right hand side. This is the norm for most saltwater varieties of gastropods, but not so much for the freshwater world. In fact, many of the freshwater snails collected and observed thus far during my summer research are lefties. Here is a good example of a lefty pulmonate, Physa heterostropha ( what an epic name for such a small mollusk!).
 As you can see, the aperture opens on the left! If you feel adventurous or want to explore some wetlands near you, grab a net and go! These species like a highly eutrophic, lentic environment such as a pond or swamp, where there is a plethora of green algae for them to munch on with their feet (afterall, gastropod literally translates to belly-foot!) If you have a net and really want to explore the world of the gastropod, all you need to do is just skim the surface of the water and there is a high chance that if you scoop up lots of algae, you probably have dozens of these lefties in there too! They are very active as well! I remember just observing shallow rocks and was just amused at all of the snails gliding on the rocks, from one to the next.
 
Now, onto the world of living the Prosobranchia life! In all of my research this summer, the most common prosobranch, or maybe it is my favorite because they look so cool, is Viviparus georgianus. Otherwise known as the "Banded mystery snail," these guys like to just sit on top of muddy stream beds and chill out, all the while munching on algae and whatever else might be floating around in the water column. These snails are neat in my opinion because they are so big compared to pulmonates, and they are globose, so they look kind of squished and round.
 Here is the Banded Mystery Snail hanging out in a temporary holding tank before I released them back into the wild. See the reddish-brown bandings? Pretty stunning for such a slow-mover.
 
So, in all of these bits of information about various snails, one might ask, who cares? Well, obviously I do, and it's not just because these gastropods look beautiful, but it's because they are such a vital component of aquatic ecosystems. Without them, our waters would be exploding with algae and would not be hospitable for fish and other community members. To me, and to many malacologists and limnologists, freshwater snails are the unsung heroes of water quality. Their presence and absence from certain bodies of water can indicate good, fair, or poor water quality. Gastropods also leave behind a legacy when all they leave are their spent shells behind; empty shells can be used as refuge for other small macroinvertebrates and snails. The shells also eventually are weathered, and calcium is recycled back into the water, so that other snails can utilize this important element in their shell-building mechanisms. And, of major concern on a local and global level, are the impacts of climate change on the livelihood on mollusks, including freshwater Unionid mussels (I will rant and rave about mussels in my follow-up). As rates of evaporation increase and precipitation decreases in watersheds, stress is added to the survival of gastropods. All snails, even pulmonates, require at least some water for survival. Losing streams and hotter temperatures are even more detrimental to gastropods, since some species only survive in a specific temperature range. Snails may be hiding underneath rocks and leaf litter, but the far-reaching consequences of their daily functions translate to healthy streams and ponds where there are varieties of fish and birds and frogs. Maintaining healthy water sources helps our filter-feeder friends to do their job even better, but climate change presents a tricky challenge to this astounding Order Gastropoda.
 
Photos: Katherine Bailey