Mollusks Shells and a Stormwater Drainage System

A few ponds near me and the areas between them have a variety of mollusk species I’ve observed. The largest pond is Pond A, nicknamed “Lamera Pond” by my friends who may come with me, which is a stormwater retention pond that holds, well, rainwater. There are two other ponds, Pond C and Pond B which have their own species. Corbicula, a notorious invasive clam is present in Ponds C & A, but absent from Pond B. Native pea clams in the family Sphaeriidae seem to be present in only Ponds A & B. Unionids, native freshwater mussels are present throughout all three, although Pond B only has Utterbackia imbecillis, Pond C have U. imbecillis and Toxolasma parvum, and Pond A has those two species, plus Pyganodon grandis. Native gastropods are present throughout all 3.

Corbicula in Pond A is different from Corbicula in Pond C. Pond A Corbicula is a very atypical form, with finer striae and a broader shape, comparable to that of largillierti. Pond C Corbicula is more typical. I’ve also discovered a Corbicula midden, with Pond A-form Corbicula. The midden is evidence of a Corbicula population from somewhere else where the stormwater pipes brought the shells from. In the midden, there’s also Euglesa and Musculium shells, which are Sphaeriids. Pond A appears to have at least two Euglesa species: E. compressa, and something else, which I think could be E. casertana. Pond A also has Musculium, which appears to be mostly M. lascustre. Pond C lacks pea clams entirely. Pond B has many pea clams, but all of the Musculium genus. It has two species: M. lacustre and M. securis^. Some of the *M. lacustre there is a little elongate for the species.

I have notes from a few of my observations that I’ll copy-and-paste here, so I can see them all in one place:

May 11th, 2024

A typical-form Corbicula found on land, in part of a stormwater drainage system. The 2nd photo gives context to the pond and the midden and how they are connected, although a few hundred feet apart. The 3rd photo gives context closer to the midden, where some sort of drainage pipes run underground. There’s a consistent flow of water and Corbicula through the mud, along with Unionid fragments (maybe) and Planorbella snails. The midden is in a ditch, a few feet above the drainage. Perhaps a really strong storm in the past displaced a lot of Corbicula bringing it up here, or perhaps many stray shells were brought here over time by strong currents. Either way, the pipes must’ve overflowed because the shells otherwise couldn’t have gotten here.

Shells of bivalves and snails can be found throughout the ditch between the midden and this area where rainwater flows directly into the pond

The midden also surprisingly consists of Sphaeriids. Both Euglesa and Musculium are present here, although in small amounts. I have yet to find any Unionids or Unionid fragments

April 25th, 2024

Found in the midden. Broader lateral teeth, a lower beak, and finer striae, as usual.
This observation is for the top shell in all photos except the last one, where it’s the one on the left. This shell was the only one I could find in the midden with noticeable amounts of purple on its nacre.
Almost every shell out of the thousands had a bleached white/off-white interior, with a chalk-like texture. Only a handful, including this one, had the smoother and glossier finish of a more recently dead shell. I’m tempted to ID this fragment as Corbicula largillierti but I also feel like this is just a form of Corbicula fluminea, just like what we’ve been calling the other Corbicula from this midden and the ponds surrounding it. It is very different than typical C. fluminea, but then again, it’s very similar to whatever form is present at this midden and Pond A. Is there a gradient between the morphology in the populations? Maybe not. I’ve posted more than a hundred Corbicula from this midden and pond and there seems to be a gradient between the fine-striae shells and the even-finer-striae shells, but there doesn’t seem to be a gradient between the two forms shown in the first 3 photos.
In the second to last photo, comparing it to a supposed Corbicula fluminea s.l. from a nearby pond shows that the striae aren’t as fine as some of the other shells here. In fact, most shells from this pond and midden have fairly fine striae when younger (~1cm) which are slightly less fine when more mature. Both the fine-striae and broad-striae forms exist in Pond A, with the fine-striae form clearly being more common to find. However, I have yet to find a live clam here (somehow) so I’m completely unsure of current populations (although with the amount of recently-dead clams on the pond’s edge I assume there is a living population)
There are very few shells of a similar form from other locations that I’ve seen on iNaturalist. I tried to find a few quick examples:
https://www.inaturalist.org/observations/198754765, from Brazil. From a lake with some possible Corbicula largillierti and maybe even Cyanocyclas. Comparing the interiors of the shells, it resembles many Corbicula from the midden, especially in comparison to the high-beaked Corbicula found in rivers.
https://www.inaturalist.org/observations/203511595, from a small pond in South Carolina. Similar shape to the slightly more mature clams from Pond A
https://www.inaturalist.org/observations/204651753, from Argentina, in a small lake
https://www.inaturalist.org/observations/206173596, from New York, found in a pond according to the notes. The third image looks really similar to what the small Corbicula midden(?) in front of Pond A’s stormwater “intake” pipe looks like.
https://www.inaturalist.org/observations/207223752, found in a medium river in Pennsylvania. Some nearby observations look more similar to the “Pond A Form” than others.
I might start identifying some individuals from this pond and midden as simply Corbicula if they have really fine striae or a purple interior

March 11th, 2024

At 6.5mm, this is one of the smaller shells I’ve collected, even smaller than the Musculium I found 10 minutes after this one. Most if not all of the young Corbicula in this midden have ridges finer than typical Corbicula fluminea sensu lato. The third photo compares the striae to my fingerprints.

March 10th, 2024

9mm. Found in the Corbicula midden. Only one of 2 I found; I lost the other one due to the wind. So far I’ve found thousands of Corbicula, a dozen Planorbella trivolvis, and these two Musculium in the pile.
Photos taken with an iPhone.

Publicado el 12 de mayo de 2024 a las 02:56 AM por lj_lamera