I have noticed saltwater shells in a freshwater wetland lake about 2kms from the beach. How do they get there? Do birds carry it, or did they naturally spawn there?
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Does the current in any river or stream connecting the wetland to the sea reverse direction with the tides?
Oh it just got confirmed. The wetlands was connected to the bay a few thousand years ago
That former connection might explain it. Also consider the possibility that storm surge may overflow barriers and carry sediment with shells into the wetland.
People often buy commercially available marine clams for bait, so you can sometimes find their shells near freshwater very far from the ocean.
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It might be interesting to investigate the history of land use in the area from a historical and archeological perspective. There could be marine shells deposited in middens. Shells may also have been used as a source of lime, with some discarded near or in the wetland.
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I have read threads where mollusc iNatters pranked other mollusc iNatters by deliberately dropping saltwater shells in freshwater areas (and I guess you could also do vice versa).
It’s probably not what’s happening here, but I’m bringing it up because no one else mentioned it, and it is a thing that exists at certain times.
This kind of pranking is common in the herping community, but it may be rarer among “mollusc-ers”.
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@Quercitron yeah I think indigenous people lived around there and left some middens of shells around the lake
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2km isn’t very far. Oysters are brackish water shellfish. These can be found in rivers with tidal flow. It depends on the species of shellfish. Some shellfish may look like saltwater species but may be freshwater ones instead. Blood cockles is a very common species over here that are sold commercially. So after someone ate that, there are a lot of shells. Decades or a century ago, people might just discard the shells in various ways like under a tree. A big flood or storms might carry the shell into some rivers. Surroundings of old settlements may have bits of shell fragments in the soil. or a construction project that uses sea sand. There was an article of an island in USA with lots of oyster shells. It is said that there are sea shells at the himalayas.
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A local stream, Green Mill Run, is a famous fossil site – try a web search for “Green Mill Run fossils” and you will see. These fossil beds were formed when the present-day Coastal Plain was part of the Continental Shelf. Many of the fossil mollusks in Green Mill Run look almost the same as extant marine mollusks.
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