They're Atlantic ribbed mussels, the only large bivalve found in salt marshes. They can breath air and live for over two decades. These were about 4 cm long, indicating they're at least 2 years old. That they survived so long sandwiched between mud and mattress bears testament to their tenacity. They bind the sediment with their supersilk, slowing erosion at the marsh edge. Their droppings feed the cordgrass, the plant that holds the entire marsh together. Encouraging to know something besides us is attempting to clean up the place. We also saw about a thousand little snails and some sand shrimp.
Here's Kip on our pile:
High of 40, wind from NNW @ 13 MPH, 4. high tide @4:28 PM, water level at 3.5-inch mark. Birds seen: robin-sized bird with greenish-yellow underwings.
Age and Growth Rate Determinations for the Atlantic Ribbed Mussel, Geukensia demissa Dillwyn (Bivalvia: Mytilidae) Diane J. Brousseau Estuaries, Vol. 7, No. 3 (Sep., 1984), pp. 233-241
Recruitment, Survivorship, and Age Structure of a New York Ribbed Mussel Population (Geukensia demissa) in Relation to Shore Level: A Nine Year Study David R. Franz Estuaries, Vol. 24, No. 3 (Jun., 2001), pp. 319-327
Ribbed Mussels and Spartina Alterniflora Production in a New England Salt Marsh Mark D. Bertness Ecology, Vol. 65, No. 6 (Dec., 1984), pp. 1794-1807