This is the Common Slipper Limpet (Crepidula fornicata), a small marine shellfish native to the eastern coast of North America but now found in large numbers along European coasts, including the UK. It was introduced accidentally over a century ago, likely through the import of oysters. Since then, it has spread rapidly and is now considered an invasive species because it can disrupt native marine life and habitats.

Location:
Originally from the eastern coast of North America; now widespread along European coasts, including the British Isles.

Average Size:
Typically up to 5 cm in length.

Family:
Calyptraeidae (Slipper Limpets)

Species:
Crepidula fornicata

Ecological Role:
Slipper limpets are filter feeders, drawing in water and extracting plankton and organic particles. In large numbers, they alter the seabed by trapping particles and depositing waste, affecting habitats for native species such as oysters and mussels. Their presence can reduce biodiversity and impact local fisheries by competing for space and changing water flow on oyster beds.

Reproduction:
Slipper limpets are sequential hermaphrodites. They form characteristic “stacks” on hard surfaces, with the largest, oldest individuals at the bottom functioning as females, and smaller, younger limpets above acting as males. If the female at the base dies, one of the males will change sex to maintain reproductive balance within the stack.

Conservation Status:
While not endangered, Crepidula fornicata poses ecological risks in invaded areas. Some initiatives have explored using slipper limpets as a food source to help control populations, potentially reducing their impact while introducing a novel seafood option.