Zostera marina
"Theodoxus fluviatilis" serves an indicator species for river monitoring (in Germany); however the spreading populations also have a high tolerance for degraded habitats. "Theodoxus fluviatilis" has a large phenotypic plasticity: it was found living on stones and on dead wood in freshwater environments; whereas it lives on stones and on "Fucus vesiculosus", "Potamogeton" spp. and "Zostera marina" in brackish water in the Baltic Sea. The species can also be found on aggregates of "Mytilus".