Status and occurrence of the non-indigenous dwarf surf clam Mulinia lateralis (Say, 1822) in the central Wadden Sea (southern North Sea) – a systematic survey

Abstract

Abstract The species Mulinia lateralis (Say, 1822) is native in the western North Atlantic Ocean and was first documented in European coastal waters in 2017. Since then, M. lateralis was reported several times in large abundances in the coastal waters of the Netherlands, Belgium and Germany. While the introduction vector is still unclear we assume that further dispersal in the southern North Sea will be driven by larval drift related to anti-clockwise residual tidal currents. To report its current distribution status in the central Wadden Sea, individuals were collected systematically from intertidal flats along 10 transects ranging from the outer Ems River estuary to the outer Elbe River estuary (German North Sea coast) between February and May 2022. In total, 897 specimens of M. lateralis were sampled from 392 stations (mean abundance 2.29 ± 4.97 ind./m²). The shell length ranged between 3.98 and 23.55 mm thus representing at minimum two cohorts. Regarding the increasing number of records of M. lateralis at multiple sites in Europe since 2017, the species can be considered as established in the western and central Wadden Sea.