Abstract
This paper presents the first record of the Asian date mussel Arcuatula senhousia (Benson, 1842) from the southern coast of the Algerian Basin in the Western Mediterranean Sea. The species was first observed in June 2019 in El Mellah Lagoon, a coastal lagoon located in the El Kala UNESCO biosphere reserve (northeastern Algeria). Additional individuals were also collected monthly, between July and December. Arcuatula senhousia was found in shallow subtidal habitats dominated by the seagrass Zostera noltei (Hornemann, 1832) at a maximum density of 1,321 ± 1,167 ind.m-2. The maximum observed shell length was 32 mm, indicating that A. senhousia may have existed for more than a year in adjacent area in El Mellah Lagoon and moved probably into our survey area in 2019 as either adults (via fouled vessels) or, less likely, planktonic larvae (via currents). Live specimens were observed attached to Z. noltei leaves and rhizomes and, to a lesser degree, on empty shells of the cockle Cerastoderma glaucum (Bruguière, 1789). The introduction of the invasive Asian date mussel into this lagoon may lead to changes in the structure and functioning of this unique shallow coastal ecosystem and requires further study.