The presence of Mya arenaria in the Ria de Aveiro is the third confirmed record of this invasive clam on the Portuguese coast

Abstract

The occurrence of the invasive clam Mya arenaria is confirmed in the Ria de Aveiro (northern Portugal). Some live specimens were collected from the mid-upper intertidal zone. The population density was low (about 0.15 ind m−2) and the individuals were large, of mean shell length 82.22 ± 14.85 mm. Large empty shells of M. arenaria, of mean shell length 85.32 ± 11.31 mm, were found in a life-like position, which indicates an episode of mass mortality in the sampling area and suggests that invasion by the clam in the Ria de Aveiro is not a recent event. Differences in the size-classes of empty shells of the invasive clam indicate that the clam is able to reproduce in this habitat. Occurrence of established populations of M. arenaria at different locations on the Portuguese coast, such as the Tagus estuary, the Lima estuary and the Ria de Aveiro, may be due to intentional introduction of M. arenaria in at least some cases.