Scientia Marina, Vol 75, No 2 (2011)

A field experiment on the reproductive success of the invasive clam Mya arenaria (Bivalvia) in the Tagus estuary: coexistence with the native clam Scrobicularia plana

Anxo Conde
IBB-Institute for Biotechnology and Bioengineering, Center for Biological and Chemical Engineering, Instituto Superior Técnico (IST) - Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo , Portugal

Júlio M. Novais
IBB-Institute for Biotechnology and Bioengineering, Center for Biological and Chemical Engineering, Instituto Superior Técnico (IST) , Portugal

Jorge Domínguez
Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo , Spain


A three month field experiment with tidal level (upper, middle, lower) and treatment (excavated and not excavated plots) as categorical experimental factors showed that the invasive clam Mya arenaria has reached a more advanced stage in the invasion process in the Tagus estuary. As we observed the smallest recruited juveniles of Mya arenaria (2 mm) throughout the study period, we concluded that the clam is capable of reproducing in the new habitat. Juveniles of both Mya arenaria and the bivalve Scrobicularia plana were found to avoid excavated experimental plots, showing a significantly higher abundance in the control plots. These data, strongly suggest that the recruited bivalves actively avoid unsuitable substrata. Juvenile specimens of Mya arenaria were more abundant in the mid-intertidal zone. However, juvenile specimens of Scrobicularia plana were mainly distributed in the upper intertidal level, which suggests that they have a different settlement behaviour from that observed for the juveniles of the invasive clam. Despite the divergent distribution between the juveniles of the two species in the study site, the possible interaction between these two species is considered and discussed.


Mya arenaria; reproductive success; intertidal distribution; Scrobicularia plana; Tagus estuary

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