Impacts of the alien mussel Brachidontes pharaonis on native rocky shore assemblages in the Maltese Islands

Abstract

The mussel Brachidontes pharaonis (Fischer, 1870) is a small intertidal mytilid native to the Indo-Pacific region, mainly south-eastern Asia and the Red Sea (Sara et al., 2008) (Fig. 1). It was one of the first Lessepsian migrants, which are species that have invaded the Mediterranean Sea following the opening of the Suez Canal in 1869, and it was recorded at Port Said, Egypt, less than a decade after the opening of the canal (Fuchs, 1878, as reviewed by Safriel et al., 1980). This alien species has since spread westwards (see review by Rilov et al., 2004) and it was first recorded in the Maltese Islands (central Mediterranean) in October 1970 (Sciberras & Schembri, 2007). Since then it has occurred as a few sporadic individuals on a number of rocky shores around the islands. Recently, however, Mifsud & Cilia (2009) reported that B. pharaonis beds were present in Birzebbugia Bay within Marsaxlokk Harbour (Fig. 2). This is the first time that any type of mytilid bed has been reported from the islands; although a number of indigenous species of mussel occur, (Mytilaster minimus, Mytilaster lineatus, Mytilus galloprovincialis and Perna picta), but locally none of these form beds. Therefore the B. pharaonis beds at Birzebbugia Bay constitute a habitat previously absent from the Maltese Islands.