Tropical Isognomonids in the Mediterranean Sea: When the West Atlantic Met the Indo-Pacific Region in the South Aegean Sea

The introduction and establishment of the bivalves Isognomon bicolor and Isognomon aff. legumen in the South Aegean Sea, specifically on the islands of Chalki and Alimia, marks a significant ecological event. These species, native to different parts of the world, have now been confirmed in the Mediterranean through DNA barcoding and phylogenetic analyses. These methods are crucial for accurate identification within the genus Isognomon, as traditional morphological identification is challenging due to the variable and habitat-dependent shell shapes of these bivalves. Isognomon bicolor is originally from the West Atlantic, while Isognomon aff. legumen hails from the Indo-Pacific region. Their presence in the Mediterranean, specifically in the intertidal and shallow subtidal zones, indicates they have found suitable habitats in their new environment. Over a four-year period of field observations, researchers gathered valuable ecological data, noting the species’ habitat preferences and their establishment dynamics. In July 2024, researchers observed the formation of new, extensive dense aggregations, or beds, of the invasive I. bicolor on the coastal rocks of Chalki and Alimia. The formation of these beds is a clear indicator of a progressing invasion, which poses a significant threat to the native ecosystem. The establishment of I. bicolor and I. aff. legumen could disrupt local biodiversity, outcompete native species, and alter the ecological balance in these regions. This situation underscores the importance of continuous monitoring and the use of advanced identification techniques like DNA barcoding to track and manage invasive species. Such efforts are essential to mitigate the impacts of these invasions and protect native marine ecosystems.