Expansions of cosmopolitan Copepoda Acartia tonsa Dana 1849 in the Black, Caspian and Baltic seas: morphological and genetic analyses

A comprehensive morphological and genetic investigation of the widespread copepod species Acartia tonsa Dana 1849 has been conducted across the Black, Caspian, and Baltic seas. A. tonsa is a species that occupies productive estuaries and coastal zones extending from tropical and subtropical regions to higher latitudes throughout the World Ocean. In many regions, it becomes the dominant species within the zooplankton community during the spring and summer seasons. Upon invading non-native ecosystems of higher latitudes, its high abundance allows it to dominate zooplankton communities, playing a vital role in climate-mediated food web shifts; it has the potential to displace native copepod species. Nevertheless, it continues to serve as a crucial dietary component for a wide variety of zooplanktivorous fish. The morphological identification of the genus Acartia presents significant challenges. To date, no genetic methodologies have been employed to address this issue. This research utilizes genetic analyses, including the amplification of the mitochondrial markers CO1, 16S, and Cytb, along with the nuclear marker 18S, to explore the diversity within the genus Acartia offering new insights into spatial distribution of A. tonsa in the warming World Ocean.