Two-way bioinvasion: tracking the neritic non-native cyclopoid copepods Dioithona oculata and Oithona davisae (Oithonidae) in the Eastern Mediterranean Sea

Accelerated anthropogenic changes in the Eastern Mediterranean Sea (EMS) have facilitated the introduction, spread and establishment of invasive copepod species in this region. Here, we report for the first time the introduction of two non-native cyclopoid copepods Dioithona oculata and Oithona davisae in Israeli coastal waters and describe their temporal variability. The species were identified based on morphological characteristics, DNA barcoding, and phylogenetic inference. Molecular identification and phylogenetic analysis supported the taxonomic identification, but showed cryptic speciation within D. oculata, separating the Western Pacific and EMS clades. In Israeli coastal waters, D. oculata exhibited a temporally restricted occurrence, appearing from September to December 2019 and in October 2020. D. oculata peaked in autumn, when seawater temperature was 28 degrees C. Its lowest abundance was observed in December when temperature decreased to 21 degrees C, indicating that the thermal affinity of D. oculata for warm-temperate conditions, for reproduction and the maintenance of viable populations, persisted in the introduced range. In contrast, O. davisae appeared almost year-round. It peaked at a summer temperature of 28 degrees C, as well as under the winter minimum of 17 degrees C, confirming its wide eurythermal tolerance. Based on our findings and previous observations, we suggest that D. oculata may have invaded the EMS through the Suez Canal and is now at the onset of its spread in the Mediterranean Sea, whereas O. davisae has been introduced via shipping, likely from the Northeast Atlantic, widely spreading and successfully establishing viable populations throughout the entire Mediterranean Sea to the coastal Levantine Sea.