First Record and Ecology of the Non-Indigenous Copepod Calanopia elliptica (Dana, 1849–1852) Among the Zooplankton Community of the Maltese Channel (Strait of Sicily, Central Mediterranean Sea)

This study presents the first recorded observation of the calanoid copepod Calanopia elliptica (Dana, 1849–1852) in the waters between the southern coast of Sicily (Italy) and Malta, and the Central Mediterranean Sea in general. This area is characterised by heavy traffic of cargo ships passing through the Suez Canal to enter and exit the Mediterranean Sea. Moreover, water masses from both eastern and western basin flow through the Strait of Sicily and highly influence the waters surrounding Malta. These two aspects make this area suitable for the arrival of a vast array of lessepsian and Atlantic invaders, brought by current or ballast waters, or a combination of both. For this reason, a total of 32 zooplankton samples collected during the summer of 2025 were analysed for species diversity and abundance. A total of 133 organism taxa were identified to the lowest taxonomical level possible. General community analyses revealed that the composition of the zooplanktonic community across the study area is tied mainly to water column stability. The consistent frequency (53.13%) but relatively low abundances of C. elliptica (maximum 1.747 ind/m3) across multiple samples may indicate the onset of a new colonisation, as its known invasion range had previously been confined to the eastern basin of the Mediterranean Sea. Analyses suggest that the abundance of this copepod in the study area is mainly tied with low dissolved oxygen levels and temperatures, while seemingly unrelated to the other environmental parameters and to the time of the day in which it was sampled. These findings are just at the start of the analysis of a time series of zooplankton samples in the area. Hence, future studies based on it are necessary to identify trends in the abundance of this species over the past and future years, as well as any potential impacts on the native community.