Rhodes records largest Mediterranean concentration of invasive jellyfish

Scientists have recorded the largest concentration of the invasive jellyfish species Cassiopea andromeda ever observed in the Mediterranean Sea. The massive aggregation was found in a small, semi-enclosed rocky pool covering only 430 square meters in Kallithea, Rhodes.

Approximately 14,641 jellyfish were identified within this area. Known as the ‘upside-down jellyfish’ due to their habit of spending much of their time inverted on the seabed, this species is of Indo-Pacific origin. It has established itself in the Mediterranean and has been expanding, particularly in the Eastern Mediterranean and the Aegean Sea.

Research conducted by the Rhodes Hydrobiological Station and the Institute of Oceanography of ELKETHΕ, in collaboration with the Aristotle University of Thessaloniki, confirmed the species through DNA barcoding. Measurements taken from 275 individuals showed a wide range of sizes, suggesting continuous reproduction and population growth. The findings, published in the journal BioInvasions Records, highlight the need for systematic monitoring of semi-enclosed coastal ecosystems, which can act as hubs for the establishment and spread of invasive species.