An alien species of crab may be establishing itself in the Mediterranean Sea.
The portunid crab, Gonioinfradens giardia, is usually found in the Red Sea and Indian Ocean but an individual was recorded in the Portopalo di Capo Passero, Sicily, for the first time in November 2025. By January 2026, scientists had already documented 11 more specimens off the coast of Sicily.
This is the furthest west the species has been recorded to date.
“These repeated occurrences over a short time period and within a relatively small area strongly suggest that the species is no longer an occasional arrival, but at an early phase of local establishment in the central Mediterranean,” write the authors of a new study published in Acta Ichthyologica et Piscatoria.
This “rapid expansion” of the species in the Ionian Sea has caught researchers’ attention. They want to measure the occurrence of this type of crab because of the harm non-native species can do when they settle in the region.
“Invasive alien species are now widely recognised among the primary threats to the structure, integrity and functioning of Mediterranean marine ecosystems,” write the study authors.
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Over the last 50 years, the Med has experienced “an unprecedented influx of non-indigenous species,” says the paper. These marine migrants arrive through the Suez Canal. When non-native species settle in new waters, they can bring disease, disrupt populations of other animals and upset the balance of the habitat, which can also impact fisheries.
“This case adds to a growing list of species reshaping Mediterranean ecosystems,” says the paper’s lead author Francesco Tiralongo, a researchers at the Institute for Biological Resources and Marine Biotechnologies, in a statement. One well-known example is the establishment of invasive lionfish in the region.
How the arrival of the portunid crab might affect the Mediterranean remains unclear but the heat is on to watch for clues. “Documenting these early phases of establishment is crucial for understanding future ecological scenarios and supporting informed management decisions,” says co-author Alberto Felici, a scientist at the University of Camerino in Italy.
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