The spread of new marine species is a natural process, but human activities — such as the opening and widening of the Suez Canal, overfishing, and the transfer of ballast water from commercial ships — have dramatically accelerated it.

When ecosystems are weakened by overfishing and human impact, they create “gaps” that are filled by new alien species. The result is a change in the structure and function of marine ecosystems.

Not all alien species are harmful. Some have positive effects, but those that harm biodiversity and disrupt ecosystem balance are considered invasive.

At the Archipelagos Institute, coastal habitat researchers record the spread of these species throughout the year in different parts of the Greek seas. Everyone’s participation in this effort is essential:

If you spot an unusual fish or organism while swimming, diving, or fishing, take a photo and send your observation to the Archipelagos Citizen Observatory at observations@archipelago.gr.

Every record is valuable!

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To learn how to live with the new conditions — the result of our lifestyle — it is essential to get to know the alien species that have now become part of the Mediterranean. Some characteristic examples:

Lionfish (Pterois miles)

Originating from the Indian Ocean, it is spreading rapidly in the Mediterranean!

With no natural predators, its population continues to grow, affecting marine ecosystems.

However, it is safe to eat! By catching or consuming it, we help control its population and support fishers adapting to the new conditions in our seas.

Be cautious of its venomous fin spines!

Long-spined sea urchin (Diadema setosum)

First recorded in Greek waters in 2010. In Archipelagos’ surveys over previous years, it was observed in particularly high densities — from shallow waters down to 95 meters deep.

However, in recent years, a significant population decline has been noted in the eastern Mediterranean.

Squid (Sepioteuthis lessoniana)

The only alien squid species in our seas. It migrated through the Suez Canal and was first recorded in the Aegean in 2009. In the Indo-Pacific, it is one of the most important commercial species for coastal fisheries.

Dusky spinefoot (Siganus luridus)

A herbivorous fish that has been established for decades and is now common in Greek seas. It competes with native herbivorous species like the Salpa, causing overgrazing of algae and Posidonia seagrass meadows. It has now become a popular species for consumption.

Red squirrelfish (Sargocentron rubrum)

A nocturnal species that feeds on crustaceans and small fish. It entered the Mediterranean via the Suez Canal. The first record by Archipelagos researchers was in 2004 in the northern Dodecanese.

Pempheris rhomboidea

A small nocturnal fish species that forms schools in caves and emerges at night to feed on plankton. It can be found in various parts of the Aegean, though little is still known about its spread and role in the ecosystem.