Case Study 7 – Lionfish

Case Study 7: Lionfish

(Pterois miles)

Description

The lionfish is an easily recognizable marine species native to the Indo-Pacific that has now invaded the Mediterranean. It is known as a voracious predator with a stomach capable of expanding up to 30 times its normal size while feeding. Armed with 17 venomous spines (in dorsal, pelvic and anal fins), it poses a health risk to swimmers, divers, and fishers; while usually not lethal, its sting requires specific medical attention.

Habitat

This species entered the Mediterranean through the Suez Canal and has established populations in Greece, Cyprus, and Italy. Lionfish have also been observed in Malta, Croatia and Spain. It is nearly impossible to eradicate once established in marine environments, making population control essential.

Impacts

Biodiversity: As a skilled hunter, the lionfish can reduce native fish populations by up to 95% in certain areas. Because it is new to the Mediterranean, native fish often do not recognize it as a predator.
Fisheries: Lionfish in the Mediterranean are opportunistic, generalist predators that feed on dozens of native fish species and small crustaceans. They tend to prefer small, shallow-bodied benthic (bottom-dwelling) and demersal fishes. It preys on the young of commercially important species like picarels (Spicara spp.) and the Mediterranean parrotfish (Sparisoma cretense), threatening coastal livelihoods.
Ecosystem Balance: With few natural predators in the Mediterranean—partly because large groupers and octopuses are often overfished—lionfish populations grow unchecked, disrupting the entire marine ecosystem.

Prevention and Control Actions

Targeted Removal: In specific removal sites, volunteer divers systematically remove lionfish on a monthly or bimonthly basis. These are compared against control sites to see how the ecosystem and native fish assemblages recover. Currently, the removal process is still ongoing.
Acoustic Monitoring: Researchers have deployed hydrophones (underwater microphones) to study the soundscape of the marine environment. Since lionfish are soniferous (sound-producing), the team is using baited camera traps to link specific sounds to individuals and understand their acoustic repertoire. So far, data from long-term deployed hydrophones from September to November 2025 have been extracted from all study areas and their analysis is still ongoing. Baited cameras have also been deployed several times yet still, lionfish occurrences have not been recorded. Additionally, lionfish recordings from tanks are projected to be obtained in the coming months.
Community and Stakeholder Engagement: The project promotes lionfish as a food source to reduce pressure on overfished native species like groupers. This includes cooking events, educational activities in local schools, and training for fishers on how to safely handle the venomous fish when caught in nets.
Scientific Evaluation: Visual surveys and temperature loggers are used alongside acoustic data to ensure a robust, long-term evaluation of management efforts through 2027.

Useful links

- Download the factsheet
- An interview with Maria Zotou (GuardIAS General Assembly, September 2025)

Meet the case study team

University of the Aegean: Maria Zotou, Vasilis Trygonis, Vasilis Galanos, and Stelios Katsanevakis

Case study contact: Maria Zotou, m.maryzotou@gmail.com

Anastasija Zaiko

“This project is not just about managing invasive species today—it’s about developing a proactive approach that anticipates future ecological challenges, ensuring robust ecosystems and sustainable marine environments for generations to come”

Sergej Olenin

“For over 35 years, since I first began studying non-indigenous species, I have dreamed of tools that could reveal the ‘Big Picture’ of the transfer, spread, and impacts of invasive aquatic species. Thanks to advances in new technologies, the GuardIAS project now offers an outstanding opportunity to make that vision a reality.”

There are 7 Work Packages (WP) focusing on different stages of invasive alien species ‘invasion’ in the GuardIAS project. Each Work Package is a distinct project area, but all are interlinked through GuardIAS as a whole.