The invaded sea: Dr. Francesco Tiralongo’s research on the invasive swimming crab (Gonioinfradens giardi) in the Mediterranean.
Expecting his hometown staples of swordfish, tuna, and sardines in the catches of local fishermen in the seaside city of Catania, Francesco Tiralongo was surprised to find their nets brimming with unfamiliar, even tropical, marine species. One crustacean in particular caught his attention due to its increasing presence on the eastern shores of Sicily: the swimming crab, Gonioinfradens giardi. A renowned researcher and professor of Zoology and Fishery Biology at the University of Catania, Professor Tiralongo’s education in the Mediterranean ecosystem started long before his academic and professional journey. In fact, it began with his first steps on the eastern shores of Sicily. From explorations of the coasts with his grandfather to fishing and snorkeling in the sea, Tiralongo’s childhood on the Mediterranean matured into a lifelong passion and profession.
The invaded sea
Tiralongo reflected on his long-term observations of the Mediterranean, describing it as an extraordinarily rich, yet fragile ecosystem. As a semi-enclosed sea surrounded by populous and industrialized countries with high levels of fishing, small changes in its ecological composition are often magnified and immediately noticeable to local residents, especially fishermen. The influx of invasive species forms one of the most significant ecological and economic disruptors in this region. While some alien species (i.e., species introduced outside of their natural range through human activity) are benign, a significant number are invasive and pose a direct threat to ecological balance, the local economy, and public health. Invasives are alien species that establish and reproduce successfully, disrupting ecosystems.
Professor Tiralongo explained that the focus on invasives in his research stems from the fact that the Mediterranean is one of the most invaded seas in the world. As of 2021, WWF reported 986 alien species in the Mediterranean. Tiralongo explained that the Mediterranean is particularly vulnerable to invasives due to three primary factors: the Suez Canal, connecting the Mediterranean to the Red Sea; intense maritime traffic, importing organisms via ballast water and ship hulls; and the rapid warming of the sea, favoring species of tropical origin (thermophilic species). As he observed an increasing number of unfamiliar species through underwater surveys and fish catches, it became clear to Professor Tiralongo that biological invasions were not isolated events, but a large-scale ecological transformation that merited in-depth study.
Invasive swimming crabs (Gonioinfradens giardi)
In recent decades, invasive crabs started overflowing the nets of Mediterranean fishermen, from the Levantine basin to the eastern Sicilian coast. The infamous African blue crab (Portunus segnis) from Indo-Pacific waters exploded in population in 2014, upending the Tunisian fishing industry. Other invasive crustaceans have emerged since then, including the Atlantic blue crab and now the swimming crab (Gonioinfradens giardi). The swimming crab is native to the Indo-Pacific region and was first recorded in 2009 off the coast of Turkey. The swimming crab populations have since exploded and spread to the eastern coast of Sicily, where Professor Tiralongo and his team strictly monitor and study them.
Invasives via the Suez Canal
When asked how the swimming crabs ended up in the Mediterranean, Professor Tiralongo pointed to Lessepsian migration, or the migration of marine species from the Red Sea to the Mediterranean via the Suez Canal, as the most likely pathway. This is one of the main introduction routes for marine alien species worldwide. Larval stages of the crab can be transported in the ballast water of ships, while adults and juveniles are carried on ship hulls, he explained. The swimming crabs currently populate the central and eastern Mediterranean, and are rapidly expanding their range according to reports from new areas.
When questioned about potential lapses in regulations, Tiralongo responded that enforcement and global compliance of ballast water regulations is inconsistent. “Complete prevention,” he explained, “is extremely difficult because the Suez Canal exists.”
Climate change and ecological impacts
The Suez Canal, however, only determines how the invasives arrive; what explains their expansion in foreign waters? Professor Tiralongo’s answer to this question points to climate change: warming sea temperatures greatly increases the survival chances of these species because it mimics their native tropical waters.
In addition to the warm waters, Professor Tiralongo elaborated that the swimming crabs compete with native crabs and other benthic species for food and habitat space. Over time, this interference can alter the food web and community structure, changing the whole ecosystem and disrupting fisheries.
Economic impacts on fisheries
While direct impact on economically important fish species is not yet detected, Professor Tiralongo highlighted that these invasives greatly reduce fishing efficiency by damaging fishing gear and becoming unwanted bycatch. “However, at present, the main impacts are likely indirect and much harder to quantify,” he explained. Such impacts may include subtle changes in benthic communities and food webs that can gradually affect fisheries’ productivity over time.
Monitoring
Professor Tiralongo recognized early on that crucial data for monitoring invasives did not only come from research vessels and labs, but from the local boats and docks as well. “Fishermen,” he went on to explain, “are typically the first observers of new species.” Beginning in 2012, Professor Tiralongo started cultivating relationships with local fishermen and recruited them as key partners in scientific monitoring. This collaboration created direct communication channels between fishermen and researchers. Professor Tiralongo did not stop at involving fishermen; he founded the AlienFish project in 2012, a citizen science project dedicated to studying and monitoring alien and rare species in Italian waters. The project is platformed on Facebook and managed through a group called “Fauna Marina Mediterranea,” administered by Professor Tiralongo. With more than 33,000 active users, comprising researchers, students, fishermen, and your average sea enthusiast, the “Fauna Marina Mediterranea” forms an invaluable database for researchers and the community alike. Since then, Professor Tiralongo has utilized other popular social media platforms to educate the public on marine science and fisheries, founding the “Ichthyo Project” on YouTube and Ichthyo_marine on Instagram. These accounts serve to educate the public on the latest Mediterranean-based marine science, fisheries reports, fish biology, and invasives.
Management challenges and options
Given that the reproduction rate of crustaceans like crabs is rapid, eliminating them completely is a near impossible challenge. Some fishing industries in the region adapted to certain invasives, turning them into assets: the Tunisian government established blue crab processing facilities and now exports them to S. Korea, where they are a delicacy. When asked if a similar adaptive approach would work in the context of swimming crabs (G. giardi), Tiralongo explained that their small size was not enough for direct human consumption on a large scale. “However,” he elaborated, “it could still be used in alternative ways… as raw material for fishmeal, aquaculture feed, and bait in fisheries; or even for the extraction of bioactive compounds such as chitin and chitosan used in biomedical, agricultural, or industrial applications.”
Ballast regulations and monitoring programs, while critical tools in the control of invasives, are not sufficient tools to prevent their expansion. Professor Tiralongo emphasized the need for rapid response systems for newly detected species. Early detection and rapid response systems are critical in the fight against invasive species in the region.
At present, monitoring and targeted removal through fisheries remains the most realistic strategy. Professor Tiralongo notes that it is also important to maintain and support healthy native communities, because native predators may naturally help limit the spread of invasive species when ecosystems remain balanced and functional. This reinforces the need for marine conservation in the Mediterranean in order to support optimal ecosystem health in the face of rapid change.
The reshaping of marine ecosystems
When asked about the single greatest lesson from his study of invasives, Professor Tiralongo emphasized the magnitude of their impact, not just on an ecological level, but on a socio-economic one as well: “Marine invasive species are not just a scientific issue, they are a visible sign of how human activities and climate change are reshaping marine ecosystems, with real consequences for biodiversity and livelihoods.” This implicates the health of coastal societies at large, demanding communal involvement on a deeper level. For this reason, Professor Tiralongo urges the continued citizen reporting of unusual species to scientists or environmental authorities. “Fishers, divers, and coastal communities play a crucial role in early detection; this is the reason, and the aim for which I founded the AlienFish project.”
The invaded sea: Dr. Francesco Tiralongo’s research on the invasive swimming crab (Gonioinfradens giardi) in the Mediterranean.
