Overseas
For years, it was a low-visibility fish. It lives close to the seabed, blends in perfectly, and closely resembles species that are already well known. The result is simple: it can be there without being noticed. Today, however, the diamond lizardfish (Synodus synodus) is emerging from the margins—at least in the data. A scientific study documents its presence between Greece and Italy, with evidence consistent with populations that are now established in the Mediterranean.
The research was published in Mediterranean Marine Science and conducted by a team from the Sicily Marine Centre of the Anton Dohrn Zoological Station. The observations concern 34 individuals recorded at 18 different sites, spread across the Cyclades Islands, Crete, and Linosa in the Pelagie archipelago. These were not sporadic encounters. Most of the specimens observed were adult fish, a key indicator of structured populations that are likely already stable.
That Synodus synodus remained under the radar for so long is hardly surprising. It is a demersal predator, strictly associated with the seabed, and relies heavily on camouflage as a core survival strategy. It can remain motionless for long periods, blending into rocky or sandy substrates, striking only when prey passes within close range. This behaviour is compounded by its strong resemblance to a species already well known in the Mediterranean, Synodus saurus. Differences do exist, but they are subtle and difficult to detect without expert observation.
This combination helps explain why the diamond lizardfish may have been present in the Mediterranean Sea longer than previously thought, without being recognised as such. It is a clear example of how marine biodiversity can change quietly—even in one of the most monitored seas in the world.
The study also clarifies another crucial point. Synodus synodus does not fall into the category of alien species directly introduced by human activity, such as the blue crab or the lionfish. Instead, it is classified as a neo-native species—an organism that has naturally expanded its range as environmental conditions became more favourable. In this case, the decisive factor is rising sea temperatures, which are making the Mediterranean increasingly similar to the subtropical environments where the species originated.
Ocean warming is accelerating a profound reshuffling of Mediterranean biodiversity. New ecological niches are opening up, previously marginal species are finding space, and long-established ecosystem balances are being gradually redefined. The diamond lizardfish fits squarely into this process: not a dramatic arrival, but a coherent signal of an ongoing climate-driven transformation.
As for potential ecological impacts, the researchers take a cautious stance. At present, it is not possible to determine with certainty how the establishment of Synodus synodus might affect native fish communities or local food webs. For this reason, the authors stress the importance of long-term monitoring.
The study also highlights the limits of traditional observation methods. Marine environments are complex and difficult to survey continuously and comprehensively, especially when dealing with cryptic species or low-mobility fish. To address these gaps, scientific research is increasingly complementing direct observation with new analytical tools.
This is where the European project CAMBioMed comes into play. Bringing together partners from across the Mediterranean, the initiative aims to harmonise monitoring programmes and improve early detection of alien and neo-native species. Among the most promising approaches is environmental DNA (eDNA) analysis, a technique that allows researchers to detect a species through genetic traces released into the water, even in the absence of direct sightings.
The story of the diamond lizardfish tells of a Mediterranean Sea that is changing quietly. Identifying these signals, interpreting them correctly, and placing them within a solid scientific framework is now essential for understanding the evolution of marine biodiversity and supporting more informed decisions in fisheries management and marine resource governance.
Have you spotted unusual fish or “out-of-place” species while diving, snorkelling, or fishing? Even a single observation can help us understand how the Mediterranean is changing. Leave a comment with location and depth, or share the article with those who spend time at sea—the more observations circulate, the clearer the picture becomes.
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