Spanish seas are increasingly hosting species that are not native to their ecosystems. The count of exotic species around Cantabria is approaching six hundred, spreading through the Mediterranean and the Atlantic. A multidisciplinary team led by the Spanish Institute of Oceanography and the Center for Advanced Studies in Blanes, along with researchers from the Autonomous Universities of Alicante, Malaga and Madrid, examined exotic species recorded in Spanish marine waters from 1800 through the end of 2021 and mapped the main routes by which these species arrived.
The rise of non native and invasive species poses a clear risk to biodiversity. These newcomers often compete with local organisms for space and food, altering how marine communities function.
This study, published recently in Variation, synthesizes data from diverse sources, including scientific journals, monitoring programs and citizen science efforts. It emphasizes that close collaboration with national and international experts was essential to verify the species list and establish an updated baseline of alien and invasive species in Spain’s coastal waters. This effort is attributed to Lydia Png of the Balearic Islands Oceanographic Center, who led the study as its first author.
In total, the research identified 574 species. About 35 percent were located in the Western Mediterranean, 34 percent along the Bay of Biscay and the Iberian coast, and 31 percent in the Macaronesia region.
Non native species have become more visible along the shores over the last two decades. They include invertebrates, primary producers such as macroalgae and microalgae, vertebrates, and even pathogens.
More than half of all documented non native species have established populations along these coasts, and roughly one in ten are classified as invasive, with a higher prevalence in the Western Mediterranean.
Shipping as a major vector for arrival
Maritime transport stands out as the primary route introducing alien species, whether via ballast water, hull-associated organisms, or other transport-related environments. This pathway accounts for about 77 percent of species recorded in the three examined regions.
A second key entry route relates to aquaculture activities, including contaminated nursery material or parasites in farmed animals. This pathway accounts for more than 10 percent of the total records, with the highest impacts seen around the Bay of Biscay and the Iberian coast.
The findings show that the introduction of exotic species is a multifaceted process driven by regional context, existing entry pathways, and environmental changes over time. The growing footprint of human activity in marine environments has propelled the emergence and spread of alien species, posing a significant threat to biodiversity and ecosystem integrity.
Over a thousand exotic species in the Mediterranean
The Mediterranean and its entire basin are among the most densely populated seas globally. More than 1,000 exotic species from other ecosystems have found new homes there in recent years, a trend highlighted in a recent overview. Climate change is also shaping these patterns, as noted by conservation organizations observing shifts in the basin.
This outcome results from a blend of factors shaping Mare Nostrum, from climate-driven changes to intense maritime trade in a geostrategic region. The natural characteristics of this semi-closed sea influence how species disperse. While the influx of exotic animals and plants rises, the risk grows for endemic Mediterranean species that have long defined the region’s uniqueness.
The Mediterranean is warming at a faster pace, with temperature increases running about 20 percent higher than the global average. This rise already exceeds pre-industrial levels by around one and a half degrees since 1880, according to assessments of climate risks in the region.
Reference: a key study with DOI 10.3390/d15050630. This work consolidates evidence from multiple sources and presents a coherent baseline for policy and science in the region.
For further details, environmental authorities can be contacted through official channels and institutional offices.