Rising Seas Are Opening a Vast New Front Line for Marine Invaders

As the ocean creeps inland across the world’s coastlines, scientists are warning that the water itself may become a delivery system for some of the planet’s most troublesome species. A new study published in Nature Ecology & Evolution projects that more than two-thirds of the coastal land expected to be flooded by rising seas this century will be environmentally suitable for 122 non-native marine animals that are already established in adjacent waters. The finding reveals a previously unexamined dimension of climate change: sea-level rise is not merely drowning habitat, it is actively creating fresh territory that marine invaders are poised to colonize, adding a new and largely unmanaged front to the global battle against biological invasions.

The research, led by Zhixin Zhang of the South China Sea Institute of Oceanology and Xuan Liu of the Institute of Zoology at the Chinese Academy of Sciences, together with an international team spanning Japan, Hungary, Italy, Finland, Canada and the United States, set out to answer a deceptively simple question. Climate change is redistributing life on Earth, and ecologists have invested heavily in forecasting how warming temperatures will shift the ranges of non-native species on land and in surface waters. But one pathway has been almost entirely overlooked: when the sea floods coastal land, that newly inundated ground becomes potential marine habitat, and the species best positioned to occupy it are the non-native animals already living in the neighboring ecoregion.

To quantify that risk, the team combined several layers of geospatial and ecological data. They mapped the coastal areas projected to fall below future sea levels under the SSP2-4.5 emissions scenario, a moderate pathway of future warming, using high-resolution coastal elevation data refined through machine-learning approaches such as CoastalDEM, which corrects the canopy and building errors that plague standard elevation models. They then modeled the climatic and environmental niches of 122 established non-native marine animals, drawing occurrence records from the Global Biodiversity Information Facility, the Ocean Biodiversity Information System, the Atlas of Living Australia, the National Biodiversity Network Atlas and published literature. Marine environmental predictors came from Bio-ORACLE version 3.0, a data suite aligned with the latest CMIP6 Earth system models, and the analyses were executed at scale on Google Earth Engine.

The modeling framework was deliberately rigorous. The researchers used ensemble species distribution modeling, combining multiple algorithms and correcting for the sampling biases that notoriously distort marine occurrence data, since records cluster around ports, research stations and popular diving sites. Spatially structured cross-validation was applied to avoid overfitting, and threshold-selection methods were used to convert continuous habitat-suitability scores into binary predictions of where each species could plausibly establish. The team then aggregated these predictions across all 122 species and overlaid them onto the inundation maps, producing a global picture of where flooded land would be simultaneously reachable and environmentally congenial to invaders waiting just offshore.

The headline result is striking in its scale. By the middle and the end of this century, approximately 290,000 to 470,000 square kilometers of newly inundated coastal land, an area larger than many European countries, is projected to be environmentally suitable for the 122 non-native marine animals already established in adjacent marine ecoregions. In other words, over two-thirds of the land the sea reclaims will, on paper, be colonizable by invaders. The geography of this risk is not uniform. The study identifies the estuaries of mid-latitude regions as particular hotspots, a pattern that reflects both where inundation will be extensive and where the environmental conditions of flooded land, including salinity regimes and temperature ranges, will match the tolerances of established non-native species.

Estuaries have long been recognized as the most heavily invaded of marine environments. Historical work on systems such as San Francisco Bay documented an accelerating invasion rate decades ago, and the reasons are structural: estuaries concentrate shipping, aquaculture and human population, they are naturally disturbed and productive, and their brackish waters filter out some native competitors while tolerating a broad range of colonists. The new study effectively extends this logic into the future. As sea-level rise pushes saline water up rivers and over coastal plains, it will convert farmland, wetlands and urban periphery into a mosaic of shallow marine and estuarine habitat, and the species that dominate nearby ports and bays will have first access to it.

History offers sobering precedents for what happens when the sea suddenly floods land. During the wartime inundation of Walcheren island in the Netherlands between 1944 and 1945, deliberately flooded polders were rapidly colonized by marine organisms, an episode documented in contemporary natural-history records. More recent studies of managed coastal realignment projects, in which seawalls are deliberately breached to restore saltmarsh, show that newly flooded habitats are colonized quickly by benthic macrofauna, and that the identity of the earliest arrivals can shape the community for years to come. Ecologists call these priority effects: the species that gets there first can lock in advantages that later arrivals struggle to overcome. If non-native crabs, ascidians, mollusks or worms reach flooded land before native species do, the resulting communities may remain invasion-dominated indefinitely.

The wider stakes are considerable. Biological invasions are already among the leading drivers of biodiversity loss worldwide, and their economic costs, estimated in the hundreds of billions of dollars annually, are rising. Invasions also interact with public health, with research showing that invasive species can facilitate the emergence of zoonotic diseases. Climate change amplifies these pressures by shifting species ranges, opening Arctic shipping routes, and, as this study demonstrates, physically constructing new habitat at the land-sea boundary. Yet most invasion risk assessments and most national biosecurity frameworks do not currently treat sea-level-driven inundation as an invasion pathway at all. The authors argue that this blind spot needs to be closed, and that sea-level rise scenarios should be built into invasion risk predictions as a matter of standard practice.

There are also practical implications for how coastal adaptation is planned. Around the world, governments are weighing managed retreat, wetland restoration and realignment schemes as defenses against flooding, and these interventions will determine which lands are allowed to flood and how. The study suggests that the timing and design of such projects matter ecologically, not just hydrologically. Rapid colonization by natives, or management actions that suppress invaders during the vulnerable early window after inundation, could tip newly created habitats toward desirable ecological trajectories. Conversely, leaving flooded land unmanaged and connected to heavily invaded port waters could produce exactly the priority-effect lock-in that favors invaders. Early-warning systems, targeted monitoring of inundation zones, and proactive management strategies will be critical as coastal lands continue to be reclaimed by the ocean.

The researchers have made their occurrence records, habitat-suitability predictions and analysis scripts openly available through the South China Sea Ocean Data Center, allowing other teams to scrutinize and extend the work. Like all projections, the estimates carry uncertainties, from the trajectory of future emissions to the ecological details of how individual species respond to newly flooded terrain. But the central message is difficult to escape: the same rising water that threatens homes, infrastructure and farmland is also quietly redrawing the map of biological invasion. As the authors conclude, the world’s coastlines are becoming a new invasion front, and recognizing that front now, before the water arrives, may be the last affordable chance to manage what comes ashore with it.

Subject of Research: Projected colonization of sea-level-rise inundated coastal lands by established non-native marine animals

Article Title: Global sea-level rise will create a new biological invasion front

Article References: Zhang, Z., Yan, Z., García Molinos, J., Yu, G., Bede-Fazekas, Á., Carlton, J. T., Kass, J. M., Kulp, S. A., MacIsaac, H. J., Mammola, S., Ding, L., Du, Y., Jin, L., Li, X., Liao, W., Xin, Y., Lin, Q., & Liu, X. (2026). Global sea-level rise will create a new biological invasion front. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-026-03181-4

Image Credits: AI Generated

DOI: 10.1038/s41559-026-03181-4

Keywords: sea-level rise, biological invasions, marine invasive species, climate change, estuaries, species distribution modeling, coastal ecosystems, biodiversity, inundation, biosecurity, Nature Ecology & Evolution, priority effects