The study, led by Hassiba Zediri of Badji Mokhtar Annaba University together with colleagues in Algeria and Italy, surveyed nine temporary ponds across the urban and peri-urban zone of the Annaba Plain between 2021 and 2024. Over four consecutive growing seasons the researchers recorded an astonishing 364 vascular plant taxa belonging to 214 genera and 72 families. For ponds sitting on the doorstep of a major industrial city, that level of floristic diversity is remarkable, and it confirms what conservationists have long suspected: temporary ponds act as refuges for rare and endemic plants even when surrounded by roads, fields and buildings.

The botanical signature of these ponds is unmistakably Mediterranean. Nearly 63 percent of the recorded flora belongs to the Mediterranean chorotype, the group of plants whose natural distribution is centred on the Mediterranean Basin. Equally telling is the life-form spectrum: 44.2 percent of the species are therophytes, annual plants that complete their entire life cycle within a single wet season, germinating as the ponds flood and setting seed before the water retreats. This boom-and-bust strategy is the classic adaptation to temporary ponds, where the timing and duration of flooding are as important as the water itself.

What makes the Annaba ponds genuinely special, however, is their conservation value. Six of the recorded species are protected under Algerian legislation, and five appear on the IUCN Red List. Among them is Rumex algeriensis, a dock classified as Critically Endangered, a plant found in the wild almost nowhere else. The presence of such species in waterbodies that are routinely trampled, grazed and drained underscores how much biodiversity can persist in small, unofficial wetlands that fall outside the usual network of protected areas.

To understand what structures this vegetation, the team measured 37 variables at each site, spanning soil chemistry, water quality, hydrology and physiography. These included organic matter, porosity, total carbon, total limestone, electrical conductivity, particle-size distribution of sand, silt and clay, pH, pond depth, surface area, perimeter, altitude, slope, exposure, and the intensity of grazing, fires and agricultural activity. Water samples were analysed for dissolved oxygen, temperature, total suspended solids, total phosphorus, nitrites and nitrates, both in situ and in the laboratory, following French and ISO standards.

A Principal Component Analysis of these variables revealed four distinct site clusters, and the factors that separated them were strikingly simple: salinity and electrical conductivity, pond surface area, and distance from the urban centre. In other words, the ponds sort themselves along two axes that ecologists care deeply about, how salty and how hydrologically variable the water is, and how strongly the city presses against each site. The first axis of the PCA alone accounted for 44.25 percent of the variance, with the second adding 27.48 percent, together explaining the bulk of the environmental variation across the nine ponds.

The researchers then went a step further, applying an Outlying Mean Index niche analysis to test whether plant species actually respond to these gradients rather than being distributed at random. The answer was a clear yes: species distribution was significantly driven by the environmental gradients, with a statistical significance of p below 0.05. The first axis, carrying 44.25 percent of the variance, reflected salinity and the hydrological regime, while the second axis, at 27.48 percent, opposed the low-altitude peri-urban ponds to the waterbodies of the urban plain. Each plant community, in effect, occupies a measurable niche defined by salt, water and geography.

From this analysis four plant community types emerged, each telling its own ecological story. A halophytic community thrives where salts accumulate, dominated by salt-tolerant species capable of coping with high electrical conductivity. A helo-hydrophytic community occupies the wetter zones, combining marsh plants with true aquatic species that depend on prolonged flooding. A psammophytic community colonises sandy substrates, its members adapted to loose, fast-draining soils, while a meso-xerophytic community inhabits the drier margins, tolerating moderate to pronounced drought stress. These four assemblages map neatly onto the environmental clusters, demonstrating that even small ponds contain sharply differentiated vegetation zones.

The darker side of the findings concerns what is filtering this diversity away. Urbanisation, agro-pastoral disturbance and salinisation emerged as the dominant ecological filters, selecting for stress-tolerant generalist species while eliminating the sensitive and endemic taxa that give Mediterranean wetlands their conservation value. Salinisation is a growing global threat to water resources in arid and semi-arid regions, and in coastal plains like Annaba it interacts with urban expansion and agricultural intensification to push plant communities toward a simplified, ruderal state. Rare species such as Rumex algeriensis sit precisely on the losing side of this filter, clinging to the few habitats where salinity and disturbance have not yet tipped the balance.

The authors argue that their results make the case for urgent conservation action in the Annaba Plain, where the remaining wetland habitats are shrinking under relentless pressure. Because the study identifies the specific gradients that control plant distribution, salinity, hydrological regime, pond size and urban proximity, it gives managers concrete levers: protect the hydroperiod of the ponds, curb salt inputs, limit grazing and fire around the most diverse sites, and prioritise the peri-urban low-altitude ponds that harbour the most distinctive communities. Temporary ponds are among the most threatened wetland ecosystems in the Mediterranean, yet this four-year census shows they can still shelter hundreds of species, including plants found nowhere else on Earth. Whether they continue to do so will depend on decisions taken now, in a plain where the city, the salt and the water are converging on the same fragile ground.

Subject of Research: Edaphic and hydrological factors structuring wetland plant communities in Mediterranean urban temporary ponds of the Annaba Plain, Algeria

Article Title: Edaphic and hydrological determinism of wetland vegetation in Mediterranean urban waterbodies: A case study from the Annaba Plain (Algeria)

Article References: Edaphic and hydrological determinism of wetland vegetation in Mediterranean urban waterbodies: A case study from the Annaba Plain (Algeria). (n.d.). https://doi.org/10.1007/s44473-026-00219-0

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00219-0

Keywords: temporary ponds, wetland vegetation, Mediterranean flora, salinity, urbanisation, Annaba Plain, Algeria, plant communities, biodiversity conservation, Rumex algeriensis, hydrological regime, ecological filters