Mediterranean temporary ponds are life-giving oases

If you spot pools of water in an unusual place, in dry or sandy areas for example, it is likely to be a temporary pond. Although water is an ephemeral presence, it is vital to maintain Mediterranean temporary ponds as valuable oases of biodiversity.

Mediterranean temporary ponds provide shelter for some unusual creatures and rare and endangered species that need to be understood and protected. However, recognition of their importance and the conservation of these valuable and ephemeral habitats have not always been priorities.

“The importance of these ponds has been underestimated,” says José Teixeira, a researcher at the Interdisciplinary Centre for Marine and Environmental Research (CIIMAR), at the University of Porto, and national coordinator of the Ponderful project, who points out that “research has shown that ponds play a key environmental role that is completely disproportionate to their small size”.

This same notion is also emphasised by biologist and teacher Paula Canha, who has a Master’s degree in Conservation Biology from the University of Évora and is passionate about this habitat which, at first sight, can be “not so appealing and easily ignored”. It is important to understand the “very special genetic heritage of these ponds, which contain living creatures that are able to withstand changing environmental circumstances and extreme conditions, making them superheroes”.

In fact, temporary ponds are home to more biodiversity than all other bodies of fresh water. In addition, they provide valuable environmental services, such as the management and supply of surface water, amongst others.

All ponds are important, whether they are in rocky, sandy, or grassy areas, but of the various types of temporary ponds, those that form part of the Natura 2000 Sectoral Plan — priority habitat 3170 – Mediterranean temporary ponds, under the Habitats Directive, are of particular importance. These ponds are rare biotopes, which are typical of regions with a Mediterranean climate that experience summer dry spells and times of great water shortages. They form in shallow depressions, are very dependent on rainfall and alternating periods of flooding and drought.

The flooding phase of these Mediterranean ponds lasts about four to five months (during winter and spring), which is longer than for other accumulations of rainwater. In addition, these temporary ponds function as a sort of “sponge”, absorbing water when there is too much of it and storing moisture in the soil, releasing it during the dry season.

In order to learn more about this high-priority habitat, the LIFE Charcos project, coordinated by the Liga para a Proteção da Natureza (the League for the Protection of Nature), took place between 2013 and 2018. As well as studying and monitoring these ponds and raising awareness of the importance of these invaluable natural habitats, this project has produced a Good Practice Manual for the Conservation of Mediterranean Temporary Ponds, which proposes sustainable management measures enabling the protection of these habitats to be reconciled alongside human activities.

In the Mediterranean temporary ponds located on the coastal plateaus of southwest Alentejo and the Vicentine coast, an inventory has been compiled of the typical flora and fauna species that have adapted to the specific features of this habitat. The presence of numerous plants of high conservation importance was noted. These include the fern Pilularia minuta and Caropsis verticillatoinundata, both classified as “vulnerable” according to the Red List of the Vascular Flora of Mainland Portugal. It was the same for the fauna species, and various endemic and rare species stand out. Worthy of special mention are the Triops vicentinus, considered “endangered” by the International Union for Conservation of Nature’s Red List, and the Lusitanian parsley frog (Pelodytes atlanticus), both endemic to southwestern Portugal.

The deterioration in water quality, the disappearance of plants typically found in these ponds, and the emergence of other anomalous plants (such as agricultural weeds or invasive plants like acacias) are all indicators of the degradation of temporary ponds.

Conservation and climate change: challenges for the coming years

Ponds require different conservation measures depending on their specific characteristics. When temporary ponds are found on private land, which might be used for agriculture or livestock, Paula Canha explains that it is necessary “to ensure that conservation measures are adapted to what kind of yield can be expected from that land”.

Generally speaking, measures may include protecting the “impermeable layer that causes rainwater to accumulate there”, and also “avoiding deepening the pond”, to conserve naturally occurring fauna and flora. Lastly, in order to conserve ponds that are low in nutrients and organic matter (or oligotrophic), the water should be protected from fertilisers or livestock droppings.

For Paula Canha, climate change is “one of the biggest concerns” when it comes to temporary ponds. In 2021, “the ponds did not even experience a flooding phase”, she says. And although this has occurred in the past, at this point there is no understanding of what changes might take place in this habitat during increasingly frequent and severe periods of drought. The behaviour of ponds in the face of climate change is therefore unpredictable, “especially in the more ephemeral ones, which have a smaller water column”. Moreover, when ponds are not sufficiently waterlogged, they give rise to woody fleabanes (Dittrichia viscosa), weeds whose presence requires these habitats to be “actively managed”.

And what do we still need to understand about temporary ponds? For Paula Canha, “probably a lot, because these are habitats where everything is so tiny that it’s very easy for something to elude us, and there are certainly things that still remain to be discovered”, she concludes.

Did you know that Mediterranean temporary ponds…

• Are home to highly diverse plant communities? A small pond can be home to 80 species, reveals researcher Carla Pinto-Cruz, from the University of Évora. Some, such as the Eryngium corniculatum, are indicator plants for the “quality” of these habitats, making it possible to determine their state of conservation.
• Are home to creatures such as bizarre large crustacean branchiopods, whose name means “gills on the feet”, i.e., breathing organs located on their feet. Some are considered “living fossils” as they have remained unchanged for many millions of years. In addition to the tadpole shrimp, Branchipus cortesi and Cyzicus grubei, among others, belong to this group. The latter only exists naturally in the Iberian Peninsula, where it is an endemic species. Its body is protected by two oval shells identical to those of a bivalve mollusc, hence its common name.
• Are an oasis for more than two dozen vertebrates. At least 13 species of amphibians (frogs, salamanders, and newts), four species of reptiles (turtles and snakes), and seven species of mammals (mice and bats) are dependant on these habitats and their surroundings for various essential functions, from searching for food and water to reproduction, says the LIFE Ponds project. The pygmy marbled newt, the European pond terrapin, and Daubenton’s bat are examples.
• Did you know that Mediterranean temporary ponds had 106 referenced habitats on the southwest Portuguese coast (in 2016), located on the heaths of the Odemira municipality and the Vila do Bispo plateau. However, it is not known exactly how many Mediterranean temporary ponds there are in Portugal. However, it is acknowledged that their numbers are declining, due to misinformation and human pressure. In fact, it is estimated that in recent decades they may have been reduced by 50%.