Unearthing the Hidden Biodiversity of Algarve's Caves: A Deep Dive into Vale Telheiro

The Enigmatic Cave Fauna of Algarve

The Algarve, known for its stunning beaches, also harbors one of the world's richest cave biodiversity. Recent studies reveal that the cave environments are becoming increasingly toxic, prompting an urgent investigation into this hidden treasure.

With a subtle scent of sea breeze, the morning air hints at the nearby Atlantic, concealing the intense southern heat of the day. Near Vale Telheiro cave in Loulé, a team of researchers prepares to delve into the earth's depths.

Navigating through dense Mediterranean brush, the spelunkers advance with difficulty, tangled in a seemingly endless labyrinth, swallowed by greenery before entering the mysterious depths through a narrow limestone crevice. Each member dons ARICA autonomous breathing equipment, similar to that used by firefighters, complete with masks and oxygen tanks.

This cave, long known to biologists and spelunkers, serves as an important habitat for unique cave fauna, but it has dangerously low oxygen levels, measuring only 17% compared to the usual 21% at the surface. Ana Sofia Reboleira, a researcher from the University of Lisbon's Center for Ecology, Evolution and Environmental Changes, leads the project, stating, "Carbon dioxide is occupying the space."

In November, measurements recorded CO₂ levels exceeding 40,000 parts per million, posing a risk of death. Methane levels and carbon isotopes were also studied, revealing that the methane presence is due to biological activity within the cave. The question remains: what is happening underground, and what does this contamination mean for this biodiversity paradise?

Image of the largest cave insect in Europe, Squamatinia algharbica, collected for further study.

Beneath the Algarve's glamorous surface lies a world of dark, humid caves rich in biodiversity yet threatened. In 2016, Science magazine classified the region as a global hotspot for cave biodiversity. So far, 25 troglobites (species adapted to cave environments) have been identified, with new discoveries emerging from each expedition.

In May 2024, a long-term project commenced to monitor local biodiversity, supported by the Belmiro de Azevedo Prize from the Foundation for Science and Technology. Over 36 months, fixed equipment will be installed, and numerous field campaigns will study the conservation and ecological restoration of Vale Telheiro cave. Meanwhile, the Loulé municipality has acquired the land above the cave as part of an initiative to transform this threatened area into a unique natural reserve.

Ana Sofia Reboleira emphasizes the significance of long-term initiatives, stating, "Studying three variables over 30 years is more relevant than 100 variables over three months." Chemical compounds and microbiome characteristics will be measured in hopes of understanding how life thrives under such adverse conditions. The project, which includes animal traps, sediment collection, and the installation of advanced sensors to evaluate the cave's atmosphere, could provide crucial insights for future expeditions to Mars.

Ana Sofia Reboleira equipped with ARICA gear to access the cave's most toxic areas.

Vale Telheiro is poised to become the first LTER cave in Western Europe (Long Term Ecological Research). Reboleira notes that environmental conditions have changed significantly, with oxygen levels plummeting and CO₂ levels soaring. Are these changes due to natural causes or human factors like urban development and illegal landfills? These ecosystems are vital for the quality of life, ensuring water purification that infiltrates aquifers and is consumed by the public.

Wearing boots, a helmet, and the characteristic jumpsuit of spelunkers, Ana Sofia reviews the numerous tools for studying the cave, including a slotter for laser mapping and various portable gas measurement sensors. Multispectral drones are also used for ecological characterization, detecting plant pathologies, and marking new cave entrances, aiding ecological restoration strategies.

Preparation of a stalagmite rock sample used in paleomagnetism studies.

These flights will serve as reference points for conservation efforts and can be compared with historical orthophotos available since 1950. Among all the high-tech devices, one simple tool stands out: an electric grinder. Its presence is justified by one of the most surprising studies in the project: paleomagnetism. By analyzing the stalagmites of Vale Telheiro, the team aims to study the evolution of Earth's magnetic field, looking for markers that could impact climate evolution.

Eric Font, a French researcher specializing in paleomagnetism, explains how magnetites are small magnetic particles carried from the surface by water, infiltrating and depositing in stalagmites according to the magnetic field orientation of the time. By dating these stalagmites, it is possible to reconstruct the magnetic North's position and the variations in Earth's magnetic field over millions of years. Inside the cave, the atmosphere is heavy, and each breath is laborious.

Eric Font researching stalagmite archives in the cave of the Earth Sciences Department at the University of Coimbra.

The larger the stalagmite, the greater the temporal record it holds, but it cannot be too large since it must be cut with minimal impact and brought to the surface through narrow passages. The Algarve is one of the regions with the highest cave biodiversity on Earth. Only moderately affected by glaciation effects, much fauna has colonized the caves. The abundant cave systems in the Algarve have thus developed a curious biodiversity, making such caves a precious testament to a tumultuous history.

Protecting a habitat requires not just scientific knowledge but also political will. In this case, both interests align: the Municipality of Loulé is committed to creating a natural reserve in Vale Telheiro cave, as part of a UNESCO candidacy for the establishment of the Algarvensis Geopark, which will also include the neighboring municipalities of Albufeira and Silves.

No truly solid nature conservation project is built without the support of local communities. This is evident in the choice of location for its public presentation: a local café, where residents learned about the municipality's plans. For Loulé's mayor, Vítor Aleixo, "the quest for a balance between nature conservation and economic development is a constant challenge, especially in a region like the Algarve. If the traditional development model does not change its trajectory, the problems will worsen."

Eric Font utilizing laser devices and a magnetic compass in Vale Telheiro cave before collecting a stalagmite sample.

In Vale Telheiro, another focus of study is the quantification of radon, a natural radioactive element resulting from uranium decay. This gas causes respiratory problems and can lead to severe illnesses by interfering with the structure of the genetic code, DNA. In the cave's deepest, least ventilated areas, concentrations reach 7,000 Bq/m3 – for reference, the legal maximum is 200.

In this isolated cave with limited air exchange, few animals are seen, but there is a great diversity of microorganisms. The study of the microbiome, composed of bacteria, archaea, and fungi that grow in the cavities, sediments, and clays, reveals that 30% of species are methanotrophic (feeding on methane). These microorganisms may have future applications in medicine, pharmaceuticals, cosmetics, or industry.

The giant pseudoscorpion of Algarve caves (Titanobochica magna), venomous and with powerful pincers, is the top predator in an ecosystem where the absence of light dictates species evolution.

As another field campaign concludes, the team prepares to ascend to the surface. Exhaustion is evident on their mud-streaked faces as they emerge from the underground, but the big smiles tell a different story. The Vale Telheiro cave harbors a unique natural treasure that urgently needs to be studied and preserved. The toxicity of its atmosphere has been rising in recent times, with consequences that are difficult to quantify, making the current long-term scientific research project by the University of Lisbon even more pressing, opening a window of knowledge into a vast underground ecosystem that extends across several regions of southern Portugal.