A microscopic glimpse of la Pedriza

Microepics sampling campaign was launched in La Pedriza last spring, in the natural granite basins or pits (pilas), on the iconic boulder El Cerdito, a favorite landmark for hikers near Cantocochino. On the top of this massive boulder there are three natural basins, like the largest that we picture below. As well as floating debris (breadcrumbs, sunflower seed shells, orange peel, sweet wrappers, assorted plastic rubbish, and so on) and a smelly organic sludge forming a several centimeter thick layer at the bottom, we noticed the water was bright green and very dense.

El cerdito
pilancon cerdito1
pilancon cerdito2

Microscopic analysis revealed a massive culture (about 1 million per millilitre) of the photosynthetic protistan flagellate Haematococcus droebakensis, shown in the micrograph at 1000 times magnification. Photosynthetic flagellates, essential components of the phytoplankton, are capable of fixing CO2 into organic compounds and are fundamental (the producers) to the trophic chain of an ecosystem. But as in this case, massive proliferation due to excess nutrients (eutrophication), can lead to a damaging impoverishment of biological diversity in an ecosystem.

Protistan flagellates like Haematococcus, are not just interesting for ecosystem function; the organic pigment astaxanthin (carotenoid) is also extracted from some of them. This compound is a potent antioxidant, and is used industrially as food for fish and crustaceans. Astaxanthin is also used clinically to treat conditions like Alzheimer’s, Parkinson’s and for cancer prevention.

In the less human-impacted weathering pits we also found other photosynthetic flagellates, such as Stephanosphaera pluvialis, though in less abundance than the Haematococcus in the El Cerdito, and accompanied by a microscopic community that is more varied and healthier. S. pluvialis is a relatively little known protist and is the only species described from this genus. It has been observed in aquatic media and also in garden birdbaths. For this reason it is thought the species might be transferred from place to place on bird plumage.


Here protists have shown us that they can be a sign of an imbalance in an ecosystem and that anthropogenic contamination can have serious consequences for the structure and dynamics of the ecosystem. We have to look after all the aquatic habitats in the National Park. The granite pits in la Pedriza, as we will see in the Microepics blog, are exceptionally diverse in microscopic life, sustain an abundant invertebrate mesofauna, and are used by mountain goats as natural watering holes.

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