During the ninth Nature Observation Marathon, held June 6–7 as part of the Nature Creativity Festival, nearly 200 observers made 10,199 nature observations over a 24-hour period. In the process, they discovered two species that had never before been recorded in Estonia.

More than 400 nature enthusiasts and scientists took part in the Nature Observation Marathon, documenting biodiversity across 36 observation sites in Estonia and Poland. They recorded a total of 2,683 species or higher taxa. All observations, except those involving strictly protected species, are publicly available through the University of Tartu Museum of Natural History and Botanical Garden's eBiodiversity data portal.

Fungus and oomycete

This year's marathon resulted in the discovery of two species never before recorded in Estonia: a tiny sac fungus that lives on the bark of pine branches, collected by Ave Suija, and goosefoot downy mildew, an oomycete species collected by Tõnu Ploompuu.

The microscopic sac fungus, found at the Kaberneeme observation site, was identified by University of Tartu mycologist Kadri Pärtel after several days of analysis as Venturioscypha nigropila.

Described only a few years ago, the species grows on the bark of pine branches, often among algae and near lichens. It belongs to the order Helotiales, the same order as the common green cup fungus. It was discovered during nighttime insect trapping. A voucher specimen of the species will be preserved in the fungal collection of the University of Tartu Museum of Natural History.

Goosefoot downy mildew (Peronospora variabilis) was found at the Nedrema observation site. Although it was once classified as a fungus, it actually belongs to the phylum Oomycota. Oomycetes are a group within the stramenopiles and are evolutionarily more closely related to algae than to true fungi.

Stramenopiles are neither plants nor fungi. Some nevertheless resemble one or the other: diatoms and brown algae carry out photosynthesis like plants, while oomycetes grow and form thread-like filaments similar to fungal mycelium. Genetic research has shown that stramenopiles form a distinct evolutionary branch among eukaryotes. Goosefoot downy mildew is a stramenopile, but not an alga; it belongs to the fungus-like oomycete lineage within the stramenopiles.

Estonian biodiversity waiting to be discovered

With this year's discoveries, the Nature Observation Marathon has now led to the first records of four species in Estonia: the gall mite Fragariocoptes setiger, which lives on creamy strawberry and was discovered in 2021; the fungus gnat Mycomya denmax, discovered in 2022; and, in 2026, the fungus Venturioscypha nigropila and the oomycete Peronospora variabilis.

"The Nature Observation Marathon shows every year how much can be discovered by working together. This year's two new species confirm that Estonia still harbors biodiversity waiting to be discovered and that every observation has the potential to be scientifically significant," said Margit Hirv, coordinator of the Nature Observation Marathon observation sites.

The highest number of species this year was recorded at the Nedrema observation site in Pärnu County where participants documented 846 species — the highest total ever recorded at a single observation site in the history of the Nature Observation Marathon. It was followed by the Kaberneeme observation site in Harju County with 638 species and the Viidumäe observation site on Saaremaa with 597. Individually, the most taxa entered into the database were recorded by Andrus Jair (519), Kaido Nei (501) and Tõnu Ploompuu (491).

Among plants, the most frequently observed species were lesser water-parsnip (63 observations), Lysimachia europaea (50) and wild chervil (46). Among birds, the most frequently recorded were the chaffinch (52 observations) and the common blackbird (46).

Ahead of the marathon, the third Nature Observation Mini Marathon for schools was held in the spring, attracting more than 1,100 students from 28 schools. Together, they submitted 3,002 nature observations and recorded more than 1,000 species across Estonia.

At several schools, species experts assisted participants during the Mini Marathon by helping identify plants, birds and insects and introducing students to nature observation methods. Observations were submitted using PlutoF GO, a mobile app developed by the University of Tartu Museum of Natural History and Botanical Garden.

The largest number of Mini Marathon observations came from Kohila in Rapla County where students from Kohila High School, guided by teacher Triinu Tõrv, recorded 267 taxa. Second place went to students from Tallinn High School No. 32 who documented 263 species at the Kõiguste field station on Saaremaa under the guidance of teacher Helen Orav-Kotta. Third was the Kohtla-Järve Forest Park observation site in Ida-Viru County where students from Kohtla-Järve High School, led by teacher Krista Piir, recorded 181 taxa.

The Nature Observation Marathon is a citizen science initiative based on the international BioBlitz format. During the event, natural scientists and nature enthusiasts work together to identify as many living species as possible within a defined area over a set period. The event is organized by the University of Tartu Museum of Natural History and Botanical Garden in cooperation with partners and volunteers across Estonia and elsewhere in Europe. It is supported by the Environmental Investment Center.

The 10th Nature Observation Marathon will take place June 5–6, 2027. The Nature Observation Mini Marathon will run from May 3 to June 4, 2027.

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