Citizen observations reveal the early flowering of Posidonia oceanica in northern Catalonia and the expansion of tropical species such as the Atlantic parrotfish and the sargassum nudibranch.
The fifth edition of the BioMARató, coordinated by the EMBIMOS Group of the Institut de Ciències del Mar (ICM-CSIC), has achieved an unprecedented milestone: obtaining marine biodiversity data from every section of the Catalan coastline. For the first time since the project began, the entire coast has been fully covered thanks to citizen participation, enabling the completion of an observation map with spatial resolution never before attained.
This full coverage, structured in 10 km² sectors, has been accompanied by a notable increase in both participation and results. Between May and October, more than 520 people contributed 94,000 observations to the MINKA platform, and 2,040 species were identified, nearly 300 more than in 2024. With these new contributions, the BioMARató Catalonia now accumulates over 380,000 observations and 2,870 documented species since 2020.
“The BioMARató demonstrates the potential of citizen science to generate information at a spatial and temporal resolution that a conventional scientific project could hardly achieve,” highlights Jaume Piera, researcher at EMBIMOS (ICM-CSIC) and coordinator of the initiative. “This complete coverage brings us closer to building key tools for the study and long-term monitoring of biodiversity, such as large-scale biodiversity maps, essential operational products for improving the management of our seas,” he adds.
The initiative, which compiles all observations on the MINKA citizen science platform, has relied on the collaboration of the Catalan Federation of Underwater Activities (FECDAS), the association Oceánicos, Plàncton Diving, Anèl·lides – Serveis Ambientals Marins, and Xatrac, particularly in organizing underwater photography, snorkelling, and diving outings across the provinces of Girona, Barcelona and Tarragona.
New records along the Catalan coast
Among the most notable findings of the 2025 BioMARató is the first record in Catalonia of the crab Afropisa carinimana, observed for the first time by participant Enric Badosa in the area of Canet de Mar. This elongated, pale-coloured species from the family Pisaidae originates from tropical Atlantic coasts. This first observation constitutes both the first record in Catalonia and the northernmost record in the Mediterranean.
In addition to this discovery, the BioMARató 2025 incorporated 159 new species into its catalogue, most of them coastal plants. Although many had been previously documented in Catalonia, this is the first time they have been observed within the BioMARató event, reinforcing the initiative’s role in expanding biodiversity knowledge and reducing information gaps along the Catalan coast.
Expansion of Tropical species
Citizen monitoring has enabled the detection of the continued expansion of tropical and subtropical species along the Catalan coastline. One prominent example is the Atlantic parrotfish (Sparisoma cretense), which increased from a single record in 2024 (in Blanes) to ten observations in 2025, distributed between Tarragona and Girona.
“We’re seeing it more and more often during shallow dives,” explains Lisa Derksen Castillo, a diver participating in the BioMARató. “Its reddish colour is unmistakable, and until recently it was unthinkable to find it here.”
The sargassum nudibranch (Scyllaea pelagica) was again observed, after being first detected in the western Mediterranean during the 2023 edition. This year, it was reported 18 times. This nudibranch species, a small, shell-less mollusc with yellow-green hues, lives on floating masses of the genus Sargassum, which are typical of tropical and subtropical waters such as the Caribbean and the Gulf of Mexico. Its increasing presence in the western Mediterranean suggests an expansion of its distribution range driven by rising sea temperatures.
Other consequences of ocean warming
The rising sea temperature can alter not only species distributions but also biological cycles and natural behaviours. A recent example is the unusually early flowering of Posidonia oceanica, documented this year in Alt Empordà: first in Cala Montgó (L’Escala) on 7 September, and a week later, even farther north, in Cadaqués, recorded by citizen observer Ferran Roure.
“Until now, the earliest flowering events reported in the BioMARató had been recorded in the province of Tarragona, so seeing them this early and this far north is surprising, likely a response to the accumulated thermal stress of this summer,” explains Xavier Salvador, MINKA technician.
Additionally, four individuals of dusky grouper (Epinephelus marginatus) were recorded showing possible signs of infection by betanodavirus, a pathogen that affects multiple fish species and whose incidence increases in warmer waters.
Analyses by ICM-CSIC confirm that recent years have been characterised by persistent warming and multiple marine heatwaves, with particularly intense episodes in September 2022, October 2024 and the second half of September 2025. According to data from the L’Estartit oceanographic time series (maintained with support from ICM-CSIC), this year also saw a significant episode at the end of June and early July, with a record of 26.8 °C and anomalies of +5 °C in the Catalan–Balearic basin, temperatures typical of August.
Even so, August 2025 was not as extreme as some recent summers, such as 2023. Overall, temperatures in 2025 remained above the 90th percentile for much of the summer and even the preceding winter. This pattern can be consulted in the ICATMAR marine heatwave maps.
The Year of Stingrays and Mantas
The year 2025 was also particularly rich in observations of stingrays and mantas, with over 390 records of elasmobranchs representing 14 different species across the three Catalan provinces. Notably, the spiny butterfly ray (Gymnura altavela), a species historically rare in Catalonia, was recorded 15 times this year, including several sightings in the province of Girona, where it had never been detected in previous BioMARató editions.
These cartilaginous fishes respond unevenly to global ocean warming: while some species tend to move closer to the coastline, with warmer waters, such as mantas (family Mobulidae) and the common stingray (Dasyatis pastinaca), others, such as skates (family Rajidae), may retreat to deeper and colder areas.
Despite the increase in records, a higher number of observations does not always indicate a greater abundance of individuals; it often reflects increased observer activity or improved coastal coverage thanks to citizen participation. This is why contextualizing these observations and maintaining long-term monitoring is so important: to accurately understand real changes in species populations.