Voluntary divers monitoring the Posidonia meadows at Cala Gració have reported an important change this year: no living Pinna nobilis nacras were observed during the latest surveys, after the species had been seen there in previous years.

The finding has raised concern among marine conservation campaigners, particularly amid continued high sea temperatures around Ibiza.

The annual monitoring programme organised through Xarxa Posidònia and supported by Salvem sa Badia de Portmany has now concluded its fieldwork for 2026.

At the end of September, eight volunteer divers carried out measurements at the two monitoring stations in Cala Bassa, while another four divers surveyed the two stations at Cala Gració.

The dives at Cala Gració and Cala Bassa took place on September 20 and 27 respectively. New volunteers also participated this year after receiving training in identifying Posidonia oceanica and carrying out measurements along the established transects.

No nacras observed at Cala Gració

The most notable observation at Cala Gració was the absence of Pinna nobilis during this year's monitoring.

According to Salvem sa Badia, nacras had been observed in previous years, but none were seen during the 2026 surveys.

The nacra, or noble pen shell, is the largest bivalve mollusc in the Mediterranean and is closely associated with Posidonia oceanica meadows.

The species has suffered a dramatic population collapse across the Mediterranean following a mass mortality event that began in Spanish Mediterranean waters in 2016. Spain subsequently declared Pinna nobilis to be in a critical situation, and it remains one of the country's most threatened marine species.

High water temperatures raise concern

Salvem sa Badia has highlighted the high temperatures recorded in the sea throughout the year as a particular concern.

A temperature logger was installed at the Cala Gració monitoring station in 2025, allowing researchers to collect continuous information on water temperatures at the site. The data gathered this year will contribute to the assessment of environmental conditions at the station.

However, the absence of nacras during the latest dives does not, on its own, establish that elevated temperatures caused their disappearance from Cala Gració.

The species is already subject to severe conservation pressures, and scientists have identified multiple factors affecting its survival.

The Posidonia meadows appear stable so far

The preliminary observations from this year's monitoring are not uniformly negative.

Although the detailed report will not be published until the first months of 2027, the initial observations suggest that the Posidonia meadows at the monitored stations are currently stable.

This distinction is important because the absence of nacras at Cala Gració does not mean that the Posidonia meadow itself has collapsed.

The monitoring programme assesses several aspects of the seagrass ecosystem, including the condition and density of Posidonia and other indicators that help track changes over time.

Monitoring expands at Cala Bassa

The 2026 programme has also expanded the monitoring work at Cala Bassa.

A second transect was established there through the collaboration between Salvem sa Badia and Xarxa Posidònia, meaning that both Cala Gració and Cala Bassa now have two monitoring transects.

The first two stations were established at Cala Gració in 2022, at depths of six and 15 metres. The first Cala Bassa station followed in 2023, while Salvem sa Badia funded the installation of a temperature logger at the Cala Gració station in 2025.

The local diving centre Arenal Diving continues to support the project by providing diving equipment, while Salvem sa Badia finances the individual monitoring outings. High Fidelity Collective also contributed audiovisual support during this year's fieldwork.

Why the finding matters

The disappearance of observed Pinna nobilis from a monitored location is significant because surviving populations of the species are now extremely limited.

Research published by the Spanish Institute of Oceanography and other scientific institutions has found that only small surviving populations remain in the Mediterranean after the mass mortality event that devastated the species.

For Cala Gració, the next step will be to analyse the full set of measurements collected during the 2026 monitoring campaign.

The detailed report expected in early 2027 should provide a clearer picture of the condition of the Posidonia meadows, the temperature patterns recorded at the station and whether the absence of nacras represents a temporary observation or a more significant change in the local population.

For now, the confirmed finding is clear: this year's monitoring team did not observe any Pinna nobilis nacras at Cala Gració, despite having recorded them there in previous years.