Posidonia prairies in the Balearics. | Ultima Hora


The Posidonia meadows in Balearic waters are in "good, but not optimal" condition, according to the 2017-2019 report by the Posidonia Monitoring Network.

All 39 fixed stations throughout the Balearic Islands are monitored periodically and the initiative is supervised by the Directorate General of Fisheries & Marine Environment and funded by the Tourism Tax.

The results were presented on Friday by Joan Mercant, Director General of Fisheries & Marine Affairs, Antoni Grau, Head of the Marine Resources Service and the Project Coordinator Elena Burgos.

"This follow-up is important because it gives references to the evolution of Posidonia prairies which are so important and the report's results are not excellent, but they are good,” said Joan Mercant.

The Monitoring Network was launched in 2002 by the Directorate-General for Fisheries & Marine Environment, but was interrupted between 2012 and 2017.

According to project data, 36 of the stations were established during the first period, three have been incorporated since then and one has been lost.

Mercant stressed that the project is possible thanks to the voluntary involvement of various Institutions, Diving Clubs and Diving Groups, whose task has been to measure the density of posidonia bundles and the coverage of the available substrate.

Posidonia Prairies

The maximum densities were detected in Son Bou in Minorca and Cala Lliteres in Majorca, with values above 1,100 bundles per m2.

The minimum values of between 270 and 300 bundles per m2, were in Cala Figuera in Majorca and Fornells in Minorca.

Substrate maximum values of between 60 and 70% were recorded in Son Bou, Tirant in Menorca and Caló de s'Oli in Formentera.

Minimum values of between 10 and 20% were recorded in Fornells, Cala Sant Esteve, Cala Blanca in Minorca and on the islet d'en Caragoler in Ibiza.

The temporal trends between the start of monitoring and the present were positive, or stable, in the vast majority of stations, both in terms of density and coverage.

Project Coordinator, Elena Burgos, indicated that the report described the general state of conservation as "good or very good" at 27 stations, "regular" at 9 stations and "bad" at 3 stations and stressed that the most affected prairies are in the Bay of Palma in Majorca.

Most stations are stable or in the process of recovery and the density of posidonia is gradually increasing, while at others density and coverage has decreased in recent decades.

On balance, since the beginning of the Monitoring Network there's been a net gain in density and coverage in the posidonia prairies in the Balearics.

Burgos says the biggest recurring threat to the prairies that are in poor and regular condition is their proximity to large ports and sites where wastewater is discharged into the sea.

The objective is to monitor the stations that are in poor condition and check the effects of water temperature.

Invasive Algae

Divers have also detected invasive algae throughout the Balearic Islands, especially the 'Acrothamnion preissi' and 'Caulerpa cylindracea' species.

Detecting invasive algae at the monitored stations is extremely relevant in determining its expansion in the archipelago and what effect it's having on the posidonia prairies.

The project shows that between 2017 and 2019 no live nacre was detected, but between 17 and 19 deaths were found at a total of 7 stations.

The Posidonia Monitoring Network has recorded the water temperature at a depth of 15 metres in the Isla del Toro Marine Reserve which was one degree warmer in August 2018 than in 2019.