The increase in temperature in the Mediterranean is killing the red and white gorgonians on the Costa Brava

The marine heat waves of recent years are taking their toll on life in the Mediterranean.

An example of this is that the gorgonians that have historically been seen on the Costa Brava between 15 and 30 meters deep are dying.

The situation "is very serious," say the experts, who predict that in fifteen years they will only be found at more than 30 meters, with the impact that this entails both at an ecological level, with loss of biodiversity, and at the level of reduced attractiveness of natural heritage for the thousands of divers who come to contemplate the richness of this coast.

To find out the real impact on the health of gorgonians, in September and October of last year, marine citizen science days were held with dives by volunteers and scientists.

The results have allowed us to conclude that all populations show mortality.

In the red gorgonian in more than half of the cases there is severe involvement (more than 60% of gorgonians affected) and in the white gorgonian it rises to 80%.

The “

sessions are part of the activities of the CorfunTED2021-131622B-I00 project, financed by the Ministry of Science and Technology and the European Union (with Next Generation funds), in collaboration with the Sea Observers and coordinated by the marine biologists Cristina Linares from the University of Barcelona (UB) and Joaquim Garrabou, from the Institute of Marine Sciences of the CSIC.

With the help of 70 volunteers and 6 diving centers, the impact of heat waves on more than 10,000 white gorgonians (

) and red gorgonians (

) was evaluated, both in Cap de Creus and on the Baix Empordà coast. , between Begur and Palamós.

The northern area is more affected, that is, a higher percentage has dead tissue due to thermal stress.

After theoretical training out of the water, volunteers and scientists submerged in 17 different points and carried out 95 censuses where they categorized the populations depending on the percentage of gorgonians affected.

This species, which is also a great attraction for the diving sector, was previously found at 10 and 15 meters deep, now they are all dead or very affected and only some healthy ones are found beyond 30. The study has concluded. that in the first 20 meters the severe affectation predominates, between 20 and 30 meters a moderate affectation and it is not until reaching beyond 30 meters that populations with low affectation are found -less than 30% of the gorgonians affected-.

Volunteers carry out a census on the state of the gorgonian on the Costa Brava.cristina linares

Coralligen is an endemic habitat of the Mediterranean formed by the accumulation of calcareous algae with a very high associated biodiversity - with more than 1,600 species that represent 10% of Mediterranean marine species.

On the Costa Brava we can find it from 15 meters deep.

It stands out for providing a high structural complexity that provides shelter to many species, the main ones being gorgonians, sponges, calcareous algae, bryozoans or ascidians.

The increase in water temperature, one and a half degrees for half a century with maximum peaks of 27.5 degrees Celsius in August 2022, has caused many species of the coralline community, such as gorgonians, corals, mollusks or the same algae, suffer worrying mortalities.

"These species begin to die at 25 degrees, the maximum temperature at which they can live has already been exceeded, we can no longer do anything about this, we can act on other impacts that we can manage, such as reducing the effect of the trawling and diving,” he points out.

It all adds up.

The risk of gorgonian loss

“Gorgonias act like trees in forests, they offer shelter to a large number of species, which is why their degradation generates the loss of important ecosystem functions and services,” warns Linares.

In the areas evaluated, the white ones are more affected because they live at a shallower depth.

“We believed that it would resist more than the red one due to its biological characteristics, and that has not been the case,” says the expert.

Both are long-lived, slow-growing species.

The red one can live a century and grows more slowly than the white one, which has half the life expectancy.

The scientist highlights that “the data obtained in this study can be extrapolated to the rest of the Mediterranean.

The difference is that the impact had not reached the Costa Brava and we began to detect it relatively late, around 2016 and 17. In France and Italy it was in 1999.

This year the idea is to repeat the study with the network of collaborators in the rest of the Catalan coast, more unknown.

“The presence of gorgonians is a sign of good health of the sea and high biodiversity.

They don't live where there is pollution,” explains Linares.

He believes that "there is a lack of information about where there are gorgonians in Barcelona - they know that an orange grows - and we know few places where there are in Tarragona."

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