Most of the specimens of one of the sponges most common and abundant Catalan coastthe Ircinia fasciculatathey have dead during the last weeks in points of the coast of Girona, a phenomenon that could be taking place in the country as a whole. So far it has been documented in the Costa Bravaand experts attribute this to the extraordinarily high temperatures that the sea has registered this summer.
The mass death of Ircinia fasciculata, a species that lives in shallow and which is highly visible along the entire coastline, has been confirmed in recent weeks by any observer who has noticed the white markings on the rocks and the presence of dead specimens on the bottom. The one who has documented it more systematically, at least in Catalonia, is the group of Observadors de Mar, a group that has volunteers especially in the Cap de Creus area, but also in Colera and Tossa, and which has already played a relevant role in the location of the few nacres that have been found you live on the Empordà coast. The group works coordinated by a joint project of the Institute of Marine Sciences, the CEAB and the CSIC.
The first volunteer who reported that Ircinia fasciculata had the characteristic whitish marks of an infection was Edward Marques, which detected the first affected specimens at the end of August in Roses, in the Almadraba area. The progression was very fast. On September 20, out of a count of 25 individuals in the same area, 15 were already dead or sick. On October 22, out of a count of 28, only 4 apparently healthy remained. On October 27, those who had not died were all affected, the vast majority seriously.
At the other end of the Girona coast, the group’s observer in Tossa de Mar located 156 sponges in the Ses Ileltes area on October 2, of which 121 were affected and 35 appeared healthyyes In the same section, the day October 15 located only 23 specimens, of which only 6 were apparently healthy. The sponges that were missing from the first count were on land, piled by the dozens against the rocks, which presented the characteristic white marks left by sponges when they die and are shed.
The data is still insufficient, but it can be pointed out that mortality exceeds 80% in the first meters of depth, where they are most abundant. Deeper down they are also affected, but observers have not counted them. Despite the fact that there are no other counts on the Mediterranean coast, experts consider that the phenomenon is most likely occurring everywhere, especially in areas where the sea temperature has been higher.
A similar case was studied in Catalonia in 2008 and 2009
Connoisseurs deduce that this case is like previous ones and, in particular, like one from 2008 and 2009 that was studied in Catalonia. In 2009, for example, mortalities of over 80% were documented at points throughout the Mediterranean, and not only Ircinia fasciculata were affected, but also other species. In Catalonia, the incidence in Tossa and the Medes Islands was studied. They believe that it cannot be considered extraordinary that an anomalous rise in temperatures generates a great loss of specimens, but they are alarmed that these episodes become more frequent and they fear that the capacity for natural regeneration is not sufficient to prevent the disappearance of the affected species in the medium term.
The scientists Maria Jesus Uriz, Emma Cebrian, Joaquim Garrabou and Enric Ballesteros, of the University of Girona, the Center for Advanced Studies of Blanes-CSIC, and the Institute of Sea Sciences-CSIC, studied in depth the mortality of 2008 and 2009 in various parts of the Mediterranean, and came to the conclusion that the cause trigger had been the impact of abnormally high temperatures on the population of cyanobacteris.
Death begins with the disappearance of the cyanobacteri
According to the 2009 study, it was lethal that the temperature remained very high not only on the surface, but to a significant depth, and for a prolonged period of time, beyond the peak of summer. The maintenance of very high temperatures throughout the water column occurs when, at a torrid environmental temperature, a long period of calm sea is added that prevents the renewal that occurs when the waves carry colder water from the deep zone to the most superficial layer. This is what has also happened this summer, with temperatures over 27 degrees maintained for many days and little waves.
In that study, published in 2011, they were able to verify that the most affected sponge was Ircinia fasciculata due to the effect that temperature has on the cyanobacteria that live in symbiosis with this invertebrate. A cyanobacteri is a microscopic organism halfway between a bacterium and an algae who lives from the photosynthesis and that produces more than half of the oxygen in the oceans. Its role in the planetary balance is decisive. With Ircinia fasciculata they form such a close symbiosis that, in some specimens, the bacterium contributes half of the animal’s mass. When the temperature interferes with the bacteria’s ability to photosynthesize, it dies and leaves part of the tissue free, which also weakens the sponge. In the abandoned area, any other type of opportunistic invasive microorganism can be located that spreads throughout the body of the invertebrate and, finally, can end up killing it.
The work of the aforementioned researchers is not conclusive about what type of bacteria would be the invader, nor about what role it has in the final death of the sponge. They consider that the animal ends up dying for the sum of everything.
“We don’t know what effect it will have on the ecosystem, but it will have”
Maria Jesús Uriz, one of the authors of the work, a researcher at the Center for Advanced Studies in Blanes and a pioneer in marine biology research in the State, explains that the death of all these specimens does not have to mean the disappearance of the species to the area, because these episodes are known and are normal, but if they occur more and more often, this invertebrate animal will not have the capacity to recover. Others, neither.
Regarding the effect that the absence of Ircinia fasciculata can have on the ecosystem as a whole, he states that “the disappearance of a species always has side effects on others, sure. In this case, we do not know exactly what they are, but we will end up seeing it. For example, there are nudibranchs that feed on these sponges, and this will make it difficult for them to survive.”
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Another of the authors of the study, Joaquim Garrabou, a researcher at the Institute of Marine Sciences, considers that this episode of mortality must be framed in the effects that the extreme temperatures of this summer have had on the ecosystem as a whole. He points out that there have also been very important reductions in white and red gorgonia, red coral and Cladocora caespitosa; other sponges such as Cacospongia scalaris, Ircinia oros, Sarcotragus spinosulus and Petrosia ficiformis; briozous such as Pentapora fascialis; molluscs such as Spondylus gaederopus and Lithophaga lithophaga, and calcareous algae such as Mesophyllum expansum.
Garrabou, who admits and regrets that the specific causes of all these phenomena will not be studied in detail because there are no resources to do so, considers it very important to understand that some of the bacteria that live with us in the sea have their behavior altered due to extreme temperatures, and that this modification can turn them into pathogens that cause infections in exactly the same way as invading organisms from the Atlantic or the Roig Sea would. “If we were to look for pathogens in the organisms that are dying, we would surely find them,” remarks the scientist. And as Iosune Uriz concludes, what makes these episodes fearsome is that, if global warming causes extreme temperatures like this year’s to be repeated often, deaths will become extinctions.