The Mediterranean Sea Forensics

In ancient Greece, the gorgons were monsters, with snakes for hair and the superpower to petrify anyone who dares to look at them. In Greek myth, the drops of blood that fell into the sea as Perseus victoriously transported Medusa’s head to Athens gave the name to what later became knowns as a type of coral in the Med called red gorgonians.

Today, 60% of the biomass of these once abundant coral colonies that have thrived in the Med for centuries, has been severely impacted in the space of the past few decades, as sea water temperature has risen by two degrees above average, according to the Centre for Mediterranean Environmental Studies (CEAM).

“What is coming is like going from a forest of hundred-year-old trees to a meadow of grasses. The landscape down there is like watching the passing of a huge forest fire," says marine biologist Joaquim Garrabo as he emerges, takes off his air tube mouthpiece and says in Catalan: "Almost all of them are dead". The breeze is cool and gentle, the Mediterranean is dark blue, crystal clear and calm, the clouds shade the sun, it is 25 degrees at the surface.

All the oceans are connected; what happens in the Mediterranean has an impact everywhere: "corals have the function of capturing CO2, because if you have a system that is working properly, such as the marine phanerogams, it is also acting as a carbon sink because it is helping to mitigate climate change by taking CO2 out of the atmosphere".

Reflecting on the state of the colonies he just witnessed as he emerged from the dive, he exclaims: “Coral colonies are completely dead or half dead. Massively. You see the sequence, of seeing some colonies that are very much alive, centuries old, and the next year they're gone. For more than 100 years they have lived peacefully and now they are suffering.”

In these 25 years, Garrabou has observed that at least 90 species of different groups of corals, gorgonians, sponges, algae, phanerogams, marine bryozoans and other invertebrates of different species have been affected by a mass mortality event, sometimes more than 30 species at the same time.

The biologist

Garrabou 57 years old, shy and friendly, has several metaphors to explain what he has just seen. For example "they are like zombies, zombie gorgonians". He has been diving in this same spot for thirty-four years and each time he does so, he sees less and less living coral. Every year, from the beginning of spring until the end of autumn, he and his team of researchers from the Institute of Marine Sciences in Barcelona get on a boat at least once a week in the port of L'Estartit, in the north of the Costa Brava, and go less than a kilometer out to sea towards the Medes Islands: an archipelago of giant rocks up to 50 meters deep, on whose walls nest the red gorgonian, an autochthonous type of coral, among other species of coral.

Garrabou's team goes down at three or four different points—on this trip they go to the walls of some islets called Pota del Llob, La Vaca and Lascons—where they leave markers hanging from the red gorgonians. They have them numbered. Now they are going to sample between ten and thirteen gorgonians at each site. The tags they are looking for have been there since 2014, when they did a study of sex differences between corals. There they discovered that at the same temperature, each gorgonian reacted differently. Most of them, when the heat rises, die. This year is worse than ever because the Mediterranean is reaching temperature peaks of
almost 30°C: it is far exceeding the historical average.

a small piece of red coral hold by pliers
Red coral is one of the indicator species of the effects of marine heat waves. These organisms visibly suffer necrosis (death). This coral, as its name indicates, has an intense red color. During periods of extreme heat, part of its organisms die, losing their characteristic color and giving rise to white spots on their structure, Spain, 2023 / Credit: Bruna Casas for RUIDO.

Garrabou's research group is on "Ecology and resilience of benthic ecosystems in a changing ocean" and has 14 researchers. They go diving in groups of three or four and do it as if they were in an office. For example, at a depth of 20 meters, they write down the state of each gorgonian colony on an acrylic board with a marker pen. They locate the corals thanks to a printed and laminated map that they hold in one hand and never let go of. Between air tubes and underwater cameras, you can see them take out a pair of scissors to cut small pieces of samples, put them in a plastic bag that they opened before they went in, put the piece of coral away and close the bag. It doesn't always work, but usually the samples stay inside. They also carry a torch to see the color of the coral because underwater everything looks blue or grey or black.

Do the gorgonians you see "half dead" have much longer to live?

They may have years left, but ecologically they are already extinct, because the function they used to perform is no longer fulfilled, they can no longer reproduce or they reproduce much less. As soon as a strong storm comes... as the adhesion system does not work, we will go one day and those colonies will no longer be there. Even if they haven't died 100% because they will fall to the bottom and that's it. We have been seeing this since 1999, when the first major mass mortality event affected mainly the coasts of France and Italy, then another one in 2003 and more and more often in more places.

The forest

There are no red gorgonians in the seas of English-speaking countries. Therefore, they may have been misinterpreted as "sea whip". Technically they should be called "Paramuricea clavata". Whatever they are called, they are important because of their structural function: living things that are essential for other living things to stay alive. They form habitats. They live for others.

Red gorgonians are trees with branches more lilac than red, with tiny individual polyps. They need to stick to a hard surface, in this case the wall of the Medes, as some other species stick to mud or sand. The polyps of a gorgonian colony are linked together by an inner layer of germs, which socialise the food, making it possible for one part of the colony to use the nutrients it has captured to feed another. The polyps are white pinchers that emerge from the branches of the gorgonian and whose hairs are like little hands to capture food. Their favourite foods are algae, organic carbon particles and zooplankton.

Mediterranean gorgonians thrive to the extent that they do not compete with algae, which is why they are deeper than tropical corals, and because they do not need to photosynthesize. In addition, there are more nutrients in this sea than in the tropics and they do not need anyone, any symbionts. A colony of gorgonians can live for a century and be half a metre tall. Alive. Dead, it is flaccid and the polyps are like pus granules. When the water is heated, the coral retracts, like an unwatered plant. Underneath the red gorgonian there is a whole community of sponges, of tunicates that find refuge there. If the structure disappears, many of these associated species are lost and there tends to be more algae, more organisms with rapid life cycles, which do not provide complexity to the sea. That impacts on fish, for example, which need that complexity to eat and reproduce. The gorgonians that are at 12 meters deep you won't even see them anymore, the deeper you go, the more chances you have of finding live gorgonians. The sea is dying from the top down.

The variation

Sandra Ramirez, 32, previously studied in Cali and Hong Kong. Now, thanks to a grant from the Colombian government, she works with Garrabou in Catalonia because he is the most representative ecologist on this subject, but also with Jean Baptiste Ledou in Porto, Portugal, who is one of the best in marine population
genetics. His focus is on cnidarians, the group that includes corals. She is now studying not only gorgonians, but also red corals, and also studied programming: all biologists need to know this language to load the information they collect into R+Study.

photo of a female scientist in her lab on the left and of corals on the right
Sandra Ramirez works on transcriptomics: the set of ARD (ribonucleic acid) molecules. She works and researches in Garrabou's team on the effects of marine heat waves on the DNA of the target species Gorgonia and red coral, species affected by rising sea temperatures, Spain, 2023 / Credit: Bruna Casas.

Why does one coral or gorgonian hold up and another does not?

At the genetic level not much is known, I am doing a classification first that has not been done before because there is a lot of variability, a lot of factors and temperature events are more frequent and longer. I am studying two populations over the course of a year, it is daring to extrapolate that to the whole of nature.

Sandra works with something called transcriptomics, which is based on one of the RNA (ribonucleic acid) molecules, which is not DNA (deoxyribonucleic acid). We all have DNA and RNA, the former identifies us, but RNA is a molecule that is synthesized from DNA and generates a function; and this occurs from the environment. It is what allows us to understand ourselves in context, it shows that the environment determines us: the functions change according to the environment we are in.

After the dive, once on dry land, Sandra looks for a shady corner to transfer the samples from the plastic bag to a small tube containing a DNA retardant, which stops the transcription of the cells, time stops passing for the gorgonian, then the scientist labels the tubes with identification codes and puts them in a picnic cooler, as soon as she arrives at the Institute of Marine Sciences she goes down to the basement, which smells like a fish market, and stores them in a fridge at -72 degrees Celsius.

Are you going back to Colombia when you finish your thesis?

I don't know, if I don't, I'll have to pay back part of the scholarship, we'll see, there are all kinds of corals there, many more populations, more species to study.

Although tropical corals are more resistant to heat, they are also dying massively in areas where they used to survive. In Florida, USA, colleagues from Garrabou are documenting that so far this summer the corals have already lost colour.

The sale

In modern times and until recently, gorgonian coral, like Mediterranean red coral and other cnidarians, has been massively extracted to make necklaces, jewelry and ornaments. They are readily available on the internet in Europe, delivered to your door: 45 cm of undyed and untreated red coral cost less than 80 euros. Even in a jewelry shop in the center of L'Estartit, a kilometer and a half from where Garrabou's team will dive, they still sell coral jewelry.

Nuria, 29, one of the team's biologists, is very indignant about this. She says that recently she felt like she had seen a horror film: "I dived down and suddenly I saw pure bone, on one of the walls it was like an ivory cemetery". When the gorgonians die, first they turn black, then they turn pale, and begin to cover themselves with small algae that look like green and white cobwebs: the color of necrosis. Nuria remembers that later, when they returned home, they passed by a souvenir shop in the city center and said: "Oh, to see this beautiful coral, do I have to pass by here, since I work underwater? Besides, it takes a year of my salary to buy it." Nuria has been immersed in the sea since she used to go on holiday to Menorca with her family, but she is from Catalonia. She has photos of herself as a child with the tourist boat from L'Estartit, also called Nuria, which still passes by here, right on top of them while they take samples. First she fell in love with the sea and then with corals, while she was in a team that went to underwater caves she saw gorgonians and said: "I want this". For her, science is the sea. Nuria says that scientific life is sometimes difficult to understand: a lot of travelling, a lot of time in the lab, a lot of thesis, a lot of field work. She says that if a boyfriend makes her choose between him and science, she will always choose science. The rest of the team listens and nods.

The temperature

There are more days with higher temperatures than before. It is not that the winter is warmer but shorter. The season in which the red gorgonian feeds the most, spring, lasts less and less. So, like the millennials, with fewer resources, the red gorgonian prioritizes survival and not reproduction. Moreover, the reproduction process is slow, they only start to reproduce when they turn ten years old. The climate is going at their own pace and they are going at their own pace, the climate is going to eat them.

A study published in July 2023 in the journal Nature found a proportional relationship between rising temperatures and the death rate of people in Mediterranean countries. In 2022, 61,000 people died of heat-related causes in Europe. At the Barcelona Institute for Global Health they say that given the trend, the continent will face an average of more than 68,000 premature deaths each summer by 2030 and more than 94,000 by 2040. Underwater, the equation is not much different:

"What we have seen with gorgonians is that when you go above 24º or 25º they suffer...they suffer a lot...that is...when we do experiments here we put them in at 25º and after two or three days they have necrosis," says Garrabou.

Garrabou's team not only goes down to hang up gorgonian plates and take samples, but also to place thermometers, which look like little torches, near the coral populations. The devices have a chip that Garrabou periodically goes down to replace and which serve to store the information for a period of time. That information is then uploaded into the system and can be viewed online at, a system of which Garrabou is the coordinating scientist. The redder the graphs, the whiter the weevils. When a colleague titled a paper a few years ago "The boiling of the Mediterranean", Garrabou told him: "Macho, you've gone three times too far". Today I would say "you've gone too far".

Image of underwater thermometers on a table
To monitor marine heat waves, Garrabou's scientific team has installed underwater thermometers at various points along the coast and at different depths that record the temperature at that point every hour, Spain, 2023 / Credit: Bruna Casas. 

The ice

Until not so long ago, those who could dedicate themselves to marine science came from socio-economic elites who did not need to live on a researcher's salary. Garrabou's team has to contend with working conditions that in Spain are more expensive than in some neighboring countries (the per diems they receive have not increased since 2002) and that often, despite being researchers, they have to spend 70% of their time on administrative matters. Garrabou says that when he decided to return to Spain after 10 years of research in France, he didn't even ask how much he was going to earn, because "this is not the profession to make money, but I want to live with dignity". They feel privileged to be masters of their time and to work in nature, but it doesn't seem fair to them that they have to accept precariousness simply because they do what they like or because there are few who can enter the career: "The scientific community lives in a parallel world to what the real world is, you know, this can only be endured out of enthusiasm".

Joaquim Garrabou's mother has always said that he learned to dive before he learned to swim, that from an early age he played with goggles and a backpack snorkel. What interests him is life under the sea, which is why he does all this and more: he leads the network of "Sea Watchers".

Garrabou says that the entire Mediterranean cannot be protected, but protected areas can be created, and that if we don't have an ocean in good condition, all these capacities will be lost.

He is not a pessimist, he says, but a realist. He thinks that nature takes time, but regenerates itself, if given the chance. He says we need to "take action to reduce greenhouse gas emissions and our dependence on fossil fuels much more forcefully". For him the impact is in focusing and getting science in tune with the outside world. He says that for this to change, everything has to be done, "the way we live is the cause", but that we have to start somewhere. 

This story was produced with support from Internews' Earth Journalism Network. It was first published in France 24 on 29 August 2023 in Spanish; this version has been adapted by EJN's Mediterranean Media Initiative.

Banner image: To monitor marine heat waves, the main enemy of corals, Garrabou's scientific team installs underwater thermometers at various points along the coast and at different depths that record the hourly temperature at that point, Spain, 2023 / Credit: Bruna Casas for RUIDO.

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