A research group from the Torre de la Sal Aquaculture Institute (IATS) of the CSIC, dependent on the Ministry of Science, Innovation and Universities (MICIU), has recently published a study in the journal Mediterranean Marine Science that identifies the cause of the death of large number of groupers in the marine reserve of the Columbretes Islands (Castellón) during the summer and autumn of 2023. Genetic analyzes identified a genus of viruses known as Betanodavirus, which infects some fish and causes nervous necrosis in them, such as responsible for the high mortality of this typical Mediterranean species that is threatened by overfishing.
During the summer and autumn of 2023, many dead grouper specimens were detected floating in the waters of the Columbretes Islands marine reserve, a small archipelago of volcanic origin located almost 60 kilometers from the coast of Castellón. This species (Epinephelus marginatus) is very vulnerable to fishing and is increasingly scarce on the coasts of the Mediterranean due to overfishing. Marine reserves like Columbretes are one of the main tools for its conservation, since fishing there is prohibited.
Upon detecting this mortality, the IATS-CSIC research group led by Diego Kersting took samples from some affected individuals, which were subsequently genetically analyzed to identify the cause of the disease. «The analyzes showed that it is a Betanodavirus, a genus of RNA virus that infects some fish and causes nervous necrosis in them, which is consistent with the symptoms that the sick groupers presented: disorientation, problems swimming and loss of control of the swim bladder,” explains the CSIC researcher.
Betanodaviruses usually affect fish raised in aquaculture facilities, but they can also affect wild populations. “Although the results obtained do not allow us to determine the origin of the virus, since there are many other species that can transmit it, this mortality shows that isolated coastal areas such as these islands can also be affected by these events,” says Kersting.
Columbretes, sentinel of climate change
The study, in which researchers from the Miguel Hernández University of Elche (UMH) participate and has the collaboration of the marine reserve guards, who have helped in taking samples and detecting affected individuals, concludes that this type of diseases can have serious consequences on the populations of these already highly vulnerable fish. In this sense, fish censuses carried out before and after the mortality show a significant drop in grouper density, which could reach up to 90% in some areas.
“The work highlights the great importance of continuous and long-term monitoring of vulnerable marine organisms in areas such as the Columbretes Islands, which allows the early detection of this type of events,” says Kersting. Thus, the Columbretes Islands marine reserve is considered a sentinel zone of global marine change. “In it we have been developing studies related to the impact of warming, invasive species and certain diseases for more than two decades,” recalls the CSIC researcher.
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