A new research, recently published in the journal Science of the Total Environment (STOTEN,) defined four key points that would explain what happened in Seno Reloncaví, in the Region of Los Lagos, where the greatest loss of the Chilean salmon industry was recorded.
Daniela Jofré, IDEAL Center. In 2016, the largest aquaculture disaster in the world was generated. Factors such as unusual weather conditions and the presence of a potentially ichthyotoxic microalgae killed thousands of salmons in the Seno Reloncaví area, in the region of Los Lagos. This event is considered the highest farmed fish mortality ever recorded, with estimated losses of 100,000 metric tons of fish and more than 800 million dollars, 15% of the estimated annual production for that year in Chile.
The Reloncaví sector, north of the Chiloé Island, is gradually recovering from the effects of the ichthyotoxic flagellate Pseudochattonella verruculosa on aquaculture centers. In parallel, an interdisciplinary team of scientists dedicated themselves to studying the factors that triggered this environmental disaster. What really happened in that year?
An investigation, headed by Dr. Jorge Mardones, a marine biologist at the Fisheries Development Institute (IFOP) and the Center for Dynamic Research in High Latitude Marine Ecosystems (IDEAL Center) of the University of Chile (UACh) addressed various parameters to define the causes for what happened in 2016: oceanography with particles dispersion through mathematical modeling, biochemical aspects (e.g. production of potential toxic agents such as free fatty acids and reactive oxygen substances), in vitro cell culture of the microalgae to determine growth rates and life cycle and histology of fish affected during the bloom.
The work in STOTEN defined four key points that would explain the fish mortality at that time: 1) extreme weather conditions (El Niño Godzilla of 2016); 2) a microalgae bloom with a complex life cycle and that developed cell densities that were probably underestimated during the growing period; 3) poorly prepared monitoring programs and mitigation systems, for the situation; 4) and a very low water exchange rate, which probably aggravated the situation of Seno Reloncaví and its surroundings.
The researcher assures that year, the weather conditions that occurred in southern Chile were unusual. “2016 was extremely hot due to the El Niño phenomenon, further enhanced by the Pacific Anticyclone, which moved southward, causing the waters to be held in that sector for a longer amount of time due to the South-North component of the winds. The anomalies of an environmental climatic event that raises the temperature are much more noticeable in semi-closed ecosystems,” he comments.
These environmental anomalies produced a strong stratification of the water column, which for several weeks stimulated the development of the bloom of P. verruculosa in Seno Reloncaví, an organism that circumvented the monitoring systems of the aquaculture industry. “Between 2004 and 2015, the taxonomy of this flagellate was largely unknown, it was even identified as the genus Chattonella. This cell has great morphological plasticity during its life cycle, so it takes a lot of experience to be able to investigate it,” explains Dr. Mardones.
The lack of information at that time on P. verruculosa led to another of the points presented by the study: The mitigation strategies of salmon farming were inefficient before the bloom of this organism. Mitigation action such as bubble curtains and/or aeration by upwelling did not have the expected effectiveness; the transfer of fish and the cessation of feeding were the only measures that helped to slightly shovel the massive mortalities.
However, according to the study, a factor of potential relevance to what happened in 2016 is related to the fact that Seno Reloncaví, like several fjords present in the Los Lagos Region, has a low rate of water exchange. “These ecosystems tend to retain water for a period of between 120 to 200 days, unlike other sectors where the exchange of water is more dynamic,” explains Dr. Mardones.
The team of scientists estimated the water exchange rate of the entire sector of the Chiloé island and the north of the Aysén Region, finding similar characteristics in the Riñihue and Comau fjords, the same places where harmful algae bloom developed in the year 1988 and in April 2021, which opens important questions about the role this variable plays in events of these characteristics.
“It is important to highlight that these phenomena are highly complex, so in order to explain a flowering of this magnitude, it is necessary to go beyond simple answers that attribute responsibility to a particular variable. The aim of this research is to lay the foundations to continue studying what happens with these biological processes, especially in a context of climate change and at the level of industrial production,” concludes the researcher.
Read the study here.