New harmful flowering detected in the fjords of Patagonia

A new event of Harmful Algal Blooms (HABs) was recently recorded in the Hornopirén area, in the Los Lagos region, produced by the flagellated microalgae Heterosigma akashiwo, the only species of the Raphidophyceae group described so far in Chile, reported the Dynamic Research Center for High Latitude Marine Ecosystems (IDEAL).

With the aim of understanding the causes of this phenomenon, an expedition led by Jorge Mardones, researcher at the Center for Harmful Algae Studies (CREAN) of the Fisheries Development Institute (IFOP) and the Center for Dynamic Research of High Latitude Marine Ecosystems ( IDEAL) of the Austral University (UACh) focused on analyzing that flowering from different disciplines: ecology, oceanography, toxicology, bioptics, fish histology, meteorology and aerial overflights.

The campaign gained special relevance in a context in which Chile has become a focus of global attention in relation to the occurrence of HABs, particularly due to the important aquaculture production in Patagonia. In recent years, HAB events have been characterized by being more intense and long-lasting, with the salmon industry being the most affected during episodes of this type. Intense and prolonged droughts seem to increase the risk of these episodes, especially in northern Patagonia, due to the alteration of the biophysical system in fjords and canals, stimulating the growth of certain types of microalgae.

Researchers Javier Paredes and Ana Flores (both from IFOP) participated in the expedition; Andrea Corredor (IDEAL Center); Marco Godoy (CIBA, San Sebastián University); René Garreaud (CR2, University of Chile); Pamela Urrutia (MOWI) and Ximena Rojas (INTESAL).

Restricted flowering

Observations at the site showed a flowering very restricted to the Hornopirén area, with intense brownish-brown patches around Isla Pelada in the Cholgo channel.

“The maximum abundances of microalgae reached 55,000 cells/mL on the water surface no more than one or two meters deep. At greater depths, the abundance of microalgae decreased drastically to only hundreds of cells per milliliter,” explains researcher Ana Flores.

Likewise, during this event and for the first time during a FAN event in Chile, researchers deployed three radiometers to measure the spectral signal of light in the atmosphere-water interaction and collect water samples to characterize the photosynthetic pigments of H. akashiwo. This set of measurements will allow obtaining the spectrum of light that is reflected by the ocean after interacting with the HABs, data that will later be associated with the reflectances of the satellite sensors to adjust an algorithm that in the future will be used for early detection.

Macroscopic analysis of the gills of the dead fish revealed the fusion of the gill filaments, a phenomenon described in farming centers as “stellate gills.” Salmonids mainly presented circulatory disorders that may be associated with prolonged exposure of fish to waters with low oxygen content.

“In addition, adaptive cellular changes were observed in the gills that are interpreted as a result of chronic exposure to previous algal blooms of other microalgae species,” explains Godoy.

A FAN that took a while, but arrived

From a meteorological point of view, the northern part of Patagonia experienced a new dry summer. “For example, in Puerto Montt only 65 mm accumulated in January-February compared to an average of 170 mm. March was close to average, but it did not compensate for the previous deficit,” explains Garreaud.

Between April 7 and 15, abnormally warm, dry conditions, high solar radiation and strong southerly winds were observed. This “autumn summer” was caused by intense and persistent high pressure immediately west of the southern tip of the continent.

“Thus, it is possible that the synoptic condition at the beginning of April was the ‘straw that broke the camel’s back’ in a context of a summer drought. The latter is part of the trend towards less rainfall that northern Patagonia is experiencing for several decades, one of the clearest symptoms of climate change in our country,” says Garreaud.

The aquaculture industry, academia and institutions linked to the State, in charge of environmental monitoring and evaluation related to HABs, had been waiting for months with uncertainty where and when an event of this type would occur.

“We are learning step by step to interpret the biological, oceanic and climatic signals that warn us of a greater probability of the occurrence of HABs in Patagonia. These multidisciplinary studies are opening new doors to our knowledge of events not only in the south of Chile, but also on the wide and productive coast of our country,” Mardones concluded.