Algae bloom kills right whales on Argentine coast | Polarjournal
Southern right whales spend the austral winter in the warmer waters off the Valdez Peninsula, where they give birth to their calves. Weighing between 50 and 80 tons, the animals are popular with local tourism officials for whale-watching tours and often display acrobatic aerial jumps. Image: Dr Michael Wenger

Many marine animals that hunt and feed in the Southern Ocean around Antarctica during the austral summer prefer to spend the cold season in temperate zones of Argentina’s Valdez Peninsula. Numerous marine mammals such as elephant seals and seabirds find good conditions there to either sit out the winter or even give birth to their offspring and prepare them for the long migration south. This is especially true for southern right whales, which also play an important role in whale watching for local tourism. But this year, just before the start of the migrations, numerous whales and other animals suddenly washed up dead on the beaches. Experts now know why.

An unusually severe and sudden increase in toxic algae killed 30 right whales, one sea lion, and many Magellanic penguins and other seabirds between late September and mid-October. This is the result of investigations by experts from the Argentine Instituto de Conservación de Ballenas ICB after the analysis of samples taken from whale carcasses washed up. The Regional Directorate for Fauna and Flora of the Chubut Province, to which the Valdez Peninsula belongs, and other institutions also come to this conclusion through their analyses.

Since the end of September, whale carcasses had been discovered on the beaches of the peninsula. Because some of the dead animals were difficult to reach, not all carcasses were sampled. But the results of the research are clear. Image: Instituto de Conservacion de Ballenas

Among the discovered whale carcasses, the experts identified mainly females (19 individuals) and 4 calves. Only 2 bulls were clearly identified; the remaining five were already too decomposed to make a clear sex determination or were too remote to get there, according to the ICB. Teams from the Southern Right Whale Health Monitoring Program, a monitoring program for right whales in the region led by ICB in conjunction with the Universities of California Davies and Utah, collected a variety of samples from a total of 9 animals that were accessible to analyze for possible cause of death. In the process, the researchers discovered paralytic shellfish toxin, a toxin derived from microscopic algae. These algae are eaten by small crustaceans and mussels, which accumulate the toxin inside them. When whales eat this animal plankton, they ingest large amounts and become poisoned. “There have been reports of poisonings and deaths of marine fauna worldwide, often affecting large numbers of animals, due to ingestion of the same debilitating biotoxins found in the bodies of whales that died in Peninsula Valdez,” the ICB wrote in its report. Other causes of death, such as hunting or ship collisions or starvation, were ruled out by the experts, as there was no evidence of them.

Southern right whale females do accumulate a large layer of blubber in the Southern Ocean during the summer to have enough energy to give birth to calves in the winter. But thanks to the plankton diversity, they can find food around the peninsula even in winter. This now explains the high casualty rate among female whales. Image: Dr Michael Wenger

The fact that among the carcasses found the largest number are female, the expert teams explain with the way of life of right whales. Right whale cows give birth to their calves in the waters around the peninsula and nurse them there as well. As a result, they require more energy than the bulls and therefore eat the animal plankton in the spring, which consists mainly of copepods and other crustaceans and shellfish. Because they also ingest large amounts of algae through their filter-feeding habits, the whales are poisoned both directly by the algae and indirectly by the crustaceans that also eat the algae. So instead of gathering energy to get ready for the upcoming migration to Antarctic waters, the animals poisoned themselves and died. This is a low blow for the ICB and the monitoring program, as just a few weeks earlier they were pleased to report that the number of animals observed had reached a new high this year.

The term “red tide” originally described the increased occurrence of a particular species of microalgae that turns the water red (left, image taken near La Jolla, California). However, it has come to mean harmful algal blooms of all kinds, such as the one off the coast of Argentina in 2006 (right). Images: Wiki Commons CC BY-SA 4.0

Southern right whales, while the species with the largest population size among right whales, are considered “non-threatened.” But surging fisheries, pollution and also warmer water temperatures are considered threats to marine mammals. Events such as this sudden algal bloom, which can occur worldwide and in seas and oceans as well as freshwater bodies, are also considered extreme events. But studies that have examined factors that promote such events conclude that increasing nutrient inputs to coastal regions and warmer waters may cause such algal blooms to occur more frequently in the future. Here, the team of experts has a particular problem. “Due to research difficulties, lethal doses of biotoxins to large whales such as the southern right whale are unknown,” they write in their report. Coupled with the fact that such phenomena can occur quite suddenly, making them difficult to predict, this is bad news for all marine life, polar or otherwise.

Dr Michael Wenger, PolarJournal

Link to Southern Right Whale Monitoring Program website.

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