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Researchers from the Ocean, Climate & Environment Group (OCA) at Universidad de Antioquia recently found an unusually high concentration of Pseudo-nitzschia pseudodelicatissima over the coastline of the Gulf of Uraba, Colombia. Pseudo-nitzschia is a marine planktonic diatom genus responsible for producing domoic acid (DA), a toxin capable of causing deaths in animals, contamination of sea food and brain damage, and ultimately impact the fishing industry.

A scanning electron micrograph (SEM) of Pseudo-nitzschia pseudodelicatissima cells. Photo courtesy of Professor Lennin Florez-Leiva.

The Gul of Uraba, one of Colombia's largest estuaries, could be threatened by the presence of one of the most harmful marine organisms ever recorded. Seawater samples taken in April this year by students from the UdeA Oceanography program have confirmed the presence of Pseudo-nitzschia pseudodelicatissima in the waters of the Gulf of Uraba.

It seems that a massive toxic algae bloom is thriving in the waters along the Gulf of Uraba. “Water sample tests revealed a significant presence of Pseudo-nitzschia,” Professor Lennin Florez-Leiva said.

Further analysis of the samples as well as the persistent smell confirmed suspicions that this species of algae has not been recorded in the Gulf of Uraba so far. “Test results suggest that this species of algae is extremely harmful,” Professor Florez said.

Water samples were sent to a National Oceanic and Atmospheric Administration’s (NOAA) laboratory, a prestigious U.S.-based organization dedicated to conduct research on harmful algal blooms (HABs). The results revealed the presence of Pseudo-nitzschia pseudodelicatissima, one of the most toxic algal species ever recorded due to its ability to produce domoic acid, a neurotoxin that poses a serious threat to both human and animal health. Additionally, DA has also been responsible for hampering the shellfish economy along the US west coast.

Dr. Vera Trainer, manager of the Marine Biotoxine Program at NOOA’s Northwest Fisheries Science Center, says the toxic algal bloom raises concerns about potential environmental impacts due to elevated domoic acid levels along the Gulf of Uraba.

“According to researchers, this harmful algal bloom may be the first of its kind ever recorded in the Colombian Caribbean. Although several species of the genus Pseudo-nitzschia have been previously identified and recorded, this is the first time that a massive algal bloom of the species P. pseudodelicatissima occurs in the region,” Professor Florez-Leiva said. 

Pseudo-nitzschia blooms have been recorded in Monterey Bay and other areas along the US west coast for about 25 years. Professor Raphael Kudela from the University of California has conducted several studies that show that high concentrations of the neurotoxin produced by this species have been found in animals such as crustaceans, anchovies and sardines. In addition, it has been shown to cause amnesic shellfish poisoning (ASP) in seabirds and marine mammals. 

“This could be the cause of several animal deaths along the Gulf of Uraba. NOAA researchers are currently analyzing concentrations of DA in the water samples and the results will be released soon,” Florez said.

Why do harmful algal blooms occur?

The occurrence of the toxic diatom Pseudo-nitzschia pseudodelicatissima in the Atlantic Ocean was first detected in cultured mussels with high levels of domoic acid. However, harmful algal blooms are spreading throughout the Caribbean Sea.

Harmful algal blooms (HABs) may be linked to factors such as ocean warming and overabundance of nutrients (mainly phosphorus, nitrogen, and carbon) in the water. However, excess fertilizer (as in the case of the Gulf of Mexico) appears to be the primary cause of this phenomenon.

Wastewater discharge also plays an important role in the formation of HABs. “The Gulf of Uraba waters are no stranger to this phenomenon as untreated sewage and tons of nutrients from fertilizer used by the banana industry flow downriver to the sea forming a thick mass of algae that gives the water a ‘thick soup’ appearance. However, further studies are needed before firm conclusions can be made,” says Professor Florez.

What effects can HABs have on the environment and human health?

Professor Florez-Leiva says one of the most challenging tasks regarding the study of this species lies in the complexity of its taxonomy and the initial characterization of the neurotoxin, which plays an important role in predicting adverse health effects.  “Canadian studies revealed that the consumption of DA-contaminated mussels causes shellfish poisoning in humans as well as neurological disorders, severe brain damage and even death. This finding raises concern due to lack of knowledge about this issue in the region. It is important to encourage locals to take actions for early detection of risk factors and report a suspected algal bloom,” Professor Florez said.