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Light Microscopy Sheds Light on Abundance of Toxic Microalgal Species in the Black Sea

In an article published in the journal Toxins, researchers applied an integrated microscopic (light microscopy) and molecular (18S rRNA gene metabarcoding and qPCR) approach complemented with toxin analysis in the northwestern part of the Black Sea for better toxin profiling and taxonomic coverage in natural populations.

Study: New Knowledge on Distribution and Abundance of Toxic Microalgal Species and Related Toxins in the Northwestern Black Sea. Image Credit: Peter Bergmann/

Problems associated with harmful algal bloom (HAB) incidents have been noted extensively during the last several decades. The health of humans and ecosystems is negatively impacted by the strong poisons generated by certain microalgal species.

Hazards Associated with Marine Algae Toxins

With a 1.5% overall death rate, marine algae toxins cause more than 60,000 human poisoning cases each year on a global scale. They also result in the deaths of marine mammals, seabirds, wild fish, and other aquatic creatures. The long-term effects of chronic toxin exposure might significantly impact human health and the survival or recovery of natural populations. Numerous phycotoxins linked to various poisoning symptoms, including azaspiracid shellfish poisoning (AZP), amnesic shellfish poisoning (ASP), neurotoxic shellfish poisoning (NSP), diarrhetic shellfish poisoning (DSP), and paralytic shellfish poisoning (PSP), are produced by poisonous marine microalgae. The forms of poisoning and the animals that cause them vary by geography.

Ecological Situation of the Black Sea

The Black Sea is a unique marine basin that is essentially cut off from the larger ocean. It exhibits severe anoxic, low salinity, and vertical stratification conditions at depths of 150–200 m.

Although six nations bound it, the Don, Dnieper, and Danube rivers' flow impacts 17 nations. Eutrophication has historically had a significant impact on the Black Sea, and phytoplankton blooms and a rise in dinoflagellate proportions have significantly concerned the ecosystem's health. Even though things have improved since 1992, the ecological situation still needs close monitoring.

The Black Sea plankton ecosystem contains a significant share of potentially harmful species, some of which bloom abundantly. Although there is little and inconsistent information on phycotoxins in the Black Sea, it has been shown that some microalgal species are harmful. Along the Russian and Bulgarian coasts, several investigations have been carried out.

Toxic Microalgal Species Bulgarian and Russian Seas

Domoic acid (DA) has been found in samples of mussels, plankton, and Pseudonitzschia calliantha that were isolated from Sevastopol Bay in the Black Sea as well as in Bulgarian seas.

In Russian seas where Prorocentrum lima, Phalacroma rotundatum, and Dinophysis caudata are present, farmed mussels and plankton samples were discovered to contain DSP toxins. The distribution, toxicity, and taxonomy of hazardous microalgae in the Black Sea are still poorly understood at the basin size, necessitating focused research.

Harmful Plankton Species Identification

This study aimed to provide fresh information on the occurrence of potentially harmful plankton species and the related phycotoxins in the western and northern Black Sea. An integrated strategy supplemented with toxin analysis was used to ensure improved taxonomic coverage and toxin profiles in wild populations.

The region under investigation included seas impacted by the Danube river flow, which has been recognized as the primary cause of eutrophication in the western Black Sea and coastal, shelf, and open water stations. For the creation and execution of efficient monitoring programs and early warning systems, data concerning the number, distribution, and toxicity of dangerous species at a regional level are essential.

Capturing CTD Profiles at 41 Stations

Data were gathered from 41 stations in the northwest Black Sea (Romanian and Bulgarian waters) from May 15 to June 4, 2019. CTD profiles were captured at each location using an SBE-911 CTD system coupled with a fluorescence sensor. A Secchi disk was used to measure the water's transparency at each location.

At each station, the surface, the bottom of the sampling layer, and the average for the sampled water column were all examined for the seawater parameters of fluorescence (Fl), salinity (S), temperature (T), and dissolved oxygen (DO) from the CTD measurements.

Significant Findings of the Study

In this study, an integrated method was used for the first time, which gave researchers a better understanding of the composition and distribution of harmful phycotoxins and microalgal species in the Black Sea.

Results show the relevance of the combined data for a better understanding of the present plankton-phycotoxin variability pattern in the NW Black Sea, considering the methodological limitations of the different approaches.

In the western Black Sea, phycotoxins and toxic microalgae are chronic problems. In the basin, PTX-1 (pectenotoxins) and PTX-13 were discovered for the first time, along with various YTX(yessotoxins) variations.

The abundance of D.acuta and PTXs, as well as L.polyedra, P.reticulatum, and YTXs were shown to be positively correlated.

Future Prospects

In the future, culture investigations will be necessary to clarify the precise toxin profiles of Black Sea strains.

The identifying capability in deciphering the microalgal variety will rise with more advanced morphological techniques, such as SEM and various DNA markers.

Given the complicated relationships found, a deeper investigation of the impact of environmental conditions on toxicity and toxic microalgae is required (covering more critical parameters, such as nutrients and pH).


Nina Dzhembekova, Snejana Moncheva, Nataliya Slabakova, Ivelina Zlateva, Satoshi Nagai, Stephan Wietkamp, Marvin Wellkamp, Urban Tillmann and Bernd Krock (2022) New Knowledge on Distribution and Abundance of Toxic Microalgal Species and Related Toxins in the Northwestern Black Sea. Toxins.

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Taha Khan

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Taha Khan

Taha graduated from HITEC University Taxila with a Bachelors in Mechanical Engineering. During his studies, he worked on several research projects related to Mechanics of Materials, Machine Design, Heat and Mass Transfer, and Robotics. After graduating, Taha worked as a Research Executive for 2 years at an IT company (Immentia). He has also worked as a freelance content creator at Lancerhop. In the meantime, Taha did his NEBOSH IGC certification and expanded his career opportunities.  


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