Research shows increasing dominance of diatom algae in the Pearl River estuary, paving the way for future study of diatom blooms

It is a common perception that waters close to the population would be more polluted than those offshore or at higher latitudes. However, researchers at the Hong Kong University of Science and Technology (HKUST) found that the ratio between two common diatom and dinoflagellate (dino) microalgae – a common benchmark for water quality, has nearly doubled in the estuary of the Pearl River (PRE), one of the most urbanized subtropical coastal waters in the world, over the past two decades.

Research led by Professor LIU Hongbin, Associate Director and Full Professor in the Department of Ocean Sciences at HKUST, has shown the increasing dominance of diatom algae in the Pearl River estuary.

Usually, the higher the Diatom / Dino ratio, the healthier the water quality is supposed to be. However, according to Professor LIU Hongbin, Associate Director and Full Professor in the Department of Ocean Sciences at HKUST who led the research, it is not conclusive that this finding indicates an improvement in water quality at PRE, as the The team found that temperature as well as the level of nutrient concentration in the ocean also adversely affected the algae population.

Algae, or phytoplankton, are important to the marine ecosystem because they not only help transform carbon dioxide into organic matter and oxygen, but are also a key food source for a wide range of sea creatures. In Hong Kong waters, diatom and dino are the two main types of algae which together made up about 80 percent of the total algae population. While the diatom has long been considered the “good algae” because it usually grows in less polluted waters, the dino is the evil brother because its toxicity can kill fish and cause hypoxia in coastal waters. The Diatom / Dino ratio has long been used as a benchmark to indicate the optimal level of a marine ecosystem. Theoretically, the higher the proportion of diatoms, the better the water quality.

Microscopic images of diatoms
Microscopic images of diatoms
Microscopic images of dinoflagellates
Microscopic images of dinoflagellates

Now, a research team led by Professor Liu, who analyzed a plethora of data ranging from temperature, nutrient concentration to oxygen levels of PRE during 18 to 2017 years, observed an increasing dominance of diatoms. , or an increase in the Diatom / Dino ratio since 2000.

However, using a combination of several data-driven statistical models, the team found that the abundance of diatoms may not be the result of improved water quality, but of a change in water quality. the nutrient composition in PRE – in particular a rapid increase in nitrates relative to a relatively constant level of ammonium and phosphate resulting from increasing anthropogenic intake. In addition, the team also found that the abundances of diatoms and dino were positively correlated with temperature, they predicted that for every 1-4 ° C increase in temperature, the Diatom / Dino ratio could increase by up to 12% under the same nutrient content.

Red tides caused by dinoflagellates
Red tides caused by dinoflagellates

While there had been numerous studies on the abundance of phytoplankton in high latitudes or offshore waters, little research has been carried out on highly urbanized subtropical or tropical coastal waters like those of PRE.

Professor Liu said, “Algae blooms are a major environmental problem, our model highlights the prediction and even the prevention of future blooms. Meanwhile, some studies suggest that not all species of diatoms are angels, some of the genus Pseudo-nitzschia – for example, can produce acid harmful to the neural system of marine mammals and birds. In the future, we will also study the ecological sequences of diatom blooms, as well as the abundance and physiology of these toxic diatoms. “

The results were recently published in the scientific journal Biology of global change.

Professor LIU Hongbin (right) and his postdoctoral fellow Dr Isaac Cheung are the co-corresponding authors of the article
Professor LIU Hongbin (right) and his postdoctoral fellow Dr Isaac Cheung are the co-corresponding authors of the article

About Hong Kong University of Science and Technology

Hong Kong University of Science and Technology (HKUST) (https://hkust.edu.hk/) is a world-class research-intensive university that focuses on science, technology and business as well as the humanities and social sciences. HKUST offers an international campus and holistic, interdisciplinary pedagogy to produce well-rounded graduates with a global vision, strong entrepreneurial spirit and innovative thinking. Over 80% of our research was rated “Internationally Excellent” or “World Leader” in the Hong Kong University Grants Committee 2020 Research Assessment Exercise. We were ranked 3rd in the 2021 Times Higher Education Young Universities Rankings, and our graduates were ranked 26th globally and among the best universities in Asia in the Global University Employability Survey 2020.

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