International Journal of Aquaculture, 2024, Vol.14, No.1, 29-36 http://www.aquapublisher.com/index.php/ija 30 In order to better address global water quality issues, this review aims to conduct in-depth research on the application of algae as biomarkers in water quality monitoring, providing more effective methods and theoretical support for global water quality monitoring, and promoting the protection and restoration of water ecological balance. By exploring the critical ecological roles of algae in aquatic ecosystems, their potential value as biological indicators, and analyzing the challenges and needs in current water quality monitoring, researchers will further scrutinize the shortcomings of existing monitoring methods and advocate for the application of emerging technologies to meet the demand for more comprehensive water quality data. 1 Classification and Characteristics of Algal Biological Indicators 1.1 Classification of algae Ecological features are crucial for the classification of algae. Algae with various habitat adaptations thrive in different types of water bodies. Taking diatoms as an example, they construct their outer shells using silicates and are therefore relatively abundant in waters rich in silicates. In freshwater systems, green algae (Chlorophyta) may dominate, while in saline lakes, Dunaliella salina, a type of salt algae, may be more common. Studies on functional groups reveal the specific ecological roles of different algae in ecosystems, such as the key role of diatoms in the silicon cycle. Morphology and genetics are the two main pillars of algal classification. Morphologically, algae can be classified based on cell shape, size, and structure. For instance, dinoflagellates, with their flagellated cell structure (Figure 1), exhibit significant differences from diatoms. With the advancement of molecular biology techniques, particularly the application of DNA sequencing, researchers can more accurately reveal the phylogenetic relationships among algae. For example, by comparing the sequences of specific genes, researchers can determine the phylogenetic relationships of some microalgae, providing a foundation for their more precise classification. Figure 1 The hazards of algal blooms (Lin et al., 2023) The spatiotemporal dynamics of algal communities are crucial for their classification and ecological studies. Regarding seasonal variations, some algae, such as diatoms, may proliferate significantly in spring and gradually decrease in summer. The spatiotemporal distribution characteristics of algae in different water bodies also show considerable variability. For example, certain euglenoids may be more abundant in rivers rich in organic matter, while they may be rare in clear lakes. The response mechanisms of algal communities to external pressures are also part of the classification, as some algae may exhibit different adaptations to pollutants or temperature changes.
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