International Journal of Aquaculture, 2024, Vol.14, No.1, 29-36 http://www.aquapublisher.com/index.php/ija 31 1.2 Characteristics of algal bioindicators The ecological adaptability of algae to environmental changes largely determines their value in water quality monitoring. Taking diatoms as an example, this group of algae exhibits robust adaptability and can thrive in various water bodies. For instance, the diatom Nitzschia palea is more adapted to environments rich in silicate, making it more common in lakes and rivers with high silicate concentrations. Its abundance and distribution changes serve as environmental indicator organisms, reflecting fluctuations in water silicate content and indicating the degree of eutrophication in the water. The sensitivity of different algal groups to water health indicators also provides detailed information for water quality monitoring. For example, Chlorophyta is sensitive to nutrients such as nitrogen and phosphorus in water quality, and its abundance changes can be related to the degree of eutrophication in the water body. The biological characteristics of algae directly relate to their applications in water quality monitoring. The growth rate of algae is a crucial indicator directly related to nutrient content in the water. Taking Cyanobacteria as an example, their growth rate is significantly influenced by nutrients such as nitrogen and phosphorus. Therefore, by monitoring the growth of Cyanobacteria, researchers can promptly detect issues related to nutrient excess in the water. Additionally, the indicator role of algal community structure in indicating water eutrophication is also a subject of considerable attention. In freshwater lakes, the decrease in diatoms may be associated with phosphorus-rich conditions in the water. Some algae, such as phytoplankton, which are sensitive to organic loads, can serve as indicator organisms in water quality monitoring, reflecting changes in organic content in the water. However, the application of algal bioindicators in complex water bodies faces challenges. The diversity of complex habitat conditions, physical and chemical parameters, and the interactive effects of different algal groups make accurate classification and interpretation of algal communities complex. Therefore, in practical applications, personnel need to consider multiple indicators to comprehensively assess the ecological condition of the water. 1.3 Relationship between algal communities and aquatic ecosystem health The structure and composition of algal communities have profound effects on the health of aquatic ecosystems, constituting a complex and subtle relationship within freshwater ecosystems. In-depth research into how different algal communities reflect the health of water bodies and their roles in maintaining ecological balance and functionality is crucial for effective water quality monitoring and the protection of aquatic ecosystems. This enhanced understanding of the relationship between algal communities and aquatic health provides a foundation and support for scientific water quality monitoring and water management. The composition and structure of algal communities are directly linked to the transparency of water bodies. Transparency refers to the degree to which light passes through the water, which is vital for the growth and development of aquatic plants. Some diatoms, such as the genus Tabellaria, are often associated with better water quality conditions. They possess strong sedimentation capabilities for suspended particles in the water, helping to maintain water transparency and providing a more suitable growth environment for benthic plants. Additionally, changes in algal communities serve as a significant indicator of water eutrophication. In nutrient-rich waters, cyanobacteria often proliferate excessively, forming cyanobacterial blooms (Li et al., 2023). Algae in these blooms may produce toxins, posing a threat to the ecological balance of water bodies and aquatic organisms (Figure 1). Nutrient enrichment issues in water bodies are often associated with factors such as agricultural runoff and urban sewage discharge. Therefore, by monitoring the structure of algal communities, potential eutrophication problems in water bodies can be detected and addressed in advance. In addition, algal communities have a direct impact on ecosystem services such as oxygen production and organic matter decomposition in water bodies. Some algae generate oxygen through photosynthesis, serving as a source of oxygen for the aquatic environment. Simultaneously, other algae contribute to the cycling of organic matter by decomposing organic substances in water bodies. The changes in the structure of different algal communities also exhibit a synergistic relationship with water body health. For instance, during the ecosystem restoration phase, the
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