Which type of algae can be problematic in high numbers but is also ecologically significant?

Green algae can be problematic in high numbers due to their ability to rapidly multiply, causing algal blooms that can harm aquatic ecosystems. These blooms can lead to oxygen depletion in the water, which poses a threat to fish and other aquatic organisms. Despite this potential for harm, green algae play an important ecological role. They contribute significantly to primary production in aquatic environments, serving as a key food source for various aquatic organisms, including herbivorous fish and zooplankton. This balance between their ecological significance and the potential challenges they pose in large quantities underscores the complexity of managing aquatic ecosystems and maintaining water quality.