What is a mode of allelopathy employed by blue-green algae?

Blue-green algae, also known as cyanobacteria, exhibit a mode of allelopathy primarily through the production of chemicals that can be toxic to various organisms in their environment. This phenomenon can inhibit the growth of competing algae and other aquatic plants, effectively allowing blue-green algae to dominate and proliferate in certain conditions. The chemicals produced are known as allelochemicals, and they can have detrimental effects on the physiology and reproduction of other organisms, including fish and invertebrates.

This allelopathic behavior plays a significant role in aquatic ecosystems, particularly in nutrient-rich waters where blue-green algae thrive. Understanding this mode of action is vital for managing aquatic environments, especially when considering the impacts of harmful algal blooms, which can lead to ecological imbalances and affect water quality.

The other options provided do describe actions or benefits associated with algae or aquatic systems but do not align with the specific mode of allelopathy defined in this context. For instance, while it is true that blue-green algae can absorb sunlight efficiently and release oxygen, these mechanisms do not represent allelopathy. Similarly, providing nutrients to the ecosystem, although important, is not an allelopathic action as it relates to the impact of blue-green algae on other organisms.