What impact can excessive algae growth have on aquatic ecosystems?

Excessive algae growth, often referred to as algal blooms, can lead to hypoxia, which is a significant reduction in dissolved oxygen levels in the water. This phenomenon occurs when algae die and decompose, a process that consumes large amounts of oxygen. When oxygen levels drop too low, aquatic organisms such as fish and invertebrates cannot survive, leading to fish kills and a decline in biodiversity. This detrimental effect on the ecosystem can disrupt food chains and harm the overall health of aquatic environments.

While increased algae might initially seem beneficial in terms of providing nutrients for some fish species or improving the aesthetic aspects of water bodies, these effects are overshadowed by the harmful consequences of hypoxia. Thus, option B accurately captures the primary and serious impact of excessive algae growth on aquatic ecosystems.