In aquatic ecosystems, what can be a result of excessive algae growth?

Excessive algae growth in aquatic ecosystems often leads to decreased dissolved oxygen levels. This phenomenon is primarily due to the process of eutrophication, where nutrient pollution, particularly from nitrogen and phosphorus, stimulates algal blooms. As algae grow and later die, their decomposition by bacteria consumes significant amounts of oxygen in the water. This reduction in oxygen levels can create hypoxic or anoxic conditions, which are detrimental to aquatic life, particularly fish and other aerobic organisms that depend on dissolved oxygen for survival.

In contrast, excessive algae growth can inhibit sunlight penetration, as thick algal blooms can block light from reaching submerged plants, hindering photosynthesis. Additionally, while increased biodiversity may occur in healthy ecosystems, excessive algal blooms often lead to monocultures that can outcompete other species, resulting in decreased biodiversity. Lastly, algae can influence water temperatures indirectly, but the primary and immediate consequence of their overgrowth is the significant impact on oxygen levels in the water.