Why can algae blooms create challenges in aquatic ecosystems?

Algae blooms can create significant challenges in aquatic ecosystems primarily because they deplete oxygen levels in the water and disrupt the balance of aquatic life. During an algae bloom, there is an overgrowth of algae, which, after they die off, are decomposed by bacteria. This decomposition process requires oxygen, leading to a reduction in dissolved oxygen levels in the water. This drop in oxygen can harm or even kill fish and other aerobic organisms that depend on sufficient oxygen to survive.

Additionally, the presence of dense algae can block sunlight from reaching submerged aquatic plants, stunting their growth and further disrupting the ecosystem. The alteration in nutrient balance can also lead to the production of toxins, which might affect both aquatic life and the health of humans who rely on these water bodies for recreation and drinking water.

The other options do not accurately reflect the ecological consequences of algae blooms. Increasing sunlight penetration, benefiting aquatic plants, and lowering water temperatures are not effects associated with algae blooms and do not capture the significant environmental issues caused by the oxygen depletion from such events.