What is a common effect of algal blooms on aquatic ecosystems?

Algal blooms commonly lead to reduced oxygen levels in aquatic ecosystems, a process often referred to as hypoxia. When algae proliferate excessively, they can cover the water's surface and block sunlight from reaching submerged plants, inhibiting their photosynthetic activity. The die-off of algae, along with any plant life affected by the bloom, leads to a significant increase in organic matter within the water. When this organic material decomposes, it consumes dissolved oxygen—a critical resource for fish and other aquatic organisms. This depletion of oxygen can create "dead zones," where aquatic life cannot survive, severely disrupting the ecosystem and causing fish kills and a decline in biodiversity.

The other options do not align with the typical consequences of algal blooms. Increased sunlight penetration is hindered rather than enhanced due to the dense coverage of algae. Biodiversity tends to suffer as the conditions created by algal blooms can favor certain organisms over others, leading to an overall decrease in species diversity. Enhanced fish growth rates are unlikely due to the adverse conditions created during and after algal blooms, such as low oxygen levels and toxic byproducts that can also arise from certain types of algae. Thus, the most accurate answer reflects the well-documented impact of algal blooms on oxygen levels within aquatic