Oysters are known to be filter feeders, meaning they filter water to obtain nutrients. They do this by drawing water in through their gills, where particles such as phytoplankton, detritus, and other small organisms are trapped. The filtered water is then expelled back into the environment. The filtration process aids in improving water quality by removing suspended solids and excess nutrients, which can contribute to algal blooms and other water quality issues.

In the context of coral reefs, oysters can help clean up the reef environment by filtering the surrounding waters. By removing suspended particles and nutrients from the water column, oysters can reduce the amount of food available for harmful algae, such as zooxanthellae, which can lead to coral bleaching and other reef degradation processes. Additionally, oysters' filtration activities can help to increase water clarity and enhance the overall health of the coral reef ecosystem.