The researchers studied how water pollution affects the types and amounts of tiny plant-like organisms called phytoplankton in a mangrove area in China over 5 years. They found that the number of phytoplankton species decreased from 2008 to 2012, with certain species becoming more common due to pollution from sewage. Factors like phosphate levels, temperature, and salinity in the water played a big role in shaping the phytoplankton community. Overall, the study shows that pollution can change the types of phytoplankton in the water, leading to a decrease in overall species diversity.