The researchers studied the types of small animals living in a river estuary in Brazil. They collected samples at different spots in the estuary during dry and wet seasons. They found a variety of creatures like insects, mollusks, and crustaceans. Some types of worms were the most common. The animals were affected by factors like saltiness and rainfall. The wet season helped more animals to live there. The researchers discovered that the type of sediment in the water influenced which animals were present. Overall, the study shows how different factors affect the creatures living in the estuary.