The researchers studied the zooplankton in the Krka river estuary in spring 2006. They found that certain types of tiny animals, like tintinnids and copepods, were most common in the area. These animals varied in abundance and species as they moved from the head to the mouth of the estuary. The smaller copepod Oithona nana was prevalent in the upper reaches, likely feeding on organic matter. Different types of copepods were more common in different parts of the estuary. The researchers recommend using a specific size of net for future studies in similar estuaries to get the best understanding of the zooplankton population.