The researchers studied the water quality in Rijeka Bay by looking at different factors like nutrients and phytoplankton. They found that the area is mostly mesotrophic, but the harbor site is eutrophic. The balance of nutrients in the water affects the growth of phytoplankton, with some areas showing potential phosphorus limitation. The amount of certain nutrients in the water can influence the growth of specific types of phytoplankton, like Phaeodactylum tricornutum. Overall, the study shows that the nutrients in the water are not being used to their full potential, impacting the trophic state of the coastal waters in the NE Adriatic Sea.