Abstract
The objective of this study is to determine microhabitat preferences of benthic species occurring in epilithic (living on stones), epipsammic (growing on sand), epipelic (growing on mud) and epiphytic (living on seagrass) assemblages of the shallows of the Gulf of Gdańsk (southern Baltic Sea). The study material was collected from 19 sites along the Gdynia–Sopot coastal zone, including the Port of Gdynia. Most of the identified diatom taxa were observed in two or three microhabitats. However, diatom species living in only one type of microhabitat and those occurring in all analyzed microhabitats were also recorded. Autecological preferences of the identified diatoms indicate organic pollution of the coastal zone of Gdynia and Sopot. However, a higher frequency of α-mesosaprobionts and polysaprobionts indicates an increase in organic pollution in the Port of Gdynia and Marina Sopot, which is associated with intense port activity and large tourist traffic.