The paper presents the results of the analysis of diatoms from surface sediments (stones, sands) and macroflora (seagrass, macroalgae) collected at 16 sampling sites located along the inner coastal zone of Puck Bay (southern Baltic Sea) along the Hel Peninsula. The main diatom species of epilithon, epipsammon and epiphyton were characterized with respect to their autecological preferences (habitat, salinity, trophic status, saprobity). Three groups of diatoms were distinguished with respect to the type of substrate based on the results of benthic flora analysis: diatoms (i) of one type of substrate, (ii) of two types and (iii) those occurring on all types of substrates. Moreover, the distribution of benthic diatom communities indicates ecological differences in the study area. Marine and brackish-water species were observed in large numbers in the coastal zone of the Outer Puck Bay, whereas freshwater flora occurred with a higher frequency in the coastal zone of the Puck Lagoon. The content of polysaprobionts and of α-mesosaprobionts indicates that the region of the Hel Tip is highly eutrophicated and very polluted. The coast in the vicinity of Kuznica is less polluted, whereas the best environmental conditions are found in the Jurata–Jastarnia region, as evidenced by the frequency of diatoms that are β-mesosaprobionts.

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.

The subject of this study was the diatom taphocoenoses preserved in the surface sediments of the northern part of Puck Bay, southern Baltic Sea. Three subbotom sedimentary cores ZP1/0518, ZP2/0518 and ZP3/0414 collected in the vicinity of the Hel Peninsula from a water depth of 65 m, 47 m and 50.2 m, respectively were analyzed with respect to diatom flora. Over 500 valves of diatoms were counted in each sample in order to estimate the percentage abundance of particular taxa. Habitat, salinity, trophy and saproby requirements of all identified species were established according to literature. The percentage content of distinguished ecological groups was counted in each core. Diatomological analysis indicates that the diatom flora observed in muddy and silty sediments of the study area was generally abundant, taxonomically diverse and well preserved. However, some valves were mechanically broken or/and chemically destroyed. In all cores anthropogenic assemblage with small sized planktic diatoms tolerating higher nutrient and pollution concentration as well as lower transparency of water column predominated. The most important components were euhalobous species Thalassiosira levanderi and mesohalobous one Cyclotella choctawhatcheeana. Both species achieved the highest frequency (up to ca. 80% and 38%, respectively) in core ZP1/0518. Other eutraphentic, α/β mesosaprobous taxa belonged to oligohalobous halophilous (Actinocyclus normanii f. subsalsa, Cyclotella atomus, C. meneghiniana) and oligohalobous indifferent (A. normanii f. normanii, Cyclostephanos dubius, Aulacoseira spp.) were observed rarely. Benthos was also dominated by diatoms preferring the high content of nutrients and organic matter. This group was represented by marine/brackish-water taxa (i.e. Catenula adhaerens, Cocconeis hauniensis, C. scutellum, Diploneis didyma, D. smithii, D. stroemii, Opephora krumbeinii) and freshwater ones (i.e. Amphora copulata, A. pediculus, Cocconeis neodiminuta, C. neothumensis). Our results clearly indicate the apparent human impact on the structure of the diatom flora in the northern part of the Puck Bay. At least two sources of anthropopressure can be determined in the vicinity of Hel Peninsula i.e. (1) at a local scale harbor in Hel city and municipal sewage linked to development of tourism, and (2) at a regional scale the Vistula River waters, which is the major source of pollution in the Gulf of Gdańsk.