This investigation of near-shore copepods in the Gulf of Gdańsk indicates that the infestation may relate to different developmental stages. Epibiosis and parasitism, to varying

degrees, were observed on adult organisms (females, males), juveniles (copepodites) and larval (nauplii) stages. All of the infestations detected on Copepoda occurred mainly on the prosome including the cephalosome, but rarely on the urosome. Usually up to 13 of the animal body surface was overgrown with organisms; only in a few cases did they cover more than 12 of the body area. The epizoic protozoans, Peritricha type II, were found for the first time on copepods belonging to Harpacticoida (Figure 1F). These organisms were observed twice in June and July 2006 at the station check details located near the mouth of the Vistula (Sw3 – 54°23.2′N, 18°58.0°E, 20–10 m depth) at respective densities of 64 and 7 indiv. m− 3. They constituted 0.22% of all harpacticoids. Representatives of Cladocera (Bosmina sp.) ( Figure 1B) infected by Ellobiopsis were noted in August 2006 at the Sopot 4 station (So4 – 54°30.7′N, 18°46.0′E, 30–20 m depth) at a density of 14 indiv. m− 3, which constituted 2.9% of the total population. The youngest Cirripedia, nauplii, ( Figure 1C) with the same parasite were found in September

at the Sopot 1 station (So1 – 54°27.0′N, 18°34.8′E, 5–0 m depth) at an abundance of 4 indiv. m− 3 – these organisms represented 0.2% of the population. Eutrophication is a significant problem in the Baltic Sea (Schiewer 2008). The Gulf of Gdańsk is BTK inhibitor one of the most seriously polluted areas of the Baltic Sea and is particularly threatened

by environmental degradation. The physicochemical conditions of this basin are determined by both natural and anthropogenic factors. The mixing of waters of the gulf with seawaters occurs on a very limited scale; this results in a consistently high level of pollution. The gradually worsening water pollution in this basin has led to serious biological changes (Sobol & Szumilas 1994). Among the zooplankton, the dominance of Copepoda of the genus Acartia, mainly A. bifilosa and A. tonsa ( Bielecka Florfenicol et al., 2000, Żmijewska et al., 2000, Józefczuk et al., 2003 and Mudrak and Żmijewska, 2007), and an increase in the numbers of Protozoa, free-living and colonial epibionts that grow on Copepoda ( Wiktor, 1993 and Wiktor and Krajewska-Sołtys, 1994), have been observed. According to Hirche (1974), the large-scale occurrence of protozoan colonies on Calanoida (Eurytemora affinis and Acartia tonsa) was the result of strong, progressive eutrophication. Wiktor (1993) considered that one reason for epibiosis and parasitism on copepods was the increasing pollution load and the increase in the organic matter content, hence the large-scale proliferation of Protozoa, organisms with a high metabolic rate.