Variation of phytoplankton composition and nutrients in near the fish cage-culture in the southern Caspian Sea, offshore Guilan

The Caspian Sea is sensitive to anthropogenic impacts as it is isolate from other seas. The environment pollutions strikingly increased in the last years. The impact of fish cage culture on the phytoplankton community was studied at the 3 stations near the cage and the 3 stations of references in the southern Caspian Sea during January and April 2013. A total of 19 phytoplankton taxa belonging to diatoms (12 species), chlorophytes (2 species), cyanophytes (2 species), and dinoflagellates (3 species) were identified at the study area. The diatoms abundance was dominated (86 % total abundance) in the study. The finding showed, the abundance of exotic species as diatoms Pseudosolenia calcar-avis and Pseudo-nitzschia seriata were dominated at beside of the fish cage culture stations as compared with the reference stations. The PCA analysis confirmed significant difference between abundance of phytoplankton at the fish cage culture stations and the reference stations. Furthermore, CCA analysis confirmed that there were strong relationship between diatoms, cyanophytes and nutrients levels (r = 0.82).
The reasons of high phytoplankton abundance and exotic species at beside of the fish cage culture stations could be related to the high nutrients concentrations due to fish nutrition and fecal. This study performed during the short periods, so the effect of fish cage culture on the Caspian Sea ecosystem should be taken into account in future studies.