Influence of environmental factors on the population dynamics of key zooplankton species in the Gulf of Gdańsk (southern Baltic Sea)

Summary: We studied the influence of abiotic environmental factors on the seasonal population dynamics’ of Acartia spp., Temora longicornis and Pseudocalanus sp. in the southern Baltic Sea in the period of 2006–2007 and 2010–2012. Zooplankton samples were being collected monthly at 6 stations located in the western part of the Gulf of Gdańsk with a WP2 net (100 µm mesh sizes) and then analyzed according to the HELCOM guidelines. Although the sampling stations did not significantly differ from each other in the terms of variability of abiotic environmental factors, the biomass of copepods developmental stages differed between them, apart from the shallow stations in both, Gulf of Gdańsk and in its inner part – Puck Bay. According to redundancy analysis, 26.1% of the total variability observed in the biomass of the copepod species has been explained by water temperature, salinity, air temperature, cloudiness, wind speed and direction and station's depth, with the first variable having the greatest power, alone explaining 13.7%. ANOSIM revealed that sampling stations in the Gulf of Gdańsk were significantly different from one another in terms of copepods’ biomasses. Generalized Additive Models fitted for water temperature and salinity were significant for all ontogenetic stages of Acartia spp. and Temora longicornis and for the majority of stages of Pseudocalanus sp. (apart from the C1 for both and the males for salinity). Keywords: Copepoda, Environmental factors, Acartia spp., Temora longicornis, Pseudocalanus sp., Biomas