Spatio-temporal variation in the distribution and abundance of marine cladocerans in relation to environmental factors in a productive lagoon (Güllük Bay, SW Aegean Sea, Turkey)

In order to understand the effects of some physical (temperature and salinity) and chemical (dissolved oxygen, nitrate and chlorophyll a) factors on the abundance and distribution of cladoceran species, zooplankton samples were seasonally collected between August 2015 and July 2016 from three stations near the entrance to the Boğaziçi Lagoon in Güllük Bay (Aegean Sea, Turkey) using a WP2 plankton net with a mesh size of 200 μm. Four cladoceran species – Penilia avirostris, Pseudevadne tergestina, Evadne spinifera and Pleopis polyphemoides – were found during all sampling events throughout the study period. They showed high abundance in August (4774 ind. m⁻³) and October (10 706 ind. m⁻³) as the dominant zooplankton group. The abundance of Penilia avirostris – the dominant cladoceran at all sampling locations – was estimated up to 10 871 ind. m⁻³ in October. Pseudevadne tergestina was the second dominant cladoceran. In September, only Pseudevadne tergestina and Pleopis polyphemoides were found in samples in small numbers. The abundance of cladocerans varied significantly throughout the seasons. Two physicochemical factors, temperature and dissolved oxygen, were the main drivers of changes in the cladoceran composition.