Temporal variation of phytoplankton composition in the Golden Horn estuary (2018-2019)

In this study, the monthly changes of phytoplankton species composition and community structure in the Golden Horn Estuary between October 2018 and September 2019 were examined. During the sampling period, the qualitative and quantitative distributions of phytoplankton were evaluated together with some physicochemical parameters measured simultaneously. A total of 150 taxa belonging to diatoms, dinoflagellates, other phytoflagellates and some freshwater forms were identified in the phytoplankton community through the microscopic examinations. 18 species of these were recorded for the first time in the study area. The diatom Skeletonema spp., cryptomonad Plagioselmis prolonga, raphidophyte Heterosigma akashiwo and euglenophytes Eutreptia sp. and Eutreptiella marina formed blooms in the spring-summer period. During the study period, 13 potentially toxic species were identified within the phytoplankton community. Among these, Alexandrium cf. minutum, Alexandrium cf. catenella and Dinophysis infundibulum were recorded for the first time in the Golden Horn Estuary. The phytoplankton ecological index values showed significant differences between seasons and stations. A positive correlation (p<0.01) was found between total phytoplankton abundance and temperature, while a negative correlation (p<0.01) was found between species diversity (H') and temperature. It was observed that environmental parameters varied by months and stations according to one-way analysis of variance (ANOVA). The Bray-Curtis similarity analysis showed that there are two important groups in the phytoplankton community having a monthly similarity of over 60%. It has been determined that phytoplankton exhibit a seasonally different community structure according to the multidimensional scaling (MDS) analysis. The results revealed that the phytoplankton composition has a spatio-temporal variationsin associatied with environmental factors and phytoplankton may be as a good indicator organism in the marine research.