Effects of environmental factors on seasonal and spatial changes in surface zooplankton in Golden Horn Estuary (Istanbul, Turkey)

Abstract

The abundance and spatial distribution of zooplankton at monthly intervals were studied in polluted Golden Horn Estuary (Istanbul, Turkey), from July 2006 to December 2007. Selected water quality parameters also were measured. The zooplankton community was characterized by the presence of freshwater, estuarine and marine species, with a total of 59 taxa. Rotifers were the most important fraction of the total zooplankton, comprising 36.52% of all the samples. The zooplankton exhibited seasonal patterns, with the highest abundance occurring in the summer (979 ind. L À1 ) and the lowest in the spring (856 ind. L À1 ). Rotifera was the most abundant group in the upper and middle estuary, whereas Copepoda usually reaches the maximum densities in the higher salinity waters in the lower estuary. The study results indicated that both the sampling time (seasons) and sampling sites jointly had significant effects on the zooplankton densities (MANOVA P < 0.05), and horizontal patterns were related to electrical conductivity, water temperature, dissolved oxygen, suspended particulate matter, pH and chlorophyll a measured in the estuary.This study is part of the PhD thesis of Zeynep Dorak, titled 'Influences of abiotic factors on seasonal changes of zooplankton in Golden Horn, Istanbul, Turkey'.

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“…The early winter maximum could be associated with the phytoplankton peak; during the study period, chlorophyll a reached highest values in September 2015. Meroplankton is an important component of plankton in the Golden Horn Estuary and high abundance of meroplankton was in spring and autumn and mollusca larvae, cirripedia larvae and polychaeta larvae dominated in the estuary (Dorak and Albay, 2016). In present study, meroplankton were more abundant in spring.…”

“…There are very few studies on zooplankton of the Golden Horn Estuary (Dorak, 2010;Dorak and Temel, 2015;Dorak and Albay, 2016), so we have compared our findings with these previous investigations. Dorak and Albay, (2016) reported 59 zooplankton species in the Golden Horn Estuary, consisting of 6 species of Cladocera, 35 species of Rotifera, 7 species of Copepoda and meroplankton such as larvae of Bivalvia and Polychaeta (Table 3). The species composition of zooplankton recorded in our investigation varied from those reported in previous studies (Dorak and Temel, 2015;Dorak and Albay, 2016).…”

“…Dorak and Albay, (2016) reported 59 zooplankton species in the Golden Horn Estuary, consisting of 6 species of Cladocera, 35 species of Rotifera, 7 species of Copepoda and meroplankton such as larvae of Bivalvia and Polychaeta (Table 3). The species composition of zooplankton recorded in our investigation varied from those reported in previous studies (Dorak and Temel, 2015;Dorak and Albay, 2016). Possible reason for this change could be the fact that after the opening of the water channel from the Istanbul Strait, more marine species had the opportunity to penetrate the Golden Horn Estuary.…”

“…By the end of 1990s, the estuary became anoxic towards the upper parts and prevailed throughout the year (Tas, Okus, & Aslan-Yılmaz, 2006). As a result, the ecosystem of the Golden Horn was greatly influenced and the ecosystem of Golden Horn Estuary was dominated by Polidora ciliata, Mytillus galloprovincialis, Podon polyphemoides and Noctiluca scintillans, highly tolerant to organic pollution (Yüksek, Okuş, Yilmaz, Aslan-Yilmaz, & Taş, 2006;Dorak and Albay, 2016). While the aquatic life in the lower regions of the estuary was limited by pollution, it completely disappeared in the upper regions (Güvengiriş, 1977).…”

“…Although there have been several studies on the phytoplankton community, pollution, physical and chemical characteristics of the estuary (e.g. Alpar, Yüce, & Türker, 2003;Aslan-Yılmaz, Okuş, & Övez, 2004;Taş, 2017), there have been a few studies about zooplankton structure (Dorak andTemel, 2015, Dorak andAlbay, 2016). There are however no data on the annual zooplankton abundance, diversity and species composition, after the opening of the water channel from the Strait of Istanbul.…”