Temporal and spatial variability of the potentially toxic Pseudo-nitzschia spp. in a eutrophic estuary (Sea of Marmara)

Abstract

Spatial and temporal variability and bloom formation of the potentially toxic diatom Pseudo-nitzschia spp. was investigated weekly to monthly from in a eutrophic estuary, the Golden Horn. Pseudo-nitzschia spp. were detected in 195 of 512 samples (38%) collected throughout the year. Two species, P. calliantha and P. pungens, were identified based on the SEM examination. Blooms of Pseudo-nitzschia occurred in the lower and middle estuary in January and May. The bloom in January mainly comprised P. calliantha. In the bloom in early May, P. calliantha made up 72% of the Pseudo-nitzschia cells and P. pungens 28%. However, the contribution of P. pungens increased to 83% in late May. The Pseudo-nitzschia blooms occurred at low temperature (9-158C) and moderate salinity (17 -18), and for P. calliantha a significant negative correlation was found with temperature and a significant positive correlation with salinity. The percentage of Pseudo-nitzschia cells decreased gradually from lower to upper estuary (59 -14%), correlating with a decrease in Secchi depth (5.5 -0.5 m). Principal components analyses (PCA) were used to explore the spatial and temporal variability of environmental factors in relation to Pseudo-nitzschia abundances, and showed that NH 4 , pH, Secchi depth and DO values were the most important factors reflecting spatial differences, while temperature, salinity, Chl-a and Si:N were more important factors showing temporal differences. High abundances of P. pungens correlated mainly with pH, Secchi depth and DO values, whereas P. calliantha also correlated with NO 3 + NO 2 . Low light availability due to high concentrations of suspended material and very variable environmental conditions (e.g. pH, DO and NH 4 ) may have limited growth of Pseudo-nitzschia in the upper estuary. Regular monitoring of Pseudo-nitzschia is important for improving the understanding of the influence of environmental parameters on bloom dynamics in the study area.

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“…During the sampling period, Pseudo-nitzschia species were found at a wider range of salinity (13.05 to 20.18) than in the previous study (Tas &Lundholm, 2015), but they reached highest cell density at 18.4 in late May 2012 along similar lines with the current study. The high Pseudo-nitzschia abundances with low temperatures and high salinity is similar to the pattern for P.calliantha in the Adriatic Sea (Caroppo, Congresti, Bracchini, & Albertano, 2005) and Pseudo-nitzschia spp.…”

“…P. delicatissima and P. pungens were present in almost every year between June 1998 and May 2002 with the highest abundance (1.6×10 6 cells L -1 ) in May and June (Tas et al, 2009). In another study carried out at the GHE, two blooms of Pseudonitzschia were reported in Jan. and May 2010 (Tas & Lundholm, 2015); however no study was performed on domoic acid occurence in the area.…”

“…Pseudo-nitzschia cells were detected in 101 of the 180 water samples (56%) analysed throughoutthis study. In general, Pseudo-nitzschia abundance was highest in spring, corresponding to the annual diatom bloom (Tas &Lundholm, 2015) , respectively). pDA levels were generally higher at station FD3 along the study area.…”

“…Thus, it is essential to understand the factors that stimulate Pseudo-nitzschia growth and DA production is essential. Some species of Pseudonitzschia have been reported in the Golden Horn Estuary (GHE) (Uysal, 1996;Tas & Okus, 2003;Tas, Yilmaz, & Okus, 2009;Tas &Lundholm, 2015). The GHE region's large human population, recreational activities and multiple fisheries make it potentially vulnerable to harmful algal blooms (HABs).…”

Pseudo-nitzschia Blooms in a Coastal Upwelling System: Remote Sensing Detection, Toxicity and Environmental Variables

“…Understanding the relationships between the abundance of these diatoms, DA, and the characteristics of the environment will provide valuable information on the variable(s) that might determine their growth, distribution, and DA production. Several authors [18][19][20][21][22][23][24] have related these…”