Scale Characteristics of the Bloom Event: a Case Study in the Iranian Coastal Waters of the Southern Caspian Sea

Scale characteristics of the bloom event: A case study in the Iranian coastal waters of the Southern Caspian Sea

Item Type article

Authors Makhlough, A.; Nasrollahzadeh Saravi, H.; Eslami, F.; Keyhansani, A.R.

DOI 10.22092/ijfs.2018.117600

Download date 28/09/2021 20:44:08

Link to Item http://hdl.handle.net/1834/40699 Iranian Journal of Fisheries Sciences 18(1) 124-139 2019 DOI: 10.22092/ijfs.2018.117600 Scale characteristics of the bloom event: A case study in the Iranian coastal waters of the Southern Caspian Sea

Makhlough A.1; Nasrollahzadeh Saravi H.1; Eslami F.1; Keyhansani A.R.1

Received: July 2016 Accepted: April 2017

Abstract Nutrient enrichment in water and sediments due to excessive anthropogenic activities in recent years has caused excessive algal growth in the Caspian Sea. The current study was conducted to determine the abundance of phytoplankton community, the dominant species and chlorophyll-a [Chl-a] concentration during algal blooms in the Iranian coastal waters of Caspian Sea through four seasons from 2013 to 2014. The minimum and maximum phytoplankton abundance recorded were 73±31 and 505±55 million cells m-3 in summer and winter, respectively. The median concentration of Chl-a increased to 5.81 mg m-3 in autumn, as compared to the annual median value (2.43 mg m-3). The results indicated that the bloom started in autumn and it continued falling with a low concentration during winter (Chl-a: 2.59 mg m-3). The three species Stephanodiscus socialis, Binuclearia lauterbornii and Thalassionema nitzschioides were classified in medium bloom class (100-1000 million cells m-3) in spring, summer and autumn, respectively. While in winter Pseudonitzschia seriata (harmful species) and Dactyliosolen fragilissima were classified in medium bloom class with high relative frequency. The scaling of bloom abundance revealed that bloom initiation coincided with 10 million cells m-3 of the dominant phytoplankton species. The bloom Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 at the regions with more than 100 million cells m-3 of total phytoplankton abundance and dominant species was overlapped with the bloom regions based on Chl-a concentration.

Keywords: Phytoplankton, Bloom, Scale characteristics, Caspian Sea, Iran

1-Caspian Sea Ecology Research Center (CSERC), Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research, Education and Extension Organization (AREEO), Sari, Iran *Corresponding author's Email: [email protected]

125 Makhlough et al., Scale characteristics of the bloom event: A case study in…

Introduction (Vershinin and Orlova, 2008). In the Excessive amounts of the majority of Iranian coast of the Caspian Sea, the nutrients in the water and sediments of first report of milky tide due to Caspian ecosystem were the result of Nodularia spumigena bloom was from human population growth and the Anzali coast in late September of anthropogenic impact on the area 2005 (CEP, 2006). Then, a red tide of (Aladin et al., 2004; Nasrollahzadeh Heterocapsa genus (Pyrrophyta Saravi et al., 2012; Samadi-Maybodi et phylum) blooms was observed from al., 2013; Nasrollahzadeh Saravi et al., Anzali to Hassanrud coasts in early 2015b; Niyazi et al., 2016). Increasing October 2006 (CEP, 2006). A visible of nutrients obviously led to more bloom of Nodularia spumigena proliferation of phytoplankton in the repeated at Tonekabon, Nowshahr and Caspian Sea which is similar to many Babolsar transects in late August 2009 other ecosystems (Anderson et al., and 2010 (Nasrollahzadeh Saravi et al., 2002; Nasrollahzadeh Saravi et al., 2011). The abundance of N. spumigena 2015a). The temporary blooms or high reached 112000 and 5830 filaments proliferation of phytoplankton under the mL-1 at dense blooms areas in 2005 and geochemical cycle is a natural 2009, respectively (Nasrollahzadeh phenomenon and is mostly beneficial to Saravi et al., 2011) (Figs. 1A, 1B). In coastal productivity. However, if this recent decades, 15 toxic and harmful event (even in seemingly harmless species and fine size phytoplankton species) occurs more than the capacity (Maximum Linear of the system it may bring up negative Dimension=MLD<10µ) with potential environmental impacts (Cullen, 2008). blooms were identified in the Iranian Impacts can be acute and severe, or basin of the Caspian Sea (Makhlough et

Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 more prolonged and chronic. Until now, al., 2011, 2017). almost 300 species of microalgae are known to cause water blooms

A B Figure 1: A: Algal bloom on MODIS satellite image, 2005, B: Algal bloom in the southern Caspian Sea, 2005 (Photo by Taghipour).

Iranian Journal of Fisheries Sciences 18(1) 2019 126

Chlorophyll-a containing organisms are [ICWSCS] based on the following in the producer level in most of the food parameters: chlorophyll-a chains, and the health and abundance of concentration, the total abundance of these primary producers affect the phytoplankton, phyla, and dominant integrity of other trophic levels. species. By classifying dominant Chlorophyll-a concentrations in the phytoplankton species at different Caspian Sea are influenced by some bloom levels this study provides important factors such as air and reliable guidelines for predicting the seawater temperatures, wind, and formation and proliferation of algal discharge of the rivers (Nezlin, 2005). bloom for further biological, ecological The concentration of chlorophyll-a is and physiological studies that aim to an important indicator for the eliminate or control probable blooms of occurrence of algal blooms in the these species. The results of this paper region (Thomalla et al., 2011). are useful for the marine aquaculture Abnormal algal blooms can cause industry and also for remedial actions in mortality in fish populations or the Caspian Sea. problems in seafood safety and human health. Meanwhile, human economic Materials and methods activities such as marine aquaculture The seasonal monitoring was carried and recreational activities may be out by boat from spring 2013 to winter suppressed because of this unfavorable and 2014 (Fig. 2, Table 1). Along the 4 event (Chorus and Bartram, 1999). Due transects (Anzali, Tonekabon, to the critical role of algal blooms on Nowshahr and Amirabad), three the ecology and economy of the region, stations located at the depths of 5, 10, this study was conducted to survey the and 20m were designated. Water

Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 temporal and spatial variations of algal samples were collected with a Niskin bloom phenomena in the Iranian coastal 1.7 litter sampler at the surface, 10 and waters of the southern Caspian Sea 20m layers.

Figure 2: Map of the locations and depths of sampling stations in Iranian coastal waters of the Caspian Sea (2013- 2014). 127 Makhlough et al., Scale characteristics of the bloom event: A case study in…

Table1: Latitude and longitude of sampling stations in Iranian coastal waters of the Caspian Sea (2013- 2014).

Depth

Transect 5m 10m 20m

Anzali Lat. 49 º 29` 49 º 29` 49 º 29`

Lon. 37 º 29` 37 º 29` 37 º 30`

Tonekabon Lat. 50 º 54` 50 º 54` 50 º 55`

Lon. 36 º 49` 36 º 49` 36 º 50`

Nowshahr Lat. 51 º 30` 51 º 30` 51 º 30`

Lon. 36 º 40` 36 º 41` 36 º 41`

Amirabad Lat. 53 º 18` 53 º 17` 53 º 16`

Lon. 36 º 52` 36 º 53 36 º 56

The samples for identification and to a constant level (10 ml). The filters enumeration of phytoplankton were were protected from light, and collected in 0.5 liter bottles and immediately transferred and kept at 4◦C preserved by adding buffered overnight. Samples were centrifuged in formaldehyde to yield a final closed tubes for 20 minutes at 3000 concentration of 2%. The samples were rpm. The absorbance of extracted let to settle for at least 10 days samples was recorded at 630, 647, 664 following which they were concentrated and 750nm (turbidity correction). Then to about 30 ml by sedimentation and chlorophyll-a concentration was centrifugation (APHA, 2005). A calculated using the formula according subsample of 0.1 ml was analyzed to APHA (2005). The spatial and under a light microscope (Nikon, AFX- temporal occurrences of algal bloom DX, Japan) (cover slip 22×22mm and were determined based on 4 data sets: with magnifications of 100, 200, 400×). total phytoplankton, Bacillariophyta, Phytoplankton taxonomic identification Pyrrophyta, dominant species

Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 was carried out using the valid abundance and chlorophyll-a identification keys of Proshkina- concentration: Lavrenko and Makarova (1968), -As a rule of thumb, the total abundance Tiffany and Britton (1971), Habit and of phytoplankton at bloom periods is Pankow (1976) and Wehr and Sheath more than average for a given region or (2003). water body (Schmidt and Schaechter, To measure Chl-a, water samples 2011). were filtered with a vacuum pump -The thresholds blooms of 750 million through Whatman GF/F 0.45 μm pore cells m-3 of total phytoplankton and 500 size glass fiber filter papers. The millioncells m-3 of Bacillariophyta and volume of sample required varied Pyrrophyta were considered (Revilla et according to the phytoplankton al., 2009). abundance which was 300-1700 ml -The blooms species was classified in during the study. The exact volume of small (10-100 million cells m-3), filtered water was recorded. The filter medium (100-1000 million cells m-3) papers were ground with a tissue and large (more than 1000 million cells grinder. Then acetone (90%) was added Iranian Journal of Fisheries Sciences 18(1) 2019 128

m-3) threshold blooms (Anderson et al., Results 2010). Seven phytoplankton phyla including -At bloom periods, the median Bacillariophyta, Pyrrophyta, concentrations of chlorophyll-a are Cyanophyta, Chlorophyta, more than median for a given region or Euglenophyta, Chrysophyta, water body (Thomalla et al., 2011). Xantophyta and fine size group The one way analysis of variance (MLD<10µ) were identified during the (ANOVA) was used to determine the sampling period. In this study, data statistically significant difference in the from 25 and 25 - 75 percentiles shows phytoplankton abundance and biomass that the phytoplankton abundance between the transect depths, layers and varied between <22 million cells m-3 seasons. Prior to the analysis, and 22-300 million cells m-3, phytoplankton data was transformed respectively. Most of the winter through rank cases (Krebs, 1999) to samples which collected at surface and normalize the data sets. 10m layers (in 10 and 20m depths) classified in 75-100 percentile with phytoplankton abundance >300 million cells m-3 (Fig. 3).

24 Percentile <25 20

12 8

million million cells/m3 4

0 layer 0

10 depth 20 5 10 20 10 20 10 20 10 20 10 20 20 5 10 20 10

station 1 2 3 4 1 2 3 4

season Spring Summer

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350 Percentile 25-75

300

250

200

150

million cells/m3 million 100

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

layer 10 10 10 20 20 10 20 10 10 10 20 10 10 20 10 10 20 10 10 20 10 20 10 10 20 10 depth 5 10201020 5 1020 5 10 5 10 20 5 1010 5 20 5 10 20 5 10 20 5 10 20 5 20 10 20 20 station 1 2 3 4 1 2 3 4 1 2 3 4 2 3 season Spring Summer Autumn Winter

2100 1800 Percentile >75 1500

1200

900

600

million cells/m3 million 300 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

layer 10 10 10 20 10 20 10 10 20 depth 10 20 10 10 5 10 20 5 10 5 10 20 5 10 20 station 1 4 4 1 2 3 4 season SpringSummerAutumn Winter

Figure 3: Phytoplankton abundance percentiles in the southern coasts of the Caspian Sea (2013-2014). 1: Anzali, 2: Tonekabon, 3: Nowshahr and 4: Amirabad. 129 Makhlough et al., Scale characteristics of the bloom event: A case study in…

The maximum and minimum means of phytoplankton was indicated during total phytoplankton abundance were autumn, but it was a major phylum recorded as 505±55 and 73±31 million during summer at Tonekabon and cells m-3 in winter and summer, Amirabad transects (Fig. 5). The respectively. Mean total phytoplankton highest abundance of Cyanophyta in abundance was observed as 156±91 and spring was observed in the Anzali 140±28 million cells m-3 during spring transect. Mean phytoplankton and autumn, respectively (Fig. 4). The abundance was not significantly abundance of Bacillariophyta formed different between layers and depths more than 75% of the total abundance (ANOVA, p>0.05), while, mean during all seasons (except summer). phytoplankton abundance (total Chlorophyta with 8% contribution in abundance, Bacillariophyta, the abundance was in the second order. Pyrrophyta, Cyanophyta, Chlorophyta In winter, the aforementioned values and fine size phytoplankton) were were 3 to 6 folds that in other seasons. significantly different between seasons The abundance of Chlorophyta stayed (ANOVA, p<0.05). at a maximum during summer. The maximum abundance of fine size

1000

100

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million cells/m3 million Spring Summer Autumn Winter 0.1 Total phytoplankton Bacillariophyta Pyrrophyta Cyanophyta Chlorophyta Small flagellates

Figure 4: Mean total abundance of phytoplankton and major phyla (log scale) during different seasons in the southern coasts of the Caspian Sea (2013- 2014).

In this study, 147 phytoplankton species (108 species) and in the Anzali were identified. The maximum number transects (111 species) (Table 2). of species was recorded during spring

Iranian Journal of Fisheries Sciences 18(1) 2019 130

Table 2: Number of species of phytoplankton phyla at different seasons and transects in the southern coasts of the Caspian Sea (2013-2014). Transect Bacillariophyta Pyrrophyta Cyanophyta Chlorophyta Euglenophyta *Other Annual phyla Anzali 51 13 19 20 5 3 111 Tonekabon 43 16 7 7 4 2 78 Nowshahr 37 18 9 8 3 2 76 Amirabad 36 16 15 8 5 2 81 Season Spring 51 14 18 17 6 2 108 Summer 40 16 12 9 2 2 81 Autumn 36 19 10 7 3 3 78 Winter 30 16 13 10 5 1 75 Annual 68 22 26 21 7 3 147 *Chrysophyta, Xantophyta

In total, sixteen species along with fine at different seasons and transects (Fig. size phytoplankton contributed to more 5). than 70% of phytoplankton abundance

1000 Spring 1000 Summer

100 100

10 10

1 cells/m3 million

million celss/m3 celss/m3 million Anzali Tonekabon Nowshahr Amirabad Anzali Tonekabon Nowshahr Amirabad 0.1 0.1

0.01 0.01 Total phytoplankton Bacillariophyta Total phytoplankton Bacillariophyta Pyrrophyta Cyanophyta Pyrrophyta Cyanophyta Chlorophyta fine size phytoplankton Chlorophyta fine size phytoplankton Bacillariophyta+ Pyrrophyta Bacillariophyta+ Pyrrophyta

Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 1000 Fall 1000 Winter

100 100

10 10 1 1

million cells/m3 million Anzali Tonekabon Nowshahr Amirabad 0.1 cells/m3 million Anzali Tonekabon Nowshahr Amirabad 0.1 0.01 0.01 Total phytoplankton Bacillariophyta Total phytoplankton Bacillariophyta Pyrrophyta Cyanophyta Pyrrophyta Cyanophyta Chlorophyta fine size phytoplankton Chlorophyta fine size phytoplankton Bacillariophyta+ Pyrrophyta Bacillariophyta+ Pyrrophyta Figure 5: Seasonal mean total abundance of phytoplankton and major phyla (log scale) at different transects in the southern of Caspian Sea (2013-2014).

Bacillariophyta had the greatest number phytoplankton species list. The of dominant species in all seasons. abundances of some dominant species Other phyla were represented by only 1 (Fig. 6) were in threshold algal blooms to 2 species in the dominant category (Table 3). As shown in the 131 Makhlough et al., Scale characteristics of the bloom event: A case study in…

table, some of the species such as Stephanodiscus socialis with relative Oscillatoria sp. (in spring), frequency of less than 4%. P. seriata Chaetoceros throndsenii (in summer), was classified at medium threshold C. peruvianus (in autumn), (100-1000 million cells m-3) with the Pseudonitzschia seriata and highest relative frequency (100%). The Cerataulina pelagica (in winter) have relative frequency of other dominant harmful or toxigenic potential: The high species in medium threshold blooms threshold (>1000 million cells m-3) were from 4 to 17%. blooms was represented by

1000 Spring 1000 Summer

100 100 10 10 1

million cells/m3 cells/m3 million Anzali Tonekabon Nowshahr Amirabad million cells/m3 cells/m3 million 0.1 1 Anzali Tonekabon Nowshahr Amirabad 0.01 0.1 Chaetoceros socialis Chaetoceros sp.2 Chaetoceros throndsenii Cyclotella meneghiniana Chaetoceros throndsenii Cyclotella meneghiniana Nitzschia acicularis Pseudonitzschia seriata Stephanodiscus socialis Oscillatoria sp. Stephanodiscus socialis Prorocentrum cordatum Binuclearia lauterbornii fine size phytoplankton Prorocentrum proximum Oscillatoria sp. Thalassionema nitzschioides Binuclearia lauterbornii fine size phytoplankton 1000 Fall 1000 Winter 100 100 10 10 Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 1

Anzali Tonekabon Nowshahr Amirabad cells/m3 million million cells/m3 cells/m3 million 0.1 1 Chaetoceros peruvianus Chaetoceros socialis Anzali Tonekabon Nowshahr Amirabad 0.01 Cyclotella meneghiniana Dactyliosolen fragilissima(summation) 0.1 Nitzschia acicularis Pseudonitzschia seriata Cerataulina pelagica Chaetoceros socialis Skeletonema costatum Cyclotella meneghiniana Dactyliosolen fragilissima Thalassionema nitzschioides Nitzschia acicularis Pseudonitzschia seriata Oscillatoria sp. Binuclearia lauterbornii Skeletonema costatum Thalassionema nitzschioides Prorocentrum cordatum Binuclearia lauterbornii

Figure 6: Seasonal mean abundance of dominant phytoplankton species (log scale) at different transects in the southern of Caspian Sea (2013-2014).

Table 3: Observed species in each (different) threshold blooms in the southern of Caspian Sea (2013-2014). Small Threshold Medium threshold Large threshold (10-100 million cells m-3) (100-1000 million cells m-3) (>1000 million cells m-3) Seasons Species Transect RPF Transect RPF Transect RPF Chaetoceros socialis Anzali 8 - - - - Nitzschia acicularis Anzali 13 Anzali 8 - - Spring Cyclotella meneghiniana Anzali 13 - - - - Oscillatoria sp. Anzali 8 - - - - Stephanodiscus socialis Anzali 13 - - Anzali 4 Chaetoceros throndsenii Amirabad 8 - - - - Summer Binuclearia lauterbornii Amirabad 17 Amirabad 13 - - Autumn Chaetoceros peruvianus Amirabad 17 - - - - Iranian Journal of Fisheries Sciences 18(1) 2019 132

Table 3 continued: Cyclotella meneghiniana Amirabad 8 - - - - Pseudonitzschia seriata Amirabad 33 - - - - Thalassionema Four Amirabad 79 13 - - nitzschioides transects Oscillatoria sp. Tonekabon, 38 - - - - Amirabad Binuclearialauterbornii Anzali, Tonekabon, 46 - - - - Amirabad Cerataulina pelagica Tonekabon, Nowshahr, 46 - - - - Amirabad,

Dactyliosolen fragilissima Four 75 Anzali 17 - - transects Nitzschia acicularis Amirabad 17 - - - - Winter Pseudonitzschia seriata Four - - 100 - - transects Skeletonema costatum Anzali, 33 - - - - Tonekabon Thalassionema Anzali, 33 - - - - nitzschioides Tonekabon Prorocentrum cordatum Tonekabon, 38 - - - - Nowshahr RPF=relative percent frequency

The annual median concentration of than 2.43 mg m-3 at all transects. In Chl-a was determined as 2.43 mg m-3. spring and winter, the median The median concentration of Chl-a was concentration of Chl-a was higher than higher than 2.43 mg m-3 at all transects the annual median (2.43 mg m-3) only in autumn, but in summer it was less in the Anzali transect (Fig. 7).

Spring Summer Autumn Winter 7.00

Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 6.00 5.00 4.00 3.00

Chl-a(mg/m3) 2.00 1.00 0.00 Anzali Tonekabon Nowshahr Amirabad All transects

Figure 7: Median concentration of Chl-a (mg m-3) in different seasons and transects in the southern of Caspian Sea (2013-2014) (vertical line is median threshold of Chl-a concentration (2.43 mg m-3).

Discussion during the past several decades mostly The frequency, intensity, and due to extra anthropogenic activities in distribution of HABs have increased 133 Makhlough et al., Scale characteristics of the bloom event: A case study in…

the coastal waters (Anderson et al., Some of the blooms species such as 2002). T. nitzschioides and B. lauterbornii are In the present study, a bloom once native and inhabitants of the Caspian occurred at the Anzali transect (770 Sea and their positive role in trophic million cells m-3) during spring based chains is beneficial for the ecosystem on total phytoplankton abundance and a (Pourgholam and Katunin, 1994). Only bloom was formed twice at Anzali (756 in spring, S. socialis was the single million cells m-3) and Amirabad (545 species in the large threshold blooms million cells m-3) transects during (>1000 million cells m-3) at the Anzali winter based on Bacillariophyta and transect. This might be related to the Pyrrophyta according to Revilla et al. high nutrient concentration due to the (2009) definition. Chorus and Bartram influence of the Anzali Wetland and (1999) stated that 200 million cells m-3 river inflows (Bagheri et al., 2014). abundance of species is a sign of an Chaetoceros throndsenii has a potential early Cyanophyta bloom event. In the to bloom because of the influences of current study, the abundance of all untreated urban wastewater Cyanophyta species was lower than 200 (Livingston, 2002). Therefore, the million cells m-3. So no bloom increase of this species at the Amirabad phenomenon of Cyanophyta was transect may be a sign of degrading recorded at all transects and seasons. water quality during summer. At the Most of the bloom species classified at Amirabad transect, warm coastal water small threshold blooms (10-100 million produced from the cooling process of cells m-3) and the highest relative the Neka Power Plant and increasing frequency (>70%) belonged to amounts of nutrients from Gohar-baran Thalassionema nitzschioides and river inflows (Pourgholam, and

Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 Dactyliosolen fragilissima in autumn Katunin, 1994; Makhlough et al., 2012) and winter, respectively (Table 3). In probably influenced the increasing general, the spatial distribution of abundance of C. throndsenii and bloom species in autumn and winter Oscillatoria sp. during summer and was more than in spring and summer. autumn, respectively. The species which were classified in The results showed that P. seriata medium threshold (100-1000 million was able to survive (with low cells m-3) blooms in spring, summer, abundance) in the warm seasons (spring autumn and winter were (Nitzschia and summer) of 2013-2014 in contrast acicularis and Stephanodiscus socialis), to 2004-2010 years (Makhlough et al., (Binuclearia lauterbornii), (T. 2011). Reproduction of P. seriata nitzschioides) and (Pseudonitzschia increased in autumn and winter. In cold seriata and D. fragilissima), seasons, vertical turbulence injected respectively. In the Amirabad transect internal sources of nutrients to the water there was at least one species with column (Kamburska et al., 2006; medium bloom category in all seasons Nasrollahzadeh Saravi et al., 2014; (except in spring). Niyazi et al., 2016) that became Iranian Journal of Fisheries Sciences 18(1) 2019 134

available for psychrophilic because the Caspian Sea environment phytoplankton such as Pseudonitzschia was in an undisturbed condition and Cerataulina (Skov et al., 1999; according to several studies based on Makhlough et al., 2011). Increase in biotic and abiotic parameters anthropogenic inputs such as (Nasrollahzadeh Saravi et al., 2015a, agricultural fertilizers from the basin 2016; Pourang et al., 2016). So, in the area might cause an increase in P. present study (2013-2014), about 73 seriata and the abundance of other percent of the annual phytoplankton harmful species (Bates and Strain, abundance, 50 percent of spring and 2006) in the Caspian Sea. 100 percent of abundance data in other The proposed thresholds of blooms seasons were considered as blooms of other ecosystems are useful with comparison to the reference value guidelines, but appropriate of 1995-96 (Table 4). In fact, the classifications are usually adopted increasing trend of phytoplankton according to local knowledge and prior started in early 2001 (Makhlough et al., monitoring history (Cullen, 2008). In 2012) and has continued until now the present study, the year of 1995-96 (Nasrollahzadeh Saravi et al., 2015a). was considered as a reference value Table 4: Mean (±SE) of phytoplankton abundance (million cells m-3) in the Iranian coast of the Caspian Sea. Spring Summer Autumn Winter Annual 1995-96 22±3 7±2 39±10 29±8 24±3 2013-14 156±91 73±31 140±28 505±55 219±33

However, considering the seasonal thresholds (small, medium and large) mean of phytoplankton abundance in proposed by Anderson et al. (2010). 2013-14 (Table 4), useful and The median concentrations of Chl-a Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 applicable results were achieved. The in autumn were more than the annual findings indicated that 8, 21, 25 and 40 median value (2.43 mg m-3) at all percent of samples in spring, summer, transects. Therefore, seasonal bloom autumn and winter were higher than started in autumn, and continued during seasonal means of phytoplankton winter in the Anzali and Tonekabon abundance, which are considered as transects. Based on the median bloom conditions according to Schmidt concentration of Chl-a, the algal bloom and Schaechter (2011). The abundance in spring only happened in the Anzali of dominant species was equal or more transect. The small threshold blooms in than 10 million cells m-3 in bloom Anderson et al. (2010) classification did samples (Fig. 6). Most of the bloom not support any bloom event based on species from regional scales were Chl-a concentration. In other words in similar to blooms species (Table 3) in the Caspian Sea, the overlapping of the Anderson et al. (2010) method. two methods (median of Chl-a Therefore, the Caspian Sea bloom data concentration and dominant species were supported by all classes of bloom abundance) of bloom events was 135 Makhlough et al., Scale characteristics of the bloom event: A case study in…

observed from the medium threshold seriata. Meanwhile, the density of other blooms of Anderson et al. (2010) species in the community with harmful, classification. toxic and invasive growth potential Chl-a concentration of water is (such as Oscillatoria sp., C. pelagica, affected by many physicochemical and C. throndsenii, C. peruvianus) should hydrobiological factors (Nezlin, 2005) be considered as a health risk to the such as transparency depth and nutrient Caspian Sea. In a conductive condition, availability as well as phytoplankton a small but continuous seasonal composition and Chl-a content of abundance of the species may act as a dominant species (Reynolds, 2006). In seed for blooms to happen. It is this study, the median of Chl-a in important to point out from this paper winter was less than in autumn, while that recurrence of T. nitzschioides in the the abundance of total phytoplankton dominant phytoplankton list of 2013-14 and dominant species in winter were in the Caspian Sea is a positive point higher than the values in autumn. This for the recovery of the Caspian Sea probably happened because of the low after ecological disturbances in several content of Chl-a in dominant species in recent decades. winter, P. seriata (Hagstrom et al., 2011) compared with the dominant Acknowledgment species Thalassionema nitzschioides in The work was supported by the Caspian autumn, and less transparency depth in Sea Ecology Research Center winter (Nasrollahzadeh Saravi et al., (CSERC), Iranian Fisheries Science 2015c). Research Institute (IFSRI), The study showed that the species Agricultural Research, Education and which have an abundance of more than Extension Organization (AREEO), -3 Downloaded from jifro.ir at 15:24 +0430 on Wednesday April 17th 2019 10 million cells m were in the bloom Iran, through the Project ‘‘The survey species lists based on the Caspian Sea of phytoplankton abundance and its data (Fig. 6) as well as Anderson et al. dynamic with an emphasis on bloom (2010) method (Table 3). Meanwhile, event in the southern part of the the bloom occurrence in a sample with Caspian Sea’’, under grant number 1- species abundance of more than 100 76-12-9125-91001. We wish to thank million cells m-3 was justified by the plankton laboratory in Mazandaran chlorophyll-a value. In addition, the province for the phytoplankton high relative frequency and abundance sampling and analyses. The authors also of bloom species has played a thank Miss Yasaman Nasrollahzadeh significant role in the severity of the for her cooperation in this paper. blooms as well as the high Chl-a concentration. There was a broad References spatial and temporal distribution of Aladin, N., Plotnikov, I. and Bolshov, Pseudonitzschia in the study. It seems A., 2004. Head of biodiversity that the highest risk of harmful algal thematic center of Caspian blooms in the Caspian Sea was from P. Environment Program, Atyrau, Iranian Journal of Fisheries Sciences 18(1) 2019 136

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