Publication Date:
2021-05-19
Description:
Abnormal algal bloom is a global issue. So the Caspian Sea such as the other aquatic environment is at risk of
algal bloom. Thus the present study in 2013-14, was conducted to get goals, firstly determination of temporal
and spatial variation of phytoplankton abundance and biomass with emphasis on dominant species with bloom
potential and secondly detemination of chlorophyll-a concentration. Mostly sampling conducted in mid-seasons
in 4 transects (Anzali, Tonkabon, Nowshahr and Amirabad) at surface, 10 and 20m layers in depths of 5, 10 and
20m. Based on the results the annual mean±SE of phytoplankton abundance was 219 ± 33 million cells/m3. The
minimum and maximum valus of abundance recorded in summer (73 ± 31 million cells/m3) and winter (505 ±
55 million cells/m3) respectively. Totally 147 phytoplankton species identified which classified in 7 phyla and
small phytoflagellates group. The major portion of abundance formed by Bacillariophta (81%). The minimum
and maximum seasonal phytoplankton biomass were in summer (90 ± 20 mg/m3) and winter (1777 ±
201mg/m3) respectively. The annual median of chlorophyll-a concentration was 2.43 mg/m3 at surface layer and
its seasonal value in spring, summer, fall and winter recorded 1.54, 1.18, 5.81 and 2.59 mg/m3 respectively.
Therefore algal blooms started in fall and it was followed with lower intensity in winter. Mean of phytoplankton
abundance and biomass in winter were 3-6 folds to other seasond. But chlorophyll-a concentration in winter was
low and closed to the values in spring and summer. Probably, decreasing of ligh availibity and low chlorophl
content of dominant species showed important roles in decreasing of chlorophyll-a concentration in winter.
As conclusion, the abundance of Stephanodiscus socialis, Binuclearia lauterbornii and Thalassionema
nitzschioides classified in the fair level of bloom (100-1000 cells/ml) in spring (in Anzali transect), summer and
fall (in Amirabad transect) respectively. In winter, Dactyliosolen fragilissima،(in all transect except Nowshahr)
and Pseudonitzschia seriata were in this group. The presence of Thalassionema nitzschioides (as valuble food in
food chain) in dominant species list (same patern to the stability year of Caspian Sea) and decreasing of percent
abundance of harmful species from 68% (in 2008-2009) to 43% (in this study) are good signs of water quality
from Caspian Sea. On the other hand, Pseudonitzschia seriata as a harmful alga (ability to produce toxin and
bloom forming) has important role in environmental issues. In current study, Pseudonitzschia seriata expanded
from cold season to other seasons (even in summer). Also, it had high percent frequency (100%) and abundance
(294 ± 30 million cells/m3) in winter which indicate to unsuitable condition of water quality in Caspian Sea.
Description:
Iranian Fisheries Science Research Institute
Description:
Published
Keywords:
Phytoplankton
;
Abundance
;
Dominant species
;
Bloom
;
Stephanodiscus socialis
;
Binuclearia lauterbornii
;
Thalassionema nitzschioides
;
Pseudonitzschia seriata
;
Water quality
Repository Name:
AquaDocs
Type:
Report
,
Refereed
Format:
78pp.
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