Publication Date:
2021-07-16
Description:
Annually, many data of hydrology and hydrobiology of the southern Caspian Sea at Iran's coasts were collected by Caspian Sea Research Institute of Ecology. The data which had been collected by researchers submitted annually in several reports but has not been processed all at once. Fluctuations of various parameters were surveyed and the relationships between them were analyzed. The main goal of this research is to analysis the data were obtained from 1994 to 2006 and show changes the concentration of various parameters in the Caspian Sea. Physicochemical data indicated that the average trend of transparency and salinity was decreased from 1994 to 2006 annually, where the salinity value was decreased from 12.37 ppt (part per thousand) to 11.5 ppt. The average of dissolved oxygen was increased from 6.4 to 8.6mg/l. pH has slightly fluctuated from 8.15 to 8.31. However, with increasing depth from surface to bottom, the average of dissolved oxygen was sharply decreased (DO concentration in surface and 800 m was 7.18 and 1.45 mg/l, respectively). The trend of salinity and pH fluctuation was very slow with depth but the salinity has an increasing with incrementing of depth but pH has a decreased trend. The average of organic and inorganic phosphorus and TP was nearly increased. The average of Nitrate and Silica sharply increased comparing to depth but the average of Nitrite and organic Nitrogen decreased. The results showed that the temperature fluctuation in different water layers was low in winter but the dramatic decreasing of temperature was occurred at 10-20 m (in spring), 20-50 m (in winter) and 50-100 m (in autumn). With increasing of depth (Slope of the Sea), transparency and salinity values have an increasing while DO and pH showed decreased. As a whole, 335 species of phytoplankton were identified, there are 70 species in advance as these species were not seen in this period but 96 of novel's species have been recorded. The lowest and the most of phytoplankton biomass was recorded in 2006 and 2001 while the biomass was 59 and 1034 mg/m^3, respectively. Albet, the lowest biomass was recorded at the depth of 100 m (24.1 mg/m^3) but the maximum was observed in surface layer (1344.1 mg/m^3). The average of phytoplankton biomass was increased after arrival of the ctenophore. There was a significant difference between the average of biomass in different seasons before and after of the ctenophore invasion (P〈0.001). Bacillariophyta and Pyrrophyta have the most cell abundance with a total of biomass of 52.7 and 37, respectively. From 1994 to 2006, species diversity (Shanon-Niner), evenness and richness were estimated between 3.02-1.29, 0.28-0.61 and 4.32-7.60, respectively. A total of 65 zooplankton species were identified with a frequent species in the Caspian Sea before the ctenophore invasion, while the species diversity decreased after the invasion. The high and the lowest of species diversity was recorded in 1994-1995 and 2006 and in 1999 the biomass of the zooplankton were observed between 12.6 mg/l and 363.8 mg/l, respectively. After arrival of ctenophore, the averages of zooplankton biomass at of the different depths were sharply decreased and were less than the ctenophore invasion. The result showed that there was a significant difference among the average of zooplankton biomass in two periods, seasons and west, middle and east regions as follows: P〈0.001, P〈0.008 and P〈0.01. The maximum abundance and biomass of zooplankton belonged to copepoda with %51.5 and %63, respectively. Rotatoria falls in the second class from 1994 to 2006 (during 1994-2006), species diversity, evenness and richness were varied between 0.19-1.6, 0.08-0.52 and 0.37-2.29, respectively. The species diversity of macrobenthic organisms at the same period s followd by zooplankton changes which sharply decreased. The average of benthic biomass reduced from 13.7 g/m^2 in 1994-1995 to 1.8 g/m^2 in 2004 but sharply increased in 2005 with a maximum value of 46.7 g/m^2. With increasing of depth, the average of benthic biomass was sharply decreased. There was a significant difference (P〈0.001) in macrobethic organisms abundance before and after the ctenophore invasion, but it did not show a significant difference between seasons and different regions (as follows: P〉0.137, P〉0.782). Before the presence of ctenophore, the worms had been constituted a dominate group with an approximately %45 of total abundance and also %20 of their biomass. After this period, their frequency was sharply increased (more than %85) but the maximum value pertains to Cardidae (more than %90). The species diversity, evenness and richness were varied between .69-2.51, 0.23-0.63 and .011-3.79, respectively. AMBI software, Shanon-Viner parameter was moderate in all seasons from 1994 to 1996 but this parameter was reduced in a bad limit (boundary) in the most seasons from 2002 to 2005. The main parameter of M-AMBI consists of several parameters and also approximately showed similar changes such as Shanon -viner parameter. On basis of this parameter, the ecological quality condition of Caspian Sea was superior limit in all seasons from 1994 to 1996 but after the following years were decreased from good to moderate limits (After the presence of ctenophore). Relationship between abiotic variants and phytoplankton indicated that there was a direct relationship between transparency and salinity while there was a powerful and reversal significant relationship between transparency water temperature, transparency in organic Nitrate, phytoplankton number and transparency phytoplankton biomass. The comparison between different variants average in two periods (before and after the ctenophore invasion) indicated that the average of Kilka catch was decreased, the relative frequency of clupeonella engrauliformis and clupenoella grimmi was sharply reduced but the relative frequency of Clupeonella cultriventris was sharply increased, the species diversity, evenness and richness and the number of zooplankton species were sharply decreased, the average of biomass and transparency was sharply reduced, the average of dissolved oxygen and liza saliens or liza auratus catch were increased. These difference were often significant (P〈0.05). Therefore, with the ctenophore invasion into the Caspian Sea, the primary production was increased, the biomass value of zooplankton and specially Kilka which fed on zooplankton were sharply decreased while the fish such as Rutilus frisii kutum and mullet (Liza salins or Liza aurratus) which fed on benthic were increased.
Keywords:
Ecology
;
Iran
;
Caspian Sea
;
Transparency
;
Salinity
;
Dissolved oxygen
;
pH
;
Nitrate
;
Nitrite
;
Species
;
Phytoplankton
;
Biomass
;
Bacillariophyta
;
Pyrrophyta
;
Diversity
;
Zooplankton
;
Rutilus frisi kutum
;
Liza salins
;
Liza aurratus
Repository Name:
AquaDocs
Type:
monograph
Format:
application/pdf
Format:
application/pdf
Format:
158
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