PHYTOPLANKTON COMMUNITY AND WATER QUALITY DURING PRE AND POST MONSOON IN THE OMAN SEA (PART OF IRANIAN WATERS)
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Date
2014-09
Authors
SARAJI, FERESHTEH
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Abstract
This study was carried out along the Iranian coastal waters of the Oman Sea in 2008 and 2010 during the pre-monsoon and post-monsoon seasons. Samples were collected at 10 transects from coastal to offshore zones and from surface to deep layers. The aims of this study were to determine the spatial and temporal variation of phytoplankton community and water quality. A total of 204 species of phytoplankton were identified which comprised of Dinophyceae (105), Bacillariophyceae (89) Cyanophyceae (6), Dictyochophyceae, (2) Euglenophyceae (1) and silicoflagellate (1). The Shannon-Wiener diversity index characterized the water quality as moderate to slightly polluted. Dinophyceae was dominant to other classes in terms of diversity and abundance, followed by Bacillariophyceae. Bacillariophyceae in the post-monsoon was more abundant compared to the pre-monsoon season. Phytoplankton density was higher in the post- monsoon season. On the other hand, the total number of species was more in the pre-monsoon season. Higher phytoplankton abundance and lower diversity of phytoplankton species were observed in the coastal waters as compared to offshore waters. The dominant species were Nitzschia seriata, Chaetoceros dichaeta, Leptocylindrus danicus, Coscinodiscus radiatus, Lauderia annulata, Rhizosolenia alata, Lioloma elongatum, Chaetoceros atlanticus, Cochlodinium polykrikoides, Gymnodinium mikimotoi, Prorocentrum belizeanum, Prorocentrum lima, Prorocentrum gracile, Oscillatoria thiebautii and Phormidium
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sp. The ANOSIM revealed a significant difference in species composition between the two seasons. Environmental parameters also showed significant differences between the two seasons and two periods of the study. High abundance of phytoplankton and chlorophyll-a concentration were recorded in the post-monsoon season. Chlorophyll -a and phytoplankton abundance decreased from surface to deeper layers and coastal to offshore waters. A gradual decrease of salinity and temperature were observed from west to east part of the study area, but nutrients concentration increased. Nutrients increased with depth and in coastal zone. Nutrients showed seasonal and annual variation. Concentrations of nutrients were the highest in the post-monsoon season. The study area showed N and P limitation. Monsoon played an important role in affecting the abundance and distribution of phytoplankton, and concentration of nutrients in the study area. Cochlodinium polykrikoides was firstly observed in the pre-monsoon season 2008 in the eastern part and then diffused to the west area. Lioloma elongatum was recorded in high abundance in 2010 during the post-monsoon season and it was the first record in the study area. Toxic dinoflagellate such as Pyrodinium bahamense, Lingulodinium polyedrum, Gymnodinium mikimotoi, Gymnodinium catenatum and Gonyaulax polygramma, were observed in low cell densities, indicating the possibility of having potential threat of harmful algae blooms in the coastal area of Iranian waters in the north of Oman Sea.
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PHYTOPLANKTON COMMUNITY AND WATER QUALITY