PJB-2024-3
SEASONAL DYNAMICS OF DIATOMS ASSEMBLAGES IN INTERTIDAL REGION OF MANGROVE ENVIRONMENT ALONG KARACHI COAST, PAKISTAN
Mahwish Shoaib
Abstract
Diatoms are dominant part of phytoplankton community and play a major role in microbial food web of any aquatic ecosystem. Mangroves are highly productive system but currently they are facing threats due to urban influence along Karachi coast. Seasonal dynamics of diatom community composition and environmental factors in intertidal region of mangrove environment were investigated. Water samples were collected during summer and winter seasons from four selected stations at Sandspit along Karachi coast, Pakistan. In the sampling stations, the highest numbers of species (13, 12) belonging to 11 genera was noted at Station 2 and Station 3 in summer, respectively. Total 18 taxa of diatoms were recorded (3 centric and 15 pennate) from all stations. It has been revealed that benthic pennate diatoms were relatively rich in diversity and dominated throughout the study period in this intertidal region. Centric diatoms were dominated by Stephanocyclus meneghinianus, whereas Cyilndrotheca closterium was the most abundant species in pennate group followed by Navicula sp., Nitzschia sp, Pleurosigma sp. and Gyrosigma sp. These forms were commonly found during both seasons at all stations. Diatom cell density varied seasonally with preponderance in summer (0.32 x 106-1.52 ×106 cells L‾1) compared to low winter values (0.15 x 106 - 0.77 x 106 cells L‾1). Significant correlation (p<0.05) was recorded for DO (r= 0.99 and 1), ammonium ion (r= 0.9 and 0.8), and Chl a (r= 0.78 and 0.8), in summer season. Diversity indices were observed highest including dominance, Shannon and Simpson (0.95, 0.75 and 0.51) in summer season respectively. K-dominance curve also revealed relative dominance of diatom species in summer with regard to seasons. Variability in the diatom abundance and diversity may be attributed to the fluctuating environmental conditions and effect of Lyari River effluents. This devastating condition in mangroves habitat calls for immediate mitigating action to restore environmental health and diversity of marine organisms.
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