As one of the most complex and valuable aquatic ecosystems, estuaries play a vital role in maintaining biodiversity and providing fisheries resources. These areas, with high primary productivity, are essential for the reproduction and growth of the early life stages of many important aquatic species.
Introduction: Musa estuary, located in the northwestern Persian Gulf, is a sensitive coastal ecosystem affected by industrial activities and urban wastewater discharge. Phytoplankton, as suitable biological indicators for water quality monitoring, were used in this study to assess the ecological status of Musa estuary based on community structure and diversity indices (Shannon–Wiener, Margalef, Pielou, and Simpson). Given the continued development of industrial activities and changes in wastewater discharge patterns in the region in recent years, the present study aimed to update information on the current status of phytoplankton communities in the industrial creeks of the Musa estuary system and to characterize the current patterns of community structure and diversity, thereby providing insights into the potential effects of recent phases of industrial development on the base of the aquatic food web.
Materials and Methods: In this study, sampling was conducted at six stations (Jafari, Oudaleh, Patil, Marinus, Ghazaleh, and Doragh) during both summer and winter of 2024. Physicochemical parameters (including temperature, salinity, pH, dissolved oxygen, turbidity, phosphate, and chlorophyll-a) were measured, along with phytoplankton identification and enumeration. Diversity indices, including Shannon–Wiener, Margalef’s richness, Pielou’s evenness, and Simpson’s index, were calculated.
Results: A total of 23 species from a single phylum (Heterokontophyta) were identified. This finding indicates a very strong dominance of diatoms in the phytoplankton composition of the region. The order Naviculales was the most abundant (21%), followed by Bacillariales (18%), Rhizosoleniales (16%), Fragilariales (15%), and Chaetocerotanae (14%) as the dominant orders in the region. The highest phytoplankton count was observed in winter at Jafari Creek (13,225 ± 309.39), while the lowest occurred in summer at Oudaleh Creek (75 ± 2.29). Jafari Creek in winter exhibited the highest Margalef richness index (1.14 ± 0.13) and Shannon–Wiener index (1.92 ± 0.14). Phytoplankton density showed significant positive correlations with phosphate concentration, dissolved oxygen, and chlorophyll-a, and a significant negative correlation with temperature (P < 0.05). Correlation and principal component analysis (PCA) results indicated that chlorophyll-a and phosphate exerted the greatest effects on phytoplankton distribution. The Shannon–Wiener index ranged from 1.17 to 1.92, indicating moderate pollution levels across all creeks.
Discussion: Seasonal fluctuations in environmental parameters, particularly temperature decline and nutrient enrichment during winter, were the primary drivers of increased phytoplankton density, especially among diatoms. The highest density and species diversity were recorded at Jafari Creek, suggesting relatively more stable conditions in this area. In contrast, Oudaleh Creek exhibited the lowest diversity and richness indices, likely influenced by high nutrient loads from adjacent industrial effluent discharges. Shannon–Wiener index values ranging from 1.17 to 1.92 indicate moderate anthropogenic impacts on the ecosystem. Overall, the study area is under moderate ecological stress and requires continuous monitoring and environmental management. The findings of this research can provide a better understanding of the region’s ecological status and offer effective guidance for fisheries management and environmental planning.