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Description
This study investigates the seasonal dynamics between physico-chemical parameters and phytoplankton diversity, community structure, and abundance in Imessouane Bay, located on the Atlantic Coast of Southern Morocco. Monthly samples were collected from February 2019 to January 2020 at three representative stations, and detailed analyses were performed on parameters such as temperature, pH, salinity, dissolved oxygen (DO), nitrate, nitrite, silicate, and inorganic phosphate (IP).
The results reveal significant seasonal variations (P < 0.0005) in these parameters, which strongly influence phytoplankton productivity. A total of 129 phytoplankton species were identified, representing six classes: Dinophyceae (41%), Coscinodiscophyceae (35%), Bacillariophyceae (13%), Fragilariophyceae (7%), Prymnesiophyceae (2%), and Dictyochaceae (2%). Seasonal variations in temperature, nutrient availability, and other physico-chemical parameters were found to drive significant changes in species composition, abundance, and community structure.
Phytoplankton reached their highest population density in spring, reflecting favorable environmental conditions, with a peak observed in April-May. In contrast, the lowest population density was observed during winter months. Diatoms dominated the phytoplankton community during winter and spring, associated with higher concentrations of silicate and moderate water temperatures. In summer and autumn, dinoflagellates took over, driven by warmer temperatures, lower oxygen levels, and water column stratification.
The Shannon-Wiener diversity index (H′) was highest in spring, indicating greater species diversity, and lowest in winter, when community composition was dominated by fewer species. Similarly, the evenness index (J’) was lower in winter, emphasizing the seasonal shifts in community structure. Canonical Correspondence Analysis (CCA) was applied to investigate the relationships between environmental factors and phytoplankton species composition. This analysis showed strong correlations, revealing that temperature, salinity, dissolved oxygen, nitrate, and inorganic phosphate were the key factors influencing phytoplankton distribution and abundance. Diatoms were found to be positively associated with silicate-rich, well-oxygenated waters during winter and spring, whereas dinoflagellates were more abundant in warmer, oxygen-poor waters during summer and autumn.
The annual monitoring of the phytoplankton community in Imessouane Bay, carried out for the first time, significantly contributes to understanding the dynamics of this critical coastal ecosystem. This monitoring effort highlights the ecological importance of Imessouane Bay in the context of the southern Atlantic coast of Morocco.
