Environmental parameters affecting the silicoflagellate (Dictyochophyceae) assemblages in El Jadida Bay and Oualidia Lagoon, Atlantic coast of Morocco

Silicoflagellates are a poorly documented component of marine phytoplankton along the Moroccan Atlantic coast of North Africa Although rarely encountered in plankton samples, they can provide valuable insights into water column dynamics and upwelling regimes. This study aimed to characterize the taxonomic composition and morphological variability of silicoflagellates in two contrasting coastal environments influenced by seasonal upwelling: El Jadida Bay and Oualidia Lagoon. In El Jadida Bay, a relatively diverse assemblage was observed, including Dictyocha epiodon Ehrenberg, an unusual morphotype of Dictyocha cf. fibula, several morphotypes of Octactis pulchra Schiller, and Stephanocha speculum (Ehrenberg) McCartney and Jordan. In contrast, the lagoon assemblage was less diverse, with only three taxa recorded: Dictyocha fibula Ehrenberg, D. fibula var. robusta Schrader and Murray, and Stephanocha speculum, the only species shared between both habitats. In addition to morphological analysis, selected environmental variables were assessed, and chemical element data from Oualidia Lagoon (Chaouite et al. 2018) were reintegrated to contextualize species distribution and potential environmental stressors. Data analysis was performed with the R software (version 4.3.1), using packages from the tidyverse (including tidyr and ggplot2), cowplot, fmsb, and Venn diagram.