The Assessment of Spatial and Temporal Changes of Ascidians in the Intertidal Zone of Chabahar Bay, the Gulf of Oman

This study aimed to identify ascidians in the coastal area of Chabahar Bay and assess their biodiversity in three stations (University, Tiss, Lipar) and four seasons for the first time. Sampling was carried out in the intertidal zone from July 2019 to May 2020, and samples were counted using the quadrate method. After narcotizing (in menthol crystal solution) and fixing (in formaldehyde solution), ascidians were identified using identification keys. The assessment of ascidians in Chabahar Bay led to the identification of Phallusia nigra, Cnemidocarpa sp., and Styela plicata. Results showed that P. nigra had the highest density in Lipar station (6.01 ± 0.72 individuals m⁻²) and during winter (6.65 ± 0.87). On the other hand, Cnemidocarpa sp. had the highest density in the University station (6.93 ± 0.84) and during fall (6.03 ± 0.96). The dispersion index showed that all ascidians identified in Chabahar Bay had an aggregated dispersion pattern. Moreover, the sustainability index showed that P. nigra and Cnemidocarpa sp. are more sustainable than Styela plicata. Assessment of each species in various seasons and stations showed that their abundance fluctuates based on their biology and effective physical factors. On the other hand, the assessment of their biodiversity using usual biodiversity indices (Shannon-Weiner index, the Simpson index, and Margalef index) showed a significant effect (P < 0.05) of seasons and stations on these indices. The discernible impact of seasonal variations becomes more pronounced, underscoring the dynamic fluctuations in ascidian biodiversity within Chabahar Bay over the course of a year.