The results of the current study revealed a distinct community composition of gastropods in different habitats of Khuran mangrove ecosystem in the Persian Gulf. A. mesopotamica and P. tigrinus were the dominant species in pneumatophore zone which highlighted their importance in shaping the gastropod community structure in mangrove ecosystem. In contrast, Pirenella cingulate and Littoraria intermedia were the dominant species in mudflats. P. tigrinus is very common sea slug in mangrove ecosystem of the Persian Gulf, mostly confined within the A. marina fringe (Hajializadeh et al., 2020). As a dominant grazer and representing important component in the food web dynamics of this mangroves, P. tigrinus actively forages for microbial mats and mangrove leaf litter at low tide (Akbari et al., 2021). It avoids being covered by water at high tide by climbing various parts of mangrove trees (personal obs.). Adult snails are preyed upon by gray heron Ardea cinerea and western reef heron Egretta gularisand the juveniles may be preyed on by crabs (personal obs.).
Overall, species richness of gastropods in Khuran mangrove system was low despite being a relatively undisturbed habitat. For example, around 50 species were found in Malay peninsula (Macintosh and Ashton, 2002), 30 species in the west coast of Thailand (Macintosh et al., 2002), and 41 species in the Segara Anakan lagoon, Indonesia (Nordhaus et al., 2009). In general, species richness of mangrove gastropods parallel to that of mangrove trees, as higher mangrove species richness provide different habitat types and food source for associated fauna (Ashton et al., 2003; Nordhaus et al., 2009). The Khuran mangrove system harbors only one mangrove tree species which provide a homogenous habitat type for different species (Delfan et al., 2021). A low richness of gastropods corresponded with a low diversity of mangrove trees in mangrove system of Qatar (Al-Khayat et al., 2019). Similarity, (Chen et al, (2007) reported that gastropods were low in a rehabilitated mangrove system in Jiulongjiang Estuary, China. Whereas, a high species richness of gastropods was observed in forests with high tree diversity in Indonesia (Nordhaus et al., 2009)
The results of two-way ANOVA for the effects of season and habitat on species diversity showed that all diversity indices significantly differed between seasons, whereas, only Pielou’s evenness index differed significantly between habitats. In addition, there was no significant interaction between season and habitat. Despite this, we observed higher species diversity in pneumatophore zone compared to bare mudflats. The species richness and density of benthic macrofouna has been traditionally attributed to the structural complexity of habitats. The structural complexity of Avicenna aerial roots provides habitat and refuge for resident fauna and the only hard substrates for benthic animal in mangrove habitats (Kamal et al., 2017; Kawaida et al., 2017; Norris et al., 2019). Hard substrates have indirect benefits for primary consumers by providing a settlement for benthic microalgae (Miller et al., 1996; Shahraki et al., 2014). Aerial roots also provides shelter from predators for many invertebrate species and protects resident fauna from wave action and storm surge (Kristensen and Alongi, 2006; Kristensen et al., 2012; Nordhaus et al., 2017). The above-ground structure of mangroves may function as a trap for suspended materials in the ecosystem and thus increasing organic matter input in mangrove habitats (Furukawa et al., 1997; Kamal et al., 2017). The trapping of suspended matters combined with decaying of plant detritus contributes to an abundant food source for gastropods (Nordhaus et al., 2011). In general, the gastropods are detritus feeders and their abundance is subject to the availability of food such as detritus and algae (Akbari et al., 2021; Rahmawati et al., 2015). They prefer habitats protected from currents, waves and direct sunlight (Rahmawati et al., 2015; Zvonareva et al., 2015). The mangrove canopy may also play a significant role in shaping the gastropod community in the pneumatophore zone (Ellis and Bell, 2004). In arid mangrove ecosystem of the Persian Gulf, shade provides refuge from desiccation and heat stress as these areas have lower temperatures than bare mudflats. Shade reduces the visibility of gastropods, making them less vulnerable to some predators. In line with the results of the current study, Sheridan (1997) reported a higher density of macrofouna in mangrove habitats compared to bare habitats. In contrast, Alfaro (2006) found that mangrove habitat had the lowest diversity among the six marine habitats in New Zealand. The observed contradiction is probably due to different sampling periods and methodologies (Nordhaus et al., 2009; Sheridan, 1997).