Ellobiid snail loss in seawall-fronted mangroves.

Seawalls are widely constructed to protect coastal communities and infrastructure against storm surges and tidal flooding; however, they often exert significant ecological pressure on adjacent wetland ecosystems. Understanding these impacts is critical for sustainable coastal management, particularly in the context of intensifying coastal squeeze. In this study, we investigated the effects of seawall construction on benthic mollusk communities within subtropical mangrove wetlands by comparing assemblages in mangroves fronting seawalls with those in adjacent, undisturbed natural mangroves. The results showed that species richness at the plot scale did not differ significantly between the two habitats (p > 0.05), highlighting the potential limitations of relying solely on species counts for ecological assessment. Conversely, Shannon and Simpson diversity indices were significantly higher in natural mangroves. Notably, two common species of Ellobiidae were entirely absent from seawall-fronted sites despite their consistent presence in the natural reference habitats. These findings suggest that ellobiid snails may serve as effective indicator species for evaluating the ecological footprint of seawall construction. Broadly, our results underscore the necessity of incorporating multi-dimensional diversity metrics, particularly those capturing abundance distributions, alongside indicator taxa to ensure robust biodiversity assessments.