The study of species distribution is a key component of ecology and biogeography. The realized ecological niche – the niche actually observed in nature – is determined by analyzing the species-environment relationship. Its study can be used to assess the impact of land use and climate change on species or to support conservation planning. The epigean gastropod Terebralia palustris is widely distributed in the mangroves of the Indo-Pacific. It is an engineering species that contributes to mangrove functioning and is used as a resource. Nevertheless, existing knowledge on its distribution remains quite contradictory and suggests highly context-dependent responses. It is thus found either only in the internal mangrove or in the whole mangrove depending on the location throughout its range. In Mayotte (France, Indian Ocean), we observed a very heterogeneous presence within the internal mangrove of 13 mangroves out of 29. We therefore aimed to distinguish the specificities of the realized niche in Mayotte from the one common to the rest of the distribution area and to evaluate what the natural environmental factors that constrain this niche are. To this end, we studied environmental conditions related to feeding, shading, soil quality, and moisture comparing sites of species presence and absence during both dry and wet seasons. Results indicate the importance of shade-related variables in explaining the presence of the species. They are found where the habitat is dominated by numerous Avicennia marina of medium size (3.70 ± 1.28 m). This improved definition of the realized niche of T. palustris makes it possible to understand which habitat must be preserved to ensure the persistence of this species. The species was not always found where these characteristics exist: further studies should explore the reasons for its absence, whether natural (competition/predation) or anthropogenic (pollution/overexploitation).