Variable niche size of the giant mangrove whelk Terebralia palustris (Linnaeus, 1767) in a subtropical estuary

Gastropods are integral components of mangrove ecosystems as they retain primary carbon by consuming leaf litter. However, alternative primary sources may make a significant contribution toward the diets of primary consumers in subtropical mangroves due to seasonal processes that impact the availability and nutritional quality of the leaf litter. The variability of the dietary niche for the giant mangrove whelk Terebralia palustris was investigated using a stable isotope approach (δ15N and δ13C) in conjunction with gut contents analysis. The size of the isotopic niche for T. palustris was different between November (summer) and July (winter). Isotopic niches were larger in July, indicating higher dietary diversity. There was no overlap between isotopic niches of different-sized T. palustris, which indicates robust resource partitioning and an ontogenetic dietary shift. The C:N ratio of mangrove leaf litter ranged from 59.34 ± 0.9 in November to 201.66 ± 4.5 in July. The high C:N ratio observed in July could be driving the dietary diversification, if T. palustris preferably consumes more nutritious sources such as microphytobenthos. The variability in the diet of T. palustris is important when considering the ecological role of this species, as a link between mangrove primary productivity and higher trophic levels.