Intertidal zone preferences of fiddler crabs in tropical mangroves reflect species specific selection across multiple spatial and temporal scales

Abstract

In mangroves, species specific spatial habitat zonation preference of fiddler crabs could influence the functioning of mangrove ecosystems. Spatial zonation of fiddler crabs in tropical Malaysian mangroves across different temporal scales has not been studied extensively. In this study, the abundance and species richness of several fiddler crab species across a mangrove intertidal zone were examined in relation to environmental variables. Fiddler crab abundance was sampled with salinity, pH, temperature, and sediment grain size in three mangrove sites in Penang Island, Malaysia. The sampling design involved collecting crabs and environmental habitat variables in six 2 m × 2 m quadrats within three mangrove study sites from March 2017 to February 2018. Data were analysed using multivariate (PERMANOVA, SIMPER, and BEST in PRIMER v7.0) and univariate analyses (ANOVA and Pearson’s r in STATISTICA v 13.30). Univariate and multivariate analysis revealed multiple spatial and temporal scales influenced each fiddler crab species differently (ANOVA p < 0.05). Fiddler crab abundance varied across and within sites, intertidal zones, and sampling months (PERMANOVA, p < 0.001). Austruca annulipes, Gelasimus vocans and Tubuca paradussumieri were found mostly at the lower intertidal zone, which was characterized by a higher sand faction. Tubuca rosea, Tubuca forcipata, and Austruca bengali occupied and coexisted in the middle and higher zones of the intertidal, although this pattern varied across the different sites in this study. BEST analysis indicated that porewater salinity and sediment particle size were important factors in structuring patterns of fiddler crab assemblages. Based on univariate correlation analyses, the total abundance of fiddler crab increased with increased temperature (temperature ranged from 26.9 °C to 31.7 °C), and increased porewater salinity (salinity ranged from 10‰ to 35‰).