Effects of fiddler crab ( Minuca rapax) feeding activity on mangrove sediment geochemistry

Fiddler crabs are important ecosystem engineers in intertidal environments due to their intense sediment processing during feeding. Although their bioturbation activity has been widely studied, the specific effects of feeding behaviour on sediment geochemistry in mangrove systems remain poorly quantified. This study evaluated the effects of fiddler crab (Minuca rapax) feeding activity on sediment granulometry and chemical composition in a mangrove tidal flat at the Juréia-Itatins Ecological Station (southeastern Brazil). Sediment and feeding pellets were collected from 35 crab burrows and combined into composite samples for sedimentological and chemical analyses. Granulometry and organic matter content were compared between processed and surrounding sediments, while nutrient and mineral concentrations were analyzed using spectroscopic methods. Repeated-measures ANOVA and two-sample t-tests indicated that feeding activity did not significantly alter sediment granulometry or organic matter content. However, Ca (two-sample t-test) and Mg (Wilcoxon test) concentrations were significantly higher in feeding pellets, suggesting selective particle processing and mineral enrichment associated with feeding. These results indicate that M. rapax feeding activity contributes to localized geochemical modification of mangrove sediments without substantially altering sediment structure. Overall, our findings reinforce the ecological role of fiddler crabs as ecosystem engineers influencing nutrient redistribution and sediment geochemistry in mangrove environments.