Leaf consumption and experimental discrimination of stable isotopes between mangrove leaves and the tree-climbing crab (Brachyura: Sesarmidae: Aratus pisonii)

Abstract

The mangrove tree-climbing crab Aratus pisonii (Sesarmidae) is one of the most abundant and iconic arboreal brachyurans in the Neotropics. Despite being traditionally regarded as an herbivorous consumer leaving visible rasping marks on Rhizophora mangle leaves, gut content analyses, field observations and experimental feeding trials also suggest facultative omnivory. In addition, there are still questions regarding the nutritional challenge of leaf consumption, particularly whether the relatively nutrient-poor mangrove leaf litter is assimilated when offered as the sole component of the diet. This study aimed to: 1) experimentally compare consumption rates of fresh (green) and senescent (yellow) Rhizophora mangle leaves during a 26 d experiment; 2) estimating stable isotope trophic discrimination of carbon and nitrogen between leaves and muscle tissue after a 58 d controlled feeding experiment with A. pisonii from the Southwestern Caribbean Sea (Atrato River Delta, Colombia). A. pisonii consumed a total of 17.11 ± 20.75 mg leaf dry wt (g crab wet wt) −1 d−1 of R. mangle leaves during the experimental trial. However, the consumption was greater for green leaves (12.05 ± 13.07 mg) than for yellow leaves (5.06 ± 13.85 mg). Our experimental estimates of mean ± SD TDFs (trophic discrimination factors) were Δ13C 5.4 ± 0.9‰ and Δ15N 3.9 ± 0.5‰, close to those suggested for other sesarmid crabs. These results can be used in future estuarine food webs studies from Neotropical mangrove habitats, and provide new insights into the importance of A. pisonii as a key herbivore converting low-quality mangrove material into nutritious secondary production (biomass), potentially linking primary producers with intermediate and top predators (both aquatic and terrestrial).