The ecosystem engineering role of the Neotropical crab Cardisoma guanhumi on mangrove soil properties

Abstract

The land crab Cardisoma guanhumi is one of the most common species in mangroves of the American Atlantic coast and Caribbean islands however, studies of its effects on the physical and chemical soil properties are scarce. This study compares specific physicochemical properties of soil between C. guanhumi burrows (B) and adjacent zones (AZ), and provides the first insights on their role as an ecosystem engineer in mangroves. The study was conducted in an estuarine system dominated by Rhizophora mangle, located at the Rio Chico estuary, Miranda state of Venezuela. Random soil samples were taken digging each burrow until reaching the bottom and at the same depth for AZ. Data analysis was carried out using Bayesian inference. Credible mean differences between B and AZ, were found for sand (B = 26.53 ± 10.76, AZ = 17.25 ± 5.7%), silt (B = 73.16 ± 10.77, AZ = 82.42 ± 5.69%), pH (B = 8.71 ± 0.36, AZ = 9.12 ± 0.30), soil organic matter (SOM, B = 0.43 ± 0.21, AZ = 0.17 ± 0.06%), total N (TN, B = 786 ± 232, AZ = 529 ± 107 µg g−1), Mg (B = 4.42 ± 0.60, AZ = 3.48 ± 0.71 cmolc kg−1) and K (B = 0.12 ± 0.05 AZ = 0.06 ± 0.02 cmolc kg−1). Chemical variables as SOM, K, Mg and TN showed the highest values of effect size (> 1.4). With the exception of the pH, all chemicals variables—which were different between B and AZ—showed strong and decisive evidences of correlations with SOM. When SOM variable was controlled, the relationships between pH–TN, TN–K and Mg–K decreased, even though the correlation evidence between each pair remained. Differences in chemical contents found in B respect to AZ suggest that the activities of C. guanhumi (feeding, moulting, excretion and defecation) within their burrows promote the spatial heterogeneity of mangrove soils.