Effects of the mangrove forest environment and tree species characteristics on fiddler crab communities

Context. South African mangrove forests consist predominantly of three tree species wherein fiddler crabs live beneath the vegetation and act as important bioengineers. Aims. To examine whether, and to what extent, tree morphology and forest structure affect fiddler crab communities. Methods. Various physicochemical parameters (sediment pH, organic matter and microphytobenthos) and tree characteristics (e.g. tree density, canopy cover and importance value) were related to the abundance or presence of these crabs within eight South African mangrove-dominated estuaries by using multivariate models. Key results. Overall, fiddler crab abundance was driven by sediment organic matter. The abundance of Austruca occidentalis was negatively correlated with sediment organic matter (C = -0.369, P = 0.013), whereas abundance of Paraleptuca chlorophthalmus was positively correlated (C = 0.115; P = 0.008). Tubuca urvillei abundance was not affected by anything. Fiddler crab presence was largely driven by sediment organic matter for all species and pneumatophore density in A. occidentalis. Conclusions. Results indicated that mangrove tree structure influences fiddler crabs indirectly at the population level, by modulating physicochemical and biological variables. Implications. Understanding mangrove tree and macrobenthic fauna co-existence patterns will be essential in developing climate-responsive management strategies for these species and the systems within which they occur.