Is the population increase of an invasive portunid crab (Charbydis hellerii) a concern? The effect on native prey

Biological invasions have the potential to change the local marine biodiversity through increasing predation pressure and interactions among species. Charybdis hellerii is a swimming crab native to the Indo-West Pacific, it was first collected in the Atlantic Ocean in 1987 and is currently found in high abundance in coastal areas of southeastern Brazil. We evaluated the presence of the invasive crab C. hellerii from the coast of São Paulo state, Brazil, analyzing the stomach contents and performing laboratory-based feeding experiments. In crabs with stomachs full enough to be analyzed (N = 19), mussels (30%) and brachyuran crabs (14.21%) were the most frequent prey items found. Based on these data, we experimentally tested how different densities and life stages (adults and juveniles - differentiated by carapace width - CW) of the invasive crab affected feeding patterns. Results indicated that predator density effects on the predation pressure were dependent on the prey type. Mussels were consumed highest at medium predator densities (30 crabs/m3), whereas crabs were consumed highest at high predator densities (60 crabs/m3). There was no influence of the life stage on prey consumption, suggesting that adults (CW = 57.12–67.59 mm) and juveniles (CW = 39.77–43.18 mm) exhibit similar predation. Charybdis hellerii is an important consumer of benthic native prey, having the potential to change food webs through predation pressure on bioengineers and associated fauna. As the removal of C. hellerii from the environment is difficult, the next step toward is to understand the effect of the invasive crab on the native trophic web.