Feeding Ecology and Feeding Habits of Blue Crab Callinectes amnicola (De Rochebrune, 1883) (Decapoda, Brachyura, Portunidae): A Study at the Ehotile National Park, Côte d’Ivoire, West Africa

Abstract

Background: Callinectes amnicola, or blue crab, belongs to the Portunidae family and the Decapoda order. This species belongs to aquatic macroinvertebrates and was therefore of vital importance. They played a vital role in aquatic ecosystems, notably in nutrient cycling, food chain interactions and as indicators of water quality and environmental change. This makes them essential to maintaining healthy aquatic environments. Aims: Knowledge of the feeding and trophic rhythms of a species is an important parameter for breeding of species.  Thus, the aim of this study was to determine feeding ecology and feeding habits of Callinectes amnicola in wild, with a view to breeding it in a controlled environment. Methodology: Diet of Callinectes amnicola from Ehotile National Park, Côte d’Ivoire, was investigated from January to December 2018. The study was carried out by the Hydrobiology and Water Ecotechnology research unit of the Climate Change and Biodiversity Department. Crabs were sampled monthly using balance crab fishing, traditional crab traps and fixednets and drift nets. Fixed nets were set without bait at low tide from 6:30 p.m. and removed at 6 a.m. the following day. Drift nets fishing began at 6 a.m. and ended at 8 a.m. Total width and length of the carapace were measured for each specimen, and crabs were dissected. Stomachs were removed, weighed, and stored in pill boxes containing 5% diluted formaldehyde. Spearman's rank correlation coefficient test was used to compare the diet of the species studied according to sex, season, and individual size. All statistical analyses were performed using Statistica software 7.1. Results: A total of 150 crab cardiac stomachs with a carapace lengths between 44.17 and 144.03 mm were examined. Six major categories of prey Macrophytes constitued by Insects, Crustaceans, Molluscs, Fishes and Annelids were found in cardiac stomach. Based on the relative importance food (RIF) and the mean intestinal coefficient (0.52 ± 0.04), Callinectes amnicola was an omnivorous species and fed primarily on invertebrates. This species also has a cannibalistic behavior.  Relationship between the length of carapace (Lc) and intestine (Li) was defined by the equation log Li = - 0.3642 + 1.0480 × log Lc. To study ontogenetic changes in diet, Callinectes amnicola individuals were divided into 3 sizes classes following the Sturge rule and Hierarchical clustering (44 – 82 ; 83 - 108, and 109 - 147 mm carapace width) representing respectively juveniles or immatures, prematures or subadults, and sexually mature or adults stages. At all stages, crabs feed mainly on macrophytes and their other prey included crustaceans, molluscs, fish, insects and annelids. Conclusion: The data provided by this study will serve as a reference for the manufacture of feed for captive breeding of this species, which is highly prized by the public and sold on the markets. Further research providing more detail on the feeding behavior of the species taking into account the differences between juvenile and adult microhabitats and how these habitats influence their feeding habits, and the nutritional value of ingested prey, will help define conservation and preservation policy for the species.