Dietary variation in the crab Aratus pisonii (H. Milne Edwards, 1837) (Decapoda, Sesarmidae) in a mangrove gradient in northwestern Venezuela

Abstract

In order to investigate if the variety of resources consumed by Aratus pisonii (H. Milne Edwards, 1837) changes along a structural mangrove gradient, the natural diet of this crab species was studied in five mangrove forests. Mangrove forests with different degrees of structural development (arboreal, arbustive, scrub) and located in different environments (estuarine, marine, hypersaline) on the northwest coast of Venezuela were considered, during the rainy and dry seasons. Rhizophora mangle Linnaeus, 1753 was the predominant mangrove species. The gut contents of 313 individuals were analysed, yielding a total of 12 prey categories. The diet of A. pisonii was based on mangrove fragments (leaves and bark). The index of relative importance (IRI) of mangrove fragments varied between 58% and 96%. Other items supplemented the diet: seagrass, algae, insects and crustaceans. The variety of resources consumed by A. pisonii was related to the mangrove structure and varied with the season. During the rainy period food diversity in the gut content increased, as mangrove heterogeneity and complexity increased, but during the dry season the trend was reversed. Aratus pisonii appears to enhance an opportunistic feeding behaviour when leaf quality decreases, which occurs during the dry season mainly in the hypersaline mangroves with less structural development (arbustive and scrub). During the drought the IRI of the items of animal origin increased in all the localities; this could be a response to the nutritional needs of the crabs during this season. In this work, we report the first documented egg consumption of its conspecifics, which supports the idea of cannibalistic behaviour associated mainly with crabs that live in the hypersaline and scrub mangrove with the lowest structural development and leaf quality.