Author: Alan P Covich,  Professor (University of Georgia)

Description:
Freshwater decapod crustaceans connect terrestrial and aquatic food webs by consuming foods produced by riparian forests and by functioning as prey for many species of fishes, wading birds, and otters. Previous studies demonstrate that these decapods feed primarily at night on a wide range of riparian-produced foods. We hypothesized that individual decapods in tropical streams have distinct feeding preferences that are identifiable by how rapidly these omnivores detect alternatively available, riparian-produced foods. We added palm fruits and artificial bait in shallow water at nightfall to determine night-time feeding activities among crabs and shrimps in a spring-fed stream, Rio Olho d’Água, in the upper Paraguay River Basin, Mato Grosso do Sul, Brazil. We used underwater digital cameras illuminated with red LED lights to video record species interactions. Our nocturnal observations on two species of tropical freshwater decapods documented differences in how they responded to increased availability of palm fruit as well as in aggressive interactions related to foraging. Large and small adult shrimp found the added bait within less than 30 minutes after nightfall but did not feed directly on the palm fruits. Adult crabs found the bait within 60 minutes. Only the adult crabs actively fed on the palm fruits by using their chelae to tear off pieces of the soft inner portions of the palm fruit and transferring these pieces to their mandibles with their chelae and the first set of walking legs. The crab's shedding of the soft portions of the fruit produced small fragments some of which accumulated within close distance to shrimp who fed on these fragments and benefitted by this indirect facilitation. Aggressive interactions were only observed among some individual shrimp who avoided direct contact with the crabs. This connection between shrimp and crab feeding on fallen fruit can provide high-quality, nutritious foods that otherwise are difficult for shrimp to process. More study of nocturnal foraging in tropical stream food webs is needed to determine the importance of behavioral interactions and access to additional food resources. 

Category: Scientific Program Abstract > Special Session > CS23 Aquatic food webs