Variable feeding behavior in Orchestoidea tuberculata (Nicolet 1849): Exploring the relative importance of macroalgal traits

The feeding behavior of algal consumers inhabiting sandy beaches and the consequences of this behavior on their performance are poorly understood. Food quality has been shown to influence the food preference of algal consumers. However, food preference can often be altered or subordinated to habitat choice. This study analyzes the feeding behavior (preference and consumption rate), absorption efficiency and growth rates of the talitrid amphipod Orchestoidea tuberculata (Nicolet, 1849) in relation to the nutritional characteristics of two of the most common macroalgae stranded in the Chilean north-central region. Our experiments show that these amphipods prefer Macrocystis integrifolia over Lessonia nigrescens when presented with fresh fragments of both algae simultaneously. However, this preference did not match the performance of the amphipods when reared on diets of a single algal species: in that growth rates were not different. These results suggest that M. integrifolia is not a superior food item compared to L. nigrescens. The lower content of proteins and total organic matter found in M. integrifolia supports this interpretation. The preference of the amphipods for L. nigrescens over M. integrifolia when dry powdered algae of each species were provided (artificial food), suggested that some aspect of the physical structure of these two algae determined food preference. When the amphipods were maintained with each of the algal species in no choice experiments, they consumed 2 times more M. integrifolia, but showed higher absorption efficiency on L. nigrescens. These results suggest that food quantity and not absorption efficiency was used to compensate for the lower nutritional quality of M. integrifolia. The feeding behavior documented in this study differs significantly from that observed in populations of the same species inhabiting southern Chile, cautioning against generalizing results obtained even within a single species. Our results suggest that physical features rather than chemical characteristics of the food drive feeding preferences, including the potential (indirect) roles played by the fronds of these seaweeds as refuges against competition and desiccation.