Cannibalism and food availability in the talitrid amphipod Orchestoidea tuberculata

The availability of limiting resources can potentially influence the intensity of intra- and interspecific interactions. Stranded macroalgae exported from adjacent coastal ecosystems supports abundant intertidal consumers on oceanic sandy beaches, including talitrid amphipods, which can be one of the numerically dominant invertebrates of the upper shore. The allochthonous nature of this donor-controlled food subsidy and its unpredictable delivery by waves and currents, results in highly variable and potentially limiting resource availability for these consumers. In Chile, adults of the talitrid amphipod, Orchestoidea tuberculata Nicolet, can influence the survival of juvenile conspecifics through cannibalism, a type of intraspecific interaction we hypothesized could be affected by the availability of macroalgal resources. We experimentally investigated the potential influence of food availability on cannibalism between age classes in O. tuberculata in laboratory mesocosms. Juvenile mortality in presence of conspecific adults was significantly higher when juveniles and adults were maintained without food. However, adult mortality was neither density dependent or food dependent. Further, juveniles did not influence adult mortality, either with or without food. The strong effect of food limitation on juvenile mortality from cannibalism by adults of O. tuberculata found here, supports our hypothesis that food resource availability on beaches can affect this intraspecific interactions. In addition these results provide evidence of the potential importance of biological interaction in the population dynamics of intertidal consumers on oceanic sandy beaches.