Predator-prey interactions as key drivers for the invasion success of a potentially neurotoxic sea slug

Abstract

Only a fraction of the species that are introduced succeed in the non-native environment, while others fail to survive, reproduce and/or disperse. Understanding the causes underlying each outcome is key to designing better early detection, prevention and management programs, and to deepen our knowledge of the invasion process. Here, we examine whether predator–prey interactions favor the invasion of a potentially neurotoxic mollusk in the South Western Atlantic (SWA). The grey side-gilled sea slug Pleurobranchaea maculata was recently detected in the SWA, where it has spread rapidly along the coast. In this work, we examine two hypotheses that may have driven the invasion success of P. maculata: (1) it has a high dietary plasticity, able to exploit resources in a variety of habitats within the invaded range and simultaneously (2) it lacks native predators that can control its abundance or spread. First, we identified the prey sources of P. maculata through experimental trials; then we compared its diet composition between different sites and seasons; and finally we experimentally assessed the effect of native potential predators. We found that diet composition is broad and varies in time and space, probably in relation to prey availability. Additionally, we observed that local predators do not recognize P. maculata as a prey. Probably, mechanisms underlying predator avoidance are related to the presence of chemical defenses that can be novel in the invaded environment. We propose that predator–prey interactions are key drivers favoring the establishment of non-native P. maculata via high levels of plasticity to exploit resources, the absence of biotic resistance and the increased availability of food associated with artificial substrates such as ports are probable mechanisms underlying the invasion success of this marine gastropod.