Invasive sea squirts: A growing global problem

Abstract

Ascidians are one of the most important taxa in fouling communities of artificial structures. These organisms can establish new populations and successfully invade new areas, spreading outside the region where they were initially introduced, due to their high reproductive and growth rates and their broad tolerance to environmental conditions. Predation pressure has also an influence on the colonization success of ascidians, with variations depending on their life stage, the fluctuations of the abundance of predators and their identity. Among these factors, the consequences of invasive and native predators on different life stages of invasive ascidians have been poorly evaluated. Thus, the goal of this work is to assess the survival of different life stages (juveniles and adults) of the two most successful invasive ascidians in the presence of different benthic predators in a cold temperate port. To evaluate this, we performed experiments offering juvenile and adult ascidians to different native and exotic benthic predators, under controlled aquarium conditions. We observed that juvenile ascidians were more vulnerable to predation than adults. Moreover, adult vulnerability differed between ascidian species probably because of different physical and chemical defences. Our results evidence the importance of evaluating the effects of predation through different stages of the life cycle of the preys, and the role of both native and exotic predators. Therefore, we hypothesize that juvenile ascidians depend on the use of different refuges, such as mussel beds and adult ascidians, to escape from predation until they reach a less vulnerable adult size. Understanding the differential effects of predation through different stages of life-history of the preys, and the interaction between native and exotic species helps to comprehend the causes of success in the establishment of invasive species.