Invasive alien species and their effects on marine animal forests

Nonindigenous species are increasingly transported around the world through multiple pathways by a diversity of vectors. Invasive species are a subset of those that are introduced into the receptor community, where they establish and increase their population to a size where they impact the native system. Marine invasive species can therefore interact with and modify native animal forests and/or create novel ones resulting in simple-to-complex changes in material cycling, energy flow, ecosystem structure, and function. Despite the ever increasing number of studies dealing with marine invasive species, mostly biological invasions are mentioned generically as one of a number of threats of direct and indirect effects of human activities on animal forests. In order to redress this imbalance, this chapter focuses on invasive species as modifiers and creators of marine animal forests. As well as some theoretical consideration of biological invasion, we consider how pathways and vectors have changed over time and the importance of historical collections. We overview the available information regarding the main taxonomic groups of marine species that are invasive to animal forests, what makes them successful invaders, and how they interact with and effect the receptor community. The establishment of novel animal forests through biological invasion is also reviewed. We identify knowledge gaps and present perspectives and challenges for future research.