Role of non-indigenous species in structuring benthic communities after fragmentation events: an experimental approach

Habitat loss and fragmentation, and biological invasions are widely considered the most significant threats to global biodiversity. While marine invasions have already shown dramatic impacts around the world’s coasts, many of these habitats are becoming increasingly urbanized, resulting in fragmentation of natural landscape worldwide. This study developed in Madeira (NE Atlantic) aims to understand the synergistic interactions between fragmentation and biological invasions using submerged experimental settlement panels in the field for 3 months. We fragmented crustose coralline habitats, decreasing patch size without an overall habitat loss, and determined its effects on the patterns of abundance of marine fouling organisms across limiting assemblages with or without the presence of non-indigenous species (NIS, considered invaded and non-invaded systems in this study). The presence of crustose coralline algae suppressed the recruitment of some NIS ( Parasmitina alba and Botrylloides niger ). Our results also showed that the abundance of NIS (e.g. B. niger ) could be prompted in highly fragmented habitats, colonizing bare substrates very efficiently. Overall, evidence indicates that fragmentation events modulate biotic interactions and consequently determine the structure of the fouling communities. Future research should address both processes when analyzing biotic resistance to invasion in urban marine habitats.