Effect of colonial tunicate presence on Ciona intestinalis recruitment within a mussel farming environment

Aquatic invasive species decrease yields and increase costs in aquaculture operations worldwide. Anecdotal evidence from Prince Edward Island (PEI, Canada) estuaries suggested that recruitment of the non-indigenous solitary tunicate Ciona intestinalis may be lower on aquaculture gear where colonial tunicates (Botryllus schlosseri and Botrylloides violaceus) are already present. We tested this interspecific competition hypothesis by comparing C. intestinalis recruitment on un-fouled settlement plates to those pre-settled with Botryllus schlosseri or Botrylloides violaceus. C. intestinalis occurred on all plates after 2 month, but it was much more abundant (~80% coverage) on unfouled plates than on pre-settled plates (