Aquarium molluscs as a case study in risk assessment of incidental freshwater fauna

Because biological invasions may cause loss of biodiversity, accurate predictions are necessary for implementing effective restrictions aimed at specific high-risk taxa. The majority of freshwater macroinvertebrate invaders are molluscs and crustaceans. The pet trade has been considered one of the main pathways for new introductions of such species. Risk assessment is usually focused on traded ornamental species whereas, despite their potential importance, incidental hitchhiking molluscs are usually given only minimal consideration. We surveyed the Czech Republic, which is one of the leading markets for aquarium species in the European Union (EU), and found 41 freshwater mollusc species (25 ornamental gastropods, 6 ornamental clams, and 10 hitchhiking gastropods) representing 13 families. We extrapolated data from the Czech Republic and, using Climatch v. 1.0, matched the climate in each species' native range to the entire territory of the EU. We also assessed the risk associated with each species by FI-ISK. Hitchhiking gastropods were found to be significantly more hazardous and with higher potential to become established within the EU than were ornamental gastropods and bivalves. Many hitchhikers may be easily overlooked due to their small size and cryptic coloration or shape. Thus, they easily can be accidentally imported in association with aquarium plants. Therefore, we recommend here to disinfect imported ornamental plants to eradicate these unwanted faunal assemblages.