Richard Shucksmith

Non-native Aquaculture Species Releases: Implications for Aquatic Ecosystems

* Corresponding author Abstract Aquaculture is undergoing a rapid worldwide expansion. Of significant concern is the increasing use of non-native species, with subsequent escapes of these species and their associated pathogens and parasites posing a serious threat to native biodiversity, economic value and ecosystem function, particularly in regions rich in endemic species. The contribution of non-native species to the growth of the global aquaculture industry and the economic benefits that it has brought to many developing countries cannot be underestimated. However, minimizing the escapes of non-native aquaculture species must be a high priority for resource managers, conservationists and the aquaculture industry. This paper reviews intentional and unintentional non-native aquaculture introductions and the environmental consequences that escapes can have on the aquatic environment and presents a potential system of risk evaluation, management and funding mechanisms to assist in the long term sustainable development of the aquaculture industry.

Competition between the non-native amphipod Caprella mutica and two native species of caprellids Pseudoprotella phasma and Caprella linearis.

Competition plays an important role in invasion dynamics. According to Eltons biodiversity and invasibility hypothesis, non-native species must be competitively superior to the resident species in order to successfully invade. An invader that is ecologically similar to a native species may cause intense interspecific competition as they both require the same resource. Furthermore, an increase in the density of an invading competitor may enhance the intensity of the competitive interaction, however, this may be reduced if the inferior competitor has a refuge that reduces the amount of time it is in direct contact with the superior competitor. In laboratory-based competition experiments between the non-native caprellid Caprella mutica and two ecologically similar native caprellids Caprella linearis and Pseudoprotella phasma, C. mutica successfully displaced both species from homogeneous artificial habitat patches after 48 hours. Patches that contained a refuge reduced the number of C. linearis being displaced but only when C. mutica was at a low density. Potentially aggressive interactions between C. mutica and the native C. linearis may have caused C. linearis to be displaced from the patches and could have caused significantly higher mortality of C. linearis compared to the controls. This is the first study to show that the non-native C. mutica has the ability to displace ecologically similar native species when the resource space is limited and when the density of C. mutica was significantly (10 times) lower than the density of C. linearis .