Grass carp and incidental invaders from aquaculture: a study of impacts on zooplankton communities and invader origins

摘要

The movement of fish from aquaculture facilities has led to invasions of non-native species globally, including of ‘hitch-hiking’ species, resulting in impacts on the composition of communities in recipient ecosystems. This thesis employs both community scale analysis and sensitive molecular techniques to assess the effects of grass carp translocations on zooplankton communities and to determine the origins of an incidental non-native invader. In the first component, I tested the effects of grass carp translocations from aquaculture facilities on ponds in the Auckland region, New Zealand. Zooplankton community composition was quantified in 34 ponds that had been subject to grass carp release and 31 which had no grass carp introductions. A significant difference in zooplankton community composition was observed between ponds that had received grass carp translocations and those that had not. Differences in zooplankton community composition between ponds with and without carp releases were attributable to: 1) the establishment of zooplankton originating from aquaculture ponds, including non-native species; and 2) the effects of grass carp activity, through habitat modification. Effective measures to curb the proliferation of non-native taxa within aquaculture facilities, and to mitigate the unintentional movement of non-native taxa with translocations from these facilities, are required to reduce future introductions.In the second component of this thesis I used a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene to more precisely identify the origins of invasions of freshwater calanoid copepod Skistodiaptomus pallidus (Herrick 1879). This was applied to populations sampled from within New Zealand, which have been linked to the release of fish from aquaculture facilities, and to populations found in Germany, which have possible links to a shipping vector. The S. pallidus COI sequences placed both the New Zealand and German specimens with those from the most easterly regions of the USA (e.g., New York, Virginia and Georgia). However, several haplotypes were found to be divergent between the New Zealand and German populations, indicating the exact sources of the introductions were likely different for each country. German sequences had greater haplotype diversity than those from New Zealand, supporting the suggestions of a shipping related vector of introduction to Germany. Both German and New Zealand populations contained haplotypes that were closely related to North American sequence records. However, further sampling of the native range will be required to determine the exact origin of the non-indigenous S. pallidus populations. With this additional information it may also be possible to determine more precisely the vectors of introduction. Collectively, the two research chapters provide a broader understanding of invasion processes and the effects of grass carp translocations on the zooplankton communities within recipient ponds in New Zealand. My research has immediate application in the re-evaluation of fish translocation management practises and impacts.