How common are ‘exotic’ invertebrates in public and botanical garden ponds?

by Ian Duggan, School of Science, The University of Waikato

Botanical and other public gardens have been responsible for an extensive movement of plants globally. Less appreciated, gardens have also been responsible for the movement of small animals, hitchhiking with the plants. The 1906 publication “The wild fauna and flora of the Royal Botanic Gardens, Kew”, for example, compiled a list of animal life recorded in Kew Gardens that was not native to the UK, and included a variety of insects, spiders, worms, and even frogs.

There have been similar introductions of aquatic invertebrates. A freshwater jellyfish, native to the Yangtze river valley, was not just first recorded — but actually described — from the ‘Victoria regia’ tank at the Royal Botanic Society’s Gardens in Regent’s Park, London (this species has since invaded New Zealand). New Zealand has similar examples. A small Japanese copepod species, Sinodiaptomus valkanovi, first described from the botanical gardens in Bulgaria in 1938, was found in the wintergardens in Auckland Domain in the early 2000s. At a similar time, the North American copepod Skistodiaptomus pallidus was recorded in ponds at Auckland Botanic Gardens. Further, Hamilton Gardens has an Australian copepod, Boeckella minuta, present in Turtle Lake. Overall, these findings suggested that garden ponds might be hot spots for invasions globally.

To test this hypothesis, my wife in tow, I visited ten public gardens in 2010, three in the UK and seven in the USA, to determine whether there was a widespread presence of non-native zooplankton in garden ponds; Royal Botanic Gardens, Edinburgh; Oxford University Gardens; Royal Botanic Gardens, Kew (UK); New York Botanical Gardens; Longwood Gardens, PA; Sarah P. Duke Gardens, Durham, NC; United States Botanical Gardens, Washington DC; Missouri Botanic Gardens, St. Louis, MO; Lincoln Park Conservatory, Chicago, IL; and Garfield Park Conservatory, Chicago, IL (USA).

Over 100 zooplankton species were found, but interestingly, not a single non-native species was recorded. This indicated that the threat of zooplankton invasions from botanical garden ponds does not appear to be as high as expected. This finding was surprising, given the rich history of gardens in spreading non-indigenous species, but may be indicative of two factors. Firstly, many zooplankton populations that have established in gardens are likely to have died out or had their habitats destroyed in the intervening period. For example, the ponds where the Japanese copepod Sinodiaptomus valkanovi was first recorded in Bulgaria has subsequently been destroyed, making New Zealand the only known place outside of Japan where this species is currently known. Secondly, the probability of new non-native species being introduced to gardens from their native ranges is now smaller than it was in the past; new aquatic plants are likely not entering botanical gardens from the wild.

As such, the prevalence of such invaders in New Zealand garden ponds is seemingly an anomaly. But why? This is a question I hope can be answered by surveying New Zealand garden ponds more widely in the future.

For more information, see: Duggan, I.C. & Duggan, K.S. (2011), Are botanical gardens a risk for zooplankton invasions? Biological Invasions 13: 2997-3003.