The potential for waterbirds to act as a vector for zooplankton dispersal in the North Island, New Zealand
Permanent link to Research Commons versionhttps://hdl.handle.net/10289/15608
Zooplankton are essential components of freshwater ecosystems by controlling algal growth and sustaining higher trophic levels. Freshwater zooplankton are geographically isolated and are incapable of active dispersal to new freshwater sites. The dispersal of zooplankton can occur through natural dispersal vectors (e.g., wind, rain or waterfowl) or through human-mediated dispersal vectors (e.g., accidental or deliberate introductions). Dispersal of zooplankton is vital for maintaining gene flow between isolated sites and colonising new habitats. Zooplankton diapause eggs are well suited for dispersal as they are resistant to harsh conditions, e.g., digestion, drying and freezing. Diapause eggs increase the chance of survival in unfavourable conditions and are an important part of a zooplankton’s life cycle. This paper analyses New Zealand waterbirds’ dispersal of zooplankton internally (endozoochory) and externally (ectozoochory). This study quantified the dispersal of zooplankton internally (endozoochory) using the faecal droppings collected from waterbirds at two New Zealand Lakes. Faecal droppings were collected from Mallard Ducks, Canadian Geese, Greylag Geese, Black Swans and Australian Coots from Lake Rotoroa and Lake Rotorua. A total of 50 eggs were found in the faecal droppings of waterbirds, with a mean number of 0.75 eggs found per dropping. These results indicate that waterbirds are consuming zooplankton eggs. However, no significant difference was observed in the propagule count among waterbird species. Therefore it was unlikely that the waterbird species impacted the abundance or viability of diapause eggs. The sediment experiment showed zooplankton are inhabiting the shores of Lake Rotorua and Lake Rotoroa, where waterbirds are likely to come in contact with diapause located within the sediment. In Lake Rotorua, diapausing eggs from six species of rotifers, cladocerans, copepods and ostracods hatched from the littoral sediments. Strikingly, no hatching was observed in the littoral sediments from Lake Rotoroa. These results suggest that diapausing eggs are readily available to be picked up by waterbirds for external dispersal (ectozoochory). This study quantified the potential for zooplankton to be dispersed by waterbirds internally (endozoochory) and externally (ectozoochory). Results suggest that waterbird dispersal of zooplankton is occurring, but the numbers being transported are low. Although, the transport of a few individuals may be enough to achieve gene flow. Waterbirds are not be the primary vector for the dispersal of zooplankton. Human-mediated contributions e.g., shipping-related activities (ballast tanks), may play a more significant role than waterbirds in the dispersal of zooplankton.
The University of Waikato
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