Odonata: Libellulidae) on the Move
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The Weta 50:10-17 10 Tramea loewii (Odonata: Libellulidae) on the move Tyler Mathesona, Olivier Balla*, Stephen Poheb aNorthTec, Department of Applied and Environmental Sciences, Whangarei bUniversity of Canterbury, School of Biological Sciences, Christchurch *Email: [email protected] Abstract The dragonfly Tramea loewii has recently become established in New Zealand, with a known distribution on the Aupouri Peninsula north of Kaitaia. To determine whether the species has spread further south, the littoral zones of eleven central Northland lakes from Ahipara to Waipu were sampled. Searches for exuviae and adults of T. loewii were also conducted at each lake. Larval T. loewii were only found at the Uretiti sand pit lake near Ruakaka, south of Whangarei. Many exuviae and adults in flight were also observed at the lake, indicating the species is established there. This represents a substantial range expansion and is the southernmost record of T. loewii to date. Keywords: dragonfly, lakes, littoral zone, New Zealand, Northland, self-introduced Introduction The dragonfly, Tramea loewii (Odonata: Anisoptera: Libellulidae) is known from Australia, Indonesia, Papua New Guinea and New Caledonia, as well as scattered islands in the western Pacific and Indian oceans (ABRS 2014). Morphologically, it is quite distinctive. Larvae can be recognised by the prominent, seta-covered, lateral spines on abdominal segments 8 and 9 (Figure 1), and adults from the red abdomen and the dark markings at the bases of their hind wings (Figure 2) (Rowe et al. 2011). Tramea loewii was first observed in New Zealand in 2005 (Rowe et al. 2011) and is now established in the far north of New Zealand (Winterbourn et al. 2011). It was found in 8 of 17 dune lakes surveyed on the Aupouri Peninsula in 2008, the southernmost being Lake Heather near Kaitaia (Winterbourn et al. 2011). The aim of our study was to determine whether T. loewii also occurs south of Kaitaia by sampling eleven central Northland lakes 11 Tyler Matheson et al. between Ahipara and Waipu. Incidental observations of other species of Anisoptera encountered were also made. Figure 1. Tramea loewii larva showing the seta-covered lateral spines on abdominal segments 8 and 9 (Photo: Steve Pohe). The Weta 50:10-17 12 Figure 2. Male T. loewii showing red abdomen and the dark markings at the hind wing bases (photo: Deane Lewis). Methods We searched for T. loewii by collecting odonate larvae from the littoral zones of eleven Northland lakes, from Ahipara in the north to Waipu in the south, between 17 February and 11 March 2015 (Table 1). The littoral zone of each lake was sampled at four well-spaced, accessible, sites. A triangular hand held net (mesh size 0.5 mm, mouth area 0.1 m2) was swept through submerged vegetation (macrophytes and submerged parts of the littoral sedge beds) and the surface layer of sediment to collect larvae. An area of approximately 3 m2 was sampled at each site (i.e. 12 m2 at each lake). The contents of the net were emptied into a tray for sorting. All anisopteran larvae were removed and transferred to containers of 80% ethanol for later identification in the laboratory using a dissecting microscope. All remaining macroinvertebrates were returned to the lakes. While visiting each lake, we also searched for T. loewii by observing and identifying adult dragonflies in flight. Any anisopteran exuviae found were collected and identified. Anisopteran larvae and exuviae were identified using the keys of Rowe (2006) and Landcare Research (2015). 13 Tyler Matheson et al. Table 1. Lakes surveyed for T. loewii in the current study. Physical features of the lakes and their trophic states where known1 are also given. Lakes are listed from north to south. Lake GPS location2 Lake type Depth Area Trophic state (m) (ha) Waimimiha 1615300/6110620 Dune/natural <5 9.2 Hypertrophic South Manuwai 1678800/6108160 Artificial >10 133 Eutrophic Omapere 1672600/6086600 Volcanic/natural 2.0–2.6 1197 Supertrophic Owhareiti 1685210/6084490 Volcanic/natural 16 95.9 Eutrophic Waro 1716670/6061100 Artificial 5–6 4.7 Oligotrophic Kai Iwi 1659250/6036410 Dune/natural 16 22.6 Oligotrophic Ora 1716200/6049130 Volcanic/natural - 2.2 Hypertrophic? Whau 1716620/6047350 Artificial 16.6 19.7 Eutrophic? Valley Millington 1711550/6045310 Artificial 12 2.5 Eutrophic? Road Uretiti sand 1731370/6023350 Artificial - 2.7 - pit (north) Waipu Golf 1731870/6021200 Artificial - 0.6 Eutrophic? Course 1Information on lake physical features and trophic state was collated from Wells et al. 2007, Ballinger et al. 2013 and NRC 2013, as well as information from Lisa Forrester, Rohan Wells, Andrew MacDonald, Terry Harris and Mike McGlynn. A dash (-) denotes no data were available; a question mark indicates a best guess with limited data available. 2East/North: NZGD 2000: NZTM Results One late instar T. loewii larva was found at the Uretiti sand pit lake (Table 2) (sampled on 28/2/15). The littoral zone of this lake was dominated by submerged macrophytes and extensive beds of emergent raupo (Typha orientalis). A number of exuviae of T. loewii were also seen there and numerous adults were flying. A single adult was captured and photographed to confirm the identity of the species. No larvae, exuviae, or adults of T. loewii were detected at any of the other 10 lakes. Hemicordulia australiae was the most commonly encountered species at the lakes, with both larvae and adults often abundant. Neither H. australiae nor any other anisopterans were found at the highly The Weta 50:10-17 14 eutrophic Lake Omapere. Hemianax papuensis was found at five of the 11 lakes, though larvae were only found at the Uretiti sand pit lake. Table 2. Presence of the various life stages of T. loewii and two other dragonfly species in the 11 surveyed lakes (L = larvae, E = exuviae, A = adults, - = not detected at any life stage). Lake Tramea Hemicordulia Hemianax loewii australiae papuensis Waimimiha South - L,A A Manuwai - A A Omapere - - - Owhareiti - L,E,A E,A Waro - L,A - Kai Iwi - E,A - Ora - L,A - Whau Valley - L,A - Millington Road - L,A A Uretiti sand pit (north) L,E,A L,E,A L,E,A Waipu Golf Course - A - Discussion Discovery of larvae, as well as exuviae and flying adults, at the Uretiti sand pit lake near Ruakaka, indicates that T. loewii has established a population there. This represents a range expansion in a south-easterly direction of around 150 km from Lake Heather, and is the southernmost record of T. loewii to date. However, as no other populations were found in this study, it is not possible to conclude that T. loewii also occupies the area between Kaitaia and Ruakaka. Thus, the Uretiti sand pit lake population may be an isolated one. Confirmation of the absence of a species can be very difficult. Could our sampling have missed T. loewii at some of the lakes where it was in fact present? The probability of detecting T. loewii would be affected by many factors including weather, seasonal life history patterns and lake-specific factors. Sampling in Lake Heather, Winterbourn & Pohe (2013) showed that final instars of T. loewii were present from December 2011 to February 2012 and early/small instars were present in March 2011. However, in February 2011 they found no larvae of T. loewii. The timing of our surveys coincided with this “transition 15 Tyler Matheson et al. period”, so the likelihood of detecting larvae may have been low. Nevertheless, the finding of a late instar larva at the Uretiti sand pit lake on 28 February 2015 agrees with the seasonal life history pattern observed by Winterbourn & Pohe (2013). Although false negative results should not be discounted, the fact that we searched for larvae, exuviae and adults reduces the likelihood that T. loewii was overlooked. The rapid range expansion of T. loewii in New Zealand is not unexpected, given that it is a powerful flier and known to disperse long distances (Farrow 1984, Rowe et al. 2011). However, it needs to be acknowledged that the Uretiti sand pit lake population could represent a new colonisation event from Australia or elsewhere in the western Pacific, rather than a range expansion from the Aupouri Peninsula. Whether a population of T. loewii persists at the Uretiti sand pit lake remains to be seen, as the Aupouri Peninsula further north is already close to the likely southern limit of its range relative to its distribution in Australia (Rowe et al. 2011). However, being an easily recognised and mobile species, T. loewii could be a useful climate change sentinel. Hemicordulia australiae was the most abundant and widespread dragonfly found in our study. This was also the case in a survey of dune lakes on the Aupouri Peninsula (Ball et al. 2015). However, we did not find Aeshna brevistyla or Diplacodes bipunctata in the present study, despite both of them being widely distributed and sometimes abundant in the more northern lakes. Acknowledgements We are grateful to Deane Lewis (http://dl.id.au) for supplying the photo of an adult T. loewii. Lisa Forrester, Cameron Bunton and Ashlee Lawrence (Northland Regional Council) kindly assisted with lake sampling, and Lisa Forrester, Andrew Macdonald (Northland Regional Council), Rohan Wells (NIWA), Terry Harris (Mangawhai) and Mike McGlynn (freshwater fish contractor) provided incidental observations about some of the lakes sampled. We also thank Mike Winterbourn (University of Canterbury) for assisting with species identifications and for providing helpful comments on an earlier draft. Finally, we are grateful to the owners and managers of all of the lakes for granting permission to sample. The Weta 50:10-17 16 References ABRS. 2009: Australian faunal directory.