Hydrobiologia (2009) 624:71–79 DOI 10.1007/s10750-008-9667-7 PRIMARY RESEARCH PAPER Susceptibility of larval dragonflies to zebra mussel colonization and its effect on larval movement and survivorship Ola M. Fincke Æ Diana Santiago Æ Stephen Hickner Æ Rosalie Bienek Received: 11 April 2008 / Revised: 19 November 2008 / Accepted: 4 December 2008 / Published online: 24 December 2008 Ó Springer Science+Business Media B.V. 2008 Abstract Colonization by the zebra mussel, Dreis- Compared to uncolonized individuals, Epitheca and sena polymorpha, was quantified for five dragonfly Progomphus with mussels emerged closer to the species that differed in size and larval habits in a water line. Among colonized Didymops, the distance Michigan lake. Both larger size and a non-burrowing traveled on land before emerging decreased with habit independently increased susceptibility to colo- increasing mussel load. Of the colonized Didymops nization. In 2005, over 50% of the final instars of the that could right themselves, righting time increased sprawlers Didymops transversa and Hagenius brevi- with mussel load. Because the two common species stylus were colonized, as well as younger instars. of sprawlers were disproportionately colonized, and Rarely colonized were Progomphus obscurus and mussel attachment decreased their chances of emerg- Dromogomphus spinosus, whose larvae burrow under ing, our results suggest that D. polymorpha has the sand, and the sprawler Epitheca princeps, whose final potential to affect the community structure of this instars were lightly covered with sand. Hagenius guild of aquatic and terrestrial predators. larvae that had been preyed upon carried more mussels than those dying of other causes. More Keywords Hagenius Didymops Á Á generally, mussel attachment decreased the probabil- Epitheca Prognomphus Dromogomphus Á Á Á ity that sprawlers left the water to emerge, the Dreissena Invasive species Mobility distance that some species traveled before emerging, Dragonfly communÁ ity structureÁ Á and the ability of an overturned sprawler to right itself. On average, final instars of Didymops and Hagenius remaining in the water carried three times Introduction as many mussels as individuals known to emerge. Since its introduction to the Great Lakes in the mid- 1980s, the zebra mussel, Dreissena polymorpha, has Handling editor: R. Bailey devastated native unionid mussel populations (Haag et al., 1993; Nalepa, 1994; Schloessner & Nalepa, O. M. Fincke (&) Department of Zoology, University of Oklahoma, 1994; Lauer & McComish, 2001), and has affected Norman, OK 73019, USA ecosystems more generally (e.g. Greenwood et al., e-mail: fi[email protected] 2001; Haynes et al., 2005). Although zebra mussel attachment on dragonflies has been documented, their O. M. Fincke D. Santiago S. Hickner R. Bienek University of MichiganÁ BiologicalÁ Station,Á Pellston, impact on these important aquatic predators remains MI 49769, USA unknown. In a review of the occurrence of zebra 123 72 Hydrobiologia (2009) 624:71–79 mussels on final instar larvae from the families thorax through which the adult dragonfly emerges Gomphidae, Corduliidae, and Libellulidae in Europe, (Fig. 1B), zebra mussels can prevent feeding or Canada, and the US, Weihrauch & Borcherding eclosion directly. If larval mobility interferes more (2002) mentioned only incidental sightings of zebra generally with foraging ability and/or predator avoid- mussels on a few larvae per site. ance, then final instars with mussels should be smaller In sandy bottom habitats that provide relatively few than those without mussels, and/or more likely to nonliving substrates for zebra mussel attachment, a exhibit evidence of predation (Fig. 1C). And because decline in large-shelled unionids may increase the all final instars of the study species must crawl out of colonization risk other living substrates such as the water to emerge, another fitness cost of zebra benthic odonate larvae. For example, in Douglas mussel attachment may be to prevent a larva from Lake, a mesotrophic kettle lake in northern Michigan, reaching shore, or, once there, from traveling a D. polymorpha, was first recorded in 2001. The initial sufficiently safe distance from water before emerging. rise in the zebra mussel population was followed by a The burrowers’ Progomphus obscurus and Dromo- decrease in unionid mussels (R. Vande Kopple, pers. gomphus spinosus typically emerge on the beach, comm.). At this site, zebra mussels were first observed although the latter can also emerge on trees adjacent on dragonfly larvae in the lake in 2003 (B. Scholtens, to shore. Larvae that emerge at the water’s edge risk pers. comm.). In May 2005, McCauley & Wehrly getting doused by waves before their wings have fully (2007) quantified high rates of colonization on final extended, making subsequent flight impossible. instars of the dragonflies Hagenius brevistylus and Hagenius brevistylus often emerges on the beach but Didymops transversa. However, their one-day study can occasionally be found as high as a meter up on did not address any fitness consequence of mussel trees in the forest. D. transeversa larvae travel far attachment. from shore, climbing as high as 9 m before emerging The aim of the current study was two-fold. First, we on a tree (O. M. Fincke, unpubl. data). In addition to asked whether some species in the Douglas Lake impeding travel on land, its mussel load may hamper odonate community were more susceptible than others the ability of a larva to right itself when overturned, as to colonization by zebra mussels. Secondly, we asked sometimes occurs if it encounters wave action while how zebra mussels affected larval growth, survivorship, crawling or swimming to shore, or falls while and mobility. Our study species were five common crawling up a vertical surface (O. M. Fincke, unpubl. dragonflies from three families that differed in final data). We predicted that increasing mussel load: (1) is instar size and larval behavior. Of the five, Hage- negatively correlated with distance traveled on land nius brevistylus (Gomphidae), Didymops transversa before emergence, and (2) decreases the ability of a (Micromiidae), and Epitheca princeps (Corduliidae), larva to right itself. are classified as ‘sprawlers’ because their larvae rest on top of the substrate (Needham et al., 2000). The largest of the five species, H. brevistylus, is unique in having a Materials and methods discoid abdomen, which may make it more susceptible to mussel colonization, despite the fact that its larvae The study site was the eastern portion of Douglas Lake hide under debris (Walker, 1958). In contrast to the and its shoreline at the University of Michigan Biolog- sprawlers, the larvae of Dromogomphus spinosus and ical Station (UMBS, 45°350N, 84°420W) near Pellston, Progomphus obscurus (Gomphidae) burrow 1–2 in. MI, USA. The study species can take up to 4 years into the sand, hiding from predators and potential prey to develop (Corbet, 1999). At this site, Didymops trans- (Walker, 1958). We predicted that dragonflies with a versa emerges from late May to early August. sprawling lifestyle and relatively large final instar size Epitheca princeps, Dromogompus spinosus, Progom- were at increased risk of colonization by zebra mussels. phus obscura, and Hagenius brevistylus emerge from We hypothesized that zebra mussels negatively late May or early June to mid July (O. M. Fincke, affect larval fitness by decreasing larval mobility, and unpubl. data). For simplicity, the study species are thereby indirectly decreasing growth rate and/or hereafter referred to by genus only. survivorship to emergence. Of course, by covering Between 28 June and 5 August 2005, larvae found the mouthparts (Fig. 1A) or the area of the dorsal in the water and on the beach were collected along a 123 Hydrobiologia (2009) 624:71–79 73 Fig. 1 Effects of zebra mussels on dragonfly fitness: A emergence in D. transversa, C evidence of predation on a D. transversa with zebra mussel attachment that impedes prey heavily colonized H. brevistylus, which is missing its head capture, B zebra mussels positioned such that they prevent transect that ran from the eastern end of South considered evidence of a successful emergence. An Fishtail Bay to Pine Point. In areas of shallow water, intact, dead larva with mussels blocking the central larva were collected as far out as 12 m but were more portion of the thorax where the larva emerges was regularly collected 5–7 m from the water line, which considered a failed emergence due to mussels. Dead was marked off in 1 m sections with flagging. Most larvae that were lacking the head or part of the body sampling in the water was done between 06:00 and were considered to have died from a predation event. 10:00 h when the water was calm and larvae could be The cause of mortality was otherwise undetermined. detected most easily. Species identity of larvae and For each live individual or exuvia, the number of exuvia and their distance from the water line were attached zebra mussels was noted. recorded. Although on a daily basis, the width of To determine the effect of larval size on the beach was stable at a given location (i.e. tidal effect probability of colonization across species, and to was minimal), the water line receded seasonally. To assess indirect effects of zebra mussel load on the avoid recounts of the same individual, all exuvia were growth of final instars, for a subset of dragonflies collected. Unless marked with paint and released (see head width, body length, and abdominal width at the Fig. 1B), live individuals found in the water were widest part, and the length of all attached mussels held in tanks of lake water at Lakeside Lab for were measured with calipers. Body area was esti- observations, and returned to the lake at the end of mated as the product of body length and width. A few the study. live individuals of similar size with and without zebra To assess whether mussel attachment increased the mussels were patted dry and weighed to estimate probability of predation or premature death of a final variation in mussel loads.