Effects of invasive crayfish on fine sediment accumulation, gravel movement, and macroinvertebrate communities Lindsey K. Albertson1,2 and Melinda D. Daniels1,3 1Stroud Water Research Center, 970 Spencer Road, Avondale, Pennsylvania 19311 USA Abstract: Crayfish are one of the most prolific freshwater invaders, yet the role of crayfish as ecosystem engineers that structure benthic substrates in their nonnative habitat is rarely studied. We used an in situ experimental manipulation to document changes in sediment dynamics and macroinvertebrate density and richness caused by the presence or absence of invasive rusty crayfish (Orconectes rusticus). Rusty crayfish reduced fine-sediment ac- cumulation and increased pit and mound structures in the river bed by moving gravels at the bed surface. We predicted that this omnivorous species would directly reduce macroinvertebrate density and richness, but we found that macroinvertebrate density was higher in treatments with rusty crayfish present and that mac- roinvertebrate richness did not differ between treatments with and without crayfish. Our findings suggest that rusty crayfish, which are spreading throughout the northeast USA, are probably important engineers of physical habitat structure in stream ecosystems. Rusty crayfish may also have unexpected, facilitative consequences for other benthic species by reducing fine-sediment accumulation in streams that are sediment impaired. Our study illustrates that biological forces can influence benthic gravel-size distributions and topography and suggests that crayfish may be important drivers of substrate-sorting dynamics and disturbance regimes, with consequences for community structure in streams where they are invasive. Key words: ecosystem engineering, biophysical interactions, exotic, streams, sediment transport Invasive species pose one of the world’s most pressing Many invaders are ecosystem engineers (Crooks 2002), environmental problems (Vitousek et al. 1997, Jenkins which are organisms that affect abiotic features of eco- 2003). Invasions are occurring across a variety of habitats, systems, including physical habitat characteristics and but freshwater systems are particularly sensitive to inva- biogeochemical cycles (Jones et al. 1994, Jones 2012). In sion by nonnative species compared with their terrestrial streams, animals can substantially alter habitat structure, counterparts (Ricciardi and Rasmussen 1999). For example, sediment transport, and nutrient cycling (Moore 2006, in freshwater ecosystems, invaders such as carp (Cyprini- Albertson and Allen 2015). Aquatic animals ranging from dae; Koehn 2004, Gozlan et al. 2010) and Zebra Mussels nutria to fishes to macroinvertebrates move gravels, alter (Dreissena polymorpha; MacIsaac 1996) have dramatically riverbank formation, and make changes to bed topogra- influenced native species diversity, productivity, and eco- phy. For example, fish can create divots as they build nests system function (Strayer 2010). A significant amount of for egg protection, and insects can agitate fine sediments funding is allocated toward invasive control and reintro- as they search for food (Zanetell and Peckarsky 1996, duction of natives because of substantial changes to natu- Moore et al. 2004). Biota can regulate substrate dynamics, ral habitats and the loss of ecosystem function attributed including grain-size distributions, sediment erosion dur- to invasive species in many instances (Bernhardt et al. ing floods, and fine-sediment suspension levels (Mont- 2005, Pimentel et al. 2005). However, the effects of inva- gomery et al. 1996, Albertson et al. 2014, Harvey et al. sive species on the structure of ecosystems in the growing 2014). number of urbanized and impaired streams are not well Crayfishareoneofthemostprolificgroupsofinvaders studied and may differ from effects in pristine systems across the globe (Lodge et al. 2000, 2012, Savini et al. 2010, (Ricciardi 2001, Smucker and Detenbeck 2014). Twardochleb et al. 2013). Invasive crayfishposeaparticu- E-mail addresses: 2Present address: Montana State University, Department of Ecology, Bozeman, Montana 59717 USA, [email protected]; [email protected] DOI: 10.1086/685860. Received 22 March 2015; Accepted 21 September 2015; Published online 12 February 2016. Freshwater Science. 2016. 35(2):644–653. © 2016 by The Society for Freshwater Science. This content downloaded from 153.090.050.040 on May 27, 2016 09:18:19 AM All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c). Volume 35 June 2016 | 645 larly significant threat to freshwater ecosystems because dence of the physical effects of O. rusticus invasions on crayfish are ecosystem engineers of both aquatic commu- gravel disturbance and consequences for benthic commu- nity structure and physical habitat. Current evidence for the nities and ecosystem processes. effects of crayfish on benthic communities suggests a signif- icant reduction in macroinvertebrate, fish, and macrophyte density, shifts in macroinvertebrate and fish community METHODS composition, and an increase in the breakdown of detritus Study site (Momot et al. 1978, Wilson et al. 2004, Bobeldyk and We conducted our study in Valley Creek (lat 40°04′N, Lamberti 2008, 2010). Crayfish are bioturbators that also long 75°27′W), situated in Valley Forge National Historic can engineer physical habitat by disrupting benthic sedi- Park, King of Prussia, PA, from 24 October to 14 No- ments as they forage or build shelters (Parkyn et al. 1997, vember 2014. Valley Creek is an urbanized, perennial Statzner et al. 2003, Creed and Reed 2004). Disturbance by 3rd-order tributary of the Schuylkill River. In autumn, it crayfish can loosen riverbed gravels, which subsequently in- is ∼10 m wide and 0.24 m deep. In the heavily populated creases sediment erosion during floods (Statzner et al. 2003, Schuylkill River basin, 77% of streams are in fair or poor Statzner and Peltret 2006). The bioturbating activities of condition, and forest buffer zones have been reduced some crayfish species can be extensive and cause complete along many waterways (Jackson 2009). Valley Creek is riverbank collapse (Guan 1994, Barbaresi et al. 2004), and classified as an impaired stream (VFNHP and PFBCCP the role of crayfish as agents of disturbance may have im- 2004, Jackson 2009). Excessive sedimentation, excessive portant consequences for biodiversity and benthic commu- stormwater, polychlorinated biphenyl (PCB) contamina- nity recovery following high-flow events (Resh et al. 1988, tion, and channel instability have been identified as pri- Lake 2000). Crayfish also can alter fine-sediment dynamics mary drivers of impairment. The hydrologic regime is flashy. (Harvey et al. 2014), which may influence feedbacks be- Base flows range from 0.28 m3/s in autumn to 1.70 m3/s in tween sediment suspension, turbidity, and biofilm commu- spring, interspersed with frequent flood events. Discharge nities (Wood 1997, Lawler et al. 2006) and regulate suitable averaged 0.57 m3/s during the study period, and 2 moder- habitat for fish egg development (Suttle et al. 2004). In ate flow events peaked at 1.12 m3/s on 1 November and invasions of Europe by Pacifastacus leniusculus and Pro- 0.85 m3/s on 6 November (US Geological Survey gage cambarus clarkii,crayfish altered aquatic communities and 01473169; Fig. 1). Rusty crayfish were first documented in substantially affected gravel-bed morphology, erosion, and Valley Creek in 2008 (http://www.nps.gov/kids/features fine-sediment suspension (Barbaresi et al. 2004, Johnson /2014/crayfishCorps.cfm#). The National Park Service man- et al. 2011, Harvey et al. 2014). ages rusty crayfish populations in Valley Creek primarily The rusty crayfish (Orconectes rusticus) is native to the by using an intensive, volunteer-based removal effort called Ohio River basin and has become invasive in the north- the Crayfish Corps. eastern USA. Spread of the invasive rusty crayfish has been identified as a threat for >4 decades (Lodge et al. 2000, Wilson et al. 2004) and has significantly reduced native crayfish diversity (Taylor et al. 1996). Orconectes rusticus moved into southern Pennsylvania (PA), the loca- tion of our research, in the 1960s–1970s (Kuhlmann and Hazelton 2007, Lieb et al. 2011). It can outcompete native crayfish species, reduce macroinvertebrates and detritus (Lodge et al. 1986, Olden et al. 2006), cause shifts in fish populations (Roth and Kitchell 2005), and reduce stand- ing stock of macrophytes (Roth et al. 2007). Several studies now illustrate the strong physical- engineering role of invasive crayfishes, but despite its rapid spread, few investigators have explored the role of invasive O. rusticus in structuring benthic substrate dynamics. We conducted a field experiment to investigate the influence of rusty crayfish on benthic substrates and macroinver- tebrate communities. We used an in situ manipulation of the presence or absence of O. rusticus to address the fol- lowing questions: 1) Does O. rusticus change riverbed to- pography, sediment sorting, and fine-sediment accumula- Figure 1. Discharge in Valley Creek during the study period. tion? 2) How does O. rusticus influence macroinvertebrate Over the course of the experiment, discharge averaged 0.57 m3/s communities? Our study provides some of the first evi- (cms). Closed circles indicate mean discharge per day. This content downloaded from 153.090.050.040 on May 27, 2016 09:18:19 AM All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).