Insect Conservation and Diversity (2012) doi: 10.1111/j.1752-4598.2012.00210.x Aquatic insect assemblages associated with subalpine stream segment types in relict glaciated headwaters JOSHUA S. KUBO,1,2 CHRISTIAN E. TORGERSEN,2 SUSAN M. 1 2 1 BOLTON, ANNE A. WEEKES and ROBERT I. GARA 1School of Environmental and Forest Sciences, University of Washington, Seattle, WA, USA and 2U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Cascadia Field Station, University of Washington, Seattle, WA, USA Abstract. 1. Aquatic habitats and biotic assemblages in subalpine headwaters are sensitive to climate and human impacts. Understanding biotic responses to such perturbations and the contribution of high-elevation headwaters to riverine biodiversity requires the assessment of assemblage composition among habitat types. We compared aquatic insect assemblages among headwater stream seg- ment types in relict glaciated subalpine basins in Mt. Rainier National Park, Washington, USA. 2. Aquatic insects were collected during summer and autumn in three head- water basins. In each basin, three different stream segment types were sam- pled: colluvial groundwater sources, alluvial lake inlets, and cascade-bedrock lake outlets. Ward’s hierarchical cluster analysis revealed high b diversity in aquatic insect assemblages, and non-metric multidimensional scaling indicated that spatial and temporal patterns in assemblage composition differed among headwater stream segment types. Aquatic insect assemblages showed more fidelity to stream segment types than to individual basins, and the principal environmental variables associated with assemblage structure were temperature and substrate. 3. Indicator species analyses identified specific aquatic insects associated with each stream segment type. Several rare and potentially endemic aquatic insect taxa were present, including the recently described species, Lednia borealis (Bau- mann and Kondratieff). 4. Our results indicate that aquatic insect assemblages in relict glaciated sub- alpine headwaters were strongly differentiated among stream segment types. These results illustrate the contribution of headwaters to riverine biodiversity and emphasise the importance of these habitats for monitoring biotic responses to climate change. Monitoring biotic assemblages in high-elevation headwaters is needed to prevent the potential loss of unique and sensitive biota. Key words. Aquatic biomonitoring, aquatic insect assemblages, beta diversity, headwater stream types, subalpine headwaters. Introduction Correspondence: Joshua S. Kubo, PO Box 352100 School of Environmental and Forest Sciences, University of Washington, Environmental shifts caused by climate change are pre- Seattle, WA 98195, USA. E-mail: [email protected] dicted to strongly influence streams in alpine and high lat- Joshua S. Kubo and Anne A. Weekes are not currently itude ecosystems (Malmqvist & Eriksson, 1995; Solomon affiliated with U.S. geological survey, but were affiliated at the et al., 2007; Brown et al., 2007, 2009a,b; Hannah et al., time of this research. 2007). Aquatic insect assemblages in these streams © 2012 The Authors Insect Conservation and Diversity © 2012 The Royal Entomological Society 1 2 Joshua S. Kubo et al. may provide indicators for monitoring the effects of such processes (Weekes et al., 2012 in review-b; Brardinoni & environmental perturbations because they are integral to Hassan, 2006, 2007). These geohydrologic processes oper- aquatic food webs, and their distribution and abundance ate hierarchically, governing the type, structure, and are strongly influenced by temperature and stream flow dynamics of stream habitats. Within relict glaciated (Malmqvist & Eriksson, 1995; Milner et al., 2001a, 2001b; basins, longitudinal valley-step headwater habitats include Hauer & Resh, 2006; Hannah et al., 2007; Brown et al., the following stream segment types: colluvial groundwater 2009b; Muhlfeld et al., 2011). However, more information sources, alluvial lake inlets, and cascade-bedrock lake out- is needed on variation in assemblage composition among lets (Weekes et al., in review-a). For these stream segment geohydrologic stream habitat types (Weekes et al.,in types to be useful strata for biomonitoring, their relation- review-a). Such information could be used to better eluci- ship with aquatic biota needs to be quantified (Hawkins date the linkages between geohydrologic and ecological et al., 2000). processes. Headwater ecosystems provide an array of iso- Our goal was to compare aquatic insect assemblages lated, heterogeneous habitats that support genetically dis- among and within relict glaciated subalpine headwater tinct, rare, and often endemic species (Gomi et al., 2002; basins. Specifically, we evaluated associations between Clarke et al., 2008; Meyer et al., 2007; Price and Neville, aquatic insect assemblages and stream segment types. 2003). Although headwater streams are thought to be rel- Throughout our article, we refer to b diversity as the vari- atively depauperate, with low site-specific (a) diversity, ation in assemblage composition across stream segment Finn et al. (2011) found that headwaters not only have types (Anderson et al., 2011). We focused on aquatic high variations in diversity among sites (b), but signifi- insects because they account for more than 80% of fresh- cantly influence regional (c) diversity. Changes in stream water macroinvertebrate taxa (Heino, 2009), and have flow and temperature associated with climate change are been widely used for biomonitoring and habitat assess- expected to reduce biotic variation among headwater hab- ments (Vinson and Hawkins, 1998; Wallace and Webster, itats (Brown et al., 2007; Finn et al., 2011). Similarly, rare 1996; Townsend and Hildrew, 1994; Rosenberg et al., and endemic species may be highly sensitive to environ- 2008). Our first objective was to characterise spatial mental shifts (Gaston, 1994; Cao et al., 1998). Document- patterns in aquatic insect assemblage structure among ing and monitoring headwater taxa and habitat types is colluvial groundwater source, alluvial lake inlet, and therefore essential for conserving biodiversity within cascade-bedrock lake outlet stream segment types. We riverine ecosystems. However, few headwater studies have hypothesised that assemblage composition would vary focused on variation in assemblage composition among among these headwater segment types and that specific habitats in headwater systems (Heino et al., 2003a,b; Finn assemblages would be associated with each stream seg- & Poff, 2005, 2011; Clarke et al., 2008; Finn et al., 2011). ment type (Finn & Poff, 2005, 2011; Bogan & Lytle, 2007; In addition, there is a need to assess further headwater Brown et al., 2009a; Monaghan et al., 2005; Weekes assemblages within various ecoregions to evaluate the et al., in review-a). Our second objective was to compare influence of headwater systems in riverine b and c diver- temporal patterns in aquatic insect assemblage composi- sity (Heino et al., 2003b; Finn & Poff, 2005; Finn et al., tion among stream segment types and basins. We hypoth- 2011). esised that assemblage composition and temporal There has been much research on aquatic insect assem- variation would be related to geohydrologic processes blage patterns in active glaciated headwater systems (Weekes et al., in review-a). Our third objective was to (Lods-Crozet et al., 2001; Milner et al., 2001a,b; Friberg examine the taxonomic composition of aquatic insect et al., 2001; Hieber et al., 2005; Milner et al., 2009; Jacob- fauna unique to these stream segment types to identify sen et al., 2010; Hamerlik & Jacobsen, 2011). However, potentially rare and endemic species (Meyer et al., 2007; additional studies on assemblage patterns and geohydro- Brown et al., 2007, 2009b; Baumann & Kondratieff, logic-ecological linkages in relict (i.e. formerly) glaciated 2010). high-elevation headwaters are needed to assess location- specific ecological responses. In order for conservation and biomonitoring strategies to better facilitate global Methods progress in headwater ecology, research efforts must focus on the applicability of documented patterns and rela- Study area tionships throughout various headwater systems. Because headwater biomonitoring requires an accurate assessment Aquatic insect assemblages were assessed in three relict of distinct physical attributes and biotic assemblages glaciated subalpine basins in Mt. Rainier National Park, (Hawkins et al., 2000), stratifying the spatial and tempo- Washington, USA (Fig. 1). The basins that were selected ral variation in hydrologic, geomorphic, and biological for sampling were representative of valley-step channel attributes is essential for determining ecologically distinct classifications characterised by Weekes et al. (in review-a) processes (Gomi et al., 2002). Specifically, within relict which are based on longitudinal landscape units in mon- glaciated subalpine basins, predictable areas of a land- tane drainages (Montgomery and Buffington, 1997; scape can be characterised based on suites of related phys- Brardinoni & Hassan, 2006, 2007). These small valley-step ical attributes including hydrologic and geomorphologic basins had comparable elevations, slopes, and aspects © 2012 The Authors Insect Conservation and Diversity © 2012 The Royal Entomological Society, Insect Conservation and Diversity Subalpine aquatic insect assemblages 3 Sample site parameters At each stream segment sample location, point mea- surements of water temperature,