Aquatic Insect Assemblages Associated with Subalpine Stream Segment Types in Relict Glaciated Headwaters

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 segment types in relict glaciated subalpine basins in Mt. Rainier National Park, Washington, USA. 2. Aquatic insects were collected during summer and autumn in three headwater basins. In each basin, three different stream segment types were sampled: 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 subalpine 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

Sample site parameters

At each stream segment sample location, point measurements of water temperature, pH, and conductivity were recorded for general site descriptions. In addition, within the sample area for each stream segment type, substrate was qualitatively assessed by visually estimating the relative percent cover of silt, sand, gravel, cobble, boulder, bedrock, coarse particulate organic matter, ﬁne particulate organic matter, coarse wood, and moss/grass (see Cum- mins, 1962). Point measurements of temperature, electrical conductivity, and pH for each stream segment type were measured mid-day (between 11:00 and 14:00) using a por- table meter (YSI meter, model 63) during each sample visit. The probe was placed at 10 cm depth, allowed to equilibrate for approximately 60 s, and was calibrated three times throughout the sample season.

Field sampling and insect identiﬁcation

Fig. 1. Locations of sampled stream segments within relict glaci- Stream segment types were sampled for aquatic insects ated subalpine basins in Mt. Rainier National Park, Washington, every other week from 28 June to 20 October in 2010 USA. using a 30.5-cm-wide D-frame kick net with a 20-cm-long net and 250-lm mesh. Within each stream segment type, multiple kick net sweeps were collected and combined for (Table 1). Within each basin, aquatic insects were collected a total area of 2 m2. Kick net sweeps in alluvial lake inlet in a section of the channel longitudinal profile in three and cascade-bedrock lake outlet stream segments were headwater stream segment types: colluvial groundwater collected along a perpendicular transect across each sources (CGS), alluvial lake inlets (ALI), and cascade- stream type. In colluvial groundwater sources, coarse col- bedrock lake outlets (CBLO). Within each basin, stream luvium, narrow wetted widths, and minimal stream depths segment types were sampled at similar elevations made it difficult to use perpendicular transects, so a com- (Table 2). Colluvial groundwater sources originated from bination of longitudinally connected patches were com- boulder-rock talus slopes and were associated with bined for the 2-m2 sample area. Aquatic insects were groundwater or subsurface inputs (Weekes et al.,in collected by agitating streambed substrates upstream with review-a). Colluvial source segments flowed into alluvial the D-frame kick net held downstream for 1 min (Wil- lake inlet segments that were influenced by surface and liams and Feltmate, 1992). Samples were preserved in mixed hydrologic inputs. Maximum stream distance 90% rather than 70% ethanol to account for the absorp- between the colluvial source sample sites and alluvial tion of ethanol by organic matter incidentally collected in lake inlet sample sites was 82 m. Alluvial lake inlet the samples (Merritt et al., 2008). Identification of speci- segments drained into cirque lakes, which emptied into mens was conducted 2–4 weeks after the samples were cascade-bedrock lake outlets. Cascade-bedrock lake out- collected. All sampled aquatic insects were identified and lets were primarily influenced by cirque lake drainage enumerated at the lowest possible taxonomic level. Early and other mixed inputs. Maximum stream distance instars of some limnephilids, nemourids, and perlodids, as between alluvial lake inlet sample sites and cascade- well as several dipteran larvae, could not be identified to bedrock lake outlet sample sites was 365 m. genus or species; thus, family level identification was

Table 1. Characteristics of relict glaciated subalpine basins sampled for headwater aquatic insects.

Catchment Basin mean Basin max. Basin min. Basin Sample events area (ha)* slope (%) Basin aspect elev. (m) elev. (m)

Deadwood Lakes 7 76 28 N 1890 1597 Owyhigh Lakes 4 105 46 N 1915 1584 Snow Lake 8 156 28 NE 2036 1430

*Catchment area upstream of sample sites.

Table 2. Taxonomic richness, Shannon diversity index, and sample site parameters for colluvial groundwater source (CGS), alluvial lake inlet (ALI), and cascade-bedrock lake outlet (CBLO) stream segment types in Deadwood Lakes (DLB), Owyhigh Lakes (OLB), and Snow lakes (SLB) basins.

Stream Taxonomic Shannon Wetted Sample site Coordinates Average Average Average segment richness diversity width (m) elevation (m) (Lat./Long.) temp. (°C) pH conductivity (lS)

DLB_CGS 23 2.74 0.8 1612 46°53′04′′ 121°31′11′′ 3.4 5.69 19.6 OLB_CGS 13 2.32 0.7 1590 46°51′58′′ 121°34′52′′ 3.4 5.47 28.4 SLB_CGS 22 2.45 1.6 1433 46°45′16′′ 121°41′59′′ 3.5 5.73 4.6 DLB_ALI 22 2.54 0.6 1585 46°53′07′′ 121°31′13′′ 6.2 5.80 19.2 OLB_ALI 8 1.91 1.8 1585 46°51′59′′ 121°34′54′′ 7.1 4.95 32.7 SLB_ALI 12 1.74 6 1425 46°45′22′′ 121°41′59′′ 4.1 5.82 6.6 DLB_CBLO 22 2.67 1.2 1610 46°53′16′′ 121°31′23′′ 13.1 6.13 26.3 OLB_CBLO 18 2.53 2.4 1580 46°52′05′′ 121°35′05′′ 10.2 5.75 31.4 SLB_CBLO 28 2.69 4.5 1428 46°45′33′′ 121°41′52′′ 7.8 5.54 5.5

reported. Identified samples were preserved in 70–80% and ‘cluster’ (Maechler et al., 2012) community ecology ethanol in 2- or 4-dram patent lip vials with neoprene packages of the R statistical environment (R Development stoppers. Voucher specimens were deposited at the Mt. Core Team, 2011). Rainier National Park Museum in Longmire, Washing- To evaluate b diversity among stream segment types, ton, USA. Bray–Curtis dissimilarity of aquatic insect densities was assessed graphically with hierarchical cluster analysis (Costa & Melo, 2008; Legendre et al., 2005). Cluster anal- Statistical analyses ysis was performed on aquatic insect densities from all sample weeks combined using Ward’s minimum variance Instream temperature, electrical conductivity, and pH (Legendre and Legendre, 1998). Cluster analysis displays were compared among stream segment types using a one- Bray–Curtis dissimilarity through dendrogram distance way analysis of variance (ANOVA). A separate ANOVA was (Costa & Melo, 2008; Legendre et al., 2005), providing a conducted for each of the three sampled basins to deter- visual interpretation of b diversity across stream segment mine whether patterns among stream segments were simi- types as well as comparative groupings among basins. lar across basins. In addition, dominant substrate types, Ward’s minimum variance was chosen due to its ability to based on percent cover, were summarised within each weigh squared distances by cluster size and to account for stream segment and across sampled basins. Taxonomic unequal sampling efforts and varying ranges of taxa den- richness and Shannon diversity were used to provide a sities. Cluster diagnostics included a cophenetic correla- general description of the sampled aquatic insect assem- tion, which determined how well dendrogram results blages. A list of primary cold-water, spring-seep, and/or preserved pairwise distances between original data points. rare taxa (R.W. Wissemann and B.C. Kondratieff, pers. A scree plot was used to determine the number of signifi- comm.) was developed to identify the taxa groups unique cant cluster groups by indicating where the change in dis- to our study area and to provide references for potentially similarity stabilised. rare and endemic taxa. Aquatic insect assemblages and temporal variation The number of sampling events was not equal for each among stream segment types were assessed with nonmet- subalpine basin due to field conditions. Late snowmelt ric multidimensional scaling (NMDS) paired with an anal- prevented early access into Deadwood Lakes basin, and ysis of similarity (ANOSIM) (Legendre and Legendre, 1998). fewer samples were collected in Owyhigh Lakes basin NMDS was performed on aquatic insect densities col- because it was added to the study design on 10 Septem- lected from each sample week (hereafter referred to as ber. The density of aquatic insects within each stream seg- biweekly densities) to examine temporal patterns in assem- ment type was calculated based on sample area as well as blage composition and to test for statistically significant the number of times each segment was visited. The result- differences in composition among stream segment types. ing densities were log transformed due to the large vari- NMDS is an ordination method based on ranked dis- ability of counts in rare versus abundant taxa. This tances between objects and was used because of its flexi- transformation retains potential rare and indicator taxa bility with any distance metric as well as its performance likely relevant to biomonitoring (Clarke et al., 2008). with non-normally distributed species data (Legendre and Bray–Curtis dissimilarity (Legendre and Legendre, 1998) Legendre, 1998). Additionally, with NMDS, the underly- was used as the primary association coefficient to assess ing assumption of linearity is not required (Legendre and the variation and resemblance of aquatic insect assem- Legendre, 1998). NMDS iterations were run 100 times to blages across stream segment types. All multivariate anal- ensure convergence on local minimum stress (lack-of-fit yses were performed in the ‘vegan’ (Oksanen et al., 2012) between ranked dissimilarities and ranked ordination

© 2012 The Authors Insect Conservation and Diversity © 2012 The Royal Entomological Society, Insect Conservation and Diversity Subalpine aquatic insect assemblages 5 distance). Observed stress and statistical significance were ilar among basins (Table 3). Colluvial groundwater source verified with Monte Carlo randomisation. Despite the ten- segments were dominated by boulder, cobble, and moss dency of stress to decrease with dimensionality, a two per grass substrates (70%), whereas alluvial lake inlet dimensional solution was used to simplify interpretation. segments were primarily characterised by gravel, sand, In addition, a goodness-of-fit of the NMDS ordination and silt substrates (72%). Cascade-bedrock lake outlet results was assessed through a linear regression of segments were dominated by bedrock, boulder, and coarse observed Bray–Curtis dissimilarities and NMDS ordina- woody debris substrates (73%), and no other stream seg- tion distances. NMDS was paired with ANOSIM to test for ment type had any visible surficial bedrock. differences in aquatic insect densities within and among stream segment types. We used ANOSIM because of its similarity to NMDS in that significance was based on the Aquatic insects ranked distances between objects. ANOSIM provides an R statistic and P-value, which were used to assess the A total of 9871 aquatic insect specimens were collected relative similarity within groups and dissimilarity among during the eight sampling weeks. Sixty-six taxa groups groups. were used for subsequent multivariate analyses (see Appen- The relationships between aquatic insect assemblages dix for a complete list of taxa). Taxonomic richness ranged and environment attributes were examined with overlays from 8 taxa in the alluvial lake inlet segment of Owyhigh of environmental vectors in NMDS ordination space (Ok- Lakes basin to 28 taxa in the cascade-bedrock lake outlet sanen et al., 2012). NMDS vector loadings were computed of Snow Lake basin (Table 2). Alluvial lake inlet segments from a linear regression between each environmental attri- displayed generally lower taxonomic richness among seg- bute and NMDS axis scores (Oksanen et al., 2012). A ment types in Owyhigh and Snow Lakes basins. All stream permutation test assessed the statistical significance segments in Owyhigh lakes basin had lower taxonomic (P < 0.05) of environmental vectors. Axis correlations and richness compared to the other basins. The Shannon diver- significant environmental vectors were used to interpret sity index was relatively similar among stream segment environmental gradients associated with each aquatic types, with alluvial lake inlet segments displaying lower insect assemblage and stream segment type. diversity in Owyhigh and Snow Lakes basins. To identify the taxa associated with each stream We collected several cold-water, spring-seep, and/or segment type, we performed an indicator species analysis rare taxa, including mayflies Baetis bicaudatus (Dodds), (Dufrene & Legendre, 1997). Indicator values and signifi- Cinygmula sp., Ephemerella alleni (Jensen and Edmunds), cance (P < 0.05) for associated taxa were calculated stoneflies Lednia borealis (Baumann and Kondratieff), from the relative frequency and relative average Despaxia augusta (Banks), Setvena tibialis (Banks), Zap- abundance within each stream segment type. Indicator ada columbiana (Claassen), and caddisflies Allomyia sp., values and significance were verified with Monte Carlo Chyranda centralis (Wiggins), Ecclisocosmoecus scylla randomisation. (Ross), Homophylax sp., Neothremma didactyla (Ross), Rhyacophila vagrita (Milne), R. alberta group, and R. rickeri (Ross). In addition, several Lednia instars were Results collected that aided in the description of L. borealis (Baumann & Kondratieff, 2010). Most of the cold-water, Sample site parameters spring-seep, and/or rare taxa were collected in colluvial stream segment types. Stream temperatures differed among each segment type in Deadwood Lakes (ANOVA, F2,18 = 35.824, P < 0.001), Owyhigh Lakes (ANOVA, F2,9 = 55.331, P < 0.001), and Aquatic insect b diversity and assemblage patterns Snow Lake basins (ANOVA, F2,21 = 16.854, P < 0.001). Stream temperature was coldest in colluvial groundwater Hierarchical cluster analysis showed high b diversity in source segments and was warmer in alluvial lake inlet and aquatic insect assemblages among colluvial groundwater cascade-bedrock lake outlet stream segments; however, source, alluvial lake inlet, and cascade-bedrock lake outlet there were differential rates of warming among basins stream segments for all sampled basins (Fig. 2). The (Table 2). There were no statistically significant (P < 0.05) inflection point in the scree plot indicated that three differences among stream segment types in conductivity groups constituted the most parsimonious solution, and (Deadwood Lakes: ANOVA, F2,18 = 2.814, P = 0.086, Owy- the cophenetic correlation (0.79) indicated a strong fit of high Lakes: ANOVA, F2,9 = 0.358, P = 0.708, and Snow dendrogram groupings with Bray–Curtis dissimilarity dis- Lake basins: ANOVA, F2,21 = 2.705, P = 0.090) and pH tances. Cluster diagnostics supported high b diversity, (Deadwood Lakes: ANOVA, F2,18 = 1.127, P = 0.346), Owy- with each stream segment type representing a separate high Lakes: ANOVA, F2,9 = 6.360, P = 0.187, and Snow cluster. Cluster analysis also showed that patterns of b Lake basins: ANOVA, F2,21 = 0.080, P = 0.923). Dominant diversity were similar among all of the sampled basins. substrates were different among stream segment types, The branched pattern in the dendrogram indicated that whereas segment substrate composition was relatively sim- aquatic insect assemblages were more similar in colluvial

Table 3. Percent substrate cover for colluvial groundwater source (CGS), alluvial lake inlet (ALI), and cascade-bedrock lake outlet (CBLO) stream segment types in Deadwood Lakes (DLB), Owyhigh Lakes (OLB), and Snow lakes (SLB) basins. Abbreviated substrate categories include ﬁne particulate organic matter (FPOM) and coarse particulate organic matter (CPOM).

Substrate (% cover)

Stream segment Silt Sand Gravel Cobble Boulder Bedrock FPOM CPOM Coarse wood Moss & grass

DLB_CGS 0 5 10 15 40 0 0 10 10 10 OLB_CGS 0 5 10 20 40 0 0 10 5 10 SLB_CGS 5 15 0 10 50 0 0 5 5 10 DLB_ALI 5 55 10 5 0 0 5 10 5 5 OLB_ALI 15 50 5 10 0 0 10 5 5 0 SLB_ALI 10 55 10 5 5 0 5 5 0 5 DLB_CBLO 5 0 5 5 20 40 0 5 15 5 OLB_ CBLO 10 0 5 5 20 35 5 10 5 5 SLB_ CBLO 0 0 0 5 25 40 0 10 15 5

groundwater source and alluvial lake inlet segments com- (a) = CGS Silt pared to cascade-bedrock lake outlet segments. FPOM Sand 1.0 = ALI The 2-D NMDS ordination showed that biweekly = CBLO aquatic insect assemblages were grouped according to stream segment type (Fig. 3a) across all sampling dates 0.5 (Fig. 3b). The NMDS analysis reached a final stress Temperature of 17.841 and was statistically significant (P < 0.001). 0.0 The goodness-of-fit (R2=0.835) indicated that ranked 2 Axis Bray–Curtis dissimilarities were accurately reflected in –0.5 CPOM ordination space. ANOSIM results showed that assemblages Bedrock Cobble differed significantly among stream segment types Coarse Wood = < –1.0 Moss & Grass (R 0.749; P 0.001). Boulder

(b) = DLB 1.4 6 1.0 = SLB = OLB 1.2 7 9 5 8 0.5 8 1 1.0 7 6 2 7 6 4 3 4 8 9 8 3 2 5 2 0.8 7 0.0 8 6 6 6 3

Axis 2 Axis 8 7 3 3 5 5 5 4 2 7 2 0.6 4 8 4 6 3 1 1 –0.5 9 4 6 2 7 5 0.4 8 6 7 Bray-Curtis dissimilarity distance Bray-Curtis dissimilarity SLB_CGS 0.2 DLB_ALI –1.0 SLB_ALI OLB_ALI 8 7 DLB_CGS OLB_CGS OLB_CBLO –1.0 –0.5 0.0 0.5 1.0 SLB_CBLO DLB_CBLO Axis 1 Cascade- Alluvial lake Colluvial bedrock inlet groundwater lake outlet source Fig. 3. Two-dimensional NMDS ordination of biweekly aquatic insect densities within stream segment types (stress: 17.841, Fig. 2. Ward’s minimum variance cluster dendrogram of com- P < 0.001; each point represent a sample event) with signiﬁcant bined aquatic insect densities among stream segment types for (P < 0.05) environmental attribute vectors (a), and temporal dis- three relict glaciated subalpine basins (cophenetic correlation: tribution patterns across basins (b). Point symbols (a) indicate 0.79). Clusters were derived from Bray–Curtis insect density dis- colluvial groundwater source, alluvial lake inlet, and cascade-bed- similarities with dendrogram distance representing dissimilarity. rock lake outlet stream segment types and plotting symbols (b) Dendrogram code is a concatenation of basin and stream seg- indicate sample week in Owyhigh Lakes, Snow Lakes, or ment codes, where ‘DLB’ = Deadwood Lakes basin, ‘OLB’ = Deadwood Lakes basins. The ordination is calculated from Bray– Owyhigh Lakes basin, ‘SLB’ = Snow Lake basin, ‘CGS’ = colluvial Curtis insect density dissimilarities. Abbreviated environmental groundwater source, ‘ALI’ = alluvial lake inlet, and ‘CBLO’ = attributes include ﬁne particulate organic matter and coarse cascade-bedrock lake outlet. particulate organic matter.

Assemblage–environment relationships Table 4. Correlations (r2) of environmental attributes with aquatic insect assemblages axis scores in the non-metric multidimen- The biplot of environmental vectors in the NMDS ordi- sional scaling (NMDS) ordination. Significance of correlation nation of aquatic insect assemblages indicated that princi- was based on 1000 randomisation permutations. Abbreviated pal environmental variables associated with assemblage environmental attributes include fine particulate organic matter structure were temperature and substrate (i.e. fine particu- (FPOM) and coarse particulate organic matter (CPOM). late organic matter, coarse particulate organic matter, 2 moss per grass, coarse wood, silt, sand, cobble, boulder, Attribute Axis 1 Axis 2 r P-value and bedrock) (Fig. 3a; Table 4). Assemblages in colluvial Temperature À0.76 0.20 0.62 <0.001 stream segment types were associated primarily with boul- pH À0.01 0.02 0.00 0.977 der, cobble, and moss per grass, whereas assemblages in Conductivity À0.25 0.16 0.09 0.084 alluvial lake inlet stream segment types were associated Silt 0.09 0.78 0.62 <0.001 primarily with fine particulate organic matter, silt, and Sand 0.27 0.78 0.68 <0.001 sand. Assemblages in cascade-bedrock lake outlets were Gravel 0.11 0.28 0.09 0.094 primarily associated with temperature, coarse particulate Cobble 0.43 À0.53 0.46 <0.001 À < organic matter, coarse wood, and bedrock. Boulder 0.23 0.82 0.72 0.001 Bedrock À0.80 À0.29 0.72 <0.001 FPOM 0.06 0.84 0.71 <0.001 À À Taxa associated with stream segment types CPOM 0.31 0.33 0.20 0.002 Coarse wood À0.53 À0.60 0.64 <0.001 Moss & grass 0.36 À0.75 0.70 <0.001 Indicator species analyses showed that specific aquatic insects were associated with each stream segment type (Table 5). Of the 66 identified taxa groups, 28 were identi- a = fied as significant ( 0.05) indicator taxa. Although taxa The similarities in assemblages between upstream segments presence was not completely uniform across basins, several may result from similar hydrological attributes, local taxa were consistently found among comparable stream migration of adults (Finn and Poff, 2005), and short drift- segment types. Chironomids were found in high densities; ing distances required for eggs and immatures. Cascade- however, the distribution was spread among several stream bedrock lake outlets had relatively different assemblages types, resulting in a non-significant indicator value. compared to upstream segments and had the highest number of taxa groups per sampled area. Our observations are similar to other studies that have shown that lake out- Discussion lets support distinct invertebrate assemblages (Richardson and Mackay, 1991; Malmqvist and Eriksson, 1995). Lakes Aquatic insect b diversity and assemblage patterns may affect downstream physical conditions and the avail- ability of food, thereby influencing species distribution and Cluster analysis revealed high b diversity in aquatic faunal diversity (Burgherr & Ward, 2000; Hieber et al., insect assemblages among colluvial source, alluvial lake 2002, 2005; Milner and Petts, 1994; Hamerlik & Jacobsen, inlet, and cascade-bedrock lake outlet stream segments 2011). Additionally, lake outlet invertebrate assemblages in Deadwood Lakes, Owyhigh Lakes, and Snow Lake may be distinct due to the transitional habitat zone between basins. Furthermore, NMDS and ANOSIM indicated that lentic and lotic systems that juxtaposes multiple species spatial and temporal variation in assemblage composition groups (i.e. lake taxa, lake outlet filter specialists, and lotic among stream segment types was similar across all sample taxa) (Malmqvist and Eriksson, 1995). weeks and basins. These results corroborate previous findings that high-elevation headwaters support unique aquatic insect assemblages among local habitats types Assemblage–environment relationships (Finn & Poff, 2005, 2011; Bogan & Lytle, 2007; Brown et al., 2009a; Monaghan et al., 2005). In addition, these Our results showed a strong similarity in aquatic insect results are consistent with findings by Finn et al. (2011), assemblage composition among comparable stream seg- who demonstrated that headwater streams display high b ment types across three sampled basins. Similarities in diversity influencing regional riverine diversity. The shorter assemblage composition among basins may indicate the cluster-dendrogram distances between aquatic insect presence of similar environmental gradients among stream assemblages in colluvial groundwater sources and alluvial segment types (Hieber et al., 2005), as well as similar lake inlet segments, as compared to cascade- aquatic insect population dynamics (e.g. dispersal abilities bedrock lake outlet segments, may be a result of spatial and colonising species pools). The results of our NMDS separation between stream segment types. Colluvial ordination and biplot are consistent with several other sources flowed directly into alluvial lake inlet segments, studies which showed that differences in aquatic insect and both of these upstream segments were separated from distribution and assemblage composition are associated cascade-bedrock lake outlets by cirque lakes and ponds. with temperature (Vinson and Hawkins, 1998; Vannote

Table 5. Densities and indicator values for aquatic insects associated with stream segment types. Taxa included in the table were calculated from an indicator species analysis (a = 0.05) for Deadwood Lakes (DLB), Owyhigh Lakes (OLB), and Snow Lake (SLB) basins.

Density (number per m2)

Stream segment Taxon Indicator value DLB OLB SLB

Colluvial groundwater source Plecoptera Lednia borealis 0.37 3.9 Setvena tibialis 0.68 0.9 2.9 1.6 Zapada columbiana 0.40 3.4 5.8 0.1 Trichoptera Allomyia 0.51 1.0 5.8 0.1 Eocosmoecus 0.34 1.2 0.6 0.1 Homophylax 0.90 2.2 2.9 0.7 Neathremma didactyla 0.26 1.1 Rhyacophila rickeri 0.47 1.1 5.8 Rhyacophila vagrita 0.31 0.5 0.2 Rhyacophila verrula gr. 0.26 0.2 1.7 Diptera Pedicia 0.42 0.1 1.1 0.1 Alluvial lake inlet Ephemeroptera Ameletus 0.61 7.6 5.8 9.1 Plecoptera Moselia infuscata 0.32 8.6 Trichoptera Psychoglypha 0.59 6.7 4.1 1.9 Diptera Ceratopogonidae 0.50 3.2 17.6 Cascade-bedrock lake outlet Ephemeroptera Baetis bicaudatus 0.40 0.5 0.3 6.8 Cinygma 0.66 16.1 28.3 8.4 Ephemerella alleni 0.21 39.3 Paraleptophlebia 0.72 9.9 14.1 31.2 Plecoptera Sweltsa 0.39 7.0 6.5 0.6 Yoraperla 0.95 3.1 1.6 21.4 Zapada cinctipes 0.68 3.1 3.1 Zapada oregonensis gr. 0.85 2.7 4.3 8.7 Trichoptera Micrasema 0.53 0.6 2.4 0.4 Rhyacophila grandis 0.32 4.6 Rhyacophila voﬁxa gr. 0.29 1.9 Diptera Simuliidae 0.84 28.2 9.4 32.4 Coleoptera Cleptelmis addenda 0.37 14.6

and Sweeney, 1980; Ward and Stanford, 1982) and sub- results) were observed in colluvial groundwater sources. strate (Huryn & Wallace, 1987; Lancaster & Hildrew, These high abundances may reflect the influence of 1993; Rempel et al., 2000). Although elevation is known cooler water temperatures associated with subsurface and to be a significant driver in assemblage composition groundwater inputs (Hieber et al., 2002; Brown et al., (Hawkins et al., 1982; Ward, 1994), high elevational gra- 2009a,b; Finn & Poff, 2011). dients are not likely to be a primary factor influencing the observed aquatic insect distribution due to the minimal change in elevation among stream segment types in a Taxa associated with stream segment types given basin. We speculate that the observed distribution of taxa characteristic of thermal zonation may indicate Our analyses identified specific aquatic insects that were the influence of thermal gradients associated with ground- associated with stream segment types. Because high-eleva- and surface-water inputs. For example, high abundances tion headwaters display high variability among local of several cold-water and spring-seep taxa (listed in the assemblages, it may be necessary to characterise specific

© 2012 The Authors Insect Conservation and Diversity © 2012 The Royal Entomological Society, Insect Conservation and Diversity Subalpine aquatic insect assemblages 9 and sensitive assemblages across multiple headwater types systems (Rodriguez-Iturbe et al., 2009; Brown et al., 2011; (Finn & Poff, 2005; Clarke et al., 2008; Heino, 2009; Finn et al., 2011). Future assessments of the habitats, Monaghan et al., 2005; Finn et al., 2011). Identifying diversity patterns, and life history strategies of taxa in these unique assemblage types may be essential for design- high-elevation headwaters are needed so that monitoring ing effective monitoring strategies that are capable of and conservation can prevent the loss of unique and sensi- detecting ecological shifts and identifying potentially sen- tive biota. sitive habitats and fauna (Muhlfeld et al., 2011). Although the geographical scope of our indicator species list is narrow, these results may provide a useful reference for (i) Acknowledgements characterising unique assemblages associated with subalpine stream types, (ii) identifying potential taxa groups We are grateful to Robert Wisseman and Boris Kon- associated with short- and long-term geohydrologic and dratieff for help with insect identification and manuscript ecological processes (Milner et al., 2009), and (iii) locating review. We also thank Barbara Samora and the staff at potential monitoring sites for sensitive fauna (Brown Mt. Rainier National Park for providing permits and et al., 2009b). For example, most of the cold-water, allowing site access. Special thanks to Julian Olden for spring-seep, and/or rare taxa that we collected were found consultation in the multivariate analyses, and to Audrey in colluvial groundwater sources. These headwater seg- Taylor, Scott Miller, Fabio Lepori, Yoshitaka Tsubaki, ments may be important locations for monitoring fauna and four anonymous reviewers for their constructive com- that are sensitive to shifts in thermal regimes and sub- ments that significantly improved the quality of this man- strate disturbance patterns. The taxa specific to colluvial uscript. Partial funding was provided by the USGS groundwater sources may provide suitable biotic indica- Natural Resource Preservation Program and the USGS tors for instream conditions associated with changes in Youth Internship Program. Any use of trade, product, or precipitation, temperature, substrate, and water source firm names in this publication is for descriptive purposes contribution. The pairing of stream types with specific only and does not imply endorsement by the US indicator assemblages and taxa may, therefore, provide a Government. useful sampling methodology for biomonitoring in relict glaciated subalpine headwaters. The recent description of L. borealis and the collection of additional cold-water, spring-seep, and/or rare taxa References emphasise the need to document fauna that are unique to relict glaciated subalpine basins. Headwaters with meltwa- Anderson, M.J., Crist, T.O., Chase, J.M., Vellend, M., Inouye B. ter inputs from glaciers, ice, and/or snowpack are known D., F., A.L., S., N.J., C., Comita, L.S., Davies, K.F., Harrison, S.P., Kraf, N.J.B., Stegen, J.C. & Swenson, N.G. (2011) Navi- to support a number of rare and endemic aquatic insect gating the multiple meanings of beta diversity: a roadmap for species (Winterbourn et al., 2008; Brown et al., 2007; the practicing ecologist. Ecology Letters, 14,19–28. Snook and Milner, 2001). In addition, documenting rare Baumann, R.W. & Kondratieff, B.C. (2010) The stonefly genus and endemic taxa is important for state records (Kon- Lednia in North America (Plecoptera:Nemouridae). Illiesia, 6, dratieff & Lechleitner, 2002) and providing biological 315–327. information that is essential for optimising management Bogan, M.T. & Lytle, D.A. (2007) Seasonal flow variation allows and monitoring efforts (Baumann & Kondratieff, 2010). ‘time-sharing’ by disparate aquatic insect communities in mon- This study provides information on the presence and dis- tane desert streams. Freshwater Biology, 52, 290–304. tribution of several cold-water, spring-seep, rare, and pos- Brardinoni, F. & Hassan, M.A. (2006) Glacial erosion, evolution sibly endemic taxa; however, more research is needed to of river long profiles, and the organization of process domains in mountain drainage basins of coastal British Columbia. Jour- help identify species range limits, vulnerability, and the nal of Geophysical Research, 111, F01013. strength of observed geohydrologic-ecological linkages Brardinoni, F. & Hassan, M.A. (2007) Glacially induced organi- (Brown et al., 2009b). Due to the potential sensitivity of zation of channel-reach morphology in mountain streams. rare and endemic high-elevation aquatic insects, informa- Journal of Geophysical Research, 112, F03013. tion on these species and their ecological associations are Brown, L.E., Ce´re´ghino, R. & Compin, A. (2009b) Endemic needed to predict responses and develop conservation aquatic invertebrates from southern France: diversity, distribu- plans (Brown et al., 2009b). Prioritising headwater inter- tion and conservation implications. Biological Conservation, actions may help to identify potential responses (positive 142, 2613–2619. or negative) to changes in climate and shifts in hydrology Brown, L.E., Hannah, D.M. & Milner, A.M. (2007) Vulnerability and physico-chemical habitat characteristics (Milner et al., of alpine stream biodiversity to shrinking glaciers and snow- packs. Global Change Biology, 13, 958–966. 2009). Elucidating the strength and nature of these Brown, L.E., Hannah, D.M. & Milner, A.M. (2009a) ARISE: a responses will lead to a better understanding of the resil- classification tool for Alpine River and Stream Ecosystems. ience of headwater species, and ultimately will aid in their Freshwater Biology, 54, 1357–1369. future conservation. In addition, understanding the contri- Brown, B.E., Swan, C.M., Auerbach, D.A., Grant, E.H.C., Hitt, bution of headwaters to b and c diversity will help in pre- N.O.P., Maloney, K.O. & Patrick, C. (2011) Metacommunity dicting patterns of biodiversity distribution across stream theory as a multispecies, multiscale framework for studying the

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Appendix

Cumulative densities of taxa in Deadwood Lakes, Owyhigh Lakes, and Snow Lake basins in colluvial groundwater source (CGS), alluvial lake inlet (ALI), and cascade-bedrock lake outlet (CBLO) stream segments. Densities were calculated as number of individuals/m2.

Deadwood Lakes basin Owyhigh Lakes basin Snow Lake basin

Taxon CGS ALI CBLO CGS ALI CBLO CGS ALI CBLO

Ephemeroptera Ameletus 3.6 7.6 0.4 5.8 20.5 0.4 9.1 0.6 Baetis bicaudatus 0.1 0.5 0.3 6.8 Baetis tricaudatus 0.4 Cinygma 3.8 16.1 28.3 8.4 Cinygmula 0.1 0.6 Ephemerella alleni 39.3 Paraleptophlebia 0.5 11.5 9.9 14.1 0.3 31.2 Plecoptera Despaxia augusta 0.1 Lednia borealis 3.9 Moselia infuscata 0.2 8.6 0.3 Nemouridae 1.0 Perlodidae 0.2 1.1 4.5 2.5 0.1 Podmosta 0.1 Setvena tibialis 0.9 2.9 1.6 0.4 Soyedina 0.6 Sweltsa 2.6 3.5 7.0 6.3 0.4 6.5 0.1 0.6 Yoraperla 3.1 1.6 21.4 Zapada cinctipes 3.1 3.1 Zapada columbiana 3.4 5.8 0.1 1.9 Zapada frigida 0.4 0.8 0.1 Zapada oregonensis group 0.4 2.7 4.3 8.7 Trichoptera Allomyia 1.0 0.1 5.8 0.1 Apatania 0.2 Chyranda centralis 0.1 Desmona mono 1.5 Dicosmoecus atripes 0.3 0.1 Dolophilodes 0.1 Ecclisocosmoecus scylla 0.1 0.2 Ecclisomyia 0.1 Eocosmoecus 1.2 0.1 0.6 0.1 Homophylax 2.2 0.1 2.9 0.7 0.1 Limnephilidae 1.4 0.4 0.1 0.4 Micrasema 0.6 2.4 0.4 Neothremma didactyla 1.1 Parapsyche elsis 0.4 Psychoglypha 3.4 6.7 0.1 1.0 4.1 0.5 1.9 0.2 Rhyacophila alberta group 0.6 0.2 0.8 Rhyacophila grandis 4.6 Rhyacophila rickeri 1.1 5.8 Rhyacophila rotunda group 0.7 2.4 0.1 Rhyacophila vagrita 0.5 0.2 Rhyacophila vemna group 0.1 0.1 0.1 Rhyacophila verrula 0.4 Rhyacophila verrula group 0.2 1.7 Rhyacophila voﬁxa group 0.6 1.9

Appendix (Continued)

Deadwood Lakes basin Owyhigh Lakes basin Snow Lake basin

Taxon CGS ALI CBLO CGS ALI CBLO CGS ALI CBLO

Diptera Ceratopogonidae 3.2 0.3 17.6 Chironomidae 8.2 9.5 16.1 40.3 15.3 20.4 22.6 59.9 28.4 Clinocera 0.1 0.1 0.1 Dicranota 0.7 0.9 Dolichopodidae 0.1 Hesperoconopa 0.1 1.6 Limnophila 0.1 Metachela 0.1 0.4 Molophilus 0.1 Mystacides 0.1 Oreogeton 0.4 Pedicia 0.1 1.1 0.1 Simuliidae 28.2 9.4 32.4 Tipula 0.1 Twinnia 1.1 Coleoptera Amphizoa 0.1 Carabidae 0.1 Cleptelmis addenda 14.6 Dytiscidae 0.8 Hydrobius 0.2 0.1 0.1 Odonata Anax junius 0.1