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Associations of Epiphytic Macroinvertebrates within Four Assemblages of Submerged Aquatic Vegetation in a Recovering Urban Lake
Lucas J. Kirby and Neil H. Ringler

Northeastern Naturalist, Volume 22, Issue 4 (2015): 672–689

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Northeastern Naturalist 672 L.J. Kirby and N.H. Ringler 22001155 NORTHEASTERN NATURALIST 2V2(o4l). :2627,2 N–6o8. 94 Associations of Epiphytic Macroinvertebrates within Four Assemblages of Submerged Aquatic Vegetation in a Recovering Urban Lake Lucas J. Kirby1,* and Neil H. Ringler2 Abstract - Onondaga Lake in Syracuse, NY, is recovering from a century of industrial and municipal pollution. The distribution and diversity of aquatic macrophytes have increased significantly in the past decade, and the plants currently cover 80% of the littoral area. To assess the effects of aquatic vegetation on aquatic biota, we employed quantitative sampling to examine associations of epiphytic macroinvertebrates in 4 assemblages of submerged aquatic vegetation in Onondaga Lake in 2010 and 2011. Two assemblages were predominantly monocultures—one of Stuckenia pectinata (Sago Pondweed) and the other of Chara sp. (stonewort). The third was dominated by Potamogeton foliosus (Leafy Pondweed) and Potamogeton pusillus (Small Pondweed), and the fourth was a heterogeneous community that included Ceratophyllum demersum (Coon’s Tail), Myriophyllum spicatum (Eurasian Watermilfoil), and Elodea canadensis (Canadian Waterweed). Measures of invertebrate community composition—which included taxa richness, ETO richness, family richness, and NCO richness—were not consistently different in any particular macrophyte assemblage. Overall densities of epiphytic macroinvertebrates were similar to or higher than those reported in other quantitative studies of epiphytic macroinvertebrates. We found differences in the abundance of specific macroinvertebrate taxa associated with a particular macrophyte assemblage. Stonewort and the heterogeneous beds supported a similar community of gastropods and amphipods in both years, which was distinct from the high densities of Oligochaeta and Chironomidae associated with Sago Pondweed. Our observations suggest that the current distribution of aquatic macrophytes and the high density of associated macroinvertebrates provide abundant prey for sizable populations of fishes and waterfowl that prey on macroinvertebrates. Introduction Aquatic macroinvertebrates are an important, but often over looked component of the littoral-zone community. Most management of lakes and ponds is focused on either weed control or fish production, with little consideration given to the importance of aquatic macrophytes and epiphytic macroinvertebrates. The heterogeneity of aquatic macrophytes provides physical structure and refuge for epiphytic algae, macroinvertebrates, and fishes (Diehl and Kornijow 1998, Perrow et al. 1999). Habitats with higher levels of spatial heterogeneity are more complex, which increases the potential diversity of associated organisms (MacArthur and MacArthur 1961). Dense aquatic macrophytes have been shown to provide protection 1State University of New York College of Environmental Science and Forestry, 127 Illick Hall, 1 Forestry Drive, Syracuse, NY 13210. 2State University of New York College of Environmental Science and Forestry, 200 Bray Hall, 1 Forestry Drive, Syracuse, NY 13210. *Corresponding author - lkirby@syr.edu. Manuscript Editor: Hunter Carrick Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. Ringler 2015 673 for macroinvertebrates from fishes and large invertebrate predators (Baker 1918, Crowder and Cooper 1982, Diehl 1992), and the secondary production of macroinvertebrates within the macrophytes is important for littoral fish (Osenberg et al. 1992) and dabbling duck foraging, growth, and survival (Krull 1970). Traditionally, the value of an aquatic macrophyte species for production of epiphytic macroinvertebrates has been determined by the density and complexity of the macrophytes (Crowder and Cooper 1982, Dibble et al. 2006, Lillie and Bud 1992). However, there is conflicting evidence as to which species or types of macrophytes support the highest macroinvertebrate density or diversity. Submerged macrophytes with finely divided leaves have greater spatial complexity and surface area, and have been shown to support greater diversity and abundance of macroinvertebrates than broad-leaved, floating-leaved, or emergent macrophyte species (Dibble et al. 1997, Lillie and Budd 1992, Peets et al. 1994, Rosine 1955, Schramm et al. 1987, Watkins et al. 1983). In contrast, Brown et al. (1988) and Voigts (1976) found that the variability of macrophyte growth forms (floating/emergent/submerged) within a macrophyte bed had more effect on macroinvertebrate richness and abundance than the level of leaf complexity of individual species. Other research has indicated that the value of particular macrophyte species for macroinvertebrate production depends on the complexity of the aquatic plants at multiple scales (Dibble et al. 2006). The growth habit of macrophytes over the course of the growing season may also be important (Lillie and Budd 1992). For example, Myriophyllum spicatum L. (Eurasian Watermilfoil) is a macrophyte with finely divided leaves, but low complexity (Cheruvelil et al. 2001, 2002; Dibble et al 1997). The structure of Eurasian Watermilfoil shifts from even distribution of stems and leaves in late spring to the majority of the biomass occurring at the water’s surface by late summer (Cheruvelil et al. 2001, Lillie and Budd 1992). Low complexity and shifting distribution would likely decrease the capacity to support macroinvertebrates as the season progresses, when compared to diverse native plant populations (Theel et al. 2008). The objectives of this study were to investigate the distribution and abundance of epiphytic macroinvertebrate communities associated within 4 distinct assemblages of fine-leaved species of submerged aquatic macrophytes common in the eastern US. This study investigated the epiphytic macroinvertebrate community within 2 monocultures of Stuckenia pectinata (L.) Börner (Sago Pondweed) and Chara sp. (stonewort), an assemblage dominated by Potamogeton foliosus Raf. (Leafy Pondweed) and Potamogeton pusillus L. (Small Pondweed), which we will refer to as mixed pondweeds, and within a heterogeneous community that included Ceratophyllum demersum L. (Coon’s Tail), Eurasian Watermilfoil, Elodea canadensis Michx. (Canada Waterweed), and to a lesser extent, Najas sp. (waternymph) and Potamogetn crispus L. (Curly Pondweed). Even though the species that comprise the 4 aquatic macrophyte communities are all fine-leaved, we hypothesized that there would be significant differences among the macroinvertebrate communities because of differences in growth forms and plant densities. We hypothesized that the heterogeneous aquatic macrophyte assemblage would support the highest richness and abundance of macroinvertebrates because of its increased habitat Northeastern Naturalist 674 L.J. Kirby and N.H. Ringler 2015 Vol. 22, No. 4 complexity and that Sago Pondweed would support low taxa richness because of low leaf-complexity. Methods Study site Onondaga Lake is a 1200-ha urban lake north of the city of Syracuse, NY, which was used for the discharge of municipal and industrial waste for more than a century (Effler 1996). The discharge of industrial waste containing Cl-, Na+, Ca2+, Hg, and PCBs, coupled with nutrient-loading from a sewage-treatment plant had a lasting impact on habitat structure and the aquatic community (Auer et al. 1996). The once-mesotrophic lake became hypereutrophic, with low water-clarity, high salinity, and elevated precipitation rates of CaCO3 (Effler 1996). The combination of low water-clarity and high-salinity levels led to low biodiversity and minimal coverage by aquatic macrophytes (Auer et al. 1996, Madsen et al. 1996). With the closure of the soda-ash facility in 1986, and upgrades to the Syracuse metropolitan sewage-treatment plant in 1999, 2004, and 2006, Onondaga Lake has undergone a transition from hypereutrophic to mesotrophic (Effler and O’Donnell 2010). Aquatic macrophytes have increased in richness from 5 species in 1991 (Madsen et al. 1996) to 23 species in 2010 (EcoLogic et al. 2012) and littoral-zone coverage has increased from 13% (Madsen et al. 1996) to 80% (Kirby 2009, 2013). Onondaga Lake is currently dominated by the 4 above-mentioned aquatic plant assemblages, with the most prevalent being a heterogeneous assemblage. Aquatic macrophyte sampling We conducted aquatic macrophyte-community sampling in the littoral zone of Onondaga Lake in July of 2008, 2009, 2011, and 2012 and in June of 2010 using the point-intercept method (Madsen 1999). We sampled aquatic macrophytes at water depths of 0–4 m using a grid of points that were spaced every 800 m, for a total of 319 points. We imported the coordinates for the aquatic macrophyte points into a Fisher Mark II GPS with a point accuracy of 1–3 m. We followed the method of Madsen (1999) that allows for the collection of aquatic macrophytes to determine species presence or absence. During each sampling event, we maneuvered the boat over each point, attached a rope to the head of a steel thatching rake, tossed the rake head into the water, allowed it to settle on the lake bottom, dragged it back to the boat and collected the vegetation from the tines. Quantitative aquatic macroinvertebrate sampling We collected samples of aquatic macrophytes and associated aquatic macroinvertebrates on 30 July 2010, 2 and 5 August 2010, and 27 and 31 July 2011. In 2010, we used a stratified, systematic sampling design. We identified 4 sites in the north basin of Onondaga Lake that had large beds of the target aquatic macrophyte assemblages (Fig. 1). High levels of pollution still occurred in the southern basin (Parsons Inc. et al. 2010); thus, we avoided that area. At each site, we sampled 2 sets (rows) of samples separated by 100 m and collected 8 samples (10 m apart) per set. In 2011, we sampled 1 row of 8 samples (10 m apart) in 8 macrophyte beds Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. Ringler 2015 675 (Fig. 1). We sampled 2 separate beds of each assemblage to ensure that the macroinvertebrate communities were associated with that plant type and not the particular area of the lake. We designed and built a modified Gerking sampler for the quantitative sampling of shallow (less than 1 m) aquatic macrophytes and their associated macroinvertebrate communities (Gerking 1957, Kirby 2013). We chose this method because it sampled a large area of aquatic macrophytes with minimal disturbance, which minimized escape by active aquatic macroinvertebrates. We deployed the sampler open in water depths of ~75 cm and slowly lowered it over the aquatic macrophytes. Once in place, we used pruning shears to cut the stem bases of the enclosed aquatic macrophytes. We then pushed the screen closed and lifted the sampler from the water, allowing the water to fall through the screen and retaining the macrophytes and macroinvertebrates within the sampler. Once on the boat, we pushed the screen open, removed the sample from the screen, and preserved it in 10% buffered formalin in a whirl-pack bag labeled with site and date information. Figure 1. Sampling sites in Onondaga Lake, Syracuse, NY, in 2010 and 2011. P. spp represents the mixed pondweed sites. Northeastern Naturalist 676 L.J. Kirby and N.H. Ringler 2015 Vol. 22, No. 4 In the lab, we spread the sample of aquatic vegetation across a shallow tray with a labeled grid of 10 cells. We randomly drew a number to identify the cell that would comprise the subsample and removed a volume of up to 100 ml of plant material from that cell. New cells were selected until 100 ml of plant material was attained from that sample. We separated the remainder of the sample by species, dried each in an oven at 50 °C for a minimum of 24 h to a constant weight, and weighed them to the nearest milligram with a Mettler BB240 top-loading scale. While viewing the macrophyte subsamples under a dissecting microscope, we separated all aquatic macroinvertebrates and placed them into a labeled vial with 70% ethanol. To subsample the Chironomidae larvae, we poured the larvae into a petri dish, lightly mixed the sample with forceps, and randomly chose 50 larvae for removal. We mounted and cleared them on slides with CMC-10. We identified Chironomidae and the other aquatic macroinvertebrates to the lowest taxonomic level achievable (Jokinen 1992, Merritt et al. 2008, Peckarsky 1990). We then separated by species, dried in an oven at 50 °C, and weighed to the nearest milligram the aquatic macrophyte subsample from which we removed the macroinvertebrates. Data analysis In 2010, 1 sample in the stonewort bed had an aquatic macrophyte assemblage that was dominated by species that were characteristic of the heterogeneous community (waternymph, Canada Waterweed, and Cladophora sp. (filamentous green algae), and 2 samples within the mixed pondweed bed had a larger percentage of Sago Pondweed than Leafy Pondweed or Small Pondweed. Our analysis was based on plant type and not site; thus, we grouped these samples based on macrophyte composition for community metrics, principal-component analysis, and analysis of variance. Prior to statistical analysis, we log(x+1)-transformed all data to normalize variance. We used SAS software® to perform 1-way analysis of variance (ANOVA) with post hoc Waller-Duncan pairwise means testing—with significance set at α = 0.05—to detect significant differences in macroinvertebrate-community metrics among the 4 aquatic macrophyte assemblages. Macroinvertebrate-community metrics included: taxa richness, family richness, richness of Ephemeroptera, Trichoptera, and Odonata (ETO) taxa, non-Chironomidae and Oligochaeta richness (NCO), subsample abundance, and estimated abundance of macroinvertebrates using the following equations: abundance per m2 = (S/s)*M*5.17 Equation 1, where: s = dry weight of 100-ml aquatic macrophyte subsample, S = dry weight of complete aquatic macrophyte sample, M = abundance of macroinvertebrates in 100-ml subsample, and 5.17 = 1 m2/ the area of the sampler; and abundance per kg plant material = (S/s)*M*(kg/S) Equation 2, where: s = dry weight of 100-ml aquatic macrophyte subsample, S = dry weight of complete aquatic macrophyte sample, M = abundance of macroinvertebrates in 100-ml subsample, and Kg = 1 kilogram. Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. Ringler 2015 677 Using SAS software, we conducted principal-component analysis (PCA) to identify taxa that would be further tested with ANOVA for significance among plant types. We excluded rare taxa from PCA if they were found in less than 10% of the subsamples and if they represented less than 2% of the total number of organisms counted. We analyzed 15 taxa in 2010 (n = 62) and 17 in 2011 (n = 64) (Table 1). Taxa that had significant Pearson correlations (α = 0.01) with principle components 1 or 2 (Scree test) were further tested with one-way ANOVA with post hoc Waller- Duncan pairwise means testing for significant differences in abundance among the 4 aquatic macrophyte assemblages. Results Aquatic macrophyte distribution (2008–2012) and community composition The richness of aquatic macrophyte species increased from 10 species in 2008 to 16 species in 2012, but the distribution of aquatic macrophytes remained at 80% of littoral-zone points from 2009–2012 (Table 2). The most prevalent aquatic macrophytes in Onondaga Lake were associated with what is termed here as the heterogeneous macrophyte assemblage. Sago Pondweed maintained a fairly consistent distribution from 2008–2012, and on average was located at 15% of the sampling points. Some species increased in frequency each year; e.g., the distribution of Heteranthera dubia (Jacq.) MacMill. (Grassleaf Mudplantain) increased from occurring at less than 3% of points in 2008 to >40% in 2012, stonewort increased from less than 1% in 2009 to 10% in 2012, and the invasive species Nitellopsis obtusa (Desvaux in Louseleur) J. Groves (Starry Stonewort) increased from 0 in 2010 to 4% in 2012. The aquatic macrophyte communities sampled in 2010 (Fig. 2) and 2011 (Fig. 3) Table 1. Macroinvertebrate taxa that were included in principal component analysis (PCA) of epiphytic- macroinvertebrate communities among 4 aquatic macrophyte communities in Onondaga Lake, NY, in 2010 (n = 62) and 2011 (n = 64). * Indicates taxa that were significantly correlated (α = 0.01) with PC 1 or 2 and subsequently examined with analysis of variance. 2010 2011 Amphipoda* Amphipoda* Chironomidae* Ceratopogonidae* Coenagrionidae* Chironomidae* Dreissenidae Coenagrionidae* Hirudinea* Culicidae Hydrobiidae* Dreissenidae* Hydrachnidae Hirudinea Hydroptilidae* Hydrobiidae* Leptoceridae* Hydrachnidae* Oligochaeta* Hydroptilidae* Physidae* Leptoceridae* Planorbidae* Oligochaeta* Tricladida Physidae* Pyralidae* Planorbidae* Valvatidae* Tricladida Pyralidae* Valvatidae* Northeastern Naturalist 678 L.J. Kirby and N.H. Ringler 2015 Vol. 22, No. 4 Table 2. Percent presence of aquatic macrophyte species in Onondaga Lake, NY, in July (2008, 2009, 2011, and 2012) and June (2010) in the littoral zone (less than 4 m water depth). Species 2008 2009 2010 2011 2012 Average Coon’s Tail 23.2 34.2 24.8 39.8 57.1 35.8 Stonewort 0.0 0.3 6.0 4.4 10.0 4.1 Canada Waterweed 42.0 53.3 53.3 37.3 42.0 45.6 Fontinalis sp. (an aquatic moss) 0.0 0.0 0.0 0.3 0.9 0.3 Grassleaf Mudplantain 2.5 5.0 12.2 22.3 43.3 17.1 Lemna sp. (duckweed) 1.3 2.5 0.3 0.3 0.3 0.9 Eurasian Watermilfoil 33.5 45.5 50.8 43.6 41.7 43.0 Waternymph 16.6 9.1 8.5 16.3 32.0 16.5 Starry Stonewort 0.0 0.0 0.0 3.1 4.1 1.4 Polygonum amphibium L. 0.0 0.0 0.0 0.0 0.3 0.1 (Water Knotweed) Curly Pondweed 16.9 29.8 55.5 26.6 13.8 28.5 Mixed pondweeds 36.4 38.9 29.2 36.7 8.5 29.9 Ranunculus longirostris Godr. 0.0 0.0 0.0 0.0 1.3 0.3 (Longbeak Buttercup) Spirodela polyrhiza (L.) Schleid. 0.0 0.9 0.0 0.0 0.0 0.2 (Common Duckmeat) Sago Pondweed 9.4 20.1 11.6 16.0 17.9 15.0 Vallisneria americana Michx. 0.3 0.0 0.0 0.6 1.3 0.4 (American Eelgrass) Littoral zone coverage 69.9 82.8 79.6 80.3 81.2 78.7 Figure 2. Percentage of individual species within the sampled aquatic macrophyte assemblages based on dry-weight biomass, in Onondaga Lake, NY, in July of 2010. Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. Ringler 2015 679 were representative of the 4 communities that were observed in Onondaga Lake prior to sampling. Analysis of biotic metrics among macrophyte communities We identified a total of 47 epiphytic macroinvertebrate taxa in Onondaga Lake in 2010 and 63 in 2011. In 2010, the 4 aquatic macrophyte communities had significantly different levels of taxa richness (ANOVA, P = 0.001), ETO richness (ANOVA, P = < 0.001), NCO richness (ANOVA, P = 0.013), estimated abundance of organisms m-2 (ANOVA, P = < 0.001), and estimated abundance of organisms per kg plant matter (ANOVA, P = < 0.001) (Table 3). Post hoc Waller Duncan means testing indicated that the stonewort bed had significantly higher average taxa richness than the other communities of aquatic macrophytes (Table 3). The mixed pondweed bed had significantly higher richness of ETO taxa than the Sago Pondweed and heterogeneous macrophyte beds (Table 3). The heterogeneous and Sago Pondweed beds had significantly higher abundance of organisms m‑2 than the stonewort and mixed pondweed beds (Table 3). In 2011, with the exception of ETO richness (ANOVA, P = 0.191), significant differences occurred among all of the biotic metrics (Table 3). Taxa richness (ANOVA, P = 0.035) was significantly higher in the heterogeneous macrophyte assemblage than the stonewort bed. The heterogeneous community and mixed pondweed bed supported a significantly higher number of families (ANOVA, P = 0.042) than stonewort bed (Table 3). Subsample abundance (ANOVA, P = < 0.001), estimated abundance m‑2 (ANOVA, P = < 0.003), and estimated abundance per kg Figure 3. Percentage of individual species within the sampled aquatic macrophyte assemblages based on dry-weight biomass, in Onondaga Lake, NY, in July of 2011. Northeastern Naturalist 680 L.J. Kirby and N.H. Ringler 2015 Vol. 22, No. 4 of dried plant material (ANOVA, P = < 0.001) was highest in the mixed pondweed and Sago Pondweed beds (Tables 3, 4). Table 3. Analysis of variance of macroinvertebrate community metrics within 4 communities of aquatic macrophytes in Onondaga Lake, NY, in 2010 and 2011. Mean and ± SE are shown as well as post hoc Waller-Duncan groups. Mean values within a row followed by different letters are significantly different. Heterogeneous Mixed Stonewort grouping pondweeds Sago Pondweed Mean (SE) Mean (SE) Mean (SE) Mean (SE) P-value 2010 Taxa richness 21.7 (0.6) A 17.9 (0.9) B 18.1 (0.6) B 17.2 (0.7) B 0.001 Family richness 12.6 (0.4) A 12.2 (0.5) A 12.2 (0.5) A 11.4 (0.5) A 0.270 ETO 3.8 (0.4) AB 1.8 (0.4) C 4.6 (0.2) A 3.1 (0.4) B less than 0.001 NCO 13.6 (0.6) A 11.8 (0.5) AB 13.4 (0.5) A 11.3 (0.7) B 0.013 Subsample abund. 417.0 (63.6) A 411.6 (69.8) A 542.9 (86.9 A 452.3 (37.1) A 0.278 Est. abundance m-2 6051.8 17,079.5 3876.4 15,862.0 less than 0.001 (1201.2) B (2273.2) A (780.6) B (1798.6) A per kg plant 62,568.4 70,393.5 C 184,052.5 86,912.2 less than 0.001 (11,416.3) C (8926.4) B (36,424.6) A (8701.3) B 2011 Taxa richness 12.4 (0.9) B 17.1 (1.0) A 14.8 (1.0) AB 14.4 (1.3) AB 0.035 Family richness 9.8 (0.5) B 12.9 (0.5) A 11.8 (0.5) A 10.3 (1.0) B 0.042 ETO 1.6 (0.3) A 2.6 (0.4) A 1.9 (0.4) A 2.2 (0.3) A 0.191 NCO 9.5 (0.6) AB 12.1 (0.8) A 10.9 (0.5) A 8.8 (1.1) B 0.009 Subsample abund. 103.5 (11.8) C 152.2 (19.5) BC 225.8 (20.6) A 199.2 (34.2) AB less than 0.001 Est. abundance m-2 4634.7 6493.8 7431.0 11,534.6 0.003 (880.2) C (1174.2) BC (870.8) AB (1885.3) A per kg plant 20,213.3 45,874.8 78,150.8 63,798.9 less than 0.001 (2934.6) C (7744.4) B (8074.8) A (12,146.1) B Table 4. Total density (m-2 and per kg dried plant) of epiphytic macroinvertebrates in Onondaga Lake, NY, compared to similar studies. Source Site Density Current study Onondaga Lake, NY, 2010 3876–17,080/m2 Current study Onondaga Lake, NY, 2011 4645–11,635/m2 Brown et al. 1998 Lake St. Clair, MI less than 5000/m2 Watkins et al. 1983 Orange Lake, FL less than 5000/m2 Thorp et al. 1997 Potomac River, MD 27,960/m2 Peets et al. 1994 Lake Seminole, GA 12,855 /m2 Schramm et al. 1987 Orange and Henderson Lakes, FL 12,257–17,596/m2 Van den Berg et al. 1997 Lake Veluwerneer, The Netherlands 6000/m2 Van den Berg et al. 1997 Lake Worlderwijd, The Netherlands 15000/m2 Current study Onondaga Lake, NY, 2010 62,568–184,052/kg Current study Onondaga Lake, NY, 2011 20,213–78,151/kg Andrews and Haster 1943 Lake Mendota, WI 20,000–52,000/kg Krull 1970 Montezum, NY 3060–20,590/kg Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. Ringler 2015 681 Analysis of macroinvertebrate communities among macrophyte communities In 2010, 47% of the variance was explained by the first 2 PCA axes. We identified 2 groupings: the stonewort (C) and the heterogeneous (H) sites formed groups that overlapped and Sago Pondweed (S) and mixed pondweeds (F) clustered together (Fig. 4). Principal component (PC) 1 (31.5% of variance) separated the stonewort and the heterogeneous sites from the mixed pondweed and Sago Pondweed sites (Fig. 4). Physidae, Valvatidae, Tricladida, Planorbidae, Hydrobiidae, and Amphipoda had positive loadings (>0.25) with PC 1 and the stonewort and the heterogeneous community. Chironomidae and Pyralidae had negative loadings (less than -0.25) with PC1, and were more representative of the macroinvertebrate community associated with mixed pondweeds and Sago Pondweed. PC 2 (15% of variance) separated the stonewort from the heterogeneous sites (Fig. 4). Leptoceridae, Hydroptilidae, Oligochaeta, and Chironomidae had positive loadings (>0.25) with PC 2; greater abundances were associated with stonewort and mixed pondweeds. Thirteen of the 15 macroinvertebrate taxa used in PCA from 2010 had significant Pearson correlations (α = 0.01) with PC 1 or 2, and we individually tested them for significant differences among plant communities. Hirudinea, Valvatidae , and Leptoceridae were significantly more abundant (ANOVA, P < 0.001) in the stonewort sites than the other 3 plant assemblages. The heterogeneous assemblages Figure 4. Principal component analysis of epiphytic macroinvertebrate communities associated with aquatic macrophytes (S = Sago Pondweed, F = mixed pondweeds, C = Stonewort, and H = heterogeneous community) in Onondaga Lake, NY, in 2010. Northeastern Naturalist 682 L.J. Kirby and N.H. Ringler 2015 Vol. 22, No. 4 and stonewort supported significantly higher abundance (ANOVA, P ≤ 0.001) of Physidae, Tricladida, and Amphipoda (Table 5). Sago Pondweed and mixed pondweeds had a significantly higher abundance of Oligochaeta (ANOVA, P = 0.005) and Chironomidae (ANOVA, P = < 0.001) (Table 5). In 2011, 43% of the variance was explained in the first 2 PC axes. The stonewort and Sago Pondweed formed relatively distinct clusters, while mixed pondweeds and the heterogeneous macrophyte assemblages were mostly grouped together (Fig. 5). Sago Pondweed was associated with negative scores along PC 1 (24% of the variance); Chironomidae and Oligochaeta had negative loadings of less than -0.25. Dreissena sp., Planorbidae, Hydrobiidae, Valvatidae, and Amphipoda all had positive loadings (>0.25) with PC 1 and were associated with mixed pondweeds, stonewort, and the heterogeneous community. PC 2 (19% of the variance) separated the stonewort sites from the mixed pondweed and heterogeneous sites (Fig. 5). Coenagrionidae, Hydroptilidae, Hydrachnidae, Physidae, Pyralidae, Planorbidae, Oligochaeta, and Planorbidae had positive loadings (>0.25) with PC 2 and had higher abundance in mixed pondweed and heterogeneous sites (Fig. 5). Fourteen of the 17 taxa used in PC analysis from 2011 had significant Pearson correlations (α = 0.01) with PC 1 or 2, and we individually tested for significant differences among plant communities (Table 6). Dreissenidae (ANOVA, P = 0.003) and Planorbidae (ANOVA, P = less than 0.001) were significantly highest in the stonewort beds (Table 6). Physidae (ANOVA, P = less than 0.001) and Pyralidae (ANOVA, P = < 0.001) were significantly highest in mixed pondweeds, while Oligochaeta (ANOVA, P = < 0.001) and Chironomidae (ANOVA, P = < 0.001) were highest in Sago Pondweed (Table 6). Table 5. Analysis of variance of macroinvertebrate taxa that were found to have significant correlations with PCA axes in Onondaga Lake, NY, in 2010. Mean values within a row followed by different letters are significantly different. Heterogeneous Mixed Macroinvertebrate Stonewort grouping pondweeds Sago Pondweed taxon Mean (SE) Mean (SE) Mean (SE) Mean (SE) P- value Amphipoda 119.7 (36.9) A 72.9 (16.7) A 9.7 (3.2) B 13.6 (10.7) B less than 0.001 Chironomidae 71.9 (11.6) B 97.5 (27.6) B 302.6 (56.6) A 209.6 (30.1) A less than 0.001 Coenagrionidae 2.5 (0.6) B 1.2 (0.5) C 2.0 (0.5) BC 4.2 (0.6) A 0.006 Hirudinea 3.7 (1.0) A 1.4 (0.4) B 0.7 (0.5) BC 0.4 (0.2) C less than 0.001 Hydrobiidae 21.8 (3.2) A 27.4 (5.5) AB 13.8 (3.9) B 3.7 (1.9) C less than 0.001 Hydroptilidae 3.9 (0.8) B 1.1 (0.4) C 25.1 (7.9) A 5.8 (3.6) BC less than 0.001 Leptoceridae 3.6 (0.7) A 1.6 (0.5) BC 4.0 (1.6) AB 1.3 (0.4) C 0.016 Oligochaeta 32.1 (6.0) B 30.5 (9.2) B 71.8 (17.5) A 88.3 (13.2) A 0.005 Physidae 5.0 (1.2) A 8.8 (1.8) A 0.9 (0.6) B 2.3 (1.0) B less than 0.001 Planorbidae 5.9 (1.2) B 26.8 (4.0) A 6.3 (1.6) B 3.3 (0.7) B less than 0.001 Pyralidae 0.6 (0.3) D 2.2 (0.7) C 6.1 (1.6) B 11.9 (1.9) A less than 0.001 Tricladida 23.6 (7.9) A 10.3 (3.0) A 4.0 (1.8) B 2.9 (1.5) B 0.001 Valvatidae 19.7 (5.8) A 8.0 (2.1) B 4.9 (2.4) B 1.1 (0.4) C less than 0.001 Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. Ringler 2015 683 Table 6. Analysis of variance of macroinvertebrate taxa that were found to have significant correlations with PCA axes in Onondaga Lake, NY, in 2011. Heterogeneous Mixed Macroinvertebrate Stonewort grouping pondweeds Sago Pondweed taxon Mean (SE) Mean (SE) Mean (SE) Mean (SE) P- value Amphipoda 18.4 (3.9) A 25.8 (5.1) A 25.9 (9.2) A 1.6 (0.5) B less than 0.001 Ceratopogonidae 0.0 (0.0) A 0.3 (0.2) A 0.0 (0.0) A 0.6 (0.4) A 0.116 Chironomidae 7.1 (2.3) B 9.7 (2.1) B 10.2 (2.6) B 110.6 (30.5) A less than 0.001 Coenagrionidae 0.3 (0.2) C 1.4 (1.0) B 0.9 (0.6) BC 2.8 (0.7) A less than 0.001 Dreissenidae 14.9 (3.7) A 9.4 (3.2) B 5.7 (3.0) B 4.4 (1.9) B 0.003 Hydrachnidae 0.3 (0.2) C 3.6 (2.1) BC 10.8 (3.7) A 4.1 (1.4) AB 0.001 Hydrobiidae 19.0 (4.6) B 16.4 (4.1) B 45.9 (7.6) A 4.7 (1.6) C less than 0.001 Hydroptilidae 1.6 (1.0) A 3.5 (1.0) A 1.9 (0.6) A 4.1 (0.7) A 0.130 Leptoceridae 1.8 (0.5) A 1.4 (0.4) A 1.0 (0.5) A 0.6 (0.3) A 0.067 Oligochaeta 2.4 (0.7) C 11.9 (1.7) B 11.1 (3.1) B 30.8 (7.0) A less than 0.001 Physidae 1.1 (0.4) C 4.1 (0.6) B 11.7 (2.7) A 2.3 (0.5) C less than 0.001 Planorbidae 14.3 (2.3) A 26.5 (7.7) B 74.6 (10.5) B 8.1 (2.4) C less than 0.001 Pyralidae 0.1 (0.8) D 2.3 (0.5) C 10.7 (1.6) A 7.0 (1.9) B less than 0.001 Valvatidae 13.4 (2.7) A 12.7 (3.1) A 13.5 (4.1) A 5.4 (2.7) B less than 0.001 Figure 5. Principal component analysis of epiphytic macroinvertebrate communities associated with aquatic macrophytes macrophytes (S = Sago Pondweed, F = mixed pondweeds, C = Stonewort, and H = heterogeneous community) in Onondaga Lake, NY, in 2011. Northeastern Naturalist 684 L.J. Kirby and N.H. Ringler 2015 Vol. 22, No. 4 Discussion Epiphytic macroinvertebrate community We hypothesized that increased heterogeneity within the heterogeneous macrophyte bed would lead to higher macroinvertebrate richness—a result reported in other studies (Andrews and Hasler 1943, Brown et al. 1988, Krecker 1939, Mormule et al. 2011, Rosine 1955). The results of this study did not support our hypothesis, but were similar to those of Theel et al. (2008) and Van den Berg et al. (1997) in that the richness of macroinvertebrates was not significantly different among macrophyte assemblages. We found that no particular plant community supported higher richness of macroinvertebrate taxa, families, NCO taxa, or ETO taxa in both years. Our findings were likely caused by the fact that although different species were dominant in each assemblage, all 4 aquatic macrophyte assemblages were dominated by macrophytes with similar morphology (i.e., small leaves). The macrophyte assemblages in Onondaga Lake, including the heterogeneous bed, lack variability in growth forms (emergent/floating) that have been found to increase macroinvertebrate richness (Brown et al. 1988, Voigts 1976). Assemblages of small-leaved macrophytes have less niche diversity than those with more variability in macrophyte structure, and therefore may support less richness of specialized taxa. Another factor that likely contributed to the low richness of macroinvertebrates we observed is that the community does not appear to have fully recovered from the extensive pollution to which the area was exposed for much of the past century (Kirby 2013). Using the same sampling techniques, Kirby (2013) found that adjacent unpolluted aquatic systems (Otisco Lake, Seneca River/Onondaga Outlet, and Oneida Lake) had higher taxa richness per subsample than we found in Onondaga Lake subsamples in 2011. A larger number of pollution-intolerant taxa were also documented in these systems than we recorded in Onondaga Lake (Kirby 2013). Even though there was no apparent relationship between macroinvertebrate richness and macrophyte assemblage, we detected differences in the abundance of particular macroinvertebrates within the different macrophyte assemblages. PCA analysis explained a low proportion of variability, but provided a visual representation of sites with similar macroinvertebrate assemblages that we verified with ANOVA. The most distinct macroinvertebrate community was associated with Sago Pondweed, which supported the lowest richness of NCO taxa in both years. The assemblage was characterized by low abundance of Gastropoda and Amphipoda and a significantly higher abundance of Chironomidae (mainly Tanytarsini Paratanytarsus sp. and Orthocladiinae Cricotopus sylvestris [Fabricious]), Oligochaeta, and Coenagrionidae in both years. The value of Sago Pondweed to macroinvertebrates is debatable; Berg (1949) suggested that Sago Pondweed has limited value because its leaves are too small to support leaf miners or case-making Trichoptera. Krecker (1939) found that Sago Pondweed supported a high number of macroinvertebrates that were likely using the plant for cover, and Dibble et al. (1997) indicated that the plant has high structural complexity. Sago Pondweed in Onondaga Lake was associated with silt/fine sand sediment substrates (L. Kirby, pers. observ.), a finding reported from other lakes (Case and Madsen 2004), and in Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. Ringler 2015 685 both years there was a large amount of silt/sand sediment on the plant leaves. It is possible that the sediment that we observed on Sago Pondweed contributed to the associated macroinvertebrate community. The 2 most abundant Chironomidae in the Sago Pondweed bed were Paratanytarsus sp. and Cricotopus sylvestris, which are tube-dwelling grazers that construct ridged tubes of sediment and silk—used primarily as retreats from predation—along stems and branches of aquatic macrophytes (Hershey 1987). We observed many Chironomidae using sand retreats when we examined our Sago Pondweed samples. The high abundance of Coenagrionidae within Sago Pondweed beds can be attributed to the large abundance of small prey (Chironomidae and Oligochaeta) associated with this macrophyte type. Coenagrionidae and other Zygoptera feed predominantly on Chironomidae larvae (Hershey 1987, Lawton 1971). Lawton (1971) found that Oligochaeta were also heavily preyed on by an early instar Zygoptera Pyrrhosoma nymphula (Sulzer). The low abundance of gastropods and amphipods we detected in Sago Pondweed samples indicates that this macrophyte community does not support strong development of periphyton in Onondaga Lake. In 2010, the mixed pondweed sites supported the same abundance of Chironomidae and Oligochaeta as the Sago Pondweed beds. In that year, the mixed pondweed sites were located in an area dominated by silt/sand substrate (L. Kirby, pers. observ.); Sago Pondweed was found intermixed with half of the mixed pondweed samples, and the samples had sediment on the leaves. In 2011, the mixed pondweed at the initial site senesced and decayed before sampling, so we sampled 2 other sites where mixed pondweed was the dominant assemblage. The substrate at these new sites was an even mix of sand and gravel substrate, with no sedimentation noted on the plant leaves; also Sago Pondweed was not intermixed. In 2011, the mixed pondweed beds supported significantly higher abundance of Gastropoda (Hydrobiidae and Physidae) and Pyralidae than the other macrophyte communities and had significantly less Chironomidae and Oligochaeta than were found in the Sago Pondweed beds (Table 4). It is likely that the change in macroinvertebrate communities was not caused entirely by site differences, because in both 2010 and 2011 the mixed pondweed sites were located in areas with moderately high-wave energy (Kirby 2009, Parsons Inc. et al. 2010). The presence of Sago Pondweed and possibly sediment on the leaves in the mixed pondweed samples from 2010 may have contributed to the large number of tube-dwelling Chironomidae and Oligochaeta. We did not investigate the possible relationship between sedimentation on macrophytes and its influence on aquatic macroinvertebrate communities in our study, but it should be examined in the future. The macroinvertebrate communities associated with stonewort and the heterogeneous macrophyte bed were similar and practically indistinguishable in both years. They were characterized by high numbers of amphipods and gastropods with low abundance of Chironomidae and Oligochaeta. This macroinvertebrate community is comparable to those observed in other studies of similar macrophyte communities, and along with Chironomidae, are often the most dominant taxa associated with Coon’s Tail and Eurasian Watermilfoil (Andrews and Hasler 1943, Brown et al. 1988) and stonewort (Van den Berg et al. 1997). The high abundance Northeastern Naturalist 686 L.J. Kirby and N.H. Ringler 2015 Vol. 22, No. 4 of grazers within these aquatic macrophyte assemblages indicates a higher availability of periphyton on the submerged vegetation. The relationship between aquatic macrophytes, epiphytes/periphyton, and macroinvertebrate grazers is well documented (Allen 1971, Cattaneo 1983, Cattaneo and Kalff 1980, Cattaneo and Mousseau 1995, Jaschinski et al. 2011). The abundance of macroinvertebrate grazers is determined by the development of epiphytic algae (Osenberg 1989, Van den Berg et al. 1997), and aquatic plants have a positive response to the removal of attached epiphytes (Underwood et al. 1992). Epiphytic macroinvertebrate abundance One of the primary benefits of using a modified Gerking sampler was the ability to estimate densities of macroinvertebrates per area and plant biomass. Sago Pondweed had the highest estimated abundance of macroinvertebrates m-2 of bottom area in both 2010 and 2011 (Table 3) mainly because these sites had high biomass of aquatic vegetation in each sample. The abundance of macroinvertebrates m-2 was similar to what has been found in other systems, while the abundance of organisms per kg of dried plant biomass was higher (Table 4). The estimated abundance of organisms per kg of dried plant-biomass is likely a conservative estimate because a portion of the attached sediment remained on the samples/subsamples when they were weighed. The high density of macroinvertebrates, whether expressed as m-2 or per kg of dried plant biomass, suggests that the macrophyte beds in Onondaga Lake provide a large amount of prey for fish, ducks, and other wildlife. We predict that the heterogeneous macrophyte assemblage (~40% of the littoral area), stonewort (~10% as of 2012), and mixed pondweed (~30%) support high levels of fish production because of the high abundance of macroinvertebrates and moderate macrophyte density which tends to allow high levels of foraging by fish (Crowder and Cooper 1982, Gotceitas 1990). Kirby (2009), studying fish diets in Onondaga Lake, found that Lepomis gibbosus (L.) (Pumpkinseed Sunfish) fed predominantly on Amphipoda, Lepidoptera, and Gastropoda, and Lepomis macrochirus Raf. (Bluegill Sunfish) mainly fed on amphipods. Lepomis sp. (sunfish) are currently a dominant littoral-zone fish in Onondaga Lake; they are major components in the littoral food web and are instrumental to the future of recreational fishing at the site. We suggest that the epiphytic macroinvertebrate community associated with Sago Pondweed has limited direct value for larger-adult fish because this plant tended to grow at very high densities and the community is numerically dominated by small macroinvertebrates (Chironomidae and Oligochaeta). However, Sago Pondweed beds provide quality habitat and forage for young-of-the-year fish and invertebrate predators, so these assemblages are important components of the Onondaga Lake food web. Sago Pondweed also provides high-quality forage for dabbling ducks (Martin and Ulher 1939, Wersal et al. 2005), and the high abundance of attached macroinvertebrates would supply ducks with an excellent source of additional protein (Krull 1970). At its current and apparently stable distribution of approximately 15% of the littoral zone, the Sago Pondweed assemblage provides a large area of quality forage for ducks and young fish. Northeastern Naturalist Vol. 22, No. 4 L.J. Kirby and N.H. 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