Chautauqua Lake's Eurasian Watermilfoil and Factors Influencing

Monitor and Evaluate the Impacts of Herbivorous Insects on Eurasian Watermilfoil Growth in Chautauqua Lake, New York 2007 Report Jason D. Johnson Nicholas Sledziona Jason A. Toner Joellen M. Riggs-Larson Robert L. Johnson Cornell University Research Ponds Department of Ecology & Evolutionary Biology Corson Hall, Cornell University Ithaca, New York 14853 Cover Photo Robert L. Johnson Healthy Eurasian watermilfoil vs. Eurasian watermilfoil Eaten by Caddis 2 We submit this report, Monitor and Evaluate the Impacts of Herbivorous Insects on Eurasian Watermilfoil Growth in Chautauqua Lake, New York authored by J. D. Johnson, Sledziona, N., Toner J. A., Riggs-Larson J. M., and Johnson R. L., to the Chautauqua Lake Association Inc. in fulfillment of our contract June 1, 2007 - May 31, 2008 for the following continuing project. Monitor and Evaluate the Impacts of Herbivorous Insects on Eurasian Watermilfoil Growth in Chautauqua Lake, New York 2007 - 2008 Projection Completion Report, December 2008 Submitted by: Dr. Nelson G. Hairston Jr. [email protected] Robert L. Johnson [email protected] Department of Ecology & Evolutionary Biology Corson Hall, Cornell University Ithaca, New York 14853 This report summarizes a cooperative project between the Chautauqua Lake Association Inc., the Chautauqua County Government, including the County Executive and the Planning and Economic Development Department, and the Department of Ecology and Evolutionary Biology, Cornell University, Ithaca NY. The project focus is on the control of the growth of the exotic invasive Eurasian watermilfoil by insect herbivores and restoration of native submersed aquatic plant communities in Chautauqua Lake. In addition, the identification, estimate of abundance and location of plant growth throughout the lake’s littoral zone remains a major part of the project. 3 Photo on Title Page Caddis abundance in Burtis Bay October 2007 4 Executive Summary In 2007, we conducted aquatic plant research for the Chautauqua Lake Association to define the role that Eurasian watermilfoil (Myriophyllum spicatum) plays in the ecology of Chautauqua Lake. This effort continues our research begun in 2002 and focuses on the herbivores that eat watermilfoil, as well as the changing abundance and composition of this very valuable aquatic plant community. 2007 Major Findings Aggressive watermilfoil growth seen at Burtis Bay breaking the surface and flowering very early in 2006 (Keith et al. 2007), did not repeat in 2007 (Johnson Personal Observation). In the south basin, where early watermilfoil growth in 2006 overwhelmed weevil (Euhrychiopsis lecontei) (Figure 8) herbivory (Keith et al. 2007), weevils in 2007 reduced watermilfoil by feeding and moving across Burtis Bay early in the season with high populations (Table 1, Figures 5, 6). Densities of the weevil in the north basin continue to be high with the herbivore sampling locations south of the Chautauqua Institution (B), Camp Mertz (C, H), and at Maple Springs (M) having very high populations and accompanying damage to watermilfoil (Table 1). Herbivore populations (our recorded insect densities) are variable within a season and between years, therefore, to reveal long-term trends in weevil populations and identify locations with consistent population densities; we have averaged the aggregated 2007 weevil data and the prior 2002 – 2006 densities (Figures 2, 3). Graphs suggest differing population densities at individual lake locations. Moth (Acentria ephemerella) (Figure 7) densities also vary; therefore, we have averaged the aggregated 2007 data and prior 2002 – 2006 densities. The moth graph (Figure 4) suggests differing moth densities around the lake, and that the moth populations follow definite life cycle patterns. Moth densities recorded in 2007 show the greatest numbers at the moth addition location near the Bell Tower as they had in 2006 (Keith et al. 2007), which suggests previously added moth larvae (Figure 10) resulted in sustained increases in moth populations. These are greater than at other lake herbivore sampling locations that did not have additions (Table 2). The outbreak of the native caddis Nectopsyche albida (Figure 9) in the south basin in late 2007 appears to have a negative effect on overall plant growth, especially Eurasian watermilfoil. Recommendations Encourage the growth of native submersed plants that are non-canopy forming, or low growing, allowing the development of a bottom carpet of plants to aid in improving water clarity. Conserve watermilfoil herbivores by limiting interfering plant control measures such as harvesting and herbicide use in the areas of the lake requiring less active management. This may allow herbivores a “safe haven” from which they can increase their numbers. Continue to assess the insect herbivore control of plant growth in the lake and look closely at the role that additional herbivores such as the native caddis Nectopsyche albida (Figure 9), play in influencing aquatic plant communities and affecting overall plant growth. Limit the flow of nutrients and soil into the Lake by increased focus on land use and by implementing tertiary treatment for wastewater flowing into Chautauqua Lake. 5 Contents Title Page………...…………………………………………….……………….……3 Executive Summary …………………………………….…………………………...5 Table of Contents……………………….…………….… ………………………….6 Figures and Tables …………………….……………………………………...……..7 Introduction…………………………………………………………………....…….8 Methods…………………………………………………………….…….………….9 Results and Discussion…………………………………………………………..….10 Chautauqua Lake Eurasian Watermilfoil Herbivory by the Weevil and Moth……10 Description of a Caddis Fly Found to be a Major Herbivore in 2007……………..11 Chautauqua Lake Aquatic Plant Growth…………..…………………………..…..21 References……………………………………………….………………….………23 Appendix…………………………………………………..………………………..24 6 Figures and Tables Figure 1. Chautauqua Lake map noting indigenous herbivore survey locations sampled in 2007……..…….9 Figure 2. Summary of estimated weevil populations from 2002-2007 for Chautauqua Lake’s north basin………………………..………………………………………………………………..13 Figure 3. Summary of estimated weevil populations from 2002-2007 for Chautauqua Lake’s south basin……………………………………………………………..…………………………..14 Figure 4. Summary of estimated moth populations from 2002-2007 using a best-fit line graph for Chautauqua Lake’s north basin……………………………………………..…………………15 Figure 5. Locations of tip sampling points taken on June 21, 2007 in Burtis Bay…………………………..16 Figure 6. Average number of weevils per apical stem (+ 1SE) at varying distances from shore, as sampled on June 21, 2007 in Burtis Bay…………………………………………………….........16 Figure 7. Postcard descriptions of the life cycle of the aquatic moth, Acentria ephemerella……………….17 Figure 8. Postcard descriptions of the life cycle of the aquatic weevil, Euhrychiopsis lecontei………….....18 Figure 9. Postcard descriptions of the life cycle of the caddis fly Nectopsyche albida…………………......19 Figure 10. Locations of moth larvae augmentations north of the bell tower at the Chautauqua Institution and at Maple Springs………………………………………..…………………………20 Figure 11. Contrast of macrophyte abundance showing relative abundance of all aquatic plant species combined as determined by rake-toss sampling for five selected locations from 2004 - 2007………………………………………………………………………………………..22 Figures 12a – 25a. Mean moth numbers ± 1SE (includes only larvae + pupae life stages of the moth) and mean weevil numbers ± 1SE (includes all life stages, eggs, larvae, pupae, and adults) recorded in 2007 at herbivore sampling locations per 25cm length apical stem (n = 25 apical stems searched unless noted).………………………………………….…………………..25 Figures 12b – 25b. Herbivore damage to 25cm length apical stems of Eurasian watermilfoil at herbivore sampling locations shown as a mean rating ± 1SE of herbivore damage to 25 apical stems..…………………………………………………………………………………..25 Table 1. Mean numbers of weevils ± 1SE (all life stages – eggs, larvae, pupae and adults) and moths (larvae and pupae) recorded on milfoil apical stems and a mean damage rating for apical stems at Chautauqua Lake herbivore sampling locations in 2007………………….………………..........12 7 Introduction We, at the Cornell University Research Ponds in the department of Ecology and Evolutionary Biology, conducted research on Chautauqua Lake in 2007 under a contract with the Chautauqua Lake Association. The Association’s long-term goal is to reduce the impacts of the invasive exotic Eurasian watermilfoil (Myriophyllum spicatum) on the recreational uses of the lake. Our objective is to assess the role Eurasian watermilfoil herbivores (insects in Chautauqua Lake) have in influencing the growth of watermilfoil. The control of watermilfoil growth and the prevention of watermilfoil’s dominance of Chautauqua Lake’s desirable native plant species population are essential to protect the recreational needs, as well as the overall health of the lake’s ecosystem. In 2002, we began with frequent measurements of watermilfoil herbivore densities at ten locations in the lake in order to establish the species and numbers of those species present in the lake. We soon increased the number of our sampling locations to fourteen, and in 2007, we continue to monitor twelve. This report shows the variation in herbivore densities recorded not only seasonally but also between locations around the lake. Variability or unpredictability of measurement data is common in most, if not all, ecosystems such as Chautauqua Lake. However, because of our multiyear monitoring some clear trends

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