jc.. WI !::, Aquatic Community Nat . 3 : Interactions of T 4/ 156 Submerged Macrophytes Phytoplankton Zooplankton G' I S[l. Macrophytes ,. r:.'f. • Fishes Benthos Technical Bulletin No. 156 DEPARTMENT OF NATURAL RESOURCES Madison, Wisconsin 1985 "When one tugs at a single thing in nature, be finds it attached to everything else in tbe world." -John Muir FOREWORD Dominating the shallows o! many this shallow impoundment is impor­ cles will detail (1 l impacts of harvest­ lakes are large flowering plants. Essen­ tant not for its recreational value, but ing lake vegetation on Halverson Lake, tial as fish and waterfowl habitat, these as a model to understand plant com­ (2) mechanicaJ harvesting programs in underwater prairies are so intricately munity interactions unhampered by Wisconsin, and (3) creative lake-use bound to the food web of lakes that excessive runoff, pesticides, speed boat­ plans for managing with macrophytes. eradicating them for boating or swim­ ing, and other disturbances. Frequent The latter is introduced in the conclud­ ming has not always been successful reference to relevant literature on ing section of t he present work. or desirable. A comprehensive study of aquatic plants broadens the base of the I hope that this technical bulletin the ecology of macroscopic plants was study. will ultimately serve lake managers as needed to move forward with develop­ This treatise forms the core of sev­ a useful reference source for informa­ ing new management strategies. eral publications dealing with innova­ tion and ideas on macrophytes and This study, conducted by the tive approaches to plant management. their ecology. DNR's Bureau of Research, details the Drawdown and bottom blanketing, re­ seasonal wax and wane of plants and movable screening, and mechanical associated li!e in Halverson Lake. Nes­ harvesting are subjects of previous Kent E. Klepinger tled in Wisconsin's hilly southwest, works by the author. Forthcoming arti- October 1985 ABSTRACT The community structure and interactions of submerged macrophytes were examined from 1977 through 1983 in Halverson Lake, a shallow 4-ha (10-acre) impoundment in southwestern Wisconsin. Divers sampled macrophytes along transects; an Ekman dredge, suspended multiple-plate samplers, and plant nets gathered macroinvertebrates; fishes were boom shocked; and plankton were vertically collected with a net or Kemmerer sampler. Vascular plants covered 40~70% of the bottom in June-August, stratified verti­ cally into three layers, and S{)read in zones to a depth of 3.5 m (11.5 ft). Standing crop reached 130-200 gjm2 (dry weight) in July and consisted mostly of Berchtold's, curly-leaf, and sago pondweeds (Potamogeton spp.), coontail (Cer­ atophyllum demersum L.), and water stargrass (Reteranthera dubia (Jacq.)). Macroinvertebrates congregated on or beneath macrophytes, where they were grazed by bluegiJls (Lepomis macrochirus Raf.) and largemouth bass (Micropterus salmoides (Lacepede)). Bluegills also consumed macrophytes. Black crappies (Pomoxis nigromaculatus (Lesueur)) ate zooplankton offshore. Rotifers domi~ nated the net zooplankton. Blue-green algae amassed after June, in response to nutrient runoff and macropbyte decay. Submerged macrophytes functioned to create microhabitats and microcli­ mates inshore, selectively shelter fishes and their prey, replenish detritus and benthic algae eaten by invertebrates, diversify the zooplankton, and improve wa­ ter clarity by stabilizing sediments and storing nutrients. AQUATIC COMMUNITY INTERACTIONS OF SUBMERGED MACROPHYTES I By Sandy Engel Technical Bulletin No. 156 DEPARTMENT OF NATURAL RESOURCES P.O. Box 7921 Madison, Wisconsin 53707 1985 CONTENTS 5 INTRODUCTION Bottom Fauna, 34 Association with Macrophytes, 37 5 STUDY AREA Food of Macroinvertebrates, 41 Fish Use of Habitat and Food, 43 7 METHODS Distribution and Activity, 43 Macrophytes, 7 Access to Macrophytes, 44 Macroinvertebrates, 8 Annual Diet, 44 Fishes, 9 Seasonal Changes in Diet, 46 Zooplankton, 10 Fish Size and Diet, 46 Phytoplankton, 10 Macrophytes as Food, 51 Water Quality, 10 Age and Growth, 53 Diversity and Statistical Analysis, 11 Length-Weight Relations, 54 Standing Crop, 54 11 RESULTS AND DISCUSSION Interactions with Plankton, 54 Macrophyte Community Structure, 11 Composition, 54 Taxa, 11 Seasonal Changes, 59 Growth and Succession, 12 Propagation and Winter Survival, 16 70 SUMMARY Cover, 18 ·Zonation and Depth, 25 72 CONCLUSIONS Vertical Stratification, 27 Microclimates, 28 The Dominance of Macrophytes, 72 Nutrients in Macrophytes, 29 Managing With Macrophytes, 72 Bottom and Plant Dwelling Fauna, 30 73 GLOSSARY Community Composition, 30 Macroinvertebrate Habitats, 34 74 LITERATURE CITED LIST OF TABLES TABLE 1. The Halverson Lake drainage basin ..................... 5 TABLE 21. Diversity of macroinvertebrates on macrophytes sampled in June and July 1980-82 ................................ 41 TABLE 2. Morphometry of Halverson Lake....................... 6 TABLE 22. Food habits of macroinvertebrates in Halverson TABLE 3. Submerged and floating macrophytes sampled in Lake for 1977-82, as reported in the literature. Data are Halverson Lake from 1977 through 1983 ......................... 12 percentage of organisms sharing each food category ............. 42 TABLE 4. Emergent vascular plants, with submerged roots TABLE 23. Abundance and gut contents of non-biting midge and crowns, observed at the water's edge in Halverson Lake larvae (Diptera: Chironomidae) found on macrophytes.......... 43 from 1977 through 1983 ........................................... 12 TABLE 24. Feeding strategies of macroinvertebrates in !ABLE 5. Dates of final complete ice-up and ice-out, mean Halverson Lake for 1977-82, as reported in the literature. Ice and snow depths around Station B for February 10-21, Data are the percentage of organisms employing each and durations of ice cover and open water........................ 14 feeding strategy................................................... 43 TABLE 6. Total production and areal cover of submerged TABLE 25. Size, condition factor, and age (mean± 95% macrophytes for Transects 2-15 ................................... 14 CL) of fishes examined for stomach content on 40 dates in 1977-82 ............................................................ 45 TABLE 7. Flowering and fruiting times of submerged macrophytes and types of propagules relied upon in summer TABLE 26. Percent occurrence (%FO) and relative and winter ......................................................... 17 abundance (%No.) of major prey in fish stomachs for 40 dates in 1977-82 ................................................... 45 TABLE 8. Percent frequency of submerged macrophytes at Transects 2-15 ..................................................... 25 TABLE 27. Percent occurrence (%FO) and relative abundance (%No.) of cladocerans and copepods eaten by fishes on 40 dates in 1977-82 ...................................... 46 TABLE 9. Water temperatures (C) through and just outside macrophyte beds in a sheltered (Transect 1) and unsheltered (Transect 3) bay on July 14, 1983 ................................ 30 TABLE 28. Major prey consumed per 10 fish stomachs on 40 dates in 1977-82 (mean number ± 1 SE) ......................... 46 TABLE 10. Nutrient content of whole macrophyte shoots sampled in 1977-82 (values are mean percent dry weight ± 1 TABLE 29. Relative importance values (mean ± 1 SE) of SE) ................................................................. 30 major prey consumed by fishes per sampling date in 1977-82. Percent of dates when prey were consumed is in parentheses.... 47 TABLE II. Diversity of macroinvertebrate, zooplankton, and phytoplankton communities of Halverson Lake in 1977-82. .. 31 TABLE 30. Relative frequency of habitats used for feeding by fishes during mid-May through August 1977-79, based on prey habitat preferences ........................................... 47 TABLE 12. Number of taxa identified in bottom samples and from plants in Halverson Lake in 1977-82 ........................ 31 TABLE 31. Relative abundance of prey consumed by at least 5% of fishes of three sizes in mid-May through August 1977- TABLE 13. Insects identified in Halverson Lake in 1977-82. .. 32 79 ................................. , ................................ 50 TABLE 14. Free-living macroinvertebrates, other than TABLE 32. Relative abundance of prey comprising at least insects, identified in Halverson Lake in 1977-82 .................. 33 5% of the crappie diet for mid-May through August 1977- 79, grouped by size class of prey .................................. 50 TABLE 15. Percent macroinvertebrate taxa contributing at least 5% of all individuals or samples during 1977-82 ............ 34 TABLE 33. Electivity indices (mean ± 1 SE) of microcrustaceans consumed by crappies on 8 dates from TABLE 16. Percentage of samples containing mid-May through August 1977-79 ................................ 50 macroinvertebrates from different habitats in 1977-82 ........... 35 ' TABLE 34. Number of total taxa and taxa contributing at TABLE 17. Percent of total number of macroinvertebrates least 5% of prey consumed by fishes of three sizes from mid- comprising at least 1% of those collected in different May through August 1977-79 ..................................... 50 habitats in 1977-82 ................................................ 36 TABLE 35. Shannon-Weaver diversity index (log2) of all TABLE 18. Habitat preferences of macroinvertebrates in taxa consumed by fishes of three size