Species-Specific Responses of Aquatic Macrophytes to Fish Exclusion in a Prairie Marsh: a Manipulative Experiment

WETLANDS, Vol. 26, No. 2, June 2006, pp. 430±437 q 2006, The Society of Wetland Scientists SPECIES-SPECIFIC RESPONSES OF AQUATIC MACROPHYTES TO FISH EXCLUSION IN A PRAIRIE MARSH: A MANIPULATIVE EXPERIMENT Vincent D. Evelsizer1 and Andrew M. Turner Department of Biology Clarion University Clarion, Pennsylvania, USA 16214 1Present address: Iowa Department of Natural Resources 109 Trowbridge Hall University of Iowa Iowa City, Iowa, USA 52242 Abstract: An exclosure experiment was carried out at two sites in Delta Marsh, Manitoba, Canada to investigate the role of ®sh in limiting the growth of submersed macrophytes. The experiment consisted of three treatments: (1) ®ne-mesh exclosures designed to exclude both planktivorous ®sh and carp, (2) coarse- mesh exclosures designed to exclude adult carp but admit smaller ®sh, and (3) reference plots marked with corner stakes but without sides. Treatments were established in mid-May, and macrophyte biomass was sampled from within the exclosures in late August to assess treatment effects. Exclosure treatments had strong effects on the macroalgae Chara, with biomass 11.9-fold greater in full-exclosure plots than in reference plots, and 3-fold greater in carp exclosures than in reference plots. Exclosure treatments had no effect on above-ground or below-ground biomass of Stuckenia pectinata, the most widespread and abundant macrophyte in Delta Marsh. Thus, ®sh appear to limit macrophyte growth in Delta Marsh, but the effect of ®sh exclusion was dependent on species composition of the macrophyte assemblage. Key Words: macrophytes, biomanipulation, turbidity, wetland restoration, Chara, Stuckenia, Delta Marsh, carp INTRODUCTION tal approaches are necessary to identify the underlying mechanisms. Shallow lakes and marshes tend to exist in one of One potential determinant of macrophyte abundance two alternative conditions: a clear water state charac- in wetlands is the abundance of planktivorous and ben- terized by high water transparency and abundant sub- thivorous ®sh. A number of studies have shown that mersed macrophytes, and a turbid state characterized high densities of zooplanktivorous ®sh are capable of by low water clarity and few submersed macrophytes depressing zooplankton standing crop, which in turn (Timms and Moss 1984, Jeppesen et al. 1990, Scheffer reduces phytoplankton grazing by zooplankton and 1998, Bayley and Prather 2003). Nutrient loading, leads to high phytoplankton standing crops and thus food web structure, herbivory, and wave exposure are low water clarity (Turner and Mittelbach 1992, Car- among the factors that in¯uence lake state. Many shal- penter and Kitchell 1993, Schriver et al. 1995, Jep- low lakes and marshes in North America and Europe pesen et al. 1997). Low water clarity usually limits the have recently experienced increases in turbidity and growth and species diversity of submersed aquatic decreases in the abundance of submersed macrophytes plants (e.g., Chambers and Kalff 1985, Duarte et al. (Chow-Fraser 1998, Scheffer 1998). Often, the decline 1986, Kantrud 1990). Benthivorous ®sh, such as com- of macrophytes is associated with human-induced dis- mon carp (Cyprinus carpio Linneaus) can contribute turbances such as the stabilization of water levels, in- to turbidity by resuspending sediments as they forage vasion of planktivorous and/or benthivorous ®sh, or (Meijer et al. 1990, Breukelaar et al. 1994). Carp may increased nutrient loading (Scheffer et al. 1993, Bouf- also limit the growth of aquatic macrophytes in a direct fard and Hanson 1997). However, because these dis- manner by uprooting plants during feeding or spawn- turbances often disrupt several mechanisms simulta- ing activities (Anderson 1950, Tryon 1954, Atton neously, the speci®c factors most responsible for mac- 1959, Robel 1961, King and Hunt 1967). Thus, a key rophyte decline are usually unknown, and experimen- to the restoration of submersed macrophytes in marsh- 430 Evelsizer & Turner, FISH AND SUBMERSED MACROPHYTES 431 es may be the limitation of planktivorous and benthi- (Goldsborough 1995). Water pH ranges from 8.2 to vorous ®sh (e.g., biomanipulation; Shapiro and Wright 9.0, and total alkalinity averages 338 mg/l CaCO3, 1984, Benndorf 1987, Jeppesen et al. 1990). European largely as bicarbonate (Anderson and Jones 1976). investigators have repeatedly tested these ideas and Delta Marsh historically had greater water clarity have accumulated substantial evidence documenting and supported dense beds of submersed macrophytes the important roles of ®sh in in¯uencing submersed (Hinks and Fryer 1936, Walker 1959, 1965). Large macrophytes in shallow lakes and marshes (e.g., numbers of waterfowl used the marsh as a migratory Scheffer et al. 1993, Jeppesen et al. 1997), but the role stop-over and breeding site (Hochbaum 1944, 1955). of ®sh in North American wetlands has not been as However, the common carp invaded Lake Manitoba widely evaluated (but see Hanson and Butler 1994, and the marsh in 1948 (McCrimmon 1968), and Fair- Zimmer et al. 2001, 2002). ford Dam was built at the lake's outlet in 1961, which Here, we evaluate the effect of ®sh exclusion on stabilized the water level of Delta Marsh. Since that submersed macrophyte biomass in East Delta Marsh, time, water clarity in the marsh has decreased, the Manitoba, Canada. Delta Marsh is one of North Amer- abundance of submersed macrophytes has been re- ica's most prominent wetlands and has been the site duced, and waterfowl use of the marsh has declined of important research in wetland ecology (e.g., Murkin (Batt 2000). Fish, including common carp and fathead et al. 2000) but, like many wetlands, has experienced minnows (Pimephales promelas Ra®nesque), are now increased turbidity, a decrease in the abundance of extraordinarily abundant in the marsh (LaPointe 1986, submersed macrophytes, and a reduction in waterfowl Kiers and Hann 1995, Batt 2000, Evelsizer 2001). We use (deGeus 1987, Batt 2000). We experimentally ex- conducted the exclosure experiment at two sites, Di- cluded benthivorous ®sh and planktivorous ®sh from vision Bay and 22-Bay (Figure 1). These sites were plots within the marsh and monitored the response of chosen based on historical data showing that S. pec- submersed macrophytes. Our goal was to test potential tinata was present at these sites in 1973±74 (Anderson strategies for remediation at small scales to improve and Jones 1976) and 1997 (T. Arnold and D. Wrub- methods for subsequent ecosystem level manipula- leski, personal communication). tions. Exclosure Study METHODS The experiment consisted of three treatments: (1) a Study Sites ®ne-mesh exclosure designed to exclude all ®sh (hereafter, full exclosure), (2) a coarse mesh exclosure de- Delta Marsh, located in south central Manitoba, signed to exclude adult carp but admit smaller ®sh Canada (508119 N, 988199 W), is a large (;22,000 ha) (hereafter, carp exclosure), and (3) reference plots lacustrine marsh bordering the southern shoreline of marked with corner stakes but without sides. Study Lake Manitoba (Figure 1). Nearby upland areas south plots were 3 3 3 m square and were placed in open of the marsh are intensively farmed. East Delta Marsh, water areas of known macrophyte beds and spaced at the site of our studies, is a shallow (, 2.5 m depth) least 4 m apart. Full exclosures were built with sides network of bays, channels, and ponds bordered by hy- of 0.25-mm nylon mesh attached to a frame of welded brid cattail Typha X glauca Godr. and common reed wire fence and supported by corner posts. Carp exclo- (Phragmites australis (Cav.) Trin ex. Steud.) (deGeus sures were built with 5 3 10 cm welded steel mesh 1987, Shay et al. 1999). Sago pondweed (Stuckenia fencing. In addition to excluding large carp, the mesh pectinata (L.) Borner) is the most abundant submersed fencing may have reduced access of other large ani- macrophyte in the marsh (Anderson and Low 1976, mals (e.g., turtles and muskrats) to the plots, but we Anderson 1978). Summer water clarity is generally never sighted either of these species during our regular low, with vertical extinction coef®cient values (kd, visits to the exclosures. For both treatments, exclosure photosynthetic active radiation) of 3.2±5.0 m21 and sides extended at least 15 cm into the sediments, and turbidity values of 12±25 NTU (Evelsizer 2001). The exclosures were covered with poultry-wire mesh fenc- marsh is moderately brackish (classi®cation of Stewart ing. Reference plots were marked at all four corners and Kantrud 1972), with speci®c conductivity values with 2.1 m steel fence posts. that generally range between 1000 and 3000 mS/cm Each of the two study sites received seven full ex- and total dissolved solids concentrations ranging from closures, seven carp exclosures, and 14 reference plots. 519 to 3230 mg/l (Goldsborough 1995, Evelsizer Treatments were randomly assigned to plots, and plots 2001). The waters are nutrient-rich, with water-column were arranged parallel to shore and placed so as to nitrogen: phosphorus ratios generally .16 and total standardize water depth (mean depth within cages 5 phosphorus concentrations generally . 50 mg/l 76 cm in Division Bay, 56 cm in 22-Bay) and maintain 432 WETLANDS, Volume 26, No. 2, 2006 Figure 1. Map of east Delta Marsh, Manitoba, Canada showing location of study sites in 22-Bay and Division Bay. uniform sediment characteristics. Exclosures were Peak standing crop of S. pectinata foliage occurs by constructed on shore and transported to each site with mid-August to early September (Anderson and Low an airboat to minimize disturbance to the study site. 1976). Therefore, we sampled vegetation biomass in Placement of exclosures was completed on May 25, each exclosure between 15 and 22 August. Four ran- less than one month after ice-out and before signi®cant domly selected locations within the interior of each above-ground macrophyte growth had begun. Two exclosure (. 0.5 m from edge in order to minimize minnow traps were placed within each full-exclosure any edge effects) were sampled for estimation of plot to capture any ®sh that invaded as eggs or larvae, above-ground and below-ground biomass.

Load more