Influences of productivity, vegetation, and fish on ... - Springer Link

Springer 2005

Hydrobiologia (2005) 543: 147–157 DOI 10.1007/s10750-004-6952-y

Primary Research Paper

Influences of productivity, vegetation, and fish on macroinvertebrate abundance and size in Midwestern USA impoundments Paul H. Michaletz1,*, Kathy E. Doisy2 & Charles F. Rabeni2 1

Missouri Department of Conservation, 1110 South College Avenue, Columbia, MO 65201, USA U.S. Geological Survey, Missouri Cooperative Fish and Wildlife Research Unit, University of Missouri, 302 AnheuserBusch Natural Resources Building, Columbia, MO 65211-7240, USA (*Author for correspondence: E-mail: [email protected]) 2

Received 27 April 2004; in revised form 11 October 2004; accepted 30 November 2004

Key words: macroinvertebrates, impoundment productivity, benthivorous fish, macrophytes

Abstract The influences of productivity, vegetation coverage, and benthivorous fish abundance on macroinvertebrate abundance and mean size were examined in Midwestern USA impoundments. While impoundment productivity was not strongly related to total abundance and mean size of macroinvertebrates, it was related to specific taxa. As productivity increased, Ephemeroptera and Odonata abundance decreased and Diptera abundance increased. Despite the shift in taxonomic composition, mean individual size of the macroinvertebrate community varied little with changes in impoundment productivity. Relationships between macroinvertebrates and benthivorous fish were mixed. Macroinvertebrate abundance, especially Diptera, increased with increases in bluegill Lepomis macrochirus Rafinesque abundance and decreased with increases in channel catfish Ictalurus punctatus (Rafinesque) (which are stocked annually) abundance. Fish were not related to the mean size of macroinvertebrates. Macrophyte coverage was not related to macroinvertebrate abundance or mean size. Overall, macroinvertebrate abundance was mostly related to productivity and benthivorous fish in these impoundments. Mean size of macroinvertebrates did not differ with productivity, fish abundance, or macrophyte coverage.

Introduction Macroinvertebrate abundance varies greatly among lentic waters and the reasons for this variability are not entirely understood. It has been positively associated with lake productivity in some studies (Hanson & Peters, 1984; Rasmussen & Kalff, 1987; Rasmussen, 1988), but not in others (Johnson & Weiderholm, 1989; Dinsmore et al., 1999; Paukert & Willis, 2003). Generally, it is positively related to macrophyte coverage (Gerking, 1957; Gerrish & Bristow, 1979; Wiley et al., 1984) and negatively related to benthivorous fish abundance (Post & Cucin, 1984; Hayes et al., 1992; Svensson et al., 1999). However, the stron-

gest effects of fish on macroinvertebrates were observed when their abundance changed greatly because of intentional reductions (Hayes et al., 1992; Svensson et al., 1999) or introductions (Post & Cucin, 1984). Macroinvertebrate abundance was not related to benthivorous fish over a more ‘‘natural’’ range in fish abundances among shallow prairie lakes (Paukert & Willis, 2003). The effect of fish predation on macroinvertebrate abundance may vary with macroinvertebrate taxa (Crowder & Cooper, 1982; Gilinsky, 1984) and macrophyte coverage (Diehl, 1993). Size structure of the macroinvertebrate community may also be influenced by lake productivity, macrophyte cover, and benthivorous fish

148 abundance. As lake productivity increases, the average size of macroinvertebrates may decrease due to changes in species composition (Hayward & Margraf, 1987; Rasmussen, 1993). Rasmussen (1993) found that the biomass of small macroinvertebrates increased with increases in submerged macrophyte biomass, reducing the average size of individuals in the macroinvertebrate community. Many benthivorous fish selectively prey on larger macroinvertebrates, shifting the size-structure of the macroinvertebrate community to smaller sizes (Crowder & Cooper, 1982; Diehl, 1995; Svensson et al., 1999). Many studies relating macroinvertebrate abundance and size to environmental variables have been conducted in north temperate natural lakes in Europe, Canada, and the United States. No studies were found relating macroinvertebrates to environmental conditions in Midwestern USA impoundments. Midwestern USA impoundments are considerably different than north temperate lakes (Stein et al., 1996); differing in morphometry, hydrology, water chemistry, productivity, plant and animal assemblages, and in the climatic conditions they experience. Thus, inferences derived from studies of north temperate lakes may not apply to these waters. Factors that may influence macroinvertebrate density, biomass, and size were assessed among 30 Midwestern USA impoundments that varied greatly in productivity, macrophyte cover, and benthivorous fish abundance. The objective was to determine if impoundment productivity, macrophyte coverage, and fish abundance related to macroinvertebrate abundance and average size. An understanding of these relationships will enable biologists to better manage these ecosystems for sport fish, many of which rely on macroinvertebrates as prey.

Methods Study sites Thirty impoundments (8.9–331.8 ha surface area) within the state of Missouri, USA were sampled (Table 1). They are relatively shallow with mean depths usually less than 5 m and thermally stratify from mid June to mid September, during which

Table 1. Environmental characteristics of the 30 Missouri impoundments Variable

Mean

SE

Surface area (ha)

41.2

11.3

8.9–331.8

Secchi depth (m) Chlorophyll (mg/m)3)

1.2 36.3

0.1 8.5

0.3–2.8 2.4–189.6

Total phosphorus (mg/m)3) 61.0 Total nitrogen (mg/m)3)

910.8

Range

9.2

11.0–188.5

88.5

326.7–2120.0

SE=standard error. Productivity data was collected in 2001– 2002 and provided by the University of Missouri (J. Jones, unpublished data).

the hypolimnions are usually anoxic. They vary in productivity from oligotrophy to hypereutrophy, with total phosphorus concentration ranging from 11 to 188 mg/m)3 (Table 1). Some lack vegetation while others contain abundant vegetation. The impoundments provide valuable sport fisheries. The most common sport fish are bluegill Lepomis macrochirus Rafinesque, largemouth bass Micropterus salmoides (Lacepede), crappies Pomoxis spp., and channel catfish Ictalurus punctatus (Rafinesque). Ictalurus punctatus are stocked annually in order to maintain populations. No other fish species is routinely stocked. Gizzard shad Dorosoma cepedianum (Lesueur) and common carp Cyprinus carpio Linnaeus, which are not sought by anglers and other Lepomis spp. are also present in some of the impoundments. Sampling Macroinvertebrates were sampled with an Ekman grab sampler (23 · 23 cm) at 20–25 locations in the littoral zone (1–3 m depth) in each impoundment once during mid June to early July during 2001 and 2002. Sampling was done in the littoral zone so that the potential relationships with benthivorous fish could be assessed. Benthivorous fish were restricted to foraging in the littoral zone throughout much of the growing season because of hypoxia in deeper waters. Ekman grab samples were placed on ice and later frozen. In the laboratory each sample was thawed and then rinsed into a white enamel pan and inspected for invertebrates with inorganic cases. These specimens were removed and returned to the sample bag. The remaining macroinvertebrates were separated from debris and sediment using a

149 sugar floatation procedure described by Anderson (1959). Each sample was repeatedly hydrated with distilled water and re-floated until no new specimens were discovered during a 5-min inspection. After sorting, all specimens were placed into distilled water for 20 min to regain their original size. Organisms were identified mainly to order or family and counted. Ten randomly-selected individuals per taxon were measured for length with an ocular micrometer. However, if the taxon contained more than one distinct mode of sizes (indicating different cohorts or species), 10 specimens from each mode were measured, and all members of each size mode were counted separately. This most frequently occurred for larval Chironomidae, Ceratopogonidae, Odonata, Ephemeroptera, and Pelecypoda. Biomass of each taxon was estimated using density estimates (organisms/m)2) and individual mass estimates derived from published length–dry mass equations (Smock, 1980; Meyer, 1989), except that we developed our own length–dry mass equation for Pelecypoda. Initially, total macroinvertebrate biomass was computed for 10 samples from each impoundment for each year. The means, standard deviations, and coefficients of variation (CV) were calculated using 10, 9, 8…,2 samples to determine if the variation in biomass among the samples was adequately reduced with 10 samples (CVs reached an asymptote). If the variation was not sufficiently reduced, additional samples were processed until the CVs leveled off. Usually only 10 samples were required, but as many as 20 were needed for some impoundment-year combinations. The mean density and biomass of invertebrates in these samples were used as estimates of abundance. The most common benthivorous fish in the study impoundments are L. macrochirus and I. punctatus. Both species rely heavily on macroinvertebrates for food (Werner et al., 1983; Schramm & Jirka, 1989; Hubert, 1999; Olson et al., 2003). L. macrochirus and I. punctatus were sampled with standardized surveys conducted by regional fisheries management staff of the Missouri Department of Conservation (MDC). L. macrochirus were sampled with electrofishing in April to early June during one or more years from 1999 to 2003. I. punctatus were sampled in 2001 and 2003 using tandem hoop net sets baited with

cheese and fished for 3 days (Michaletz & Sullivan, 2002). Data for both species were averaged across years for each impoundment. Relative abundance was indexed in two ways for each species: catchper-unit-effort (CPUE, fish/h)1 of electrofishing for L. macrochirus and fish/set)1 for I. punctatus) and biomass-per-unit-effort (BPUE, kg/h)1 of electrofishing for L. macrochirus and kg/set)1 for I. punctatus). Biomass was determined from length–frequency data and length–wet mass equations for each species. Length–mass equations were developed for each impoundment for I. punctatus. However, L. macrochirus were not weighed during the surveys, so we used a length– mass equation derived from L. macrochirus in another Missouri impoundment (P. Michaletz, MDC, unpublished data). Submergent macrophyte coverage information was supplied by a survey of regional MDC fisheries biologists (J. Bonneau, MDC, unpublished data). Common macrophytes included Potamogeton spp., Najas spp., Ceratophyllum spp., Elodea spp., and Chara spp. Vegetation was classified as absent, moderate ( 0.09). Both density (Wilks’ lambda = 0.045, p = 0.0002) and biomass (Wilks’ lambda = 0.078, p = 0.004) of dominant macroinvertebrate taxa were associated with fish abundance, but mean individual mass (Wilks’ lambda = 0.094, p = 0.61) was not associated with fish abundance. The first two pairs of canonical variates were significant for macroinvertebrate density (Table 6). The first and second canonical variates of macroinvertebrate

variables, accounting for a combined 32% of the macroinvertebrate variance (Table 7), were related mostly to Diptera and Mollusca density, respectively (Table 6). The first and second canonical variates of fish variables, accounting for a combined 58% of the fish variance (Table 7), were related mostly to L. macrochirus BPUE and I. punctatus BPUE, respectively (Table 6). The first and second macroinvertebrate canonical variates explained 22% of the variance of fish abundance, whereas the first and second fish variates explained 41% of the variance in macroinvertebrate density (Table 7). The two macroinvertebrate canonical variates explained 77% of the variance in L. macrochirus BPUE (Table 7). The two fish canonical variates explained 39% of the variance in Diptera density and 47% of the variance in Mollusca density (Table 7). Diptera densities increased with increase in L. macrochirus BPUE (Fig. 4). While Mollusca densities were significant in the model, there was no strong relationship with either I. punctatus or L. macrochirus BPUE (Fig. 4). Only the first pair of canonical variates was significant for macroinvertebrate biomass and fish (Table 8). The first canonical variate of macroinvertebrate biomass, accounting for 20% of the

153 Table 6. Correlation coefficients between macroinvertebrate density and fish variables versus their canonical variates (CVAR) Macroinvertebrate

Variable

Fish

CVAR1

CVAR2

Diptera

0.672

Ephemeroptera

0.032 0.439 )0.231

Mollusca Odonata

CVAR1

CVAR2

)0.233

0.601

)0.177

0.185

0.029

0.140

0.744 )0.386

0.392 )0.207

0.564 )0.292

Megaloptera

0.077

0.290

0.069

0.220

Others

0.554

)0.138

0.496

)0.104

Lepomis macrochirus CPUE

0.634

)0.379

0.709

)0.501

Lepomis macrochirus BPUE

0.854

)0.198

0.955

)0.261

Ictalurus punctatus CPUE

0.003

0.314

0.003

0.415

Ictalurus punctatus BPUE

0.188

0.450

0.210

0.594

)1

Catch-per-unit-effort (CPUE) equals fish/h of electrofishing for Lepomis macrochirus and fish/tandem hoop net set)1 for Ictalurus punctatus. Biomass (kg)-per-unit-effort (BPUE) equals kg/h)1 of electrofishing for L. macrochirus and kg/tandem hoop net set)1 for I. punctatus.

Table 7. Percentage of standardized variance of the variables of macroinvertebrate density and fish explained by their own and opposite canonical variates (CVAR) in the canonical redundancy analysis Variable

Macroinvertebrate

Fish

CVAR1

CVAR2

CVAR1

CVAR2

Macroinvertebrate

16.8

31.8

29.1

41.2

Fish

13.5

22.0

36.4

57.5

Diptera

36.1

39.2

Ephemeroptera Mollusca

0.1 15.4

2.1 47.2

Odonata

4.3

12.8

Megaloptera

0.5

5.3

24.6

25.6

Others Lepomis macrochirus CPUE

40.2

54.6

Lepomis macrochirus BPUE

72.9

76.8

0.0 3.5

9.9 23.8

Ictalurus punctatus CPUE Ictalurus punctatus BPUE

Catch-per-unit-effort (CPUE) equals fish/h)1 of electrofishing for Lepomis macrochirus and fish/tandem hoop net set)1 for Ictalurus punctatus. Biomass (kg)-per-unit-effort (BPUE) equals kg/h)1 of electrofishing for L. macrochirus and kg/tandem hoop net set)1 for I. punctatus.

macroinvertebrate variance (Table 9), was related mostly to Diptera biomass (Table 8). The first canonical variate of fish abundance, accounting for 36% of the fish variance (Table 9), was related most closely to I. punctatus CPUE (Table 8). The first macroinvertebrate canonical variate explained

25% of the variance of fish data, but the first fish canonical variate explained only 14% of the variance in macroinvertebrate biomass (Table 9). The first macroinvertebrate canonical variate was most strongly correlated with I. punctatus CPUE (R2 = 0.44), whereas the first fish canonical variate

154 Table 8. Correlation coefficients between macroinvertebrate biomass and fish variables versus their canonical variates (CVAR) Variable

Macroinvertebrate Fish CVAR CVAR

Diptera

0.885

0.741

Ephemeroptera

)0.610

)0.511

Mollusca

)0.024

)0.020

Odonata

0.118

0.099

)0.082

)0.069

Others

0.196

0.164

Lepomismacrochirus CPUE

0.401

0.478

Megaloptera

Lepomis macrochirus BPUE 0.389

0.464

Ictalurus punctatus CPUE

)0.665

)0.794


)0.495

)0.591


ate vegetation category than for the other two categories. Figure 4. Scatter plots showing relationships between Diptera and Mollusca density (organisms/m)2) and bluegill Lepomis macrochirus biomass-per-unit-effort (BPUE, kg/h)1) and between Mollusca density (organisms/m)2) and channel catfish Ictalurus punctatus biomass-per-unit-effort (BPUE, kg/set)1).

was most strongly correlated with Diptera biomass (R2 = 0.55; Table 9). Diptera biomass declined with increases in I. punctatus CPUE (Fig. 5). Vegetation Macroinvertebrate total density, total biomass, and overall mean individual mass were not related to macrophyte coverage in the impoundments (all p > 0.19). There were 9 impoundments with no vegetation, 10 impoundments with moderate vegetation, and 11 impoundments with abundant vegetation. Neither were densities, biomass, and mean individual mass of Diptera, Ephemeroptera, Mollusca, Odonata, nor Megaloptera related to macrophyte cover (all p > 0.07), except that mean individual mass of Odonata differed with macophyte cover (F = 3.52; df = 2, 22; p = 0.05). Post-hoc testing revealed that individual mass of Odonata was significantly smaller for the moder-

Discussion Macroinvertebrate abundance was related to impoundment productivity, but relationships varied with taxa. Total macroinvertebrate biomass was not strongly related to productivity, similar to findings by Johnson & Weiderholm (1989) and Dinsmore et al. (1999). However, macroinvertebrate density was related to productivity. Studies reporting strong positive relations between total macroinvertebrate biomass and lake productivity used macroinvertebrate biomass estimates from the profundal zone of natural lakes (Hanson & Peters, 1984; Rasmussen & Kalff, 1987; but see Dinsmore et al., 1999). Biomass estimates of macroinvertebrates derived from the littoral zone (such as ours) were not consistently related to lake productivity (Rasmussen & Kalff, 1987; Rasmussen, 1988; Paukert & Willis, 2003). Paukert & Willis (2003) reported that macroinvertebrate density in shallow prairie lakes declined with increasing lake productivity. Some of the discrepancies among study results probably relate to differences in taxonomic

155 Table 9. Percentage of standardized variance of the variables of macroinvertebrate biomass and fish explained by their own and opposite canonical variates (CVAR) in the canonical redundancy analysis Variable

Macroinvertebrate

Fish

CVAR

CVAR

Macroinvertebrate

20.2

14.2

Fish

25.0

35.6

Diptera Ephemeroptera

54.9 26.1

Mollusca

0.04

Odonata

1.0

Megaloptera

0.5

Others

2.7

Lepomis macrochirus CPUE

16.0

Lepomis macrochirus BPUE Ictalurus punctatus CPUE

15.1 44.2


24.5


Figure 5. Scatter plot showing the relationship between Diptera biomass (g/m)2) and channel catfish Ictalurus punctatus catch-per-unit-effort (CPUE, fish/set)1).

composition of the macroinvertebrate community. Diptera became more abundant with increasing impoundment productivity while Ephemeroptera and Odonata became less abundant; consistent with changes in the macroinvertebrate community in Lake Erie in response to eutrophication (Hayward & Margraf, 1987). In our study impoundments, Diptera (79% Chironomidae by biomass) dominated the macroinvertebrate communities in hypereutrophic impoundments,

Figure 6. Mean biomass (g/m)2) of macroinvertebrate taxa in oligo-mesotrophic (MES, N = 6; chlorophyll concentrations [CHLA] £7 mg/m)3), eutrophic (EUT, N = 17; CHLA >7 and £40 mg/m)3), and hypereutrophic (HYP, N = 7; CHLA >40 mg/m)3) impoundments. Trophic status was classified using criteria described by Jones & Knowlton (1993).

whereas Ephemeroptera and Mollusca dominated communities in oligo-mesotrophic impoundments (Fig. 6). Similarly, Pieczyn´ska et al. (1999) found that Chironomidae abundance increased with increases in lake productivity. They also found that Gastropoda abundance declined with increases in productivity. The macroinvertebrate communities studied by Paukert & Willis (2003) were dominated by Gastropoda and this may explain the negative relationship between macroinvertebrate abundance and lake productivity. There were no significant relations between mean individual size of macroinvertebrates and impoundment productivity. Rasmussen (1993) observed increases in the biomass of small invertebrates with increasing lake productivity. Hayward & Margraf (1987) reported decreases in average size of invertebrates with increasing eutrophication of Lake Erie, due to a shift in species composition from Ephemeroptera and Amphipoda to Chironomidae and Oligochaeta. While there also was a shift from Ephemeroptera to Chironomidae with increasing productivity in this study, there was not a significant decline in average size of individuals with increases in productivity. However, the highest mean individual masses were found in impoundments with chlorophyll concentrations less than 25 mg/m)3 (Fig. 1). Macroinvertebrate abundance, but not mean individual size, was related to the relative abundances of benthivorous fish. In general,

156 macroinvertebrate abundance, especially Diptera abundance, increased with L. macrochirus abundance but decreased with I. punctatus abundance. Most previous studies have documented a negative relation between benthivorous fish and macroinvertebrate abundance and size (Crowder & Cooper, 1982; Post & Cucin, 1984; Hayes et al., 1992; Diehl, 1993, 1995; Svennsson et al., 1999; Kangur et al., 2003). Zimmer et al. (2001) found that fathead minnows Pimephales promelas Rafinesque reduced invertebrate biomass but did not alter their size structure. Other researchers reported no relationship between fish and macroinvertebrate abundance (Thorp & Bergey, 1981; Paukert & Willis, 2003). However, Hanson & Legget (1982) found a strong positive relationship between fish and macroinvertebrate abundance as observed for L. macrochirus in this study. Perhaps this positive relationship reflects ‘‘bottom-up’’ control of L. macrochirus abundance among these impoundments. L. macrochirus feed almost exclusively on macroinvertebrates in these impoundments (P. Michaletz, MDC, unpublished data), and their abundance probably depends on the magnitude of macroinvertebrate production. In contrast, I. punctatus, which are stocked annually, exhibited a negative relationship with Diptera biomass. Because these fish are stocked, their biomass can reach artificially high levels and exceed the carrying capacity of these waters. At high abundances, I. punctatus may depress Diptera in these impoundments. Neither macroinvertebrate abundance nor size was related to macrophyte coverage except for Odonata size. Many studies have shown a positive relationship between macrophyte cover and macroinvertebrate abundance (Gerking, 1957; Gerrish & Bristow, 1979; Wiley et al., 1984; Rasmussen, 1988; Paukert & Willis, 2003). However, these relationships may vary depending on the macroinvertebrate taxa. For example, Chironomidae abundance may be negatively related to submergent macrophyte cover (de Szalay & Resh, 2000; Paukert & Willis, 2003), whereas Gastropoda are positively related (Paukert & Willis, 2003). The lack of relationships between macrophyte cover and macroinvertebrates in this study probably is in part due to the methodology. Macrophyte cover was not precisely quantified but rather broad

vegetation categories were used. This probably hindered the ability to detect relationships between plants and macroinvertebrates. More importantly, invertebrates within macrophyte beds were not sampled. Macroinvertebrate communities may considerably differ between vegetation and open sediments (Mittelbach, 1981; Rasmussen, 1988, 1993), so macroinvertebrate communities in vegetated impoundments may not have been adequately characterized. However, the macroinvertebrate community found in the open sediments can be influenced by macrophyte cover. Paukert & Willis (2003), using similar macroinvertebrate sampling methodology to this study, found that macrophyte coverage did influence the macroinvertebrate community found in open sediments. Rasmussen (1988, 1993) determined that as submergent vegetation increases, the proportion of macroinvertebrates in the sediments decreases, and the proportion of smaller-sized organisms increases.

Acknowledgements We thank D. Obrecht and J. Jones for providing water quality data. M. Palmer, G. Pitchford, P. Pitts, R. Meade, S. Banks, R. Dames, L. Martien, T. Priesendorf, M. Boyer, M. Anderson, D. Brown, S. Ryan, C. Gemming, T. Yasger, M. Bayless, and D. Thornhill for providing fish survey data. T. Thorp and A. Rettig assisted with macroinvertebrate sampling. M. Wallendorf provided statistical advice. This study was partially funded through Federal Aid in Sport Fish Restoration, project F-1-R-50, study I-36 provided to the Missouri Department of Conservation.

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