FreshwalerBiology (\9M)U,3\l-3l6

The macroinvertebrates and fish of a Colorado streamduring a period of fiuctuating discharge

STEVEN P. CANTON. LEO D. CLINE, ROBERT A. SHORT* and JAMES V. WARDDepartment of Zoology and Entomology, Colorado State University, Eort Collins.Colorado, U.S.A.

SUMMARY. 1. During a 2-year study of the fish and macroinvertebratesof a third-order montane stream, a severe drought in thefirst year resultedin a temporary cessation of surface flow. Flow was continuous during thesecond year.

2. Some taxa (e.g. Ophiogomphus severus) exhibited higher densityduring the drought year, others declined in abundance during low flow(e.g. Baelis spp.), whereas a few (e.g. Tricorythodes minuius) appearedunaffected. Total macroinvertebrate density decreased by 5{)% during thelow flow year compared to the normal flow year. Mayflies were mostseverely affected, but also exhibited the most dramatic recovery.

3. The collector-gatherer functional feeding group was abundant onlyduring the normal flow year, whereas shredders and predators exhibitedincreased relative abundance during low flow.

4. Fish populations were severely reduced in the low flow year. However,fishes rapidly invaded the area following resumption of normal flow.

Introduction

Severe fluctuations in flow can have adverseeffects on the biota of normally permanentlyflowing streams. Reduced discharge has beenshown to affect macroinvertebrates through lossof riffle habitat, reduced periphytic food anddesiccation (Hynes, 1958; Larimore, Childers&Heckrottlc. 1959; Kamler & Reidel. 1960;Iversen et ai, 1978; Ladle & Bass, 1981).Reduced flow usually occurs during late summerand early autumn, a period of rapid growth formany of the organisms inhabiting permanentstreams, such as mayflies, stoneflies and caddis-flies (Hynes, 1970). In general, invertebrates arebetter able to withstand the effects of drought

"Present address: Aquatic Station. Southwest TexasState University. San Marcos. TX78666. U.S.A.

Correspondence; Mr Steven P. Canton. Chadwickand Associates. 5767 S. Rapp Street. Littleton. CO80120, U.S.A.

than fish because of egg, nymphal or pupaldiapause; emergence as aerial adults; or byburrowing into the stream bed. Recolonizationis rapid following resumption of flow (Hynes,1975; Larimore et ai, 1959; Townsend &Hildrew, 1976; Williams & Hynes. 1976a, b,1977).

Reduced stream flow adversely affects fishpopulations by restricting them to shallow pools.which often become too warm, stagnant orcrowded to sustain normal populations andgrowth rates (Hynes, 1958; Larimore et ai,1959). but after flow resumes, fish return toaffected reaches quickly, primarily due to themovements of young fish (Larimore elai, 1959;Williams & Coad. 1979).

This paper summarizes research on theinvertebrate and fish populations of TroutCreek, a small stream in central Colorado.during a 2-year period with marked differencesin stream discharge.

311

This file was created by scanning the printed publication.Errors identified by the software have been corrected;

however, some errors may remain.

312 Steven P. Canton et ai

Site description

Trout Creek is a small third-order stream in theupper South Platte River basin of eentralColorado, U.S.A.. on the east slope of theRocky Mountains. It flows roughly south tonorth through the Manitou Experimental Forestof the U.S. Forest Service. The 1.4 km studyarea is a low gradient segment at 2235 melevation lined with willows {Salix spp.). Thesubstrate is primarily gravel and coarse sand inthe riffles. The green alga Cladophora glomerata(L.) Kuetzing was abundant throughout thestudy area during summer. Smalt beds of theaquatic macrophyte Veronica sp. were sporadi-cally abundant by late summer. Three sections(upper, middle and lower) were sampled in thestudy area and were 650, 390 and 400 m long,respectively.

Methods

Mean daily discharge was determined at theupper end of the study area using a Parshallflume. Water temperature was also continuouslymonitored at this site.

Macroinvertebrates were collected monthlyfrom June to October, 1978 and 1979, using acore sampler whieh enclosed 477 cm'. Organ-isms were removed by stirring the substrate andstraining the water with a hand net (mesh size250 ij.vn). Substrate was then placed in a bucketand the remaining organisms were thoroughlyelutriated into the net. Four sample units weretaken from each of the upper, middle and lowersections of the study area on each occasion. Inaddition, drift samples were taken at the middleand lower sections. Drift nets with 250 /xm meshwere placed in the stream overnight once eachmonth. Water depth and current speed at the netmouth were measured when the nets were setand prior to removal. The initial and finaldischarge values were averaged to determine thevolume of water sampled assuming a lineardecrease over time (Hemsworth & Brooker.1979). Organisms were preserved in the fieldwith 807r ethanol and returned to the laboratorywhere they were sorted from the debris,identified and counted. Identifications weremade to the lowest practical taxonomic levelusing available keys. Statistical analysis of theinvertebrate data was run on log jn transformed

data to 'normalize' the data allowing the use ofparametric tests (Elliott, 1977). Functionalanalysis was conducted by assigning taxa to oneof five functional feeding groups (collector-gatherer, collector-filterer, scraper, shredder,and predator) using the designations in Merritt& Cummins (1978).

Fish were sampled on 12 September 1978 and1979 by making one pass through the threesections of the study area with backpackelectrofishing gear. All fish captured wereidentified, counted, weighed and the lengthmeasured. Narrow stream width, shallow waterdepth, good water clarity, and the relativepaucity of overhanging riparian vegetationpermitted reliable counts of those small fishwhich were not captured. These data wereadded to the number of captured fish for anestimate of number of fish 100 m' ' . Scales weretaken from selected fish for age and growthanalyses. In the laboratory, scales were dried,soaked in UWc NaOH and rinsed in distilledwater prior to mounting on glass slides. Scaleswere magnified at 80x and measured accordingto the procedures of Bagenal & Tesch (1978).The condition factor, K, was calculated from theformula: /i'-WlO^ L^^, where W=weight ingrams and L=length in millimetres.

Results

Discharge

Discharge measurements depict an overallpattern of low and high stream flow years (Fig.1). Mean daily discharge values averaged 0.78m"' min"' in 1978 the low flow year, in contrastwith a more normal stream flow of 3.98 m' min"'in 1979 the normal flow year.

During early summer (June and July), dailystream discharge values were much lower in1978 (Fig. 1). During August and September,drought conditions reduced stream discharge tonegligible levels in the upper and middle studysection in 1978, and the streambed was drythroughout the lower section. Flow never ceasedduring the normal flow year. Despite thesedifferences in discharge, the temperature did notdiffer between the 2 years of study, indicatingthe major influence of groundwater on thisalluvial stream segment.

Drought effects on invertebrates and fish 313

10 20 30 10 20 30 10 20 30 10 20 30June July August September

FIG. 1. Stream discharge for 5 day intervals based onaverage daily discharge values obtained at the upperend of the study area on Trout Creek. Colorado, 1978and 1979.

Macro in vertebrates

During the 2 years of study, seventy-twoinvertebrate taxa were collected from TroutCreek in the study area although only twentywere common (Table 1). Many taxa exhibitedhigher densities during the low flow year of 1978followed by reduced numbers after resumptionof more normal flow in 1979 (e.g. Hydroptilasp., Ophiogomphus severus Hagen. Cricotopussp., Eukiefferiella sp., Palpomyia sp. and Tipulasp.). Two species, Cricotopus sp. and Palpomy-ia sp.. had statistically significant lower popula-tions in the normal flow year, 1979 (ANOVA./'=0.0U8). Other taxa (e.g. Baetis spp. andGlossosoma sp.) exhibited the opposite patternwith significantly higher densities during the1979 normal flow year (ANOVA. ^-0.006). Afew taxa (e.g. Tricorythodes minutus Traver andchloroperlid stoneflies) exhibited no significantchange in density during the 2 years of study(ANOVA, P=[).\l).

Notably, one species, Rhithrogena hageniEaton, was extremely rare in 1978, the droughtyear, and was not collected in 1979; although itwas abundant in previous studies on TroutCreek (Short el ai. 1978). Other taxa (e.g.Capnia sp., Ablabesymia sp.. Hydracarina andOligochaeta), which were not abundant pre-viously (Short et ai. 1978). appeared to haveestablished populations in Trout Creek duringthe drought.

Nonetheless, for most taxa, density was muchgreater in 1979 than in 1978. Total densityexhibited a significant increase (ANOVA.F-0.03) from 1978 to 1979 with mayfliesexhibiting a highly significant increase (ANO-VA. P-0.001) (Table 1). Among the majorgroups, only Odonata exhibited decreaseddensity in 1979.

In addition to the structure of the benthiccommunity, the functional aspects of the benth-os were also examined. Collector-gathererswere most important in 1979 normal flow year(Table 2). primarily reflecting the increasedabundance of mayflies during this year. Shred-ders and predators exhibited higher relativeimportance during the 1978 low flow year.Collector-filterers had greater abundance in thenormal flowyear (1979) as a result of significant-ly (ANOVA, P=0.02) higher number of Hyd-ropsyche sp. and Sinndium arcticum Malloch.Scrapers were never abundant.

During both years, drift density increased asdischarge declined throughout the summer(Table 3). Mayflies and dipterans dominatedthe drift with other groups only occasionallyabundant. Terrestrial organisms were neverabundant in the drift. The peak in drift densityoccurred in August during both years although itwas greater in 1979. The large number ofexuviae in August suggests that the mayflieswere beginning to emerge.

Fish

Three fish species were collected during thestudy: Salvelinus fontinalis (Mitchill) (brooktrout), Catostomus catostomus (Foster) (long-nose sucker) and C. commersoni (Lacepede)(white sucker). Notable differences were de-tected between the three stream sections sam-ples (Table 4). In 1978,fish were virtually absentin the lower two sections of the study area.During this year, the lower 400 m section

314 Steven P. Canton et ai

TABLE 1. Mean numbers of organisms m"^ of selected invertebrate taxa, Trout Creek,Colorado, 1978-79 (standard error in parentheses)

Taxa

INSECTAEphemeroptera

Baetis spp.Ephcrmerella ineimis EatonParaleptophlebia licteronea (McDunnough)Tricorythodes minutus Tra\'er

PlecopteraCapnia sp.Chloroperlidae

TrichopteraGlosso.soma sp.Hydropsyche sp.Hydroptila sp.

DipteraAblabesmyia sp.Cricotopus sp.Eukiefferiella sp.Palpomyia sp.Rheotanytarsus sp.Simidium arcticum MallochTipula sp.

ColcopteraOptioservus castanipeniiis (Fall)

OdonataOphigogomphus severus Hagen

HYDRACARINA

OLIGOCMAETA

TotalNo. of taxa

197S

22191096

—129854

1232.190820553

12146316

55425278092453396818538288873

271

100

105

1082458

(587)(424)

(51)(228)(447)(313)(240)(300)(11)

(122)(141)

(1031)(104)(244)(54)(50)

(160)(767)(350)

(52)(31)

(75)

(54)

(54)

(1604)

1979

89066653

341282875

19941098778920196487

9795421241

87

68814

338311

29729!

82

338

223

2287653

(1995)(1880)

(18)(424)(226)(760)(709)(127)(254)(105)(174)(16)

(2546)(183)(39)

(13)(320)

(1835)(6)

(84)(84)

(18)

(72)

(56)

(3577)

TABLE 2. Relative abundance (",; of totaldensity) of invertebrate functionai feedinggroups from Trout Creek, Colorado, 1978and 1979

Functional group 1978 1979

Collector-gathererCollector-fiitererScraperShredderPredator

27167

2228

542246

14

contained only eleven small exposed pools,which did not contain fish. The middle 390 m didhave running water, but it was restricted to thecentre of the channel with few pools. Themajority offish collected in 1978 were found inthe upper 650 m reach where flowing water andpools were more prevalent. Densities of fish in1979 were sharply higher than those in 1978(Table 4), indicating rapid recovery from thedrought. Suckers were well distributed through-out the study area in 1979. but the brook trout

densities were still highest in the upstreamportion.

Brook trout collected in 1978 were thin andmoribund when handled. Average weight valuesfor each age class were lower than expected onthe basis of other North American studies(Carlander, 1969) and, as a result, the meancondition factor {K) value was lower in 1978(1.10) than in 1979 (1.16), although these valueswere not statistically different (Mest, / '>0.05).Fish collected in 1979 appeared normal.

Longnose suckers also displayed lower Kvalues in 1978 (0.94) than in 1979 (1.03),although again this difference was not significant(Mest. /'>0.G5). Apart from having loweraverage length values than found iti other NorthAmerican studies (Carlander, 1969). fishappeared normal when handled.

Regenerated scales, which often indicateenvironmental stress, were found on many fishIn 1979, after the drought year of 1978. In a fewcases, especially on white suckers and brook

TABLE 3. Density (iiumLiers IOO1978 and 1979

Drought effects on invertebrates and fish 315

of drifting invertebrates in Trout Creek. Colorado, June-October

Taxa

EphemeropteraTrichopteraPlecopteraDipteraHydracarinaGastropoda

OtherExuviae (appro.x.)Terr, organismsTotalNo. of taxa*

June

1978

3

-

-

6

-

-

-

113

23

12

1979

+--2

-++2

13

1712

July

1978

28

2-

342

9

1

5481

211

17

1979

8

++68

+2

2

6

14

100

22

August

1978

26

318

118

9

5

13

40

18

250

27

1979

19781020

16826

36

19

172

82

2511

19

September

1978

N0

1o

w

1979

212

12

24-

21

4

36

5305

21

October

1978

!1

4706

118

+81

10

18

6

954

26

1979

8

+32

8—

2

1

6

9

68

19

+ =less than I 100 m"^.* Excluding exuviae and terrestrial organisms.

TABLE 4. Estimated numbers 100 m-^ of salmonid and caiostomid fishes for three seclions of TroutCreek, Colorado, September 1978 and 1979

Upper Middle Lower

Satvelinus font imil isCato.stomus catostomusCatostomus commersoniCatostomus spp.SalnLonidae and Catostomidae*Totai

1978

31

01519

1979

173

160

2460

1978

— o

oo

o

1

1979

46

140

40

64

1978

000000

1979

332

1494

116

* Fish not captured but counted.

troul, only regenerated scales were found.Regenerated scales were not observed in 1978.

Discussion

Marked year-to-year differences in the flowregime of Trout Creek had major effects oninvertebrates and fishes. The large increase intotal density in 1979 indicated a rapid recoveryof the stream invertebrate community from thedrought of the previous year. This recovery wasprobably a result of survival of eggs in moistsubstrate, subsequent oviposition by aerialadults and the drift of invertebrates fromupstream reaches when flow resumed (Fisher etal, 1982; Gray & Fisher. 1981; Williams &Hynes. 1976a. b. 1977). Mayflies appeared to bemost severely affected by reduced dischargewiiereas Diptera were slightly favoured. Lowdischarge seemed to affect the invertebrates

primarily through loss of habitat since tempera-ture was not significantly affected.

Functional feeding group analysis showed thatcollector-gathers and collector-filters were re-latively more important during the normal flowyear whereas shredders and predators hadgreater importance during the low flow year.The lesser importance of gatherers and filterersduring the drought year may be related to acombination of factors such as loss of habitat,decreased suspended matter and increasedpredation pressure. Invertebrate predators,such as the dragonfly O. severus, appeared to befavoured by the low flow, which would tend toconcentrate prey into the remaining channelwhile reducing fish predation on the nymphsthemselves.

Drift densities exhibited peak values inAugust during both years. Despite much higherbenthic density in 1979. numbers of drifting

316 Steven P. Canton et ai

organisms were greater in 1978 during three outof the five months of study and this may beattributable to the redueed flow conditions(Minshall & Winger. 1968).

Fish population densities were significantlyreduced by the drought with no fish collected inmost of the study area. After resumption ofnormal discharge, fish were abundant through-out the study area although the greater abund-ance of trout at the upper end of the study areasuggests migration of trout from Manitou Lakedownstream to the study area. This lakeprobably acted as a refuge for stream fish duringthe drought year. The rapid recovery of fishpopulations from drought has been noted inprevious studies (Larimore et ai, 1959; Starrett,1950; Stehr & Branson, 1938).

Acknowledgments

We thank Mr Howard L. Gary, Rocky Moun-tain Forest and Range Experiment Station, MrBill Knotts. Manitou Experimental Forest, MissNancy Flaming and Miss Nancy Heisler. Re-search was supported by grants awarded to J. V.Ward from the Rocky Mountain Forest andRange Experiment Station. U.S. Forest Service.

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(Manuscript accepted 10 August 1983)