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2006 SOUTHEASTERN NATURALIST 5(1):165–174
Chironomid Emergence and Relative Emergent Biomass
from Two Alabama Streams
STEVEN K. REYNOLDS, JR.1,2,* AND ARTHUR C. BENKE1
Abstract - Chironomid pupal exuviae were sampled monthly using drift nets and
hand sieves over an annual cycle from Hendrick Mill Branch (HMB; Blount County,
AL) and Payne Creek (PC; Hale County, AL). Taxon richness, community composition,
and emergence phenologies were similar despite marked differences in
physical/chemical characteristics of the study streams. The highest emergence rates
were observed in spring (PC) or both spring and fall (HMB). However, there was no
significant relationship between emergence/emergent biomass and date. Estimates of
daily emergence and emergent biomass were much higher in HMB than in PC. These
patterns may have resulted from a more consistent flow regime, higher substrate
stability, lower variation in temperature/chemical characteristics, greater channel
surface area, and a more significant hyporheic zone in HMB than in PC.
The emergence of adult chironomids from aquatic habitats represents
a potential significant vector of the transport of energy (in the form of
adult biomass) within and between aquatic habitats and to surrounding
terrestrial areas (Jackson and Fisher 1986, Stagliano et al. 1998). For
accurate estimations of energy flow (secondary production) into and out
of aquatic habitats, it is necessary to quantify emergence (Benke et al.
1999, Jackson and Fisher 1986, Stagliano et al. 1998). Many studies have
documented that larvae of the family Chironomidae are ubiquitous and
abundant in streams, often contributing substantially to the energy budgets
of various habitats (Benke 1998, Coffman and Ferrington 1996).
However, few lotic studies have quantified the emergence of this family
at taxonomic levels below family (i.e., Coffman 1973, Ferrington et al.
1995, Wartinbee 1979). Furthermore, comparatively few studies have
quantified chironomid emergence within the context of overall energy
flow simultaneously from different types of streams.
In our study, pupal exuviae, the shed cuticles of the pupal stage remaining
in the water after adult eclosion, were collected from two small perennial
streams differing substantially in parent geology within two physiographic
provinces of Alabama: the Valley and Ridge and the Coastal Plain. Pupal
exuviae samples are representative of adult emergence from all microhabitats
within a given stream segment (e.g., benthic, hyporheic, hygropetric,
1Department of Biological Sciences, Aquatic Biology Program, A-122 Bevill, Box
870206, University of Alabama, Tuscaloosa, AL 35487-0206. 2Current address - US
EPA, National Risk Management Research Laboratory, Robert S. Kerr Environmental
Research Center, PO Box 1198, Ada, OK 74821-1198. *Corresponding author -
166 Southeastern Naturalist Vol. 5, No. 1
etc.) because all adult midges emerging at the water surface can be directly
sampled from this area (Ferrington et al. 1991, 1995). We compared genuslevel
emergence phenologies and magnitudes of the potential export of adult
biomass from pupal exuviae sampled from these two streams.
Hendrick Mill Branch (HMB), in the Valley and Ridge physiographic
province (Blount County, AL) is a small perennial stream within the Black
Warrior River drainage, with a stable dolomite cobble/boulder/bedrock substrate
and relatively deep hyporheic zone (≈ 40–50 cm, Reynolds 2002).
HMB has a high alkalinity (> 100 mg CaCO3/L) and specific conductance
(≈ 200 mS/cm) and a slightly basic pH (≈ 8). Water temperature variation is
relatively low, ranging from 10 to 17 °C (mean = 15.5 °C) throughout the
year (Huryn et al. 1995). Payne Creek (PC), in the Coastal Plain physiographic
province (Hale County, AL) is also a small perennial stream within
the Black Warrior River drainage; however it has a fine- to medium-grained
sand substrate and limited hyporheic zone (≈ 5–20 cm, Reynolds 2002). PC
has a low alkalinity (< 10 mg CaCO3/L) and slightly acidic pH (≈ 5–6).
Water temperature variation in PC shows a much greater annual range
(6–24 °C, mean = 18.5 °C) than HMB (G.M. Ward, University of Alabama,
Tuscaloosa, AL, unpubl. data). Mean annual discharge and maximum current
velocity are higher in HMB (0.065 m3/s and 20.9 cm/s, respectively)
than in PC (0.015 m3/s and 9.9 cm/s, respectively). Mean annual current
velocities across the active channel are similar in PC and HMB (6.4 and 5.2
cm/s, respectively—vector transect and water depth method using a Marsh-
McBirney current meter; Reynolds 2002).
Daily emergence of chironomid taxa was determined by collecting pupal
exuviae monthly (on consecutive dates every 28 to 32 d) from 5 sites in
HMB and 4 sites in PC from March 1999 to February 2000. Exuviae were
taken directly from the water surface using a 45-mm hand sieve, under
littoral vegetation and around emergent macrophytes/large woody debris.
Sampling effort was standardized between sites and dates by limiting the
sample time to 10 min per site. Exuviae were washed from the sieve and
preserved in the field with 80% ethanol. In the laboratory, exuviae were
sorted, identified to genus using keys in Coffman and Ferrington (1996) and
Wiederholm (1986), and counted.
Emergence and emergent biomass
Two drift nets (100-mm mesh, 0.097-m2 aperture) were used monthly in
HMB and PC to quantify emergence phenologies and calculate emergent
biomass. Sample dates were the same as those used for hand-sieve sampling.
2006 S.K. Reynolds, Jr. and A.C. Benke 167
Specific site selection was random among sample sites used and drift nets
were placed upstream from the area sampled by hand sieve. Sampled material
was collected over a 1-h period at dusk and preserved in 80% ethanol
with Phloxine-B stain. Exuviae were sorted from the gross sample and
identified to genus and counted in the laboratory, as above.
Chironomid exuviae in each drift net were counted and converted to an
estimate of hourly adult emergence per m2 of water surface (adults m-2 h-1) by
dividing the number of exuviae in the sample by the aperture width of the
drift net opening (0.312 m) and the current velocity (m/h). By extrapolation,
an estimate of total daily emergence was calculated for each stream (mean
hourly estimate [n = 12] x 24 h/d). Total emergent biomass was estimated in
a similar fashion after substitution of the hourly emergence data used above
with previously published estimates of adult biomass (from Stagliano et al.
1998). All biomass units were expressed as dry mass.
Daily emergence data were considered estimates because the period of
time and distance over which exuviae accumulated was unknown, and it is
assumed that our measurement of hourly emergence was representative of
emergence over a 24-h period.
Emergence and emergent biomass data from replicate drift nets (n = 2) in
each stream were analyzed by one-way ANOVA by sample date, alpha-level
= 0.05. Emergence phenology data from hand-sieve collections were not
compared statistically because they were only semi-quantitative. However,
samples were standardized by sampling effort, so relative abundances of
chironomid taxa through time were comparable between the two streams.
There was nearly continuous emergence throughout the year in both
streams, with maximum emergence in spring and late fall for HMB and from
February to June in PC (Fig. 1). A total of 32 and 30 genera were collected in
monthly grab samples from HMB and PC, respectively (Tables 1 and 2).
Corynoneura and Stempellinella were the most common genera, numerically
dominating exuviae samples from both streams. Additionally,
Rheosmittia, Polypedilum, and Tanytarsus were common in PC, whereas
Parametriocnemus and Rheotanytarsus were common in HMB. Approximately
20% of the chironomid genera from each stream were present in all
or nearly all the qualitative hand-sieve samples throughout the year (25 and
17% for HMB and PC, respectively). Although samples obtained by hand
sieve were not strictly quantitative, the standardized sampling period at all
sites provided an estimate of relative abundance across sample dates and
between streams. Mean daily emergence from HMB (74 exuviae/date) was
≈ 2.5 times higher than from PC (29 exuviae/date).
168 Southeastern Naturalist Vol. 5, No. 1
Emergence and emergent biomass
Emergence in HMB was highest in the spring and lowest in summer/fall
(Fig. 2). However, because of high within-date variation, one-way ANOVA
indicated no significant differences among dates (p > 0.05). Total daily
emergence and biomass in HMB based on extrapolation of the hourly drift
samples was 35.31 adults m-2 d-1 and 3.96 mg m-2 d-1, respectively (Table 3),
with highest values in spring and lowest values in summer/fall (Fig. 2).
Microtendipes, Polypedilum, Stempellinella, and Corynoneura were the numerically
dominant midges in HMB (all with > 3 adults m-2 d-1 and > 0.37 mg
m-2 d-1 emergent biomass; Table 3).
Total daily chironomid emergence estimated from hourly drift samples
from PC was 2.61 adults m-2 d-1. Total daily emergent biomass in PC was
0.22 mg m-2 d-1 (Table 3). However, on all but 3 sample dates (March, May,
and June), no pupal exuviae were collected by drift despite presence of
Figure 1. Mean total pupae abundance (no. exuviae/date) from Hendrick Mill Branch
(A) and Payne Creek (B) based on 10-min hand-sieve samples. Error bars = ± 1SE.
N = 5 for HMB, and n = 4 for PC.
2006 S.K. Reynolds, Jr. and A.C. Benke 169
exuviae in PC throughout the year. Based on these limited samples, 4 genera
(Stempellinella, Tanytarsus, Corynoneura, and Parametriocnemus) were the
numerically dominant midges emerging from PC (≥ 0.3 adults m-2 d-1 and
> 0.02 mg m-2 d-1 emergent biomass; Table 3). No statistical analysis on daily
emergence was performed because of the limited number of sample dates
with pupal exuviae collections.
In HMB and PC, monthly hand-sieve samples of chironomid exuviae
indicated that adult emergence occurred continuously throughout the year,
with emergence peaks in either spring and fall (HMB) or only spring (PC)
Table 1. Emergence phenologies for Chironomidae and mean monthly relative abundances (%)
of dominant (> 5% of mean relative abundance) taxa in Hendrick Mill Branch based on monthly
10-min hand-sieve samples. x = pupal exuviae sampled, but represent < 5% of mean relative
abundance; - = was probable given presence of exuviae on other dates, however they were not
sampled. Empty cells indicate that no exuviae were sampled nor would any be expected based
on other sample dates.
Genus M A M J J A S O N D J F Mean
Brillia x x x x - -
Corynoneura 42 29 44 31 14 57 53 87 62 61 28 42 46
Dicrotendipes x x
Eukiefferiella x x x x - - x x x x x x
Labrundinia x x - - x
Larsia - x x x
Micropsectra - x x x - x
Microtendipes x x
Nanocladius x x
Orthocladius x x x x x x x - x
Parakiefferiella x x x - x x x - x
Paramerina x x - - x
Parametriocnemus 4 3 12 17 32 14 18 4 11 12 4 3 11
Paratanytarsus x x x x x - x x x x x x
Paratendipes x x
Polypedilum x x x x x - x - x x
Psectrocladius x x x
Rheocricotopus x x x x - x
Rheotanytarsus 5 11 3 2 13 - 2 1 4 3 16 3 5
Stempellinella 9 16 4 37 10 4 9 1 1 5 24 17 11
Synorthocladius x x- x
Tanytarsus x x x x x - x - x x x x
Tvetenia x x x x x - -
170 Southeastern Naturalist Vol. 5, No. 1
(Fig. 1). The lack of temporal emergence synchrony, recognized in this
study as the continuous emergence by many taxa (Tables 1 and 2), is
common in southern temperate climates where favorable thermal conditions
allow for emergence throughout the year (Armitage 1995, Benke 1998,
Corbet 1964). Comparable emergence patterns to those seen in our study for
PC were documented in a wetland system < 1 km downstream of the current
PC study sites (Stagliano et al. 1998).
Daily emergent chironomid biomass from HMB was 3.96 mg m-2 d-1
based on drift net samples taken on single dates at monthly intervals. This
value is only approximate because of assumptions made regarding discontinuous
temporal sampling and the relationship between exuviae on a unit
area of water versus a unit area of stream bottom. Nonetheless, emergence
values for HMB were comparable to those from previously described temperate
lotic systems, assuming that chironomids constitute a conservative
Table 2. Emergence phenologies for Chironomidae and mean relative abundances (%) of
dominant (> 5% of mean relative abundance) taxa in Payne Creek based on monthly 10-min
hand sieve samples. x = pupal exuviae sampled, but represent < 5% of mean relative abundance;
- = emergence was probable given presence of exuviae on other dates, however they were not
sampled. Empty cells indicate that no exuviae were sampled nor would any be expected based
on other sample dates.
Genus M A M J J A S O N D J F Mean
Brillia x x x x
Cladotanytarsus x x - x x
Corynoneura 25 22 12 4 8 - 22 31 65 58 - 13 22
Cryptochironomus x - x
Cryptotendipes x x x x
Dicrotendipes x x x x x x
Eukiefferiella x - - - x
Krenosmittia - x x - -
Larsia x x x
Orthocladius x - x x x
Parakiefferiella x x - - x
Paralauterborniella x x - x
Paramerina x x x
Parametriocnemus x x x x x - - x - x - x
Phaenopsectra x - x
Polypedilum 2 2 12 8 8 - 19 - 6 - - 21 6
Psectrocladius x - - x x
Rheocricotopus x - - x x x
Rheosmittia - 38 - 1 86 - 10
Saetheria x - x
Stempellinella 33 19 39 24 40 - 16 23 12 8 5 8 19
Tanytarsus 7 4 15 46 8 - 5 - 6 - 2 31 10
Xylotopus x x
2006 S.K. Reynolds, Jr. and A.C. Benke 171
(35%; Coffman 1995) amount of total macroinvertebrate emergent biomass
(mean = 3.80 mg m-2 d-1, range = 1.96 to 6.79 mg m-2 d-1; data converted from
annual values from Jackson and Fisher 1986).
In contrast, daily emergent chironomid biomass in PC was only 0.22 mg
m2 y-1. This value was extremely low compared to the lotic systems discussed
above, and also much lower than previous estimates of emergent
biomass (1.59 mg m-2 d-1) from a wetland in the same watershed (Stagliano et
al. 1998). In our study, drift nets were placed in locations known a priori to
have continuous annual flow. However, discharge of PC declined considerably
during summer and fall, resulting in an increase in the number of
isolated pools and backwaters (S. Reynolds, pers. observ.). Drift nets placed
in areas of maximum current velocity would have undersampled exuviae
present in pools and backwaters because exuviae from the latter would likely
not have been captured by samplers in flowing water. Furthermore, peak
emergence times may have been missed by the sampling protocol in PC.
Drift was sampled in the early evening during the typically period of peak
emergence (Coffman 1973, Vilchez-Quero and Lavandier 1986), although
Figure 2. Mean hourly emergence and emergent biomass for Chironomidae from
drift samples collected monthly from Hendrick Mill Branch (A) and Payne Creek
(B). Error bars = ± 1SE. • = Density, o = Biomass.
172 Southeastern Naturalist Vol. 5, No. 1
other peak emergence times have been documented (i.e., early morning,
throughout the night and/or day; Danks and Oliver 1972, Franquet and Pont
1996, Mundie 1971, Wartinbee 1979). Consequently, whereas hand-sieve
samples would have captured exuviae in backwaters and pools during these
periods of low flow (Tables 2 and 3), daily emergent chironomid biomass
and emergence estimates for PC based on drift samples from the main
channel likely are underestimated.
Despite great differences in emergence numbers and biomass between
HMB and PC, chironomid assemblages in HMB and PC were quite similar
taxonomically. Thirty-two genera were found in HMB, 30 in PC, with 20
genera common to both streams. These patterns are comparable to previous
studies in similar habitats. Stagliano et al. (1998) identified 31 genera in a
wetland < 1 km downstream from our PC sites, and Coffman (1973) and
Frommer and Sublette (1971) identified 53 and 46 genera, respectively,
from streams similar in size, substrate and chemical characteristics to
HMB. In both Coffman (1973) and Frommer and Sublette (1971), both
larger substrate and longer stream reaches were studied, including more
types of habitat, which may explain the higher taxon richness values relative
Table 3. Total daily abundance (adults m-2 d-1) and biomass (mg m-2 d-1) of chironomid
emergence from Hendrick Mill Branch (HMB) and Payne Creek (PC) by monthly drift net
samples. - = taxon not sampled.
Taxon Abundance Biomass Abundance Biomass
Cryptotendipes - - 0.07 0.01
Dicrotendipes - - 0.16 0.03
Microtendipes 3.09 1.17 - -
Paratendipes 1.37 0.24 - -
Polypedilum 4.26 0.44 0.16 0.02
Micropsectra 1.20 0.15 - -
Paratanytarsus 2.44 0.28 - -
Rheotanytarsus 1.77 0.21 - -
Stempellinella 3.12 0.37 0.42 0.05
Tanytarsus 0.17 0.02 0.28 0.03
Corynoneura 7.80 0.46 0.98 0.06
Eukiefferiella 2.06 0.12 - -
Orthocladius 1.88 0.11 - -
Parakiefferiella 0.91 0.05 - -
Parametriocnemus 3.69 0.22 0.38 0.02
Rheosmittia - - 0.10 0.01
Tvetenia 0.39 0.02 - -
Labrundinia 0.40 0.06 - -
Larsia 0.76 0.03 0.07 < 0.01
Total Chironomidae 35.31 3.96 2.61 0.22
2006 S.K. Reynolds, Jr. and A.C. Benke 173
Taxonomic and temporal similarity of emergence phenologies acquired
by hand-sieve samples suggests that HMB and PC have similar chironomid
assemblages despite their physical differences (Tables 1 and 2). Approximately
60% of genera were common to both streams and the genera
Corynoneura and Stempellinella showed similar numerical dominance in
both streams (Tables 1 and 2). However, mean emergence (no. exuviae/
date) based on hand-sieve samples, as well as, total emergence (no. m-2 d-1)
and total emergent biomass (mg m-2 d-1) based on drift-net samples, were all
higher (2.5–17.5 times) in HMB than in PC The true measure of the difference
in emergence and emergent biomass between HMB and PC probably
falls between the 13-fold (for abundance) and 18-fold (for biomass) differences
suggested by the drift nets samples and the 2.5 to 3.5-fold differences
measured previously by either alternative pupal exuviae techniques or in
larval biomass (Reynolds 2002). Differences seen in both emergence and
emergent biomass between HMB and PC possibly resulted from different
habitat and physicochemical characteristics (pH, specific conductance, flow
and temperature variation, substrate stability, extent of the hyporheic zone,
etc.). However, greater replication of streams in each area, as well as more
rigorous quantification of the physicochemical environment and spatial
variation in emergence and drift, would be necessary to identify likely causal
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