Hydrobiologia DOI 10.1007/s10750-008-9577-8
PRIMARY RESEARCH PAPER
The influence of age-specific habitat selection by a stream crayfish community (Orconectes spp.) on secondary production Shannon K. Brewer Æ Robert J. DiStefano Æ Charles F. Rabeni
Received: 16 November 2007 / Revised: 20 August 2008 / Accepted: 24 August 2008 Ó Springer Science+Business Media B.V. 2008
Abstract We examined the hypothesis that secondary production of a community of stream crayfish (Orconectes spp.) depended upon the available suite of channel units (e.g., riffle, run, pool) and that agespecific use of channel units was the important underlying mechanism. Nine cohorts of each of three species over a 10-year period at two sites on the Jacks Fork River, Missouri, USA, were sampled. Cohortproduction estimates were calculated for specific channel units: riffles, runs, pools, backwaters and emergent vegetation patches. Orconectes luteus was the most productive species with similar production across channel units. Production of O. ozarkae and O. punctimanus was significantly greater in vegetation patches than other channel units. There were no species by channel unit differences in production between the
two sites. Although total site production for some species substantially changed over the 10-year period, relative production differences between habitats remained temporally stable. Differences in mean production between channel units were largely due to age-class habitat use rather than differences related to growth. Some channel units particularly susceptible to common anthropogenic activities that result in hydrograph alterations and homogenization of physical habitat, e.g., backwaters, vegetation patches, and pools, were particularly important as high production areas for two species. A variety of channel units appears necessary for maintaining the high secondary production and diversity of crayfish in this system. Keywords Crayfish Production Habitat Growth Biomass
Handling editor: D. Dudgeon S. K. Brewer (&) C. F. Rabeni Department of Fisheries and Wildlife Sciences, USGS Missouri Cooperative Fish and Wildlife Research Unit, 302 Natural Resources Building, University of Missouri, Columbia, MO 65211, USA e-mail:
[email protected] Present Address: S. K. Brewer US Fish and Wildlife Service, 4001 North Wilson Way, Stockton, CA 95205, USA R. J. DiStefano Missouri Department of Conservation, 1110 College Avenue, Columbia, MO 65201, USA
Introduction Crayfish serve important functional roles in the transfer of energy in many types of aquatic systems. They are consumed by more than 200 animal species (DiStefano, 2005), and in turn consume substantial amounts of detritus, algae, and other invertebrates (Momot et al., 1978; Rabeni, 1992; Momot, 1995; Whitledge & Rabeni, 1997a, b). The streams of Missouri, USA, harbor 33 species of crayfish, with some of the highest reported densities in the world (DiStefano et al., 2003a), and with biomasses equal to
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Hydrobiologia
or exceeding those of all other co-occurring benthic invertebrates (Rabeni et al., 1995). In our study stream, the Jacks Fork River, crayfish are a diet item for at least ten species of fish. They comprise a major portion of the diet of two common recreationally important fishes—the shadow bass Ambloplites ariommus and smallmouth bass Micropterus dolomieu (DiStefano, 2005), and have been shown to account for over 60% of total caloric intake of these fish (Rabeni, 1992). Mammals also prey on crayfish in this stream. The diet of river otter Lontra canadensis has been found to consist almost exclusively of crayfish during much of the year (Roberts, 2003, Masters Thesis, University of Missouri, Columbia). The objective of this study was to evaluate the influence of site-specific channel units (determined by geomorphology and hydraulic patterns) on the secondary production (Ivlev, 1961) of crayfish in the Jacks Fork River Missouri, USA. DiStefano et al. (2003a) showed crayfish species-specific associations with particular habitat types and intraspecific ontogenetic changes in habitat use. Studies measuring densities or abundances are important, however, standing crop does not necessarily represent the most ecologically relevant factor to understand how the system functions. Production (a rate function) quantifies energy pathways and indicates stream potentials, and therefore is a more useful measurement to gain understanding of ecosystem function. Understanding habitat-specific production is particularly important because of anthropomorphic alterations to many stream systems. Widespread land-use changes in the Missouri Ozark Highland Ecoregion (hereafter referred to as Ozarks) have altered, and continue to alter, stream channel morphology and hydraulic characteristics resulting in widening and shallowing of wetted channels and reducing average substrate particle size. Channel units (e.g., pools, runs, etc.), discrete morphological stream features, or habitat types (Rabeni & Jacobson, 1993) have become less distinct or have been eliminated entirely from many stream reaches. Some structural features of streams, such as the positive relation between habitat diversity and biotic diversity, are well known for fishes (Gorman & Karr, 1978) and benthic insects (Huryn & Wallace, 1987a); however, the functional importance of various habitats to crayfish production and the potential impact of habitat alterations to crayfish are unknown.
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Study site The Jacks Fork River is a 6th order stream mostly contained in the Ozark National Scenic Riverways (US Department of the Interior, National Park Service) in south-central Missouri. The stream has substantial spring influence, a mean annual discharge of 12.5 m3/s, and a moderate gradient, ca. 1 m/km, with well-developed riffle–pool topology. The channel bed is predominately cherty dolomitic limestone and gravel–cobble particle sizes are dominant. Stream width is typically 5–15 m and 1–2-m deep pools are common. Stream margins harbor intermittent beds of water willow Justicia americana. The five channel units examined were riffle, run, pool, backwater (including side channels), and emergent vegetation patches. Detailed descriptions are given by DiStefano et al. (2003a). We used best professional judgment to select two typical stream reaches (sites) for sampling: Ratcliff Ford (0.8 km in length) and Blue Springs (1.3 km in length) that contained typical amounts of each channel unit, realizing relative amounts of each habitat likely change along a longitudinal gradient and depend upon hydrologic conditions. The relative areas of each channel unit were (Ratcliff Ford and Blue Springs, respectively): riffles 8 and 9%; runs 46 and 46%; pools 41 and 35%; vegetation patches 2 and 3%; and backwaters 3 and 7%. Jacks Fork River harbors four crayfish species: O. luteus, O. ozarkae, O. punctimanus, and Cambarus hubbsi. However, C. hubbsi comprises only a small fraction (*1%) of the community (DiStefano et al., 2003a) and was therefore not included in our study.
Materials and methods Sampling The sampling gear, sampling technique, sampling design, and measures of sampling effectiveness are detailed in DiStefano et al. (2003b). A 1-m2 metal frame 0.51 m high was covered on three sides with 2 9 3-mm rectangular netting and with a 1.22-m long bag seine on the fourth (downstream) side. The sampler was secured to the stream bottom and the enclosed substrate was vigorously disturbed for 3–5 min until the substrate was penetrated to a minimum depth of 15 cm. Crayfish were swept
Hydrobiologia
downstream into the bag seine and captured. Sampling was aided by snorkeling gear and SCUBA when water depths exceeded 0.5 m. A two-step sampling strategy (DiStefano et al. 2003a) was used which stratified sampling effort among five channel unit types. Variation estimates from a pilot study determined how between 21 and 65 samples per site per time period were allocated among channel units. We were not able to determine movement of crayfish among channel units at a site. Because of the similar densities over time, we assumed that emigration was similar to immigration and minor for each channel unit. Production estimates The instantaneous growth rate method of estimating production (Benke, 1984) was used where cohort production is the product of instantaneous growth and mean biomass summed for each age class over the life span of the cohort. Production was calculated as P = (SUM) instantaneous growth (G) * mean biomass (B), where G (mgmg/wet weight per year) was calculated as ln(Wt2 - Wt1), where W is wet weight, and B of an age class was calculated as B = (Bt1 ? Bt2)/2. Habitat-specific production (g/m per cohort life span) was used to compare the importance of individual habitats. Habitat-specific production was weighted by the proportional area of that habitat to total area of habitat at a site to describe the contribution of each channel unit to total site production. Sampling was performed, one to three times a year, over 10 years (1992–2001): sampling occurred in spring and autumn in 1992–1993; spring, summer, and autumn in 1994–1998; and summer in 1999–2000. Most Orconectes individuals live a maximum of 3 years. Each species has predictable growth, and age of individuals can be determined by examining length-frequency histograms; thus, year classes of individual cohorts can be followed through time (Rabeni 1992). We tracked density, growth and survival (differences in densities over time interval) of nine cohorts for three Orconectes spp from two sites.
existed between mean production, mean growth rate, and mean biomass for individual species and channel units. Whereas 0.05 is generally the standard a chosen, a more liberal cutoff was chosen to compensate for the expected variation associated with 10 years of field data. All 10 years of data were used to determine if significant differences existed in mean production (habitat model) and mean biomass (biomass model) between channel units. For the habitat model, the main effects were cohort (9), species (3), channel unit (5), and site (2), and interactive effects were species * channel unit, species * site, channel unit * site, and species * channel unit * site. The interactions between cohort and other main effects (i.e., species, channel unit, and site) were not tested because it is obvious that interactions between cohort and species would be significant given annual variation in cohort production and known differences in population dynamics and significant interactions between the other main effects would be very difficult to interpret without long-term environmental data (e.g., flow, temperature, water quality, etc.). Main effects examined in the biomass model were species (3), channel unit (5), and age (3) and the interactive effects were species * channel unit, species * age, channel unit * age, and species * channel unit * age. Age for this analysis was separated into three groups: age 0, age 1, and age 2? (until assumed death). Data used for the growth model were truncated to include two cohorts (1994– 1996 and 1995–1997 cohorts) that had the same sampling periods (spring, summer, and autumn) for the entire life span because the increments of time should be the same when calculating growth rates. Main effects examined in the growth rate model were species (3), channel unit (5), and age (3) and interactive effects were species * channel unit, species * age, channel unit * age, and species * channel unit * age. The Tukey–Kramer post hoc test was used to determine where significant differences (P B 0.10) existed given the ANOVA models were significant.
Statistical analysis
Results
Data were analyzed using Statistical Analysis System (SAS, 2000). Analysis of variance (ANOVA) for factorial designs (Proc GLM; SAS 2000) was used to determine if significant differences (P \ 0.10)
The overall species by channel unit by site factorial ANOVA (habitat model) was significant for production (F37, 232 = 21.98, P \ 0.0001) (Table 1). Significant differences occurred for the main effects
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species (Tables 2, 3). No significant differences existed in mean production by O. luteus between channel units (Fig. 3). Mean cohort production by O. punctimanus was significantly greatest in vegetation-patch channel units; however, production in pools contributed disproportionately to overall site production at Ratcliff Ford (Table 2) and production in runs contributed disproportionately to overall site production at Blue Springs (Table 3). Similar to O. luteus 35 30
Production (g/m2)
of cohort, species, and channel unit (P \ 0.0001), whereas the only significant interactive effect occurred between species, and channel unit (P \ 0.0001). Production was spatially consistent between the two sites (P = 0.14; Table 1) with most variation in site production occurring in O. punctimanus (Fig. 1). Because production was spatially consistent, subsequent figures are limited to one site, Ratcliff Ford. Overall site production was threefold higher for O. luteus than the other two species. Considerable variation among individual cohort production was exhibited by each species; however, O. luteus was much more temporally consistent than the other species (Fig. 2). Orconectes punctimanus showed a consistent, almost linear decline in production over the study period. Production by O. luteus was relatively high in all channel units when compared to other
25 20 15 10 5
Table 1 The factorial ANOVA (species * channel unit * site) for production by three species of crayfish in five channel units from two study sites, Jacks Fork River, Missouri
0 1
2
3
4
5
6
7
8
9
7
8
9
Cohort
DF
F value
P
Cohort
8
4.65
\0.0001
Species
2
324.01
\0.0001
Channel unit
4
19.36
\0.0001
Species * channel unit
8
4.74
\0.0001
Site
1
2.25
0.14
Species * site
2
1.73
0.18
Channel unit * site
4
0.37
0.83
Species * channel unit * site
8
0.68
0.71
O. punctimanus 3 2.5
Production (g/m2)
Source
2 1.5 1 0.5
Degrees of freedom are indicated by DF
0 1
2
3
4
5
6
Cohort 8
O. ozarkae
7
20
Production (g/m2)
Mean site production (g/m2)
25
15 10 5
6 5 4 3 2 1 0
0
O. luteus
O. punctimanus
O. ozarkae
1
2
3
4
5
6
7
8
9
Cohort
Fig. 1 Mean site production (production weighted for relative area of each channel unit and summed; n = 2 sites) ± 90% confidence intervals for three species of Orconectes in the Jacks Fork River
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Fig. 2 Channel unit-weighted site production for nine cohorts of three species of Orconectes crayfish from Ratcliff Ford, Jacks Fork River, Missouri
Hydrobiologia O. luteus Cohort production (g/m2)
30
a
25 20
a
a
a
a
15 10 5 0 Riffle
Run
Pool
Vegetation Backwater patch
O. punctimanus Cohort production (g/m2)
16
b
14 12 10 8 6 4 2
a a a
a
0 Riffle
Run
Vegetation Backwater patch
O. ozarkae
16
Cohort production (g/m2)
Pool
b
14 12 10
a,b
8 6 4
a,b
a a
2 0
Riffle
Run
Pool
Vegetation Backwater patch
Fig. 3 Channel-unit specific cohort production for each of three Orconectes species at Ratcliff Ford, Jacks Fork River, Missouri. Different letters above 90% confidence intervals indicate significant differences (P \ 0.10)
O. punctimanus, mean cohort production by O. ozarkae was greatest in vegetation patches, though not significantly different from pool or backwater channel units (Fig. 3). Production in run and pool channel units contributed disproportionately to overall site production at Ratcliff Ford (Table 2) and Blue Springs (Table 3). Factorial ANOVA for growth rate (species * channel unit * age) was significant (F44, 45 = 4.41, P \ 0.0001) (Table 4). Significant differences occurred for the main
effects of species (P = 0.0001) and age (P \ 0.0001) and the interactive effects between species and age (P \ 0.0001) and species and channel unit (P = 0.08). Significant differences occurred between growth rates of all species (P B 0.06), with mean growth rates highest for O. luteus (1.09) and lowest for O. punctimanus (0.24). Mean growth rates were highest among crayfish age 0 to age 1. Significant differences existed between mean growth rates of age 0 and other age classes (P \ 0.0001), but no significant differences were evident between age1 and age-2? crayfish. Species by age interactions revealed significantly higher growth rates for age-0 and age-1 crayfish when compared to age-2 crayfish (P \ 0.0001) for all species except O. punctimanus, where no differences were found in growth rates between any of the age classes. Regardless of age, growth rate was not significantly different between channel units by species, but did differ between species in particular channel units. However, there were no significant differences (P = 0.47) among growth rates in any channel unit when age, species, and habitat were considered simultaneously. Significant differences (F44, 810 = 4.41, P \ 0.0001) occurred for all main and interactive effects of the factorial ANOVA for mean biomass (Table 5). Orconectes luteus had significantly higher biomass (mean = 4.94 g/m2) (P \ 0.0001), followed by O. ozarkae (mean = 1.10 g/m2) and O. punctimanus (mean = 0.67 g/m2). Regardless of species, mean biomass (3.13 g/m2) was significantly higher in vegetation patches than all other channel unit types (P \ 0.0001). Mean biomass was also significantly different between pools (mean = 1.77 g/m2) and runs (mean = 2.25 g/m2, P = 0.06). Regardless of age class, biomass of O. luteus was highest in runs (mean = 5.64 g/m2), and significantly different than pools (P \ 0.001). Biomass was significantly higher in vegetation patches than all other channel units for O. punctimanus (P \ 0.0001, mean = 2.33 g/m2), and higher than riffles (P = 0.006) and runs (0.10) for O. ozarkae (P B 0.01, mean = 1.87 g/m2). Regardless of species, mean biomass was significantly higher (mean = 3.47 g/m2) for age-1 crayfish than age-0 (mean = 1.76 g/m2) or age-2? (mean = 1.48 g/m2) crayfish. There were no significant differences in biomass between age classes of O. punctimanus or O. ozarkae. Mean biomass was significantly higher (mean = 8.21, P \ 0.003) for age-1 O. luteus than all other age classes. Regardless
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Hydrobiologia Table 2 Channel-unit specific and site production (% contribution of each habitat type to total site production) for Orconectes luteus, O. ozarkae, and O. punctimanus from Ratcliff Ford, Jacks Fork River, Missouri O. luteus
O. ozarkae
Channel unit production (g/m2)
Site production (%)
O. punctimanus
Channel unit production (g/m2)
Site production (%)
Channel unit production (g/m2)
Site production (%)
Riffle
17.66
6
1.84
3
0.77
8
Run
24.65
52
3.57
38
0.18
10
Pool
19.67
37
5.49
52
0.89
46
Vegetation patch
22.35
2
9.67
4
10.56
27
Backwater
19.47
3
4.66
3
2.35
9
Channel unit production is mean production for that channel unit whereas site production is the sum of production for all channel units, weighted for the proportion of the channel unit represented in the sample reach, and represented as a proportion of that reach Table 3 Channel-unit specific and site production (% contribution of each channel unit to total site production) for Orconectes luteus, O. ozarkae, and O. punctimanus from Blue Spring, Jacks Fork River, Missouri O. luteus
O. ozarkae
Channel unit production (g/m2)
Site production (%)
O. punctimanus
Channel unit production (g/m2)
Site production (%)
Channel unit production (g/m2)
Site production (%)
Riffle
17.46
7
2.41
3
0.34
1
Run
23.41
49
6.16
42
2.73
56
Pool
22.91
36
8.16
42
0.83
13
Vegetation patch
21.63
3
12.50
6
11.23
15
Backwater
15.77
5
6.74
7
4.72
15
Channel unit production is mean production for that channel unit whereas site production is the sum of production for all channel unit types, weighted for the proportion of the channel unit represented in the sample reach, and represented as a proportion of that reach Table 4 Results from factorial ANOVA (species * channel unit * age) for growth rate by three species of Orconectes in five channel units for three age classes (0, 1, and 2?) in the Jacks Fork river, Missouri
Table 5 Results from factorial ANOVA (species * channel unit * age) for biomass by three species of Orconectes in five channel units for three age classes (0, 1, and 2?) in the Jacks Fork River, Missouri
Source
DF
Source
DF
F value
P[F
Species
2
11.04
0.0001
Species
2
590.92
\0.0001
Channel unit
4
1.54
0.21
Channel unit
4
17.72
\0.0001
Species * channel unit
8
1.88
0.08
Species * channel unit
8
6.90
\0.0001
Age
2
48.52
\0.0001
Age
2
116.29
\0.0001
Species * age
4
8.31
\0.0001
Species * age
4
84.87
\0.0001
8 16
0.55 1.00
0.82 0.47
8 16
4.78 1.94
\0.0001 0.01
Channel unit * age Species * channel unit * age
F value
P
Channel unit * age Species * channel unit * age
Degrees of freedom are indicated by DF
Degrees of freedom are indicated by DF
of species, mean biomass was highest for age-1 crayfish in each channel unit, with vegetation patches (mean = 4.81 g/m2) having the highest biomass compared to all other channel units. Mean biomass of individual age classes differed by channel unit for some species. There was no significant difference in
biomass between habitats for age-0 O. luteus; however, riffle, run, and vegetation-patch channel units had the highest mean biomass of age-1 crayfish (Fig. 4). The highest mean biomass of age-2? crayfish was in riffles and runs. Mean biomass of
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Hydrobiologia Age 0 Age 1 Age 2+
5 4.5
4 3.5
3.5
Growth rate
Growth rate
4 3 2.5 2 1.5
3 2.5 2 1.5
1
1
0.5
0.5
0 Riffle
Run
12
Pool
a
a
0
Vegetation Backwater patch
Riffle
a
a
6
a
a
a
a a
2
b 0 Riffle
Run
Pool
Pool
Vegetation Backwater patch
b
a
5
b
Biomass (g/m2)
Biomass (g/m2)
c 8
Run
6
c
10
4
Age 0 Age 1 Age 2+
4.5
b
Vegetation Backwater patch
Fig. 4 Age-specific mean growth rates and biomasses for Orconectes luteus at Ratcliff Ford on the Jacks Fork River, Missouri. Different letters above 90% confidence intervals indicate significant differences (P \ 0.10) within an age class
age-0 O. ozarkae, though not significant, was greatest in vegetation patches (Fig. 5). Mean biomass of age-1 crayfish in vegetation patches was significantly greater than all other channel units except backwaters. No differences in mean biomass of age-2? crayfish were found between channel units. Mean biomass of all age classes of O. punctimanus was significantly higher (P \ 0.001) in vegetation patches compared to all other channel units (Fig. 6).
Discussion The uninterrupted 10-year sampling program on this stream is unprecedented for quantitative crayfish collections and offers insights into spatial and temporal changes in crayfish populations. Whereas variation is inherent in all ecological systems, crayfish production in this stream was remarkably spatially consistent. The lack of significant statistical differences in production between the two sites for
4
a a
3
a b a
2
a 1
a a
a a
a a
a,b a
0 Riffle
Run
Pool
Vegetation Backwater patch
Fig. 5 Age-specific mean growth rates and mean biomass for Orconectes ozarkae at Ratcliff Ford on the Jacks Fork River, Missouri. Different letters above 90% confidence intervals indicate significant differences (P \ 0.10) within an age class
every channel unit and species indicates a spatial consistency which could be extrapolated throughout the stream and perhaps ecoregion. The relative consistency of production over time for O. luteus, and the consistently decreasing trend in production over time for O. punctimanus, and to a lesser extent O. ozarkae, may indicate variation associated with being a habitat (channel unit) specialist. Orconectes punctimanus relied heavily on vegetation patches of J. americana. These plants tend to grow under fairly specific depth conditions. Highly variable hydraulic conditions either inundating the plant beds or leaving them dry for extended periods of time would likely adversely influence crayfish populations. However, patterns of increasing or decreasing flows across the sampling period were not evident in monthly, seasonal, or annual USGS gage records for this stream. Whereas the mechanism responsible for the temporal production declines remains elusive, these results indicate the value of long-term data sets for
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Hydrobiologia 3
Age 0 Age 1 Age 2+
Growth rate
2.5 2 1.5 1 0.5 0 Riffle
Run
Pool
Vegetation Backwater patch
5
b
4.5
b
Biomass (g/m2)
4 3.5 3
b
2.5 2
a a
1.5 1 0.5 0
a a
a
Riffle
a a Run
a
a
a a
Pool
a Vegetation Backwater patch
Fig. 6 Age-specific mean growth rates and mean biomass for Orconectes punctimanus at Ratcliff Ford on the Jacks Fork River, Missouri. Different letters above 90% confidence intervals indicate significant differences (P \ 0.10) within an age class. Mean site production (g/m2)
documenting population characteristics before generalizing conclusions about population dynamics or production. Missouri Ozark streams have been modified by a succession of human activities including timber removal, cultivated fields and pastures, open range livestock grazing, and annual burning of uplands (Jacobson & Primm, 1994) since the early 1800s which have contributed to hydrograph alterations and the homogenizing effects of gravel and finer sediment movement. Beds of J. americana are often confined to a narrow band parallel to the flow in particular depths and current velocities (Penfound, 1940). High variation in flow during the growing season often leaves these plants inundated for short periods or on dry land for extended periods. Backwaters and side channels are also some of the first habitats to be affected by reduced discharge or permanent changes to channel morphology. In our study, two crayfish species had high production in two relatively scarce
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habitats—vegetation patches and backwaters. These two stream-margin habitats are particularly susceptible to the changes in hydrology and channel morphology that accompany land-use alterations. The importance of habitat heterogeneity to crayfish production in this study was species dependent. Because mean production of O. luteus was fivefold greater than the other two species and its production was relatively high in all channel units (ranging between 17 and 24 g/m2), the elimination of any one channel unit and substitution by another would likely affect this species’ production the least. However, vegetation patch channel units had substantially greater production than other habitats for O. punctimanus and O. ozarkae. Although the extent of this habitat was small, accounting for \5% of the total area, it was particularly important to O. punctimanus, where they contributed about a third of total site production at both sites. Cohort production in crayfish is determined by the number of viable eggs, biomass, and growth rates. Growth rates may vary widely between different populations because of ambient temperature conditions (Whitmore & Huryn, 1999) or within populations due to the universal trait of declining growth rate with increases in age or size. However, there is no evidence from the literature of inter-habitat differences in growth rates for a particular age group of crayfish. Momot (1984) attributed variations in production to modifications in age-specific mortality rate rather than changes in growth or fecundity rate. Growth rates in this study declined as cohorts aged, but no differences were found between channel units for any particular age class. The highly variable G within an age class resulted in substantial year-class variation in size, with age-0 individuals varying by approximately 10 mm in total length. This may be due to temporal variation in hatching, or growth depensation (Ricker, 1975) of a genetic or environmental cause. Regardless, mean growth rates in this study declined as cohorts aged, but were inconsistent between channel units for any particular age group. We conclude that differences in production between habitats were due to age (size)-specific channel unit use. Age-1 crayfish were particularly important to O. luteus production because of their high summed biomass even though their growth rates were moderate. Whereas age-0 individuals had the highest growth rate, their significant contribution to
Hydrobiologia
production required high densities (e.g., O. ozarkae). The age-2? group contributed the least to production because of the combination of low biomass and growth rates. Crayfish are influenced in their selection of habitats by a combination of factors related to bioenergetics, inter and intra-specific competition, and predation (Garvey et al., 1994), and they occupy areas based on current velocity, food availability, physical structure in the form of vegetation or substrate particle size, and water depth (Rabeni 1985). The result is a consistent pattern of age-related density (DiStefano et al., 2003a) and biomass distributions between habitats for most species. Those channel units affording conditions, for whatever reasons, for high biomass, will produce relatively high production. Secondary production has been estimated for less than a dozen stream crayfish species. Understanding the ecological importance of crayfish in any stream system requires an understanding of production within each channel unit and the spatial extent of associated habitats. Few studies have sampled and separated multiple habitats to determine habitatspecific production. Mason (1975) found over three times higher production for Pacifastacus leniusculus trowbridgii in pools than in riffles and glides. Whitmore & Huryn (1999) reported production of the New Zealand ‘‘koura’’ Paranephrops zealandicus was at least two times higher in pools as in riffles in two of three study sites. Mitchell & Smock (1991) evaluated habitats based solely on substrate particle size in a 5–6th order river in Virginia for Orconectes virilis and Cambarus bartoni and concluded larger substrate particle sizes yielded greater production. Some production studies have used randomly assigned locations throughout the stream to take samples (e.g., Huryn & Wallace, 1987b; Roell & Orth, 1992), whereas other studies sampled in approximate proportion to the area of particular habitats (Rabeni, 1992). Random or proportional sampling approaches will give results approximating total site average production, but will do nothing to distinguish relative productiveness of different habitats. Our study indicates that unless all major channel units are quantified and sampled, results and conclusions may be biased to an unknown extent. Understanding habitat-specific production of crayfish will increase our ability to conserve or restore particular channel units that contribute most to a
naturally functioning stream system. Certainly the ecology of J. americana deserves more attention because of its importance to the production of O. punctimanus and O. ozarkae. The dominant role of crayfish in the energy dynamics of many stream systems should make them a high priority when setting objectives for stream management—whether the goal relates to biotic integrity, recreational fishing, or biodiversity. Acknowledgments This research is a contribution of the Missouri Cooperative Fish and Wildlife Research Unit (US Geological Survey, Missouri Department of Conservation, University of Missouri, and Wildlife Management Institute cooperating). Major funding was provided by the Missouri Department of Conservation. We thank the numerous field technicians for assistance with crayfish collection. The manuscript was improved by comments from Jacob Westhoff, Ann Allert, and two anonymous reviewers.
References Benke, A. C., 1984. Secondary Production of Aquatic Insects. In Resh, V. H. & D. M. Rosenberg (eds), Ecology of Aquatic Insects. Praeger, New York: 289–322. DiStefano, R. J., 2005. Trophic interactions between Missouri Ozarks stream crayfish communities and sport fish predators: increased abundance and size structure of predators cause little change in crayfish community densities. Missouri Department of Conservation, Dingell–Johnson Project F-1-R-054, Study S-41, Job 4, Final Report. Columbia, Missouri. DiStefano, R. J., J. J. Decoske, T. M. Vangilder & L. S. Barnes, 2003a. Macrohabitat partitioning among three crayfish species in two Missouri streams. USA Crustaceana 76: 343–362. DiStefano, R. J., C. F. Gale, B. A. Wagner & R. D. Zweifel, 2003b. A sampling method to assess lotic crayfish communities. Journal of Crustacean Biology 23: 678–690. Garvey, J. E., R. A. Stein & H. M. Thomas, 1994. Assessing how fish predation and interspecific prey competition influence a crayfish assemblage. Ecology 75: 572–574. Gorman, O. T. & J. R. Karr, 1978. Habitat structure and stream fish communities. Ecology 59: 507–515. Huryn, A. D. & J. B. Wallace, 1987a. Local geomorphology as a determinant of macrofaunal production in a mountain stream. Ecology 68: 1932–1942. Huryn, A. D. & J. B. Wallace, 1987b. Production and litter processing by crayfish in an Appalachian mountain stream. Freshwater Biology 18: 277–286. Ivlev, V. S., 1961. The biological productivity of waters (English version 1966). Journal of the Fisheries Research Board of Canada 23: 1727–1759. Jacobson, R. B. & A. T. Primm, 1994. Historical land-use changes and potential effects on stream disturbance in the Ozark Plateaus, Missouri. US Geological Survey Open File Report 94–333. Rolla, Missouri.
123
Hydrobiologia Mason, J. C., 1975. Crayfish production in a small woodland stream. Freshwater Crayfish 2: 449–480. Mitchell, D. J. & L. A. Smock, 1991. Distribution, life history and production of crayfish in the James River, Virginia. American Midland Naturalist 126: 353–363. Momot, W. T., 1984. Crayfish production: a reflection of community energetics. Journal of Crustacean Biology 4: 35–54. Momot, W. T., 1995. Redefining the role of crayfish in aquatic ecosystems. Reviews in Fisheries Science 3: 33–63. Momot, W. T., H. Gowing & P. D. Jones, 1978. The dynamics of crayfish and their role in ecosystems. American Midland Naturalist 99: 10–35. Penfound, W. T., 1940. The biology of Dianthera americana L. American Midland Naturalist 24: 242–247. Rabeni, C. F., 1985. Habitat partitioning by stream-dwelling crayfish: the influence of body size. American Midland Naturalist 113: 20–29. Rabeni, C. F., 1992. Trophic linkages between centrarchids and their crayfish prey. Canadian Journal of Fisheries and Aquatic Sciences 49: 1714–1721. Rabeni, C. F. & R. B. Jacobson, 1993. The importance of fluvial hydraulics to fish habitat in low gradient alluvial streams. Freshwater Biology 29: 211–220.
123
Rabeni, C. F., M. Gossett & D. D. McClendon, 1995. The contribution of crayfish to the invertebrate production and trophic ecology of an Ozark stream. Freshwater Crayfish 10: 163–173. Ricker, W. E., 1975. Computation and interpretation of biological statistics of fish populations. Bulletin 191 of the Fisheries Research Board of Canada, Department of the Environment, Fisheries and Marine Service, Ottawa. 382. Roell, M. J. & D. J. Orth, 1992. Production of three crayfish populations in the New River of West Virginia, USA. Hydrobiologia 228: 185–194. SAS Institute Inc., 2000. SAS/STAT user’s guide, version 8th edition. SAS Institute. Inc, Cary, North Carolina. Whitledge, G. W. & C. F. Rabeni, 1997a. Diel and seasonal variation in food habits of crayfishes in a Missouri Ozark stream. Freshwater Crayfish 11: 159–169. Whitledge, G. W. & C. F. Rabeni, 1997b. Energy sources and ecological role of crayfishes in an Ozark stream: insights from stable isotopes and gut analysis. Canadian Journal of Fisheries and Aquatic Sciences 54: 2555–2563. Whitmore, N. & A. D. Huryn, 1999. Life history and production of Paranephrops zealandicus in a forest stream with comments about the sustainable harvest of freshwater crayfish. Freshwater Biology 42: 467–478.
