Hydrobiologia

, Volume 592, Issue 1, pp 235–247

Factors affecting the distribution of stream macroinvertebrates in geothermal areas: Taupo Volcanic Zone, New Zealand

Authors

    • National Institute of Water and Atmospheric Research
    • Centre for Biodiversity and Ecology Research, Department of Biological SciencesThe University of Waikato
  • Ian K. G. Boothroyd
    • Kingett Mitchell & Associates
    • School of Geography and Environmental ScienceUniversity of Auckland
  • David A. Speirs
    • Environment Waikato
Primary Research Paper

DOI: 10.1007/s10750-007-0748-9

Cite this article as:
Duggan, I.C., Boothroyd, I.K.G. & Speirs, D.A. Hydrobiologia (2007) 592: 235. doi:10.1007/s10750-007-0748-9

Abstract

The distribution of macroinvertebrates was investigated among sites within five geothermally influenced and two non- or minimally-influenced streams in the Taupo Volcanic Zone, New Zealand, to examine the responses of communities to broad environmental gradients within and among habitats. To date, examination of geothermal stream macroinvertebrates has typically been from single habitats, and has not been examined over a regional scale. Sites within and among streams represented a range of sizes, depths, water velocities and substrate types. Sites with little or no geothermal influence typically had temperatures less than 15°C and pH between 5 and 8. Four of the geothermally influenced streams had temperatures greater than 25°C, and ranged from alkaline (pH 9.1) to highly acidic (pH 3.0). Most taxa recorded were typical inhabitants of non-geothermal streams that are tolerant to elevated temperatures, extreme pH conditions and/or high toxicant levels. Diptera, Coleoptera and Mollusca dominated geothermal sites, and Ephemeroptera, Plecoptera and Trichoptera were absent. In addition, an obligate dweller of geothermal habitats, Ephydrella thermarum, and a nonindigenous tropical gastropod, Melanoides tuberculata, were recorded. Canonical correspondence analysis implicated multiple factors in determining the distribution of invertebrates over the region. Overall, distribution was most strongly associated with temperature gradients, particularly longitudinally within streams. This distribution was likely directly related to species temperature tolerances, but also temperature effects on algal abundance and composition, its differential effects on species’ potential competitors and predators, and its effects on toxicant availability. Differences in invertebrate composition among streams were associated with major differences in pH and substrate. Increased acidity was associated with a significant decrease in invertebrate taxa richness, with acidic sites having a limited fauna dominated by dipterans (e.g., Naonella sp., Polypedilum sp.). Stability of flow and environmental conditions may enhance competitive interactions among taxa, enhancing the importance of substrate type in these systems. The presence of non-indigenous species (e.g., M. tuberculata, Poecilia reticulata), currently limited in distribution, also affected species composition. Overall, communities become less speciose, although more unusual in composition, with increased geothermal influence.

Keywords

TemperaturepHSubstrateNonindigenous speciesHot springs

Introduction

The landscape and water bodies overlying geothermal areas are characterised by zones of high temperature, high ion concentrations and/or extreme pH conditions (Vincent & Forsyth, 1987; Pritchard, 1991). Among geothermal fields, however, the influence of geothermal activity on the temperature and chemistry of overlying waters varies widely. In addition, the influence of geothermal activity on these waters is also often highly variable within each system. Water temperature, for example, tends to decrease quite rapidly down streams as the geothermal influence wanes or water from other sources enters the system (e.g., James, 1985; Lamberti & Resh, 1985; Hayford et al., 1995). The biodiversity of these unusual habitats is typically low, as species occurring here need to be adapted to extremes in temperature, pH and/or toxicant levels (Lamberti & Resh, 1985; Vincent & Forsyth, 1987; Pritchard, 1991). In response to these conditions, however, characteristic indigenous aquatic communities have evolved. This biota includes species or varieties only found in geothermal habitats, as well as common stress-tolerant species (Robinson & Turner, 1985; Vincent & Forsyth, 1987; Pritchard, 1991).

Patterns in species occurrence and community composition at regional spatial scales are primarily associated with dispersal of organisms across the landscape (Jenkins & Buikema, 1998; Shurin, 2000). Once an organism has arrived in a habitat, local scale factors, such as the suitability of the abiotic environment and interactions with established species, determine community composition (Ricklefs & Schluter, 1993). At finer scales, gradients of abiotic and biotic factors within systems will act to further structure communities (e.g., longitudinally in rivers; Vannote et al., 1980). To date, most ecological studies of biota in geothermal waters, and in particular of the macroinvertebrate fauna, have focused on basic descriptions of the presence of different taxa, commonly noting the temperature or pH at which each were recorded. These studies have generally been undertaken at discrete geothermal localities examining, for example, the occurrences of taxa along single streams or within individual lakes (e.g., James, 1985; Lamberti & Resh, 1985; Hayford et al., 1995). Factors determining distribution within and among geothermal systems are better known for algae than for other biota, with water temperature, pH and sulphide concentrations being the most important determinants (e.g., Stockner, 1967; Brock & Brock, 1971; Castenholz, 1976; Lamberti & Resh, 1985). For macroinvertebrates, less is known about the quantitative responses of communities to gradients in the underlying geothermal resource, and in particular whether the factors determining distribution within habitats are also those responsible for distribution patterns across a landscape. Temperature is considered the most important ecological variable determining distribution within geothermally influenced streams (Pritchard, 1991), and consequently it and pH are commonly the only factors measured in association with species distributions (e.g., Robinson & Turner, 1985; James, 1985; Lamberti & Resh, 1985).

In non-geothermally influenced streams, macroinvertebrate distribution patterns are influenced by a diverse range of environmental factors, including landuse, current velocity, substrate type, shade and water depth (e.g., Collier & Winterbourn, 2000). Whether the same factors, in addition to temperature and pH, influence the community composition and abundance of macroinvertebrates within and among geothermal streams is unknown. In the current study, we measure macroinvertebrate community changes along geothermal stress gradients, and examine some habitat and environmental factors influencing this distribution. We test the hypothesis that distribution of macroinvertebrates in geothermal streams is not limited among geothermal fields, and thus species within and among these habitats are distributed in a predictable way based on environmental conditions. Also, we investigate whether macroinvertebrate distribution in geothermally influenced streams is affected by factors other than temperature and pH. We test these hypotheses among waters of the Taupo Volcanic Zone (TVZ), New Zealand, which on a world scale contains a high concentration of geothermal waters in a relatively small area (Vincent & Forsyth, 1987). Because this region contains a diverse selection of geothermal waters it provides an ideal setting to examine species distribution patterns with respect to environmental gradients. A better knowledge of significant attributes in geothermal ecosystems will allow resource managers to focus monitoring efforts on important environmental features of these systems, measure changes in ecosystem health, and develop appropriate tools and indicators for monitoring. Such knowledge is required to predict the effects of anthropogenic-induced changes on geothermal biota by, for example, decreases in temperature or flow rates through industrial extraction of geothermal fluids (e.g., James, 1985; Cody & Lumb 1992).

Methods and sampling sites

Site locations

Samples were collected from six geothermally influenced streams and one non-geothermally influenced stream in the Taupo Volcanic Zone (Fig. 1, Table 1). Each site was sampled once. Twenty sites, each comprising 30 m stream reaches, were selected to represent a broad range of environmental conditions, including pH, temperature and other habitat attributes. Seventeen sites were from the geothermal spring-fed or geothermally influenced streams; Otamakokore Stream (Waikite geothermal field; 23 May 2001), Golden Springs (Golden Springs geothermal field; 25 May 2001), Waipouwerawera Stream (Wairakei geothermal field; 23 May 2001), Hakereteke Stream (commonly known as “Kerosene Creek”; Waiotapu geothermal field; 28 May 2001), and an unnamed stream in the Waiotapu geothermal field (25 May 2001; see Fig. 1). Samples from streams with no, or with relatively little, geothermal influence, were collected from Waikokomuka Stream, which flows into Hakereteke Stream, Hakereteke Stream after convergence with Waikokomuka Stream, and Otamakokore Stream after convergence with several other non-geothermally influenced streams (all 28 May 2001).
https://static-content.springer.com/image/art%3A10.1007%2Fs10750-007-0748-9/MediaObjects/10750_2007_748_Fig01.jpg
Fig. 1

Location of the Otamakokore Stream (sites 1–7), Waipouwerawera Stream (sites 8–9), Golden Springs (sites 10–13), Hakereteke Stream (sites 14–17), Waikokomuka Stream (site 18), and the unnamed Waiotapu Stream (19–20) sites

Table 1

Values for physico-chemical and habitat variables from 20 stream sites with various levels of geothermal influence in the Taupo Volcanic Zone sampled in May 2001

 

Site

Temperature (°C)

pH

Conductivity (μS/cm @ 25°C)

Dissolved oxygen (mg/L)

Oxygen saturation (%)

Stream velocity (m/s)

Water depth (m)

Channel width (m)

Substratum

Otamakokore Stream

1

34.7

8.4

394

6.6

105.4

0.24

0.20

2.30

2,3

Otamakokore Stream

2

28.3

9.1

1168

7.5

110.1

0.14

0.05

0.31

1

Otamakokore Stream

3

55.7

8.1

1241

109.0

0.25

0.17

0.87

6,2,1

Otamakokore Stream

4

45.5

9.6

725

109.0

0.20

0.08

0.62

1 = 2

Otamakokore Stream

5

42.3

8.3

1153

6.7

120.1

0.24

0.26

0.60

2,1

Otamakokore Stream

6

31.7

8.2

1051

6.6

100.4

0.18

0.26

1.18

2,1

Otamakokore Stream*

7

14.6

7.0

300

8.0

78.5

0.71

1.03

3.26

2,3

Waipouwerawera Stream

8

22.9

8.0

167

8.7

101.2

0.59

0.30

1.12

3,2,1,8

Waipouwerawera Stream

9

17.5

7.3

95

8.8

91.7

0.44

0.28

1.11

2,3

Golden Springs

10

37.8

6.4

851

3.1

47.0

0.27

0.37

0.69

1

Golden Springs

11

32.7

6.6

797

2.7

36.3

0.21

0.54

2.16

1,2

Golden Springs

12

30.4

7.1

802

5.7

74.5

0.26

0.29

1.54

1,2,7

Golden Springs

13

29.0

7.5

817

6.8

89.6

0.22

0.27

1.88

2,1

Hakereteke Stream

14

29.1

3.1

690

7.0

92.1

0.48

0.59

2.94

6,3,2,5

Hakereteke Stream

15

33.7

3.0

784

6.5

91.2

0.68

0.55

3.02

2 = 6

Hakereteke Stream

16

28.8

3.1

688

7.6

98.5

0.42

0.61

2.90

2,8,4

Hakereteke Stream*

17

19.4

5.1

301

8.3

90.0

0.53

0.85

3.98

2,6,4

Waikokomuka Stream

18

11.6

6.1

115

10.3

94.7

0.41

1.14

1.52

2,1

Stream at Waiotapu

19

41.3

3.7

1265

6.0

96.2

0.33

0.25

3.30

3,4,2

Stream at Waiotapu

20

41.4

3.8

1210

6.1

97.0

0.31

0.36

2.44

2,1

All streams have some geothermal inputs except Waikokomuka Stream. Asterisks indicate stream sites sampled after the convergence with non-geothermal streams. Substratum column lists individual substrata that make up the top 80% of total substratum, in order of importance: 1 = Silt; 2 = Sand & Gravel; 3 = Small cobble; 4 = Large cobble; 5 = Boulder; 6 = Bedrock; 7 = organic detritus; 8 = Wood

Field methodology

Physico-chemical (temperature, conductivity, dissolved oxygen, pH) and habitat (water depth, stream width, stream velocity, substrate type, shade, bank height, bank erosion) factors were recorded at each site. Physico-chemical factors were recorded by taking mid-stream spot measurements using YSI 30 conductivity, YSI 60 pH, and YSI 95 dissolved oxygen meters. Stream velocity was measured with a Montedoro PSM2A flow velocity meter, generally at three points across each of three transects along a reach. Habitat factors were recorded on five transects approximately equidistant along each 30 m reach. Water depth was recorded as the maximum depth across each transect. Other variables (proportions of silt, sand/gravel, small cobble, large cobble, boulder, organic detritus and wood substratum; degree of shade; extent of bank erosion, proportion of bed covered with benthic algae) were visually estimated on a zero to 100% scale, or as a measurement (bank height).

A semi-quantitative macroinvertebrate survey of the 20 stream sites was undertaken using kick sampling (250 μm mesh). At each site a consistent three-minute sampling effort was undertaken along each 30 m reach. Substrates were mainly inorganic, with occasional allochthonous detritus or wood. None of the sample sites contained macrophytes. Macroinvertebrates were identified to the lowest taxonomic level practical, generally using the keys of Winterbourn (1973) and Winterbourn et al. (2000).

Analyses of responses of invertebrates to environmental gradients

Canonical Correspondence Analysis (CCA) was used to elucidate patterns in macroinvertebrate abundance and community composition. Taxa that occurred only at single sites, and sites from which a total of fewer than ten invertebrates were recorded in the resulting dataset, were removed (site 5 from Otamakokore Stream, site 8 from Waipouwerawera Stream, and sites 19 and 20 from the unnamed stream at Waiotapu). CCA was performed on log (x + 1) transformed abundances of macroinvertebrate taxa to downweight the effects of dominant taxa. This transformation ensured that the results of the ordination not only reflected the abundance differences of the dominant taxa between sites but also those less abundant. Some of the environmental variables were log (x + 1) transformed to improve normality of the data (stream velocity, stream depth, shade, proportions of silt of large cobble, bank height, extent of bank erosion, proportion of bed covered with benthic algae). Dissolved oxygen values from two Otamakokore Stream sites could not be recorded by our meter due to high temperatures, and these were replaced with values interpolated as the average of upstream and downstream site measurements. All environmental data were standardised to zero mean and unit variance to remove the influence of different scales of measurement. Some of the measured environmental variables were removed from the ordination because of covariability with other environmental factors, as revealed by high variance inflation factors (>20) in an exploratory CCA analysis (conductivity, dissolved oxygen, stream velocity). CCA was performed using CANOCO 4.0 (Centre for Biometry, Wageningen, Netherlands).

Results

Habitat conditions

Temperature and pH varied widely among sites (Table 1; Fig. 2). Waikokomuka Stream, which had no geothermal influence, had the lowest recorded temperature (11.6°C; site 18). The most downstream Otamakokore Stream site (site 7) also had a low temperature (14.6°C), resulting from several cold water tributaries entering the stream. Geothermal activity therefore had very reduced influence on temperature at this latter site. Waipouwerawera Stream (sites 8 and 9) and the downstream site on Hakereteke Stream (site 17) also appeared to have some, although limited, geothermal influence on temperatures (all <20°C). The remaining sites all had greatly elevated temperatures (>25°C) compared with non- or minimally-geothermally influenced streams in the area. Temperature generally decreased with distance downstream from the stream source (e.g., Golden Springs). Otamakokore Stream was a notable exception to this pattern with several points of reheating from springs occurring along the sampled length. The pH varied widely among sites, with non- or minimally-geothermally influenced sites (Waikokomuka Stream, downstream sites of Otamakokore and Hakereteke Streams) in the range 5–8 (Table 1; Fig. 2). At geothermally influenced sites, pH was as low as 3.0 (Hakereteke Stream) and as high as 9.1 (Otamakokore Stream). Conductivity was typically high in the geothermal stream sites, reaching a maximum stream average of 1237.5 μS/cm (@25°C) at the unnamed stream at Waiotapu. By comparison, typical (i.e., median value) conductivity of New Zealand streams and rivers is around 100 μS/cm (Close & Davies-Colley, 1990). Conductivity was significantly positively correlated to temperature (R2 = 0.62, P < 0.001). Dissolved oxygen concentrations were typically lower in warmer streams, although measurements of oxygen saturation showed that all of the sites except Golden Springs had >85% oxygen saturation. The sites represented a range of stream sizes, depths, water velocities and substrate types (Table 1).
https://static-content.springer.com/image/art%3A10.1007%2Fs10750-007-0748-9/MediaObjects/10750_2007_748_Fig02.jpg
Fig. 2

Temperature and pH recorded from 20 stream sites with various levels of geothermal influence in the Taupo Volcanic Zone. Numbers correspond to site numbers (see Fig. 1); O = Otamakokore Stream, Wp = Waipouwerawera Stream, H = Hakereteke Stream, Wk = Waikokomuka Stream, and Wt = the unnamed Waiotapu Stream

Macroinvertebrate community composition and dynamics

A total of 48 taxa were recorded from geothermal and non-geothermal streams of the TVZ (see Electronic supplementary material). Fourteen Diptera taxa were recorded, followed in order by Trichoptera (10 taxa), Mollusca (6) and Coleoptera (5). However, Ephemeroptera, Plecoptera and Trichoptera (EPT) were recorded only from non- or minimally geothermally influenced streams, whereas Diptera, Coleoptera and Mollusca were recorded from a range of geothermally influenced and non-geothermally influenced sites. The nonindigenous gastropod mollusc Melanoides tuberculata (Muller) was recorded for the first time in New Zealand waters from Golden Springs (sites 11 and 12). In addition to the invertebrates, a nonindigenous tropical fish, Poecilia reticulata (Peters), was collected from the same sites as M. tuberculata.

A general decrease in taxon richness was found with increasing temperature, with the greatest number of taxa recorded from the non-geothermal site (Waikokomuka Stream; 16 taxa), and lower numbers at the geothermal sites (all <8 taxa), although this relationship was not significant (R2 = 0.16; F = 3.533; P = 0.076; Fig. 3). However, we found a significant positive relationship between pH and taxon richness (R2 = 0.33; F = 8.996; P = 0.008; Fig. 3).
https://static-content.springer.com/image/art%3A10.1007%2Fs10750-007-0748-9/MediaObjects/10750_2007_748_Fig03.jpg
Fig. 3

Log (x + 1) taxa richness from 20 stream sites with various levels of geothermal influence in the Taupo Volcanic Zone against temperature and pH

CCA was used to explore the environmental variables associated with observed patterns in community composition (Fig. 4). The composition of macrofauna from samples within each stream were commonly more similar to one another than those from the other streams, at least where geothermal influence was greatest. Thus, each stream was distinguished from others based on the composition of its invertebrate community. However, it was apparent that gradients in macroinvertebrate composition occurred along environmental gradients within streams. Samples from the cooler sites occur to the right side of the CCA (i.e., sites 18, 9 and 7). The warmest sites on Otamakokore Stream occur on the left hand side (sites 4, 3 and 2), separating Hakereteke Stream samples (top) and Golden Springs (bottom left) samples (Fig. 4). The two coldest sites (Waikokomuka and Waipouwerawera Streams) are close to one another in the ordination, indicating that Waipouwerawera Stream had a similar species composition to that of streams with no geothermal influence. Of the geothermally influenced sites, macroinvertebrate composition in Hakereteke Stream was most similar to that in Otamakokore Stream, and least similar to that in Golden Springs.
https://static-content.springer.com/image/art%3A10.1007%2Fs10750-007-0748-9/MediaObjects/10750_2007_748_Fig04.jpg
Fig. 4

Ordination biplots based on CCA of macrofaunal composition from 16 stream sites with various levels of geothermal influence in the Taupo Volcanic Zone. The site (closed circles) and species (open circles) biplot is above, and the site and environmental variables (arrows) biplot is below. Numbers correspond to site numbers (see Fig. 1). Eigenvalues for axes 1 and 2 = 0.791 and 0.719, respectively. H = Hakereteke; O = Otamakokore; G = Golden Springs; Wk = Waikokomuka; Wp = Waipouwerawera

Macroinvertebrate species most strongly associated with the cooler sites were Coloburiscus humeralis (Walker; Ephemeroptera), Zephlebia dentata Eaton (Ephemeroptera), Austrosimulium sp. (Diptera), Eiseniella sp. (Oligochaeta) and Potamopyrgus antipodarum (Gray; Gastropoda). A taxonomically undescribed Chironomus species was most strongly associated with the Hakereteke Stream samples. Taxa associated with Otamakokore Stream were Ephydrella thermarum Dumbleton (Diptera), Acari and Lancetes lanceolatus (Clark; Coleoptera). Species associated most strongly with Golden Springs samples were Antiporus sp. (Coleoptera), Physa sp. (Gastropoda), Melanoides tuberculata (Gastropoda) and Hirudinea.

Results of forward selection and Monte-Carlo permutation tests from CCA indicated temperature explained the largest proportion of variability in macroinvertebrate composition and abundance among sites (lambda A = 0.59, P = 0.01). Temperature was thus strongly associated with Axis 1, the axis that explains most variation in community composition. Samples from the warmest sites are distributed on the left hand side of the ordination, intermediate temperature sites in the middle, and the coolest sites on the right hand side of the ordination. Other environmental variables influencing the observed patterns on this axis were % algae cover and silt cover (both strongly negatively associated with Axis 1), water depth, %sand & gravel cover, bank height and %small cobble (all strongly positively associated with Axis 1). As conductivity was removed from the ordination due to a strong correlation with temperature, species distributions were also strongly associated with variation in conductivity in a similar manner to that shown for temperature. These results indicate that in the current study, those sites with the highest temperatures were generally high in dissolved ions, more silty and had more luxuriant algal growths, whereas cooler streams tended to been low in dissolved ions, have sand & gravel or small cobble substrata with higher banks. Some of the variation along Axis 1, and therefore between hot and cold streams, may thus not be entirely due to temperature alone, but also due to ion concentrations and unrelated physical habitat factors that co-varied with temperature among our streams. The variation along Axis 2, and thus the factors indicated as being important for distinguishing the three streams with temperatures or acidities most influenced by geothermal inputs (Hakereteke Stream, Otamakokore Stream and Golden Springs), was related to substratum (i.e., % bedrock and % boulders were both strongly positively associated) and pH (strongly negatively associated with Axis 2). Thus, species abundant in Hakereteke Stream (e.g., Chironomus) are likely to be associated with harder substrates and lower pH, and those in Golden Springs (e.g., Hirudinea) with high pH and less stable, silty substrates.

Discussion

Factors influencing the distribution of invertebrates in the TVZ

Our examination of macroinvertebrate distribution patterns indicated that species composition varied considerably across the region, with distributions affected by a range of environmental factors. Distinct macroinvertebrate assemblages did not occur in geothermal relative to non-geothermal habitats, but composition changed over the region gradually in response to the degree of geothermal influence (e.g., temperature and pH change) and habitat quality (e.g., substratum composition). Taxa common or abundant in the geothermally influenced streams (Diptera, Coleoptera, Mollusca) were in general typical of those previously recorded from similar habitats in New Zealand (Winterbourn, 1968; Vincent & Forsyth, 1987) and elsewhere (Lamberti & Resh, 1985; Robinson & Turner, 1985). Most recorded taxa are typical non-geothermal stream inhabitants that can tolerate high temperatures (>25°C), unusual pH, and/or high toxicant levels.

CCA indicated that water temperature was the dominant gradient determining the distribution of species among and within streams. This dominance of temperature is hardly surprising given its influence on the biology of animals, and because such a wide range of temperatures was recorded among sites in the current study. At lower temperature sites a more typical stream fauna occurred (i.e., similar to that which occurs in non-geothermal streams), for example Ephemeroptera (e.g., Coloburiscus humeralis and Zephlebia dentata), Trichoptera (e.g., Hydrobiosis umbripennis McLachlan and Oecetis unicolor McLachlan), the dipteran Austrosimulium sp., and the gastropod Potamopyrgus antipodarum. At higher temperatures (>25°C), however, Diptera (e.g., Ephydrella thermarum, Tanytarsus funebris Freeman) and Coleoptera (e.g., Lancetes lanceolatus, Liodessus plicatus (Sharp), Hydrophilidae) dominated. Ephemeroptera, Plecoptera and Trichoptera were absent from our geothermal sites, and are rare components of these habitats worldwide (Pritchard, 1991). Taxa associated with warmer conditions in our study have previously been shown to have similar relationships with temperature in these and other New Zealand geothermal sites (e.g., Winterbourn, 1968; Forsyth, 1983; Vincent & Forsyth, 1987). These distributions will occur because species have different optima and tolerances to temperature largely determined by the temperature specific enzyme systems of each species (Pritchard, 1991). It has thus long been noted that temperature tolerances of biota can determine their distribution longitudinally within individual geothermally influenced streams (Vincent & Forsyth, 1987), although it has not previously been reported at the regional scale.

The non-significant decrease in taxon richness with increasing temperature is likely to reflect the small number of sites sampled at each temperature extreme (i.e., at cool-water temperatures and at those >50°C), and a post-hoc power analysis indicated a low sample size would have increased the probability of obtaining a Type II error in our temperature analysis (observed power = 0.53; i.e., a 53% chance of rejecting the null hypothesis). Lamberti & Resh (1985), for example, found macroinvertebrate species richness decreased from 15 at 27°C to zero at 45°C at Little Geysers Creek, California, U.S.A. In our study the relationship was also affected by one site, in Otamakokore Stream (site 3), where we recorded five invertebrate species (Ischnura aurora (Brauer), Hydrophilidae, Chironomus sp., Ephydrella thermarum, Tanytarsus funebris) at the extremely high temperature of 55.7°C. Macroinvertebrates are typically not recorded at temperatures above 50°C (Brock, 1985; Vincent & Forsyth, 1987; Pritchard, 1991). Such a high temperature tolerance in our study is likely spurious; we suspect that species may not have been living in the water at the temperature measured in the main channel, but rather in cooler microhabitats near the banks where water flow was slower. In New Zealand, the maximum temperature previously recorded for E. thermarum is 47°C, for Tanytarsus species 36°C, Chironomus species 33°C, and for I. aurora 34°C (Winterbourn & Brown, 1967; Winterbourn, 1968; Forsyth & McColl, 1974; Vincent & Forsyth, 1987). However, in our study sites at which invertebrates were noted at high temperatures were alkaline and non-sulfurous. This combination of conditions is perhaps less restrictive to the presence of stream taxa. For example, the significant positive relationship between pH and taxa richness in our study suggests that acidity and associated chemistry is a strong influence restricting the occurrence of species in geothermal habitats.

Other factors that co-vary with, or are caused by, temperature changes, such as increased conductivity, algal abundance (as indicated by its high loading along the same CCA axis), changes in algal composition, and the presence or absence of predators (e.g., fish), may have also resulted in changes in macroinvertebrate communities. Changes in benthic algal and cyanobacterial composition along temperature gradients are well understood (e.g., Stockner, 1967; Brock, 1985; Lamberti & Resh, 1985). Cyanobacteria are able to grow at higher temperatures than any other algal groups, and in the current study the cyanophytes Mastigocladus laminosus Cohn, Phormidium sp. (both from Otamakokore Stream) and Oscillatoria sp. (Otamakokore Stream and Golden Springs) dominated the alkaline streams at high temperatures (C. Kilroy, NIWA, unpublished data). Cyanobacteria may provide an unsuitable food source for many invertebrates, and may potentially be toxic, restricting invertebrate occurrences at high temperature, alkaline, sites (e.g., Codd, 1995). In addition, increased temperature is known to increase the sensitivity of many invertebrates to heavy metals (e.g., Rao & Khan, 2000; Gossiaux et al., 1992). Some of the variation associated with changes in temperature may also be attributed to substrate conditions, as the cooler sites sampled were generally dominated by small cobble and sand & gravel, while the warmer streams had predominantly silt substrates. This variation may in part be due to the hydraulic conditions of the streams, with the warm spring fed streams (e.g., Golden Springs and Otamakokore Stream) having stable, moderate flow conditions year round allowing for sedimentation and accumulation of fine particles. In contrast, the cooler sites in the current study were predominantly catchment fed, and therefore were more likely to have more variable flow regimes and occasional high flow events which would remove fine silt sediments from the system. We suggest that in similar future research, samples be stratified among substrate types where possible. It is also apparent that the distribution of animals may be caused by substratum composition independently of temperature gradient (with bedrock strongly positively associated with Axis 2 in the CCA). The influence of substratum size and bed stability on macroinvertebrate communities from non-geothermal streams is well known (e.g., Quinn & Hickey, 1990; Hubert et al., 1996; Miserendino, 2001).

Substratum type and pH were inferred to be the dominant factors differentiating macroinvertebrate composition among sites on the three geothermally influenced streams used in the CCA analysis. However, the apparent relationships between these factors and invertebrates also may be confounded by co-variability between them. For example, Hakereteke Stream had predominantly bedrock and boulder substrata, and also extremely high acidity (<pH 3.5), whereas Golden Springs, with its lack of these hard substratum, was less acid (>pH 6). However, the absence of Mollusca (e.g., Physa sp., Glyptophysa variabilis Gray and Potamopyrgus antipodarum) from Hakereteke Stream and the unnamed stream at Waiotapu is likely to be caused more by low pH, due to dissolution of their carbonate shells by the acidity (Vincent & Forsyth, 1987), than to substrate type. Nevertheless, if pH alone was the most important factor causing variation in community composition, we would expect Hakereteke Stream (pH 3.1) to have a species composition more similar to Golden Springs (pH 6.9) than to Otamakokore Stream (pH 8.6). The similarity between the highly acidic and highly alkaline streams may be because departures from neutrality, whether they are more acidic or alkaline, may affect taxonomic composition similarly by removing sensitive taxa (e.g., EPT taxa). Reductions in taxonomic richness with decreases in pH is a general trend in acidified waters, whether they be due to the effects of organic acids (e.g., Weatherly & Ormerod, 1987; Winterbourn & Collier, 1987), acid rain (e.g., Sutcliffe & Hildrew, 1989; Mulholland et al., 1992), mining discharge (e.g., Smith et al., 1990; Jarvis & Younger, 1997) or combinations of these factors (e.g., Townsend et al., 1983; Winterbourn & McDiffett 1996). Many Ephemeroptera are particularly susceptible to acidic conditions (e.g., Mulholland et al., 1992; Smith et al., 1990), and adults of one species of Baetis have a behavioural avoidance of acid streams (Sutcliffe & Carrick, 1973). Few New Zealand studies have found substrate to be important in affecting species distributions (Death 2000). However, due to the stable flow conditions of spring fed streams, in addition to the stability of the other environmental conditions, competitive interactions among taxa may be greater thus enhancing the importance of substratum type.

Influence of nonindigenous species

An additional factor that we believe had an influence on species composition differences in Golden Springs relative to the other streams is the presence of nonindigenous species released from tropical aquaria. The presence of Melanoides tuberculata from the lower sites of Golden Springs, and its absence from all other samples, will have affected the relationships among samples in the CCA ordination; its presence in this stream, and not some of the others, would primarily be due to colinisation opportunity rather than environmental tolerances. Melanoides tuberculata also may change habitat conditions, for example, due to their peculiar burrowing activities (Livshits & Fishelson, 1983), in such a way that populations of native species are reduced (or enhanced). Similarly, it may reduce some species abundances due to being a strong competitor for resources in stable habitats (Pointier et al., 1991, 1994; see also Duggan, 2002 for further discussion). An additional force influencing community composition in Golden Springs may be the presence of the guppy (Poecilia reticulata), another nonindigenous aquarium release, which is known to feed on a range of small insects and crustaceans (McDowall, 2000). The invertebrate fauna in New Zealand geothermal habitats would normally be relatively free of predation pressure from fish. In New Zealand, native fish species are rarely recorded from geothermal waters, although the common bully (Gobiomorphus cotidianus McDowall) has been noted in the lower reaches of Waipahihi Stream in winter (Vincent & Forsyth, 1987). Nonindigenous aquarium species are apparently becoming common inhabitants of geothermal waters worldwide (e.g., Fuller et al., 1999), and potentially pose a significant threat to the integrity of native invertebrate communities in these waters. Discussion regarding the presence, ecology and potential impacts of M. tuberculata at Golden Springs is given by Duggan (2002).

Pritchard (1991) believed that insects encountered few constraints from water chemistry but are considerably affected by temperature in geothermal streams. It is clear, however, that not only temperature, or pH, but multiple stressors determine the distribution of macroinvertebrates within and among geothermal streams. As such, resource managers need to focus monitoring efforts more broadly than temperature and pH variability.

Acknowledgements

We thank J. Horrox and G. Croker for enumeration and identification of most of the macroinvertebrates, and V. Cassie-Cooper and C. Kilroy who provided algal identifications. A. Cody aided in site selection. Access was provided to the Orakei Korako tourist area. J. Kelly (Environment Waikato, The University of Waikato) aided in the field. K. Collier provided comments that improved the manuscript. This project was jointly funded by Environment Waikato and by NIWA NSOF augmenting program CO1X0017, and completed with funds from FRST programme CO5X0201.

Supplementary material

10750_2007_748_ESM.pdf (191 kb)
ESM (PDF 191 kb)

Copyright information

© Springer Science+Business Media B.V. 2007