Publication abstracts
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Algae-substrate interactions (including crevices as refuges)
Algae on snail shells and caddisfly cases
Crayfish and other crustaceans
Algae-substrate interactions (including crevices as refuges
Bergey E. A. 2008. Does rock chemistry affect periphyton accrual in streams? Hydrobiologia 614: 141-150.
Abstract
Stones of different rock types often accrue different amounts of periphytic algae. Although algal biomass may be positively related to stone roughness, the confounding role of rock chemistry is unclear. This independent effect of rock chemistry on benthic algae was tested using the nutrient-diffusing technique, by incorporating powdered stone, rather than nutrients, into the agar matrix. Rocks tested were sandstone, obsidian, schist, greywacke, pumice, gypsum, limestone, serpentine, and phosphorite. Petri-dishes containing powdered rock and agar, and covered with a permeable cellulose filter, were incubated in eight pools in a granitic stream. Algal biomass did not differ among any of the nine rock types and plain agar control, whereas biomass differed among the concurrently placed nutrient diffusing substrates (the stream was phosphorus-limited). Algal composition was more related to an upstream-downstream gradient (for filamentous algae) and pool-specific effects (deposition of fine sediment for diatoms) than rock chemistry. This minimal effect of rock chemistry may be caused by the low dissolution rate of stones.
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Bergey, E. A. and G. M. Getty. 2006. A review of methods for measuring the surface area of stream substrates. Hydrobiologia 556: 7-16.
Abstract
Surface area measurement is a common component of benthic research, especially in the quantification of chlorophyll. Multiple techniques are available and 10 are described: artificial substrates, area-specific sampling, geometric approximation, stone shape equations, foil wrapping, grids, stamps, wetted layer, particle layer, and planar area measurement. A literature search of 130 papers indicated the most common methods: using artificial substrates of known area, subsampling a specific area using a template or sampler, measuring stone dimensions and using an equation to derive area, and using the weight of foil wrapped on stones. Methods were compared using spheres of known area, smooth and rough granite stones, and plastic macrophytes. Most methods produced highly correlated measurements and accurately estimated surface area. The wetted layer method was sensitive to stone roughness and plant complexity, but may overestimate the area of complex surfaces. Replication of one method by 10 biologists indicated that individual differences in technique can affect surface area values. Factors to consider in choosing an appropriate method include ease of use, characteristics of the substrates (e.g., porosity and flexibility), fineness of scale in measuring area, and whether methods must be field-based or can include laboratory techniques.
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Bergey, E. A. 2006. Measuring the surface roughness of stream stones. Hydrobiologia 563: 247-252.
Abstract
Measuring the fine-scale heterogeneity of stones and other substrates is a challenge for benthic ecologists. I describe a method for measuring the roughness of stones that is based on the ratio of two surface area measurements: one that follows substrate contours and one based on a similar-sized modified spheroid. This roughness index is easily measured, assesses the entire surface of stones, and enables the measurement of replicate stones. Roughness measurements of 14 rock types demonstrated that values obtained were consistent with perceived roughness and porosity. Application of the roughness index to a published dataset produced a curvilinear relationship between stone roughness and the biomass of algae in roughness associated crevices.
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Bergey, E. A. and V. H. Resh. 2006. Differential response of algae on small streambed substrates to floods. The American Midland Naturalist 155: 270-277.
Abstract
The effect of floods and base flow on temporal variation in algal biomass on small smooth streambed stones and creviced sand-cases of the caddisfly (Insecta: Trichoptera) Gumaga nigricula was examined in Big Sulphur Creek in coastal Northern California. Replicates of stones and cases were sampled 34 times over a 14 mo period that included nine floods. Stones had 2/3the algal biomass of cases, based on chlorophyll a concentration. The lower algal biomass on caddisfly cases is consistent with this species’ burrowing behavior, which reduces algal biomass by abrasion and light limitation. Algal biomass on stones was reduced by floods and generally increased in the absence of floods. In contrast, neither floods nor extended base flow affected the pattern of algal biomass on caddisfly cases, and biomass on caddisfly cases often exceeded that on stones following floods. Streambed substrates with different textures may provide different degrees of disturbance-protection for benthic microalgae, and rougher substrates in streams may have more relict algae following floods than smoother substrates.
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Bergey, E. A. 2005. How protective are refuges? Quantifying algal protection in rock crevices. Freshwater Biology 50: 1163-1177.
Abstract
1. Refuges can be functionally important if they harbour sufficient organisms during disturbance to augment population recovery. I quantified the protection of stream algae in crevice refuges using the applied, severe disturbance of scrubbing. Scrubbing effectively removed visible surface algae, and algae remaining on stones were considered protected.
2. In a field experiment, substrata with different quantities of crevice (glass bottles; greywacke; schist; pumice) were incubated in a channelised stream. The possible influence of growth conditions was investigated concurrently; half of the substrata were suspended in the water column, the rest were placed on the bottom (providing differential access to grazers and exposing them to different flow conditions).
3. Rougher substrata had greater total algal biomass than smoother substrata; this pattern resulted from more algal biomass in crevices of the rougher substrata. Protection from scrubbing ranged from about 5% of total algal biomass on glass and greywacke to 80% on pumice. In contrast, algal biomass removed by scrubbing was similar among the experimental substrata. Suspended substrata had more chironomid grazers than those onthe bottom, and also greater algal biomass, possibly because of high algal concentrations in the chironomid retreats.
4. A survey of stones from three rivers supported the experimental results; namely, rough pumice protected more algae from scrubbing than did smoother greywacke.
5. In a separate experimental assay, there was no difference in algal growth on agar plates with and without added powdered rock substrata, suggesting that crevice characteristics and not substratum chemistry produced the differences in algal assemblages between rough and smooth surfaces.
6. Results indicate that rough stream stones may protect sufficient algae to augment their recovery in streams following disturbance.
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Bergey, E. A. 2004. Crevice refuges as a source for algal colonists of disturbance-affected substrates. Archiv für Hydrobiologie 161: 235-243.
Abstract
Algae protected in crevice refuges may be a source of colonists for denuded substrates following disturbance. This study explored the ability of algae that inhabit crevices in the sand-grain cases of the caddisfly Gumaga nigricula (Trichoptera: Sericostomatidae) to colonize denuded stream stones. In three laboratory experiments, caddisflies were introduced into sterilized flasks containing stream water and stream stones, and the flasks were incubated for three weeks. Algal colonization was assessed by measuring the chlorophyll-a concentration of the stones. Algal colonization of stream stones from caddisfly cases was successful, irrespective of time of association with the caddisflies (4 or 24 hrs) or whether the caddisfly cases were empty or occupied. This demonstration of algal colonization and establishment from crevice refuges to nearby substrates supports the concept that crevice-dwelling algae that are protected from disturbance can be a source of post-disturbance colonists that contribute to the high resilience of benthic algal assemblages.
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Bergey, E. A. and J. E. Weaver. 2004. The influence of crevice size on the protection of epilithic algae from grazers. Freshwater Biology 49: 1014-1025.
Abstract
1. This study investigated how the size of crevices might affect their effectiveness as refuges for diatom-dominated algal assemblages from the grazing minnow Campostoma
anomalum.
2. Crevice size was manipulated by making fired-clay substrates, using moulds to produce eight substrates with pits from 1.17 to 22.0 mm diameter. Non-pitted clay-stones and limestone were also tested. Cages were used to control the access of Campostoma to arrays of the 10 different algal-colonised substrates. The grazing treatments were: open and grazed, caged and ungrazed, and a grazed cage control. The experiment was replicated in eight large outdoor tanks. After 3 weeks, substrates were brushed and chlorophyll a concentrations of the removed algae and the algae remaining in pits were measured.
3. The experiment was field-validated by exposing arrays of substrates to grazing Campostoma in five pools of a limestone stream.
4. The clay-stone and limestone substrates accrued similar algal biomass and assemblages.
5. Smaller crevices provided more protection against grazing than larger crevices. Specifically, pits with openings smaller than 2 mm protected the enclosed algal assemblages in both the tank and field experiments. Larger pits provided less protection and pits over 7 mm in diameter were heavily grazed and may even be preferentially grazed by Campostoma.
6. None of the tested pit sizes were protective against larval chironomid grazers in the tank experiment, demonstrating that differences in the grazer size influence the effectiveness of crevice refuges.
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Bergey, E. A. 1999. Crevices as refugia for stream diatoms: Effect of crevice size on abraded substrates. Limnology and Oceanography 44: 1522-1529.
Abstract
This study explored the mechanisms by which crevices act as refugia for small algae during abrasive disturbances. Four substrates with different crevice features were subjected to three levels of abrasion in a stream-based experiment. Substrates were sand-grain caddisfly cases and three glass rod substrates that mimicked caddisfly cases in size and shape, as well as forming a gradient of larger crevices (i.e., smooth with no crevices, sanded with shallow pits, and scratched with deeper grooves). Substrates were subjected to no, low, or high abrasion levels during 18 d of incubation by pulling substrates through a sand–gravel mixture in floating enclosures that housed the experiment. Diatom density, relative biovolume, location in crevices, detritus accumulation, and filamentous algal density were compared among substrate types and abrasion levels. Across all abrasion levels, diatom and filamentous algal densities were higher on caddisfly cases than on all three glass rod substrates. Although abrasion greatly reduced overall diatom density, diatoms within crevices were largely protected. Crevice size influenced diatom size and composition. The small crevices of sanded rods contained primarily small diatoms of a single species (Achnanthidium minutissimum), whereas the larger crevices of scratched rods and caddisfly cases contained a greater range of diatom size and, consequently, greater species diversity. Detritus accumulated in all crevices, and accumulation increased with level of abrasion. Diatom biovolume decreased and location in crevices increased with the level of abrasion on the less textured smooth and sanded glass rods. Abrasion level had little effect on algal assemblages on caddisfly cases. This study demonstrates that crevices can be important refugia from abrasive disturbances, and that the size of crevices relative to organismal size can influence the protective value of crevices.
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Algae on snail shells and caddisfly cases
Abbott, L. L. and E. A. Bergey. 2007. Why are there so few algae on snail shells? The effects of grazing, nutrients and shell chemistry on the algae on shells of Helisoma trivolvis. Freshwater Biology 52: 2112-2120.
Abstract
1. Freshwater snails often lack visible growths of algae on their shells. We tested three possible mechanisms that may account for this (grazing, snail-derived nutrients and
chemical defences), using the ramshorn snail Helisoma trivolvis.
2. The experiments were carried out in floating plastic enclosures in a pond and comprised seven treatments. Grazing treatments were: a lone snail (ungrazed, as self-grazing does not occur), Helisoma with conspecifics, Helisoma with the co-occurring pond snail Physa sp., empty shells with Helisoma, and ungrazed empty shells. Nutrient effects were possible in all treatments with occupied shells (lone snail; Helisoma with conspecifics, and with Physa) versus absent in other treatments. Testing for chemical defences compared algae on fresh empty shells, weathered shells (outer organic periostracum layer absent) and boiled fresh shells (with denaturization of susceptible proteins).
3. Diatoms dominated algal assemblages on snail shells. Although the upright diatom Gomphonema gracile was abundant on all shells, it was dominant on the shells of snails housed with other snail grazers (either Helisoma or Physa).
4. Only the lone snail (nutrients but no grazing) showed higher algal biomass, so presumably any nutrient effect in the treatments with grazers was masked. Both Helisoma
and Physa were observed apparently grazing on Helisoma shells, and consequently algal biomass in multi-snail treatments was similar to that on empty shells. Scanning electron microscopy revealed that algal density was highest near the aperture of live snails, but not empty shells; this is consistent with a nutrient addition effect. There was no evidence of chemical defenses against algal growth.
5. In soft-bottomed freshwater habitats with abundant snails, shells of living snails provide nutrient-augmented substrata that may indirectly boost overall snail production.
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Bergey, E. A. and V. H. Resh. 1994. Effects of burrowing by a stream caddisfly on case-associated algae. Journal of the North American Benthological Society 13: 379-390.
Abstract
Diel burrowing behavior of Gumaga nigricula (McL.) (Trichoptera: Sericostomatidae) was investigated in Big Sulphur Creek (Sonoma Co., California). Most of the population burrows during the day and surfaces at night, a behavior that facilitates feeding on periphyton while retaining many of the advantages of burrowing (e.g., protection from predators). Because of daytime burrowing, case algae (primarily diatoms) are potentially light-limited by overlying substrate and, indeed, chlorophyll a concentrations on stream-collected cases and diatom colonization on cleaned cases increased dramatically when daytime burrowing was prevented. Cases and case-associated algae are normally abraded during burrowing; therefore experimental abrasion had little effect. However, after cases were cultured to accrue algae, experimental abrasion drastically reduced the accrued algae. Blue-green algal filaments and diatoms were removed from exposed surfaces but were protected in crevices between sand grains. Comparison of cases of different caddisfly genera showed a trend between abrasion level and case-associated algae. Under low abrasion, grazer-resistant diatoms occurred on exposed surfaces and upright diatoms occurred in crevices (e.g., Glossosoma and Discosmoecus cases). As abrasion increased, diatoms were lost from exposed surfaces, although they remained in crevices (e.g., Gumaga cases); with continuous burrowing, cases were nearly devoid of algae (e.g., Agarodes cases).
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Bergey, E. A. and V. H. Resh. 1994. Interactions between a stream caddisfly and the algae on its case: factors affecting algal quantity. Freshwater Biology 31: 153-163.
Abstract
1. Field experiments were conducted to examine interactions between larvae of the caddisfly Gumaga nigricula and the algae (primarily diatoms) located on their sand grain cases. Floating experimental enclosures were placed in sunlit pools of a California stream. Treatments applied to occupied cases, or to those from which caddisflies had been removed, included variations in grazer density, addition of nutrients, and modification of illumination using shade cloth.
2. Neither faecal-enriched agar in empty cases nor injections of faecal material into plugged cases affected case chlorophyll a concentration; injected nutrients (N and P), however, did increase chlorophyll a concentration. Faecal material may be nutrient poor, or nutrients may not be readily released. In addition, the relatively impermeable case wall may reduce the likelihood that nutrients from caddisflies reach the algae on the outer case surface.
3. Although a Gumaga larva may graze algae from its own case, grazing by conspecifics and the caddisfly Helicopsyche borealis causes a greater reduction in the chlorophyll a content of cases.
4. Chlorophyll a content of empty cases was decreased by experimental reduction of light. Because of shading associated with burrowing, chlorophyll a content of cases occupied by Gumaga was low and was unaffected by experimental light reduction.
5. Removal of Gumaga from its case results in rapid accrual of algae. Thus, the net effect of larval presence is to diminish the algal content of its case.
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Suren, A., B. J. Biggs, C. Kilroy, and L. Bergey. 2003. Benthic community dynamics during summer low flows in streams with contrasting enrichment: (1) Periphyton. New Zealand Journal of Marine and Freshwater Research 37: 53-70.
Abstract
Many foothill rivers in the eastern regions of New Zealand undergo severe reductions in flow during summer. These reductions are often exacerbated by abstractions for out-of-river uses. It has been observed that at such times some river ecosystems are more detrimentally affected by reduced flows than others. We hypothesised that the degree of degradation in river ecosystems during summer low-flows is dependent on a river’s enrichment status. We examined the effect of low flows on periphyton community dynamics in two Canterbury rivers of contrasting enrichment. Three runs in each river were sampled on four occasions over a summer low-flow period, during which discharge was amongst the lowest on record for these rivers. Percentage cover of major periphyton groups on the riverbed was estimated across five transects in each run, and periphyton was scraped from five replicate rocks per run to quantify taxonomic richness, community composition, and chlorophyll a biomass. Periphyton communities in each river were quite different. Diatoms with a low biomass dominated the communities in the unenriched Okuku River. These communities did not change significantly in composition or biomass over the 6-week study period. Conversely, in the enriched Waipara River, the communities had a high biomass and there was a succession in dominant taxa from diatoms and cyanobacteria to filamentous green algae over summer. This resulted in the Waipara River exceeding guidelines for the maintenance of in-river recreational and fisheries values, whereas the Okuku River did not. Thus, degree of enrichment should be taken into account when assessing in-river flow requirements. We suggest that enriched rivers will be more sensitive to flow abstraction (i.e., they will become more degraded), and so may require higher minimum flows to maintain river health, than unenriched rivers.
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Suren, A., B. J. Biggs, M. Duncan, and L. Bergey. 2003. Benthic community dynamics during summer low flows in streams with contrasting enrichment: (2) Invertebrates. New Zealand Journal of Marine and Freshwater Research 37: 71-83.
Abstract
We examined the effects of summer lowflow on invertebrate communities in two New Zealand rivers of contrasting enrichment and associated periphyton development. Quantitative benthic samples were collected and hydraulic measurements made from three runs in each river over a 6-week period. Although hydraulic conditions and time since last flood disturbance were similar in both rivers, invertebrate communities were dissimilar. This dissimilarity reflected differences in periphyton communities within each river. The invertebrate community in the low enrichment river (Okuku River) was dominated by high numbers of “clean-water” insect taxa, and this community changed little over time. Periphyton biomass was low here, and the community was composed of diatoms. Major changes occurred to the invertebrate community in the high enrichment river (Waipara River) over the summer, where the relative abundance of dominant invertebrate taxa changed from insects and snails to ostracods. Periphyton biomass was high in this river, which was originally dominated by diatoms and cyanobacteria but which became dominated by filamentous green algae. Changes to invertebrate communities were linked to this increase in filamentous green algae. Multiple regression analysis showed that changes to the invertebrate community in the enriched river were strongly correlated with the number of days at low flow, suggesting that successional processes occurred during the low-flow period. Such changes may occur naturally during summer low-flows in enriched rivers or could be exacerbated if velocities are reduced by abstraction. Our results suggest that a river’s degree of enrichment should be considered when assessing minimum flows for consents or for the development of flow management guidelines.
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Bergey, E. A. 1995. Local effects of a sedentary grazer on stream algae. Freshwater Biology 33: 401-409.
Abstract
1. Larvae of the sedentary aquatic caterpillar Petrophila confusalis (Walker) construct silken retreats around which they feed; outside these clearly demarcated grazed areas, stream algae are exposed to a variety of mobile grazers. Comparisons of the algal community inside and just outside grazed zones were made for third- and fifth-instar Petrophila in the South Fork of the Eel River, California.
2. Densities of both the filamentous macroalga Cladophora and diatom assemblages were significantly reduced within the grazed areas during both larval instars. Grazing of diatoms was taxonomically non-selective.
3. In spring, the grazed zones were relatively large (mean = 22.7 cm2) and visibly increased epilithic spatial patchiness.
4. Per cent composition of diatom assemblages inside and outside the grazed areas differed during the third instar but not during the fifth instar. During the third instar, the grazed zone contained more Synedra ulna (a common immigrant) and less Gomphonema olivaceum (a late-successional species).
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Bergey, E. A., C. A. Boettiger, and V. H. Resh. 1995. Effects of water velocity on the architecture and epiphytes of Cladophora glomerata (Chlorophyta). Journal of Phycology 31: 264-271.
Abstract
The architecture of the filamentous green alga Cladophora glomerata (L.) Kütz. and the composition of this alga's epiphytes [primarily the diatoms Epithemia turgida (Ehrenb.) Kütz., Epithemia sorex Kütz., and Cocconeis pediculus Ehrenb.] were examined in different velocity regimes. After transferring algal-bearing cobbles among velocities, the effects of changes in velocity were also examined. Cladophora branching pattern did not initially differ among slow, medium, and fast velocities, indicating that stable water velocities did not affect branching pattern. Two weeks after cobble transfer, Cladophora in fast velocity had fragmented more (i.e. had fewer filaments and fewer branch points per length of filament and had a higher percentage of unbranched filaments) than Cladophora in slow velocity. Fragmentation was greatest in tufts moved from slow velocity, suggesting velocity-associated differences in susceptibility to breakage. Epiphytic assemblage composition differed among slow, medium, and fast velocities and between locations on the filament (base and apex). Cocconeis pediculus dominated where exposure to high velocity was greater (filament apices in medium and fast velocities), whereas the Epithemia spp. dominated where lower velocities occurred (filament bases in all velocities and apices in slow velocity). Two weeks after the cobble transfer, the translocated diatom assemblages had changed and the original pattern of diatom distribution was restored.
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Bergey, E. A., S. F. Balling, J. N. Collins, G. A. Lamberti and V. H. Resh. 1992. Bionomics of invertebrates within an extensive Potamogeton pectinatus L. bed of a California marsh. Hydrobiologia 234: 15-24.
Abstract
Fourteen samples of sago pondweed (Potamogeton pectinatus L.) and associated invertebrates were collected every two weeks over a single season of plant growth in a large monospecific pondweed-bed located in Coyote Hills Marsh (Alameda Co., California, USA), using pull-up samplers that collect plants, epiphytic macroinvertebrates, and microcrustaceans throughout the water column. The macro-invertebrate fauna was dominated by insects, primarily chironomids. Semi-aquatic neustonic taxa, including an aphid and a springtail, were common; this is in contrast with most aquatic plant-invertebrate studies, in which neustonic insects are seldom collected because of sampling bias. Over the entire season, P. pectinatus biomass and the densities of four insect taxa (Anopheles spp. mosquitoes, Hydrellia sp. brineflies, Ademon sp. parasitic wasps, and coenagrionid damselflies) were significantly correlated. These correlations resulted from both similar overall phenologies of the plant and each of the insect taxa, and ecological relationships in which P. pectinatus provides either a specialized habitat or food source. macroinvertebrate numbers were highest in mid-summer, when P. pectinatus forms a dense floating canopy; microcrustaceans were more common during plant senescence in early autumn. Individuals of some taxa may be distributed in proportion to plant biomass; this occurred commonly in damselflies, perhaps as a result of territoriality in these nymphs.
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Bergey, E. A. and J. V. Ward. 1989. Upstream-downstream movements of aquatic invertebrates in a Rocky Mountain stream. Hydrobiologia 185: 71-82.
Abstract
Simultaneous collections of drift and organisms moving either upstream or downstream in association with the substrate were made using a specially designed sampler. Samples were taken in a diel series along a transect across the study riffle of a Colorado foothills stream on six dates over an annual cycle. In addition to longitudinal movements, taxonomic composition and diel periodicity were evaluated. The insect-dominated fauna showed a net downstream displacement. Only the caddisflies Helicopsyche borealis and Hesperophylax occidentalis exhibited net upstream movement, primarily a result of low drift frequencies. The taxonomic composition of moving invertebrates differed from that of the benthos. Drift resembled downstream moving substrate-associated invertebrates in composition, but differed from that of the upstream directed fauna. Taxa collectively exhibited four types of diel patterns: 1) similar downstream (drift and substrate-associated movements) patterns, which generally differed from the upstream pattern; 2) similar benthic (upstream and downstream) patterns, which differed from that of drift; 3) aperiodic patterns; and 4) independent patterns for each type of directional movement. Analysis of size classes based on head capsule width for the mayfly Baetis tricaudatus showed significantly smaller size in stationary individuals compared with moving individuals in the population and revealed that nymphs moving during the day were smaller than those moving at night.
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Thorp, J. H. and E. A. Bergey. 1981. Field experiments on responses of a freshwater benthic macroinvertebrate community to vertebrate predators. Ecology 62: 365-375.
Abstract
We examined the seasonal importance of vertebrate predators in potentially regulating the abundance and diversity of the benthic macroinvertebrates in the littoral zone of a soft-bottom reservoir that receives thermal effluent from a nuclear production reactor. Thirty-six predator (fish and turtle) exclusion cages (4 m^2) were placed in shallow water at six locations along a thermal gradient in Par Pond, a 1100-ha cooling reservoir on the Savannah River Plant near Aiken, South Carolina, USA. An additional 36 control plots (4 m^2) were also set up. Cages were in place during three, 3-mo test periods beginning in September 1977. Estimates of benthic density, taxon richness, and distribution within functional groups (defined by feeding mechanism) were calculated for each test period. Effects of temperature on predator-prey relationships were also determined. Experimental results of this study suggest that vertebrate predation was not the fundamental parameter organizing the benthic macroinvertebrate community in the littoral zone of this reservoir. Neither taxon richness nor density of total macroinvertebrates was conclusively related to predator treatment. Relationships between predator treatment and community response (changes in density and taxon richness) were generally unaffected by either plot locality, temperature fluctuations from thermal effluent, or seasonal changes. When data from caged and control plots were pooled, however, both location and water temperature individually had direct impacts on the benthic community. From our results and other field studies we hypothesize that individual species of @`keystone@' benthic predators (Paine 1969b) do not occur in the littoral zone of freshwater lentic environments with soft bottoms. This hypothesis is based on the following four arguments. First, environmental heterogeneity should reduce predator efficiency relative to that found in rocky intertidal systems where keystone predation may be present. Second, relative food web complexity should reduce the community importance of an individual predator species. Third, the apparent relatively greater resource partitioning of space and food in the freshwater littoral zone hinders monopolization of rate-limiting environmental resources by a single dominant prey species. Fourth, the effects of predation may not be extensive enough in time or area to provide sufficient resource space (and thus food) for exploitation by fugitive species. Possible regulation by a guild of predators and cases where the general hypothesis might be falsified are discussed.
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Thorp, J. H. and E. A. Bergey. 1981. Field experiments on interactions between vertebrate predators and larval midges (Diptera: Chironomidae) in the littoral zone of a reservoir. Oecologia 50: 285-290.
Abstract
A field experiment was designed to test a frequent assumption in the literature that vertebrate predators (in this case, fish and turtles) are capable of regulating the seasonal abundance and diversity of benthic communities in the littoral zone of lentic environments. Effects of thermal effluents from a nuclear reactor on predator-prey relationships were also examined. Benthic samples were removed after each of three, 3-month test periods from 36 predator exclusion cages (4m2) and 36 control plots located along a thermal gradient in Par Pond, a 1,100 ha freshwater reservoir in the southeastern United States.
Results of our field experiments provide little evidence to suggest that either a single 
keystone
species or vertebrate predators as a group were capable of regulating the abundance, diversity or productivity of chironomids in Par Pond. The relationship between predator treatment and community response (changes in density and species richness) was generally unaffected by either plot location or temperature fluctuations. When data from caged and control plots were pooled, however, both location and water temperature individually had significant impacts on the chironomid community. Alternative hypotheses are proposed to explain the lack of regulatory control of the benthic community by individual species or guilds of predators.
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Bergey, E. A., W. J. Matthews, and J. E. Fry. 2008. Springs in time: fish faunal changes in springs over a 20-year interval. Aquatic Conservation: Marine and Freshwater Ecosystems 18: 829-838.
Abstract
1. Despite the range of threats to springs and the number of spring-endemic species, studies of temporal changes of the fauna of springs have been little reported. Changes in the fishes of 22 Oklahoma (USA) springs were compared among surveys in 1981, 1982, and 2001.
2. Twenty-year assemblage differences were correlated with physical alteration of specific springs and stocking of native fishes, which was made possible by past habitat changes that produced pools. Physical alteration of springs is a major ongoing threat to Oklahoma springs.
3. Variation in spring fish assemblages among the three surveys was apparently affected by fish movement in and out of springs, and the greater rain-induced connectivity between springs and streams during one year.
4. Although flow reduction is a commonly cited threat to springs, there was little evidence of flow reduction impacts in this study because Oklahoma springs may have been impacted prior to 1981 and high-flow springs, which most often contain fish, were in areas with low groundwater water use.
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Gray, L. J., J. V. Ward, R. J. Martinson and E. A. Bergey. 1983. Aquatic macroinvertebrates of the Piceance Basin, Colorado: Community response along spatial and temporal gradients of environmental conditions. Southwestern Naturalist 28: 125-135.
Abstract
A long-term study of the aquatic biotopes of the Piceance Basin has enabled analyses of macroinvertebrate communities along spatial (downstream) and temporal (year-to-year) gradients of environmental conditions. Cluster analysis indicates four distinct aquatic habitat types: spring sources, springbrooks, and the middle and lower reaches of Piceance Creek. Spatial differences in temperature and flow constancy influence habitat stability with respect to substrate, degree-day distribution, ice conditions, and the distribution and abundance of aquatic macrophytes. Despite great differences in thermal patterns, total annual degree-days were ca. 3000 in all four habitat types. The principal energy source for macroinvertebrates in autochthonous detritus. Trophic structure shifts from shredders-collectors-scrapers in the headwaters to collectors-predators in lower reaches. Year-to-year variations in discharge altered the density and composition of macroinvertebrates, and were reflected in the thermal regimes at mainstream locations. Data suggest that groundwater discharge from upper reaches is important in maintaining the structural and functional integrity of aquatic systems in the Piceance Basin.
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Nimmo, D. W. R., R. W. Johnson, M. A. Preul, R. W. Pillsbury, J.R. Self, and E. A. Bergey. 2006. Determining site-specific toxicity of copper to daphnids and fishes in a brown-water ecosystem. Journal of Freshwater Ecology 21: 481-491.
Abstract
The question in this study was the degree of influence that dissolved organic carbon (DOC) had on the toxicity of copper to aquatic species in the Swamp Creek, Wisconsin watershed. We conducted the study in response to a possible underground copper and zinc-sulfide mine about two kilometers upstream of the Mole Lake Band of Lake Superior Chippewa Indian Reservation. Copper was added to Swamp Creek water with DOC then tested for toxicity using a daphnid Ceriodaphnia dubia, larval fathead minnows Pimephales promelas, and larval walleye Stizostedion viterum. Parallel testing was conducted in laboratory-prepared reconstituted (Recon) water with copper added but no DOC. Results showed the toxicity of copper to all species in Swamp Creek water, which contained between five and 18 mg/L DOC, was significantly lower than in Recon water with no DOC. In successive tests, by experimentally reducing the DOC in Swamp Creek water and using C. dubia as the test species, we found as the DOC decreased, the toxicity of copper increased. Although we cannot rule out some influence of pH, hardness and alkalinity, we believe that in the Swamp Creek watershed that the DOC is the primary factor in reducing the toxicity of copper and should be the principal focus where site-specific criteria involving copper and perhaps other metals are being considered.
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Nimmo, D. W. R, M. A. Preul, C. J. Castle, R. W. Pillsbury, J. R. Self, and E. A. Bergey. 2003. Effects of excess copper on the growth of wild rice (Zizania palustris) seedlings tested in reconstituted and natural waters. Environmental Management 32: 466-475.
Abstract
Dissolved copper was toxic to wild rice (Zizania palustris) seedlings when exposed in water from the seed collection site of Swamp Creek, Crandon, Wisconsin, USA, and in laboratory-prepared artificial or reconstituted water. Seeds for the study were harvested, then held through a portion of dormancy, in Swamp Creek. After 60 days they were shipped to a laboratory, chilled, and tested with copper after germination. The end point of the tests was net gain in wet weight of the seedlings; additionally, a pronounced reduction in root development was observed. Using measured concentrations, the lowest no-observable-effect concentration (NOEC) in our study was 37 μg/liter in Swamp Creek water and the lowest-observable-effect concentration (LOEC) was 59 μg/liter. However, it appeared that there was a point at which concentrations of copper above 400 μg/liter did not result in any measurable effect or exhibit a definitive dose–response. Because the results in Swamp Creek water were more relevant to the possibility of local metals additions and the association of reduced seedling growth by copper was more powerful in this water, we derived an equation to express the relationship between copper concentration and toxicity for Swamp Creek water. As an example, we would expect a 3.0% reduction in seedling growth at 5.0 μg/liter copper. Seedling roots were particularly affected and the resultant plants may be less well anchored and more susceptible to dislodging than plants not exposed to copper. Further refinement of the methodology may be used to address effects of other contaminants impacting rice beds in North America.
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Kilroy, C., Sabbe, K., E. A. Bergey, W. Vyverman, and R. Lowe. 2003. New species of Fragilariforma (Bacillariophyceae) from New Zealand and Australia. New Zealand Journal of Botany 41: 535-554.
Abstract
Two new species of Fragilariforma Williams & Round, F. cassieae sp. nov. and F. rakiuriensis sp. nov., are described from material from New Zealand and Tasmania. The new species are similar in shape and size to Fragilariforma lata (Cleve-Euler) Williams & Round and F. hungarica var. tumida (Cleve-Euler) Hamilton but are separated on the basis of areola and stria density, and shape. We discuss the relationships of the new species within the genus Fragilariforma, and also discuss the possible existence of further related taxa in the material examined, based on differences in morphological progression during cell division. The two species described represent further evidence of a higher degree of endemism in Southern Hemisphere freshwater diatoms – and particularly in New Zealand and Tasmania (Australia) – than has previously been assumed.
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Sabbe, K., K. Vanhoutte, R. L. Lowe, B. J. F. Biggs, E. Bergey, S. Francouer, D. Hodgson, and W. Vyverman. 2001. Six new Actinella (Bacillariophyta) species from Papua New Guinea, Australia and New Zealand: further evidence for widespread diatom endemism in the Australasian region. European Journal of Phycology 36(4): 321-340.
Abstract
Examination of sediment samples from oligo-and dystrophic ponds, lakes and streams in Papua New Guinea, Australia and New Zealand revealed a hitherto unknown diversity of the diatom genus Actinella Lewis. Six new species are proposed, viz. Actinella aotearoaia sp. nov., A. giluwensis sp. nov., A indistincta sp. nov., A. muylaertii sp. nov., A. parva sp. nov. and A. pulchella sp. nov. All species are heteropolar, both in girdle and valve view. Novel information on the genus Actinella includes the observations of two ribbon-shaped, valve-appressed plastids in A. aotearoaia and A. pulchella, and the presence of long mucilage stalks in A. aotearoaia. It is argued that, despite recent proposals to reduce the genera Actinella and Desmogonium Ehrenberg to the rank of subgenera of Eunotia, they should be kept separate until the taxonomic significance of their distinctive morphological features (such as heteropolarity) is fully assessed. The new species appear to be endemic to Australasia and have distinct biogeographies within this region. Except for A. aotearoaia, all species are present in Tasmania; A. indistincta and A. pulchella have also been found in New Zealand (Stewart Island). A. aotearoaia is common in several localities in New Zealand but was also found near Sydney on the Australian mainland. Actinella giluwensis has only been observed in material from Papua New Guinea. The record of A. punctata for the latter country constitutes the first confirmed record for this species outside North America and Europe. The discovery of the new Actinella species again confirms the importance of the Australasian region as a major centre of microalgal biodiversity and endemism.
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Bergey, E. A., J. T. Cooper, and B. C. Phillips. 2010. Substrate characteristics affect colonization by the bloom-forming diatom Didymosphenia geminata. Aquatic Ecology 44: 33-40.
Abstract
The long-stalked Didymosphenia is capable of forming large blooms and is expanding its range. To better understand the colonization dynamics of this species, we investigated the role of substrate characteristics—rock roughness and biofilm condition—on Didymosphenia colonization in a montane Colorado stream. Rocks differing in roughness (shale and sandstone) were treated to manipulate the diatom-dominated biofilm by scrubbing or submersion in 30% hydrogen peroxide. Initial chlorophyll concentration differed among rock types (sandstone > shale) and biofilm treatments (untreated > scrubbed > hydrogen peroxide-treated). Rocks were placed in a Didymosphenia bloom area for 8 days. More Didymosphenia colonized the rougher sandstone than the smoother shale, and more colonized stones with intact biofilms than stones with reduced biofilms (intact > scrubbed > hydrogen peroxide). These results suggest that rougher stones may be targeted for surveillance for new populations and that the colonization of intact biofilms is consistent with Didymosphenia’s habitat in regulated rivers, where biofilm-scouring spates may be suppressed.
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Bergey, E. A., J. T. Cooper, and C. R. Tackett. 2009. Occurrence of the invasive diatom Didymosphenia geminata in southeast Oklahoma. Publications of the Oklahoma Biological Survey 9:13-15.
Abstract
Diatoms are a major food source for aquatic grazing snails and insects, thereby contributing to aquatic food webs. Diatoms are microscopic and are seldom visible; an exception is colonies of Didymosphenia geminata. Didymosphenia secrete long extracellular stalks that can form mats several centimeters thick. Mats occur on single rocks or may cover areas of a streambed. Recently, this species has expanded from its original boreal or alpine, oligotrophic habitat and is appearing in blooms on rocky habitats below dams in regulated rivers. In April 2009, Didymosphenia geminata was collected in the Mountain Fork downstream of Broken Bow Lake, where colonies up to 13 cm in diameter were observed. This is the first record of this species in Oklahoma and is the southernmost known occurrence in the United States. Oklahoma is outside the modeled area of potential occurrence and the artificially low temperature maintained for the trout fishery likely enabled the establishment of Didymosphenia. Didymosphenia mats are unsightly, alter benthic communities, and may affect fish growth, condition, and spawning. In response to the establishment of Didymosphenia, public education, a surveillance program, and local ecological studies are recommended.
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Crayfish and other crustaceans
Robison, H. W., B. G. Crump, C. T. McAllister, C. Brummett, and E. A. Bergey. 2009. Distribution, life history aspects, and conservation status of the Mena crayfish, Orconectes (Procericambarus) menae (Decapoda: Cambaridae). Proceedings of the Oklahoma Academy of Science 89: 47-55.
Abstract
The Mena crayfish, Orconectes (Procericambarus) menae (Creaser)is an endemic crayfish of the Ouachita Mountains physiographic province of Oklahoma and Arkansas. Originally described from a tributary of the Irons Fork of the Ouachita River at Mena, Polk County, Arkansas, O. menae has now been reported from additional sites in Polk and Montgomery counties, Arkansas, and LeFlore and McCurtain counties, Oklahoma. This crayfish inhabits areas under rocks and rubble both in swifter, shallow runs and in shallow pool margins of clear streams (stream order 1-3) where rocks and rubble frequent. Form I males were found in mid-March to June. We document several new localities for O. menae as well as providing a summation of all known localities for the species. In addition, various aspects of the biology of O. menae are discussed. We recommend a conservation status of threatened for O. menae.
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Jones, S. N. and E. A. Bergey. 2007. Habitat segregation in stream crayfishes: implications for conservation. Journal of the North American Benthological Society 26: 134-144.
Abstract
Three-quarters of the world’s crayfish fauna are found in the US and Canada. Small natural ranges, habitat disturbance, and introduced crayfish species threaten many species, and nearly ½ are imperiled. Naturally small ranges are considered the leading factor for crayfish vulnerability to loss, yet species with small ranges have received little research attention. Orconectes saxatilis is a rare crayfish species with a range restricted to the upper Kiamichi River watershed in southeastern Oklahoma. We examined the distribution, habitat use, and life-history characteristics of O. saxatilis and 2 sympatric crayfish species in the upper Kiamichi River watershed to determine factors that might limit its distribution. Surveys for O. saxatilis expanded its known range and confirmed its restriction to tributaries of the upper Kiamichi River. Orconectes saxatilis showed a strong affinity for riffles, contrary to previous data, whereas Orconectes palmeri longimanus, a regionally abundant sympatric species, showed an equally strong affinity for pools. Tributaries of the upper Kiamichi River are intermittent, and surface flow typically ceases in late summer and early autumn. During dry periods when habitat was limited to disconnected pools, O. saxatilis aestivated beneath cobbles and boulders in dry riffles. The strict use of riffles by O. saxatilis and its need for habitat conducive to aestivation probably contribute to its small range and put this species at risk. Year-round monitoring of populations susceptible to imperilment is needed to make informed conservation decisions. For O. saxatilis and other imperiled crayfish species, conservation efforts should emphasize identification of habitat types required for species survival, avoiding alterations to those habitat types, and protecting natural flow regimes.
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Lewis, J. J., G. O. Graening, D. B. Fenolio, and E. A. Bergey. 2007. Caecidotea mackini, new species, with a synopsis of the subterranean asellids of Oklahoma (Crustacea: Isopoda: Asellidae). Proceedings of the Biological Society of Washington 119: 563-575.
Abstract
A survey of cave and spring fauna in Oklahoma resulted in the discovery of Caecidotea mackini, new species, which is described from specimens collected in Long's Cave, Delaware County. Within the hobbsi group of the genus Caecidotea, C. mackini belongs to a subset of nine species termed the tridentata assemblage. All nine are subterranean, but several retain vestigial eyes or pigmentation. Correlated with zoogeographic and climatic evidence, the invasion of groundwaters by an epigean progenitor during the middle to late Tertiary is suggested. Besides C. mackini, new records for C. macropropoda, C. acuticarpa, C. stiladactyla, C. steevesi, C. ancyla, C. antricola, C. adenta, and C. simulator expand the known ranges of these cryptic species. With the recognition of two patterns of fourth pleopod morphology in C. acuticarpa, the species specificity of this character has become questionable. Although previously used to differentiate C. simulator and C. steevesi, further splitting or synonymy based on this pleopod anatomy is reserved until a better understanding of its differentiation is achieved.
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Graening, G. O., J. R. Holsinger, D. B. Fenolio, E. A. Bergey, and C. C. Vaughn. 2006. Annotated checklist of the amphipod crustaceans of Oklahoma, with emphasis on groundwater habitats. Proceedings of the Oklahoma Academy of Science 86: 65-74.
Abstract
Summarized here for the first time are all known records of amphipod crustaceans in
Oklahoma. Data sources consisted of a thorough literature review as well as unpublished state, county, and site records by the authors and contributors to regional databases. Fourteen species in four families are currently recognized: Allocrangonyctidae (Allocrangonyx pellucidus); Crangonyctidae (Bactrurus hubrichti, three species of Crangonyx, and five species of Stygobromus); Gammaridae (three species of Gammarus); and Hyalellidae (Hyalella azteca). This list includes two species endemic to the Arbuckle Mountains and another species endemic to Mayes County. The majority of Oklahoman amphipods are closely associated with groundwater or cave habitats and seven species are found only in these habitats. Current global distributions and conservation statuses are summarized, and new rarity rankings are suggested.
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Jones, S. N., E. A. Bergey, and C. A. Taylor. 2005. Update to the checklist of Oklahoma crayfishes. Proceedings of the Oklahoma Academy of Science 85: 43-46.
Abstract
The crayfish fauna of Oklahoma was recently summarized by a checklist that included new state records. These state records were based on recent surveys and on museum records. In this paper, the 2004 checklist is updated by adding one species (Procambarus dupratzi), subtracting another (Cambarus setosus), and listing earlier records of Orconectes deanae and O. macrus that were not considered in the 2004 checklist. The known crayfish fauna of Oklahoma remains at 28 species.
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Taylor, C. A., S. N. Jones, and E. A. Bergey. 2004. The crayfishes of Oklahoma revisited: new state records and checklist. The Southwestern Naturalist 49: 250-255.
Abstract
Examination of museum records and field observations have included 4 new records for species of crayfish in Oklahoma (Cambarellus puer, Orconectes deanae, O. lancifer, and O. macrus) and a new drainage record for O. neglectus neglectus. These records bring the number of crayfish known in Oklahoma to 28 and emphasize the importance of revisiting aquatic habitats in regions that have been visited previously. Such records can help in determining the conservation status of poorly known taxonomic groups.
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