Elizabeth A. Bergey

A Review of Methods for Measuring the Surface Area of Stream Substrates

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.

Habitat segregation in stream crayfishes: implications for conservation

Abstract Three-quarters of the worlds 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.

New species of Fragilariforma (Bacillariophyceae) from New Zealand and Australia

Abstract Two new species of Fragilariforma, F. cassieae sp. nov. and F. rakiuriensis sp. nov., are described from material from New Zealand, with reference to populations found in Australia. The new species are similar in shape and size to Fragilariforma lata and F. hungarica var. tumida but are separated on the basis of areola and stria density, and shape. The distinguishing features of F. cassieae are a rhombic shape with narrow protracted ends, and striae with prominent areolae. In F. rakiuriensis, small forms are similar in shape to F. cassieae, but larger cells are elongated with a constriction at the centre. The striae are more widely spaced than in F. cassieae with a slightly irregular appearance and fine, closely spaced areolae. 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, or marked shifts in form in their 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 Australia, than has previously been assumed.

Effects of Burrowing by a Stream Caddisfly on Case-Associated Algae

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).

Exploring the status of motility, lipid bodies, deformities and size reduction in periphytic diatom community from chronically metal (Cu, Zn) polluted waterbodies as a biomonitoring tool.

Taxonomic metrics of diatoms are regularly used for aquatic biomonitoring, including testing for heavy metal stress. In contrast, non-taxonomical parameters in diatoms are rarely assessed. In the present study, taxonomical features of diatoms, such as cell density, chlorophyll a, species richness, and the Shannon index, were reduced at severely polluted (Cu, Zn) sites compared with less polluted sites. Some non-taxonomic parameters, such as, lipid bodies (LBs) number and size, carotenoid/chlorophyll a ratios, and frustule deformities were elevated at the severely polluted sites in comparison to the less polluted sites in both the areas. Cell size diminished and motility changed from smooth to erratic with increasing Cu and Zn pollution. Some of these behavioral and physiological changes were easily assessed (e.g., motility and formation of LBs), while morphological alterations (cell wall deformities and changes in cell size) requires more time and human expertise in diatom taxonomy. These parameters were consistent across metal concentrations of sediments, in the water, and in cells. The results illustrate the usefulness of these non-taxonomic parameters in biomonitoring, especially as early warning tools for ecotoxicity assessment and testing for sublethal effects. Some of these parameters, such as cell size and cell wall deformities, can be easily incorporated into traditional protocols, although LBs and motility metrics will require more effort.

Measuring the surface roughness of stream stones

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 data set produced a curvilinear relationship between stone roughness and the biomass of algae in roughness-associated crevices.

The use of diatoms in ecotoxicology and bioassessment: Insights, advances and challenges

Diatoms are regularly used for bioassessment and ecotoxicological studies in relation to environmental and anthropogenic disturbances. Traditional taxonomical diatom parameters (cell counts, biovolume estimates, species richness, diversity indices and metrics using sensitive and tolerant diatom species) are regularly used for these studies. In the same context, very less focus was given on new endpoints of diatoms (life-forms, nuclear anomalies, alteration in photosynthetic apparatus shape, motility, lipid bodies, size reduction and deformities), in spite of their numerous merits, such as, their easiness, quickness, cheapness, global acceptation and no especial training in diatom taxonomy. In this review we analyzed 202 articles (from lab and field studies), with the aim to investigate the bioassessment and ecotoxicological advancement taken place in diatom research especially in terms of exploring new endpoints along with the traditional taxonomical parameters in a perspective which can greatly enhance the evaluation of fluvial ecosystem quality for biomonitoring practices.

Environmental and biological factors affect desiccation tolerance of algae from two rivers (Thailand and New Zealand) with fluctuating flow

Abstract Flow variation associated with hydropower production causes periodic exposure of zones along the banks of regulated rivers. These zones have reduced algal biomass and lower productivity. We investigated whether algal assemblages in regulated rivers differed in tolerance to aerial exposure because understanding such tolerance could be used to alter water releases to improve downstream productivity. In field experiments, we tested algal tolerance to aerial exposure in 3 assemblages: green filamentous and cyanobacterial assemblages in Thailand and a mixed (filamentous green + cyanobacteria) assemblage in New Zealand. Algae-bearing stones were exposed at night, during the day (in sun or shade, with or without simulated rain), or continuously, or were continuously submerged (with a handling control). Exposure reduced cyanobacterial chlorophyll a, and reduction was greater with day than with night exposure. Mixed algal assemblages showed a similar pattern in chlorophyll a, but ash-free dry mass (AFDM) did not change (bleached algae remained). In contrast, green filamentous algae survived better when exposed than when submerged, and when exposed during the day than at night. Snails consumed green filamentous algae, and submersion resulted in high grazing loss of filamentous algae but not cyanobacteria. Grazing pressure was presumably lower at night during water release. For cyanobacteria, shade and rain slightly increased chlorophyll a retention. For filamentous green algae, shade had no effect, and rain was beneficial in the shade but not the sun. Our experiments demonstrated an interaction among variable hydraulic conditions, activity of grazing snails, and availability of grazing-susceptible algae. A longer wet–dry cycle, daytime water release, and a shaded riparian zone reduced aerial exposure effects on algal assemblages, indicating that water releases can be regulated to improve productivity in the downstream exposed zone.

Trading in snails: plant nurseries as transport hubs for non-native species

The plant trade provides a major mechanism for the long-distance dispersal of land snails, including slugs, which have low natural mobility. Whereas inspections at national borders intercept many in-coming snails, dispersal within countries is much less well regulated and documented. To investigate the role of plant nurseries as a source for the distribution of non-native invertebrates, particularly land snails, we surveyed snails in 28 nurseries in Oklahoma (United States) and compared our survey with similar surveys worldwide. We found 36 taxa, including 16 species not native to the region; 11 of these were new state records. Snail species richness increased with increasing outside area of snail-appropriate habitat, but not with enclosed greenhouse area. Species composition was similar among nurseries and Oklahoma nurseries shared several species with nurseries in Hawaii and Europe. Appropriate models for the dispersal of snails via plant nurseries are the transport hub model (snails moving as contaminants on plants coming into and leaving nurseries) and, for snail populations already established in nurseries, the stratified diffusion model (contamination of plants by snails within nurseries, followed by long-distance jumps as plants are sold and transported). Potted plants are portable habitats that protect snails from detection, pesticides and desiccation. Dispersing snails may survive in urban habitats, where mulching and watering may ameliorate hot, dry summers and cold winters.

CRAYFISHES OF OKLAHOMA REVISITED: NEW STATE RECORDS AND CHECKLIST OF SPECIES

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.