Single Assemblage Research Articles

Diatoms as indicators of isolated herbaceous wetland condition in Florida, USA

Abstract Benthic, epiphytic, and phytoplanktonic diatoms, as well as soil and water physical–chemical parameters, were sampled from 70 small (average 0.86 ha) isolated depressional herbaceous wetlands located along a gradient of human disturbance in peninsular Florida to (1) compare diatom assemblage structure between algal types; (2) develop biological indicators of wetland condition; (3) examine synecological relationships between diatom structure and environmental variables, with the ultimate goal of developing an index of biological integrity using a single assemblage. Collected diatom samples were enumerated to 250 valves and identified to species or subspecies. An assessment of wetland condition was made using a landscape-scale human disturbance score (Landscape Development Intensity index, LDI), calculated for each site using land use maps and GIS. Assemblages from both impaired and reference sites were compared using blocked multi-response permutation procedures, the percent similarity index, and visually examined using non-metric multidimensional scaling (NMDS). No ecologically significant compositional differences were found within sites. Mantel's test (Mantel's r = 0.29, p 0.50, p Metrics to assess wetland condition were developed using epiphytic abundance data. Epiphytic taxa sensitive or tolerant to human landscape modification were identified using Indicator Species Analysis, and autecological indices relating diatom sensitivity to nutrients, pH, dissolved oxygen levels, saprobity, salinity, and trophic status were calculated. Fourteen final metrics were identified, scored on an ordinal scale, and combined into the Diatom Index of Wetland Condition (DIWC). The DIWC was highly correlated with the disturbance score (Spearman's rs = −0.71, p

Calculated phase equilibria in K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O for silica‐undersaturated sapphirine‐bearing mineral assemblages

AbstractSilica‐undersaturated, sapphirine‐bearing granulites occur in a large number of localities worldwide. Such rocks have historically been under‐utilized for estimating P–T evolution histories because of limited experimental work, and a consequent poor understanding of the topology and P–T location of silica‐undersaturated mineral equilibria. Here, a calculated P–T projection for sapphirine‐bearing, silica‐undersaturated metapelitic rock compositions is constructed using THERMOCALC for the FeO‐MgO‐Al2O3‐SiO2 (FMAS) and KFMASH (+K2O + H2O) chemical systems, allowing quantitative analysis of silica‐undersaturated mineral assemblages. This study builds on that for KFMASH sapphirine + quartz equilibria [Kelsey et al. (2004) Journal of Metamorphic Geology, vol. 22, pp. 559–578]. FMAS equilibria are significantly displaced in P–T space from silicate melt‐bearing KFMASH equilibria. The large number of univariant silica‐undersaturated KFMASH equilibria result in a P–T projection that is topologically more complex than could be established on the basis of experiments and/or natural assemblages. Coexisting sapphirine and silicate melt (with or without corundum) occur down to c. 900 °C in KFMASH, some 100 °C lower than in silica‐saturated compositions, and from pressures of c.≤1 to ≥12 kbar. Mineral compositions and composition ranges for the calculated phases are consistent with natural examples. Bulk silica has a significant effect on the stability of sapphirine‐bearing assemblages at a given P–T, resulting in a wide variety of possible granulite facies assemblages in silica‐undersaturated metapelites. Calculated pseudosections are able to reproduce many naturally occurring silica‐undersaturated assemblages, either within a single assemblage field or as the product of a P–T trajectory crossing several fields. With an understanding of the importance of bulk composition on sapphirine stability and textural development, silica‐undersaturated assemblages may be utilized in a quantitative manner in the detailed metamorphic investigation of high‐grade terranes.

MANGALA VALLES, MARS: ASSESSMENT OF EARLY STAGES OF FLOODING AND DOWNSTREAM FLOOD EVOLUTION

The Mangala Valles system is an ∼ ∼900 km fluvially carved channel system located southwest of the Tharsis rise and is unique among the martian outflow channels in that it heads at a linear fracture within the crust as opposed to a collapsed region of chaos as is the case with the circum-Chryse channels. Mangala Valles is confined within a broad, north–south trending depression, and begins as a single valley measuring up to 350 km wide that extends northward from a Memnonia Fossae graben, across the southern highlands toward the northern lowlands. Approximately 600 km downstream, this single valley branches into multiple channels, which ultimately lose their expression at the dichotomy boundary. Previous investigations of Mangala Vallis suggested that many of the units mapped interior to the valley were depositional, related to flooding, and that a minimum of two distinct periods of flooding separated by tens to hundreds of millions of years were required to explain the observed geology. We use infrared and visible images from the THermal EMission Imaging System (THEMIS), and topographic data from the Mars Orbiting Laser Altimeter (MOLA), to investigate the nature of the units mapped within Mangala Vallis. We find that the geomorphology of the units, as well as their topographic and geographic distribution, are consistent with most of them originating from a single assemblage of volcanic flow deposits, once continuous with volcanic flows to the south of the Memnonia Fossae source graben. These flows resurfaced the broad, north–south trending depression into which Mangala Vallis formed prior to any fluvial activity. Later flooding scoured and eroded this volcanic assemblage north of the Mangala source graben, resulting in the present distribution of the units within Mangala Vallis. Additionally, our observations suggest that a single period of catastrophic flooding, rather than multiple periods separated by tens to hundreds of millions of years, is consistent with and can plausibly explain the interior geology of Mangala Vallis. Further, we present a new scenario for the source and delivery of water to the Mangala source graben that models flow of groundwater through a sub-cryosphere aquifer and up a fracture that cracks the cryosphere and taps this aquifer. The results of our model indicate that the source graben, locally enlarged to a trough near the head region of Mangala, would have required less than several days to fill up prior to any spill-over of water to the north. Through estimates of the volume of material missing from Mangala (13,000–20,000 km3), and calculation of mean discharge rates through the channel system (∼ ∼5 × 106 m3 s−1), we estimate that the total duration of fluvial activity through the Mangala Valles was 1–3 months.

Management of the Falkland Islands Multispecies Ray Fishery: Is Species-specific Management Required?

A multispecies commercial fishery for rajids has been managed in Falkland Islands waters since 1987. In the absence of detailed biological knowledge and catch-at-age data, management policies currently consider a single assemblage rather than individual species. Simple production models with aggregated catch and effort data are used to estimate sustainable levels of exploitation. Biological data, now available from recent research surveys and an ongoing observer program, provide an opportunity to examine the potential impact of the rajid fishery at a species level. This in turn will help determine whether current management policies are still appropriate. An updated assessment of the northern ray population indicates that the assemblage has been surprisingly robust to fluctuations in fishing pressure. A spatial analysis of the relative abundance of animals showed no evidence of local depletions in biomass. At a species level, a declining trend in the relative abundance of three species (Bathyraja griseocauda, B. multispinus, and an undescribed Bathyraja sp. 3) was found at the same time as an increase in two Rajid species (R. doellojuradoi and R. flavirostris). A preliminary analysis of the distribution and movements of R. flavirostris, coupled with length frequency and maturity data, suggest that this species has a broad distribution, which, unlike B. griseocauda, may not form a resident population within Falkland Island waters. While no loss of diversity has been reported, closure of the once heavily exploited area to the south of the Islands provides at least one refuge for species such as B. griseocauda.

Coral variation in two deep drill cores: significance for the Pleistocene development of the Great Barrier Reef

Variations in lithology and coral assemblages in drill cores from outer- and inner-shelf reefs are used to characterize the Pleistocene development of the Great Barrier Reef. Based on petrographic, isotopic and seismic characteristics, the outer-shelf core from Ribbon Reef 5 is divided into three sections: (1) a main reef section from 0 to 96 m is composed of six reef units, (2) a rhodolith section from 96 to 158 m is interbedded with two thin reef units and (3) a basal section from 158 to 210 m is composed of non-reefal skeletal grainstones and packstones. Two distinct coral assemblages identified in this core represent a shallow, high-energy community and lower-energy community. These two assemblages are repeated throughout the main reef section, with some units recording transitions between assemblages, and others composed of only a single assemblage. These coral assemblage data also correlate with transitions recorded by coralline algae. Using similar criteria, the inner-shelf core from Boulder Reef is divided into two sections: (1) an upper carbonate-dominated section from 0 to 34 m is comprised of four reef units and (2) an underlying mud section from 34 to 86 m is composed of siliciclastics and two thin, coral-bearing units. The four reef units in the upper section are dominated by a single coral assemblage representing a community typical of low energy, turbid environments. Taken together, these data indicate that: (1) reef growth on the inner shelf initiated later than on the outer shelf, (2) true reef ‘turn-on’ in outer shelf areas, as represented by the main reef section in Ribbon Reef 5, was preceded by a transitional period of intermittent reef development and (3) the repeated occurrence of similar coral assemblages in both drill cores indicates that the Great Barrier Reef has been able to re-establish itself, repeatedly producing reefs of similar composition over the last 500 ky, despite major environmental fluctuations in sea level and perhaps temperature.

Interactive effects of native and exotic earthworms on resource use and nutrient mineralization in a tropical wet forest soil of Puerto Rico

Investigation of single or mixed assemblages of native Estherella sp. and exotic Pontoscolex corethrurus from a rain forest in Puerto Rico was undertaken to understand resource use patterns, and linkages with C and N mineralization in a 19-day incubation. Resource use was explored with addition of 15N-enriched leaf litter and 13C-enriched glucose to reconstructed organic and mineral soil horizons. Juvenile Estherella sp. became at least 6.06‰ more enriched in 13C than sub-adult Estherella sp. or adult P. corethrurus. Sub-adult Estherella sp. became >3.6‰ enriched in 13C over P. corethrurus. δ15N acquired by P. corethrurus was greater by 0.83–1.56‰ in the mixed-species than the single-species assemblages. δ15N of sub-adult Estherella sp. was enriched by 0.73–0.81‰ over juvenile Estherella sp. in the single-species assemblage. Net N immobilization occurred in the organic layer of all 15N-enriched treatments. Net N mineralization in mineral soil layers was significantly greater in microcosms with P. corethrurus than in those containing only Estherella sp.. Cumulative respiration was greatest in P. corethrurus assemblages, however, assemblages with only Estherella sp. released more 13C in respiration. P. corethrurus assimilated different N resources when incubated with, as compared to without, native Estherella sp.. δ13C and δ15N signatures acquired by assimilation of 13C and 15N differed by species, developmental stage, and competitive interactions. The results showed that alone, exotic P. corethrurus induced higher mineralization rates than native Estherella sp., but that the interaction of exotic and native species impinged on resource use by P. corethrurus, reducing the effect of the exotic species on C and N mineralization. Invasion of exotic P. corethrurus may change the mineralization potentials of C and N and their biogeochemical cycling in soils.

Intraspecific dental variability in cf. Coryphodon anthracoideus (Mammalia: Pantodonta) from Roehler's Coryphodon Catastrophe Quarry, Washakie Basin, Wyoming

Roehler9s Coryphodon Catastrophe Quarry (Wasatch Formation, lower Eocene) in the Washakie Basin, Wyoming is a paucispecific assemblage containing a minimum of 10 individuals from a single population of cf. Coryphodon anthracoideus . The RCCQ Coryphodon assemblage provides a relatively rare opportunity to assess intraspecific variation in a genus that has historically been difficult to classify due to variation from specimen to specimen and species to species. Variation in metric features of the dentition (i.e., length, width, and molar area) in the RCCQ Coryphodon is within the range observed in comparable sexually dimorphic extant species. The RCCQ Coryphodon assemblage is also compared to another paucispecific, single population assemblage of Coryphodon molestus from New Mexico. Intraspecific metric variation characterizing these two assemblages is also comparable. In both assemblages, overall intraspecific metric variation is most pronounced in the third molar, suggesting sexual dimorphism as the source of variation.

Movement of oceanic fronts south of Australia during the last 10 ka: interpretation of calcareous nannoplankton in surface sediments from the Southern Ocean

Preservation of calcareous nannoplankton in surface sediment samples from the Southern Ocean south of Australia and adjacent to New Zealand record a single assemblage. The dominant species are Emiliania huxleyi, Gephyrocapsa muellerae, Calcidiscus leptoporus, Helicosphaera carteri and Coccolithus pelagicus. The assemblage varies little in abundance and diversity with minor correlation to present-day overlying surface water masses and oceanic fronts. Increase in abundance of H. carteri and C. pelagicus in the region of the Subtropical Front may reflect higher nutrients associated with this front. The assemblage, although altered by dissolution, represents a warmer climatic interval than present-day with the presence of preferentially dissolved, warm-water species preserved as far south as the Polar Front. The presence of warm-water species under sub-Antarctic waters at the Polar Front is interpreted as a relic population from the Holocene climatic optimum of 10–8 ka. The absence of coccoliths in sediments poleward of the Polar Front suggests an equatorward shift of this front following the climatic optimum, resulting in increased productivity of siliceous phytoplankton associated with the colder waters and increased dissolution of coccoliths. Movement of the Subtropical Front for the same interval is not recorded in the preserved coccoliths. The more heavily calcified form of E. huxleyi which dominates the living assemblage north of the Subtropical Front is subject to dissolution in this region and is poorly preserved in the sediment assemblage.

ALLMON, W. D. & BOTTJER, D. J. (eds) 2000. Evolutionary Paleoecology. The Ecological Context of Macro evolutionary Change. xi+357 pp. New York: Columbia University Press. Price US $45.00, £29.00 (hard covers), US $25.00, £16.00 (paperback). ISBN 0 231 10994 6; 0 231 10995 4 (pb).

The word ‘palaeoecology’ was once applied to almost any palaeontological study that treated fossils as living organisms rather than simply organic shapes of utility in stratigraphy. There followed a time during which community palaeoecology – the reconstruction of ancient communities and their trophic interactions – took centre stage. We are now entering a new phase of palaeoecology epitomized by the subtitle of this book: ‘The ecological context of evolutionary change’. Just as ecologists are becoming increasingly concerned with patterns of biotic distribution on large spatial scales (‘macroecology’), so palaeoecologists are looking beyond studies of single assemblages to interpretation of ecological changes across vast stretches of geological time as a backcloth to macroevolution. This collection of 11 papers, dedicated to the late Jack Sepkoski, arose from a GSA Symposium held in 1996. Like most volumes with a similar background, it is an assortment of research papers which are varied in their generality, focus and quality. The editors …

A study on octopodids from the eastern Weddell Sea, Antarctica

A comprehensive study of octopodids in the Weddell Sea was conducted during cruise ANT XIII/3 of RV "Polarstern". The study yielded eight species of incirrate octopodids, three of which were undescribed. There appeared to be no differences in octopodid species assemblage in the two sampling areas (Kapp Norvegia and south of Drescher Inlet), supporting the theory that there is a single macrobenthic assemblage on the eastern shelf of the Weddell Sea. Six of the octopodid species belonged to the genus Pareledone, illustrating the extensive radiation of this endemic genus within the Southern Ocean. The fragmented nature of suitable habitats and disturbance caused by glaciation cycles are proposed as mechanisms for this radiation. Comparative data illustrate that both the number of octopodid species present and their abundance are greater at higher latitudes than close to the Antarctic Polar Frontal Zone.

Comparative Analysis of Solar Array Fragments Degradation at Different Structure Scales during and after Long-Term Exposure Overboard the ‘Mir’ Space Station

Generalized comparative analysis of the results of model specimens and fragments of standard solar array degradation studies before and after prolonged exposure and during operation in low Earth orbits (LEOs) is made. The studies gave a unique opportunity to reveal new information on the influence of the space environment on solar array materials and components, determine the degree of degradation and understand the mechanism of their degradation. It was determined that the degrees of power and current degradation in the MSA1 wing of the Mir space station mountable solar array and its panels are high and non-uniform. Most of the solar cell blocks and single cells (about 70%), materials, structure assemblages and components had stood up to more than 10 years exposure in LEO environment satisfactorily. Thermocycle effects and optical performance decrease are the main causes of power and current losses in undamaged solar cells. About 30% of the cell blocks had suffered severe damage to their structure and interconnects from hot-spotting processes due to strip shadowing of the blocks by space station structure elements such as pantograph members. These processes governed the power and current losses in solar arrays.

Perennial domination of phytoplankton by Botryococcus and Peridinium in a discontinuously polymictic reservoir (tropical Australia)

The effect of holomixis and wet season inflow on the phytoplankton composition of Darwin River Reservoir (DRR) is examined. Both phenomena constitute potential disturbances to the pelagic environment of this shallow (average depth 6 m) tropical reservoir and its phytoplankton community. Over the two year study period, the phytoplankton concentration of DRR remained much the same (0.48-2.4 mm(3)/L). At least half the biovolume comprised two species, Botryococcus braunii and Peridinium gutwinskii. These two taxa, together with other Peridinium species and desmids (predominantly Staurastrum and Cosmarium) constituted 68-98% of the reservoir's total phytoplankton biovolume. Potential disturbance by wet season inflow and 13 holomictic events had minimal affect on the domination of the Botryococcus-Peridinium-Desmidaceae assemblage, owing mainly to their short duration (4-5 days) and minor influence on light intensities in the mixed layer. Some holomictic events, however, favoured the growth of the diatom Aulacoseira granulata which reached a maximum of 17 % of the reservoir's total phytoplankton biovolume. Fast growing, small r-selected phytoplankton, which are favoured by nutrient rich waters, constituted a minor component (<1 % total biovolume) of the reservoir's phytoplankton, probably owing to the phosphorus impoverishment of the mixed layer. B. braunii colonies and P. gutwinskii have many characteristics of K-selected (slow growing) S-species, which mark the later stages of autogenic succession. There was no evidence of phytoplankton autogenic succession with the onset of thermal stratification in DRR. The perennial domination of the reservoir's phytoplankton by a single assemblage, and notably by two species, suggests the reservoir's phytoplankton community is in dynamic equilibrium (or steady-state) with the environment, supporting the contention that climax communities are self-sustaining.

Comparison of fish and macroinvertebrate bioassessments from South Carolina coastal plain streams

Abstract Stream bioassessments are usually based on a single taxonomic assemblage, often fishes or macroinvertebrates, with the assumption that this assemblage is representative of ecological conditions. However, ecological and physiological differences between taxonomic groups may result in different assessment results. In this study, concurrent fish and macroinvertebrate bioassessments from South Carolina coastal plain streams were compared on the basis of precision, sensitivity, accuracy, and agreement. Multimetric indices used in this comparison were a modified Index of Biotic Integrity based on electrofishing data and a benthic macroinvertebrate multimetric index based on data collected with Hester-Dendy artificial substrates. Benthic macroinvertebrates were also collected from natural substrates for comparative purposes. The Index of Biotic Integrity was more precise than the HesterDendy multimetric index but the average difference between disturbed and reference sites was greater for the latter resulting in equal sensitivity (i.e., ability to measure disturbance in relation to index variability). The two indices were significantly correlated (r=0.62, p &amp;lt;0.001), but agreement between them was weak for slightly and moderately disturbed sites. Analysis of species richness and abundance data indicated that fish and macroinvertebrates responded differently to some disturbances regardless of whether macroinvertebates were collected from HesterDendy samplers or natural substrates. Disagreement between macroinvertebrate and fish assessments at moderately disturbed sites indicated that biological condition could not always be adequately evaluated from a single taxonomic group. Identification of disturbed sites was most accurate when based on both indices suggesting that future research should emphasize cost-effective sampling and integration of information from multiple taxonomic groups.

Clovis and Early Archaic Crania from the Anzick Site (24PA506), Park County, Montana

The Anzick archaeological site in Montana, known since 1968, has been recognized since 1974 as Clovis age because of the lithic material recovered. Now it is possible to assert that some, but not all, of the recovered skeletal material is also Clovis age. The site contained more than 100 stone and nonhuman bone artifacts in association with the partial skeletal remains of a young child. All were covered with red ocher. The partial cranium of a second youth, not stained red, was also recovered. Recently, radiocarbon dating of these two crania produced two separate ages, 2000 years apart. Forensic examination of the remains, completed in 1999, has determined their ages at death. This site, an important addition to New World prehistory, contains not only the largest single assemblage of Clovis artifacts but also the only known Clovis skeletal remains.

A phylogeny of the land snails (Gastropoda: Pulmonata)

We have undertaken the first large-scale molecular phylogenetic analysis of the Stylommatophora. Sequences of the ribosomal RNA gene-cluster were examined in 104 species of snails and slugs from 50 families, encompassing all the currently recognized major groups. It allows an independent test of the present classification based on morphology. At the level of families our molecular phylogeny closely supports the current taxonomy, but the deep branches within the tree do not. Surprisingly, a single assemblage including the families Achatinidae, Subulinidae and Streptaxidae lies near the base of the tree, forming a sister group to all remaining stylommatophorans. This primary division into 'achatinoid' and 'non-achatinoid' taxa is unexpected, and demands a radical reinterpretation of early stylommatophoran evolution. In particular, the Orthurethra appear to be relatively advanced within the 'non-achatinoid clade', and broadly equivalent to other super-familial clusters. This indicates that supposedly primitive features such as the orthurethran kidney are derived. The molecular tree also suggests that the origin of the Stylommatophora is much earlier than the main period of their diversification.

The Use of a Multivariate Graphic Display Technique as an Exploratory Tool in the Analysis of Inter-assemblage Lithic Variability: a Case Study from Qafzeh Cave, Israel

In the course of the last four decades, Middle Palaeolithic inter-assemblage lithic variability has been studied by relatively standardised quantitative methods. Still, it has been difficult to present any single assemblage as a “sum” of its lithic properties in relation to other assemblages, and to gauge the degree of similarities and dissimilarities among assemblages on this basis. This paper presents the application of a statistical procedure, which displays the distances among assemblages graphically, and allows their intuitive evaluation. The procedure is applied to a series of Mousterian lithic assemblages from the terrace of Qafzeh Cave, Israel, in an attempt to test through the lithic analysis hypotheses about diachronic changes in settlement patterns on the site.The matrices used, and the resulting display, also enable identification of those variables which most influence the emerging pattern. Therefore, the procedure can be employed as an exploratory tool in the initial stages of research, for identifying potentially fruitful directions of future analyses. We emphasise that the utility of the statistical procedure depends on the archaeological meaning of the variables selected for analysis.

A new plant assemblage (microfossil and megafossil) from the Lower Old Red Sandstone of the Anglo–Welsh Basin: its implications for the palaeoecology of early terrestrial ecosystems

Lower Old Red Sandstone deposits penetrated by a series of cored boreholes near Newport (South Wales) have been sedimentologically logged, and recovered plant assemblages (microfossil and megafossil) investigated. Sedimentological logging indicates that the deposits are typical of the extensive terrestrial-fluviatile floodplain deposits of the Anglo–Welsh Basin. Palynomorph assemblages have been recovered from a number of horizons and comprise entirely terrestrial forms (spores and phytodebris). They essentially represent a single assemblage, belonging to the middle subzone of the micrornatus-newportensis sporomorph assemblage biozone, and indicate an Early Devonian (mid-Lochkovian) age. The new biostratigraphical data enables correlation with other Lower Old Red Sandstone deposits of the Anglo–Welsh Basin, and the deposits are assigned to the lower part of the St. Maughan's Group. A plant megafossil/mesofossil assemblage recovered from one of the spore-bearing horizons includes a zosterophyll assigned to Zosterophyllum cf. fertile. This is the earliest reported zosterophyll from the Anglo–Welsh Basin. The new palynological/palaeobotanical data provide important information on the palaeoecology and palaeobiogeography of the vegetation of the southeastern margin of the Old Red Sandstone continent during Lochkovian times. Palaeogeographical variation in the distribution of plant microfossils and megafossils is interpreted as reflecting differences between the flora of the lowland floodplain and inland intermontaine basins, although this is to a certain extent overprinted by variation due to localized differences in environmental conditions.

Abundance patterns of European breeding birds

The frequency distribution of national population sizes of breeding birds was examined for each of 48 European countries, including autonomous regions, using data from the European Bird Database. The frequency distribution of logarithmically transformed abundance was left skewed in 40 countries: there was significant left skew in 10, and positive skew, in 2 countries. The inclusion of data classed as of low quality did not alter the conclusion that abundance patterns were predominantly left skewed. Abundance patterns of resident and migrant breeding birds differed; residents were left skewed, migrants were lognormal. Skewness was correlated negatively the number of species within a country. At low sample size, both left and right skews were evident, but left skews predominated at larger samples sizes. This pattern was driven partly by a difference between breeding populations on islands and on continental countries. Resampling procedures with fixed sample size showed that resident and migrant birds differed consistently in their patterns of skew, independent of sample size. If the birds of Europe were treated as a single assemblage, their abundance pattern was left skewed but this was driven by a very small number of vagrant breeders.

Within-catchment effects of flow alteration on fish assemblages in the Hawkesbury-Nepean River system, Australia

Streamflow in the Hawkesbury–Nepean River system has been progressively regulated and diverted since 1888 by the construction of 29 dams 7 m or more in height and another 52 smaller structures to supply water for the populations of Sydney, Wollongong and the Blue Mountains. This study identifies differences in fish assemblages between reaches of the river system affected by dams, flow diversion and regulation, and rivers unmodified for water supply. Fish were sampled in the upper-reach tributaries above five major dams, in slopes reaches within 1 km downstream of the dams, and in the lowland reaches of the Nepean and Hawkesbury rivers. Corresponding upper, slopes and lowland reaches were sampled in two unregulated tributaries. Fish were also sampled within the impoundments. Seven fish assemblages were identified by multivariate analyses, which revealed a separation of assemblages in habitats affected by dams or flow alteration. Fish within the lowland reaches of all three rivers formed a single assemblage, which became progressively fragmented with increasing distance upstream, and with increasing differences between regulated and unregulated rivers. Gambusia holbrooki and Anguilla reinhardtii were more abundant in the upper reaches of unregulated rivers, whereas Galaxias brevipinnis and Retropinna semoni were abundant in upper reaches above dams, but not recorded in upper reaches of unregulated rivers. In slopes reaches, Gambusia holbrooki and Gobiomorphus coxii were more abundant in unregulated reaches while Retropinna semoni, Philypnodon grandiceps and Anguilla reinhardtii were more abundant in regulated reaches. Characteristic species in lowland reaches included Macquaria novemaculeata, Mugil cephalus, Philypnodon grandiceps, Cyprinus carpio and Potamalosa richmondia. However, the true effects of flow alteration in the system are confounded by geomorphic and climatic variation and other disturbances within the catchment. Sustainable development of water resources in the catchment requires a more detailed analysis of biotic responses to river flows, accounting for confounding factors. Copyright © 1999 John Wiley & Sons, Ltd.

Recording the Preservational Condition of Archaeological Insect Fossils

The state of preservation of archaeological fossils may provide information crucial to their interpretation and for making curatorial decisions concerning the buried heritage. An established scheme for recording the condition of archaeological insect remains preserved by anoxic waterlogging is examined and found inadequate, failing to represent the complexity of decay properties and pathways. A particular weakness was its focus on whole assemblages rather than the individual remains of which they were composed. A new scheme is proposed which takes account of the heterogeneity of preservation in single assemblages, and makes use of a wider set of properties including colour changes. Range, mode, mode strength and distribution of values are recorded for the major properties (i.e. erosion or chemical degradation, fragmentation or mechanical damage, and colour changes). A form and accompanying flow sheet designed to ensure systematic recording of these properties under the new scheme are presented, and its success to date considered.