The spectral absorption and scattering properties of dissolved and particulate components in relation to the underwater light field of some tropical Australian fresh waters

SUMMARY. 1. The inherent optical properties (scattering coefficients and absorption coefficients across the photosynthetic waveband) are presented from diverse tropical water bodies (billabongs) in the Alligator Rivers Region of northern Australia.
2. The data are used to interpret observed characteristics of the underwater light field as exemplified by the spectral distribution, and overall rate of attenuation, of photosynthetically available radiation (PAR).
3. Attenuation of PAR, especially in the blue waveband, is caused primarily by intense light absorption by the yellow-brown humic pigments, both soluble and particulate, in the water.
4. It was estimated that in six moderately turbid billabongs, light scattering increased attenuation by an average of 58% above that attributable to absorption alone, whereas in a highly turbid billabong the increase was 111%.
5. A distinguishing feature of the optical character of these billabongs, compared with previously studied water bodies in southern Australia, is the great contribution to light absorption made by the particulate humic material.     

The influence of a planktivorous fish on zooplankton assemblages in experimental billabongs

This paper discusses the influence of predation by a planktivorous fish on zooplankton assemblages within experimental billabongs. Results suggest that the presence of a small planktivorous fish in experimental billabongs had only a small influence on the structure of zooplankton assemblages and densities of rotifers. Microcrustacean populations were dominated by juveniles, however there were greater numbers of juveniles when the planktivorous fish were present.     

Bacterial assemblages in rivers and billabongs of Southeastern Australia

Billabongs, lentic waterbodies common to the floodplain of Australian rivers, differ considerably from the lotic riverine environment in terms of hydrology, physiochemical characteristics, and biological assemblages present. As little is known regarding the bacterial ecology of billabong habitats, a comparison was made of the bacterial assemblages in the water column of seven paired river/billabong sites in the Murray-Darling Basin of southeastern Australia. Billabongs supported larger populations of bacteria (1–157×10⁹ cells liter⁻¹; 11–10,270 μg C liter⁻¹) than did rivers (1–10×10⁹ cells liter⁻¹; 6–143 μg C liter⁻¹). Phospholipid analyses confirmed that billabongs (14–111 μg phospholipid fatty acid liter⁻¹) had larger bacterial populations than rivers (<12 μg liter⁻¹). Bacterial production, measured with³H-leucine, was also greater in billabongs (0.28–3.05 μg C liter⁻¹ hour⁻¹) than rivers (0.05–0.62 μg C liter⁻¹ hour⁻¹). Production calculated from the frequency of dividing cells confirmed this conclusion, and suggested bacterial production in some billabongs could exceed 100 μg C liter⁻¹ hour⁻¹. An INT-formazan method indicated that usually <25% of bacterial cells were active in either habitat, but this was probably an underestimate of the bona fide value. Turnover times of glucose were usually shorter in billabongs, and the cell-specific activity greater for billabong than river assemblages. The factors most likely to be responsible for the differences between the bacterial assemblages in rivers and billabongs relate to hydrological regime and the availability of organic carbon substrates.     

Effects of hydrological variation and planktivorous competition on macroinvertebrate community structure in experimental billabongs

1. To study two factors which are predicted as causing changes to community structure in cut-off meanders (colloquially known in Australia as billabongs, a term of aboriginal origin), 16 experimental billabongs were constructed. These were designed to test two hypotheses: (a) that the structure of macrophyte and invertebrate communities within billabongs is altered by changing the pattern of flooding; and (b) that the presence of small planktivorous fish alters invertebrate community structure and diversity within billabongs.
2. An increase in the duration of flooding seems to favour animals better adapted to a greater availability of macrophyte habitat. Changing the seasonality of flooding resulted in prolonging of the time water was available over the summer months.
3. The presence of a planktivorous fish appears to affect macroinvertebrate communities through competition with other planktivores. Variable top-down pressure may create differing successional patterns and ultimately different communities at lower trophic levels.     

Impact of water regime and fish predation on zooplankton resting egg production and emergence

The emergence of zooplankton from ephemeral areas upon re-wettinghas been suggested as a significant contributor to billabongproductivity. Sixteen experimental billabongs were designedto test two hypotheses (i) that changing the pattern of floodingalters zooplankton abundance within billabongs, and (ii) thepresence of small planktivorous fish alters the zooplanktoncommunity structure and diversity within billabongs. Resultsindicated that flooding caused microcrustaceans to increasein abundance but not rotifers. This response was not modifiedby changing the time of flooding. The presence of the planktivorousfish had only a small influence on the structure of rotiferassemblages, whereas microcrustacean assemblages became dominatedby juveniles. Emergence of rotifers and microcrustaceans fromsediment taken from the experimental billabongs and incubatedunder controlled conditions indicated the existence of a largereservoir of resting stages. The number of resting stages inthe sediment had not been modified by changing the season offlooding in the experimental billabongs, but it was modifiedby permanent inundation, which may have removed environmentalcues. The presence of planktivorous fish also appeared to influencethe number of resting stages that accumulated in the sediment.Emergence under stable laboratory conditions was rapid. Thiswas not the case under more variable natural conditions.     

Establishing the condition of lowland floodplain rivers: a palaeo-ecological approach

1. Current approaches for determining river ‘health’ rely on the establishment of a ‘reference’ condition. This is often difficult to achieve for lowland floodplain river systems because of the lack of pristine or pre-impacted sites and process models capable of predicting the effect of natural and human disturbances. 2. Using examples from the River Murray, Australia, this paper highlights the benefits of using palaeo-ecological studies in deciding on benchmark or pre-European settlement conditions for lowland floodplain river systems. 3. Physical, chemical and biological analyses of sediment obtained from shallow cores (< 2 m) extracted from a variety of floodplain sites on the River Murray and its tributaries reveal the extent and timing of catchment disturbances on this lowland river. Rates of sedimentation have increased by an order of magnitude since settlement; sediments now being deposited are finer, having implications for the nutrient status of the floodplain and the accumulation of heavy metals associated with these sediments. There has also been a sustained drop in the macrophyte cover of billabongs in the area, as inferred by chydorid cladoceran assemblages. The pre-European settlement diatom assemblages do not resemble those presently accumulating in billabongs in the region. 4. Whilst initially developed for lentic studies, palaeo-ecological studies are relevant to the establishment of benchmark conditions for lowland floodplain rivers. They are relatively straightforward, incorporate both historical and contemporary ecological information and can be applied to any lowland system.     

Possible causes of high species diversity in tropical Australian freshwater macrobenthic communities

A total of 133 benthic macroinvertebrate species was recorded in four permanent freshwater lagoons (billabongs) and a stream riffle in the Magela Creek catchment, Northern Territory, Australia. 101 species were lentic in occurrence. Each billabong supported at least as many species as larger tropical and Australian temperate lakes, and was an exception to the species-poor status of Australian lentic macrobenthic communities. > 98% of the total benthic biomass was contributed by a mussel species; the remaining species' combined standing crop was an order of magnitude lower than in other lentic systems, further highlighting the diversity of the Magela benthos. Rarefaction (removal of organisms) and predictable environmental heterogeneity, both related to monsoonal variations in flow and water quality, were probably important determinants of the high diversity of these communities.     

Structure and dynamics of zooplankton communities,Alligator Rivers Region,N.T., Australia

Biological monitoring in the Alligator Rivers region, northern Australia, provides baseline ecological information to assess the impact of uranium mining and milling and settlement in the area. Spatial and temporal variations 1978–1980 in zooplankton communities of the Magela Creek, a tributary of the East Alligator River, are described. Extremely diverse plankton assemblages occur late in the wet season (Dec.–May), with up to 80 taxa of rotifers and microcrustacea in some billabongs (= ox-bows), while there is a decrease in diversity but increase in population density as the dry season progresses. Natural fluctuations in water quality may be extreme, and limiting to plankters common elsewhere in the tropics. The plankton is composed largely of littoral or epiphytic taxa, with endemic species in all groups.     

Rotifera from Western Australian wetlands with descriptions of two new species

The rotifer fauna of 100 fresh and saline wetlands of southwest Western Australia is documented. A systematic list of 83 recorded taxa is given, with eleven new records for the continent and two new species (Brachionus pinneenaus n. sp. and Lecane boorali n. sp.) described and figured. Species assemblages are distinct from those of eastern Australia, with predominant taxa halophilous or indicative of ephemeral waters. Evolutionary and biogeographical relationships of the Western Australian rotifers are considered.     

Studies on fish movement dynamics in a tropical floodplain river: Prerequisites for a procedure to monitor the impacts of mining

Abstract Towards the end of the Wet season in the tropical coastlands of northern Australia, there are dramatic upstream movements of many fish species in some seasonally flowing streams. These movements are considered to be a part of refuge-seeking migrations. Aspects of the dynamics of the movements in Magela Creek (in the ‘Top End’ of the Northern Territory) downstream from the Ranger Uranium Mine have been examined with a range of techniques (mainly direct observation) to facilitate the development of a possible procedure for monitoring impacts of the mine on the fish community of the creek system. Data on diel patterns of movements validated that monitoring, for 1 h at midday at a single point adjacent to the mine, reflects day-to-day changes in total diel movements. To help identify the location of any impacts arising in the future, information on upstream progress rates, longitudinal changes in movements, and movements between the creek and lowland billabongs, were used to (i) demonstrate the creek-long continuity of movements and (ii) indicate the possible sources and destinations of fish approaching the mine. Marked differences in sources were apparent for two groups of species: terapontids originating from the lowland creek channels, and chequered rainbowfish and ambassids originating from the floodplain and lowland billabongs. Identification of the relative contributions from these habitats will require additional monitoring effort.     

Global diversity of rotifers (Rotifera) in freshwater

Rotifera is a Phylum of primary freshwater Metazoa containing two major groups: the heterogonic Monogononta and the exclusively parthenogenetic Bdelloidea. Monogononta contains 1,570 species-level taxa, of which a majority (1,488) are free-living fresh or inland water taxa. Bdelloidea contains 461 “species,” only one of which is marine, but with many limnoterrestrial representatives or animals of unknown ecology. Actual numbers may be much higher, considering the occurrence of cryptic speciation in Monogononta and the unsatisfactory nature of taxonomic knowledge. Rotifers, mostly monogononts, occur in all types of water bodies, worldwide. They are particularly diverse in the littoral zone of stagnant waterbodies with soft, slightly acidic water and under oligo- to mesotrophic conditions. The rotifer record is highest in the Northern hemisphere, which may be due to the concentration of studies in those regions. Diversity is highest in the (sub)tropics; hotspots are northeast North America, tropical South America, Southeast Asia, Australia, and Lake Baikal, endemicity is low in Africa (including Madagascar), Europe, the Indian subcontinent, and Antarctica. Although the lack of fossil evidence and of molecular phylogenetic studies are major hindrances, contrasting hypotheses on the origin and evolutionary history of Brachionus, Macrochaetus, and Trichocerca are presented. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Temperate macroalgae impacts tropical fish recruitment at forefronts of range expansion

Warming waters and changing ocean currents are increasing the supply of tropical fish larvae to temperature regions where they are exposed to novel habitats, namely temperate macroalgae and barren reefs. Here, we use underwater surveys on the temperate reefs of south-eastern (SE) Australia and western Japan (~33.5°N and S, respectively) to investigate how temperate macroalgal and non-macroalgal habitats influence recruitment success of a range of tropical fishes. We show that temperate macroalgae strongly affected recruitment of many tropical fish species in both regions and across three recruitment seasons in SE Australia. Densities and richness of recruiting tropical fishes, primarily planktivores and herbivores, were over seven times greater in non-macroalgal than macroalgal reef habitat. Species and trophic diversity (K-dominance) were also greater in non-macroalgal habitat. Temperate macroalgal cover was a stronger predictor of tropical fish assemblages than temperate fish assemblages, reef rugosities or wave exposure. Tropical fish richness, diversity and density were greater on barren reef than on reef dominated by turfing algae. One common species, the neon damselfish (Pomacentrus coelestis), chose non-macroalgal habitat over temperate macroalgae for settlement in an aquarium experiment. This study highlights that temperate macroalgae may partly account for spatial variation in recruitment success of many tropical fishes into higher latitudes. Hence, habitat composition of temperate reefs may need to be considered to accurately predict the geographic responses of many tropical fishes to climate change.

     

Structure of rotifer assemblages in shallow waterbodies of semi-arid northwest Iran differing in salinity and vegetation cover

Rotifers are important components of freshwater ecosystems and sensitive indicators of environmental changes. This study was carried out to test the hypothesis that, among environmental variables, salinity and aquatic vegetation have significant effects on rotifer diversity and abundance. We analyzed rotifer assemblages in the littoral zone of 22 hydromorphologically different shallow waterbodies in West Azarbaijan, Iran. Rotifer diversity and abundance were not significantly associated with basin morphology, but were positively correlated with the percentage of vegetation cover. Salinity and electroconductivity positively influenced rotifer abundance, while they had significantly negative effects on rotifer diversity. Halobiont species from the genera Brachionus, Hexarthra, Synchaeta, and Notholca reached their highest abundances in the waterbodies with pronouncedly higher salinities. Our findings are in agreement with recent records showing that distinct rotifer assemblages occur in saline and non-saline waterbodies. The role of salinity and aquatic vegetation as the most important environmental drivers in shaping rotifer communities is confirmed. The results of this study suggested that environmental changes could be significant on the micro-biogeographical level, and that the interaction of salinity and observed human impact, i.e., trophic level, promote rotifer abundance as sensitive indicators of environmental changes.     

The Biogeography of Cladocera (Crustacea) in Tropical Australia

Ninetysix species of Cladocera, comprising 8 Sididae, 50 Chydoridae, 17 Macrothricidae, 5 Moinidae, 2 Bosminidae, and 14 Daphniidae, occur in tropical Australia. Of this number 38% are cosmopolitan including so-called cosmopolitan species, 13.5% are circumtropical, 13.5% occur as well innear by countries, and 35% are endemic. North Queensland is a major area of speciation. Species richness varies from north to south and from wetter coastal areas to the drier inland. Major factors influencing richness and distribution are the relative proportion of floodplain billabongs in an area, coupled with rainfall reliability. The most common species include Alonella clathratula, Chydorus nr. pubsecens, Macrothrix triserialis, Oxyurella singalensis, Ephemeroporus nr. barroisi, Dadaya macrops, Diaphanosoma sarsi, Ceriodaphnia cornuta, and Dunhevedia crassa.     

Tasmanian rotifera: Affinities with the Australian fauna

Plankton was collected from more than 100 lentic and lotic habitats in Tasmania. Of the 131 rotifer taxa identified, 126 are first records for the island, and 9 are first records for Australia. Three new species, Aspelta tilba, sp. nov., Lepadella tyleri sp. nov., and Testudinella unicornuta sp. nov. are described and figured. Horaëlla brehmi, which has a disjunct distribution (equatorial regions and southeastern Australia), also occurs in Tasmanian waters. The morphology and development of this rare species are discussed. Geographical affinities of the Tasmanian assemblage are considered. There appears to be a significant tropical component in the Tasmanian Rotifera.     

Spring-Summer Succession of Planktonic Rotifers in a South Andes Lake

The dynamics of planktonic rotifer in Laguna Ezquerra (Rio Negro, Argentina) was studied from October 1988 to March 1989, in relation to food resources and cladoceran populations. During the spring and summer period, total rotifer density differed markedly. In spring rotifer populations remained at low density and an inverse relationship with cladoceran biomass was found. In contrast, in summer, the rotifer densities increased greatly and a positive relationship with cladoceran biomass was observed. Food resources decreased during mid January and this seemed to give rotifers a competitive advantage over cladocerans. Bosmina longirostris and Ceriodaphnia dubia were both present during the spring, but only Bosmina prevailed in summer. The composition of cladoceran assemblages together with food resources seem to be an important factor in rotifer dynamics.     

Australian Tropical and Subtropical Rain Forest Community Assembly: Phylogeny,Functional Biogeography,and Environmental Gradients

To compare community assemblage patterns in tropical northeastern and subtropical central eastern Australia across selected gradients and scales, we tested the relationship of species traits with phylogenetic structure, and niche breadth. We considered phylogenetic relationships across current‐day species in assemblages in relation to rain forest species pool sizes, and trait values along gradients including elevation and latitude. Trait values were quantified across scales for seed size, leaf area, wood density and maximum height at maturity for 1137 species and 596 assemblages using trait gradient analysis (TGA). Local assemblages of subtropical species had narrower trait ranges, and higher niche breadth values than corresponding assemblages of tropical species. Leaf size and seed size increased at low latitudes, and community phylogenetic structure was most strongly correlated with seed traits in the subtropics, reflecting dispersal and re‐colonization processes. Elevation accounted for little of the variance in community phylogenetic structure or trait variation across local and regional scales. Stable moist forest areas retained many species from ancestral rain forest lineages across a range of temporally conserved habitats; species within assemblages were less related; and rain forest assemblages had higher functional diversity, but lower niche breadth. This suggests that on average, assemblages of species in stable areas had greater trait variation and narrower distributions. Historic and recent rain forest contraction and re‐expansion can result in recolonized areas that are dominated by species that are more related (phylogenetically) than by chance, have smaller, widely dispersed seeds, and greater niche breadth (broader distributions).     

Seasonal dynamics of rotifers in relation to physical and chemical conditions of the river Yamuna (Delhi), India

We examined the seasonal succession of the rotifer assemblages in the backwaters of the Delhi segment of the river Yamuna in relation to 18 physical–chemical variables across one year. These shallow, weedy, and perennial aquatic biotopes support a diverse and abundant zooplankton. A total of 89 rotifer species belonging to 34 genera and 18 families were recorded. Their seasonal dynamics were characterized by (i) maxima and minima in total densities during spring–early summer and winter, respectively; (ii) individual species reaching maximum and minimum densities during different seasons; and (iii) an absence of seasonal variation in species diversity. The relative importance of various physical and chemical factors in determining rotifer community structure and seasonal succession is evaluated and Pearson-product moment correlations between physical–chemical variates and rotifer densities are analyzed and discussed.     

The ecology of periphytic rotifers

The ecology of rotifer assemblages in the periphyton has received little attention relative to that of pelagic rotifers. This paper reviews the ecology of periphytic rotifers, with particular emphasis on the role of macrophytes in the structuring of rotifer assemblages spatially and temporally, and compares these aspects with the dynamics of better known pelagic rotifer communities. Littoral rotifer periphyton communities are typically diverse in lakes, and have composition dissimilar to that of the open water. In rivers, diversity and composition in the pelagic and littoral appear to be similar. Rotifers show preference for macrophyte species they associate with, probably through differences in physical structure or complexity, food concentration or composition, chemical factors, macrophyte age, and differences in the degree of protection from predation provided by macrophytes. These mechanisms are in general not well investigated in rotifers. Factors affecting the seasonal dynamics of periphytic communities appear to be similar to pelagic communities, with seasonal dynamics of substrates and disturbance by flooding or drying also being important.     

Notes on the rotifers of coal mine water in Eastern Poland

The species composition and quantitative structure of the rotifer fauna was investigated in a reservoir containing coal mine water. Only nine mainly planktonic species of rotifers, were found. Two of these were dominating: Brachionus angularis and B. rubens. They are typical indicators of eutrophic waters. Chlorides and sulphates may have an influence on the occurrence and quantitative structure of rotifer assemblages in the investigated reservoir.