Drought, differential mortality and the coexistence of a native and an introduced fish species in a south east Australian intermittent stream

Synopsis The longitudinal distribution ofSalmo trutta andGalaxias olidus, a small salmoniform fish, was mapped over four summers (1985–1988) in the upper reaches of the Lerderderg River, an intermittent stream in central Victoria. Over the four successive summers of the study, the distribution ofS. trutta expanded upstream. Coincident with the expansion ofS. trutta was a contraction in the distribution ofG. olidus upstream. In the summer of 1988, an extended dry spell resulted in high levels ofS. trutta mortality at the upstream limits of their distribution. This suggested that the upstream distribution ofS. trutta could ultimately be constrained by an inability to tolerate prolonged periods of low stream flow and high temperatures that tended to occur in the headwaters of the stream. A study of summer mortality was conducted over three successive summers (1989–1991) at three reaches along the river. The two downstream reaches contained onlyS. trutta, the upstream reach contained bothS. trutta andG. olidus. Salmo trutta mortality was consistently higher at the most upstream reach compared with lower reaches. High levels ofS. trutta mortality at the two downstream reaches were only observed in 1991, a particularly dry year. In contrast,G. olidus survived in scattered small pools throughout the upper reaches of the stream. The results of the study suggest a shifting pattern ofS. trutta andG. olidus distribution determined by the duration of low stream flow periods and summer high temperatures.     

Production,population biology and diet ofNeomysis integer (Leach) in a shallow Frisian lake (The Netherlands)

TheNeomysis integer population of a shallow Frisian freshwater lake, situated in the north of the Netherlands, was studied from May until October 1980. The results were compared with observations on populations in other Frisian lakes, and with the results reported by other authors on brackish-water and marine populations of this species.Three generations were observed: one overwintering generation and two summer generations. Reproduction stopped completely during winter. During 1980 population densities ofN. integer were relatively low in all Frisian lakes. In Slotermeer the maximum population density was only 6 individuals m^–2, production amounted to 10 mg dry wt m^–2 yr^–1. The annual P/B ratio was 4.0. The diet ofN. integer consisted, in terms of biomass, of more than 95% detritus and animal food, the latter mainly consisting ofBosmina and cyclopoid copepods. Feeding intensity reached a maximum at sunset. It was still high during first part of the night and was low in the morning just after sunrise.     

Production of Gammarus pulex L. (Amphipoda) in a small Danish stream

Quantitative samples of Gammarus pulex L. taken from a small Danish stream during 1975 showed mean annual population densities varying from 500 m^–2 in early May to 5 500 m^–2 in late September. The mean annual biomass was 1.5 g dry weight m^–2. No discrete cohorts could be distinguished from the size frequency distributions. Annual production, estimated by the size-frequency method, was 3.9 g dry weight M^-2 and P/B ratio was 2.6. The contribution to trout energetics may have been as much as 17%.     

Light acclimation and photoinhibition in threeSpirulina platensis (cyanobacteria) isolates

Three isolates ofSpirulina platensis (Norst) Geitler marked BP, P4P and Z19/2 were compared with respect to their response and acclimation capability to high photon flux densities (HPFD). Cultures exposed to HPFD (1500–3500 mol photon m^–2 s^–1) exhibited a marked decrease in light-dependent O₂ evolution rate. P4P was more sensitive to HPFD than the two other isolates. All three isolates recovered from photoinhibition when placed under low PFD. The BP isolate was able to recover also in the dark but to a lower extent and at a lower rate, while no recovery was observed in the other two isolates under dark conditions. No recovery was observed when protein synthesis was inhibited using chloramphenicol. Cultures grown at 200 mol photon m^–2 s^–1 differed from cultures grown at 120 mol photon m 2 s-1 by their lower maximal photosynthetic rate (P _max ) and higher light saturation (I _k ) value, while being more resistant to HPFD stress. The ability ofSpirulina isolates to acclimate and withstand HPFD may provide useful information for the selection of strains useful for outdoor mass cultivation.Author for correspondence     

DSP toxin contents inDinophysis fortii and scallops collected at Mutsu Bay,Japan

Cell densities of toxic phytoplankton species responsible for diarrhetic shellfish poisoning (DSP) were monitored at a sampling site in Mutsu Bay, Japan, in 1995.Dinophysis fortii almost completely dominated the toxic phytoplankton community. Okadaic acid (OA) and dinophysistoxin-1 (DTX1) contents in bothD. fortii cells and midgut glands of scallops collected at the same sampling site were determined by HPLC — fluorometry. DTX1 was detected fromD. fortii and scallops. The contents of DTX1 inD. fortii changed markedly during the experimental periods (5–252 pg cell^–1). The highest concentration of DTX1 in the midgut glands of scallops coincided with the period of relatively high cell densities ofD. fortii with the highest content of DTX1 (252 pg cell^–1). The results demonstrate that toxin content in the cells is an important factor affecting the toxicity of shellfish.     

Restriction fragment length polymorphisms of the phytohemagglutinin genes inPhaseolus andVigna (Leguminosae)

Restriction fragment length polymorphisms at the phytohemagglutinin (PHA) locus were determined among 21 genotypes ofPhaseolus vulgaris, P. coccineus, P. acutifolius, P. lunatus, and threeVigna species, using five restriction enzymes and one double digestion, in order to provide molecular evidence for their genetic relatedness. The dissimilarity between genotypes was estimated from binary RFLP data. The dissimilarity was high among species (from 0.75 to 0.95), and of variable extent among genotypes of the same species (0.33–0.89). InP. vulgaris, two different DNA hybridization patterns were found, giving further evidence for two major gene pools in that species. The restriction patterns ofP. vulgaris var.aborigineus, the putative ancestral form ofP. vulgaris, exhibit clear homology toP. vulgaris genotypes. An undefined landrace from Taiwan could be identified as aP. vulgaris genotype. RFLP-based trees for the phytohemagglutinin genes of the species studied were computed with several distance matrix and parsimony methods.     

Conservation of rDNA inPolystichum (Dryopteridaceae)

Restriction site variation in the nuclear 18S–25S ribosomal RNA genes (rDNA) was analyzed hierarchically in a species complex in the fern genusPolystichum. Two distinct rDNA repeat types were present in all individuals ofPolystichum examined. No variation was detected among individuals within a population ofP. munitum, among populations ofP. munitum orP. imbricans, or among the six diploid species ofPolystichum from North America, including the circumborealP. lonchitis. The identity of rDNA repeats across all six North American species ofPolystichum may reflect an overall similarity of the nuclear genomes of these species, an observation supported by isozyme data as well. However, this nuclear similarity contrasts sharply with the highly divergent chloroplast genomes of these six species. The conservative nature of the rDNA inPolystichum also is in contrast to the much more variable rDNAs of most angiosperms investigated. Perhaps the tempo and mode of evolution of rDNA in ferns differ from those of angiosperms; however, the data base for fern rDNA is very small. Furthermore, the number of repeat types per individual is consistent with a diploid, rather than polyploid, condition despite the high chromosome number (n = 41) of these plants, although homogenization of multiple, divergent rRNA genes cannot be disproven.     

Lagenidium infection in eggs and larvae of mangrove crab (Scylla serrata) produced in Indonesia

A fungal infection occurred in the eggs and larvae of mangrove crab (Scylla serrata) in seed production in Bali, Indonesia. The causative fungus was classified as a member of the genusLagenidium (Oomycetes, Lagenidiales). After comparison of its biological and physiological characteristics with those ofL. callinectes ATCC 24973, a known parasite of various crustaceans, was concluded that the isolate is a new species ofLagenidium, L. thermophilum, because of its rapid and thermotolerant growth and unique discharge process. Fungal growth was observed on PYG agar containing 0–5.0% (w/v) NaCl and 0–2.5% (w/v) KCI. Similar pathogenicity toward the zoeae of swimming crab (Portunus trituberculatus) was demonstrated.     

Culture ofPavlova lutheri (Droop) Green (Prymnesiophyta) in diluted wastewater

Cell concentrations in large-scale (14-1) laboratory cultures ofPavlova lutheri in seawater enriched with a mixture of the effluents of the aerobic digestion ofMacrocystis pyrifera and of cow and chicken manures, were close to 2× 10⁶ cells mL^–1, similar to those obtained with a conventional medium with nitrogen concentrations about one order of magnitude higher. The biomass produced had similar protein contents which, in the case of the non-conventional medium, accounted for all the nitrogen, including organic nitrogen, available in the medium. In 125-mL cultures, cell concentrations were significantly higher in the nitrogen-rich medium, showing thatP. lutheri was nitrogen-limited in waste-enriched seawater.Growth in unenriched seawater with nitrogen-rich and nitrogen-deficient inocula showed thatP. lutheri can store enough nitrogen for about five cell divisions and that it can use dissolved nitrogen at concentrations 0.05 mmol L^–1.     

Population ecology ofPimelodella kronei,troglobitic catfish from Southeastern Brazil (Siluriformes,Pimelodiae)

Synopsis Pimelodella kronei, a cave derivative of the pimelodid catfishP. transitoria, has been found in five caves of the Ribeira River valley, SE Brazil. I investigated the ecology of the most conspicuous population, that from Areias Caves, by capture-mark-recapture. During the two-year study, 170 specimens ofP. kronei were marked, 81 were recaptured at least once, multiple recaptures were frequent. These blind catfishes tended to be recaptured in the same site where they were marked, suggesting a sedentary life and possibly territoriality. The home range was 200 m along the stream, or more where food was scarcer.P. kronei population size in 800 m of permanent stream was 150–200 individuals.P. transitoria also inhabits the cave, at a density ten times lower. The growth rate ofP. kronei was less than 0.1 cm × month^–1, and longevity was 10–15 years. These data, and evidences of an infrequent reproduction, indicate a K-selected life cycle, probably as a consequence of food scarcity.     

Biomass relationship to growth and phosphate uptake ofPseudomonas fluorescens,Escherichia coli andAcinetobacter radioresistens in mixed liquor medium

The ability ofPseudomonas fluorescens, Escherichia coli andAcinetobacter radioresistenns to remove phosphate during growth was related to the initial biomass as well as to growth stages and bacterial species. Phosphate was removed by these bacteria under favourable conditions as well as under unfavourable conditions of growth. Experiments showed a relationship between a high initial cell density and phosphate uptake. More phosphate was released than removed when low initial cell densities (10²–10⁵ cells ml^–1) were used. At a high initial biomass concentration (10⁸ cells ml^–1), phosphate was removed during the lag phase and during logarthmic growth byP. fluorescens. Escherichia coli. at high initial biomass concentrations (10⁷ cells ml^–1), accumulated most of the phosphate during the first hour of the lag phase and/or during logarithmic growth and in some cases removed a small quantily of phosphate during the stationary growth phase.Acinetobacter radioresistens, at high initial cell densities (10⁶, 10⁷ cells ml^–1) removed most of phosphate during the first hour of the lag phase and some phosphate during the stationary growth phase.Pseudomonas fluorescens removed phosphate more thanA. radioresistens andE. coli with specific average ranges from 3.00–28.50 mg L^–1 compared to average ranges of 4.92–17.14 mg L^–1 forA. radioresistens and to average ranges of 0.50–8.50 mg L^–1 forE. coli.     

Biology ofChironomus piger Str. (Diptera: Chironomidae) and its role in the self-purification of a river

Chironomus piger larvae are widespread in small rivers and canals strongly polluted with domestic sewage. Despite this, almost nothing is known concerning the biology of the species under natural conditions and its role in the process of river self-purification. For two years, benthic samples were collected in the Sestra River at a site about 250 m downstream of the effluent discharge drains of a sewage treatment installation where the greatest concentrations of the larvae occurred. The number and biomass ofC. piger larvae were subject to marked fluctuations,viz. 96,000–348,000 ind m^–2 and 420–1,800 g m^–2. 460 degreedays (on average) was required for development of one generation.C. piger has 5 or 6 generations per year depending on the hydrometeorological conditions during the growing season.C. piger larvae play an important role in self-purification of the river. They utilize precipitating seston for food and for building their dwelling tubes. According to our calculations the amount of organic matter assimilated in the area of maximum larval concentration ranged 80–177 g wet weight m^–2 day^–1, and 32–71 g wet weight m^–2day^–1 was mineralized.     

Studies on Ephemerella ignita (Poda) in a chalk stream in Southern England

The nymphs ofEphemerella ignita occurred in all months except October in the Bere Stream at Bere Heath, a small chalk stream in Southern England. Peak densities of 1,498 m^–2 and 753 m^–2 were recorded in May by two sampling methods used simultaneously. The seasonal patterns of growth and abundance are compared with the findings of other authors. A maximum biomass of 0.82 g m^–2 preserved dry weight is compared with figures for two of the most common invertebrate groups present; the Simuliidae and Oligochaeta.     

Epidemiology of anther-smut disease (Microbotryum violaceum) and numeric regulation of populations ofSilene dioica

Summary The interaction between the anther smutMicrobotryum violaceum and its hostSilene dioica was studied during 1985–1990 in 47 populations of different ages, sizes and densities, in an archipelago area in northern Sweden. The sizes of these populations had also been surveyed in the early 1970s. Our results indicate that establishment ofMicrobotryum violaceum is host-size and density dependent. Firstly, young populations ofSilene dioica that became diseased during the study were larger and tended to be more dense than young populations that remained healthy. Secondly, populations diseased in both 1985 and 1990 were found to be larger and tended to be more dense than populations healthy in both years. We were able to document that the pathogen actually failed to establish in two small young populations (diseased plants died shortly after they appeared) and did go extinct in one small old population. Disease incidences within populations did not show large fluctuations between years. The highest increases in disease incidence during the study were found in three relatively young populations that were disease-free at the start of the study. Older populations highly diseased at the start showed less of an increase. Our study indicates thatMicrobotryum violaceum acts as a regulatory factor influencing the rate of increase inSilene dioica populations, once they are sufficiently large to maintain the pathogen. Firstly, seedling density decreased with increased incidence of disease and a seed addition experiment indicated seed-limited recuritment in highly diseased populations. Secondly, those populations that reached very large sizes or densities were either healthy or had very low incidences, indicating the potential for populations that for one reason or another escape an epidemic. However, in the comparison of changes in population size over 16–18 years there was no simple correlation between expansion rate and disease incidence.     

Effect of salinity on competition between the rotifers Brachionus rotundiformis Tschugunoff and Hexarthra jenkinae (De Beauchamp) (Rotifera)

We studied the effect of different concentrations (0, 3, 6, 9 and 12 g l^–1) of sodium chloride at one food level of Chlorella (1×10⁶ cells ml^–1) on competition between the rotifers B. rotundiformis and H. jenkinae, both of which were isolated from a saline lake. The population growth experiments were conducted for 3 weeks. Both the rotifer species did not survive beyond one week at a salinity of 0 g l^–1. Regardless of salt concentration and the presence of a competitor, H. jenkinae reached higher densities than B. rotundiformis. When grown alone, both B. rotundiformis and H. jenkinae showed optimal peak population densities at the salinity of 6 and 9 g l^–1. Since biomass wise, B. rotundiformis was larger than H. jenkinae, it showed a lower numerical abundance. Thus, the maximum peak population densities of B. rotundiformis and H. jenkinae recorded in this study were 107±3 and 203±28 ind. ml^–1. The maximal rates of population increase for B. rotundiformis and H, jenkinae when grown alone were 0.264±0.003 and 0.274±0.004, respectively. Our results also indicated that B. rotundiformis and H. jenkinae coexisted better at a salinity of 6 and 9 g l^–1 of sodium chloride while a salinity of 3 g l^–1 favoured Hexarthra over B. rotundiformis. At 12 g l^–1, both the rotifer species grown alone or together showed lower growth rates compared to those at lower salinity levels. Except 0 g l^–1, in all other salinity treatments, H. jenkinae was a superior competitor to B. rotundiformis.     

Effect of Host Plant on the Potential ofPaecilomyces fumosoroseus(Deuteromycotina: Hyphomycetes) for Controlling the Silverleaf Whitefly,Bemisia argentifolii(Homoptera: Aleyrodidae) in Greenhouses

We determined host plant effect on susceptibility of the silverleaf whitefly,Bemisia argentifolii, to the entomopathogenic fungusPaecilomyces fumosoroseus. Whiteflies were reared on three vegetable species (cucumber, cabbage, and tomato) and three cultivars of tomato (Heatwave, Better Boy, and Rutgers). Second instars were sprayed with 5 × 10⁴conidia/cm²ofPfr97, aP. fumosoroseusstrain, used as a microbial control agent of whiteflies. Trials were conducted in an experimental greenhouse, where temperature and relative humidity were adjusted to favor infection (22–33°C, and 68–100% RH). Larval susceptibility to fungal infection was high and not significantly affected by the host plant. Mortality was > 70% 1 week after treatment and increased further during the second week. Percentages of cadavers with subsequent production of conidia observed in the greenhouse did not vary significantly either with the host vegetable species (85–93% 7 days after treatment and 99–100% 14 days after treatment), or with the cultivar of tomato (96–97% 7 days after treatment and 99–100% 14 days after treatment). After incubation under optimal laboratory conditions, the percentages based on the total number of sporulating cadavers (includingin situsporulating individuals and cadavers sporulating afterin vitroincubation) were not significantly influenced either by host vegetable or cultivar of tomato. According to the conditions prevailing in the series of experiments with the three vegetable species or in the series of experiments with the three cultivars of tomatoes, the production of newly formed conidia varied from approximately 10,000 to 18,000 conidia/cadaver. However, in both series, there was no significant influence of the host vegetable species or cultivar. The survival of the newly formed conidia harvested 7 days following treatment reached more than 50% but was not affected by host plant. These results indicate thatP. fumosoroseusshows potential as a microbial control agent for controllingB. argentifoliion greenhouse crops.     

Intra- and interspecific variation in body size ofProtohermes (Megaloptera: Corydalidae)

The life history of three populations ofProtohermes grandis and two populations ofProtohermes immaculatus (Megaloptera: Corydalidae) was compared. In general, the larvae lived in stream riffles for 2 years and the adults appeared in summer. Adult body size differed between these closely related species and also between the populations ofP. grandis. Dwarfism occurred inP. immaculatus, a species that is endemic to the small, isolated island, Amami Island. The population ofP. grandis on Yaku Island, located between Amami Island and the mainland Kyushu, had an intermediate body size between that ofP. immaculatus and the mainland population ofP. grandis. Despite being an insular population,P. grandis on Tsushima Island had a similar body size to mainlandP. grandis. In these populations with large adults, some larvae lived in the streams for 3 years. The size distribution of benthic animals, which are the prey available toProtohermes larvae, differed between the streams studied. The density of large prey was lowest on Amami Island, intermediate on Yaku Island, and highest on the mainland and Tsushima Island. Different size distributions of available prey may be caused by the differences of benthic fauna; most of Ecdyonuridae and Ephemerellidae (large mayflies) and Perlidae (large stoneflies) were not found on Amami and Yaku Islands. Thus, there is a tendency to dwarfism in the populations ofProtobermes inhabiting streams where the density of large prey is low.     

The spring-time abundance and feeding ofEurytemora affinis (Poppe) in Volkerak-Zoommeer,a newly-created freshwater lake system in the Rhine delta (The Netherlands)

Eurytemora affinis, a calanoid copepod, has been encountered in Volkerak-Zoommeer (Rhine delta region, S.W. Netherlands) both before this lake system was isolated in 1987 from the estuarine influence, and after. It was the main particle-feeding crustacean at all the 3 sampling stations in March–April 1990 when it reached densities of up to 215 ind.l^–1. Its decline from mid April onwards, and low densities through summer, coincided with increase in cladocerans, especiallyDaphnia spp. (D. pulex andD. galeata), a decrease in seston (<33m) and chlorophyll concentrations and in primary production rates. The clearance rates (CR) ofEurytemora measured in the spring period varied enormously (0.6–24 ml.ind^–1.d^–1) depending mainly on size (0.44–1.06 mm), food concentration (0.8–2.2 mg C.l^–1), and the water temperature which varied only narrowly (8.0–9.0°C). Mean ingestion rates of the animals measuring 0.68±0.02 mm during the study was 6.7±3.2 gC.ind^–1.d^–1; and assimilation efficiency varied between 27 and 53% (mean: 41±9%). The weight specific CR (SCR) varied between 0.96 and 6.4 litre.mg^–1 body C.d^–1. Pooled regression of SCR on the animal's body weight at the 3 study stations revealed a significant inverse relationship. Also daily ration and specific assimilation ofE. affinis varied greatly and inversely with the body weight. This calanoid contributed from about 50 to 100% to the zooplankton community grazing rates and assimilation rates, the former often exceeding the phytoplankton primary production.     

On the distribution patterns and population dynamics of sublittoral and profundal oligochaeta fauna from Lake Banyoles (Catalonia,NE Spain)

Oligochaeta assemblages from Lake Banyoles were composed of one species of Naididae and eight species of Tubificidae, Potamothrix heuscheri (8–1350 ind. m^–2) being the most abundant and widely distributed species, followed by Limnodrilus hoffmeisteri (25–858 ind. m^–2) and Psammoryctides barbatus (12–792 ind. m^–2). The remaining species were Potamothrix hammoniensis, Potamothrix bavaricus, Limnodrilus claparedeanus, Branchiura sowerbyi, Aulodrilus pigueti and Dero digitata, all of which occurred at lower densities and with restricted distributions.Regardless of sampling depth, maximum densities of oligochaetes were found in winter (up to 5,142 ind. m^–2 in December) and secondarily in June. Immature Tubificidae with hair setae and mature P. heuscheri were present and dominant throughout the year. Cestode parasites were recorded infesting L. hoffmeisteri and P. heuscheri populations.Oligochaeta densities increased with depth, but low oxygen concentrations (less than 1 mg l^–1) during a long period (4 months) in some basins of the lake acted as a key factor in reducing the density of worms and the species richness to one species, Potamothrix heuscheri.     

Pollination of sevenPlectranthus spp. (Lamiaceae) in southern Natal, South Africa

The genusPlectranthus (Lamiaceae) shows remarkable radiation on the sandstones of southern Natal and northern Transkei in South Africa, where six endemic species occur. Two of these endemic species,P. hilliardiae andP. oribiensis, are included in this study, as well asP. reflexus, for which only limited data are available. The other species that were studied areP. ambiguus, P. ciliatus, P. ecklonii, P. madagascariensis andP. zuluensis. Four of these taxa,P. ambiguus, P. hilliardiae, P. reflexus andP. saccatus var.longitubus, have uniquely long corolla-tubes (20–30mm) and this is related to pollination by nemestrinid flies of the genusStenobasipteron that have proboscides of similar length. Other nemestrinid species of the genusProsoeca have shorter proboscides and pollinate two species ofPlectranthus with shorter corolla-tube lengths (6–15mm). Acrocerid flies, tabanid flies and anthophorid bees are also important visitors to these species. This study on the pollination of seven species of varying corolla-tube lengths shows a correlation between floral tube length and proboscis length of insect visitors, many of which are recorded for the first time as pollinators ofPlectranthus.