The organization of macroinvertebrate communities in the major tributaries of the LaTrobe River, Victoria, Australia

SUMMARY.

• 1 Seventeen sites were each sampled six times over 2 years for macroinvertebrates. A range of physicochemical variables was also measured to determine which factors were related to the distribution of species.
• 2 Numerical classification of the faunal data indicated that four groups of sites or communities were distinguishable: lowland sites; sandy upland sites; cobble upland sites from the northern catchment; cobble upland sites from the southern catchment.
• 3 Multiple discriminant analysis and multiple regression analysis demonstrated that particle size of the sediment, concentration of dissolved ions and altitude were the physicochemical features that were most strongly associated with changes in the faunal distribution.
• 4 Abundances of shredders and predators did not vary between the site groups while those of scrapers, gatherers and filterers did: scrapers were most abundant at cobble sites while gatherers and filterers were least abundant on sand and increased in abundance downstream. The distribution of the feeding groups showed some similarity with that predicted by the River Continuum Concept, but the fact that the shredders did not decrease in abundance downstream was a notable difference.
• 5 Abundance of the total fauna at a site was inversely related to the amount of benthic organic matter. This feature is contrary to the pattern usually reported from rivers in the northern hemisphere.

     

The distribution and production of Gammarus pseudolimnaeus (Crustacea: Amphipoda) along a reach of the Credit River, Ontario

SUMMARY. The population density of the univoltine amphipod Gammarus pseudolimnaeus was estimated monthly from April 1977 to June 1978 along a 600-m reach using a form of removal sampling at 0.5, 1.5 and 2.5 m from the bank. The probability of catching an amphipod with three sweeps over an area of 0.15 m² was 0.95. Drift and upstream migration were measured for 24 h, also monthly. Population density varied from 1600 m⁻² (newly-hatched young in July) to 26 m⁻² (adults) within 3 m of the bank with 95% confidence limits of 40–60% of the mean; density was highest < 1 m from the bank and beyond 3 m it declined to insignificant levels. No significant difference could be shown between the total catches in the drift and upstream nets over a year and there appeared to be no net migration of amphipods. Mean drift was 2 amphipods day⁻¹.
Growth was estimated from the length composition of monthly samples. Annual production ( P ) was 29.4 kg ha⁻¹ for one generation of the amphipod with a P/B ratio of 4.65. Egg production accounted for only 2% of this estimate. Recruitment was calculated from regressions relating female length to clutch size and egg development time to temperature in the laboratory; mean temperature was measured in the field.
Mortality was greatest in July at the beginning of the generation. It was high again in September and during winter; at these later times it was suggested that starvation occurred in addition to predation. Annual consumption ( C ) of organic matter for the generation calculated from published data on feeding rate was 1547 kg ha⁻¹ which results in a P/C ratio of 1.9%.     

Epidermal club cells and the innate immune system of minnows

Thousands of fish species belonging to the Superorder Ostariophysi possess specialized club cells in their epidermis. Damage to the cells, as would occur during a predator attack, releases chemical substances that evoke antipredator responses in nearby shoalmates. These chemical substances have often been referred to as alarm substances and the cells that release them as alarm cells. Understanding the evolution of the cells in an alarm context has been difficult. The fish needs to be captured prior to the chemicals being released, hence the benefit to the receiver is unclear. Recent studies have suggested that the club cells are part of the immune system and are maintained by natural selection owing to the benefits that they confer against pathogens, parasites, and general injury to the epidermis. In the present study, we gave fathead minnows intraperitoneal injections of cortisol, a known immunosuppressant, or injections of a control substance (corn oil). We found that fish exposed to cortisol had suppressed immune systems (as measured by a respiratory burst assay) and that they also reduced their investment in club cells. This is the best evidence to date indicating that the club cells of Ostariophysan fishes are part of the innate immune system and that the alarm function of the cells evolved secondarily. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 891–897.     

The use of AUSRIVAS predictive models to assess the response of lotic macroinvertebrates to dams in south-east Australia

1. Sites immediately below seven dams in Victoria and 12 in southern New South Wales (NSW) were sampled for macroinvertebrates using rapid bioassessment techniques. Specimens were identified to the lowest taxonomic level. The dams had different operating and discharge regimes and thus potentially different downstream effects on this fauna.
2. The AUStralian RIVer Assessment Scheme (AUSRIVAS) predictive models for macroinvertebrate composition were applied to the families and genera observed at Victorian sites and to the families only at the NSW sites. Lists of predicted taxa, their probabilities of occurrence and ratios of observed to expected taxa (O/E scores) were obtained from these models.
3. The mean O/E score for Victoria was 0.46 at the genus level and 0.63 at the family level; for NSW the mean score at the family level was 0.62. There was no significant difference between family level scores for the two states. Thus about 40% of expected families were missing at all sites. Family level scores were highly correlated ( r =0.84–0.86, P  < 0.001) with numbers of families or species at a site.
4. There was no correlation between family O/E scores (or family and species richness) and the degree to which current discharge levels below a dam differ from the natural patterns. Thus increased hydrological deviation did not result in greater biological degradation. In addition, there was no association between these biological characteristics and whether dams released surface or bottom water.
5. All the dams seemed to cause much the same disruption to the fauna. Of the families predicted to have widespread occurrence, 9–12 were found at most sites (tolerant taxa), while a larger number (14–24) were missing (intolerant taxa). The limited recolonisation below dams may well be because of the fact that dams act as barriers to drift, the most prominent route for invertebrate colonists.     

Evolution in Spartina (Gramineae) IV. The cytology of S. alterniflora Loisel. in North America

A cytological survey of Spartina alterniflora Loisel. populations in Canada and north-eastern U.S.A. establishes the widespread and seemingly exclusive occurrence of the 2 n = 62 chromosome number in that region. The data indicate that the introduced and relict populations of S. alterniflora in Southampton Water, Britain (whence arose S. × townsendii ) are not cyto-logically atypical of the main body of this species in North America, and there is therefore no reason to doubt, on the grounds of aberrant chromosome number, the role of S. alterniflora as a parent of S. × townsendii.
2 n = 62 is anomalous with respect to the basic number of x = 10 generally found in the genus. The present results indicate that 2 n = 62 is widespread in north-eastern North American S. alterniflora , and no other chromosome number has been found in a survey of the region. But the species is wide-ranging and the possibility of 2 n = 60 occurring in other areas, especially in the south of its range, cannot be ruled out. However, the only chromosome number so far confirmed in southern populations is a count of 2 n = 62 from Texas.     

Flagellate nutritional versatility as a key to survival in two contrasting Antarctic saline lakes

1. Seasonal patterns of grazing and photosynthesis were investigated in two saline Antarctic lakes (Highway and Ace) in the Vestfold Hills (68°S). The phototrophic nanoflagellate (PNAN) community was dominated by Pyramimonas gelidicola and two morphological forms of a cryptophyte species that occurred throughout the year. Both species were mixotrophic on bacteria, and in Highway Lake they also exploited dissolved organic carbon as determined by the uptake of fluorescently labelled dextrans. 2. Clearance rates ranged between 0.02 and 0.21 nL h^?1 cell^?1 in Ace Lake and 0.004–1.05 nL h^?1 cell^?1 in Highway Lake. On occasion cryptophyte grazing equalled that of the heterotrophic nanoflagellates (HNAN). 3. Photosynthetic rates showed similar trends in both lakes, but there were differences in chlorophyll a specific rates and photosynthetic efficiency, probably related to the meromictic characteristic of Ace Lake. Primary production was measurable in winter and peaked in summer following the maxima of mixotroph grazing. 4. The HNAN community of Highway Lake achieved clearance rates of 0.02–1.80 nL h^?1 cell^?1 and removing between 50 and 693 ng bacterial carbon L^?1 day^?1, with highest impact in winter when HNAN were most abundant. The HNAN also ingested fluorescently labelled dextrans showing a preference for 4 and 500 kDa molecules. The more diverse HNAN community of Ace Lake had lower clearance rates (0.04–0.37 nL h^?1 cell^?1) and exerted a lower grazing pressure on bacterioplankton. In Highway Lake, where the HNAN community was dominated by the choanoflagellate Diaphanoeca grandis, there was a significant correlation between mean cell volume and clearance rate. 5. The major feature was that the microbial plankton functioned throughout the year by employing nutritional versatility.     

Effects of multiple disturbance on macroinvertebrate communities in the Acheron River,Victoria

In the Acheron River, southern Victoria, patches of riffle substratum (ca 1 m²) were disturbed every 10 days by kicking and raking. After 20 days, i.e. three disturbances, a further set of patches was disturbed once. For the next 70 days macroinvertebrate dynamics were monitored in the two sets of disturbed patches and also in contiguous control patches. There were no differences in the temporal changes in total species richness, number of species per sample, densities of individuals, or species diversity (H’) between the two disturbance regimes. The composition of the fauna colonizing each disturbance regime was similar, and after 33 days the number of species per sample was similar in disturbed and control patches. The fauna appears to be well adapted to physical disturbance and current ideas linking species richness and disturbance cannot be readily applied to stream communities at the temporal and spatial scales of this experiment.     

Newly developed PCR primers for polymorphic microsatellite loci from the marine isopod Limnoria sp.

Nine microsatellite loci are isolated and characterized for the marine isopod Limnoria sp., a model invertebrate species for the study of connectivity of marine brooders with high potential of dispersal through rafting. Analysis of 35 individuals of one population revealed a mean number of alleles of 12.66 and mean expected heterozygosity of 0.83, indicating a high level of variability at most loci. These polymorphic microsatellite loci should be useful to the study of the geographical distribution of the genetic diversity of this species of Limnoria.     

Field estimates of oxygen consumption for the brine shrimp Parartemia zietziana Sayce (Crustacea: Anostraca) in two salt lakes in Victoria, Australia

SUMMARY. Oxygen consumption of P. zietziana was measured monthly in two saline (>60‰ salinity) lakes from November 1973 to November 1975 with short (<2 h) in situ incubations in BOD bottles. Tests in which oxygen decline was monitored continuously showed that there was no handling effect and respiratory rate was constant down to 1.8–1.9 mg O₂ 1⁻¹, about 40% of the usual initial concentration. Incubations over 24 h demonstrated no diurnal fluctuations in oxygen consumption. Multiple regression analysis indicated that 90% of the variance in respiratory rate ( R in mg O₂x10⁻⁴h⁻¹ individual⁻¹) was accounted for by changes in salinity (3%; S in ‰), temperature (7%; T in °C) and dry weight (8%; W in mg × 10⁻³): log R =−1.123+0.0025+0.021 T+ 0.756 log W. From this equation and data on population density, population respiration was calculated: 91864.5 mg O₂ m⁻² year⁻¹ in Pink Lake and 12367.5 mg O₂ m⁻²year⁻¹ in Lake Cundare.