Interannual variability in phytoplankton biomass and species composition in a subtropical reservoir

• 1 The interannual variability of the dominant phytoplankton populations is described in a subtropical reservoir in Queensland using weekly data for a 16-year period between 1978 and 1994. North Pine Dam, Brisbane, is in an area characterized by strong interannual variability in rainfall. This variability is linked to El Nino Southern Oscillation (ENSO) events. Between 1978 and 1994 periods of drought (during strong ENSO events) were interspersed by periods of flooding rains. Rainfall on the catchment and temperature and oxygen within the dam showed strong 40-day periodicities which also varied in strength interannually in response to ENSO events. Similar patterns of fluctuations in the 40-day periodicity have been found elsewhere in SE Australia. Seasonal cycles of stratification in the dam were a function of both hydrographic and hydrological events. Intermittent rain storms caused partial turnovers and large outflows. As much as 90% of the dam volume was exchanged in a single flood event.
• 2 The dominant phytoplankton species were similar to those frequently found in tropical and subtropical lakes and reservoirs. The phytoplankton community switched between cyanobacterial blooms (Cylindrospermopsis, Microcystis) during drought and falling water levels and diatom blooms (Aulacoseira) in response to inflows and seasonal turnovers. There appeared to be a subtle interaction between inflows, water column stability, the periodic overturns and the occurrence of the dominant species. All the dominant species showed long periods (2–4 years) of exponential increase or decrease superimposed on top of the seasonal fluctuations in abundance. These patterns of abundance led to marked interannual variability in the phytoplankton biomass. Climate variability had a major impact on the seasonal and interannual changes of the dominant phytoplankton species.
• 3 Phytoplankton biomass tended to be depressed for about 3 months after individual storm events but the data also displayed long-term lag effects (2–4 years) which destroyed any significant correlation between water residence time and biomass. Summer maxima of biomass dominated by cyanobacteria disappeared between 1985 and 1990 and were replaced by smaller winter peaks. The data presented here are not capable of unequivocally identifying the precise reason for these longer-term effects. Because of the implications for water quality management in subtropical and tropical reservoirs they warrant further study.

     

Nesting activity,breeding success and colony size for the Wedge-tailed Shearwater Puffinus pacificus on Heron Island

Abstract The Capricorn Group of islands in Australia's Great Barrier Reef Marine Park sustains one of the world's largest breeding populations of the Wedge-tailed Shearwater Puffinus pacificus. Heron Island, a 13.5 ha coral cay which supports tourist and research station leases as well as a national park, is the third largest nesting island in the group. Sample censuses of breeding burrows were conducted each year between 1985 and 1990 and a further survey was completed in 1993. These returned estimates of between 13 264±1387 and 16 337±1545 active burrows (Y±SE). Burrow densities within each of the habitats monitored showed no significant trends between years, although there were large differences in burrow density between habitats. There were roughly the same number of burrows in the developed (west) and national park (east) halves of the cay. A miniature video camera system (burrowscope), which allowed nesting chambers at the ends of burrows to be inspected, was used in 1989, 1990 and 1993. This demonstrated that around half the burrows were occupied by incubating birds. Variations were found in the distribution of incubating birds between habitats, although this did not remain constant between the years. In the 1993 season, breeding activity was traced from the burrow establishment to fledging stage. Fifty-one per cent of burrows were used for breeding (eggs laid), 77% of eggs hatched and 80% of chicks produced a fledgling. Overall breeding success for the island was estimated at 61%. In 1993 the area designated as Buildings was found to have significantly lower hatching success compared with natural habitats. Most mortality occurred at the egg stage; however, in the Fringe habitat, mortality was highest at the chick stage. Previous surveys have estimated the breeding population from burrow counts. It now appears that only about 30% of such burrows produce fledglings.     

MDMP Action: Degradative Effects on Polyribosomes from Wheat Roots and the Inhibition of Protein Initiation

The rapid action of MDMP in promoting the conversion of polyribosomesinto monoribosomes in wheat roots suggests that the compoundmay interfere with the attachment of ribosomes to messengerRNA. The action is stereospeeffic: the L-lsomer has no effecton polyribosomes and does not compete with D-MDMP with respectto polyribosome degradation or the inhibition of initiation-dependentamino acid incorporation in vitro.     

Use of Shields stress to reconstruct and forecast changes in river metabolism

1. Discharge patterns of streams and rivers may be substantially affected by changes in water management, land use, or climate. Such hydrological alterations are likely to influence biotic processes, including overall ecosystem metabolism (photosynthesis and respiration). One regulator of aquatic ecosystem metabolism directly tied to hydrology is movement of bed sediments. 2. We propose that ecosystem metabolism can be reconstructed or predicted for any suite of hydrological conditions through the use of quantitative relationships between discharge, bed movement and metabolism. We tested this concept on a plains reach of the South Platte River in Colorado. 3. Movement of bed sediments was predicted from river discharge and the Shields stress, a ratio of velocity‐induced stress to sediment grain size. Quantitative relationships were established empirically between metabolic response to bed movement and recovery from bed movement, thus linking metabolism to hydrology. 4. The linkage of metabolism to hydrology allowed us to reconstruct daily photosynthesis and respiration over the 70‐year period for which discharge is known at our study site on the South Platte River. The reconstruction shows major ecological change caused by hydrological manipulation: the river has lost two‐thirds of its photosynthetic potential, and the ratio of photosynthesis to respiration is now much lower than it was prior to 1960. 5. The same approach could be used to anticipate ecological responses to proposed hydrological manipulations, to quantify benefits of hydrological restoration, or to illustrate potential effects of change in climate or land use on flowing‐water ecosystems.     

Leaf breakdown in an Atlantic Rain Forest stream

The hypothesis of this study was that colonizers in decaying leaf litter prefer native species (Erythrina verna) to exotic ones (Eucalyptus camaldulensis and Protium heptaphyllum). Therefore, native species are expected to show higher breakdown rates, increased biomass, richness and density of invertebrate species, and increased biomass of decomposer fungi. Breakdown of leaf litter from these three species was assessed in an Atlantic Rain Forest stream. Four samples were collected during a period of 90 days and washed on a sieve to separate the invertebrates. Then, a series of leaf disks were cut to determine ash‐free dry mass and fungal biomass, and the remaining material was oven‐dried to determine the dry weight. Eucalyptus camaldulensis and E. verna showed higher breakdown rates than P. heptaphyllum, due to differences in leaf physical and chemical characteristics. The harder detritus (P. heptaphyllum) broke down more slowly than detritus with high concentrations of labile compounds (E. camaldulensis). The density of the invertebrates associated with detritus increased with time. There were no differences in density, taxonomic richness or biomass of invertebrates among the leaf types, which indicated that the invertebrates did not distinguish between exotic and native detritus. Fungal colonization varied among samples; E. camaldulensis showed the lowest ergosterol concentrations, mainly due to a high concentration of total phenolics. The detritus with the highest hardness value was colonized most slowly by fungi. These results showed that leaf breakdown in Atlantic Rain Forest streams could be affected either by changes in riparian vegetation, or by becoming more savanna‐like process due to climate change.     

Characterization of Plant Epidermal Lens Effects by a Surface Replica Technique

Optical replicas of leaf surfaces were made for characterizingthe lens properties of individual epidermal cells. Using a dentallatex, moulds were made of leaf surfaces and subsequently usedto produce agarose replicas. The replicas focused light in amanner similar to intact epidermal cells and it was possibleto measure both focal lengths and intensifications within leafreplicas of Thermopsis montana, Mahonia repens, and Smilacinastellata which had epidermal cells of different diameter. Focallengths ranged from 74—130 µm which indicated thatlight was concentrated within the underlying photosynthetictissues of these leaves. Focal intensifications were measuredsensiometrically and were 1.5 for T. montana and 2-6 for theother species. These values compare favourably with calculatedfocal lengths and measurements taken from isolated epidermallayers. The results indicate that the epidermis can concentratelight within the leaf to amounts well in excess of ambient light.Furthermore, the replicas faithfully reproduced fine anatomicaldetails from a wide variety of leaves and they provide a non-destructiveway to reproduce surface characteristics for anatomical andphysiological studies.     

Effect of increased CO2 concentration and temperature on the phyllosphere mycoflora of winter wheat flag leaves during ripening

The impact of elevated carbon dioxide (CO₂, 600/700 μmol mol^-1) and temperature (+ 4°C) on phyllosphere fungi colonising flag leaves of mini crops of winter wheat cv. Mercia between anthesis and harvest was determined in a computer-controlled environment facility in 1993 and 1994. In both years the total fungal populations (cm² leaf) were found to have increased due to exposure to either elevated CO₂ and elevated CO₂+ temperature treatments. This was mainly due to significant increases in populations of Cladosporium spp. (C. cladosporioides and C. herbarum) on the flag leaves during ripening. Other phyllosphere component species such as white and pink yeasts were not markedly affected by treatments. The range of fungal species found in such controlled environment chambers was narrower than that commonly found on flag leaves of field grown crops. Common and important colonisers of leaves and ripening ears such as Aureobasidium pullulans, Epicoccum nigrum and Fusarium spp. were seldom isolated.