ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00181.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00200.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTGrowth and different phases in the life histories of Bos‐trychia tenella (Vohl.) J. Ag., Caloglossa leprieurii (Mont.) J. Ag., andCatenella impudica (Mont.) J. Ag. were estimated for 23 months from January 1986 to December 1987 in the Gautami Godavari estuary of lndia. Seasonal data on hydrographical conditions, biomass, and plant length were collected from three stations in this estuary. Biomass was minimum in August and September and maximum in January and February, as was frond length of tetrasporic and vegetative plants. Temperatures of 24°–27°C and salinities of 5–20 ppt coincided with optimal growth for all three algae. In all three species, tetrasporophytes were present in all months of the year without any seasonal periodicity, and nearly 50% of the plants were tetrasporophytes. The gametophytes ofB. tenellaandC. leprieuriiand cystocarpic plants ofC. impudicaoccurred from October to May, with greatest abundance in January. The abundance of spermatangial and cystocarpic plants in the populations ofB. tenellaandC. leprieuriiranged from 3 to 15%. Spermatangial plants ofCatenella impudicacould not be identified, and the abundance of cystocarpic plants was v

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00209.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTDNA: ATP and carbon: DNA (C:DNA) ratios were measured in a total of 14 species of marine microalgae and bacteria. Comparison of several DNA assay methods with results obtained with cultures uniformly labeled with33P indicated that by far the most accurate results were obtained using diaminobenzoic acid (DABA) or diphen‐ylamine, with DABA having the highest precision. Both the Hoechst and DAPI methods seriously underestimated DNA concentrations in algal cultures. Average DNA: ATP ratios in the algal and bacterial cultures were I7 and 34 by weight, respectively, with almost all values lying in the range of 10–40. DNA: ATP ratios in the microalgae showed no correlation with growth conditions but varied by about a factor of 3 among species. C:DNA ratios for individual species of microalgae and bacteria ranged from 21 to 155 by weight and averaged 50 for the microalgae and bacteria taken together. Growth rates of microalgal species grown in cyclostats were estimated to within 8% of dilution rates when calculated from the uptake of3H‐adenine and the DNA: ATP ratio of the species. Use of the3H‐adenine method for estimating microalgal growth rates in the field may thus be a useful tool for investigating the physiology of microalgae in

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00215.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThroughout the summer, abundance ofUlva lactucaL. declined while biomass ofCladophora vagabunda (L.) van den Hoek andGracilaria tikvahiaeMcLachlan increased in a New England embayment undergoing eu‐trophication (Waquoit Bay, Massachusetts). We investigated the physiological basis for the summer dieback, focusing on temporal variations in photosynthetic performance and tissue nitrogen (N). We also compared photosynthetic and N uptake capabilities ofU. lactucawith other abundant species in this eutrophic system. Photosynthetic egiciency and capacity ofU. lactucadeclined markedly at 25°C, compared with a spring (15°C) peak in photosynthetic performance; Pmaxwas 4.6 ± 0.3 and 1.8 ± 0.6 μmol O2.m−2.s−1during spring and summer, respectively. Notably, summer pmaxof other abundant species of the embayment was 1.5–3 × higher than that measured forU. lactuca. Ulva lactucashowed a signifciant photosynthetic response to dissolved inorganic carbon enrichment during summer, when water‐column‐dissolved CO2levels were 20% of spring values. Although ammonium uptake rates ofU. lactucawere extremely high at both subsaturating (15μM) and saturating (75 μM) N concentrations, as predicted by the functional‐form hypothesis, tissue N fell to 1% by late summer. We suggest that a carbon imbalance, initiated by rising water temperatures and declining water‐column N; thermal stress; and biological factors (competition, grazing) all contribute to the recurrent summer decline ofU. lactucain this shallow, eutrophic embayment. Thus, while the morphology of U. lactucamight be considered a successful strategy for disturbed, or “stressed”(sensuLittler and Littler 1980), habitats, its inability to persist and flourish in this environment emphasizes the complexity of factors

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00223.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTIn a eutrophic embayment (Waquoit Bay, Massachusetts), Cladophora vagabunda (L.) van den Hoek occurs in thick (sometimes>1 kg dry wt ‐m−2), nearly monospecific unattached mats in deeper regions (2 m), whereasGrac‐ilaria tikvahiaeMcLachlan is largely restricted to shallow (<1 m) areas. We explored these distribution patterns, investigating competitive interactions between these opportunistic species by varying the limiting resource, photon flux density (PFD), and species composition under conditions of N sufficiency in microcosms. Under lower biomass loadings, neither species showed a difference in growth rates in single‐ and mixed‐species stands. With a 25% increase in initial biomass loading, Gracilaria tikvahiaehad significantly higher growth rates under saturating PFD and consistently showed greater performance when grown in single‐species rather than in mixed‐species stands. While growth rate was 2×greater forC. vagabundain single‐species than in mixed‐species stands at saturating PFD, this pattern was reversed under limiting irradi‐ances. In mixed‐species stands at high PFD (comparable to shallow regions of the bay), the growth rate ofG. tikvahiaewas over 4×higher than that of C. vagabunda. Cladophora vagabundagrew at a faster rate thanG. tikvahiaeonly in the low PFD, mixed‐species treatment. Results of this study suggest that the observed distributional patterns of these macroalgae are due in part to interspecific exploitative competition but that tolerance of low PFD byC. vagabundahas led to dominance of these species in distinctive

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00229.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe resistance of stream periphyton to structural disturbance by increases in shear stress (simulating a spate) was investigated in a laboratory flow tank. We monitored loss of biomass from a filamentous community (dominated byMelosira varians)under four different levels of shear stress. In each case, any loss that was going to occur did so within 10 min for this community. In a second experiment, we tested the resistance of four different communities (two dominated by nonfilamentous diatoms and two dominated by filamentous green algae/diatoms) to increases in shear stress. Nine different levels of shear stress were used, ranging from 1‐ to 70‐fold higher than the conditions to which the communities were acclimated. All communities were 14 days old, but some differences in initial biomass occurred that influenced the degree of resistance independently of species composition. Overall, the nonfilamentous diatom communities were the most resistant, and the filamentous communities were the least resistant. The kinetics of the sloughing process varied among community types, with a community dominated byMelosira varians/Gom‐phonema parvulumlosing 50% of its biomass with only a 3‐fold increase in shear stress. In contrast, a community dominated by the nonfilamentous diatomsFragilaria vaucheriae/Cymbella minutalost90.0 N.m−2for theFragilaria vaucheriae/Cymbella minutacommunity. These results show that spates without bedload movement can potentially have widely differing disturbance effects on periphyton loss among streams depending on the initial taxonomic composition of resident communities. These results have important implications for stream ecosystem

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00233.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA mat‐forming cyanobacterium(Phormidium mur‐rayiWest and West) isolated from an ice‐shelf pond in Antarctica was grown under white light combined with a range of UVA and UVB irradiances. The 4‐day growth rate decreased under increasing ultraviolet (UV) radiation, with a ninefold greater response to UVB relative to UVA. In vivoabsorbance spectra showed that UVA and to a greater extent UVB caused a decrease in phycocyanin/ chlorophyllaand an increase in carotenoids/chlorophylla.The phycocyanin/chlorophyllaratio was closely and positively correlated to the UVB‐inhibited growth rate. Under fixed spectral gradients of UV radiation, the growth inhibition effect was dominated by UVB. However, at specific UVB irradiances the inhibition of growth depended on the ratio of UVB to UVA, and growth rates increased linearly with increasing UVA. These results are consistent with the view that UVB inhibition represents the balance between damage and repair processes that are each controlled by separate wavebands. They also underscore the need to consider UV spectral balance in laboratory and field assays of UVB

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00242.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe patterns of occurrence of the peptide hepatotoxin microcystin‐LR (MC‐LR) was studied in three hypereu‐trophic hardwater lakes (Coal, Driedmeat, and Little Beaver) in central Alberta, Canada, over three open‐water seasons. MC‐LR concentration was based on high‐performance liquid chromatography detection and expressed as μg.g−1of total plankton biomass, ng.L−1of lake water, and μg.g−1ofMicrocystis aeruginosaKuetz. emend. Elenkin. MC‐LR was highly variable temporally (differences up to 3 orders of magnitude) within each lake over an individual year, between years in an individual lake, and between lakes in any year. Seasonal (within‐year) changes in MC‐LR concentration (expressed in the preceding units) were positively correlated to the abundance and biomass Of the cyanobacteriumM. aeruginosa (r =0.60–0.77), total and total dissolved phosphorus concentration(r =0.46–0.59), pH (r=0.38–0.58), and chlorophylla (r=0.25–0.59). Surprisingly, there was no relationship between MC‐LR concentration and water temperature (range: 7°‐24°C, r =‐0.13 to 0.02) and a negative correlation with nitrate concentration(r =–0.27 to ‐0.34). In two synoptic surveys examining spatial variability, MC‐LR concentrations were quite variable (CV of 185 and 36% between sampling sites for Coal and Little Beaver lakes, respectively). Spatial distribution of MC‐LR on any one day was correlated with the abundance and biomass ofM. aeruginosa.Over a 24‐h period, MC‐LR concentration inM. aeruginosadecreased more than 6‐fold at night relative to daytime concentrations. In general, analytical and within‐site variation of MC‐LR was relatively small (CV<4 and 9%, respectively) but greatest both within and bet

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00248.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe architecture of the filamentous green algaCladophora glomerata (L.) Kütz. and the composition of this alga's epiphytes [primarily the diatomsEpithemia turgida (Ehrenb.) Kütz., Epithemia sorexKütz., andCocconeis pediculusEhrenb.] were examined in different velocity regimes. After transferring algal‐bearing cobbles among velocities, the effects of changes in velocity were also examined. Cladophorabranching pattern did not initially differ among slow, medium, and fast velocities, indicating that stable water velocities did not affect branching pattern. Two weeks after cobble transfer, Cladophorain fast velocity had fragmented more (i.e. had fewer filaments and fewer branch points per length of filament and had a higher percentage of unbranched filaments) thanCladophorain slow velocity. Fragmentation was greatest in tufts moved from slow velocity, suggesting velocity‐associated differences in susceptibility to breakage. Epiphytic assemblage composition differed among slow, medium, and fast velocities and between locations on the filament (base and apex). Cocconeis pediculusdominated where exposure to high velocity was greater (filament apices in medium and fast velocities), whereas theEpithemiaspp. dominated where lower velocities occurred (filament bases in all velocities and apices in slow velocity). Two weeks after the cobble transfer, the translocated diatom assemblages had changed and the original pattern of diatom distribution was re

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00264.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY