Life history and reproductive potential of the agarophyte Gelidium robustum in California

The reproductive potential of the tetrasporangial phase of Gelidium robustum was studied for 16 months at two sites off Santa Barbara, California. In all samples tetrasporangial thalli were always more abundant than gametangial ones. Tetratrasporangial sori were present throughout the duration of the study but relative fecundity was highest [300–400 sori g^–1 (w. wt)] in spring/summer samples of consecutive years, as a result of increasing numbers both of tetrasporangial branchlets per plant and of sori per branchlet. On the other hand, laboratory experiments showed that tetraspore release per sorus was highest (150–250 spores sorus^–1 d^–1) in winter. Inferring from these field and laboratory data plants released up to ± 34 000 tetraspores g^–1 (w. wt) d^–1 in the spring/summer of the second study year. Tetraspore germination, under defined culture conditions, also showed a marked seasonality increasing sharply from less than 10% in winter up to almost 60% in spring/summer, thus coinciding with the period of maximal spore output per plant. These results suggest that although relatively high numbers of tetraspores may be released by G. robustum plants all year round these might not always have the potential to germinate and recruit.     

Differential reattachment capacity of isomorphic life history phases of Gelidium sesquipedale

Vegetative reproduction is an important phenomenon in the propagation of Gelidium species, having significant implications for its ecology and commercial cultivation. This work is an experimental study of one of five sequential processes included in the vegetative propagation of Gelidium sesquipedale: the reattachment of rhizoidal filaments differentiated from apical fragments.Two different factors: light (25 µmol m^–2 s^–1 and long-day conditions, and 50 µmol m^–2 s^–1 and short-day conditions) and life history phases (female gametophytes and tetrasporophytes) were combined in a 2 × 2 factorial experiment. Reattachment of apical portions was induced in the laboratory under spray cultivation conditions and occurs mainly at the first stage of development when in contact with the substratum. Light conditions in these experiments (photoperiod + instantaneous photon flux densities) had no effect on the percentage of reattached neofilaments per fragment. Significant differences between percentages corresponding to both phases suggest, however, a probable competitive advantage of sporophytic fronds.     

Reproduction ofChondrus crispus Stackhouse (Rhodophyta,Gigartinales) in sublittoral Prince Edward Island,Canada

The influence of size (as biomass), morphology and depth on reproductive patterns was examined in populations ofChondrus crispus in the sublittoral zone of Prince Edward Island, Canada. Fronds of ≥ 10 mg wet wt were considered, and a minimum biomass could not be related to reproduction. However, as frond biomass increased, the frequency of reproductive structures also increased. Reproductive maturity was related to the number of dichotomies. Fronds with less than two dichotomies were only occasionally reproductive, while those with two or more dichotomies could bear sori. Depth in the Prince Edward Island environment had no apparent influence on reproductive maturity, and there was no apparent relationship between depth and the vertical distribution of cystocarpic or tetrasporic fronds.     

Sporulation ofEnteromorpha spp. (Chlorophyta) and overwintering of spores in sediments of the Wadden Sea,Island Sylt,North Sea

For the last two decades dense mats of species of the filamentous green algaeEnteromorpha spp. have regulary occurred on tidal flats of Köningshafen Bay (island Sylt, North Sea, FRG). In calm areas overwintering of adult plants or plant fragments is a common process to guarantee the mass development during the next season. In contrast, the distribution ofEnteromorpha on exposed sandy tidal flats depends on recruitment by juvenile stages. In 1993Enteromorpha spore settlement was recorded regularly in the field. Polyethylene dishes were placed in the field and left for a period of seven days and lateron cultivated in the laboratory to checkEnteromorpha germling development. During summer 1993 — at a minimum distance of 200 m to the nearest adultEnteromorpha populations — a total of at least 82×10⁶ spores m^–2 settled. During winter the number of spores attached to the collecting dishes was close to zero and the adjacent sand flats were free of any visibleEnteromorpha plants. In further experiments it was shown that the development ofEnteromorpha juveniles in the next spring depended on the overwintering capacity of spores. More than 2×10⁶ spores m^–2 attached to large sand grains and other substrata (e.g. Hydrobia ulvae) survived the winter. In a laboratory experiment several species ofEnteromorpha were able to survive in total darkness for at least 10 months.     

IS THERE AN ECOPHYSIOLOGICAL EXPLANATION FOR THE GAMETOPHYTE–TETRASPOROPHYTE RATIO IN GELIDIUM SESQUIPEDALE (RHODOPHYTA)?1

In the fall, when 61% of the fronds of the Gelidium sesquipedale (Clem.) Born. et Thur. population located in Albufeira (southern Portugal) were reproductive, about 90% of these fronds were tetrasporophytes, whereas an equal percentage of female and male gametophytes was found (5%). The comparison of physiological performances of the reproductive phases (males, females and tetrasporophytes) did not reveal a physiological advantage of tetrasporic fronds. There were no significant differences either in the photosynthesis, nitrogen uptake, nitrate reductase activity, or biochemical composition of adult fronds. On the other hand, vegetative recruitment and spore production in the laboratory were significantly different. The re‐attachment to calcareous substrate and the subsequent rhizoidal growth were faster in tetrasporophytes. Particular levels of temperature, rather than irradiance, had an important effect on the phase differences in the spore release, attachment, and germination rates. Significant results were the higher release of carpospores at all irradiances at 17°C, and the higher attachment percentage of carpospores at 13°C versus tetraspores. Under higher temperatures (21°C), tetraspores showed higher attachment rates while carpospores germinated more. G. sesquipedale cystocarps released carpospores for 2 months, while tetrasporangia stopped shedding tetraspores after 1 month, resulting in a 3‐fold higher production of carpospores than tetraspores. Results showed that vegetative and spore recruitment may explain the low gametophyte–tetrasporophyte ratio of the studied population of G. sesquipedale as opposed to the physiological performance of phases.     

The impact of nutrition on spore yields for various fungal entomopathogens in liquid culture

Spore yields were measured for various fungal entomopathogens grown in six nutritionally different liquid media with low and high carbon concentrations (8 and 36 g l^–1, respectively) at carbon-to-nitrogen (C:N) ratios of 10:1, 30:1 and 50:1. Six fungi were tested: two Beauveria bassiana strains, three Paecilomyces fumosoroseus strains and one Metarhizium anisopliae strain. Spore yields were examined after 2, 4 or 7 days growth. In general, highest spore yields were obtained in media containing 36 g/l and a C:N ratio of 10:1. After 4 days growth, highest spore yields were measured in the three Paecilomyces isolates (6.9–9.7 × 10⁸ spores ml^–1). Spore production by the B. bassiana isolates was variable with one isolate producing high spore yields (12.2 × 10⁸ spores ml^–1) after 7 days growth. The M. anisopliae isolate produced low spore concentrations under all conditions tested. Using a commercial production protocol, a comparison of spore yields for the coffee berry borer P. fumosoroseus and a commercial B. bassiana isolate showed that highest spore concentrations (7.2 × 10⁸ spores ml^–1) were obtained with the P. fumosoroseus isolate 2-days post-inoculation. The ability of the P. fumosoroseus strain isolated from the coffee berry borer to rapidly produce high concentrations of spores prompted further testing to determine the desiccation tolerance of these spores. Desiccation studies showed that ca. 80% of the liquid culture produced P. fumosoroseus spores survived the air-drying process. The virulence of freshly produced, air-dried and freeze-dried coffee berry borer P. fumosoroseus blastospores preparations were tested against silverleaf whiteflies (Bemisia argentifolii). While all preparations infected and killed B. argentifolii, fresh and air-dried preparations were significantly more effective. These results suggest that screening potential fungal biopesticides for amenability to liquid culture spore production can aid in the identification of commercially viable isolates. In this study, P. fumosoroseus was shown to possess the production and stabilization attributes required for commercial development.     

Reproductive biology of Stictosiphonia hookeri (Rhodomelaceae,Rhodophyta) from Argentina,Chile, South Africa and Australia in laboratory culture

The red alga Stictosiphonia hookeri is epilithic in shaded habitats of the upper intertidal zone from 30 to 55° S. Thalli of this species from Argentina, Chile, South Africa and Australia, usually without reproductive structures when collected, all developed tetrasporangia in culture. Although good vegetative growth occurred in all nine isolates at 20–25 °C, 12:12 light: dark cycle, 10–30 µmol photons m^–2 s^–1, none reproduced in these conditions except one isolate from Australia. At 15 °C the four South African (34 °S) isolates developed tetrasporangial stichidia, and three completed a Polysiphonia-type life history. Gametophytes were unisexual or bisexual. At 15 °C one isolate from Chile (36 °S) formed tetrasporangia, but sporelings were not viable. At 10 °C isolates from Argentina and Chile (53 °S and 54 °S) formed tetrasporangia; however, only the Chile isolate completed a Polysiphonia-type life history with unisexual gametophytes. The temperature required to induce sporogenesis correlates with the range of water and air temperatures in the natural habitats of each isolate. In irradiances >50 µmol m^–2 s^–1 the thalli became yellow- brown within two weeks because of phycobiliprotein loss, but this did not impair growth or reproduction. The Argentina and Chile isolates were resistant to freezing in seawater for at least two days, showing no cell damage. The protein cuticle of the outer cell wall is repeatedly shed in culture. This may serve to minimize the attachment of epiphytes in the field.     

Airborne Ascomycotina on the island of Crete: Seasonal patternsbased on an 8-year volumetric survey

An 8-year study was conducted on the island of Crete in order to identify airborne ascospores and to determine their seasonal pattern. A Burkard 7-day, volumetric spore-trap was continuously operated in the city of Irakleion – located in the center of the island – from 1994 through 2001. Relatively „high” ascospore counts (20 – 48 spores/m ³) were obtained from mid-spring through summer, while the rest of the year exhibited lower activity (8–16 spores/m³). The predominant ascospores identified were those of Leptosphaeria and Chaetomium; their concentrations varied from 1 or 2 spores up to a few dozens of spores/m³. Other spores encountered sporadically were: Ascobolus, Endophragmiella, Didymella, Diatrypaceae, Leptosphaerulina, Massaria, Pleospora, Sporormiella, Xylaria. The mean daily concentration of all identified ascospores was 30/m³ for the entire study period, corresponding to 13.9% of the total fungal load. Ascospores have been recognized as important inhalant allergens and have been implicated as contributing to symptoms of both rhinitis and asthma.     

Application of response surface methodology in medium optimization for spore production of <Emphasis Type="Italic">Coniothyrium minitans</Emphasis> in solid-state fermentation

Summary Spore production of Coniothyrium minitans was optimized by using response surface methodology (RSM), which is a powerful mathematical approach widely applied in the optimization of fermentation process. In the first step of optimization, with Plackett–Burman design, soluble starch, urea and KH²PO⁴ were found to be the important factors affecting C. minitans spore production significantly. In the second step, a 2³ full factorial central composite design and RSM were applied to determine the optimal concentration of each significant variable. A second-order polynomial was determined by the multiple regression analysis of the experimental data. The optimum values for the critical components for the maximum were obtained as follows: soluble starch 0.643 (36.43 g. l⁻¹), urea −0.544 (3.91 g l⁻¹) and KH²PO⁴ 0.049 (1.02 g l⁻¹) with a predicted value of maximum spore production of 9.94 × 10⁹ spores/g IDM. Under the optimal conditions, the practical spore production was 1.04 × 10¹⁰ spores/g IDM. The determination coefficient (R²) was 0.923, which ensure an adequate credibility of the model.     

Animal and worker exposure to dust and biological particles in animal care houses

An aerobiological study was performed to evaluate the potential exposure of animals and workers to dust constituents generated during routine animal house work. Different rooms of air conditioned (A, control) and passively ventilated (B, non-air conditioned) animal facilities were sampled, in order to evaluate total airborne culturable fungi and bacteria, fungal spore concentrations and particle levels. Airborne room particles were analyzed gravimetrically and for endotoxin content. All parameters, except for culturable fungi, were higher in facility B and statistically significant, with respect to those from the control facility A. Median values for airborne particle concentration, endotoxin and fungal spores in facility B were: 115 µg m^–3, 25 EU m^–3, and 2173 spores m^–3, respectively. Median values for facility A were: 66 µg m^–3, 9 EU m^–3, and 248 fungal spores m^–3. Broncheoalveolar lavage from rats kept in the rat room of B, presented median concentrations of total cells and lactate dehydrogenase, higher than those found in the control facility (4.4 × 10⁵ vs. 1.1 × 10⁵ and 2.7 UmL^-1 vs. 0.39 UmL^–1, respectively). Values of total and biological particles of both facilities, as well as the time spent in different rooms, showed that worker exposure was higher during cage washing. It was especially high in the passively ventilated facility (airborne particles 686 µg m^–3 3.5 h^–1 vs. 976 µg m^–3 3.5 h^–1, endotoxin 70 EU m^–3 3.5 h^–1 vs. 108 EU m^–3 3.5 h^–1). The type of basidiospores and ascospores found, as well as the significant correlation between particle levels and endotoxin contents suggests that wood chip bedding disturbance during cage washing is an important source for airborne biological particles. The changes in broncheoalveolar lavage components found in rats from these facilities and previously reported changes in pro-inflammatory cellular responses found in workers, indicate that these relatively low levels of exposure are enough to induce a biological response. Studies considering the composition of mixed organic dusts, would be needed to reevaluate current occupational standards.     

The Beltsville method for soilless production of vesicular-arbuscular mycorrhizal fungi

A low-cost, low-maintenance system for soilless production of vesicular-arbuscular mycorrhizal (VAM) fungus spores and inoculum was developed and adapted for production of acidophilic and basophilic isolates. Corn (Zea mays) plants were grown with Glomus etunicatum, G. mosseae or Gigaspora margarita in sand automatically irrigated with modified Hoagland's solution. Sand particle size, irrigation frequency, P concentration, and buffer constituents were adjusted to maximize spore production. Modified half-strength Hoagland's solution buffered with 4-morpholine ethane-sulfonic acid (MES) automatically applied 5 times/day resulted in production of 235 G. etunicatum spores/g dry wt. of medium (341000 spores/pot) and 44 G. margarita spores/g dry wt. of medium (64800 spores/pot). For six basophilic isolates of G. mosseae, CaCO₃ was incorporated into the sand and pots were supplied with the same nutrient solution as for acidophilic isolates. The increased pH from 6.1±0.2 to 7.2±0.2 resulted in spore production ranging from 70 to 145 spores/g dry wt. (102000–210000 spores/pot). Spore production by all isolates grown in the soilless sand system at Beltsville has exceeded that of traditional soil mixtures by 32–362% in 8–12 weeks.     

Agars from Chilean Gelidiaceae

Cystocarpic, tetrasporic and vegetative thalli of Gelidium chilense were extracted with water at 95 °C. The contents of 3,6-anhydro-galactose and sulfate group of the hydrocolloids correspond to those of an agar-type polysaccharide. The percentages of 6-O-methyl-galactose and of pyruvic acid ranged between 5.7–6.2% and 0.42–0.54%, respectively. The gel melting and gelation temperatures of Gelidium chilense, G. rex and G. lingulatum agars were determined. A correlation between 6-O-methylgalactose content and gelation temperatures was not observed. It was found by anion-exchange chromatography that 19.8% of tetrasporic and 4.9% of vegetative G. chilense agars are unsulfated polymers. Structural studies on the neutral fraction from tetrasporic G. chilense agar by partial hydrolysis and ¹H NMR spectroscopy have shown that it is mainly composed of agarose. Methylation analysis, oxidative hydrolysis and partial hydrolysis, followed by ¹H NMR spectroscopy, have shown that the neutral fraction of the agar from tetrasporic Gelidium rex is agarose. The results obtained in this work are compared with previously reported data on studies of agars from Chilean Gelidium species.     

Effect of high concentration of nutrients onBacillus thuringiensis cultures

Summary Bacterial insecticide production using a strain ofBacillus thuringiensis var. kurstaki was studied in batch culture considering the influence of increasing concentration of components of a glucose — yeast extract — mineral salts medium.It was found that spore counts were increased from 1.08×10¹² spores. 1^–1 to 7.36×10¹² spores. 1^–1 and toxin level from 1.05 mg.ml^–1 to 6.85 mg.ml^–1, when the concentration of glucose was increased from 8 to 56 (g 1^–1), with the corresponding increase in the rest of medium components. Higher concentration of nutrients inhibit either spore count or toxin production.Preliminary experiments of fed-batch cultures which allows the use of high amounts of nutrients were also carried out. In this case spore counts of 1.2×10¹³ spores.1^–1 were achieved.     

Biomass and litter dynamics in a Melaleuca forest on a seasonally inundated floodplain in tropical,northern Australia

Litterfall from a Melaleuca forest was investigated as part of chemical cycling studies on the Magela Creek floodplain in tropical, northern Australia. The forest contained two species of tree, Melaleuca cajaputi and Melaleuca viridiflora, with a combined average density of 294 trees ha^–1. The M. viridiflora trees had diameter breast height measurements ranging from 11.8 to 62.0 cm, median class 25.1–30.0cm and a mean value of 29.2±1.0 cm, compared to 13.0 to 66.3 cm, 30.1–35.0cm and 33.5±1.0cm for M. cajaputi trees. A regression model between tree height, diameter breast height and fresh weight was determined and used to calculate average tree weights of 775±1.6kg for M. viridiflora and 1009±1.6kg for M. cajaputi, and a total above-ground fresh weight of 263±0.3t ha^–1. The weight of litter recorded each month on the ground beneath the tree canopy ranged from 582±103 to 2176±376 g m^–2 with a monthly mean value of 1105±51 g m^–2. The coefficient of variation of 52% on this mean indicates the large spatial and temporal variability in litter distribution over the study site. This variability was greatly affected by the pattern of water flow and litter transport during the Wet season. Litterfall from the trees was evaluated using two techniques - nets and trays. The results from these techniques were not significantly different with annual litterfall collected in the nets being 705 ± 25 g m^–2 and in the trays 716±49 g m^–2. The maximum monthly amount of litterfall, 108 ±55g m^–2, occurred during the Dry season months of June–July. Leaf material comprised 70% of the total annual weight of litter, 480±29 g m^–2 in the nets and 495 ± 21 g m^–2 in the trays. The tree density and weight of litter suggest that the Melaleuca forests are highly productive and contribute a large amount of material to the detrital/debris turnover cycle on the floodplain.     

Agars from Gelidium rex (Gelidiales,Rhodophyta)

Gelidium rex grows in the rocky intertidal of central Chile. Extraction of vegetative G. rex with water at 95 °C yielded 17.9% of agar with a gel strength value of 590 g cm^–2. The gel strength increased up to 1272 g cm^–2 when the alga was treated with alkali prior to extraction. Cystocarpic and tetrasporic thalli of G. rex were extracted with distilled water at 95 °C, affording soluble polysaccharides in 36.0% and 15.7% yield respectively. Polysaccharides of both life history phases were fractionated by chromatography on DEAE Sephadex. Elution with distilled water gave fractions devoid of sulfate; the fraction from cystocarpic plants contained 45.5% of 3,6-anhydrogalactose whereas the neutral fraction from tetrasporic plants contained 40.0% of 3,6-anhydrogalactose. Further elution with 0.1, 0.4, 0.8 and 1.5 molar aqueous solutions of KCl afforded four fractions for each polysaccharide. Chemical analysis of these fractions showed that the agars from cystocarpic and tetrasporic Gelidium rex are mixtures of related polysaccharides that range from neutral polymers to highly sulfated galactans.     

Sorus development on median and marginal parts of the sporophyte of Laminaria japonica Areschoug (Phaeophyceae)

Sorus formation on median and marginal parts of Laminaria japoncia Areschoug was investigated by cultivating sporophytes from December 1996 to September 1997 in Southern Hokkaido, Japan. Simultaneously, discs (ca. 3 cm in diameter) that were cut off monthly from median and marginal parts of the cultivated sporophytes were incubated in our laboratory. All the cultivated sporophytes formed sori on the median parts from January to August, while all the median and marginal discs formed sori at 10 under 46 μmol photon m^-2s^-1 (12L:12D) in enriched medium. There was no difference in sorus area between median and marginal discs. These results indicated that the marginal parts are able to produce sori, although the greater part of them are actually washed away before forming sori in the sea. The marginal part is probably in a state of `resource limitation' on the reproduction because the resource outflowed from this part to the basal part for the growth of sporophytes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative spatial distribution, size, biomass and growth rate of two varieties of bracken fern (Pteridium aquilinum L. Kuhn) in a neotropical montane habitat

A comparative field study of caudatum and arachnoideum, the two Pteridium aquilinum varieties of the caudatum subspecies known to grow in the neotropics, was performed in a montane savanna habitat of the Venezuelan Andes that was affected by wildfire. Frond size, ramet density and spatial distribution, blade and rhizome biomass, and frond elongation and expansion rates were measured in separate, isolated stands each containing only one bracken variety and covering approximately the same area (540 m²). In addition to clearly discernible morphological differences, caudatum and arachnoideum were found to possess distinct features: caudatum tends to develop open stands of relatively shorter blades of 76.6±0.89 cm (±SE) of rachis length and lower ramet density (1.6 fronds m^-2, max.=7 fronds m^-2) whereas arachnoideum grows into longer, more expanded fronds 124±1.6 cm tall and significantly higher ramet density (5.1 fronds/m², max.=14.6 fronds m^-2). The sum of aerial and underground biomass was found to be notably larger for arachnoideum (8522±614 Kg/ha) than for caudatum (1929±131 Kg ha^-1) in stands growing under the same habitat conditions. Therefore the spatial distribution of arachnoideum appeared considerably more compact than that of caudatum. Blade growth rates and development time were also very different. Newly emerged caudatum croziers developed into mature blades within 42 to 48 days following an inverse exponential curve whereas arachnoideum blades required 70 to 75 days to reach maturity following a linear development. All the above dissimilarities are interpreted as the hitherto unreported indication of diverging growth strategies of two cohabitant bracken varieties following fire.     

Antibiotic production by the immobilized cyanobacterium,Scytonema sp. TISTR 8208, in a seaweed-type photobioreactor

A photobioreactor was constructed using either anchored polyurethane foam strips (1 × 1 × 40 cm, PU-strips) fixed on a stainless-steel ring to prevent flotation, or free-floating polyurethane foam blocks (1 × 1 × 1 cm, PU-blocks) as biomass supporting materials (BSM). The cyanobacterium,Scytonema sp. TISTR 8208, which produces an antibiotic, was immobilized onto PU-strips or -blocks. The free-floating PU-blocks could immobilize only about 70% of the total cells, while the anchored PU-strips could immobilize as much as 97%. PU-strips were chosen as the BSM and we named this type of reactor, seaweed-type bioreactor (STB). Optimal physical conditions for antibiotic production were determined in the STB. Inoculum density was 0.4 g l^–1 and cells were sparged with air containing 5% CO₂ circulated at the gas flow rate of 250 ml min^–1 and illuminated at a light intensity of 200 mol photon m^–2 s^–1. The production of antibiotic could be increased 3-fold.Author for correspondence     

Cultivation ofMonostroma nitidum (Chlorophyta) in a river estuary,southern Japan

The green seaweedMonostroma nitidum Wittrock is cultivated in brackish waters of southern Japan and an ecological survey of its cultivation was carried out in the estuary of R. Shimanto over three years. Artificial seed culture began by collecting many gametes in April. The zygotes adhered to a plastic settlement board (20–30 cm long and 10 cm wide). The cultivated zygotes in the indoor tank increased gradually in size from 8 to 40m till early September. Maturation of the zygote was promoted by providing dark conditions for 2–3 weeks. The production of a concentrated zoospore solution was achieved by adding freshwater 2–3°C above that of the zygote culture tank and a photon flux density of 100mol m^–2 s^–1).The culture nets were set our horizontally at a level exposed for 4 h and were harvested 3–4 times till March. The total production was approximately 6–10 kg dry weight per net during culture periods. The total production of nets harvested 3–4 times per year was greater than that of nets harvested only once.     

Control of phosphorus loading and flushing as restoration methods for Lake Veluwe,The Netherlands

As a result of high nutrient loading Lake Veluwe suffered from an almost permanent bloom of the blue-green algaOscillatoria agardhii Gomont. In 1979, the phosphorus loading of the lake was reduced from approx. 3 to 1 g P.m^–2.a^–1. Moreover, since then the lake has been flushed during winter periods with water low in phosphorus. This measure aimed primarily at interrupting the continuous algal bloom. The results of these measures show a sharp decline of total-phosphorus values from 0.40–0.60 mg P.l^–1 (before 1980) to 0.10–0.20 mg P.l^–1 (after 1980). Summer values for chlorophylla dropped from 200–400 mg.m^–3 to 50–150 mg.m^–3.The increase in transparency of the lake water was relatively small, from summer values of 15–25 cm before the implementation of the measures to 25–45 cm afterwards. The disappointing transparency values may be explained by the decreasing chlorophylla and phosphorus content of the algae per unit biovolume. Blue-green algae are gradually loosing ground. In the summer of 1985 green algae and diatoms dominated the phytoplankton for the first time since almost 20 years. To achieve the ultimate water quality objectives (transparency values of more than 100 cm in summer), the phosphorus loading has to be reduced further.