Filamentous Cyanophytes Research Articles

Enlisting Aero-algal Flora and Algal Allergens Using Fan Dust Sampling Method from Pune, Maharashtra

Algae in the atmosphere are one of the bio-components of the environment. Despite the fact that they may have a negative impact on human health, they are the least studied organism in the field of aerobiology. Airborne algae continue to be viable in the atmosphere in the form of spores and filaments. In order to investigate the intramural diversity of airborne algae in Pune, eight residences were chosen, from which 16 fan dust samples were collected over a ten-day period. Total (108) aero-algal forms were recorded. Out of which 107 were Cyanophyta, and only one was Chlorophyta. The dominance of Cyanophyta members is attributed to the presence of a thick mucilaginous sheath around them, which allows them to tolerate the dryness. Overall, filamentous cyanophytes (71) outnumber coccoid cyanophytes (36). However, both fan dust slide samples and culture slide samples show variance. Coccoid cyanophytes (53) outnumber filamentous cyanophytes (11) in direct slide scans, although filamentous cyanophytes (25) were somewhat more numerous in culture samples than coccoid Cyanophyta (19). This increase in filamentous forms might be because of hormogonia of filamentous algae, which remained unidentified in direct slide scan and upon inoculation underwent reproduction increasing number of filamentous algae in culture slides. Chrooccocus, Gloeocapsa, Lyngbya, Nostoc, and Stigonema were among the forms found on the first and tenth days of fan dust sampling, indicating that they were a common inhabitant of fan dust during the study and that the fan, as an aero sampler, was able to capture them, demonstrating its potency as an aero sampler. Soil can be a substantial factor in the creation of fan dust, as these genera were frequently separated from the soil. Gloeocapsa, Phormidium, Lyngbya, Schizothrix, Cylindrospermum, Nostoc, Anabaena, Scytonema, Calothrix, and Scenedesmus were among the allergic aero-algal genera discovered during the investigation.

Discovery of Organic Matter and Palynomorphs from the Neoproterozoic Zor Diamictite of the Ramsu Formation in the Ramban District, Jammu and Kashmir, India

Abstract The presence of medium-grade organic matter confirmed by Raman spectroscopy is reported for the first time from the Zor diamictite of the Ramsu Formation, Tethyan Himalaya. The organic matter has undergone overmature thermal evolution. The sediment shows low total organic carbon (TOC) and low total sulfur (TS) values of <0.25% and <0.01%, respectively. Low TS/TOC < 0.08 suggests oxic bottom waters during the deposition of the Zor diamictite. The recovered palynomorph assemblage includes Leiosphaeridia spp., Kildinosphaera verrucata, Trachyhystrichosphaera sp., the filamentous cyanophyte Taeniatum sp., the clusters of simple, spheroidal forms Myxococcoides sp., and the colonial cyanobacteria Synsphaeridium sp. This palynomorph assemblage suggests a Neoproterozoic age for the Zor diamictite of the Ramsu Formation.

An Exploratory Survey of Summer Water Chemistry and Plankton Communities in Lakes near the Sutton River, Hudson Bay Lowlands, Ontario, Canada

We provide the first assessment of regional water chemistry and plankton (phytoplankton and crustacean zooplankton) for a suite of lakes near the Sutton River region of the north-central Hudson Bay Lowlands (HBL). We use ordination analyses to examine the spatial variation in water chemistry and plankton across lakes, and to explore the factors that may explain this variation. Based on data collected during summer from 2009 to 2011, we found that in addition to geology, water chemistry was strongly influenced by a lake’s proximity to salt water and the degree of permafrost development within its catchment. Phytoplankton composition varied across lakes based on differences in water depth and nutrient concentrations, with non-filamentous cyanobacteria and chlorophytes more common in shallow lakes, and deeper lakes dominated by planktonic diatoms or filamentous cyanophytes. Crustacean zooplankton community composition and richness in the HBL lakes was similar to communities found in Ontario lakes in more temperate regions within the Precambrian Shield. These baseline data provide a foundation upon which future surveys in this climatically sensitive region may be compared.

Microphytobenthic dynamics in a Wadden Sea intertidal flat – Part II: Seasonal and spatial variability of non-diatom community components in relation to abiotic parameters

The microphytobenthos colonizing the intertidal flats forms an important component of the Wadden Sea. Ten sampling points along a 1-km transect were studied in a fringe area of the Solthörn tidal flat, southern North Sea, in order to determine seasonal differences in the microphytobenthos. An accompanying paper deals with the major component of the flora, the diatoms; here we, focus on the minor taxonomic groups. From May 2008 to May 2009 surface sediments were collected during low tide. Variation of environmental factors as well as microphytobenthic density (abundance and chlorophyll a) were monitored. The area investigated was a mixed-sediment mudflat, with a gradient from coarse to fine. Highest biomass was obtained in summer 2008 with 215.9 ± 12.6 mg chlorophyll a m–2. In late autumn the chlorophyll a concentration decreased continuously at all investigated stations. Lowest values were detected in December 2008. Species abundances varied considerably both along the transect and seasonally, depending on species-specific requirements as well as hydrodynamic conditions (tidal currents). Higher densities of benthic pro- and eukaryotic microalgae were observed in sites characterized by fine sediments. Apart from the diatoms, the most abundant microphytobenthic group was the cyanophytes. Coccoid cyanophytes, mainly Merismopedia sp., were most abundant during summer, with cell numbers up to 5.72 × 106 cells cm−2, while diatoms dominated in winter, spring and autumn. Filamentous cyanophytes, particularly Microcoleus chthonoplastes, were most abundant during autumn, while coccoid chlorophytes (spring: Chlorococcum submarinum, Crucigenia tetrapedia, Tetraselmis suecica), euglenophytes (summer: Euglena obtusa), dinophytes (autumn: Amphidinium operculatum, A. herdmanii) and cryptophytes (autumn: Hillea marina, Hemiselmis virescens) contributed to the microphytobenthos during warmer seasons. The statistical analysis confirmed that the composition of the microphytobenthos was related to sediment features and to characteristics of particular seasons.

Discovery of large conical stromatolites in Lake Untersee, Antarctica

Lake Untersee is one of the largest (11.4 km(2)) and deepest (>160 m) freshwater lakes in East Antarctica. Located at 71°S the lake has a perennial ice cover, a water column that, with the exception of a small anoxic basin in the southwest of the lake, is well mixed, supersaturated with dissolved oxygen, alkaline (pH 10.4) and exceedingly clear. The floor of the lake is covered with photosynthetic microbial mats to depths of at least 100 m. These mats are primarily composed of filamentous cyanophytes and form two distinct macroscopic structures, one of which--cm-scale cuspate pinnacles dominated by Leptolyngbya spp.--is common in Antarctica, but the second--laminated, conical stromatolites that rise up to 0.5 m above the lake floor, dominated by Phormidium spp.--has not previously been reported in any modern environment. The laminae that form the conical stromatolites are 0.2-0.8 mm in thickness consisting of fine clays and organic material; carbon dating implies that laminations may occur on near decadal timescales. The uniformly steep sides (59.6 ± 2.5°) and the regular laminar structure of the cones suggest that they may provide a modern analog for growth of some of the oldest well-described Archean stromatolites. Mechanisms underlying the formation of these stromatolites are as yet unclear, but their growth is distinct from that of the cuspate pinnacles. The sympatric occurrence of pinnacles and cones related to microbial communities with distinct cyanobacterial compositions suggest that specific microbial behaviors underpin the morphological differences in the structures.

Vertical distribution of phototrophs in the pelagic zone of three small Lobelia lakes

Vertical distribution of phototrophs in the pelagic zone of three small Lobelia lakes The community structure and biomass of pelagic phototrophs, with a particular focus on the picoplanktonic fraction, were studied in three small, soft-water lakes in the Pomerania Lake District (north Poland). The smallest phototrophs were usually dominated by picocyanophytes, both single-celled and colonial. Picochlorophytes were less frequent, and they formed dense populations only in one lake. The nano- and microplankton included many groups of organisms, but the main groups were comprised of dinoflagellates, chrysophytes and chroococcoid and/or filamentous cyanophytes and large raphidophytes. Community structure changed significantly with depth and in all lakes remarkable differences were observed between the epilimnion and both the meta- and hypolimnion. The hypolimnion was characterized by the presence of photosynthetic green sulfur bacteria or their symbiotic consortia.

Fast repetition rate fluorometry is not applicable to studies of filamentous cyanobacteria from the Baltic Sea

Fast repetition rate (FRR) fluorometry has been used successfully to investigate the variable fluorescence characteristics of cyanobacteria in oceanic Case 1 waters. In these waters, the effective absorption bands of the light harvesting pigments for photosystem II (PSII) of the dominant cyanobacterial taxa overlap with the peak of the FRR excitation at 470 nm. The effective PSII absorption of the ecologically‐significant filamentous cyanophytes in the Baltic Sea—Nodularia spumigena (Mertens ex Bornet and Flahault 1886) and Aphanizomenon sp. ((L.) Ralfs ex Bornet and Flahault 1886)—is, however, restricted to beyond 550 nm. We tested the applicability of a currently commercially available FRR fluorometer to studies of these two cyanobacterial taxa. We propose that the FRR technique should not be used in studies on these taxa, or on any cyanophyte containing phycoerythrocyanin instead of phycoerythrin, the former having inefficient PSII light harvesting in the wave band of the FRR excitation. This issue should be taken into account whenever field studies utilizing the FRR system are planned in those Case 2 water bodies, in which cyanobacteria lacking phycoerythin are among the dominant phytoplankton groups.

Phytoplankton–zooplankton seasonal timing and the ‘clear‐water phase’ in some English lakes

SUMMARY 1. An examination is made of the relative seasonal timing of the postwinter increase of phytoplankton and zooplankton populations in four English lake basins. It centres upon weekly sampling over 20 years and rough counts of larger Crustacea, as copepods and cladocerans, from filtered samples that were used for chlorophyll a (Chl) estimation.2. Typically, a spring maximum of phytoplankton, dominated by diatoms and earlier in the shallower lakes, is accompanied or followed by a maximum of copepods and then one of cladocerans dominated by the Daphnia hyalina–galeata complex. Regarding timing, the maximum of copepods has no apparent relation with phytoplankton abundance (Chl). The maximum of cladocerans appears to be largely independent of variation in the phytoplankton maximum, but is generally associated with a minimum in Chl. Evidence for some direct causality in this inverse correlation after the spring phytoplankton maximum is best displayed by the shallow Esthwaite Water in which the peaks of Chl and cladocerans are separated further than in the deep Windermere basins where phytoplankton growth is delayed. In Esthwaite Water, and possibly often in Windermere, a principal minimum in Chl is ascribable to grazing by Daphnia.3. The typical inverse relationship of Chl and cladocerans is lost in some years when relatively inedible large phytoplankters (e.g. colonial chrysomonads, filamentous cyanophytes) are abundant and Chl minima are less pronounced, although maxima of cladocerans still occur. Conversely, available edible phytoplankters include various small forms grouped as μ‐algae and Cryptomonas spp.; their probable depletions by Daphnia appear to be sequential and may limit the latter's maxima, whose inception is temperature‐dependent.4. The spring–summer maxima of cladocerans and minima of Chl are generally coincident with a main seasonal maximum of Secchi disc transparency and light penetration – to which removal of non‐phytoplankton particles by filtering cladocerans may contribute.

Soil algae from marlstone-substratum based biotopes in the Nature park Džbán (Central Bohemia, Czech Republic) with special attention to the natural treeless localities

The soil algal species composition of some marlstone-substratum based biotopes of Džban region (Central Bohemia, Czech Republic) was investigated. A total of 54 species representing 42 genera were recovered. Chlorophytes were the most abundant group in all investigated sites. The most common green algal species encountered were Mychonastes homosphaera, Stichococcus bacillaris and Klebsormidium flaccidum. Other frequently occuring species were the cyanophytes Nostoc commune and Phormidium autumnale f. autumnale and diatoms Pinnularia borealis and Nitzschia palea. The investigated sites were compared according to their soil algal floras, The natural treeless localities share similar soil algal synusiae with some typical non-forest features - higher frequency of filamentous cyanophytes and diatomes, occurrence of some desmids. The species list from an investigated secondary meadow is dominated by chlorococcal algae with lower occurrence of other groups. This could be determined by lower pH of the soil from this locality The beech dominated forest locality shares some features typical for temperate forests - lower species richness, common occurrence of green flagellates and unicells, low occurrence of cyanophytes.

Effects of a grazing fish, Plecoglossus altivelis (Osmeridae), on the taxonomic composition of freshwater benthic algal assemblages

The effects of grazing fish, Plecoglossus altivelis (ayu), on freshwater benthic algal assemblages were investigated by experiments in outdoor water tanks with fish (2.2 indiv./m 2 ) and without fish for 25 d. To simulate the condition of running water in each tank, a water current was generated with a water pump. In three replicate experiments, algal biomass and diatom biovolume were reduced in presence of the fish. The biovolume of the filamentous cyanophyte, Homoeothrix janthina increased in response to grazing, and finally predominated in presence of the fish. Observations of grazing scars by scanning electron microscopy verified the supposition that the basal cells of Homoeothrix janthina, which were the hormogones attached to the substrate, had relatively higher resistance to fish grazing. The grazing resistance of the basal cells would contribute to colonization of the filamentous cyanophytes under fish grazing. These results show that grazing fish regulated algal assemblages dominated by filamentous cyanophytes through their foraging activities.

Responses of phytoplankton and epilithon during acidification and early recovery of a lake

1. Lake 302S in the Experimental Lakes Area of Canada was acidified from pH 6.7 (1981) to 5.1 (1986). The pH was further reduced to 4.5 in 1987 and held at that level until 1991. From 1992 to 1995, the pH was allowed to increase to a target value of 5.8.2. The response of the phytoplankton community to decreasing pH from 6.0 to 5.1 was similar to that observed in another experimentally acidified lake (223) and in other atmospherically acidified lakes. Acidification affected species diversity of both the phytoplankton and epilithon. Phytoplankton diversity was positively correlated with pH. Epilithic algal diversity was more variable and did not correlate with pH.3. Phytoplankton biomass was enhanced by acidification as the assemblage shifted from a dominance of chrysophytes to large dinoflagellates (Gymnodinium sp. and Peridinium inconspicuum). Epilithon biomass was unaffected, but dominance shifted from filamentous cyanophytes (Lyngbya) to acidophilic diatoms (Tabellaria quadriseptata and Anomoeonis brachysira).4. The only taxon to be similarly affected in both the phytoplankton and epilithon was the cyanobacteria, being significantly reduced below pH 5.1. During early recovery (pH 5.5–5.8), cyanobacteria increased and species present prior to acidification recolonized both habitats.5. In the early stages of recovery, planktonic and benthic assemblages remained more similar to acidified than natural assemblages, but more profound change began at pH > 5.5.

Vertical and seasonal distri bution of epiphytic algae on water chestnut (Trapa natans)

Changes in density, biomass, Shannon-Wiener diversity and equitability of epiphytes on different parts of Trapa natans (lamina, petiole, stem and roots) are described during the life cycle of this floating-leaved aquatic plant in the shallow eutrophic lake, Lago di Candia, northern Italy. The seasonal standing crop of epiphyton paralleled that of water chestnut, although the maximum biomass of epiphyton preceded by one month that of the host plant. Epiphytic algal succession moved from prostrate chlorophytes and adnate diatoms towards basally attached species and later to filamentous cyanophytes. Epiphytic algal assemblages showed clear differences according to the different plant parts and depths. There was a decrease in the mean abundance, biomass and cell size of epiphytes from upper to lower parts of the plant and species succession in lower parts was delayed and shortened compared with that in the upper parts. There was a greater presence of filamentous green algae, desmids and filamentous N 2 -fixing cyanophytes on the lamina and petiole than on the stem and roots, where communities were mostly comprised of small diatoms and a filamentous cyanophyte. Species dynamics on stem and roots situated at the same depths were similar. Several factors accounted in determining the composition and abundance of epiphytic communities, such as plant architecture and age, and physicochemical variables, such as light within the Trapa belt.

Planktic cyanophytes and their ecology in the shallow Lake Mikri Prespa, Greece

Cyanophytes dominated the phytoplankton of shallow Lake Mikri Prespa during the period May 1990 to September 1992 (76.5 and 52.0% of the total phytoplankton biomass in 1990–1991 and 1991–1992, respectively). Biomass peaks were observed in autumn (from 5.2 to 34.5 g m‐3) when low dissolved inorganic nitrogen, high phosphate phosphorus and low Zcu to Zmix ratio prevailed. The dominant species were Microcystis aeruginosa and M. wesenbergii. These represented 64 and 86% of the cyanophyte biomass in 1990–1991 and 1991–1992, respectively and revealed similar patterns of seasonality forming biomass peaks in late summer ‐ autumn. Small chroococcalean cyanophytes (< 2 μm) showed also similar temporal distributions. Of the filamentous cyanophytes, the most important species was Anabaena lemmermannii var. minor which formed peaks in late summer and autumn (2.6 and 1.1 g m‐3 in 1990 and 1992, respectively). Rainfall and the N:P ratio were probably the main factors influencing the seasonality of all of the filamentous cyanophytes in the lake. Cyanophytes, tended to increase at temperatures higher than 16 °C and at inorganic nitrogen concentrations lower than 100 μg 1‐‐1. The frequent mixing of the water column did not seem to prohibit the substantial increase of the group.

Algal Symbionts in the Tunics of Six New Zealand Ascidians (Chordata, Ascidiacea)

Filamentous eukaryotic algae were found completely embedded in the tunic matrix of 6 species of ascidians from the cold-temperate waters of southern New Zealand: the aplousobranch Aplidium thomsoni (Polyclinidae) and 5 solitary stolidobranchs, Asterocarpa humilis (Styelidae) and Pyura cancellata, P. carnea, P. pulla, and P. suteri (Pyuridae). All the ascidians appeared to be completely healthy, and the stolidobranchs showed evidence of tunic blood vessel hypertrophy in the regions of algal filaments. Only those individuals growing in at least a low-light environment contained algae; individuals of the same species growing in dark conditions contained none. The algal symbionts include Neevea repens (Rhodophyta), Pseudendoclonium submarinum and Ostreobium quekettii (Chlorophyta), and an unidentified filamentous (probable) phaeophyte. Dense growths of Neevea and Pseudendoclonium were found in the tunic matrix in all six ascidians, most abundantly just under the tunic cuticle but extending several millimeters into the tunic. Subsequent recent discovery of filamentous chlorophytes in the tunic of two species of American Pacific coast solitary ascidians leads us to conclude that this algal habitat may be a widespread phenomenon that has been overlooked in the supposition that the algae were merely epizoic. Most of these ascidians also contained numerous alga-filled tunic pockets probably formed during the incorporation of sand grains with epipsammic algae that later proliferated. Though previously noted anecdotally in the literature, this report is the first compilation of this algal assemblage. They include Sarcinochrysis marina (Chrysophyta), unidentified diatoms, unicellular chlorophytes, and the prokaryote cyanobacteria Dermocarpa, Xenococcus, and Synechococcus. Similar species, along with Oscillatoria, Spirulina, and Anabaena, were also found in the inter-tunic cavity of the peculiar double-tunic ascidians Pyura cancellata and P. carnea. Additional key words: Pyura, Pseudendoclonium, Neevea, Ostreobium, algae Adult ascidians are sessile, filter-feeding organisms usually found attached to rocks in the low intertidal and subtidal. The body of adult ascidians is covered by a tunic consisting of a vascularized extracellular matrix comprised of proteins and polysaccharides in which free cells move about. The matrix is covered by a thin cuticle (Hirose et al. 1992). In some species, sand grains incorporated into the growing tunic impart an extra rigidity to this covering. Most ascidians have a well-developed immune system and do not harbor endobionts, but a few species have evolved a mutualistic relationship with endobiotic algae (Lewin & Cheng 1989). With a single exception, all the algal species examined to date that live within ascidian tunics are prokaryotes: Prochloron and filamentous cyanophytes. These have been recorded only in tropical waters (the Great Barrier Reef and many islands in the Indo-Pacific and Caribbean; see Lewin & Cheng 1989 for review). The only record of a eukaryotic alga growing completely within an ascidian tunic is a brief report of the filamentous red alga Neevea repens embedded in the tunic of the phlebobranchs Phallusia mammillata and Ascidia mentula from Brittany, France (Feldmann 1967). In this paper we report the presence of filamentous eukaryotic algae occurring completely embedded within the tunic matrix of 6 species of ascidians from the cold-temperate waters of southern New Zealand. The ascidians include the solitary stolidobranchs Asterocarpa humilis (Styelidae), Pyura cancellata, P. carnea, P. pulla, and P. suteri (Pyuridae), and the aplousobranch Aplidium thomsoni (Polyclinidae). The This content downloaded from 207.46.13.110 on Fri, 09 Dec 2016 05:19:07 UTC All use subject to http://about.jstor.org/terms Lambert, Lambert, & Waaland algal symbionts include 4 filamentous species: Neevea repens (Rhodophyta), Pseudendoclonium submarinum and Ostreobium quekettii (Chlorophyta), and an unidentified species (probably Phaeophyta). This is the first record of algal symbionts in the tunic of solitary ascidians of the order Stolidobranchia, only the second record of eukaryotic algae in ascidian tunic and the first from the southern hemisphere. Several of the above-mentioned ascidians also contain numerous tunic pockets, apparently formed during incorporation of sand grains. These pockets are packed with diatoms and unicellular and filamentous cyanobacteria, probably as a result of proliferation of cells adherent on the trapped sand. Although these algae are not actually within the tunic matrix, they frequently constitute a large bulk of the tunic. They form an assemblage never before described in detail; we include here descriptions of the most abundant forms. Similar algal species are described from the seawater-filled inter-tunic cavity of Pyura cancellata and P. carnea, two New Zealand ascidians that have an unusual double tunic with the two layers connected by struts of

Multivariate analysis of phytoplankton and related environmental factors, in a shallow hypertrophic lake

Data on some relevant environmental variables and phytoplankton species composition, collected from the hypertrophic shallow lake Albufera of Valencia (Spain) during 1980–88, were examined using Redundancy Analysis (RDA). The hydrological cycle of the lake is manipulated for rice cultivation in the area. Seasonality and the particular hydrological cycle of the lake were the principal factors influencing long-term phytoplankton dynamics. Annual or horizontal differences were less important than the seasonal factor. However, a trend of phosphate increase and underwater illumination decrease was observed between 1980 and 1988. These changes might be related to some species year-to-year variations, although in general interannual phytoplankton changes were scarce. Spatial phytoplankton differences were much smaller than physical and chemical differences, which were mainly related to loading and residence times at the different sampling zones. Shallowness, hypertrophy and the regular hydrological cycle of the Albufera for rice yield, seem to contribute to the maintenance of an almost stable and homogeneous algal community, mainly composed of filamentous cyanophytes. RDA analysis has proved to be an efficient method in yielding valuable information on phytoplankton-environment interactions and trends over a long series of data. It seems also a feasible technique to monitor the results of lake management and restoration in the future.

Diversity of the phytoplankton assemblages of a polymictic hypertrophic lake

Diversity of phytoplankton assemblages from the shallow hypertrophic lake, the Albufera of Valencia (Spain), was studied for the period 1980 - 1988. The lake serves as a reservoir for the surrounding rice cultivation, with two seasonal periods of water retention to keep ricefields flooded. The seasonal hydrological cycle seems to be the primary factor driving phytoplankton community changes, compounding the disturbances due to water mixing. The lake is dominated throughout by filamentous cyanophytes. A Shannon-Weaver function was used to measure phytoplankton diversity. Phytoplankton steady-states, defined as the periods when more than 80 % of total phytoplankton biomass was shared by only 1-3 species, were assumed for comparative purposes. Phytoplankton diversity and the assemblages showed a high degree of interannual regularity during the study period. Phytoplankton was mainly limited by light and water flushing from November to April, and more by nitrogen and phosphorus during summer. Low diversities were related to stable community states, while higher diversities corresponded to non-steady state periods, the former lasting longer. Four annual phytoplankton associations were found, both steady and non-steady states being characterized by two different algal communities. Diversity reached a steady-state, lasting from November to june. From january to March, water flushing high nutrient levels and oligophotic conditions selected in favour of large unicellular phytoplankton species. The onset of spring quiescence resulted in the lowest values of diversity and species richness, due to the overwhelming dominance of vernal crops of Planktothrix agardhii, whose selfshading populations would have excluded many less well-adapted species. By june, nutrient decrease and increasing temperatures and irradiance, moved phytoplankton towards an intermediate assemblage dominated by smaller and faster growing species. Thereafter, long-summer water stabilization and nutrient depletion interacted to enhance diversity and the onset of a non-steady state, characterized by an immature summer assemblage of large colonies, potentially motile (e.g. Microcystis) and with high nutrient storage capacity. During the autumnal period when the ricefields are drained for harvest, diversities reached maximal levels, including species from the surrounding habitats (ricefields and drainage ditches). Lake reisolation by November-December led to another phytoplankton steady-state, when the phytoplankton reverted toward a composition similar to that of June. Storms increased diversity and the presence of small-sized species, contributing to a more rapid species replacement or arresting the establishment of an steady-state, depending upon their intensity frequency and occurence. Stagnation always selected in favour of cyanophytes, while flushing rates enhanced the presence of other algal groups, mainly diatoms. The annual flushing cycle of the lake is regarded as a potential tool for the future lake restoration. Our results confirm the view of regarding the phytoplankton of polymictic Oscillatoria-dominated lakes, as sub-climatic communities mainly limited by light, and agree with some postulates based on the IDH-diversity theory

A Test of Hypotheses to Explain the Sigmoidal Relationship between Total Phosphorus and ChlorophyllaConcentrations in Canadian Lakes

We tested five hypotheses to explain the sigmoidal relationship between total phosphorus (TP) and chlorophyll a (Chl a), two assuming that the nonlinearity is an artifact of various measurement biases and three assuming that it is based on underlying ecological interactions. Our first hypothesis was rejected; accounting for differences in extraction protocol of Chl a among published studies did not affect the sigmoidality. Our second hypothesis could not be rejected; there was an uncoupling between Chl a and PHYTO in oligotrophic lakes which may explain the initial nonlinearity. Our third hypothesis was upheld; the initial nonlinearity may be attributed to the presence of a disproportionately large fraction of unavailable phosphorus, since Chl a varied linearly with the proportion of total biologically active phosphorus in the TP fraction. The proportion of filamentous cyanophytes varied significantly with TP concentrations, and this was consistent with our fourth hypothesis that the higher Chl a:TP ratio at intermediate TP concentrations is attributable to reduced grazing impact of zooplankton in more productive lakes. Finally, Chl a varied linearly with total nitrogen, and this was consistent with our fifth hypothesis that the departure from linearity at extremely high phosphorus concentrations is indicative of nitrogen limitation.

Symbiotic associations among the microplankton in oligotrophic marine environments, with special reference to the Gulf of Aqaba, Red Sea

Instances of symbiotic consortia in the microplankton of highly oligotrophic seas are discussed on the basis of case studies and long-term observations off the Israeli coast of the Gulf of Aqaba, Red Sea, and the inshore and offshore waters of the Eastern Mediterranean. Associations described include diatoms with filamentous cyanophytes, diatoms with protozoans, tintinnids with attached or encrusted diatoms, and acantharians with algal endosymbionts. Noted among the case studies is the frequent occurrence of the endosymbiont cyanophyte Richelia inrracellularis , capable of molecular nitrogen fixation, in diatoms, including three species of Hemiaulus . For one of these associations, seemingly with Hemiaulus sinensis , this is the first photographic record. The consortia are considered in relation to their seasonal distribution in depth profiles from the northern end of the Gulf of Aqaba, and in relation to their occurrence in the Eastern Mediterranean and also worldwide in similar environments. These aspects and the easily identifiable symbiotic nature of the consortia described herewith make them useful as indicator species of warm water oligotrophic seas.

Development of Daphnid Communities in Diatom- and Cyanophyte-Dominated Lakes and Their Relevance to Lake Restoration by Biomanipulation

(1) Development of cladoceran communities was followed in two contrasted lakes in the Norfolk Broadland and in fine netting enclosures, lacking a fish community, placed in the lakes. (2) Both lakes were highly nutrient-rich but, probably because of differences in flushing rate, Hoveton Great Broad had a phytoplankton dominated in summer by diatoms whilst Ranworth Broad had prolific populations of the cyanophyte Oscillatoria. (3) Daphnia hyalina was present in both lakes in early summer but declined in July in Hoveton Great Broad and in June in Ranworth Broad. These declines occurred in both fish-free enclosures and in the open lakes which were not fish-free. The earlier decline in Ranworth Broad is attributed to decline in food quality. (4) For a given body length, smaller eggs were produced by Daphnia hyalina in Ranworth Broad. Such eggs are likely to give smaller neonates, perhaps better able to survive in water dominated by filamentous cyanophytes likely to occlude the feeding apparatus of larger animals. (5) Very large populations of the large-bodied Daphnia pulex and Daphnia magna developed in July and August in the enclosures in Hoveton Great Broad but not in the open lake nor at all in Ranworth Broad or its enclosures. This suggests that food quality was suitable in Hoveton Great Broad but not in Ranworth Broad, and that in the presence of adequate food and the absence of fish predation, large grazer communities of Daphnia can be maintained from May to September in shallow eutrophic lakes. (6) The implications of the results for attempts at restoration of lakes from eutrophication by biomanipulation are discussed.

Influence of Substrate Conditioning on Periphytic Growth in a Heterotrophic Woodland Stream

The influence of in situ substrate conditioning on periphyton colonization and growth was investigated during fall and spring in Walker Branch, a shaded, woodland stream in eastern Tennessee. Ceramic cylinders were conditioned by placing them in the stream under black plastic for >75 d. After conditioning, pairs of conditioned and unconditioned cylinders were placed in a shaded riffle and periphyton development was monitored for 35 (spring) or 40 (fall) d. The only variable measured that was significantly greater on conditioned than on unconditioned cylinders in both seasons was ATP, but significant differences only lasted until day 9. Taxonomic structure of the algae differed among seasons. Achnanthes spp. dominated during the fall experiment and their relative abundances were significantly greater on conditioned than on unconditioned cylinders through day 8 of the experiment, but not after. Meridion circulare dominated early in spring, whereas filamentous cyanophytes were only observed on day 35. Neither these taxa nor the other dominant taxa demonstrated a consistent preference for one substrate type over another. Conditioning never resulted in enhanced densities of algal cells or units during spring, when discharge was high and variable; only rarely did conditioning lead to enhanced algal settlement or growth during fall, when discharge was low and stable. Results from this study suggest that the influence of substrate conditioning on periphyton growth and development is relatively short-term. Conditioning is predicted to have more important consequences on stream structure and function in systems with a high frequency of disturbance, where periphyton communities are continuously set back to an early seral stage, than in systems with a low frequency of disturbance.