Dominant Algal Species Research Articles

Changes in fish abundance do not cascade to sea urchins and erect algae in one of the most oligotrophic parts of the Mediterranean

The abundance of fish, sea urchins, and erect algae over carbonated and non-carbonated rocks was measured in two areas differing in the level of fishing intensity off northern Minorca (Balearic Islands, western Mediterranean) to test the hypothesis that changes in the abundance of invertebrate-feeding fish cascade to erect algae through changes in the density of sea urchins in oligotrophic areas, as has been reported previously for eutrophic areas in the northwestern Mediterranean. Although the biomass of invertebrate-feeding fish and the cover of erect algae increased where fishing intensity decreased, independently of rock type, the biomass and the horizontal test size of sea urchins, represented almost exclusively by Paracentrotus lividus, also increased. Furthermore, the total cover of erect algae and that of the two dominant algae species were not correlated with sea urchin density or sea urchin biomass. Rock type did not affect the total cover of erect algae, but Cystoseira brachycarpa J. Agardh preferred non-carbonated rocks and Dictyota dichotoma v. intricata (C. Agardh) Greville favoured carbonated ones. The only herbivorous fish ( Sarpa salpa) and the omnivorous breams of the family Sparidae were more abundant around carbonated rocks, although only inside the marine protected areas. The wrasses of the family Labridae were insensitive to rock type and the level of fishing intensity. The overall evidence indicates that trophic cascades do not operate in the area studied, as changes in the abundance of invertebrate-feeding fish did not cascade to sea urchins and changes in the abundance of sea urchins did not affect erect algae. The limited recruitment of fish and sea urchins due to extreme oligotrophy is invoked as an explanation, in agreement with the ecosystem exploitation paradigm.

Effects of avian grazing on the algal community and small invertebrates in the rocky intertidal zone

AbstractIn this study of a rocky intertidal habitat in northern Japan, feeding by avian consumers had significant effects on algal assemblages and small herbivorous invertebrates. The effects of the birds on algae were different from those of invertebrate grazers such as urchins and gastropods. The abundance of the dominant algal species decreased during the grazing period, increased again after the grazing period, and indirectly affected algal species richness and evenness. Avian grazing also decreased the density of tube‐dwelling amphipods on the dominant alga, but did not change the density of mobile and free‐living isopods. These results suggest that avian grazers may act as habitat modifiers rather than exploitative competitors for the small herbivorous crustaceans. Avian herbivores consumed only the upper parts of large algal fronds, apparently reducing the amount of suitable microhabitat for the small herbivorous crustaceans, which are subject to a variety of physical or biological stress. Thus, avian herbivores function as ecosystem engineers, regulating community structure in a manner different to invertebrate herbivores in rocky intertidal habitats.

Characteristics and Structure of Benthic Algal Community in Pohang New Port Area

Community structure and biodiversity of benthic marine algae were studied in the rocky shore of Phohang New Port, Yeoungil Bay. A total of 79 species of marine algae including 8 Chlorophyta, 23 Phaeophyta and 48 Rhodophyta are listed. The dominant algal species were Corallina pilulifera in all seasons, and Sargassum homeri in winter. Lomentaria catenata, Lomentaria hakodatensis, Grateloupia laceolata, Sargassum thunbergii, Chondria crassicaulis, Ulva pertusa, and Hypnea charoides were subdominant at different seasons. The algal biomass per unit area of the benthic algal community in Pohang New Port under construction was 14506 - 398.93 g dry wt m-2, which means that its annually averaged value is 273.45 g dry wt m-2 . The seasonal change in algal biomass showed highs in winter and spring, and lows in summer and autumn. The algal species diversity (H') based on algal biomass was 2.07 annually in average, with 2.42 in winter, 2.65 in spring, 1.79 in summer and 1.43 in autumn. It was high in winter and spring seasons and low in summer and autumn seasons. It is caused by that spring and winter are the profitable growth time for algae and species components in this study were dominated by the annual or seasonal rather than perennial plants.

Toxicity of Fluoranthene and Its Biodegradation by Cyclotella caspia Alga

AbstractFluoranthene is one of the polynuclear aromatic hydrocarbons with four benzene rings. Because of its toxicity, mutagenicity, and carcinogenicity, fluoranthene is on the black lists of 129 and 68 priority pollutants established by US Environmental Protection Agency and the People's Republic of China, respectively. In recent years, the amount of fluoranthene in the aquatic environment has been increasing with increases in anthropogenic discharge. Based on the biological investigation of tidal water in the Futian mangrove, Cyclotella caspia was selected as the dominant algal species to determine the toxicity of fluoranthene towards C. caspia alga and to investigate the biodegradation of fluoranthene by C. caspia under pure culture. The toxicity experiment showed that the 96‐h EC50 value for fluoranthene was 0.2 mg/mL. Four parameters, namely C. caspia algal growth rate, chlorophyll (Chl) a content, cell morphology, and superoxide dismutase (SOD) activity, were chosen as indices of toxicity and were measured at 6 d (144 h). The results showed that: (i) the toxicity of fluoranthene towards C. caspia alga was obvious; (ii) C. caspia algal growth rate and Chl a content decreased with increasing concentrations of fluoranthene; and (iii) the rate of cell deformation and SOD activity increased with increasing concentrations of fluoranthene. The biodegradation experiment showed that: (i) the rate of physical degradation of fluoranthene was only 5.86%; (ii) the rate of biodegradation of fluoranthene on the 1st and 6th days (i.e. at 24 and 144 h) was approximately 35% and 85%, respectively; and (iii) the biodegradation capability of C. caspia alga towards fluoranthene was high. It is suggested that further investigations on the toxicity of fluoranthene towards algae, as well as on algal biodegradation mechanisms, are of great importance to use C. caspia as a biological treatment species in an organic wastewater treatment system.(Managing editor: Ping He)

Optical changes associated with cyanobacterial bloom termination by viral lysis

Optical changes that accompanied a collapse of the population of filamentous cyanobacteria from a shallow, eutrophic lake were studied in laboratory-scale enclosures (LSEs). The experimental conditions are known, from previous work on these systems, to cause a dramatic collapse of the dominant algal or cyanobacterial species, which in turn can be associated with viral activity. Within 2 weeks of continuous addition of nutrient-rich growth medium, near-complete collapse of the dominant population occurred over the span of a few days. The collapse was repeatedly and reproducibly observed and was primarily characterized by a marked increase in water transparency. Scattering of light decreased by ∼80%, absorption decreased by 20–80%. There was high similarity in optical changes between several experiments, carried out in different seasons. An increase of dissolved material and submicron-sized particles (SMP) that showed chlorophyll a (Chl a) absorption was observed during the collapse. The phycocyanin (PC): Chl a ratio and phaeopigment : Chl a ratio proved to be good indicators of the observed collapse. Reflectance spectra that were modelled using a constant volume-scattering function indicated that mass mortality of this magnitude can be detected in natural systems using current remote sensors.

DIFFERENTIAL LIFE HISTORY PHASE EXPRESSION IN TWO COEXISTING SPECIES OF SCYTOSIPHON (PHAEOPHYCEAE) IN NORTHERN CHILE1

The identity of two phaeophycean taxa that monopolized the middle‐lower rocky intertidal zone of a coastal area chronically exposed to copper mine wastes in northern Chile was unraveled. One of them was preliminarily identified as the gametophytic stage of Scytosiphon lomentaria (Lyngbye) Link. The other, a dark crust, resembled the alternate stage of some Scytosiphon species. Comparative analysis of morphology, life history, and DNA sequences strongly suggests that crusts corresponded to sporophytic S. tenellus Kogame and confirm that erect thalli belonged to S. lomentaria. A clear segregation of erect and crustose thalli was found using internal transcribed spacer region 1 and RUBISCO spacer sequences. Furthermore, whereas crusts always grouped with S. tenellus, erect thalli always grouped with S. lomentaria. Life history studies failed to connect the two entities. First, field‐collected S. tenellus produced progeny that either recycled the crust, which reproduced by unilocular zoidangia, or developed into erect thalli. The latter, unlike typical gametophytic S. lomentaria, developed patchy sori of plurilocular zoidangia. Second, S. lomentaria displayed a direct‐type life cycle, in which progeny from erect individuals only developed into erect thalli and produced only plurilocular zoidangia. This constitutes the first experimental study on Scytosiphon from the Pacific coast of South America and the first report of S. tenellus on this coast. It is also the first report of the crustose stage of Scytosiphon appearing as a perennial and dominant algal species in a temperate rocky intertidal system.

Structure of the Phytoplankton Community and Its Relationship to Water Quality in Donghu Lake, Wuhan, China

The phytoplankton community structure, in terms of species composition, total standing crop, and abundance of the dominant algal species, at four stations in Donghu Lake, Wuhan, China, was investigated monthly from January 1994 to December 1996. A total of 260 taxa was observed, of which Chlorophyta (106 taxa) contributed the highest portion of the total number of taxa, followed by Bacillariophyta (82 taxa) and Cyanophyta (32 taxa). The total standing crop measured by means of chlorophyll a content, cell density, and cell biovolume, as well as the abundance of the dominant species, declined in the order of Station I to Station IV. Seasonal changes of the standing crop varied greatly among the four stations. Although the cell density at the four stations showed a single peak within a year, the peak density varied from July to November, dependent on the sampling year and the station. For chlorophyll a content and cell biovolume, multiple peaks were observed at Stations I and II, but a single peak was found at Stations III and IV. The phytoplankton community structure indicated that the trophic status was the highest at Station I (most eutrophic), followed by Station II; Stations III and IV were the least trophic areas. The long-term changes in phytoplankton community structure further suggested that changes in phytoplankton community structure were correlated with water quality, and eutrophication of Donghu Lake had been aggravated since the 1950s.

Anatoxin-a toxin in the cyanobacterium Planktothrix rubescens from a fishing pond in northern Italy.

A heavy algal bloom occurring in a fishing pond in northern Italy full of Salmo trutta was examined for algae taxonomy and toxic production. The dominant algal species (98%) was identified as the cyanobacterium Planktothrix rubescens (D.C. ex GOMONT) Komarek Anagnostidis, based on morphological examination, and it was revealed to be toxic in mouse and Vibrio fischeri bioassays. The toxin was identified as anatoxin-a using high-performance liquid chromatography and confirmed using liquid chromatography-mass spectrometry (LC-MS). The mouse bioassay gave signs of poisoning, as previously reported for anatoxin-a. The LC-MS confirmed the presence of an anatoxin-a peak at m/z 166 (M+H+). The content of toxin in the field population was estimated at 12.13 microg/g of fresh cells. The bloom was sustained by the very high N/P ratio in the water. This is the first report in Italy of an anatoxin-a-producing Planktothrix rubescens population.

Optimal strategy for algae control in potable water treatment facilities

This paper presents both a current review of the state-of-the-art in algae removal, and an experimental study of algae removal in potable water supply. Established techniques were investigated by jar-testing on surface raw water samples derived from a lowland river, with the dominant species of algae being Scenedesmus sp (a green algae). These tests were conducted both in isolation and in combination to determine the optimum operational strategy for an actual water treatment facility. Employing 1 mg/L of Cu2SO4 could remove algae by up to 50.6%, though this might lead to the release of algal toxin. The most effective single technique was PAC addition, which could reduce the algae population by up to 97.6%, although doses above 30 mg/L created turbidity. The maximum reduction ratio achieved with polyaluminium chloride in the absence of pH control was 79.1%, employing a dosage of 14 mg/L; careful pH control during addition of poly-AlCl3 coagulant increased algae removal by up to 35%.

Use of in situ and airborne reflectance for scaling-up spectral discrimination of coral reef macroalgae from species to communities

In principle, a priori knowledge of organism-scale spectral signatures for key ecological end-members is a basic requirement for identifying coral reef benthic communities using hyper- spectral remotely-sensed imagery. Spectral signatures of end-members are now relatively well known for predominant reef taxa (coral, algae) and for the background of the living communities (e.g. sediments). What remains unclear is whether the criteria for spectral discrimination between end- members at the millimeter or centimeter scale remain valid when attempting to process images at several meters resolution. In other words, is it possible to scale-up spectral criteria of identification from species/organisms to communities? We address this issue with in situ and 'compact airborne spectrometer imager' (CASI) hyperspectral measurements of the tropical marine flora of 2 South Pacific Ocean coral reefs. Targets were the dominant algal species and communities encountered in the shallow (0 to 3 m) barrier and fringing reefs of Moorea Island and the outer margin of the rim of Rangiroa Atoll (French Polynesia). Stepwise wavelength selection and linear discriminant analysis highlighted the key non-redundant wavelengths necessary to achieve good separation between the predefined ecological groups. Comparison of the wavelengths identified from in situ and airborne measurements allowed definition of a subset of common wavelengths that were robust to changes in spatial scale and still provided excellent discrimination and classification accuracy between the eco- logical groups. These results suggest that continuous spectral signatures acquired in situ at the centi- meter scale can be used to select key discrete wavelengths for remote-sensing observations of com- munities at the meter scale despite the spatial heterogeneity in benthic cover and the resulting spectral mixing.

Biodiversity and Community Structure of Marine Benthic Organisms in the Rocky Shore of Dongbaekseom, Busan

Species composition, community structure and biodiversity of marine benthic community were studied in the rocky shore of Dongbaekseom, Busan. A total of 82 species of marine algae including 4 Cyanophyta, 11 Chlorophyta, 20 Phaeophyta and 47 Rhodophyta are listed. The dominant algal species were Ulva pertusa, Chondria crassicaulis, Corallina spp. and Melobesioidean algae. Sargassum thunbergii, Chondracanthus intermedia, Gelidium divaricatum and Ralfsia verrucosa were subdominant in cases of different seasons and vertical layers. Chthamalus challengeri, Littorina brevicula and Mytilus edulis were dominant zoobenthic species upper-middle layer of the intertidal zone. The community structure of this area seemed to be controlled by spatial competition with benthic marine algae. The species diversity indices estimated from different sources were quite different. Indices from coverage were 1.87, 3.98 from frequency, 2.26 from the average of total frequency and coverage and 2.15 from importance value. The similarity indices on the present study showed decreasing trends comparing to the previous benthic algal composition researches.

High Organic Carbon Export Precludes Eutrophication Responses in Experimental Rocky Shore Communities

We studied the effect of nutrient inputs on the carbon (C) budget of rocky shore communities using a set of eight large experimental mesocosms. The mesocosms received a range of inorganic nitrogen (N) and phosphorus (P) additions, at an N:P ratio of 16. These additions were designed to elevate the background concentration, relative to that in eutrophic Oslofjord (Norway) waters, by 1, 2, 4, 8, 16, 32 μmol dissolved inorganic nitrogen (DIN)l−1 (and the corresponding P increase). Two unamended mesocosms were used as controls. The nutrients were added continuously for 27 months before gross primary production (GPP), respiration (R), net community production (NCP), and dissolved organic carbon (DOC) production were assessed for the dominant algal species (Fucus serratus) and for the whole experimental ecosystem. Inputs and outputs of DOC and particulate organic carbon (POC) from the mesocosms were also quantified. The F. serratus communities were generally autotrophic (average P/R ratio = 1.33 ± 0.12), with the GPP independent of the nutrient inputs to the mesocosms, and maintained a high net DOC production during both day (0.026 ± 0.008 g C m−2 h−1) and night (0.015 ± 0.004 g C m−2 h−1). All the experimental rocky shore ecosystems were autotrophic (P/R ratio = 2.04 ± 0.28), and neither macroalgal biomass nor production varied significantly with increasing nutrient inputs. Most of the excess production from these autotrophic ecosystems was exported from the systems as DOC, which accounted for 69% and 58% of the NCP of the dominant community and the experimental ecosystem, respectively, the rest being lost as POC. High DOC release and subsequent export from the highly energetic environments occupied by rocky shore communities may prevent the development of eutrophication symptoms and render these communities resistant to eutrophication.

Continuing trophic cascade effects after 25 years of no-take marine reserve protection

Between 1978 and 1996 benthic communities in the Leigh Marine Reserve shifted from being dominated by sea urchins to being dominated by macroalgae. This was a result of a trophic cas- cade thought to be an indirect effect of increased predator abundance. We assessed further changes in communities from 1996 to 2000, differences in benthic communities between reserve and adjacent unprotected sites, and the stability of these patterns from 1999 to 2001. Since 1996, densities of sea urchins Evechinus chloroticus have continued to decline in shallow areas of the reserve (<8 m), and all sites classified as urchin barrens in 1978 are now dominated by large brown algae. Comparisons between reserve and non-reserve sites revealed differences consistent with a trophic cascade at reserve sites. The greatest differences in algal communities between reserve and non-reserve sites occurred at depths where E. chloroticus was most abundant (4 to 6 m). Reserve sites had lower urchin densities and reduced extent of urchin barrens habitat with higher biomass of the 2 dominant algal species (Ecklonia radiata and Carpophyllum maschalocarpum). At reserve sites densities of exposed E. chloroticus (openly grazing the substratum) declined so that urchin barrens were completely ab- sent by 2001. Lower density of the limpet Cellana stellifera and higher densities of the turbinid gas- tropod Cookia sulcata at reserve sites are thought to be responses to changes in habitat structure, representing additional indirect effects of increased predators. The overall difference in community types between reserve and non-reserve sites remained stable between 1999 and 2001. Localised urchin mortality events due to an unknown agent were recorded at some sites adjacent to the marine reserve. Only at 1 of these sites did exposed urchins decline below the critical density of 1 m -2 , which resulted in the total replacement of urchin barrens with macroalgae-dominated habitats. At other sites urchin barrens have remained stable. Declines in the limpet C. stellifera occurred across all sites between 1999 and 2001 and may be indirectly associated with urchin declines. Long-term changes in benthic communities in the Leigh reserve and the stability of differences between reserve and non- reserve sites over time are consistent with gradual declines in urchin densities due to increased pre- dation on urchins, thus providing further evidence for a trophic cascade in this system. The rapid de- clines in urchin numbers at some unprotected sites, however, demonstrate how short-term disturbances, such as disease, may result in shifts in community types over much shorter time frames.

Microcystin-producing cyanobacteria in recreational waters in southwestern Germany.

Toxin-forming species of freshwater cyanobacteria have been detected in all parts of Germany. Because of the high number of lakes (more than 2000) in Baden-Württemberg, in southwestern Germany, only a representative selection of lakes (155) was intensively monitored for mass development of cyanobacteria and the formation of toxins in 1999. Nutrients, dominant algal species, chlorophyll, and toxins were determined from waters with cyanobacterial blooms. Toxin analyses were performed using HPLC, the PP1 inhibition test, and the microcystin ELISA. In 45% of the monitored lakes, the phytoplankton assemblage consisted mainly of cyanobacteria; in an additional 24% of the lakes cyanobacteria were detected. More than 26% of the lakes contained toxigenic cyanobacteria. The highest amount of microcystins detected outside scum areas was 11-560 microg/L. In relation to biomass, cyanobacteria contained up to 1100 microg/g dry matter and up to 2.6 microg/microg Chl a. The dominant form of microcystin detected was microcystin-LR, one of the most toxic known microcystins. The results of the present study have been used to develop a stepwise monitoring scheme for lakes with permanent cyanobacterial populations to protect human health and livestock.

Correlations Between Reflectance Spectra and Contents of Chlorophyll-a in Chaohu Lake

Chaohu Lake is one of the biggest freshwater lakes of China. This study was conducted to establish correlations between reflectance spectra and contents of chlorophyll a in Chaohu Lake, which was in eutrophic status. Reflectance spectra were measured during November, 2001 by using ASD FieldSpec HandHeld radiometer. Water samples for chlorophyll a measurements and dominant algal species determination were collected at the same time. The features of the spectral reflectance of the lake were discussed. The correlation between the spectral reflectance of single band and the content of chlorophyll a was low. The reflectance ratio of R 705nm / R 680nm and the reflectance first derivative of 690nm were found to be significantly correlated with the contents of chlorophyll a, and the r 2 gained using the reflectance ratio was higher than gained from the reflectance first derivative of 690nm's.

Interplay of encrusting coralline algae and sea urchins in maintaining alternative habitats

In proximity of shelters, grazing by sea urchins plays a fundamental role in establishing and maintaining areas dominated by encrusting corallines. Much attention has been given to the effects of urchins on algal assemblages in shallow subtidal reefs, but few studies attempted to clarify the role played by encrusting coralline algae in this system. It has been shown that encrusting corallines are able to reduce settlement of potential competitors, suggesting that they do not rely on grazing by herbivores to prevent swamping by erect algal species. In shallow subtidal reefs of the Mediterranean Sea, the sea urchins Para- centrotus lividus and Arbacia lixula are the main herbivores, whose grazing commonly leads to a mosaic of areas dominated alternatively by encrusting corallines and turf-forming algae. This study aims to separate the effects of urchins and encrusting corallines on the re-colonisation of encrusting coralline- dominated patches (barren habitat) by surrounding erect algal species (turf-forming algae). Different hy- potheses were tested by means of multivariate and univariate analyses. The multivariate hypothesis was that the algal assemblage developing when encrusting corallines and urchins are simultaneously removed would be more similar to that establishing in stands of turf-forming algae, than that developing when none or only 1 of the 2 factors is manipulated. The univariate hypotheses tested were: (1) that there is a nega- tive effect of sea urchins and encrusting corallines on the re-colonisation of barren areas by surrounding turf-forming algal species and (2) that the effects of encrusting corallines are weaker than those of urchins, but that they operate in the same direction. These hypotheses were tested by means of an orthogonal ma- nipulation of urchins and encrusting corallines. At each of 3 study sites, 2 replicate barren patches were assigned to each of these treatments: (1) +corallines+urchins; (2) +corallines-urchins; (3) -corallines+urchins; (4) -corallines-urchins. The results suggest that the occurrence of areas domi- nated by encrusting corallines on shallow subtidal reefs in the northwest Mediterranean is not simply the result of grazing by sea urchins on turf-forming species. The removal of encrusting corallines also affected the abundance of dominant algal species and determined the development of an algal assemblage resembling those occurring within stands of algal turfs. The effects of the removal of urchins on turf- forming species were generally positive, while those of encrusting corallines varied from negative (Padina pavonica) to positive (Acetabularia acetabulum and filamentous algae). Therefore, the role played by encrusting corallines in maintaining alternative habitats on shallow subtidal reefs should be taken into account, thus avoiding the overestimation of the effects of grazing by sea urchins.

Bacterial community structure associated with a dimethylsulfoniopropionate-producing North Atlantic algal bloom.

The bacteria associated with oceanic algal blooms are acknowledged to play important roles in carbon, nitrogen, and sulfur cycling, yet little information is available on their identities or phylogenetic affiliations. Three culture-independent methods were used to characterize bacteria from a dimethylsulfoniopropionate (DMSP)-producing algal bloom in the North Atlantic. Group-specific 16S rRNA-targeted oligonucleotides, 16S ribosomal DNA (rDNA) clone libraries, and terminal restriction fragment length polymorphism analysis all indicated that the marine Roseobacter lineage was numerically important in the heterotrophic bacterial community, averaging >20% of the 16S rDNA sampled. Two other groups of heterotrophic bacteria, the SAR86 and SAR11 clades, were also shown by the three 16S rRNA-based methods to be abundant in the bloom community. In surface waters, the Roseobacter, SAR86, and SAR11 lineages together accounted for over 50% of the bacterial rDNA and showed little spatial variability in abundance despite variations in the dominant algal species. Depth profiles indicated that Roseobacter phylotype abundance decreased with depth and was positively correlated with chlorophyll a, DMSP, and total organic sulfur (dimethyl sulfide plus DMSP plus dimethyl sulfoxide) concentrations. Based on these data and previous physiological studies of cultured Roseobacter strains, we hypothesize that this lineage plays a role in cycling organic sulfur compounds produced within the bloom. Three other abundant bacterial phylotypes (representing a cyanobacterium and two members of the alpha Proteobacteria) were primarily associated with chlorophyll-rich surface waters of the bloom (0 to 50 m), while two others (representing Cytophagales and delta Proteobacteria) were primarily found in deeper waters (200 to 500 m).

COLONIZATION OF PERIPHYTIC ALGAE ON ARTIFICIAL SUBSTRATES IN A TROPICAL STREAM

Standard periphyton samplers were used to examine the colonization pattern of periphytic algae on an artificial substrate (glass slides) in the Lam Tsuen River, Hong Kong, between October 1995 and August 1996. Changes in the taxonomic composition, species diversity (Shannon-Wiener diversity index), total standing crop, as well as the abundance of individual algal species were monitored over a six-week period in each season. Diatoms were most dominant in terms of cell density and biovolume, while green algae were important in terms of cell biovolume in autumn and summer. Of the 81 algal species observed, the pennate diatoms were most abundant. Dominant algal species included Achnanthes minutissima, Gomphonema parvulum, G. angustatum, G. rhombicum, Synedra rumpens var. familiaris, Nitzschia palea, Cocconeis placentula, Mougeotia spp., Spirogyra spp., Stigeoclonium aestivale and Schizothrix calcicola. A maximum algal density of 3.45 × 106 cells per cm2 was observed after a 4-week field incubation in spring (April and May), while maximum algal biovolume (1.20 × 106 μm3 cm−2) was recorded after a 6-week field incubation in summer (July and August). In general, the standing crop reached its maximum at week 4. Seasonal variations in the succession patterns of the periphytic algal communities are described.

Algal growth on organic compounds as nitrogen sources

Two experimental series were run to evaluate the potential of algal development on dissolved organic nitrogen (DON) compounds as the sole source of nitrogen (N) nutrition. Mono- cultures of several common Lake Kinneret algae (Pediastrum duplex, Synechococcus sp., Microcystis aeruginosa, Aphanizomenon ovalisporum and Cyclotella sp.) were incubated for 3 weeks in the laboratory with different inorganic (NH4 + , NO3 - ) or organic (hypoxanthine, urea, guanine, ornithine, glucosamine, lysine) nitrogen sources. Even though the cultures were not axenic, marked differences were observed in algal growth response. Pediastrum, Cyclotella and Aphanizomenon grew well on most N sources, and cyanobacterial growth and yield were consistently greatest when urea was the only N source. We also followed algal growth and eventual species dominance in batch samples of GF/F-filtered lake water, supplemented with orthophosphate and different inorganic or organic N compounds and inoculated with concentrated lake phytoplankton. Although no clear impact on phytoplankton growth (as chlorophyll concentration) was observed, in seven out of 11 experiments we could discern changes in the algal species that became dominant in flasks with different organic and inorganic N sources. Our results are consistent with the proposition that components of the DON pool are not only an important potential, direct or indirect N source for phytoplankton, but also that different algal species can exploit these sources with varying capabilities so that different N substrates may selectively stimulate the development of dominant algal species.

Combined effects of alachlor and atrazine on benthic algal communities in artificial streams

AbstractA duplicated factorial approach was used to assess the combined effects of three environmentally realistic levels of alachlor (0.0, 5.0, and 90.0 μg/L), cross‐classified with three environmentally realistic levels of atrazine (0.0, 12.0, and 150.0 μg/L), on indigenous epipelic algae (mud‐dwelling species, characteristic of agricultural streams). The experiment was conducted in 18 recirculating laboratory streams over a 4‐week period. Biovolume of viable algal cells and relative abundance of the six dominant algal species were utilized as experimental endpoints. Community biovolume was impacted throughout the experiment in streams treated with 12.0 and 150.0 μg/L atrazine and in streams containing 90.0 μg/L alachlor, but only in samples collected at 4 weeks. The effects of atrazine and alachlor together on algal community biovolume appeared to be additive rather than synergistic. The relative abundance of two dominant algal taxa were impacted in streams treated with alachlor, but only one species remained affected over time. The lack of significant interactions is most likely attributable to the different modes of action of atrazine and alachlor. The additive nature of these two herbicides should be an important consideration in the development of water quality criteria.