Effects of depth, sediment and grazers on the degradation of drifting filamentous algae (Cladophora glomerata and Pilayella littoralis)

Eutrophication in the northern Baltic Sea promotes growth of annual filamentous algae. The algae detach, gather at the bottom and give rise to algal mats of varying size, density, composition and condition. Dense mats of filamentous algae induce anoxia, which in turn leads to faunal mortality. By a set of field experiments, we have studied the fate of the abundant Cladophora glomerata after detaching from the rocky substrate, and the effect of water depth and sediment on its decay. Further, we have studied the importance of common mesograzers (Gammarus and Idotea) on the rate of degradation of C. glomerata and Pilayella littoralis.Our results show that loose algae at shallow sites (8 m) decompose faster than algae in deeper (18 m) areas. Drifting C. glomerata on the sediment is more rapidly broken down and dissolved than algae floating in the water column, which depends on higher microbiological activity. Dominant amphipods (Gammarus spp) colonise near-shore drift algae quickly, and juvenile bivalves (Cerastoderma glaucum) utilise algae in the water column for settling. Moderate natural densities of grazers (Gammarus spp and Idotea baltica) in the drifting algae did not increase the degradation rates of C. glomerata and P. littoralis. C. glomerata was completely decomposed in 4 months.Our experiments demonstrate the effects of position (depth, water/sediment) and grazing on the degradation of drifting filamentous algae. Mass developments of opportunistic algae occur annually in the study area, and information on the destiny of detached drift algae may help us to predict their longevity and the damage they cause, and hence, to decide on long-term measures needed to improve environmental conditions.     

Growth of enterobacteria on algal mats in the eastern part of the Gulf of Finland

Model experiments on a possibility that pathogenic enterobacteria Salmonella enteritidis (Gartneri) can grow on decaying algal mats with prevalence of the filamentous algae Cladophora glomerata (L.) Kütz were carried out. Samples of algal mats have been collected in the eastern part of the Gulf of Finland in the Baltic Sea. A bacterial culture of Salmonella enteritidis was placed into tubes containing samples of mats. The intensive growth of salmonella was noted in alga samples collected in the freshwater zone (salinity 0.2–1.5‰); growth was practically absent in the samples of algae collected in a zone with salinity 2–3‰, while salmonella remained viable in the control tubes with water without algae. The growth of coliform enterobacteria initially inhabited in the algal mats was discovered in all experiments. Studies carried out in 2009 show that the thickness of the algal mats in the costal zones of the Gulf of Finland reached 20 cm and their biomass reached a few tons per 1 km². These experiments showed that dead algal mats stimulate the growth of enterobacteria in the littoral zone of the Baltic Sea, especially in the freshwater part, and can promote the development of these pathogenic microorganisms.     

Water chemistry and algal vegetation of streams in the Asir Mountains,Saudi Arabia

Surveys of water chemistry and algal vegetation at nine stream sites in the Asir Mountains, Saudi Arabia, were made in March, 1984. The waters were moderately to highly calcareous with a relatively high Mg: Ca ratio and high concentrations of reactive-Si (x = 12.2 mg l^–1) and F (x = 0.73 mg l^–1). Ammonia typically constituted about one-sixth of the inorganic nitrogen. Filamentous algae (Cladophora and/or Spirogyra) were abundant at all but one site. However two sites, Wadi Habaqah and Al Tanoumah, differed considerably from the others in their overall floristic composition, with various species of Rivulariaceae, Nostoc verrucosum, Schizothrix lardacea and certain other blue-green algae present only here. With one minor exception, heterocystous blue-green algae were absent at the other sites. Tufa was deposited at these two sites, but not elsewhere. Species which appeared to play an active role in calcification included Dichothrix gypsophila, Calothrix parietina, Cladophora glomerata and the moss Bryum sp. A community apparently not previously recorded in the literature was abundant at Wadi Habaqah. This consisted of thick mats of Cladophora glomerata, with a thin surface layer of Zygnemales and numerous colonies of Nostoc verrucosum inside, or towards the underside, of the mat.     

Potential use of green algae as a biosorbent for hexavalent chromium removal from aqueous solutions

The hexavalent chromium Cr(VI) poses a threat as a hazardous metal and its removal from aquatic environments through biosorption has gained attention as a viable technology of bioremediation. We evaluated the potential use of three green algae (Cladophora glomerata, Enteromorpha intestinalis and Microspora amoena) dry biomass as a biosorbent to remove Cr(VI) from aqueous solutions. The adsorption capacity of the biomass was determined using batch experiments. The adsorption capacity appeared to depend on the pH. The optimum pH with the acid-treated biomass for Cr(VI) biosorption was found to be 2.0 at a constant temperature, 45?°C. Among the three genera studied, C. glomerata recorded a maximum of 66.6% removal from the batch process using 1.0?g dried algal cells/100?ml aqueous solution containing an initial concentration of 20?mg/L chromium at 45?°C and pH 2.0 for 60?min of contact time. Langmuir and Freundlich isotherm equations fitted to the equilibrium data, Freundlich was the better model. Our study showed that C. glomerata dry biomass is a suitable candidate to remove Cr(VI) from aqueous solutions.     

Activated chemical defenses suppress herbivory on freshwater red algae

The rapid life cycles of freshwater algae are hypothesized to suppress selection for chemical defenses against herbivores, but this notion remains untested. Investigations of chemical defenses are rare for freshwater macrophytes and absent for freshwater red algae. We used crayfish to assess the palatability of five freshwater red algae relative to a palatable green alga and a chemically defended aquatic moss. We then assessed the roles of structural, nutritional, and chemical traits in reducing palatability. Both native and non-native crayfish preferred the green alga Cladophora glomerata to four of the five red algae. Batrachospermum helminthosum, Kumanoa holtonii, and Tuomeya americana employed activated chemical defenses that suppressed feeding by 30–60 % following damage to algal tissues. Paralemanea annulata was defended by its cartilaginous structure, while Boldia erythrosiphon was palatable. Activated defenses are thought to reduce ecological costs by expressing potent defenses only when actually needed; thus, activation might be favored in freshwater red algae whose short-lived gametophytes must grow and reproduce rapidly over a brief growing season. The frequency of activated chemical defenses found here (three of five species) is 3–20× higher than for surveys of marine algae or aquatic vascular plants. If typical for freshwater red algae, this suggests that (1) their chemical defenses may go undetected if chemical activation is not considered and (2) herbivory has been an important selective force in the evolution of freshwater Rhodophyta. Investigations of defenses in freshwater rhodophytes contribute to among-system comparisons and provide insights into the generality of plant–herbivore interactions and their evolution.     

Effects of small‐scale environmental variation on metaphyton condition and community composition

1. Metaphyton mats typically originate as benthic algal biofilms that experience higher solar radiation and temperatures, and reduced access to nutrients, once they reach the water surface, but the impacts of these physicochemical changes on metaphyton condition and community composition have received little attention. 2. Using microprobes positioned at 0, 2, 4 and 6 cm depth, we recorded small‐scale differences in water chemistry within metaphyton mats constrained in floating nets during an 8‐week period. Concurrent weekly samples of filamentous algae and their diatom epiphytes were collected from the top, middle and bottom of the mats and were analysed for changes in ash‐free dry mass (AFDM) and chlorophyll‐a, nutrient (N, P, C, Si) content and taxonomic composition. 3. Light intensity, temperature and dissolved oxygen declined both with increasing depth in the mat and over the study period. The autotrophic index (=AFDM/chlorophyll‐a) was greatest at the top of the mats and increased over time; samples also had higher C/P and C/N ratios than samples deeper within the mat. 4. Pithophora was consistently the dominant algal filament throughout the study (representing 85% of all filaments averaged over time and depth); epiphytic diatom cover on Pithophora (calculated as epiphyte area index) declined over time, particularly at the top of the mat. 5. Densities of the diatom epiphytes Gomphonema, Cocconeis and Fragilaria increased with increasing depth within the mat, whereas Cymbella/Encyonema was more common in surface samples. 6. Our results indicate that metaphyton mats are highly dynamic communities, spatially organised in part by small‐scale environmental variation and subject to changes in taxonomic composition following their arrival at the water surface.     

Seasonal Physical,Chemical and Algal Changes in Five Rivers Flowing Through the Oil Sands Region of Alberta,Canada

Seasonal studies concentrating upon physical and chemical parameters and the epilithic algal community were conducted at specific sites in five tributary rivers flowing through the oil sands region of northeastern Alberta, Canada into the Athabasca River. Numerically cyanophycean algae (Lyngbya aerugineo-caerulea, Phormidium sp., Calothrix braunii, Nostoc spp. and Anabaena affinis) dominated followed by diatoms (Achnanthes lanceolata, Cocconeis pediculus, Cocconeis placentula, Epithemia sorex, Epithemia turgida, Gomphonema acuminatum, Gomphonema longiceps v. subclavata, Gomphonema olivaceum, Nitzschia fonticola, Nitzschia palea, Synedra rumpens, and Synedra ulna). One exception was the Hangingstone River where chlorophycean algae (Stigeoclonium pachydermum and Cladophora glomerata) were next in importance to the cyanophytes. Seasonal fluctuations in algal species and numbers were influenced by a myriad of interacting parameters. Physically disruptive forces (current velocity and discharge) appeared more important than dissolved nutrients. They were also responsible for affecting the chemical composition of the water itself.     

Algal response to a thermal effluent: study of a power station on the provo river,Utah, USA

The effect of a thermal effluent on the attached algae of the Provo River, Utah, USA, was studied from 1975 to 1977. Data for macroscopic and microscopic algae were collected and analyzed. Diatoms, Cladophora glomerata, and Hydrurus foetidus dominated the flora. The thermal effluent significantly affected the algal flora in a section of river 100 to 135 meters long immediately below the discharge point. Cladophora growth was increased and Hydrurus was absent in this area. In addition, diatom production was often higher and diversity lower than in the rest of the river. Community structure was unique from all other adjacent areas. Small temperature increases which occured as effluent and river waters mixed farther downstream were apparently not as important to the algal flora as other environmental factors.     

Floristic studies on freshwater algae of Lake Gondwana,Northern Victoria Land (Antarctica)

Benthic algal mats and phytoplankton of Lake Gondwana (Northern Victoria Land, Antarctica) were investigated. Biomass, chlorophyll content and floristic analyses were carried out on algal mats. The mats are composed of two layers different in colour, floristic composition and chlorophyll content. The algal flora of the mats amount to 34 taxa (19 Cyanophyta, 7 Bacillariophyta, 8 Chlorophyta). The phytoplankton community is species-poor (only 5 taxa). Crytophyta account for about 98% of total algal density.     

Influence of the Thin Drift Algal Mats on the Distribution of Macrozoobenthos in Kõiguste Bay, NE Baltic Sea

Macrozoobenthic communities within and outside of the drift algal mats were compared in Kõiguste Bay, NE Baltic Sea. The patches of the drift algae were on average 0.5–1 km wide in diameter covering about 25% of the total bottom area of the bay. Thickness of the mat did not exceed 6 cm. The biomass of the mat varied between 35 and 1391 g dw m^?2. The drift algal mats had no clear negative effect on macrozoobenthos except for a few infaunal species. The drift algae favoured several detrivorous, herbivorous and carnivorous species. Among the studied variables, the thickness of algal mat and oxygen concentration at near-bottom layer explained the best the structure of macrozoobenthos. Total number of invertebrate species increased curvilinearly with the thickness of algal mat having the peak value at 3–5 cm thick algal mat. To conclude, moderate drift algal mats increased habitat complexity and, thus, the diversity of benthic faunal assemblages in otherwise poorly vegetated coastal areas.     

DNA SEQUENCE VARIATION IN THE RIBOSOMAL INTERNAL TRANSCRIBED SPACER REGION OF FRESHWATER CLADOPHORA SPECIES (CHLOROPHYTA)1

Freshwater species of Cladophora (Chlorophyta) are globally distributed and occupy an unusually wide range of ecological habitats. Delineating species is difficult because most easily observed morphological traits are highly variable and because sexual reproduction has not been clearly documented. Synthesizing ecological data on freshwater Cladophora species is problematic because it is unclear whether freshwater Cladophora species comprise many genetically distinct species or a few ecologically and morphologically variable and/or plastic species. We determined nucleotide sequences of the internal transcribed spacer (ITS) region of the nuclear ribosomal cistron of freshwater Cladophora species from a wide range of habitats and geographic locations. We compared these sequences to those derived from culture collections of C. fracta and C. glomerata, the two most commonly reported freshwater Cladophora species. Cladophora fracta and C. glomerata had very similar ITS sequences (95.3%). All other sequences were identical to those from the C. fracta or C. glomerata culture collections with the exception of one California sample that was similar to both C. fracta (95.6%) and C. glomerata (92.4%). ITS genotypes did not correlate with morphology or geography. This analysis shows that common freshwater Cladophora species comprise very few (possibly one) ecologically and morphologically variable species.     

Barley straw as an inhibitor of algal growth I: studies in the Chesterfield Canal

The presence of rotting barley straw in a dis used canal reduced the amount of filamentous algae. No effect on algae was observed during the first season after the introduction of straw but algae were decreased in three subsequent years. Algal growth on microscope slides suspended in the water downstream of the straw was reduced by 90%, compared with slides upstream of the straw. A similar result was obtained forCladophora glomerata grown in chambers in the canal. Phosphate, nitrate and ammonium concentrations were not altered significantly by the presence of straw, but nitrite concentrations were increased during summer months. Neither the nitrite increase, nor the possibility of pesticides being washed off the straw were considered likely causes of algal growth inhibition. Growth ofC. glomerata was inhibited in cages from which macro-invertebrate grazers were excluded. No obvious deleterious environmental effects were noted and the technique shows promise as a long-term method of controlling algae.     

Grazing by Talorchestia longicornis on an algal mat in a new England salt marsh

Grazing experiments using ¹⁴C and an analysis of fecal pellets and gut contents established that the gammaridean amphipod, Talorchestia longicornis Say, ingests blue-green algae on algal mats in a Massachusetts salt marsh. This grazing had a measurable effect on the lower algal mat, where the density of T. longicornis was high. Exclusion of amphipods resulted in increases in chlorophyll a content, carbon incorporation, and nitrogen fixation. This effect was not seen on the upper mat where T. longicornis was less abundant. The assimilation efficiency of T. longicornis feeding on a diet consisting mainly of blue-green algae was surprisingly high (67 %) considering that blue-green algae are usually considered as a poor quality food for herbivores. The population of T. longicornis seems to be annual, with growth of the overwintered juveniles in spring and early summer.     

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g⁻¹ vs. 107 μg g⁻¹, respectively) and soil TP (284 μg g⁻¹ vs. 145 μg g⁻¹). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m⁻²). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate community. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Isolation of chlorophylls and carotenoids from freshwater algae using different extraction methods

Usually marine algae are an excellent source of pigments for different commercial sectors. Freshwater macroalgae can be exploited as a good source of biologically active compounds provided an appropriate extraction method is developed. The efficiency of four methods, like microwave‐assisted (MAE), ultrasound‐assisted extraction (UAE), supercritical fluid extraction (SFE) with ethanol as a co‐solvent, as well as conventional Soxhlet extraction were studied in the same conditions (time, solvent and temperature) for the recovery of chlorophylls and carotenoids from three freshwater green algae species: Cladophora glomerata, Cladophora rivularis and Ulva flexuosa. UV‐Vis spectrophotometry was used to determine chlorophyll a, chlorophyll b and total carotenoid content in obtained extracts. The results of this study showed that the advantages of novel extraction techniques (MAE and UAE) include higher yield and, in consequence, lower costs compared to traditional solvent extraction techniques. These methods were much more efficient in freshwater green algae pigment recovery than the classic Soxhlet extraction as well as SFE.     

The aquatic microphytes and macrophytes of the Transvase Tajo-Segura irrigation system, southeastern Spain

The aquatic plant communities of the irrigation channels of the Transvase Tajo-Segura project are described in order to assess the various options for the control of nuisance vegetation. The low flow rate permits relatively complex planktonic assemblages in addition to epipelic cyanophytes, diatoms and chlorophyes. The only macrophytes to establish themselves in the bottom sediment and form well developed mats were Cladophora glomerata and Potamogeton pectinatus. The water quality of these channels is characterised by high temperature, pH, conductivity and sulphate and chloride concentrations. Moreover, the channels may remain dry for several months.     

Identification of teratogenic polymethoxy-1-alkenes from Cylindrospermopsis raciborskii,and taxonomically diverse freshwater cyanobacteria and green algae

Cylindrospermopsis raciborskii is among the most commonly recognized toxigenic cyanobacteria associated with harmful algal blooms (HAB) in freshwater systems, and specifically associated with multiple water-soluble toxins. Lipophilic metabolites from C. raciborskii, however, were previously shown to exert teratogenicity (i.e. inhibition of vertebrate development) in the zebrafish (Danio rerio) embryo model, specifically suggesting the presence of additional bioactive compounds unrelated to the currently known toxins. In the present study, a series of known teratogenic polymethoxy-1-alkenes (PMA) were identified, purified and chemically characterized from an otherwise well-characterized strain of toxigenic C. raciborskii. Although PMA have been previously identified in other cyanobacteria, this is the first time they have been identified from this recognized HAB species. Following their identification from C. raciborskii, the taxonomic distribution of the PMA was additionally investigated by chemical screening of a freshwater algal (i.e. cyanobacteria, green algal) culture collection. Screening suggests that these compounds are distributed among phylogenetically diverse taxa. Furthermore, parallel screening of the algal culture collection, using the zebrafish embryo model of teratogenicity, the presence of PMA was found to closely correlate with developmental toxicity of these diverse algal isolates. Taken together, the data suggest PMA contribute to the toxicity of C. raciborskii, as well as apparently several other taxonomically disparate cyanobacterial and green algal genera, and may, accordingly, contribute to the toxicity of diverse freshwater HAB.     

Effect of physical factors on the distribution of filamentous green algae in the Tama River

 The distribution of stream-specific filamentous green algae (SSFG) was investigated in the middle reach of the Tama River, Japan. Cladophora glomerata (L.) Kützing and Stigeoclonium sp. dominated among five taxa of SSFG collected in the riverbed with fast currents. These two species were abundant in shallow (<20 cm) riffles with high current velocity (>30 cm s⁻¹), a habitat characterized by high light intensity and extensive aeration. SSFG biomass fluctuated greatly (range, 1.2–85.3 cm² m⁻²), exhibiting no clear seasonal trend. The tufts of SSFG grown on riffle cobbles decreased rapidly when these cobbles were transferred to habitats with either deep water, low current velocity, or both. Laboratory experiments revealed that aeration retarded the decrease in SSFG in incubation vessels. These results suggest that the turbulent conditions of riffle habitats are important for the growth and survival of SSFG in the Tama River. Received: September 5, 2001 / Accepted: April 25, 2002     

Stoichiometric impacts of increased carbon dioxide on a planktonic herbivore

The partial pressure of carbon dioxide (pCO₂) in lake ecosystems varies over four orders of magnitude and is affected by local and global environmental perturbations associated with both natural and anthropogenic processes. Little is known, however, about how changes in pCO₂ extend into the function and structure of food webs in freshwater ecosystems. To fill this gap, we performed laboratory experiments using the ecologically important planktonic herbivore Daphnia and its algal prey under a natural range of pCO₂ with low light and phosphorus supplies. The experiment showed that increased pCO₂ stimulated algal growth but reduced algal P : C ratio. When feeding on algae grown under high pCO₂, herbivore growth decreased regardless of algal abundance. Thus, high CO₂‐raised algae were poor food for Daphnia. Short‐term experimental supplementation of PO₄ raised the P content of the high CO₂‐raised algae and improved Daphnia growth, indicating that low Daphnia growth rates under high pCO₂ conditions were due to lowered P content in the algal food. These results suggest that, in freshwater ecosystems with low nutrient supplies, natural processes as well as anthropogenic perturbations resulting in increased pCO₂ enhance algal production but reduce energy and mass transfer efficiency to herbivores by decreasing algal nutritional quality.     

Oxidative stress tolerance in the filamentous green algae Cladophora glomerata and Enteromorpha ahlneriana

Cladophora glomerata (L.) Kütz. and Enteromorpha ahlneriana Bliding are morphologically similar filamentous green algae that are dominants in the upper littoral zone of the brackish Baltic Sea. As these two species co-exist in a continuously fluctuating environment, we hypothesised that they may have different strategies to cope with oxidative stress. This was tested in laboratory experiments through stressing the algae by high irradiance (600 μmol photons PAR m⁻² s⁻¹) at two different temperatures (15 and 26 °C) in a closed system. Thus, oxidative stress was created by high irradiance (photo-oxidative stress) and/or carbon depletion. The extent of lipid oxidative damage, antioxidant enzyme activities and the amount of hydrogen peroxide excreted by the algae to the surrounding seawater medium were measured. The results suggest that the two species have different strategies: the annual C. glomerata could be classified as a more stress-tolerant species and the ephemeral E. ahlneriana as a more stress-susceptible species. Low temperature in combination with high irradiance created less lipid oxidative damage in C. glomerata than in E. ahlneriana, which was probably related to the higher regular activities of the hydrogen peroxide scavenging enzymes catalase and ascorbate peroxidase in C. glomerata, whereas in E. ahlneriana high activities of these enzymes were only obtained after the induction of oxidative stress. Superoxide dismutase activities were similar in both species, but the mechanisms to remove the hydrogen peroxide produced by the action of this enzyme were different: more through scavenging enzymes in C. glomerata and more through excretion to the seawater medium in E. ahlneriana. The high excretion of hydrogen peroxide, possibly in combination with brominated volatile halocarbons, by E. ahlneriana may have a negative effect on epiphytes and may partly explain why this alga is usually remarkably devoid of epiphytes and grazers compared to C. glomerata.