Presence Of Cyanobacteria Research Articles

Setae thickening in Daphnia magna alleviates the food stress caused by the filamentous cyanobacteria

It is assumed that daphnids adjust the filter screen morphology in order to minimize the interference with cyanobacterial filaments. The aim of this study was to investigate the impact of filamentous cyanobacteria (Aphanizomenon gracile Lemmermann, Cylindrospermopsis raciborskii Woloszynska Seenaya et Subba Raju) on the thickness and length of setae of the third pair of thoracic limbs of Daphnia magna. The second objective was to assess whether the setae modifications could improve the performance of daphnids in the presence of cyanobacteria. Three clones of Daphnia magna Straus were cultured with: green algae; green algae with filaments of Cylindrospermopsis; and green algae with filaments of Aphanizomenon. The size and age of animals in the first reproduction cycle as well as the number of offspring were recorded. Setae thickness and length were measured in the central part of each endopodite. Additionally, we analyzed how the changes in setae morphology affect the fitness of experimental animals using the intrinsic rate of population increase calculated with the Euler–Lotka equation. The results showed that the thickness and length of setae increased in the presence of filamentous cyanobacteria. Moreover, cyanobacteria-induced setae thickening was positively correlated to the fitness of daphnids, which may indicate setae thickening as a phenotypic adaptation to cope with food stress caused by filamentous cyanobacteria.

Can cyanobacteria infect underground water sources? Evidence from a small scale monitoring of natural mineral water drinking source

The expansion of harmful cyanobacterial blooms is of worldwide concern as they have increased globally in frequency and intensity in recent decades. A cyanobacterial colony was found in a bottle of natural mineral water of a small water company in July 2012, which led to a further examination for a period of five months (July-November 2012) of both the bottled filtered water and the originating groundwater source (N. Greece) for the occurrence of Cyanobacteria. Cyanobacteria occurrence was monitored by microscopy and cyanospecific 16S rDNA amplification; potentially toxic species occurrence was screened by mcyA gene (known to take part in the MC-biosynthetic gene cluster) amplification. The highest abundance of cyanobacterial cells without the simultaneous presence of the mcyA gene, was measured in July, in contrast to October when the presence of cyanobacteria was only identified by tracing cyanospecific 16S rDNA and the mcyA gene region in the underground water source. The results of this small scale monitoring program indicate the potential existence of an emerging danger for human health in a relatively manageable product such as the bottled natural mineral water.

Streptophage-mediated control of off-flavour taint producing streptomycetes isolated from barramundi ponds

Off-flavour taint of aquaculture products is a global issue reducing consumer confidence in the farmed produce as they are taken up via the gills of fish, and deposited in the lipids of the animal. If the fish are not purged, resulting undesirable muddy earthy flavour taint can be tasted by consumers. These undesirable flavour and odour is caused by the terpenoid compounds namely geosmin and 2-methylisoborneol, produced as secondary metabolites by certain bacteria including the cyanobacteria and actinomycetes. Current strategies to remediate the problem rely on treating the symptoms not the cause and involve the use of time consuming purging methods and costly chemicals.Biological control using bacteriophages, specific to the problem causing bacteria, offers a natural alternative to chemical control, which might reduce further complications of copper based algaecides and its subsequent implications on water quality. In an adaptation of such biological control approach streptomycetes isolated from barramundi ponds were tested for their susceptibility to streptophages to understand whether host destruction via phage lysis would subsequently eliminate off-flavour taint productions by these isolates.Following the determination of the streptophage susceptibility of the isolates one of the most odourous streptomycete species (USC-14510) was selected to be tested further using different pond simulations resembling real-life applications. Geosmin was tested as the indicator of off-flavour taint production and as it has been previously reported that the cyanobacteria-actinomycete interactions occurring in ponds result in even greater levels of geosmin and 2-methylisoborneol, the geosmin levels for the isolate in the presence of cyanobacteria and streptophages were also tested. Findings indicated that the highly odourous Streptomyces species (USC-14510) once infected with streptophages, can lose its capacity to produce off-flavour taints. Pond simulation studies also revealed geosmin production was significantly reduced when streptophages were introduced into the pond water where streptomycete species were grown. The bacteriophage control method developed in the presented study might again confirm significant potential for the bacteriophage-mediated remediation strategy to be adapted by the aquaculture industry.

Identification and assessment of water quality risks associated with sludge supernatant recycling in the presence of cyanobacteria

This study focussed on the fate of cyanobacteria cells and associated metabolites during the sludge management processes that follow the conventional drinking water treatment train. The topic is of importance, as the release of metabolites during sludge treatment may pose a risk to water quality if supernatant is recycled to the head of the plant. The study of the kinetics of cell damage and metabolite release into the supernatant is complicated by simultaneous and rapid natural removal processes. In this study, the release of organic material from cyanobacterial sludge was monitored simultaneously with secondary metabolites (microcystins (MCs), cylindrospermopsin (CYN), and geosmin (GSM)) as an additional parameter to aid in understanding the range of processes occurring in sludge. Only GSM produced by Dolichospermum circinale was found to represent a low risk, as the compound is readily degraded. In contrast, the metabolites CYN and MC were shown to increase in concentration during simulated sludge treatment, suggesting that this could occur within full scale sludge treatment facilities with a range of cyanobacteria species, metabolites and water quality. A generic risk matrix was developed, incorporating the type of cyanobacteria, metabolite production, and the treatment processes available to water utilities for the mitigation of the identified risks.

CaCl2 applied to the extraction of Moringa oleifera seeds and the use for Microcystis aeruginosa removal

The Moringa oleifera seed coagulant provides high efficiency for water treatment, especially for bacteria removal and potentially cyanobacteria. The present study evaluates the difference between two saline extracts of M. oleifera Lam seeds in the removal of Microcystis aeruginosa cells, using dissolved air flotation (DAF). Samples were generated by synthetic water spiked with humic acid and M. aeruginosa cells to obtain 25NTU. The saline extracts were obtained by seed extraction using 1M NaCl or CaCl2, and dosages from 25 to 200mgL−1 were applied from each of the extractions. The CaCl2 coagulant extract showed a better efficiency, achieving 78.9% cell removal when applying a dosage of 50mgL−1. Comparison of saline extractions and aqueous extraction suggested that calcium ions participate in coagulation/flocculation process, as a response of its double-valency. The CaCl2 extract of the M. oleifera seeds is indicated for the treatment of water with the presence of cyanobacteria, even in water with low turbidity, a condition not commonly evaluated in other studies.

Cyanobacteria Affect Fitness and Genetic Structure of Experimental Daphnia Populations.

Zooplankton communities can be strongly affected by cyanobacterial blooms, especially species of genus Daphnia, which are key-species in lake ecosystems. Here, we explored the effect of microcystin/nonmicrocystin (MC/non-MC) producing cyanobacteria in the diet of experimental Daphnia galeata populations composed of eight genotypes. We used D. galeata clones hatched from ephippia 10 to 60 years old, which were first tested in monocultures, and then exposed for 10 weeks as mixed populations to three food treatments consisting of green algae combined with cyanobacteria able/unable of producing MC. We measured the expression of nine genes potentially involved in Daphnia acclimation to cyanobacteria: six protease genes, one ubiquitin-conjugating enzyme gene, and two rRNA genes, and then we tracked the dynamics of the genotypes in mixed populations. The expression pattern of one protease and the ubiquitin-conjugating enzyme genes was positively correlated with the increased fitness of competing clones in the presence of cyanobacteria, suggesting physiological plasticity. The genotype dynamics in mixed populations was only partially related to the growth rates of clones in monocultures and varied strongly with the food. Our results revealed strong intraspecific differences in the tolerance of D. galeata clones to MC/non-MC-producing cyanobacteria in their diet, suggesting microevolutionary effects.

Breakthrough of <i>Oscillatoria limnetica</i> and microcystin toxins into drinking water treatment plants – examples from the Nile River, Egypt

The presence of cyanobacteria and their toxins (cyanotoxins) in processed drinking water may pose a health risk to humans and animals. The efficiency of conventional drinking water treatment processes (coagulation, flocculation, rapid sand filtration and disinfection) in removing cyanobacteria and cyanotoxins varies across different countries and depends on the composition of cyanobacteria and cyanotoxins prevailing in the water source. Most treatment studies have primarily been on the removal efficiency for unicellular Microcystis spp., with little information about the removal efficiency for filamentous cyanobacteria. This study investigates the efficiency of conventional drinking water treatment processes for the removal of the filamentous cyanobacterium, Oscillatoria limnetica , dominating the source water (Nile River) phytoplankton in seven Egyptian drinking water treatment plants (DWTPs). The study was conducted in May 2013. The filamentous O. limnetica was present at high cell densities (660–1 877 cells/mL) and produced microcystin (MC) cyanotoxin concentrations of up to 877 μg∙g -1 , as determined by enzyme-linked immunosorbent assay (ELISA). Results also showed that conventional treatment methods removed most phytoplankton cells, but were ineffective for complete removal of O. limnetic a. Furthermore, coagulation led to cell lysis and subsequent microcystin release. Microcystins were not effectively removed and remained at high concentrations (0.37–3.8 μg∙L -1 ) in final treated water, exceeding the WHO limit of 1 μg∙L -1 . This study recommends regular monitoring and proper treatment optimization for removing cyanobacteria and their cyanotoxins in DWTPs using conventional methods. Keywords: cyanobacteria, removal, conventional drinking water treatment

Assessment of the roles of reactive oxygen species in the UV and visible light photocatalytic degradation of cyanotoxins and water taste and odor compounds using C–TiO2

Visible light (VIS) photocatalysis has large potential as a sustainable water treatment process, however the reaction pathways and degradation processes of organic pollutants are not yet clearly defined. The presence of cyanobacteria cause water quality problems since several genera can produce potent cyanotoxins, harmful to human health. In addition, cyanobacteria produce taste and odor compounds, which pose serious aesthetic problems in drinking water. Although photocatalytic degradation of cyanotoxins and taste and odor compounds have been reported under UV-A light in the presence of TiO2, limited studies have been reported on their degradation pathways by VIS photocatalysis of these problematic compounds. The main objectives of this work were to study the VIS photocatalytic degradation process, define the reactive oxygen species (ROS) involved and elucidate the reaction mechanisms. We report carbon doped TiO2 (C–TiO2) under VIS leads to the slow degradation of cyanotoxins, microcystin-LR (MC-LR) and cylindrospermopsin (CYN), while taste and odor compounds, geosmin and 2-methylisoborneol, were not appreciably degraded. Further studies were carried-out employing several specific radical scavengers (potassium bromide, isopropyl alcohol, sodium azide, superoxide dismutase and catalase) and probes (coumarin) to assess the role of different ROS (hydroxyl radical OH, singlet oxygen 1O2, superoxide radical anion O2•−) in the degradation processes. Reaction pathways of MC-LR and CYN were defined through identification and monitoring of intermediates using liquid chromatography tandem mass spectrometry (LC-MS/MS) for VIS in comparison with UV-A photocatalytic treatment. The effects of scavengers and probes on the degradation process under VIS, as well as the differences in product distributions under VIS and UV-A, suggested that the main species in VIS photocatalysis is O2•−, with OH and 1O2 playing minor roles in the degradation.

Breakage of cyanobacterial filaments by small- and large-sized Daphnia: are there any temperature-dependent differences?

Filamentous cyanobacteria disturb food collection in Daphnia by mechanical interference with the filtering apparatus by the long trichomes. The intensity of this interference depends on the water temperature and the Daphnia body size. However, Daphnia are capable of breaking down the filaments, therefore improving the palatability of the cyanobacteria. The main objective of this study was to test whether the shortening of cyanobacterial filaments and the ensuing clearance rate of Daphnia would increase at higher temperatures to a greater degree in small-bodied Daphnia species than in large-bodied one. Laboratory feeding experiments were conducted in order to measure variation in the length of Cylindrospermopsis raciborskii trichomes and to calculate clearance rate. The filament length and the cyanobacteria clearance rate by Daphnia were calculated following their exposure to grazing by large-bodied D.pulicaria and small-bodied D. longispina in 20, 24, and 28°C. Rising temperature did not affect the intensity of breakage of C. raciborskii trichomes by D. pulicaria and caused decrease in clearance rate of this species, whereas for D. longispina, the temperature increase enhanced both filament breakage and clearance rate. We suggest that these temperature-related changes may affect relative competitive performance of Daphnia species in the presence of cyanobacteria.

PRESENCE AND ABUNDANCE OF CYANOBACTERIA IN SELECTED AQUACULTURE PONDS IN PERAK, MALAYSIA AND THE RELATIONSHIPS WITH SELECTED PHYSICOCHEMICAL PARAMETERS OF WATER

The presence of cyanobacteria in aquaculture ponds can disrupt the water quality. This study was conducted to determine the abundance of cyanobacteria in selected aquaculture systems in Perak, Malaysia. This study also aimed to identify the relationships between cyanobacterial biomass with physicochemical properties of water. In this study, a total of 40 aquaculture fish ponds were sampled between December 2013 to March 2014 from 10 locations in Perak, Malaysia. The results revealed that cyanobacteria were present in all of the sampled aquaculture ponds. Among all, 75% of the sampled ponds contained chlorophyll-a exceeded 50 µg chl-a L-1 and the highest chlorophyll-a concentration was recorded at 436 µg chl-a L-1. This indicates that cyanobacteria are present in abundance in aquaculture water and could pose health risk to human through aquaculture fish consumption. Pearson’s correlation analysis suggests that cyanobacterial biomass was significantly correlated to temperature, DO and pH. However, there was no correlation detected among nutrients with cyanobacterial concentration in water column. Regular monitoring of temperature, DO and pH are crucial for an early detection of cyanobacterial occurrence in aquaculture industry in order to avoid economic losses, as well as adverse health impact to consumer.

The continuous re-equilibration of carbon isotope compositions of hydrous Mg carbonates in the presence of cyanobacteria

The hydrous magnesium carbonate minerals dypingite (Mg5(CO3)4(OH)2·5H2O) and nesquehonite (MgCO3·3H2O) were precipitated in the presence and absence of Gloeocapsa sp. and Synechococcus sp. cyanobacteria in batch reactors. The Δ13Cmineral–DIC is similar in both biotic and abiotic systems. Stable carbon isotope analyses of the precipitated minerals and co-existing fluids indicated that the δ13C values of the precipitated carbonates co-vary over time with the δ13CDIC of the fluid phase, even after the precipitation of the carbonate is complete. This observation indicates the continuous isotopic exchange between the carbonates and the fluid, a process that efficiently resets the original δ13C values of the solids. Therefore although cyanobacterial-induced Mg carbonates are 10±5‰ enriched in 13C compared to inorganic carbonates, the δ13C values of natural hydrous Mg carbonates may reflect post precipitation processes and may not be reliable for paleo-environmental reconstructions.

Cyanobacterial occurrence and detection of microcystins and saxitoxins in reservoirs of the Brazilian semi-arid

Aim:The rapid spread of cyanobacteria in water sources and reservoirs has caused serious environmental damage and public health problems, and consists in a problem that challenges the institutions responsible for providing water to the population. In this study, the quantification of microcystin, saxitoxins and cyanobacteria levels was performed over 3 years in the semi-arid reservoirs of Rio Grande do Norte (Brazil). In addition, we analyzed the seasonal distribution of cyanotoxins and the percentage of cyanobacteria and cyanotoxins which were above the limit established by Brazilian law.MethodsThe study was conducted between 2009 and 2011 in four dams with six sites: Armando Ribeiro Gonçalves (ARG) in Itajá, San Rafael (SR) and Jucurutu; Passagem das Traíras (PT); Itans and Gargalheiras (GARG). Cyanobacteria presence were quantified and identified and the presence of microcystins (MCYs) and saxitoxins (STXs) was investigated by ELISA.ResultsThe densities of cyanobacteria were found to be above the permitted in 76% of cases. The ELISA results showed that of the 128 samples analyzed, 27% were above the maximum allowed by the Brazilian Ministry of Health Order 2914/2011. A seasonal pattern for the presence of MCYs was found (0.00227 to 24.1954 µg.L–1), with the highest values in the rainy season. There was no clear seasonal pattern for STXs (0.003 to 0.766 µg.L–1).ConclusionsThis study showed the importance of establishing a water quality monitoring for human consumption and its potability standards since the concentration of MCYs in some samples was above the maximum limit allowed by Brazilian law, thus posing a risk to public health since the conventional water treatment is not able to eliminate these potent hepatotoxins.

Combined effects of calcium deficiency, cyanobacteria, and warming on the population fitness of three cladocerans

Aqueous calcium decline is a novel and widespread threat to soft-water lakes and usually co-occurs with other stressors. A three-way full factorial design was used to investigate the combined effects of a chemical stressor (calcium decline from 20 to 5 mg L -1 ), a biological stressor (50 % Microcystis aeruginosa in diets), and a physical stressor (temperature increase from 25 to 29 °C) on the population fitness of three common cladocerans with distinct body sizes. Both Ca deficiency and increasing cyanobacteria significantly depressed fitness in the large-bodied Daphnia pulex, while warming did not. The combined effect of Ca deficiency and increasing cyano- bacteria was significantly synergistic in D. pulex with a greater fitness reduction in the presence of cyanobacteria. Ca deficiency significantly depressed Simocephalus vetulus fitness only at 29 °C. Ca deficiency and warming had a synergistic effect on S. vetulus fitness, but the combined effect of warming and cyanobacteria was antagonistic. The fitness of the small-bodied B. longirostris increased with temperature, but was not influenced by Ca deficiency, cyanobacteria, or the interactions of the three stressors. These results suggest that D. pulex was most vulnerable to ongoing Ca decline. The non-additive effects of multiple stressors should be considered when predicting zooplank- ton responses in soft-water lakes.

Application of ancient DNA to the reconstruction of past microbial assemblages and for the detection of toxic cyanobacteria in subtropical freshwater ecosystems

Ancient DNA (aDNA) analysis of lake sediments is a promising tool for detecting shifts in past microbial assemblages in response to changing environmental conditions. We examined sediment core samples from subtropical, freshwater Laguna Blanca (Uruguay), which has been severely affected by cultural eutrophication since 1960 and where cyanobacterial blooms, particularly those of the saxitoxin-producer Cylindrospermopsis raciborskii, have been reported since the 1990s. Samples corresponding to ~1846, 1852, 2000 and 2007 AD were selected to perform denaturing gradient gel electrophoresis (DGGE) analysis of the 16S-23S rRNA intergenic transcribed spacer (ribosomal ITS) to compare their prokaryotic assemblage composition. Each stratum showed different ITS patterns, but the composition of 21st century samples was clearly different than those of mid-19th century. This compositional change was correlated with shifts in sediment organic matter and chlorophyll a content, which were significantly higher in recent samples. The presence of saxitoxin-producing cyanobacteria was addressed by quantitative real-time PCR of the sxtU gene involved in toxin biosynthesis. This gene was present only in recent samples, for which clone libraries and ITS sequencing indicated the presence of Cyanobacteria. Phylogenetic analyses identified C.raciborskii only in the 2000 sample, shortly after several years when blooms were recorded in the lake. These data suggest the utility of aDNA for the reconstruction of microbial assemblage shifts in subtropical lakes, at least on centennial scales. The application of aDNA analysis to genes involved in cyanotoxin synthesis extends the applicability of molecular techniques in palaeolimnological studies to include key microbial community characteristics of great scientific and social interest.

Improving Inland Water Quality Monitoring through Remote Sensing Techniques

Chlorophyll-a (chl-a) levels in lake water could indicate the presence of cyanobacteria, which can be a concern for public health due to their potential to produce toxins. Monitoring of chl-a has been an important practice in aquatic systems, especially in those used for human services, as they imply an increased risk of exposure. Remote sensing technology is being increasingly used to monitor water quality, although its application in cases of small urban lakes is limited by the spatial resolution of the sensors. Lake Thonotosassa, FL, USA, a 3.45-km2 suburban lake with several uses for the local population, is being monitored monthly by traditional methods. We developed an empirical bio-optical algorithm for the Moderate Resolution Imaging Spectroradiometer (MODIS) daily surface reflectance product to monitor daily chl-a. We applied the same algorithm to four different periods of the year using 11 years of water quality data. Normalized root mean squared errors were lower during the first (0.27) and second (0.34) trimester and increased during the third (0.54) and fourth (1.85) trimesters of the year. Overall results showed that Earth-observing technologies and, particularly, MODIS products can also be applied to improve environmental health management through water quality monitoring of small lakes.

Effect of poor manageability and low nutritional value of cyanobacteria on Daphnia magna life history performance

Cyanobacteria may reduce Daphnia fitness through their toxicity, low nutritional value or poor manageability. In this study, the relative importance of the low nutritional value and poor manageability of cyanobacteria on Daphnia life history were determined. To separate these two aspects of cyanobacteria impact, short or long filaments of Cylindrospermopsis raciborskii were given as food to five clones of Daphnia magna either alone or together with the green alga Scenedesmus obliquus. Feeding with short cyanobacterial filaments caused reductions in growth rate (,45%) and fecundity (,60%) in some clones. The deleterious effects caused by cyanobacterial poor nutritional quality could be completely overcome by supplementation with highquality food. Long cyanobacterial filaments caused greater reductions in growth rate (,65%) and fecundity (,80%) in the most affected clones, and the addition of high-quality food only partially diminished the effects of poor filament manageability. In Daphnia fed with long filaments, there was no correlation between body size at maturity and fecundity, and the maximum fecundity was reached by individuals of intermediate size. Decreased body size may, thus, represent an adaptive mechanism against interference with food collection caused by long filaments. The pattern of responses to different food regimes was similar in all Daphnia clones, but they differed in the absolute values of the life history parameters affected. Differences in the fecundity of Daphnia caused by the presence of cyanobacteria may affect clonal composition of cladoceran assemblages, thus, cyanobacteria can shape microevolutionary changes in Daphnia populations.

Evidence for iron‐regulated cyanobacterial predominance in oligotrophic lakes

Summary Cyanobacterial harmful algal blooms (cyanoHABs) are most often associated with large eutrophic lakes. In the past decade, an increase in the incidence of cyanoHABs in small oligotrophic lakes within the Laurentian Great Lakes‐St. Lawrence River Basin has been documented. We explored macro‐ and micronutrient conditions during peak phytoplankton biomass that result in high cyanobacterial densities. We hypothesised that the availability of biologically available iron (Fe) both limits the assimilation of phosphorus by competing taxa and selects for the predominance of cyanobacteria. We tested this hypothesis with a comparative study of 25 oligotrophic lakes in central Ontario, Canada. These lakes were sampled during peak phytoplankton biomass for 3 years (from 2009 to 2011) for concentrations of total phosphorus (TP), total nitrogen (TN), ammonium (), nitrate (), total dissolved Fe (TDFe) and pH for comparison with phytoplankton community biomass and composition. Correlation analyses indicated that predominance of cyanobacteria was assured at all TP levels when the availability of Fe was low. Proportionally high cyanobacterial density occurred at relatively low TP in lakes with a molar ratio of dissolved inorganic N (DIN):TP of 8:1 and a modelled ferric Fe concentration <1.0 × 10−19 m at which cyanobacteria have been shown to be competitive for Fe in laboratory experiments. Regression tree analysis confirmed the minimal influence of P and N, implying that cyanobacteria thrive in low Fe environments. Our findings suggest that an increased susceptibility of oligotrophic lakes to cyanobacterial bloom formation is based on the presence of cyanobacteria that have adapted sufficiently to low Fe environments and are able to multiply rapidly when pulses of P are made available to the ecosystem. Physiologically prepared transitionary cyanobacteria do not have to compete with the eukaryotic species but rather exploit the new P and replicate faster.

Projected marine climate change: effects on copepod oxidative status and reproduction

Zooplankton are an important link between primary producers and fish. Therefore, it is crucial to address their responses when predicting effects of climate change on pelagic ecosystems. For realistic community-level predictions, several biotic and abiotic climate-related variables should be examined in combination. We studied the combined effects of ocean acidification and global warming predicted for year 2100 with toxic cyanobacteria on the calanoid copepod, Acartia bifilosa. Acidification together with higher temperature reduced copepod antioxidant capacity. Higher temperature also decreased egg viability, nauplii development, and oxidative status. Exposure to cyanobacteria and its toxin had a negative effect on egg production but, a positive effect on oxidative status and egg viability, giving no net effects on viable egg production. Additionally, nauplii development was enhanced by the presence of cyanobacteria, which partially alleviated the otherwise negative effects of increased temperature and decreased pH on the copepod recruitment. The interactive effects of temperature, acidification, and cyanobacteria on copepods highlight the importance of testing combined effects of climate-related factors when predicting biological responses.

Two species of Halimeda, a calcifying genus of tropical macroalgae, are robust to epiphytism by cyanobacteria

Cyanobacteria, an increasingly important epiphyte on macroalgae and seagrass, have been shown to have strong effects on its hosts; this association has been identified as a driving mechanism that maintains algal blooms on coral reefs. We examined both the costs and benefits of epiphytism on 2 algal congeners of Halimeda (H. tuna and H. opuntia), both of which are abundant members of tropical reef communities in the Caribbean. To evaluate potential benefits of an associational defense as well as costs to growth, we manipulated herbivore access to (uncaged/caged) and cyanobacteria presence on (epiphytized/cleaned) 2 species of Halimeda on shallow patch reefs in Belize and measured change in branch length and segment number after 10 (H. tuna) and 5 (H. opuntia) days. Cyanobacterial epiphytes did not serve as an associational defense from herbivory as there were no differences between caged and uncaged treatments for either response variable. The presence of cyanobacterial epiphytes did not affect the growth of branches or net generation of new segments, demonstrating there was also no cost to growth. The robustness of both species of Halimeda to epiphytism contrasts strongly with recent research that found strong effects of epiphytes on several other species of tropical algae. Our results may be attributed to the unique characteristics of Halimeda, a heavily physically and chemically defended algal genus, and the shallow nature of the patch reefs reducing the potential for significant light limitation. These findings suggest that close interactions such as epiphytism may not be as generalizable as originally assumed; studies must consider differences among host species, as this may lead to a better understanding of community-wide effects.

Accumulation and precipitation of Mn2+ by the cells of Oscillatoria terebriformis

The cyanobacterium Oscillatoria terebriformis was shown to exhibit resistance to high manganese concentrations, remaining viable at 2.5 mM MnCl2 in the medium. Cyanobacterial cells were capable of considerable manganese consumption from the medium. Dynamics of Mn sorption by the cells was the same in all experimental variants, independent on the manganese concentration. Manganese concentration in the biomass peaked after 2-3 days and depended on Mn2+ concentration in the medium and on the amount of biomass introduced. In the case of O. terebriformis, manganese removed from the medium may be subdivided into Mn absorbed by the cell, Mn bound to the cell wall, Mn absorbed by the glycocalix, and chemically precipitated Mn. Of the total 21.25 ± 1.0 mg of consumed manganese, biological absorption and chemical precipitation were responsible for 11.78 ± 0.98 and 9.2 ± 0.8 mg, respectively. In the presence of cyanobacteria, Mn removal from the medium was 2.28 times higher than in the control. This process depended considerably on Mn sorption by exopolysaccharides. At 1.3 mM Mn2+, a lamellar mat was formed with interlayers of manganese carbonate.