Benthic Cyanobacteria Research Articles

Genetic Diversity of Filamentous Cyanobacteria from Shore Regions of Okinawa

Benthic marine cyanobacteria are ubiquitous oxygenic photosynthetic bacteria and they form major components of various communities, including epiphytic, epilithic and microbial mats, in coral reef environments. Filamentous groups may form almost monospecific macroscopic colonies, and sometimes make potentially harmful algal blooms (HABs). HABs bring serious problems for marine tourism but marine filamentous cyanobacteria are good resource for drug discovery. However, cultivation and identification of such filamentous cyanobacteria are difficult and there are taxonomic confusions. In this study, we investigate 17 samples from coral reef area of 10 localities in Okinawa. Macroscopic mats or cushions of filamentous cyanobacteria were collected. The samples were divided into three parts: (1) for morphological observation, (2) for molecular work, and (3) cultivation for further study. Dominant cyanobacteira of each sample identified morphologically as Anabaena, Hydrocoleum, Lyngbya, Oscillatoria, Phormidium, Schizothrix and Symploca. Molecular results of partial 16S rDNA sequences revealed six groups that composed of heterocystous group, Leptolyngbya group, Symploca group, Moorea group, Oscillatoria group and unknown group, respectively. Some samples corroborated between morphology and molecular results but some were not. In addition, four out of six groups closely related with natural product producers. These results suggest that there are high biodiversity of marine benthic filamentous cyanobacteria in Okinawa that may become seeds of HABs as well as providing promising resources for drug discovery.

Asymmetric response of sedimentary pool to surface water in organics from a shallow hypereutrophic lake: The role of animal consumption and microbial utilization

Despite of the importance for tracking sources and fates of organics in determining carbon cycling and assessing the overall health of lacustrine ecosystems, little is known of organics behaviors in shallow eutrophic lakes. In this study, for relating the benthic organics to pelagic sources, an ecosystem-level investigation was performed in hypereutrophic Lake Taihu, China, by using source-specific fatty acid biomarkers on the molecular level. Results exhibited the unexpected asymmetric phenomena of organics between surface water and sediments. In the abundance, the dominant organics shifted from cyanobacteria in surface water to terrestrial plants in sediments. In the spatial pattern, as opposed to terrestrial plants, cyanobacteria were found not site-to-site symmetrical, although both of their spatial distributions varied strongly. Essentially, these asymmetric phenomena ascribed to a more considerable loss of cyanobacteria compared to terrestrial plants during sinking, caused by aquatic animal consumption and microbial utilization with different degree. Combined dual stable isotopes (δ13C and δ15N) and fatty acid biomarkers revealed that there were only subtle differences in the diets of benthic and pelagic animals and cyanobacteria were their main food source. Concomitantly, results of δ13C of bacteria-specific fatty acids demonstrated that bacteria equally and profoundly affected organics accumulation or preservation in the sediments, because they preferentially utilized labile cyanobacteria as their carbon source instead of terrestrial plants (>95% within these two sources). Consequently, these novel findings clarify that not only in deep lakes, but also shallow eutrophic ones, the extensive losses of autochthonous organic matter can be expected during sedimentation coupling with the dramatical modifications of biogeochemical processes.

Musty odor producing benthic cyanobacteria in the Tama River (Japan) and identification of species by genetic analysis

In upstream reaches of the Tama River, musty odor substance (2-methylisoborneol (2-MIB)) began to be detected in 2008 and the concentration has been increasing thereafter. Then, in 2012, 2-MIB in raw water of a water treatment plant reached 210 ng/L. It was suspected that cause of musty odor was benthic cyanobacteria ( Phormidium ) which attached to stones on the riverbed. However, identification of the benthic Phormidium by microscopic observation had been difficult, thus genetic analysis was carried out. In genetic analysis, almost full-length 16S ribosomal DNA and internal transcribed spacer region gene of benthic Phormidium strains, which include the strain isolated from the Tama River, a strain in the Yoshino River (350 km away from the Tama River) and standard strains, were sequenced and compared. From homology search of these sequences, 2-MIB producing Phormidium in the Tama River was classified into Phormidium autumnale . Furthermore, it was found that P . autumnale in the Tama River was the same species in the Yoshino River. In addition, the result of in vitro cultivation shows that the P . autumnale inhabiting the Tama River thrives and produces more 2-MIB at high temperature, but it can grow and produce 2-MIB even at low temperature.

Morphological, genetic and physiological characterization of Hydrocoleum, the most common benthic cyanobacterium in tropical oceans

ABSTRACTPopulations of the benthic diazotrophic cyanobacterium Hydrocoleum Kützing (1843) are widely distributed in coral reefs and lagoons of tropical oceans, where they contribute to benthic nitrogen fixation. We compared the morphological, molecular and physiological features of 31 freshwater and marine Hydrocoleum populations from geographically different localities and five specimens from herbaria. Our aims were to compare the features of Hydrocoleum with the morphologically and phylogenetically related genera Trichodesmium Ehrenberg ex Gomont 1892 and Blennothrix Kützing 1843, and to provide the basis for the validity of the genus Hydrocoleum. The Hydrocoleum populations were distributed over a wide range of sizes, showing no consistent inter-population grouping and leaving no gaps between groups that were traditionally attributed to different species. Transmission electron microscopy showed regular cell division rhythms in all Hydrocoleum populations with each cell division completed before the next one was initiated, similar to that described for Trichodesmium. In contrast, Blennothrix populations exhibited multiple initiation of cross-wall formation. Most Hydrocoleum populations fixed nitrogen at consistently higher nightly rates. The phylogenetic analysis of 16S rRNA and nifH gene sequences placed all morphologically distinct Hydrocoleum and Trichodesmium populations within a tight cluster. Neither of the analysed genes brought any further resolution of phenotypically and ecologically distinguished forms. However, freshwater morphospecies of Blennothrix together with the type species Blennothrix vermicularis Kützing were separated from the Trichodesmium/Hydrocoleum cluster, which further supported the genotypic distinction between the compared taxa, in addition to the fact that they also differ in morphology and ecology. We concluded that the genus Hydrocoleum possesses unique features that warrant its maintenance in the botanical classification system and that its introduction in bacteriological manuals as a valid cyanobacterial genus is acceptable.

Cyanobacteria as bioindicators and bioreporters of environmental analysis in aquatic ecosystems

Knowledge of the incidence of anthropogenic pressure on water ecosystems is one of the main focus of integrated water resource management. The use of biological methods to assess water quality is of particular importance since organisms show an integrating response to their environment. Tolerances or ecological ranges of individual species can differ depending on the taxon, which leads to distinct bioindicator values of cyanobacterial taxa. In addition, a number of morphological and physiological features are known to relate with the environment in which they occur, which makes them excellent environmental indicators. Therefore, we review literature data of the main cyanobacterial methods used to obtain information about changes in running water quality, mainly related to eutrophication processes, which are found as the main cause of disturbance in rivers, with the focus on benthic cyanobacteria, as habitat recommended for monitoring studies. Further, their trophic independence and ease of cultivation make them very useful in the field of bioreporters of environmental monitoring and ecotoxicology. In fact, several cyanobacterial strains have been already genetically engineered to construct bioreporters which respond to different types of pollutants as well as limiting nutrients. The potential of cyanobacteria both as in situ bioindicators as well as bioreporters of environmental analysis in aquatic ecosystems will be discussed.

퇴적층 배양에 따른 식물플랑크톤 군집 형성과 이취미물질 발생 특성

In this study, Uiam-sediment(US) and Gongji-sediment(GS) were incubated to analyze the formation of phytoplankton community and occurrences of odorous compounds from benthic cyanobacteria. For the phytoplankton, 45 and 40 taxa were found in GS and US, respectively. The phytoplankton species detected in the harmful algae included Microcystis, Anabaena and Oscillatoria. As a result, a standing crop of phytoplankton appeared to be in the range of <TEX>$0.9{\sim}71.8{\times}10^3$</TEX> cells/mL in GS, <TEX>$0.8{\sim}51.2{\times}10^3$</TEX> cells/mL in US, and as the incubation progressed, benthic cyanobacteria was increased. The highest number of akinetes was shown in the initial incubation, and akinetes was reduced by 10% on day 4 of incubation start. After reduction of akinetes incubated for 4 days in US and 15 days in GS, Anabaena appeared from the surface water. Benthic cyanobacteria such as Oscillatoria tenuis, O. limosa and Lyngbya hieronymusii was dominant in GS (max. <TEX>$3.96{\times}10^6cells/cm^2$</TEX>) and US (max. <TEX>$5.77{\times}10^6cells/cm^2$</TEX>), forming cyanobacterial mats in sediment surface. Cyanobacterial mats were suspended after 10~12 days incubation in GS and US. Before and after the suspension of cyanobacterial mats, the concentration of geosmin was the highest in GS(115 ng/L) and US(175 ng/L). In the second suspension of cyanobacterial mats in GS, the concentration of 2-MIB was increased to the range of 22~92 ng/L.

Multi-detection method for five common microalgal toxins based on the use of microspheres coupled to a flow-cytometry system

Freshwater and brackish microalgal toxins, such as microcystins, cylindrospermopsins, paralytic toxins, anatoxins or other neurotoxins are produced during the overgrowth of certain phytoplankton and benthic cyanobacteria, which includes either prokaryotic or eukaryotic microalgae. Although, further studies are necessary to define the biological role of these toxins, at least some of them are known to be poisonous to humans and wildlife due to their occurrence in these aquatic systems. The World Health Organization (WHO) has established as provisional recommended limit 1μg of microcystin-LR per liter of drinking water. In this work we present a microsphere-based multi-detection method for five classes of freshwater and brackish toxins: microcystin-LR (MC-LR), cylindrospermopsin (CYN), anatoxin-a (ANA-a), saxitoxin (STX) and domoic acid (DA). Five inhibition assays were developed using different binding proteins and microsphere classes coupled to a flow-cytometry Luminex system. Then, assays were combined in one method for the simultaneous detection of the toxins. The IC50's using this method were 1.9±0.1μgL−1 MC-LR, 1.3±0.1μgL−1 CYN, 61±4μgL−1 ANA-a, 5.4±0.4μgL−1 STX and 4.9±0.9μgL−1 DA. Lyophilized cyanobacterial culture samples were extracted using a simple procedure and analyzed by the Luminex method and by UPLC–IT-TOF-MS. Similar quantification was obtained by both methods for all toxins except for ANA-a, whereby the estimated content was lower when using UPLC–IT-TOF-MS. Therefore, this newly developed multiplexed detection method provides a rapid, simple, semi-quantitative screening tool for the simultaneous detection of five environmentally important freshwater and brackish toxins, in buffer and cyanobacterial extracts.

Bloom of the cyanobacterium Moorea bouillonii on the gorgonian coral Annella reticulata in Japan.

Coral populations are in decline due to environmental changes and biological attacks by predators and infectious diseases. Here, we report a localized bloom of the benthic filamentous cyanobacterium Moorea bouillonii (formerly Lyngbya bouillonii) observed exclusively on the gorgonian (sea fan) coral Annella reticulata at around 20 m depth in Japan. The degree of infection has reached 26% among different sizes of Annella colonies. Thick and continuous growth of Moorea may be sustained partly by symbiotic alpheid shrimp, which affix Moorea filaments to gorgonian corals for use as food and shelter. Most filaments get entangled on the coral colony, some penetrate into the stem of the coral with a swollen end like a root hair, which appears to function as an anchor in Annella. In addition to the cyanobacterium–shrimp interaction, the new trait of anchoring by the cyanobacterium into gorgonian coral may contribute to persistence of this bloom.

Algal chemical ecology in a changing ocean

Macroalgae and benthic cyanobacteria are becoming increasingly abundant on reefs, and many of these dominant algae produce diverse secondary metabolites. Abundant brown and green macroalgae and nuisance blooms of cyanobacteria occur regularly throughout Florida and on the Belizean barrier reef. Crude extracts and compounds from some macroalgae and cyanobacteria deter feeding by natural assemblages of fishes and the sea urchin Diadema antillarum. In addition, macroalgal and cyanobacterial secondary metabolites may serve multiple ecological functions, including inhibition of microorganisms and competition for space. The role of allelopathy (chemical inhibition) in mediating the interactions between chemically rich species of algae and cyanobacteria and different life history stages of corals was tested. Extracts and isolated compounds from Dictyota spp., Lyngbya spp. and other cyanobacteria negatively influenced the settlement and metamorphosis of coral larvae. On reefs experiencing increased abundance of chemically defended macroalgae and benthic cyanobacteria, the restocking of adult coral populations may be slowed due to recruitment inhibition caused by algal secondary metabolites. These compounds protect some algae from herbivory (allowing increased space occupation) and reduce coral recruitment, both of which may perpetuate a “phase shift” from coral to algal dominated communities.

Biogeography of planktonic and benthic cyanobacteria in coastal waters of the Big Island, Hawai'i

Cyanobacteria are biogeochemically significant constituents of coral reef ecosystems; however, little is known about biotic and abiotic factors influencing the abundance and composition of cyanobacterial communities in fringing coral reef waters. To understand the patterns of cyanobacterial biogeography in relation to coastal environmental factors, we examined the diversity of planktonic and benthic cyanobacteria at 12 sites along the west coast of Hawaii's Big Island. We found distinct cyanobacterial communities in sediments compared to the water column. In both sediments and water, community structure was strongly related to overall biomass (chlorophyll a concentration), although both these communities corresponded to different sets of biotic/abiotic variables. To examine the influence of freshwater input on planktonic cyanobacterial communities, we conducted a mesocosm experiment where seawater was amended with freshwater from two sources representing high- and low-human population influence. Planktonic cyanobacterial abundance decreased over time in mesocosms, although chlorophyll a concentration significantly increased with time, indicating cyanobacteria were likely outcompeted by other phytoplankton in incubations. Our results show that cyanobacterial community structure may be affected by runoff from terrestrial habitats, but that the composition of cyanobacterial communities inhabiting these locations is also structured by factors not measured in this study.

Cyanophycin mediates the accumulation and storage of fixed carbon in non-heterocystous filamentous cyanobacteria from coniform mats.

Thin, filamentous, non-heterocystous, benthic cyanobacteria (Subsection III) from some marine, lacustrine and thermal environments aggregate into macroscopic cones and conical stromatolites. We investigate the uptake and storage of inorganic carbon by cone-forming cyanobacteria from Yellowstone National Park using high-resolution stable isotope mapping of labeled carbon (H13CO3 −) and immunoassays. Observations and incubation experiments in actively photosynthesizing enrichment cultures and field samples reveal the presence of abundant cyanophycin granules in the active growth layer of cones. These ultrastructurally heterogeneous granules rapidly accumulate newly fixed carbon and store 18% of the total particulate labeled carbon after 120 mins of incubation. The intracellular distribution of labeled carbon during the incubation experiment demonstrates an unexpectedly large contribution of PEP carboxylase to carbon fixation, and a large flow of carbon and nitrogen toward cyanophycin in thin filamentous, non-heterocystous cyanobacteria. This pattern does not occur in obvious response to a changing N or C status. Instead, it may suggest an unusual interplay between the regulation of carbon concentration mechanisms and accumulation of photorespiratory products that facilitates uptake of inorganic C and reduces photorespiration in the dense, surface-attached communities of cyanobacteria from Subsection III.

Responses of freshwater mussel (Elliptio complanata) hemocytes exposed in vitro to crude extracts of Microcystis aeruginosa and Lyngbya wollei

Lyngbya wollei is a benthic filamentous cyanobacterium that produces a toxin analogous to the neurotoxic saxitoxin known as lyngbyatoxin (LYNGTX). Microcystis aeruginosa form blooms in the pelagic area of eutrophic lakes and produce a series of potent hepatotoxins-microcystins (MCYST). The aim of this study in vitro study was to examine the difference between the crude extracts of either M. aeruginosa or L. wollei toward the immune system of Elliptio complanata mussels. Freshly isolated hemolymph was plated and exposed to the crude extract of each species at LYNGTX or MCYST equivalent concentrations of 5, 10 and 25μg/L for 18h. Immunocompetence was characterized by following changes in hemocyte numbers, metabolic activity (viability), and phagocytosis. Hemocyte counts were not affected, indicating no turnover of hemocytes. Hemocyte metabolic activity was higher in cells exposed to crude extracts of L. wollei. Exposure to L. wollei extracts led to decreased pro-inflammatory precursors such as reactive oxygen species (ROS) and cyclooxygenase (COX) activities. Phagocytosis increased at 25μg/L for both types of crude extracts. However, hemocytes exposed to crude extracts of M. aeruginosa produced more ROS and COX compared to hemocytes exposed to crude extracts of L. wollei. In conclusion, the data suggest that the crude extract of M. aeruginosa was more toxic than crude extract of L. wollei to mussel hemocytes.

Polyphasic studies of cyanobacterial strains isolated from benthic freshwater mats in Canterbury, New Zealand

Planktonic cyanotoxin poisoning events are well documented. More recently, benthic cyanobacteria have also been associated with bird, cattle and dog fatalities. Extensive mats of benthic cyanobacteria can contain high concentrations of toxins. This study investigated cyanotoxin production in cyanobacterial strains isolated from benthic freshwater mats dominated by cyanobacteria in Canterbury, New Zealand. Twenty-seven strains were isolated from ten water bodies and characterized using morphological and molecular phylogenetic characteristics. All strains were screened for genes involved in the biosynthesis of common cyanotoxins. Positive results were confirmed and cyanotoxin concentrations quantified using liquid chromatography–mass spectrometry. One chroococcalean, twenty oscillatorialean and six nostocalean strains were isolated into culture. All strains were cryopreserved and banked in the Cawthron Institute Culture Collection of Micro-algae. Genes associated with anatoxin-a biosynthesis were identified in nine Phormidium strains. Anatoxin-a was detected in all these strains, one of these strains also produced homoanatoxin-a.

Microcystin-LR equivalents and their correlation with Anabaena spp. in the main reservoir of a hydraulic system of Central Mexico

The occurrence of cyanobacterial blooms is a characteristic of eutrophic inland water bodies. Valle de Bravo reservoir (Mexico State, Mexico) is the main source of water for the Cutzamala Hydraulic System, which supplies drinking water to the west of Mexico City (~6 million consumers) and suburban areas of Mexico State. The goal of this study was to determine the presence of microcystins (MC-LR equivalents) and their relationship with toxic populations of cyanobacteria recorded some years ago in this important reservoir. We measured the concentration of MC-LR equivalents using a commercial kit (EnviroLogix) based on the ELISA test. The calculation of abundance and biovolume was carried out monthly from February to November 2010. The presence of MC-LR equivalents was related to the biovolume of Anabaena planctonica. The values of this toxin from February to June exceeded the World Health Organization (WHO) provisional guideline (1 μg L−1) for finished drinking water sources, particularly in April when the highest value was recorded (5.56 μg L−1). In addition, in April, May, June, and August, the abundance of cyanobacteria exceeded the WHO moderate risk level (10 × 104 cells mL−1) for recreational activities. This study furthers investigations ranging from the characteristics of the water column to benthic cyanobacteria and molecular biology tests to establish which species are toxic in the reservoir.

Overgrowth of reef organisms by benthic cyanobacteria in the Colombian Caribbean

Los afloramientos de cianobacterias marinas bentónicas parecen ser recurrentes en varias localidades arrecifales del Caribe colombiano. Sin embargo, su efecto sobre las comunidades locales aún no se han dimensionado. En esta nota documentamos algunas interacciones entre cianobacterias y organismos arrecifales.

Cylindrospermopsin Accumulation and Release by the Benthic Cyanobacterium Oscillatoria sp. PCC 6506 under Different Light Conditions and Growth Phases

We have studied the dynamics of cylindrospermopsin concentration (CYN) of a benthic cyanobacterium of the genus Oscillatoria under various light conditions over the different growth phases. The present study is the first one reporting on the effect of abiotic factors on the CYN accumulation and release by a benthic species. In particular we have measured the concentrations of both intracellular and extracellular CYN. We found that the total CYN content is highest during the exponential growth phase at intermediate light level (10 μE m(-2) s(-1)) and during the stationary growth phase at more extreme lower and higher light levels. Our results also indicate that the amount of the extracellular form varied between 56 % and 96 % of the total CYN concentrations. We found no relationship between CYN content and growth rates. These results suggest many similarities with planktonic species but also highlight some differences.

High resolution δ13C stratigraphy through the Selli Oceanic Anoxic Event (OAE1a) in the Apulia carbonate platform: the Borgo Celano section (western Gargano Promontory, Southern Italy)

We show that the global-scale environmental perturbations leading to the Selli OAE1a were clearly recorded in the middle Bedoulian Apulia carbonate platform at Borgo Celano, in the western Gargano Promontory (Southern Italy). The studied section (Bari Limestones), which is 72.45 m thick and spans the Late Barremian p.p. -latest Early Aptian time interval, has been logged with an average resolution of 3 samples per metre for chemostratigraphic analyses and up to 7 samples per metre for facies analysis in the aim of detailed paleocologic and paleoceanographic investigation. It contains the complete biosedimentary and chemostratigraphic record across the Selli OAE1a, as suggested by a consistent match of the observed isotope excursions with those documented in the Cismon pelagic reference section and the lack of significant non-depositional or erosional hiatuses within the chemostratigraphic Selli level: biostratigraphic and sedimentary-diagenetic analyses document a continuous record of fully subtidal conditions. Furthermore, the Borgo Celano section allows correlation of the shallow- and deep-water records without intervening stratigraphic breaks. Upper Barremian-Lower Bedoulian, chlorozoan-type carbonates showing subtidal-intertidal Milankovitch-type cyclicities characterize the lower part of the Borgo Celano section (C2 pro parte isotopic segment). Starting from the latest C2 segment, a remarkable Crisis Interval (CI) about 4 m thick shows an increasing frequency of bivalves ( Chondrodonta and requieniids), the disappearance of green algae and a reduced diversity of foraminiferal assemblages (foramol-type carbonates). This interval is sharply overlain by an interval, about 3.70 m thick, that is largely dominated by “out-of-balance” microbial limestones almost devoid of metazoans, apart from sparse, small-sized requieniids and Chondrodonta , which accompanies the C3-middle C4 isotope segment. It is interpreted to reflect a sharp hyperthermal and acidification event induced by excess p CO 2 . Starting from the upper C4 segment, less severe but still threatening environmental conditions permitted the deposition throughout the lower C5 segment of peculiar shallow-water tropical-like carbonates, which are dominated by oncoidal floatstones and microbial wackestone/packstone emphasizing the enduring influence of benthic cyanobacteria during the Selli OAE1a. Upsection guilds are dominated by foraminiferal and peloidal wackestones/packstones with sparse bivalves and green algae (upper C5-lowermost C7 isotope segments). Similarly to other carbonate platforms of the central Tethyan Realm (e.g., Apennine and Adriatic), the resilience of the Apulia carbonate platform inner shelf to the environmental perturbations that led to the coeval drowning of its margin, the starvation of its slope and to the deposition of black shales in the bounding Ionian basin is a striking supraregional feature. The inception of the resilience of the Apulia carbonate platform inner shelf is coincident with the lithostratigraphic boundary in between the Borgo Celano and Chondrodonta and requieniids members of the Bari Limestones and physically corresponds in the field with the base of a significant, 1 m thick, Chondrodonta -rich marker bed. These observations confirm the value of routinely applied field and laboratory studies for precise chemostratigraphic and bio-chronostratigraphic correlations on a regional scale. Furthermore, chemostratigraphic data presented here corroborate recent paleoceanographic and stratigraphic models proposed for the Lower Aptian across the transition between the Apulia carbonate platform and the bounding Ionian basin, and provide further elements for regional reconstructions of historical patterns.

A cost-effective microbial fuel cell to detect and select for photosynthetic electrogenic activity in algae and cyanobacteria

This work describes the development of an easily constructed, cost-effective photosynthetic microbial fuel cell design with highly reproducible electrochemical characteristics that can be used to screen algae and cyanobacteria for photosynthetic electrogenic activity. It is especially suitable for benthic varieties, those that attach to surfaces. The anode chamber of the cell uses disposable polystyrene sample bottles (pottles) with a simple-to-apply carbon coating. These chambers can be used to grow photosynthetic microorganisms without a cathode for electrochemical characterization or with a cathode and load applied to provide electrogenic selective pressure. The utility of the design for screening, isolating and analysing photosynthetic electrogenic microorganisms under a wide variety of conditions is demonstrated. Several genera of benthic cyanobacteria from both New Zealand and Antarctica were shown to be electrogenic including Pseudanabaena, Leptolyngbya, Chroocococales, Phormidesmis, Microcoleus, Nostoc and Phormidium. A benthic strain of the eukaryote Paulschulzia pseudovolvox (Chlorophyceae) was isolated and identified, which had very good electrogenic qualities.

Determination of microcystins in reservoirs of different basins in a semiarid area

Intracellular benthic microcystins and microcystins dissolved in water were detected in seven reservoirs in the Segura and Jucar basins located in a semiarid area in the province of Alicante (SE, Spain). Three varieties of intracellular benthic microcystins were identified: Mc-LR, Mc-RR and Mc-YR. Generally, all the microcystin varieties were present in the same reservoir and Mc-LR, considered the most powerful carcinogen known, predominated in most of them. Total microcystins absolute values per dry weight varied from 0.055 μg g−1 in the Elx reservoir in summer to 1.032 μg g−1 in the Crevillent reservoir in spring. Microcystins dissolved in water were not frequent in the reservoirs and were detected in Guadalest throughout the year, with values of between 0.041 and 0.069 ppb. In the Crevillent reservoir, dissolved microcystins were recorded only in summer with 0.163 ppb and were not recorded in the other reservoirs in any season. The cyanobacterial presence varied throughout the year, but no significant difference was seen for interseasonal microcystins production (ANOVA, p > 0.1). The principal component analysis (PCA) and Pearson's correlation coefficient results showed that physico-chemical parameters did not significantly account for both intracellular and dissolved microcystins occurrence. Moreover, the PCA indicated that the evolution of the concentrations of dissolved and intracellular microcystins followed different patterns. The fact that benthic organisms could release intracellular toxins into water may be due to stress caused by changes in water levels and by colonies’ senescence. However, they may also perform antigrazing and/or allelopatic functions. A significant difference was found for conductivity, phosphates and the presence of microcystins Mc-LR and Mc-Tot in the oligo- and eutrophic reservoirs (t test, p 0.1). In fact, microcystins were never detected in the more eutrophic reservoirs, e.g. Tibi and Beniarres, both of which correspond to the River Jucar basin. This fact indicates a significant difference for conductivity and the presence of microcystins Mc-RR (t test, p < 0.1) between the River Segura basin and that of the River Jucar. The identification of microcystins in benthic cyanobacteria from the less eutrophic semiarid studied reservoirs showed that hepatotoxin production was restricted to neither planktonic species nor the physico-chemical parameters considered typical for the occurrence of cyanobacterial toxins.

MICROBIAL DIVERSITY AND DENSITY IN THE CORAL REEF ENVIRONMENT OF THE GULF OF MANNAR

Microbes are important in the coral reef environmen t in the recycling of nutrients and as a source of food to a variety of animal species. They also have an important trophic role to play in the reef environment, goverened by different physico-chemical and biotic factors. The present study has reveale d the presence of more THB (total heterotropic bacter ia) population density in water (5.2 to 22.5 ◊ 10 5 CFUml -1 ) and in the sediments (7 to 24.2 ◊ 10 7 CFUg -1 ) than in the surrounding coastal environments. A total of 24 species of planktonic cyanobacteria and 11 species of benthic cyanobacteria were recorded. Among them, Phormidium tenue was the most dominant species and the families Osc illatoriaceae and Chroococcaceae were predominant in the present study. A total of 35 species of fungi belonging to 20 genera representing the families Labyrinthulomycete s, Oomycetes, Zygomycetes and Deuteromycetes were isolated. Among them, the deuteromycetous fungi formed the bulk of the mycoflora of all the samples at both stations.