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1.
《Harmful algae》2014
Seven-day-ahead forecasting models of Cylindrospermopsis raciborskii in three warm-monomictic and mesotrophic reservoirs in south-east Queensland have been developed by means of water quality data from 1999 to 2010 and the hybrid evolutionary algorithm HEA. Resulting models using all measured variables as inputs as well as models using electronically measurable variables only as inputs forecasted accurately timing of overgrowth of C. raciborskii and matched well high and low magnitudes of observed bloom events with 0.45 ≤ r2 > 0.61 and 0.4 ≤ r2 > 0.57, respectively. The models also revealed relationships and thresholds triggering bloom events that provide valuable information on synergism between water quality conditions and population dynamics of C. raciborskii. Best performing models based on using all measured variables as inputs indicated electrical conductivity (EC) within the range of 206–280 mS m−1 as threshold above which fast growth and high abundances of C. raciborskii have been observed for the three lakes. Best models based on electronically measurable variables for the Lakes Wivenhoe and Somerset indicated a water temperature (WT) range of 25.5–32.7 °C within which fast growth and high abundances of C. raciborskii can be expected. By contrast the model for Lake Samsonvale highlighted a turbidity (TURB) level of 4.8 NTU as indicator for mass developments of C. raciborskii.Experiments with online measured water quality data of the Lake Wivenhoe from 2007 to 2010 resulted in predictive models with 0.61 ≤ r2 > 0.65 whereby again similar levels of EC and WT have been discovered as thresholds for outgrowth of C. raciborskii. The highest validity of r2 = 0.75 for an in situ data-based model has been achieved after considering time lags for EC by 7 days and dissolved oxygen by 1 day. These time lags have been discovered by a systematic screening of all possible combinations of time lags between 0 and 10 days for all electronically measurable variables. The so-developed model performs seven-day-ahead forecasts and is currently implemented and tested for early warning of C. raciborskii blooms in the Wivenhoe reservoir. 相似文献
2.
《Harmful algae》2014
Blooms of the toxin producing dinoflagellate Karenia brevis occur routinely on the West Florida Shelf of the Gulf of Mexico. Nutrient supplies are thought to play a large role in the formation and maintenance of these blooms. The role of top-down control has been less well studied, but grazing, or the lack thereof, on these toxic species may also enhance the formation of large biomass blooms in this region. Zooplankton community structure and copepod species composition were analyzed from samples collected on the West Florida Shelf (WFS) during a NOAA funded ECOHAB regional Karenia Nutrient Dynamics project during October 2007–2010. In 2008 there was no statistical difference in the abundance of zooplankton at bloom and non-bloom stations, however in 2009 there was a statistically significant difference (p < 0.05) between the abundance of zooplankton at stations with Karenia present. To investigate copepod ingestion rates in relation to K. brevis, shipboard and laboratory experiments of the single label method of 14C labeled phytoplankton culture, and time course ingestion experiments with isolated copepods were performed. Calculated ingestion rates suggest that the copepod species Centropages velificatus, and Acartia tonsa ingested K. brevis, however rates were variable among collection sites and K. brevis strains. Parvocalanus crassirostris did not ingest K. brevis in any of the experiments. 相似文献
3.
《Harmful algae》2014
The biological role of cyanobacteria secondary metabolites is relatively unknown although several possible hypotheses have been discussed. In the following study the effect of cylindrospermopsin (CYN) and metabolites of non-CYN producing Cylindrospermopsis raciborskii strain on growth, alkaline phosphatase (ALP) activity and microcystin-LR (MC-LR) production in Microcystis aeruginosa was evaluated. Higher concentrations of CYN (10 and 50 μg L−1) induced toxicity effects demonstrated by significant growth inhibition and M. aeruginosa cell necrosis. Lower concentrations of CYN (1 and 5 μg L−1) slightly decreased growth rates but significantly up-regulated ALP activity. Moreover, under all studied CYN concentrations MC-LR production strongly decreased. Spent C. raciborskii medium mimicked the CYN action by inducing strong inhibition of M. aeruginosa growth and MC-LR production and through up-regulation of ALP activity. On the other hand, spent M. aeruginosa medium did not affect C. raciborskii growth and no alterations in ALP activity were observed. Co-culturing of these two species resulted in an increase of C. raciborskii contribution at the expense of M. aeruginosa. From the results we conclude that CYN can be involved in interspecific competition in cyanobacteria and that non-CYN producing C. raciborskii strains may produce a hitherto unknown bioactive compound(s) which can mimic CYN action. 相似文献
4.
《Harmful algae》2011,10(6):578-589
Shipboard grazing experiments were conducted in the Gulf of Maine and on Georges Bank during of June 2006 to estimate zooplankton community grazing impact on a natural bloom of the toxic dinoflagellate Alexandrium fundyense. Surface seawater samples containing natural populations of grazers and A. fundyense from 23 stations were incubated at ambient temperatures. Concentrations of A. fundyense after incubations were compared to those at the start of each experiment to determine net increases due to population growth, or decreases presumed to be primarily due to grazing losses. Abundances of both microzooplankton (tintinnids, oligotrich ciliates, rotifers, copepod nauplii and heterotrophic dinoflagellates) and mesozooplankton (copepod nauplii, copepodites and adult copepods, rotifers, marine cladocerans, and meroplankton) grazers in experimental aliquots were also determined. The total zooplankton community had minimal grazing impact on natural populations of A. fundyense at most stations. At 70% of the stations where grazing experiments were performed, there were no significant differences in initial and final concentrations of A. fundyense. This indicated that growth of, and grazing on A. fundyense were in approximate balance. At 2 stations, which had the highest A. fundyense abundances of the cruise (>104 cells l−1), % of the A. fundyense population grazed per day was significantly negative, indicating that net population growth of A. fundyense exceeded grazing losses. At 5 stations, which had low concentrations of A. fundyense (102–103 cells l−1), % of the A. fundyense population grazed per day was significantly positive, indicating that losses of A. fundyense due to grazing exceeded net population growth. For stations with significant differences between Initial and Grazed concentrations of A. fundyense, grazing had the greatest impact at lower concentrations of A. fundyense, and grazing impact by the larger mesozooplankton was inversely related to zooplankton abundance. There was no relationship between microzooplankton abundance and grazing impact on A. fundyense. Grazing exceeded growth only where A. fundyense abundance was low, and growth exceeded grazing only where A. fundyense abundance was high. The inverse relationship between grazing impact and A. fundyense abundance implies that grazing may be capable of retarding bloom development at low concentrations typical of the early stages of a bloom, but at higher concentrations once a bloom becomes established, either grazing maintains a balance with A. fundyense growth, or growth exceeds grazing losses at highest concentrations. 相似文献
5.
《Aquatic Botany》2007,86(4):337-345
The seasonal dynamics of seagrass and epiphytic algal primary production were measured in an eelgrass (Zostera marina) bed in the Akkeshi-ko estuary, Hokkaido, Japan (43°02′N, 144°52′E). During spring and early summer, eelgrass biomass increased, with a high production (maximum: 2.89 g C m−2 day−1), but the production and biomass of epiphytic algae remained low. In contrast, epiphytic algae bloomed in August, with a high production (5.21 g C m−2 day−1), but eelgrass production ceased and its biomass subsequently decreased. Therefore, the major primary producers in this eelgrass bed switched seasonally from eelgrass in spring and early summer to epiphytic algae in late summer and autumn. Epiphytic algae maintained similar productivity because of the change of photosynthetic kinetics and the dominant epiphytic diatom changed from highly adhesive species to less adhesive or filamentous small species during the bloom. This suggests that the change of epiphyte density and biomass was due to change of its loss rate, possibly due to herbivorous grazing rate. Moreover, competition between epiphytic algae and eelgrass for nutrients and light may also affect the dramatic seasonal changes in the major primary producers. 相似文献
6.
《Harmful algae》2013
Over 1200 samples were collected from Louisiana estuarine and coastal shelf waters between 1989 and 2002, and analyzed to examine the population dynamics of Pseudo-nitzschia and to assess the potential threat posed by domoic acid (DA), a potent neurotoxin produced by some members within this toxigenic diatom genus. Results demonstrated that three species in this region (Pseudo-nitzschia multiseries, P. pseudodelicatissima complex, P. delicatissima) produce DA, and that particulate toxin levels were highest (up to 3.05 μg L−1) during the spring bloom, while cellular concentrations were highest in the winter/early spring when P. multiseries was most abundant (up to 30 pg cell−1). These particulate toxin levels are comparable to those seen in other regions (e.g., United States west coast) where DA poisoning events have occurred in the past. Pseudo-nitzschia were most abundant under dissolved inorganic nitrogen-replete conditions coupled with lower silicate and/or phosphate concentrations, and in the early spring months when temperatures were cooler. Pseudo-nitzschia were occasionally well-represented in the phytoplankton assemblage (≥106 cells L−1 in 14% of samples, over 50% of total phytoplankton in 5% of samples), indicating that planktivores (e.g., Gulf menhaden, Brevoortia patronus) may have little choice but to consume Pseudo-nitzschia cells, thereby providing potential vectors for DA transfer to higher trophic levels. By comparison, eastern oysters (Crassostrea virginica) present in estuarine waters may be more exposed to this toxin when Pseudo-nitzschia cells are part of a mixed assemblage, reducing selective grazing by these bivalves. C. virginica may thus represent the most effective vector for DA exposure in humans. 相似文献
7.
《Harmful algae》2015
Confined to Texas, USA, for more than 20 years, brown tides caused by Aureoumbra lagunensis emerged in the Indian River Lagoon and Mosquito Lagoon, Florida, USA, during 2012 and 2013, affording the opportunity to assess whether hypotheses developed regarding the occurrence of these blooms are ecosystem-specific. To examine the extent to which top-down (e.g. grazing) and bottom-up (e.g. nutrients) processes controlled the development of Aureoumbra blooms in Florida, nitrogen (N) uptake, nutrient amendment, and seawater-dilution, zooplankton grazing experiments were performed and the responses of Aureoumbra and competing phytoplankton were evaluated. During the study, Aureoumbra comprised up to 98% of total phytoplankton biomass, achieved cell densities exceeding 2 × 106 cells mL−1, and contained isotopically lighter N compared to non-bloom plankton populations, potentially reflecting the use of recycled N. Consistent with this hypothesis, N-isotope experiments revealed that urea and ammonium accounted for >90% of N uptake within bloom populations whereas nitrate was a primary N source for non-bloom populations. Low levels (10 μM) of experimental ammonium enrichment during blooms frequently enhanced the growth of Aureoumbra and resulted in the growth rates of Aureoumbra exceeding those of phycoerythrin-containing, but not phycocyanin-containing, cyanobacteria. A near absence of grazing pressure on Aureoumbra further enabled this species to out-grow other phytoplankton populations. Given this alga is generally known to resist zooplankton grazing under hypersaline conditions, these findings collectively suggest that moderate loading rates of reduced forms of nitrogenous nutrients (e.g ammonium, urea) into other subtropical, hypersaline lagoons could make them susceptible to future brown tides caused by Aureoumbra. 相似文献
8.
《Harmful algae》2013
Massive blooms of the dinoflagellate Cochlodinium polykrikoides occur annually in the Chesapeake Bay and its tributaries. The initiation of blooms and their physical transport has been documented and the location of bloom initiation was identified during the 2007 and 2008 blooms. In the present study we combined daily sampling of nutrient concentrations and phytoplankton abundance at a fixed station to determine physical and chemical controls on bloom formation and enhanced underway water quality monitoring (DATAFLOW) during periods when blooms are known to occur. While C. polykrikoides did not reach bloom concentrations until late June during 2009, vegetative cells were present at low concentrations in the Elizabeth River (4 cells ml−1) as early as May 27. Subsequent samples collected from the Lafayette River documented the increase in C. polykrikoides abundance in the upper branches of the Lafayette River from mid-June to early July, when discolored waters were first observed. The 2009 C. polykrikoides bloom began in the Lafayette River when water temperatures were consistently above 25 °C and during a period of calm winds, neap tides, high positive tidal residuals, low nutrient concentrations, and a low dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphorous (DIP) ratio. The pulsing of nutrients associated with intense but highly localized storm activity during the summer months when water temperatures are above 25 °C may play a role in the initiation of C. polykrikoides blooms. The upper Lafayette River appears to be an important area for initiation of algal blooms that then spread to other connected waterways. 相似文献
9.
《Harmful algae》2017
Allelopathic interactions among phytoplankton species are regarded as one of the important factors contributing to phytoplankton species competition and succession. The role and extent of allelopathic effects of blooming freshwater cyanobacteria on other phytoplankton species in eutrophied waters, however, are still unknown. We examined the allelopathic effect of Microcystis aeruginosa on two common green algae (Scenedesmus quadricauda, Chlorella pyrenoidosa) and a diatom (Cyclotella meneghiniana) by adding exudates from different growth phases and in co-culture tests. Exudates of M. aeruginosa from the exponential growth phase and the stationary phase significantly inhibited the growth of S. quadricauda, C. pyrenoidosa and C. meneghiniana, whereas those from the decline phase increased their growth. The presence of M. aeruginosa extremely inhibited the growth of all tested species in co-cultures within 24 h. Our results indicate that under the tested environmental conditions (25 °C, light 80 μmol quanta m−2 s−1, manual shaking twice a day), allelopathic effects of M. aeruginosa on other phytoplankton species can significantly contribute to their competitive success. 相似文献
10.
《Environmental and Experimental Botany》2007,59(1):92-98
Recycling of wood-ash to boreal forests has been suggested to prevent depletion of essential soil nutrient or reduce the negative effects of acidification of surface waters. The aim of this investigation was to study the effects of different concentrations of wood-ash (5, 10 and 12.5 g l−1 diluted in cultivating medium) on chlorophyll a fluorescence in Euglena gracilis and Chlamydomonas reinhardtii under laboratory conditions. The green alga C. reinhardtii was more susceptible to wood-ash solutions than the flagellate E. gracilis. Two different forms of wood-ash solutions were tested. In the first solution no adjustment of pH was made and after 7 days of incubation with wood-ash the pH for the different wood-ash concentrations (5, 10 and 12.5 g l−1) were 8, 9 and 11, respectively. In the second solution, the pH was adjusted to 7. The results show that no negative effect on fluorescence yield (Fv/Fm), relative electron transport rate (ETR), photochemical quenching (qP) or non-photochemical quenching (NPQ) was observed in E. gracilis. In contrast, C. reinhardtii displayed strong inhibition at concentrations of 10 and 12.5 g l−1 with non-adjusted pH. The negative effects of high pH on photochemical activity in C. reinhardtii could either be related to (1) the destruction of the ΔpH across the thylakoid membranes or (2) other parts in the photosynthetic systems that are negatively affected by changing pH. The results indicate that elevated pH levels due to wood-ash application could be an environmental stress factor to phytoplankton communities and may lead to loss of diversity among primary producers in aquatic ecosystems. If wood-ash application was to become general practice in or near aquatic ecosystems a rapid change in pH induced by wood-ash must be avoided. 相似文献
11.
《Harmful algae》2014
Cochlodinium polykrikoides is a globally distributed, ichthyotoxic, bloom-forming dinoflagellate. Blooms of C. polykrikoides manifest themselves as large (many km2) and distinct patches with cell densities exceeding 103 ml−1 while water adjacent to these patches can have low cell densities (<100 cells ml−1). While the effect of these blooms on fish and shellfish is well-known, their impacts on microbial communities and biogeochemical cycles are poorly understood. Here, we investigated plankton communities and the cycling of carbon, nitrogen, and B-vitamins within blooms of C. polykrikoides and compared them to areas in close proximity (<100 m) with low C. polykrikoides densities. Within blooms, C. polykrikoides represented more than 90% of microplankton (>20 μm) cells, and there were significantly more heterotrophic bacteria and picoeukaryotic phytoplankton but fewer Synechococcus. Terminal restriction fragment length polymorphism analysis of 16S and 18S rRNA genes revealed significant differences in community composition between bloom and non-bloom samples. Inside the bloom patches, concentrations of vitamin B12 were significantly lower while concentrations of dissolved oxygen were significantly higher. Carbon fixation and nitrogen uptake rates were up to ten times higher within C. polykrikoides bloom patches. Ammonium was a more important source of nitrogen, relative to nitrate and urea, for microplankton within bloom patches compared to non-bloom communities. While uptake rates of vitamin B1 were similar in bloom and non-bloom samples, vitamin B12 was taken up at rates five-fold higher (>100 pmol−1 L−1 d−1) in bloom samples, resulting in turn-over times of hours during blooms. This high vitamin demand likely led to the vitamin B12 limitation of C. polykrikoides observed during nutrient amendment experiments conducted with bloom water. Collectively, this study revealed that C. polykrikoides blooms fundamentally change microbial communities and accelerate the cycling of carbon, some nutrients, and vitamin B12. 相似文献
12.
Clarissa R. Anderson David A. Siegel Raphael M. Kudela Mark A. Brzezinski 《Harmful algae》2009,8(3):478-492
The Santa Barbara Channel, CA is a highly productive region where wind-driven upwelling and mesoscale eddies are important processes driving phytoplankton blooms. In recent years, the spring bloom has been dominated by the neurotoxin-producing diatom, Pseudo-nitzschia spp. In this paper, we relate a 1.5-year time series of Pseudo-nitzschia spp. abundance and domoic acid concentration to physical, chemical, and biological data to better understand the mechanisms controlling local Pseudo-nitzschia spp. bloom dynamics. The data were used to define the ranges of environmental conditions associated with Pseudo-nitzschia spp. bloom development in the Santa Barbara Channel. The time series captured three large toxic events (max. particulate domoic acid concentration, pDA ~6000 ng L?1; max. cellular domoic acid concentrations, cDA ~88 pg cell?1) in the springs of 2005–2006 and summer 2005 corresponding to bloom-level Pseudo-nitzschia spp. abundance (>5.0 × 104 cells L?1). In general, large increases in Pseudo-nitzschia spp. abundance were accompanied by increases in cDA levels, and cDA peaks preceded pDA peaks by at least one month in both the springs of 2005 and 2006. Statistical models incorporating satellite ocean color (MODIS-Aqua and SeaWiFS) and sea surface temperature (AVHRR) data were created to determine the probability that a remotely sensed phytoplankton bloom contains a significant population of toxic Pseudo-nitzschia spp. Models correctly estimate 98% of toxic bloom situations, with a 7–29% rate of false positive identification. Conditions most associated with high cDA levels are low sea surface temperature, high salinity, increased absorption by cDOM (412 nm), increased reflectance at 510/555 nm, and decreased particulate absorption at 510 nm. Future efforts to merge satellite and regionally downscaled forecasting products with these habitat models will help assess bloom forecasting capabilities in the central CA region and any potential connections to large-scale climate modes. 相似文献
13.
《Harmful algae》2009,8(1):103-110
Cultural eutrophication is frequently invoked as one factor in the global increase in harmful algal blooms, but is difficult to definitively prove due to the myriad of factors influencing coastal phytoplankton bloom development. To assess whether eutrophication could be a factor in the development of harmful algal blooms in California (USA), we review the ecophysiological potential for urea uptake by Pseudo-nitzschia australis (Bacillariophyceae), Heterosigma akashiwo (Raphidophyceae), and Lingulodinium polyedrum (Dinophyceae), all of which have been found at bloom concentrations and/or exhibited noxious effects in recent years in California coastal waters. We include new measurements from a large (Chlorophyll a > 500 mg m−3) red tide event dominated by Akashiwo sanguinea (Dinophyceae) in Monterey Bay, CA during September 2006. All of these phytoplankton are capable of using nitrate, ammonium, and urea, although their preference for these nitrogenous substrates varies. Using published data and recent coastal time series measurements conducted in Monterey Bay and San Francisco Bay, CA, we show that urea, presumably from coastal eutrophication, was present in California waters at measurable concentrations during past harmful algal bloom events. Based on these observations, we suggest that urea uptake could potentially sustain these harmful algae, and that urea, which is seldom measured as part of coastal monitoring programs, may be associated with these harmful algal events in California. 相似文献
14.
《Harmful algae》2010,9(6):864-872
The taxonomical relationship of Cylindrospermopsis raciborskii and Raphidiopsis mediterranea was studied by morphological and 16S rRNA gene diversity analyses of natural populations from Lake Kastoria, Greece. Samples were obtained during a bloom (23,830 trichomes mL−1) in August 2003. A high diversity of apical cell, trichome, heterocyte and akinete morphology, trichome fragmentation and reproduction was observed. Trichomes were grouped into three dominant morphotypes: the typical and the non-heterocytous morphotype of C. raciborskii and the typical morphotype of R. mediterranea. A morphometric comparison of the dominant morphotypes showed significant differences in mean values of cell and trichome sizes despite the high overlap in the range of the respective size values. Additionally, two new morphotypes representing developmental stages of the species are described while a new mode of reproduction involving a structurally distinct reproductive cell is described for the first time in planktic Nostocales. A putative life-cycle, common for C. raciborskii and R. mediterranea is proposed revealing that trichome reproduction of R. mediterranea gives rise both to R. mediterranea and C. raciborskii non-heterocytous morphotypes. The phylogenetic analysis of partial 16S rRNA gene (ca. 920 bp) of the co-existing Cylindrospermopsis and Raphidiopsis morphotypes revealed only one phylotype which showed 99.54% similarity to R. mediterranea HB2 (China) and 99.19% similarity to C. raciborskii form 1 (Australia). We propose that all morphotypes comprised stages of the life cycle of C. raciborkii whereas R. mediterranea from Lake Kastoria (its type locality) represents non-heterocytous stages of Cylindrospermopsis complex life cycle. 相似文献
15.
《Harmful algae》2012
An unarmored dinoflagellate bloom of Cochlodinium geminatum (Schütt) Schütt has been identified in the Pearl River Estuary, South China Sea during the severe dry season, from late October to early November, 2009, when temperature and salinity ranged between 20.0–27.2 °C and 10.6–33.4, respectively. Light and scanning electron microscopy were used to identify the characteristics of C. geminatum and provided the clear morphological structure for this species. The organism was primarily found in chains of two cells or single cell, and no longer chains were observed. Cells were irregularly spherical or slightly dorso-ventrally, with size ranged between 28 and 36 μm and longer than wide. A large nucleus in the center with numerous golden chloroplasts was present, and the cingulum made 1.5 turns around the cell. The concentration of C. geminatum ranged from 102 to greater than 107 cells l−1 during the bloom period. Nutrient concentration ranges during the bloom were 1.29–81.00 μM NO3, 0.14–12.14 μM NO2, 0.21–6.29 μM NH4, 0.23–6.26 μM PO4 and 3.29–171.43 μM SiO3, respectively. Total biomass expressed in terms of chlorophyll a ranged from 2.44 to 135.45 μg l−1, with an average 19.9 μg l−1 in surface water throughout the PRE. Two main clusters corresponding to the water sectors were defined with multivariate analysis (cluster and nMDS). Based on the composition and abundance of phytoplankton, spatial variations were observed at a significant level (ANOSIM, R = 0.44, P < 0.01). Although the pairwise correlation analysis detected no significant effect of any single environmental variable on the abundance of C. geminatum, the multivariate analysis (BIO-ENV) between biotic and abiotic variables resulted in the best variables combination with all measured factors involved (temperature, salinity, turbidity, NO3, NO2, NH4, PO4 and SiO3) which showed a combined effect during the bloom of C. geminatum in the Pearl River Estuary (ρw = 0.477). 相似文献
16.
《Harmful algae》2017
To investigate interactions between the nematocyst-bearing mixotrophic dinoflagellate Paragymnodinium shiwhaense and different heterotrophic protist and copepod species, feeding by common heterotrophic dinoflagellates (Oxyrrhis marina and Gyrodinium dominans), naked ciliates (Strobilidium sp. approximately 35 μm in cell length and Strombidinopsis sp. approximately 100 μm in cell length), and calanoid copepods Acartia spp. (A. hongi and A. omorii) on P. shiwhaense was explored. In addition, the feeding activities of P. shiwhaense on these heterotrophic protists were investigated. Furthermore, the growth and ingestion rates of O. marina, G. dominans, Strobilidium sp., Strombidinopsis sp., and Acartia spp. as a function of P. shiwhaense concentration were measured. O. marina, G. dominans, and Strombidinopsis sp. were able to feed on P. shiwhaense, but Strobilidium sp. was not. However, the growth rates of O. marina, G. dominans, Strobilidium sp., and Strombidinopsis sp. feeding on P. shiwhaense were very low or negative at almost all concentrations of P. shiwhaense. P. shiwhaense frequently fed on O. marina and Strobilidium sp., but did not feed on Strombidinopsis sp. and G. dominans. G. dominans cells swelled and became dead when incubated with filtrate from the experimental bottles (G. dominans + P. shiwhaense) that had been incubated for one day. The ingestion rates of O. marina, G. dominans, and Strobilidium sp. on P. shiwhaense were almost zero at all P. shiwhaense concentrations, while those of Strombidinopsis sp. increased with prey concentration. The maximum ingestion rate of Strombidinopsis sp. on P. shiwhaense was 5.3 ng C predator−1d−1 (41 cells predator−1d−1), which was much lower than ingestion rates reported in the literature for other mixotrophic dinoflagellate prey species. With increasing prey concentrations, the ingestion rates of Acartia spp. on P. shiwhaense increased up to 930 ng C ml−1 (7180 cells ml−1) at the highest prey concentration. The highest ingestion rate of Acartia spp. on P. shiwhaense was 4240 ng C predator−1d−1 (32,610 cells predator−1d−1), which is comparable to ingestion rates from previous studies on other dinoflagellate prey species calculated at similar prey concentrations. Thus, P. shiwhaense might play diverse ecological roles in marine planktonic communities by having an advantage over competing phytoplankton in anti-predation against potential protistan grazers. 相似文献
17.
Using ten years (2003–2012) of satellite Chlorophyll-a data, we report that annual phytoplankton bloom climax in the Northwest Pacific marginal seas (17°–58°N) delays northward at a rate of 22.98 ± 2.86 km day−1. The spring bloom is a dominant feature of the phytoplankton seasonal cycle in this region, except for the northern South China Sea, which features a winter bloom. The sea surface hourly Photosynthetically Available Radiation (PAR) intensity averaged over the bloom peak duration is nearly uniform (1.04 ± 0.10 W m−2 h−1) among the four sub-regions (i.e. the northern South China Sea, the Kuroshio waters, the Sea of Japan and the Sea of Okhotsk), although different algal species in these four distinct ecological provinces could adapt to a much larger change in other environmental parameters (including total daily PAR, day length, sea surface temperature, net surface heat flux, mixed layer depth, wind speed and euphotic depth). The differences of the hourly PAR intensity between the four provinces during their bloom periods are smaller than those during non-bloom seasons. In contrast, an increasing total daily PAR (W m−2 day−1), due to the longer day length at higher latitudes, may balance decreasing sea surface temperature and induce algal flowering. Our results point to an optimal hourly light intensity for the annual phytoplankton bloom peak timing in this entire region, which could potentially become an indicator for the requirement of these annual bloom peaks. 相似文献
18.
《农业工程》2014,34(3):170-177
In order to evaluate the potential effects of rest grazing on organic carbon storage on the Stipa baicalensis steppe in Inner Mongolia, compared the S. baicalensis steppes after rest grazing for 3 years, 6 years, and 9 years, using potassium dichromate heating method, this study analyzed the organic carbon storage of plant and soil in the steppes among different periods of rest grazing. The results indicated that as the rest grazing years prolonged, the biomass included above-ground parts, litters and underground plant parts(roots) of the plant communities all increased, meanwhile the carbon content of the biomass increased with the rest grazing years prolonged. For the zero rest grazing (RG0) steppe and the steppes after a rest grazing of 3 years (RG3a), 6 years (RG6a), 9 years (RG9a), the carbon storage in above-ground parts of plant communities were 42.60 g C/m2, 66.33 g C/m2, 83.46 g C/m2, 100.29 g C/m2 respectively; the carbon storage of litters were 7.85 g C/m2, 9.12 g C/m2, 9.18 g C/m2, 11.54 g C/m2 separately; the carbon storage of underground plant parts (0–100 cm) were 281.40 g C/m2, 576.38 g C/m2, 745.33 g C/m2, 1279.61 g C/m2 respectively; and the carbon storage in 0–100 cm soil were 22991.14 g C/m2, 24687.75 g C/m2, 26564.86 g C/m2,33041.55 g C/m2. The results suggested that as the rest grazing years prolonged, the organic carbon storage in plant communities and soil increased. The carbon storage of underground plant parts and soil organic carbon mainly concentrated in 0–40 cm soil. After rest grazing for 3 years, 6 years, and 9 years, the increased soil organic carbon were as the 81.14%, 85.84%, and 89.46% of the total increased carbon; From the perspective of carbon sequestration cost, the total cost of RG3a, RG6a and RG9a were 2903.40 RMB/hm2, 5806.80 RMB/hm2, and 8710.20 RMB/hm2. The cost reduced with the extension of rest grazing years, 0.17 RMB/kg C, 0.16 RMB/kg C, 0.09 RMB/kg C for RG3a, RG6a and RG9a respectively. From the growth characteristics of grassland plants, the spring was one of the two avoid grazing periods, timely rest grazing could effectively restore and update grassland vegetation, and was beneficial to the sustainable use of grassland. From the available data, the organic carbon storage of RG9a was the highest, while the cost of carbon sequestration was the lowest. Therefore, spring rest grazing should be encouraged to continue for it was proved to be a very efficient grassland use measures. 相似文献
19.
《Harmful algae》2014
Occurrence of toxic cyanobacterial blooms has become a worldwide problem, increasing the risk of human poisoning due to consumption of seafood contaminated with cyanotoxins. Though no such cases of human intoxication due to toxic blooms have been reported so far from India, most of the studies related to blooms have been restricted to reporting of a bloom and/or antimicrobial activity of its extract. Detailed toxicity study of cyanobacterial blooms are lacking. A study on the toxicity of a dense bloom (14.56 × 106 trichomes L−1) of the marine diazotrophic cyanobacteria, Trichodesmium erythraeum, observed in the coastal waters of Phoenix Bay, Port Blair, Andamans was undertaken. The significance of this bloom is that it was a single species and had conspicuously inhibited the growth of other phytoplankton and complete exclusion of zooplankton from the bloom region, intimating the involvement of toxins in the bloom. The cyanobacterial extracts showed prominent antimicrobial activity against certain human pathogenic bacteria and fungi. Studies on the toxicity of the cyanobacterial extracts was carried out using brine shrimp bioassay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and comet assay. The cyanobacterial extract exhibited toxic effect to Artemia salina causing mortality of up to 40% after 48 h at a concentration of 1 mg mL−1, while it induced cytotoxicity in cell lines (HepG2 and HaCat) and caused DNA damage in human lymphocytes in vitro. 相似文献
20.
《Aquatic Botany》2005,83(2):129-140
Bisexual populations of the charophyte Chara canescens (Desv. et Loisel. in Loisel., 1810) containing male and female individuals are rarely found. Two experiments were carried out to study whether male and female algae from the same site exhibit different physiological capacities, especially with respect to light acclimation.Algae from two different shore levels and from laboratory cultures acclimated to six irradiance conditions (35–500 μmol photons m−2 s−1) were compared. Field measurements showed that both female and male algae of C. canescens are able to acclimate to daily changes in solar irradiance. The quantum yield of Photosystem II (PSII) decreased with increasing irradiance in the morning and increased with decreasing irradiance in the afternoon. Growth experiments showed increasing growth rates from 35 μmol photons m−2 s−1 (∼7 mg FW) up to 500 μmol photons m−2 s−1 (∼27 mg FW) in female and male C. canescens. The irradiance saturation point for photosynthesis (Ek) was about 140 μmol m−2 s−1 for both sexes within the whole range of acclimation irradiances. The maximum photosynthesis rate at saturating irradiances (Pmax) of male algae was highest at Ek, whereas Pmax of female algae was highest at 500 μmol photons m−2 s−1. The photosynthetic efficiency in the light-limited range (α) increased in female C. canescens and decreased in male C. canescens. The ratio of the non-photochemical quenching parameter (NPQ) to the relative electron transport rates rETR(MT) increased in both sexes with irradiance, but showed a steeper increase in male than in female algae. Pigment analysis showed similar acclimation pattern for male and female C. canescens. Chl a/Chl b ratios of both sexes were constant over the whole range of Eg, whereas Chl a/carotenoid ratios in male and female C. canescens decreased from 70 μmol photons m−2 s−1 upwards. Pigment analysis pointed out that the carotenes α-, β- and γ-carotene were more prominent in male than in female algae.Our results indicate that female C. canescens are more efficient in light acclimation than male algae from the same site. Nevertheless, further investigations of bisexual C. canescens populations resolving CO2-uptake mechanisms and/or genetic differences are needed. 相似文献