Labelling patterns of carbon-14 in net plankton during a winter-spring bloom

Weekly surface samples were collected in lower Narragansett Bay, Rhode Island, during the 1975 winter-spring bloom and fractionated by nets to nannoplankton (<20 μm) and total (< 158 μm) size fractions. Each size fraction was assayed for paniculate carbon, nitrogen, carbohydrate, protein, chlorophyll a, and cell counts. The <20 μm values were subtracted from the <158 μm values to estimate the composition of the 20 μm to 158 μm fraction (termed net plankton). As nutrients (primarily nitrogen) decreased to undetectable levels with the culmination of the diatom bloom, the ratios of protein/carbohydrate, carbohydrate/carbon, and carbon/chlorophyll a in the net plankton indicated the diatom population was increasingly nutrient-limited. Each size fraction was also incubated at a saturating light intensity with carbon-14; following filtration, the cells were extracted with solvents to obtain labelled polysaccharide and protein. The daily rates of polysaccharide and protein synthesis in the net plankton declined as the bloom entered the stationary phase. When the diatom population was at its maximum density the majority of the carbon-14 was found in the ethanol-soluble fraction; this may be due to high light intensities or nutrient effects.     

Applications of Satellite Ocean Color Sensors for Monitoring and Predicting Harmful Algal Blooms

The new satellite ocean color sensors offer a means of detecting and monitoring algal blooms in the ocean and coastal zone. Beginning with SeaWiFS (Sea Wide Field-of-view Sensor) in September 1997, these sensors provide coverage every 1 to 2 days with 1-km pixel view at nadir. Atmospheric correction algorithms designed for the coastal zone combined with regional chlorophyll algorithms can provide good and reproducible estimates of chlorophyll, providing the means of monitoring various algal blooms. Harmful algal blooms (HABs) caused by Karenia brevis in the Gulf of Mexico are particularly amenable to remote observation. The Gulf of Mexico has relatively clear water and K. brevis, in bloom conditions, tends to produce a major portion of the phytoplankton biomass. A monitoring program has begun in the Gulf of Mexico that integrates field data from state monitoring programs with satellite imagery, providing an improved capability for the monitoring of K. brevis blooms.     

Distribution of Mycosporine-Like Amino Acids Along a Surface Water Meridional Transect of the Atlantic

The composition and abundance of mycosporine-like amino acids (MAAs) were investigated in the surface waters along a 13,000-km meridional transect (52° N to 45° S) in the Atlantic Ocean (Atlantic Meridional Transect programme: Cruise AMT 18: 4/10/2008-10/11/2008). MAAs were ubiquitous along the transect, although the composition of the MAAs was variable. Highest concentrations were in the far south (below 40° S; MAA >1 μg L(-1)) and in north subtropical equatorial region (NER: 0-25° N; MAA up to 0.8 μg L(-1)). Highest MAA relative to chlorophyll-a occurred in the NER (MAA/chl-a ratio between 2 and 5). MAA/chl-a significantly correlated with the preceding month's mean daily UV dose and with UV-B/UV-A. In the far south, high MAA concentrations coincided with high phytoplankton biomass, high nutrients and a deep mixed layer associated with the austral spring. Here, the phytoplankton community was dominated by micro- and nano-eukaryotes. At the NER, the high MAA/chl-a coincided with low nutrient concentrations, a shallow mixed layer depth (20-70 m) and to a lesser extent to a shallow nitracline (40-90 m). Here, the phytoplankton consisted primarily of picophytoplankton (0-0.2 μm), dominated by the pico-cyanobacteria Synechococcus sp. and Prochlorococcus sp. and by the nitrogen fixing filamentous cyanobacterium Trichodesmium. The low nitrate concentrations (<0.1 μmol L(-1)) at the NER suggest that nitrogen fixation was required for MAA production. Specific MAAs could not easily be assigned to particular groups of phytoplankton and we could not rule out the possibility that MAAs were associated with symbiotic cyanobacteria contained within heterotrophic dinoflagellates or diatoms.     

Diatom bloom in the tidal freshwater zone of a turbid and shallow estuary,Rupert Bay (James Bay,Canada)

Phytoplankton biomass and species composition were studied from June to September 1991 at the mouth of four major rivers and in the freshwater (sal. 0 %), the estuarine (sal. 2–10%) and the coastal (sal. 10–12%) zones of Rupert Bay, located at the southeast tip of James Bay, Canada.A chlorophyll a maximum (5–14 µg 1^–1) was observed in the freshwater zone from July to September. Chlorophyll values were low at the mouth of the rivers and in the estuarine and coastal zones (chl a < 1.00 µg 1^–1). Diatoms were dominant in the freshwater zone (30–80 % abundance), with flagellates dominating in the estuarine and coastal zones (60–95% abundance). Diversity was low (H: 1.5–2.5) in the freshwater zone and decreased seaward (H: 0.5–1.5).The diatom bloom was composed almost exclusively of the autochthonous planktonic diatom Cyclotella meneghiniana Kütz., which contributed 25–85% of the species composition, and of the subdominant benthic species Diploneis smithii, Navicula lanceolata and Surirella robusta. Peak abundance occurred upstream of the turbidity maximum, in the tidal freshwater zone. In this zone the mean photic depth was 1 m and residence time was from 7 to 8 days during the bloom. Residence time is considered to be the dominant factor controlling the phytoplankton bloom, with light not acting as a limiting factor. The high turbidity due to resuspension and shallow depth of the bay controlled the species composition.     

An unusual bloom of the dinoflagellate Akashiwo sanguinea off the central Oregon, USA, coast in autumn 2009

An algal bloom caused by the dinoflagellate Akashiwo sanguinea was observed in October–November 2009 along the central Oregon coast (44.6°N), off Newport, Oregon, U.S.A. In this paper, the conditions are described which led to the development and demise of this bloom. The bloom was observed for 1 month from 5-October until 4-November with the peak of abundance on 19-October (347,615 cells L⁻¹). The A. sanguinea bloom followed September blooms of the diatoms Pseudo-nitzschia spp, Chaetoceros debilis, and the dinoflagellate Prorocentrum gracile. The bloom occurred when nitrate and silicate concentrations were <2 μM and <8 μM, respectively, and when the water column was stratified. This A. sanguinea dinoflagellate bloom event was closely related to the anomalous upwelling conditions in 2009: upwelling ceased early, at the end of August, whereas a normal upwelling continues into early October. This relaxation extended to near the end of September as a prolonged downwelling event, but then active upwelling reappeared in October and November. The explanation for the occurrence of the A. sanguinea bloom in October may be related to a combination of a prior diatom bloom, a stratified water column with low nutrient concentration in September, and an active upwelling event in October. As for the ultimate source of the cells, the hypothesis is that the seed stock for the A sanguinea bloom off Oregon was southward transport of cells from the Washington coast where a massive bloom of A. sanguinea was first observed in September 2009.     

Temporal variability in egg production rates of Acartia tonsa Dana in Long Island Sound

The relationship between week-by-week variations in the in situ egg production rates of Acartia tonsa Dana and changes in chlorophyll concentration in several size fractions was investigated by incubating adult females in natural sea water for 24-h periods. Our results indicate that the egg production of A. tonsa in Long Island Sound was better related to the 10 μm chlorophyll size fraction than to the total chlorophyll concentration. The < 10 μm size fraction comprised the greatest percentage of the chlorophyll during July and August when the water column was stratified. Egg production rates were lowest (8.7 eggs · female⁻¹ · day⁻¹) in early August when less than 0.5 μg chlorophyll 1 ⁻¹ was observed in the 10 μm chlorophyll a size fraction. Following destratification in late August, the “fall” diatom bloom occurred and egg production rates increased to the maximum observed rate of 56.6 eggs · female⁻¹ · day⁻¹. At this time, the concentration of the 10μm chlorophyll size fraction was 5.5 μg 1⁻¹. Maximum egg production rates were observed at chlorophyll concentrations as low as 0.8 μg 1⁻¹ in the 10 μm size fraction.     

Additive pressures of elevated sea surface temperatures and herbicides on symbiont-bearing foraminifera

Elevated ocean temperatures and agrochemical pollution individually threaten inshore coral reefs, but these pressures are likely to occur simultaneously. Experiments were conducted to evaluate the combined effects of elevated temperature and the photosystem II (PSII) inhibiting herbicide diuron on several types of symbiotic algae (diatom, dinoflagellate or rhodophyte) of benthic foraminifera in hospite. Diuron was shown to evoke a direct effect on photosynthetic efficiency (reduced effective PSII quantum yield ΔF/F'(m)), while elevated temperatures (>30 °C, only 2 °C above current average summer temperatures) were observed to impact photosynthesis more indirectly by causing reductions in maximum PSII quantum yield (F(v)/F(m)), interpreted as photodamage. Additionally, elevated temperatures were shown to cause bleaching through loss of chlorophyll a in foraminifera hosting either diatoms or dinoflagellates. A significant linear correlation was found between reduced F(v)/F(m) and loss of chlorophyll a. In most cases, symbionts within foraminifera proved more sensitive to thermal stress in the presence of diuron (≥ 1 μg L(-1)). The mixture toxicity model of Independent Action (IA) described the combined effects of temperature and diuron on the photosystem of species hosting diatoms or dinoflagellates convincingly and in agreement with probabilistic statistics, so a response additive joint action can be assumed. We thus demonstrate that improving water quality can improve resilience of symbiotic phototrophs to projected increases in ocean temperatures. As IA described the observed combined effects from elevated temperature and diuron stress it may therefore be employed for prediction of untested mixtures and for assessing the efficacy of management measures.     

象山港硅藻赤潮过程中真菌群落演替及互作特征

[背景] 近岸海域赤潮的发生能显著改变包括真菌在内的微生物群落组成,进而影响海洋中碳氮元素循环。真菌是海洋中重要的分解者,但赤潮过程对真菌群落的影响少有报道。[目的] 探明赤潮过程对真菌群落的影响,对进一步阐释赤潮对生态系统中物质循环的影响具有重要意义。[方法] 针对2017年春季象山港硅藻赤潮,对真菌内源转录间隔区1（Internally Transcribed Spacer 1,ITS1）序列进行高通量测序,研究赤潮过程中真菌群落响应及共现性特征。[结果] 真菌群落的α多样性指数在赤潮暴发的各阶段差异显著,而且均与磷酸盐、硝酸盐和亚硝酸盐有显著相关性（P<0.05）。子囊菌门（Ascomycota,90.2%）和担子菌门（Basidiomycota,8.27%）是本次硅藻赤潮的优势菌门,其中子囊菌门遍布赤潮暴发的4个阶段;锤舌菌纲（Leotiomycetes,16.1%）和散囊菌纲（Eurotiomycetes,9.3%）是纲水平上的主要优势类群。赤潮暴发过程中硝酸盐、亚硝酸盐、磷酸盐和温度等环境因素的改变,驱动真菌群落组成及结构发生显著变化。Helotiales、Eurotiales、Xylariales、Sacc haromycetales和Agaricostilbales构成了真菌群落共现网络的主体。[结论] 真菌群落在赤潮的各阶段具有显著的演替特征,赤潮藻生消是引起真菌群落演替的主要因素,但是环境因子也扮演着重要角色。赤潮过程中,真菌群落同类群内的互作要强于不同类群间的互作,这对维持群落的稳定性具有重要意义。     

Coupling planktonic and benthic shifts during a bloom of Alexandrium catenella in southern Chile: Implications for bloom dynamics and recurrence

Cell abundances and distributions of Alexandrium catenella resting cysts in recent sediments were studied along time at two locations in the Chilean Inland Sea exposed to different oceanographic conditions: Low Bay, which is much more open to the ocean than the more interior and protected Ovalada Island. The bloom began in interior areas but maximum cyst concentrations were recorded in locations more open to the ocean, at the end of the Moraleda channel. Our results showed a time lapse of around 3 months from the bloom peak (planktonic population) until the number of resting cysts in the sediments reached a maximum. Three months later, less than 10% of the A. catenella cysts remained in the sediments. Maximum cyst numbers in the water column occurred one month after the planktonic peak, when no cells were present. The dinoflagellate assemblage at both study sites was dominated by heterotrophic cysts, except during the A. catenella bloom. CCA analyses of species composition and environmental factors indicated that the frequency of A. catenella blooms was associated with low temperatures, but not with salinity, chlorophyll a concentration, and predator presence (measured as clam biomass). However, resting cyst distribution was only related to cell abundance and location. The occurrence of A. catenella cysts was also associated with that of cysts from the toxic species Protoceratium reticulatum. By shedding light on the ecological requirements of A. catenella blooms, our observations support the relevance of encystment as a mechanism of bloom termination and show a very fast depletion of cysts from the sediments (<3 months), which suggest a small role for resting cyst deposits in the recurrence of A. catenella blooms in this area.     

Studies on the phytoplankton ecology of the trondheemsfjord. II. Chloroplast pigments in relation to abundance and physiological state of the phytoplankton

The quantitative composition of the chloroplast pigments of phytoplankton sampled weekly at one station in the Trondheimsfjord was studied by circular paper chromatography throughout 18 months. The concentrations of total chlorophyll a (T-chl a obtained by the trichromatic method) as well as of chromatographically purified chlorophyll a (chl a) followed the variations in phytoplankton concentration. Two spring blooms and a weak autumn flowering of phytoplankton were clearly reflected in the pigment contents found, namely 14–16 mg T-chl a/m³ for the spring maxima, corresponding to nearly 300 mg T-chl a/m² for the euphotic zone; and 3–4 mg/m³ or 32 mg/m² for the autumn peak. The concentrations between blooms amounted to ≈ 1 mg T-chl a/m³, while concentrations down to 0.03 mg/m³ were found for winter samples.The content of T-chl a was high in diatom cells prior to a bloom (20–40 × 10^?9 mg/cell). During rapid growth (a more or less exponential phase) the cell content of chloroplast pigments decreased (to 5–10 × 10^?9 mg). No degradation product of chlorophylls could be detected during this phase and the percentage of chl a (of T-chl a) was high (70–80 %). At the peak of the bloom, and especially when the nitrate content in the surrounding water had been exhausted, low values for T-chl a were found ($\text{0.3–0.5 × 10}{}^{\mathrm{<mtext>9</mtext><mtext>?</mtext>}}\text{mg/cell}$). As soon as the cell counts started to fall, or even before the decline could be clearly detected, the percentage of chl a dropped (to 40-20 %) and derived chlorophylls (not phaeophytin a) were present in the samples. Model studies with cultured algae showed a similar behaviour.It is concluded that the proportion of chl a to T-chl a and the occurrence of chlorophyll derivatives in phytoplankton samples can give valuable information on the stage of development of the algal populations involved.     

Annual microplankton cycles in Villefranche Bay, Ligurian Sea, NW Mediterranean

Abundance and composition of microplankton were studied overa period of 2 years at two depths in Villefranche Bay (LigurianSea, NW Mediterranean Sea). Diatoms dominated the microplanktonin late spring and autumn, whereas dinoflagellates composedthe major part of the microplankton in summer. The silicoflagellateDictyocha fibula and the diatom Thalassionema frauenfeldii dominatedin winter. Ciliates showed low variability throughout the yearwith the lowest abundance in February and an increase whichcoincided with the diatom maxima during autumn in both years.In 1998, the spring bloom (in May) was mainly composed of dinoflagellatesnear the surface and of diatoms in deeper layers. Subsurfacediatom maxima were observed in August–September and November.In 1999, diatoms peaked in May both at the surface and at thedepth of 50 m. They showed a strong maximum in October. Dinoflagellatesand tintinnids showed maxima in early November. Comparisonswith previous studies reveal that (i) changes in species compositionhave not been significant, (ii) the silicoflagellate’sabundance is lower during the present study, (iii) the sequentialspring bloom is composed of a pico-nanoplankton bloom in Marchand microphytoplankton in May, whereas in other western Mediterraneanareas the spring microphytoplankton bloom is reported in Februaryand March, (iv) high water transport through the Corsica channelcoinciding with low or negative winter values of North AtlanticOscillation (NAO) index are associated with the anomalous strongdevelopment of the spring diatom blooms in the Bay of Villefranche,whereas the usual trend is the lack of or weak development ofthe spring diatom bloom. This feature may determine the natureand the fate of primary production and the interannual variabilityin the relative importance of the microbial food web versusthe microbial loop.     

Controls on the initiation and development of blooms of the dinoflagellate Cochlodinium polykrikoides Margalef in lower Chesapeake Bay and its tributaries

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.     

Seasonality of North Atlantic phytoplankton from space: impact of environmental forcing on a changing phenology (1998–2012)

Seasonal pulses of phytoplankton drive seasonal cycles of carbon fixation and particle sedimentation, and might condition recruitment success in many exploited species. Taking advantage of long‐term series of remotely sensed chlorophyll a (1998–2012), we analyzed changes in phytoplankton seasonality in the North Atlantic Ocean. Phytoplankton phenology was analyzed based on a probabilistic characterization of bloom incidence. This approach allowed us to detect changes in the prevalence of different seasonal cycles and, at the same time, to estimate bloom timing and magnitude taking into account uncertainty in bloom detection. Deviations between different sensors stressed the importance of a prolonged overlap between successive missions to ensure a correct assessment of phenological changes, as well as the advantage of semi‐analytical chlorophyll algorithms over empirical ones to reduce biases. Earlier and more intense blooms were detected in the subpolar Atlantic, while advanced blooms of less magnitude were common in the Subtropical gyre. In the temperate North Atlantic, spring blooms advanced their timing and decreased in magnitude, whereas fall blooms delayed and increased their intensity. At the same time, the prevalence of locations with a single autumn/winter bloom or with a bimodal seasonal cycle increased, in consonance with a poleward expansion of subtropical conditions. Changes in bloom timing and magnitude presented a clear signature of environmental factors, especially wind forcing, although changes on incident photosynthetically active radiation and sea surface temperature were also important depending on latitude. Trends in bloom magnitude matched changes in mean chlorophyll a during the study period, suggesting that seasonal peaks drive long‐term trends in chlorophyll a concentration. Our results link changes in North Atlantic climate with recent trends in the phenology of phytoplankton, suggesting an intensification of these impacts in the near future.     

A Phaeocystis globosa bloom associated with upwelling in the subtropical South Atlantic Bight

We observed an unusual, subtropical bloom of Phaeocystis globosaScherffel during a strong upwelling event and confirmed itsidentity using morphological, physiological and genetic traits.This low-latitude bloom of P. globosa colonies occurred on theSouth Atlantic Bight continental shelf during the summer of2003. Maximum chlorophyll a concentration measured during thissubsurface bloom was 11.37 µg L^–1 at 31 m depth.Divers reported abundant flocculent material below the steepthermocline, and this material was identified as Phaeocystissp. using microscopy. Using morphological and physiologicaltraits as well as the sequence of the 18S small subunit ribosomalRNA gene (GenBank Accession # EF100712), this phytoplanktonwas identified as P. globosa. Interactions of physical and biologicalconditions may restrict low-latitude P. globosa blooms to strongupwelling events.     

Resolving the complex relationship between harmful algal blooms and environmental factors in the coastal waters adjacent to the Changjiang River estuary

The sea area adjacent to the Changjiang River estuary is the most notable region for harmful algal blooms (HABs¹) in China as both diatom and dinoflagellate blooms have been recorded in this region. Affected by the Changjiang diluted water (CDW²) and currents from the open ocean (i.e., Taiwan warm current, TWC³), the environmental conditions in the coastal waters adjacent to the Changjiang River estuary are quite complex. To obtain a better understanding of the mechanisms of HABs in this region, analyses based on field investigation data collected by the National Basic Research Priority Program (CEOHAB I⁴) were performed using principle component analysis (PCA⁵), multiple regression analysis (MRA⁶) and path analysis (PA⁷). The results suggested that phosphate and silicate are the major factors that directly affect the diatom bloom, while dissolved inorganic nitrogen (DIN⁸), temperature and turbidity are the factors that influence the dinoflagellate bloom. CDW and the TWC have different roles in affecting the two types of algal blooms. CDW, which has a high concentration of nitrate and silicate, is essential for the diatom bloom, while the intrusion of the TWC (mainly Kuroshio subsurface water that is rich in phosphate at the bottom) is critical for the maintenance of the dinoflagellate bloom. The results of this study offer a better understanding of the mechanisms of HABs in the East China Sea.     

Satellite detection of harmful algal bloom occurrences in Korean waters

Cochlodinium polykrikoides (p) is a planktonic dinoflagellate known to produce red tides responsible for massive fish kills and thereby serious economic loss in Korean coastal waters, particularly during summer and fall seasons. The present study involved analyzing chlorophyll-a (Chl-a) from SeaWiFS ocean color imagery collected over the period 1998–2002 to understand the spatial and temporal aspects of C. polykrikoides blooms that occurred in the enclosed and semi-enclosed bays of the Korean Southeast Sea. NOAA-AVHRR data were used to derive Sea Surface Temperature (SST) to elucidate physical factors affecting the spatial distribution and abundance of C. polykrikoides blooms. The time series of SeaWiFS-derived Chl-a gave an impression that recent red tide events with higher concentrations appeared to span more than 8 weeks during summer and fall seasons and were widespread in most of the Korean Southeast Sea coastal bays and neighboring oceanic waters. Coupled eutrophication and certain oceanic processes were thought to give rise to the formation of massive C. polykrikoides blooms with cell abundances ranging from 1000 to 30,000 cells ml⁻¹, causing heavy mortalities of aquaculture fish and other marine organisms in these areas. Our analysis indicated that Chl-a estimates from SeaWiFS ocean color imagery appeared to be useful in demarcating the locality, spatial extent and distribution of these blooms, but unique identification of C. polykrikoides from non-bloom and sediment dominated waters remains unsuccessful with this data alone. Thus, the classical spectral enhancement and classification techniques such as Forward Principal Component Analysis (FPCA) and Minimum Spectral Distance (MSD) to uniquely identify and better understand C. polykrikoides blooms characteristics from other optical water types were attempted on both low spatial resolution SeaWiFS ocean color imagery and high spatial resolution Landsat-7 ETM+ imagery. Application of these techniques could capture intricate and striking patterns of C. polykrikoides blooms from surrounding non-bloom and sediment dominated waters, providing improved capability of detecting, predicting and monitoring C. polykrikoides bloom in such optically complex waters. The result obtained from MSD classification showed that retrieval of C. polykrikoides bloom from the mixed phase of this bloom with turbid waters was not feasible with the SeaWiFS ocean color imagery, but feasible with Landsat-7 ETM+ imagery that provided more accurate and comparable spatial C. polykrikoides patterns consistent with in situ observations. The dense phase of the bloom estimated from these imageries occupied an area of more than 25 km² around the coastal bays and the mixed phase extended over several hundreds kilometers towards the Southeast Sea offshore due to exchange of water masses caused by coastal and oceanic processes. Sea surface temperature analyzed from AVHRR infrared data captured the northeastward flow of Tsushima Warm Current (TWC) waters that provided favorable environmental conditions for the rapid growth and subsequent southward initiation of C. polykrikoides blooms in hydrodynamically active regions in the Korean Southeast Sea offshore.     

Grazing impact of microzooplankton on a diatom bloom in a mesocosm as estimated by pigment-specific dilution technique

To investigate the impact of microzooplankton grazing on phytoplankton bloom in coastal waters, an enclosure experiment was conducted in Saanich Inlet, Canada during the summer of 1996. Daily changes in the microzooplankton grazing rate on each phytoplankton group were investigated with the growth rates of each phytoplankton group from the beginning toward the end of bloom using the dilution technique with high-performance liquid chromatography (HPLC). On Day 1 when nitrate and iron were artificially added, chlorophyll a concentration was relatively low (4.3 μg l⁻¹) and 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes were predominant in the chlorophyll biomass. However, both the synthetic rates and concentrations of 19′-hexanoyloxyfucoxanthin declined before bloom, suggesting that 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes weakened. Chlorophyll a concentration peaked at 23 μg l⁻¹ on Day 4 and the bloom consisted of the small chain-forming diatoms Chaetoceros spp. (4 μm in cell diameter). Diatoms were secondary constituents in the chlorophyll biomass at the beginning of the experiment, and the growth rates of diatoms (fucoxanthin) were consistently high (>0.5 d⁻¹) until Day 3. Microzooplankton grazing rates on each phytoplankton group remarkably increased except on alloxanthin-containing cryptophytes after the nutrient enrichments, and peaked with >0.6 d⁻¹ on Day 3, indicating that >45% of the standing stock of each phytoplankton group was removed per day. Both the growth and mortality rates of alloxanthin-containing cryptophytes were relatively high (>1 and >0.5 d⁻¹, respectively) until the bloom, suggesting that a homeostatic mechanism might exist between predators and their prey. Overall, microzooplankton grazing showed a rapid response to the increase in phytoplankton abundance after the nutrient enrichments, and affected the magnitude of the bloom significantly. High grazing activity of microzooplankton contributed to an increase in the abundance of heterotrophic dinoflagellates with 7-24 μm in cell size, the fraction of large-sized (>10 μm) chlorophyll a, and stimulated the growth of larger-sized ciliates after the bloom.     

Chitosan as a Biomaterial: Influence of Degree of Deacetylation on Its Physiochemical,Material and Biological Properties

Chitosan is a biomaterial with a range of current and potential biomedical applications. Manipulation of chitosan degree of deacetylation (DDA) to achieve specific properties appears feasible, but studies investigating its influence on properties are often contradictory. With a view to the potential of chitosan in the regeneration of nerve tissue, the influence of DDA on the growth and health of olfactory ensheathing cells (OECs) was investigated. There was a linear increase in OEC proliferation as the DDA increased from 72 to 85%. This correlated with linear increases in average surface roughness (0.62 to 0.78 μm) and crystallinity (4.3 to 10.1%) of the chitosan films. Mitochondrial activity and membrane integrity of OECs was significantly different for OECs cultivated on chitosan with DDAs below 75%, while those on films with DDAs up to 85% were similar to cells in asynchronous growth. Apoptotic indices and cell cycle analysis also suggested that chitosan films with DDAs below 75% were cytocompatible but induced cellular stress, while OECs grown on films fabricated from chitosan with DDAs above 75% showed no significant differences compared to those in asynchronous growth. Tensile strength and elongation to break varied with DDA from 32.3 to 45.3 MPa and 3.6 to 7.1% respectively. DDA had no significant influence on abiotic and biotic degradation profiles of the chitosan films which showed approximately 8 and 20% weight loss respectively. Finally, perceived patterns in property changes are subject to change based on potential variations in DDA analysis. NMR examination of the chitosan samples here revealed significant differences depending upon which peaks were selected for integration; 6 to 13% in DDA values within individual samples. Furthermore, differences between DDA values determined here and those reported by the commercial suppliers were significant and this may also be a source of concern when selecting commercial chitosans for biomaterial research.     

Dynamics of bacterial community composition and activity during a mesocosm diatom bloom

Bacterial community composition, enzymatic activities, and carbon dynamics were examined during diatom blooms in four 200-liter laboratory seawater mesocosms. The objective was to determine whether the dramatic shifts in growth rates and ectoenzyme activities, which are commonly observed during the course of phytoplankton blooms and their subsequent demise, could result from shifts in bacterial community composition. Nutrient enrichment of metazoan-free seawater resulted in diatom blooms dominated by a Thalassiosira sp., which peaked 9 days after enrichment ( approximately 24 microg of chlorophyll a liter(-1)). At this time bacterial abundance abruptly decreased from 2.8 x 10(6) to 0.75 x 10(6) ml(-1), and an analysis of bacterial community composition, by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments, revealed the disappearance of three dominant phylotypes. Increased viral and flagellate abundances suggested that both lysis and grazing could have played a role in the observed phylotype-specific mortality. Subsequently, new phylotypes appeared and bacterial production, abundance, and enzyme activities shifted from being predominantly associated with the <1.0-microm size fraction towards the >1.0-microm size fraction, indicating a pronounced microbial colonization of particles. Sequencing of DGGE bands suggested that the observed rapid and extensive colonization of particulate matter was mainly by specialized alpha-Proteobacteria- and Cytophagales-related phylotypes. These particle-associated bacteria had high growth rates as well as high cell-specific aminopeptidase, beta-glucosidase, and lipase activities. Rate measurements as well as bacterial population dynamics were almost identical among the mesocosms indicating that the observed bacterial community dynamics were systematic and repeatable responses to the manipulated conditions.