Dynamics of Two Picophytoplankton Groups in Mediterranean Sea: Analysis of the Deep Chlorophyll Maximum by a Stochastic Advection-Reaction-Diffusion Model

A stochastic advection-reaction-diffusion model with terms of multiplicative white Gaussian noise, valid for weakly mixed waters, is studied to obtain the vertical stationary spatial distributions of two groups of picophytoplankton, i.e., picoeukaryotes and Prochlorococcus, which account about for 60% of total chlorophyll on average in Mediterranean Sea. By numerically solving the equations of the model, we analyze the one-dimensional spatio-temporal dynamics of the total picophytoplankton biomass and nutrient concentration along the water column at different depths. In particular, we integrate the equations over a time interval long enough, obtaining the steady spatial distributions for the cell concentrations of the two picophytoplankton groups. The results are converted into chlorophyll a and divinil chlorophyll a concentrations and compared with experimental data collected in two different sites of the Sicily Channel (southern Mediterranean Sea). The comparison shows that real distributions are well reproduced by theoretical profiles. Specifically, position, shape and magnitude of the theoretical deep chlorophyll maximum exhibit a good agreement with the experimental values.     

Influence of Light Intensity on Sorbitol Metabolism, Growth, and Chlorophyll Content of Malus Tissue Cultures

Apple stem callus cultures of Malus pumila Mill., cultivars,McIntosh and Cortland, and of Malus robusta Rehd. No. 5 weregrown under light intensities of o, 850, 3350, and 7800 lx ona medium with sorbitol as the carbon source. Cortland callusgrew better in dark whereas growth of Robusta was not influencedby light. Light did not influence growth of McIntosh callusbetween o and 3350 lx, although slight stimulation in growthoccurred at 7800 lx. The chlorophyll content of the culturesincreased with light intensity, although that of Cortland wasvery low at all intensities. Tissue analysis of cultures grownin light at 7800 lx and in dark indicated that the growth ofthese callus tissues as influenced by light was directly relatedto their sorbitol and carbohydrate content. McIntosh and Cortlandshowed opposite trends in the levels of starch, sorbitol, sucrose,glucose, and total carbohydrate in light and dark. Similar tothe growth response of Robusta, the levels of these carbohydratesin this callus were apparently not influenced by light. Sucrose,accumulating in concentrations of between 45 and 62 per centof total carbohydrate, tended to be the predominant carbohydrateconstituent in both light- and dark-grown cultures.     

Thermocline Regulated Seasonal Evolution of Surface Chlorophyll in the Gulf of Aden

The Gulf of Aden, although subject to seasonally reversing monsoonal winds, has been previously reported as an oligotrophic basin during summer, with elevated chlorophyll concentrations only occurring during winter due to convective mixing. However, the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) ocean color data reveal that the Gulf of Aden also exhibits a prominent summer chlorophyll bloom and sustains elevated chlorophyll concentrations throughout the fall, and is a biophysical province distinct from the adjacent Arabian Sea. Climatological hydrographic data suggest that the thermocline, hence the nutricline, in the entire gulf is markedly shoaled by the southwest monsoon during summer and fall. Under this condition, cyclonic eddies in the gulf can effectively pump deep nutrients to the surface layer and lead to the chlorophyll bloom in late summer, and, after the transition to the northeast monsoon in fall, coastal upwelling driven by the northeasterly winds produces a pronounced increase in surface chlorophyll concentrations along the Somali coast.     

The Formation and Dynamics of Deep Bacteriochlorophyll Maximum in the Temperate and Partly Meromictic Lake Verevi

Vertical distribution of phytoplankton and the formation of deep chlorophyll maximum (DCM) in the metalimnion of a small stratified and partly meromictic temperate lake was studied in 1999 and 2000. During summer DCM usually occurred on the borderline of H₂S and oxygen-containing waters. At the depths where the bacteriochlorophyll (Bchl) maxima were observed, the sulphide concentration was usually relatively low compared to the bottom layers, where its concentration reached as high as possible saturation level. In April 2000, DCM was formed at the depth of 3.5 m, and lowered thereafter slowly to 6.5 m by October. The concentration of Bchl d reached the highest values (over 1000 μg l⁻¹) just before the water column was mixed up in autumn. In December and April Bchl d was detectable only near the bottom of the lake. The concentration of chlorophyll a yielded by the spectrophotometric phaeopigment corrected method and by HPLC (high pressure liquid chromatography), fit rather well in the upper layers. In deeper water layers chlorophyll a concentration (Chl a) measured by spectrophotometry was overestimated about 47 times if compared to HPLC values because of the high Bchl d in that layer. In most cases vertical profiles of primary production (PP) did not coincide with the vertical distribution of the pigment content; the maximum values of PP were found in the epilimnion. In some cases PP had notably high values also at the depth of DCM. In the upper layers Chl a usually did not exceeded 20 μg l⁻¹ in spring and 10 μg l⁻¹ in summer_. The moderately high Chl a in the epilimnion in spring was significantly reduced after the formation of thermocline most probably because of the establishment of the nutrient limitation in epilimnion. Decreasing Chl a concentration in the epilimnion led to increased water transparency and better light conditions for photosynthetic bacteria in metalimnion.     

蒙古栎和紫椴幼苗对光环境转变的光合作用响应

比较研究了从温室5%光强转到10%、30%和100%光强处理下,蒙古栎（Quercus mongolica）和紫椴（Tilia amurensis）幼苗的光合能力和叶绿素荧光的响应,揭示了两个树种对光环境变化的不同适应情况及其光保护机制。结果表明,光强转换后两种幼苗都发生了严重光抑制,蒙古栎幼苗的最大光化学效率（F_v/F_m）在光强转变后第3天降到最低（0.52）,紫椴幼苗在光强转变后第1天就降到了最低（0.67）,蒙古栎降低幅度明显高于紫椴。之后随着光适应时间的延长逐渐恢复到原有水平,说明短时期的光抑制没有对两种幼苗的光合机构造成光损伤;从不同光照条件来看,无论是最大净光合速率（P_max）,还是实际光化学效率（ФPSⅡ）,2种幼苗均为30%光强下的值高于10%和100%光强,说明过低或过高的光强都不利于幼苗的生长发育,只有适当的中光才利于幼苗的生长发育;与30%光强相比,蒙古栎幼苗100%光强下P_max、F_v/F_m、ФPSⅡ、NPQ的变化幅度远大于紫椴幼苗,表明高光强对蒙古栎幼苗的影响要大于紫椴;100%光强下,2种幼苗均通过大量增加非光化学淬灭（NPQ）、类胡萝卜素和叶绿素之比（Car/Chl）耗散过剩光能,降低单位鲜重叶绿素含量（Chl）以减少光能吸收,避免了光合机构光破坏。     

Potentially toxic and harmful microalgae from coastal waters of the Campania region (Tyrrhenian Sea, Mediterranean Sea)

A total number of 40 potentially toxic microalgae and 5 taxa causing discolorations have been identified along the coasts of the Campania region (South Tyrrhenian Sea, Mediterranean Sea). This number is based on results of over 20 years of research at a coastal station in the Gulf of Naples, 4 years of monitoring activity along the Campania coasts and of a series of scattered and sporadic observations. Several species of the recently erected genera Karenia and Takayama are reported for the first time in the area. Information on the period of highest abundances or most probable period of occurrence indicates the late spring and summer as the periods of maximum risk of harmful events. Despite the variety of potentially toxic species, no human health problems nor fish kills have ever been recorded in Campania. The reasons for this apparent paradox are probably to be found in the ecological factors that regulate the abundance, toxicity and spatial distribution of the potentially harmful species and reflect as well the relatively low number of aquaculture plants in the area.     

Evaluation of the Effect of Light Intensity on the Measurement of the Photosynthetic Rate in Plankton Microalgae by the Chlorophyll Fluorescence Method

The use of relative variable fluorescence (RVF) of chlorophyll, as measured in the presence of Diuron, an inhibitor of electron transfer, for the estimation of the photosynthetic activity of plankton microalgae was analyzed under a wide range of light intensities in the PAR region. Oxygen evolution rates (estimated by the method of light and dark bottles and the amperometric method), RVF, and chlorophyll a concentration were measured in parallel in natural algal cenoses and microecosystems. When the previously used regression equation, in the form A = b(F/F_d)C_chlI, where A is O₂ evolution rate (g/(m³ h), F/F_d is RVF (relative units), C_chl is chlorophyll a concentration (mg/m³), and I is light intensity (W/m²), was verified in the PAR region, we observed a nonlinear dependence of the correction coefficient b on I, which can be described by the formula b = 6.227 × 10³I. This result agrees with the hypothesis that chlorophyll a fluorescence quenching comprises photochemical (qQ) and energy (qE) components. On the basis of the energy model, we determined the upper limit b_max = 0.003 for light intensity range I< 4.4 W/m² and the lower limit b_min = 0.0003 for I = 400 W/m².     

Influence of Constant Light and Darkness,Light Intensity,and Light Spectrum on Plasma Melatonin Rhythms in Senegal Sole

Light is the most important synchronizer of melatonin rhythms in fish. This paper studies the influence of the characteristics of light on plasma melatonin rhythms in sole. The results revealed that under long‐term exposure to constant light conditions (LL or DD), the total 24 h melatonin production was significantly higher than under LD, but LL and DD conditions influenced the rhythms differently. Under LL, melatonin remained at around 224 pg/ml throughout the 24 h, while under DD a significant elevation (363.6 pg/ml) was observed around the subjective evening. Exposure to 1 h light pulses at MD (mid‐dark) inhibited melatonin production depending on light intensity (3.3, 5.3, 10.3, and 51.9 µW/cm²). The light threshold required to reduce nocturnal plasma melatonin to ML (mid‐light) values was 5.3 µW/cm². Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (λ>600 nm) failed to reduce plasma melatonin significantly, far violet light (λ_max=368 nm) decreased indoleamine's concentration to ML values. These results suggest that dim light at night (e.g., moonlight) may be perceived and hence affect melatonin rhythms, encouraging synchronization to the lunar cycle. On the other hand, deep red light does not seem to inhibit nocturnal melatonin production, and so it may be used safely during sampling at night.     

Feeding ecology of Mediterranean razorfish Xyrichthys novacula in the Tyrrhenian Sea (Central Mediterranean Sea)

The stomach contents of 196 razorfish ( Xyrichthys novacula ), collected in the Tyrrhenian Sea (Ponza Island, Italy) between July and December 1994, were examined in order to assess the diet and to analyse size-related dietary variation of the species. The diet of X. novacula showed a strict relationship with well-sorted fine sand (SFBC) benthic species, mostly Mollusca and Echinodermata, as pointed out by the analysis at the specific level of the stomach contents. Mollusca Pelecipoda, essentially Acanthocardium tuberculatum and Echinodermata, with Echinocardium cordatum , made up 90% of the volume of prey of X. novacula. Mysidacea and Gastropoda were frequent but volumetrically less important. The study showed that male and female X. novacula were not effectively segregated by trophic dimension in the study area. The niche overlap between males and females in prey composition was pronounced, as evidenced by the significantly high values of Schoener's index with larger males that showed a greater tendency towards predation of large prey. The increment in length (L.I.) in males, despite a decrease in the percentage body weight increment (B.W.I.), could represent the result of a male reproductive feature: the lack of sperm competition allows the males much more energy to devote to growth than do that of the females of this species.     

Annual trend of fish assemblages associated with FADs in the southern Tyrrhenian Sea

A study on fish assemblage associated with fish aggregating devices (FADs) in Sicily was carried out between January 2000 and January 2001. With a fortnightly periodicity, 156 experimental hauls were carried out by means of a purse seine in a FAD‐containing marine section banned to commercial fishing. A total of 14 229 fish specimens belonging to six families and 10 species was found. These species were Balistes carolinensis, Caranx crysos, Naucrates ductor, Seriola dumerili, Seriola fasciata, Tachurus picturatus, Coryphaena hippurus, Schedophilus ovalis, Thunnus thynnus, Polyprion americanus and showed all young‐of‐the‐year undergoing a rapid growth. The applied ordination technique highlighted the existence of four assemblage periods describing the annual trend. The results confirm that fish assemblages associated with FADs are related to season, following a fish colonization tied to natural recruitment. Comparison of the ecological indices across the four periods showed that the assemblages in the periods from summer to winter were more structured than those in spring. The quantity of individuals also showed a strong variation peaking in the summer period. The results of this study reveal that FADs represent a particular nursery area for the associated species that could influence their survival.     

Effect of Light Intensity on Growth, CO2 Fixation, and Chlorophyll and Polar Lipid Production in Germinating Polytrichum commune Spores

The dry matter production in Polytrichum commune protonemata was increased when the light intensity was increased from 0 to 160 μE m^?2 s^?1, and at 160 μE m^?2 s^?1 production was about 200% of that found at 17 μE m^?2 s^?1. Production of chlorophyll (Chl) was increased by increasing light intensity from 0 to 17 μE m^?2 s^?1, but decreasing at light intensities above 17 μE m^?2 s^?1. At 160 μE m^?2 s^?1 the production of Chl was only about 50% of that at 17 μE m^?2 s^?1. The rate of CO₂ fixation was low (0.31 μg CO₂/mg Chi × h) at the light intensity of 17 μE m^?2 s^?1 as compared with that at 160 μE m^?2 s^?1 (0.83 μg CO₂/mg Chi × h). Production of mono- (MGDG) and diglycosyl diglycerides (DGDG) was closely associated with that of chlorophylls. At the higher light intensity (160 μE m^?2 s^?1) production of glycolipids was about 60% of that at 17 μE m^?2 s^?1. Production of more polar lipids was less affected by light intensity. Light intensity also affected the fatty acid pattern of the lipid fractions. The effect was most pronounced in the MGDG fraction, where the proportion of C 18: 3ω3 + C 16: 3ω3 was higher at the higher light intensity.     

Relationships between Photosynthesis and Light Intensity in the Tomato

Curves were fitted to the rates of CO₂ uptake (P) of singleleaves of tomato against light intensity (I). It was shown thatan asymptotic curve of the form P = a–bp^I gave a consistentlybetter fit to the observed data than the rectangular hyperbola.Saturating rates of photosynthesis, estimated as the asymptoteof the curve, showed marked changes with leaf age, being maximalat or shortly after the start of the experiment, in small rapidlyexpanding leaves, and falling continuously thereafter. Photochemicalefficiency, measured as the slope of the curve at zero lightintensity, gave no discernable trends with time except in visiblysenescent leaves, when the value decreased appreciably.     

Petal Abscission in Rose Flowers: Effects of Water Potential, Light Intensity and Light Quality

Petal abscission was studied in roses (Rosa hybrida L.), cvs.Korflapei (trade name Frisco), Sweet Promise (Sonia) and CaraMia (trade name as officially registered cultivar name). Unlikeflowers on plants in greenhouses, cut flowers placed in waterin the greenhouse produced visible symptoms of water stress,depending on the weather during the experiment and on the cultivar.Cut Frisco roses showed no visible signs of water stress andthe time to petal abscission was as in uncut flowers. In Soniaroses the symptoms of water stress varied from mild to severe,and the number of flowers in which the petals abscised variedfrom 100% (mild stress) to 0% (severe stress). An antimicrobialcompound in the vase water of Sonia roses, or removal of theleaves, alleviated the symptoms of water stress and increasedthe number of stems in which the petals abscised. Cut Cara Miaroses showed severe symptoms of water stress in all experimentsand petal abscission was found in only a few flowers, even whenthe stems were placed at 20 °C and low photon flux (15 µmolm^-2s^-1). Abscission in Sonia and Cara Mia roses was low or absentwhen the water potential of the leaves reached values below-2.0 MPa within the first 5 d of the experiment; such low valueswere not reached in Frisco roses. Addition of sucrose to the vase solution, together with an effectiveantimicrobial compound, had no effect on the time to petal abscission,at any light intensity. Placing flowers in far-red light alsohad no effect on abscission, compared with flowers placed inred light or white light of the same photon fluence. It is concluded that petal abscission in the rose cultivarsstudied is not affected by their water status unless the plantsreach a low water potential (about -2 MPa) early on during vaselife. Petal abscission is not inhibited by low light intensitynor affected by the Pr/Pfr ratio. Abscission; light intensity; petals; phytochrome; Rosa hybrida L.; rose; sugars; water potential     

Microbial Diversity at a Hot,Shallow-Sea Hydrothermal Vent in the Southern Tyrrhenian Sea (Italy)

Microbial community thriving at shallow hydrothermal vent named Black Point, close to the Island of Panarea in the Southern Tyrrhenian Sea (Italy), was studied by microscopic, cultural and molecular methods. New strains of Bacillus and Geobacillus were isolated. Members of sulphur-oxidizing bacteria, belonging to the genera Halothiobacillus and Thiomicrospira were demonstrated by both culture-dependent and -independent methods. Genetic diversity of Bacteria was higher than that of Archaea. Bacterial 16S rRNA gene sequences from Black Point showed low levels of similarity with other yet deposited sequences, suggesting that new bacterial phylotypes are present in this site. Dominant populations of Bacteria belonged to uncultured members of Proteobacteria (mainly of the class Gammaproteobacteria), Firmicutes and Acidobacteriaceae. Primary production appeared to be supported by chemosynthetic and photosynthetic bacteria affiliated with members of Gammaproteobacteria. Most of the archaeal sequences matched those of yet-uncultivated Archaea, thus their role at this vent is not well understood.     

The Light Induced Protochlorophyll–Chlorophyll a-Transformation and the Succeeding Interconversions of the Different Forms of Chlorophyll

Curve resolution into Gaussian components of the absorption spectra during the varying stages of the Shibata shift in dark grown, irradiated leaves of barley indicates that the chlorophyll a forms formed after irradiation consist of the same main components which have been reported to be present in all hitherto investigated plant materials (peak values in the red region 662, 670, 677 and 683 nm, respectively) but in varying proportions. The spectra during the Shibata shift proper can be satisfied by a mixture of two single components gradually changing their proportions, although a four component system gives a still better fit to the measured absorption curves. It is also shown that curves taken before and after the shift and added together in the appropriate proportions will match the absorption spectrum measured with peak at the isosbestic point (after ca. 15 min at room temperature).     

Light Gradients and the Transverse Distribution of Chlorophyll Fluorescence in Mangrove andCamelliaLeaves

The light gradient and transverse distribution of chlorophyllfluorescence in mangrove andCamellialeaves, which have differentmorphological characteristics, were examined using a micro-fluorescenceimaging system reported previously (Takahashiet al., Plant,Cell and Environment17: 105–110, 1994). Epidermal cellsscattered light strongly, resulting in an increase in the fluencerate in epidermal cells. For theCamellialeaf, a light gradientwas formed by absorption of light by photosynthetic pigmentsassociated with the induction of chlorophyll fluorescence. Forthe mangrove leaf, a light gradient was formed by backward scatteredlight within a thick layer of non-assimilatory cells. Lightwith a low absorption coefficient (515 nm) penetrated deeperthan that with a higher absorption coefficient (477 nm and 488nm) in theCamellialeaf, while light of both wavelengths showedsimilar profiles in the mangrove leaf. In the mangrove leaves,scattered light declined significantly in the non-assimilatorycell layer which is in front of the assimilatory cells. Light,the intensity of which was reduced to approx. 10% of the maximum,was well scattered and induced a considerable amount of chlorophyllfluorescence in the assimilatory cells, which appear to be wellorganized to capture weak light.Copyright 1998 Annals of BotanyCompany fluorescence, intact leaf, light gradient, mangrove (Rhizophora mucronataLamk.),Camellia japonicaL.     

Distribution of recent foraminiferal assemblages near the Ombrone River mouth (Northern Tyrrhenian Sea, Italy)

Benthic foraminiferal assemblages in 127 samples, collected at water depth, ranging between 15 and 184 m on the Southern Tuscany continental shelf off the Ombrone River were analysed. Statistical analyses (Cluster and Principal Component Analysis) performed on the 48 most abundant species (>5%) and sedimentological data led to the identification of three clusters related to the size of grain sediment (sand, silt or clay). Q-mode cluster analysis singled out six groups, corresponding to six distinct foraminiferal assemblages: a typical infralittoral assemblage (15-39 m) on sandy silt, clayey silt or silty clay, dominated by Ammonia and Elphidium species, with Eggerelloides scabrus, Rectuvigerina phlegeri and Valvulineria bradyana; a second assemblage (24-78.5 m) associated with vegetated environments or sandy bottoms (Elphidium crispum, Rosalina bradyi, Asterigerinata mamilla, Neoconorbina terquemi, and Tretomphalus concinnus); a third assemblage recognised between 30 and 90 m water depth and characterised by the dominance of the opportunistic species V. bradyana (related to silty bottoms), with Bulimina marginata, R. phlegeri, Ammonia inflata and Ammonia beccarii as other common taxa; an upper circalittoral assemblage (70-100 m) on silty clays, containing B. marginata, Cassidulina carinata and V. bradyana; a lower circalittoral assemblage (95-177 m) on clayey bottoms, with B. marginata, Textularia bocki and Uvigerina mediterranea; and finally, a second lower circalittoral assemblage (104-184 m) on clayey sediments, dominated by two Uvigerina species (U. mediterranea and Uvigerina peregrina), with Sphaeroidina bulloides and B. marginata. The typical V. bradyana assemblage, characterised by relatively low diversity and high dominance, marks the most eutrophicated area running parallel to the coast. The spatial distribution of assemblages is closely associated with sea-bottom sedimentary environments and bathymetry but it is also probably influenced by the outflow of the Ombrone River. The composition, structure and distribution of V. bradyana assemblage suggest an environmental model, useful for paleogeographic reconstruction in areas characterised by a river mouth and a closed morphological setting typical of a nutrient-trap.     

Occurrence of the scalloped ribbonfish Zu cristatus(Lampridiformes) in coastal waters of the central Tyrrhenian Sea, Italy

The occurrence of two individuals of Zu cristatus at 2 m depth in coastal waters of the Gulf of Castellamare (Tyrrhenian Sea, Italy) together with records of this rare pan‐Oceanic mesopelagic species is reported. Analyses of two mitochondrial genes (12 s and 16 s; 936 bp) revealed a 2·6% sequence divergence between Mediterranean and Pacific (Japanese) samples of the species.