Succession Of Blooms Research Articles

What causes short-term oscillations in ecosystem models of the ocean mixed layer?

An ecosystem model of the oceanic upper mixed layer (UML) that simulates the differences in the annual production cycle observed between the North Atlantic and North Pacific is proposed. It is based on the model of Fasham (1993) modified as follows: (1) the diffusive mixing between the UML and the seasonal pycnocline that is due to internal wave breaking is not included; (2) the nitrate concentration in the seasonal pycnocline is considered to vary with depth rather than be constant; (3) an alternative parameterisation of Zooplankton grazing is used and (4) a number of model parameters are assigned other values. The modelled and observed ecosystem characteristics at Ocean Weather Stations (OWS) I and P are in satisfactory agreement with each other. The model solution obtained shows different regimes of seasonal variability: a periodic regime having a simple annual oscillation and a so-called biharmonic regime that also has oscillations with a period of order one month. The latter oscillations are of interest in that there are observational data showing a succession of phytoplankton blooms at OWS I, although the data are not of sufficient quality to show that the mechanisms causing the oscillations in the model are the same as those producing the oscillations in the data. A qualitative mathematical analysis of the model equations with stationary forcing shows that in the case of entrainment the sole equilibrium solution with non-zero concentrations of all of seven ecosystem components exists, while in the case of detrainment no such solution exists. Analysis of the system of the equations linearised in the vicinity of the former equilibrium state shows it to be stable or unstable and usually corresponds to monotonic changes or damped oscillations at periodic forcing. The model short-term oscillations are connected with feedbacks in the ecosystem initiated by either abrupt changes of the UML thickness in spring or strong deepening of the UML in autumn. A necessary condition of their existence is a combination of intense photosynthetically active radiation, small thickness of the UML, significant mean annual entrainment velocity and a high nitrogen concentration in the seasonal pycnocline. Such combinations are uncommon in the world ocean and this is the reason why such oscillations of the UML ecosystem are only to be expected in some regions.

Review of gross community production, primary production, net community production and dark community respiration in the Gulf of Lions

Thirty years of data were used to examine the influence of the Rhoˆne River discharge on the spatio-temporal distribution of primary production in the Gulf of Lions. These patterns are characterised for four hydrological provinces: (i) the Gulf of Marseilles, a coastal oligotrophic system exhibiting a typical diatom-based bloom succession; (ii) the mouth and plume of the Rhoˆne River, containing high levels of nutrients, constant levels of chlorophyll a, and a plankton assemblage dominated by nanoflagellates; (iii) the highly productive dilution area to the west of the Rhoˆne, with a diatom spring bloom and smaller winter diatom blooms; (iv) the southern area encompassing the oligotrophic Liguro-Provençal Current, a frontal zone of constantly high primary production and a divergence area exhibiting a typical spring bloom situation.No evidence of eutrophication due to river input was seen. In situ and in vitro net community production data suggest the Gulf of Lions as a whole is a balanced ecosystem on an annual time scale, with the mean primary production lying between 78 and 142 g C m−2 a−1.

Contrast in Biological Responses to Tidally-induced Vertical Mixing for Two Macrotidal Ecosystems of Western Europe

The dynamics of phytoplankton blooms were studied during spring 1992 in two typical coastal ecosystems of Western Europe, which differ in the influence of river discharges on the vertical stratification of the water column. The Bay of Brest is a semi-enclosed ecosystem, which is connected with the adjacent ocean and entered by two nutrient-rich rivers. The Western English Channel is an open ocean situation and the studied area was remote from any significant riverine influence during spring. Both areas are macrotidal environments and are usually considered as well-mixed. The beginning of the annual diatom bloom is delayed until late May in the Channel, in comparison with the Bay of Brest where the bloom starts by early April. Water column stability induced by freshwater runoff, and local topography are responsible for the earlier start of the phytoplankton bloom in the Bay of Brest. In both areas, the spring period is marked by a succession of diatom blooms which is strongly dependent upon the spring–neap tidal cycle. However, blooms develop under opposite mixing regimes: they occur during neap tides in the Bay of Brest and during spring tides in the Channel. In the Channel where light is not a limiting factor, increased mixing during spring tides enables nutrient replenishment from the water–sediment interface and phytoplankton responds immediately after nutrients have been renewed in the water column. In the more turbid waters of the Bay of Brest, relaxation of vertical mixing during neap tides is required before phytoplankton is able to utilize nutrients originating from freshwater inputs or in situregeneration later in the season.

Zooplankton of tikehau atoll (Tuamotu archipelago) and its relationship to particulate matter

The standing stock and taxonomic composition of zooplankton (>200 μm) were monitored in the lagoon of Tikehau atoll from April 1985 to April 1986. These data were supplemented by two 10 d studies on the variability, structure and functioning of the pelagic ecosystem. The biomass of animals >200 μm comprised 50% of the total biomass of all organisms from 35 to >2000 μm. The zooplankton populations were characterized by successive blooms of copepods, larvaceans, pteropods and salps, probably arising from the periodic input of detritus from the reef during windy periods. As a result, the ecosystem was not in a steady state and the data for the fluxes of organic matter are presented separately for April 1985 and April 1986. Using the C:N:P ratio method, net growth efficiencies, K2, were calculated for total mesozooplankton, mixed copepods, and two planktonic species, Undinula vulgaris and Thalia democratica. Combined with nitrogen and phosphorus excretion rates, these K2 values enabled the assessment of production rates. On a 24 h basis, P:B ratios (%) were close to 100 for the total zooplankton and 54, 34 and 800 for mixed copepods, U. vulgaris and T. democratica, respectively. These ratios are 5.7 times lower than that recorded for phytoplankton. High productivity may be ascribable to the high density of seston, the high temperature (29.5°C), and the kind of organisms present. Zooplankton production equalled 38 and 30% of 14C uptake during April 1985 and April 1986, respectively. Ingestion of animals >35μm was calculated by means of assimilation efficiencies and amounted to 17 and 7% of particulate organic carbon, 100 and 38% of living carbon, and 64 and 140% of primary production during the two periods, respectively. Finally, inorganic exduring was 32 and 18% of phytoplankton nitrogen and phosphorus requirements. A model based on the dimensional structure of the pelagic food-web, has been drawn to illustrate the biomass and carbon, nitrogen and phosphorus fluxes in the study area. The lagoon appears to export part of its planktonic biomass, which is 4.2 times lower one sea mile outside the main pass connecting the lagoon to the open ocean.

Growth and development of Calanus spp. (Copepoda) during spring phytoplankton succession in the North Sea

Experiments were carried out to determine growth and development rates of the herbivorous copepod Calanus finmarchicus (Gunnerus) under natural conditions during the phytoplankton spring bloom in the northern North Sea. From 28 April to 25 May 1983 copepodite stages I, IV and V were incubated for a 3-d period on board a ship in vessels with naturally occurring phytoplankton or cultured algae as food. Highest rates of growth and development were achieved while the diatom Chaetoceros sp. was the dominant phytoplankton organism. These rates decreased considerably when this chain-forming diatom was succeeded after one week by the small-celled diatom Thalassiosira conferta. Again one week later, during the bloom of the succeeding colonial microflagellate Corymbellus aureus, copepodite stage IV still managed to maintain moderate rates of growth and development, but these rates dropped to almost zero in CV, suggesting the start of a resting stage. Nevertheless, brood collected from this generation and from Calanus helgolandicus (Claus) was raised in the laboratory to the adult stage at high speed. Since temperature and the total phytoplankton concentration in the sea remained almost constant it seems that the retardation and arrestment of growth and development were an immediate response to a qualitative change of the food composition related to the successive blooms of different algal species.

SEA ICE MICROBIAL COMMUNITIES. V. THE VERTICAL ZONATION OF DIATOMS IN AN ANTARCTIC FAST ICE COMMUNITY1

ABSTRACTA distinct vertical zonation was observed among diatoms in a bottom congelation ice community at McMurdo Sound, Antarctica during the 1981 spring bloom. The bottom 20 cm of ice collected in December from four stations with variable snow cover was subdivided into 5 cm sections for analysis of algal distribution. Algal abundance was inversely related to the depth of snow cover, and generally decreased with increasing distance above the ice‐water interface. Most diatoms, including the dominant species Nitzschia stellata Manguin, Amphiprora kufferathii Manguin and Fragilaria islandica var. adeliae Manguin showed peak abundance in the bottom 10 cm of the ice, where the proportion of living to empty cells was also highest. Two species, however, an Auricula Castracane sp. and Navicula glaciei van Heurck, reached highest concentrations at depths 10–20 cm above the ice‐water interface. We considered two factors as contributing to the observed vertical zonation: (1) successive blooms at the ice‐water interface become spatially stratified within the ice by further accretion below; (2) a differential growth of species occurs along physicochemical gradients within the ice column. A comparison of early versus late season profiles suggests the latter mechanism may prevail once ice accretion has ceased.

Seasonal periodicity, heterocyst differentiation and sporulation of planktonic Cyanophyceae in a shallow lake, with special reference toAnabaena solitaria

The periodicity of eight species of Cyanophyceae is recorded over two seasons in Sawley Dene, a 9·5 ha lake in North Yorkshire. The succession of blooms of heterocystous forms followed by colonial coccoid species is similar to that found in the epilimnion of many temperate eutrophic lakes that stratify in summer, though the Yorkshire lake is too shallow for thermal or chemical stratification to occur. The periodicity is explained by the long retention time of the lake, variable column stability and summer nitrogen deficiency, conditions that favour the larger self-regulating cyanophytes. Cell degeneration, heterocyst frequencies and akinete differentiation are discussed in relation to nitrate-nitrogen concentrations and population maxima. In the decline phase after a bloom, heterocystous forms show cell degeneration and akinete formation whereas the coccoid forms undergo sinking with little cell degeneration since intact colonies are necessary for overwintering in the sediment. Forty per cent of the akine...

Dynamics of volatile organic compounds during the succession of algal blooms in a eutrophic lake

Dynamics of volatile organic compounds during the succession of algal blooms in a eutrophic lake

Allelopathic interactions among algae

Five species of green algae isolated from the Cleveland County, Oklahoma, area and a commercially obtained yellow-green alga were tested for allelopathic interactions. Axenic cultures ofPandorina morum Bory were stimulated in three sterile filtrates from nonaxenic cultures ofScenedesmus incrassatulus var.mononae G.M. Smith, with the oldest filtrate showing the least stimulation. By measuring the growth of axenic cultures inoculated into sterile filtrates of old cultures, instances of inhibition and stimulation were recorded in three screening experiments.Cosmarium vexatum West filtrate was inhibitory to the five other species, a characteristic probably important in its role of producing waterblooms in ponds and swamps. The allelopathic effects of filtrates of the five other species onBolrydium becherianum Vischer could be a key to its restriction to terrestrial sites. Instances of heat lability of the active substances were noted. These interactions, both allelopathic and stimulatory, probably play a significant role in the succession of algal blooms in nature.

Development of north sea coastal plankton communities in separate plastic bags under identical conditions

In two experiments lasting 4 to 6 weeks, communities of North Sea coastal plankton kept in separate plastic bags (of about 1400 l) and exposed to the same environmental conditions showed very similar patterns of growth and decline. This result means that the method is suitable for the evaluation of toxic effects of environmental pollutants at low concentrations on complex plankton systems. The phytoplankton in the bags produced a succession of blooms, which were probably limited by shortage of nutrients. The dominant zooplankton organisms were various species of copepods which can develop in the bags from egg to adult. Strong indications were found that mineralization of organic matter occurs in the bags. Chemical parameters and phytoplankton biomass were found not to be stratified, indicating that the contents of the bags were well mixed.

Repetitive Flowering from a Single Floral Axis in Camellia1

Abstract An unusual flowering phenomenon has been observed for 4 consecutive years on an unnamed Camellia japonica clone, PI 276119. While many faded blossoms dropped from the plants, others remained firmly attached. The inner portion of the tightly folded center of each persistant faded blossom remained pinkish-white. These centers expanded and were similar to emerging flower buds except they did not have bud scales. Elongation of the old flower axis placed the new bud slightly above the old flower. Following a resting stage of 6 weeks to about 4 months, new blossoms developed on the same axis and directly above the old flowers. During the 1970 season as many as 3 successive blooms were observed one upon the other. The physiological aspects of this phenomenon are contrary to normal flower bud development in camellia. Repetitive flowering from a single floral axis appears to violate the principle of determinate growth of flower buds.

Repetitive Flowering from a Single Floral Axis in Camellia1

Abstract An unusual flowering phenomenon has been observed for 4 consecutive years on an unnamed Camellia japonica clone, PI 276119. While many faded blossoms dropped from the plants, others remained firmly attached. The inner portion of the tightly folded center of each persistant faded blossom remained pinkish-white. These centers expanded and were similar to emerging flower buds except they did not have bud scales. Elongation of the old flower axis placed the new bud slightly above the old flower. Following a resting stage of 6 weeks to about 4 months, new blossoms developed on the same axis and directly above the old flowers. During the 1970 season as many as 3 successive blooms were observed one upon the other. The physiological aspects of this phenomenon are contrary to normal flower bud development in camellia. Repetitive flowering from a single floral axis appears to violate the principle of determinate growth of flower buds.

The Day Lily

MEMBERS of the genus Hemerocallis enjoy an increasing popularity as garden plants. The name signifies ‘beauty for a day’, and is a reliable description for individual flowers. The plant, however, maintains a succession of bloom, and is tolerant of a wide variety of cultural conditions. Mr. G. P. Baker has prepared a short monograph of the genus (J. Boy. Hort. Soc., 62, 9, 399–411, Sept. 1937,). A historical summary traces the early references to Hemerocallis flava from the time of Dioscorides, whilst the modern uses of the plant as medicine and as a flavouring in China, are set forth. Detailed descriptions of fourteen species and their variants impart much knowledge for the gardener.

A Film of the Royal Botanic Gardens, Kew

A PRIVATE view of a new ‘documentary’ film of the Royal Botanic Gardens, Kew, was given to a number of men of science in London on April 14. The film, which was made by Short Film Productions, Ltd., and produced by Mr. Harold Lowenstein with the co-operation of Sir Arthur Hill and his staff, gives a ‘cross-section’ of the activities of Kew as a public garden and as the centre of economic botany and horticulture in the Empire. The opening views give a picture of the Gardens as seen by the ordinary visitor, followed by sequences showing some of the work that goes on behind the scenes, both out of doors and under glass, in order to keep the Gardens in good condition and to provide a constant succession of bloom throughout the year. The most interesting section of the film from the scientific point of view is that illustrating the work that is carried out in the Herbarium, Jodrell Laboratory and Museums. The process of drying, pressing, mounting and storing botanical specimens is shown in the film in detail, and the method of examining and describing new species is also dealt with. The work of the Jodrell Laboratory consists largely of identifying fragments of plants (roots, stems, leaves, etc.) by microscopical examination, and one of the best sequences in the film illustrates the technique of examining a portion of stalk found in the stomach of a poisoned cow. The film ends with an impressionistic treatment of the part that Kew has played in the foundation and improvement of many of the important agricultural enterprises throughout the Empire. The introduction of Para rubber and cinchona (quinine) from South America via Kew to the East in the middle of last century is illustrated, and more recent instances show that this type of work is still being undertaken. This film will undoubtedly be of value in spreading a knowledge of the great importance of the Royal Botanic Gardens in the botanical and horticultural work of the Empire, and it is hoped that it will obtain a wide circulation, especially among schools and other educational institutions.