A laboratory simulation of diel changes affecting cellular composition of the dinoflagellate Ceratium hirundinella

SUMMARY. Changes of cellular composition of a planktonic dinoflageilate, Ceratium hirundinella , were studied over 2–1–48-h periods in the laboratory on three separate occasions. Samples from a lake population in the stationary phase of the population cycle were incubated at lake temperature under continuous illumination and in a light-dark (LD) regime of LD 14:10.
The magnitudes of diel variability in ratios of carbohydrate:chlorophyll- a , carbohydrate:carbon. carbon:nitrogen and carotenoids:chlorophyll- a for samples incubated at LD 14:10, were similar to those observed in situ at a similar phase of the population growth cycle. The ratios involving carbohydrate showed the most diel variation, which was not reduced under continuous illumination.
By appearance 'dark' and 'pale' cells of Ceratium were distinguished in the fixed samples; a persistent periodicity for the interconversion of dark and pale cells is described. The periodicity and amplitude of inter-conversions were not always in phase with those of chlorophyll- a synthesis and decomposition. The observed changes were almost certainly independent of the light-dark cycle: they were apparently induced by nutrient deficiency.     

A seasonal sequence of diel distribution patterns for the planktonic dinoflagellate Ceratium hirundinella in a eutrophic lake

SUMMARY. 1. Diel depth distribution patterns of Ceratium hirundinella were studied during eleven sampling periods, covering the seasonal growth cycle. They were shown to result from short-term periodic or non-periodic external factors, endogenous responses of the alga, and interactions between these.
2. Diel variations in wind stress resulted in the net transport of algae into or out of the sampling position due to lateral water movements. A progressive surface accumulation of Ceratium , leading to a 3-fold increase in cell numbers at the sampling site over a 24 h period, was due to wind-induced upwelling of deeper cells. Near-surface accumulation of Ceratium on a completely overcast afternoon, similar to that associated with migrations, was attributable to advection.
3. Under sufficiently calm conditions, depth-differentiation of Ceratium was regulated by its vertical swimming movements with a diel periodicity. Migration patterns observed in earlier work were confirmed and extended. The alga migrated towards the surface during the daytime and downward during the night; this rhythm had an endogenous component.
4. At high surface illumination, the alga retreated from the surface and formed discrete sub-surface maxima; at low irradiance Ceratium showed positive phototaxis and concentrated near the surface. Under either condition of irradiance Ceratium actively aggregated at depths associated with irradiance levels of about 125–155 μEinsteins m ⁻² s ⁻¹. Downward movement was restricted by anoxic conditions and possibly by thermal/ density gradients. However, given sufficient light penetration, dissolved oxygen and nutrient availability, the thermal density gradient does not apparently eliminate downward movement by Ceratium.     

Physiological and environmental constraints in the ecology of the planktonic dinoflagellate Ceratium hirundinella

SUMMARY. Constraints upon the vertical distribution of a population of Ceratium hirundinella , in a productive English lake during the summer stratification of 1976, are considered. They are interpreted in relation to vertical gradients of temperature, dissolved oxygen and irradiance, and to rates of photosynthesis and respiration measured as oxygen exchange in long- and short-term exposures. The motile cells tended to aggregate at an intermediate depth in the epilimnion, associated with a relative irradiance level of c . 10% or c . 140 μ einsteins m⁻²s⁻¹ as measured with a horizontal PAR sensor. Higher irradiances, and conditions below the oxycline, were apparently unfavourable, but the intervening layer was severely compressed at the height of summer stratification, when concentrations of inorganic nitrogen were also minimal. Thus the population apparently passed through a critical period, at which the cellular content of chlorophyll-α was much reduced. The preferred irradiance level in the lake corresponded to that at which measured rates of net photosynthesis were maximal. Increased rates of oxygen evolution were measured at higher irradiances in very short exposures; this behaviour may be of importance to cells experiencing vertical movement in nature.     

Seasonal and diet changes in ultrastructure in the dinoflagellate Ceratium hirundinella

The ultrastructure of the dinoflagellate Ceratium hirundinella(O.F.Mull.) Bergh. was studied in the plankton of a small productivelake throughout one season of its growth and during one 24-hperiod of that season. The results were related to measuredenvironmental variables. Samples for the seasonal study weretaken every 4 weeks and fixed immediately upon removal fromthe lake and samples for the diel study were fixed in situ atdepth. There was little difference in general ultra-structureof cells during the diel study or during the period of rapidgrowth but greater changes were apparent following excystmentand prior to encystment. Most changes were observed within thechloroplasts, pyrenoids and storage products. Changes in chloroplaststructure were shown to be related to the light conditions beingexperienced by the cells. Starch and lipid occurred in varyingproportions depending on the stage of the life cycle. Starchand associated pyrenoid clusters varied with irradiance levelover the 24-h period.     

Growth of Ceratium hirundinella in a subtropical Australian reservoir: the role of vertical migration

A study into the photophysiology, growth and migration of Ceratiumhirundinella in Chaffey Reservoir in subtropical northern NewSouth Wales, Australia, revealed that a proportion of cellsformed subsurface accumulations at depths that optimized lightintensity (212–552 µmol photons m^–2 s^–1)for photosynthesis and cell growth. At high incident irradiance,Ceratium migrated downwards from the near-surface waters, avoidinghigh-light-induced, slow-recovering non-photochemical quenchingof photosystem II. Overnight deepening of the surface mixedlayer by convective cooling produced homogeneous distributionsof Ceratium with a significant proportion of the populationbelow the depth where light saturation of photosynthesis occurred.Ceratium migrated towards the surface from suboptimal lightintensities, at a velocity of 1.6–2.7 x 10^–4 m s^–1.Subsurface accumulations occurred under a variety of turbulenceintensities; however, accumulation was significantly reducedwhen the turbulent velocity scale in the mixed layer was >5x 10^–3 m s^–1, beyond which turbulent diffusion dominatedadvection by swimming. The formation of subsurface accumulationswith increased computed water column integral photosynthesisby 35% compared to a uniform cell distribution.     

Temporal occurrence of Ceratium hirundinella in Spanish reservoirs

Ceratium hirundinella has traditionally been characterised as a species that thrives in warm waters and in stratified conditions. In our study, however, we found that the temporal occurrence of C. hirundinella in Spanish reservoirs greatly differs from that typically described in temperate zone aquatic systems. We analysed the temporal occurrence of C. hirundinella populations as well as physical and chemical variables in one hundred Spanish reservoirs. C. hirundinella was present in most (74%) of the reservoirs. In 78% of the reservoirs with C. hirundinella occurrence, the species was present during winter time and in 70% it was present during all four seasons.C. hirundinella was very commonly present in Spanish reservoirs in winter time despite the mixing conditions and lower temperatures and light availability. The presence of the species was positively related to water ionic content (HCO₃ ^–, SO₄ ^2-, Ca²⁺, Mg²⁺). We conclude that C. hirundinella temporal occurrence in southern north-temperate systems greatly differs from the seasonality typically described for the temperate zone and could be regulated by different factors than those operating in the northern north-temperate zone.     

The phased division of the freshwater dinoflagellate Ceratium hirundinella and its use as a method of assessing growth in natural populations

SUMMARY. The nocturnal phasing and partial synchrony of cell division in Ceratium hirundinella was investigated on four occasions for dense planktonic populations in a small productive lake (Esthwaite Water). The population growth rates deduced from the proportion of cells dividing per day are compared with the rates of increase of cell density in the lake. The maximum proportion of Ceratium cells found dividing at any time was 5.8 ± 1.0%, and the time of optimum division was 03.00 hours G.M.T. The daily rate of division during the main phase of population increases was similar to that deduced from the overall population increments at that time, although during the week of collection the increase had apparently ceased temporarily. On the other three occasions, either increase of cell numbers had ceased or the population was declining, but a continued low rate of division ( c . 3% day⁻¹) was found.
The nocturnal division of Ceratium in Esthwaite Water is compared with the division phasing of dinaflagellates described from elsewhere. Some general problems associated with the derivation of estimates of population growth rate from division frequency are also considered.     

The Nutrition of the Freshwater Dinoflagellate Ceratium hirundinella*

A defined medium was devised for a freshwater isolate of the dinoflagellate Ceratium hirundinella. Highest cell yields were produced at 7,700–10,000 lux. The optimum pH range was between 7.0 and 7.5: the optimum temperature 21°C. Ceralium hirundinella tolerated a wide range (per liter) of Ca (0.1–100 mg) and Mg (0.1–50 mg) ion concentrations. The optimum range for growth was 20–30 rns Ca and 10–30 mg Mg. Cells cultured in media lacking Ca often became teratological yet motilp and viable. Variations in the Ca:Mg ratio had little effect on cell yield if the sum of the concentrations of the 2 ions remained the same. Organic as well as inorganic sources of N and P were utilized. NH₄ sources became toxic at elevated levels (7 mg N liter^-1). Methionine was not used as N source. Cells could not be completely depleted of P, but concentrations ≤ 0.01 mg P liter^-1 resulted in poor growth. Vitamin B₁₂, but not thiamine or biotin, was required. Highest cell yields were at a PII-metals concentration of 30 ml liter^-1; a t 100-ml liter^-1 cell yield was very low. Additions (per liter) of Fe (0.5 mg) and Mo (0.1 mg) to the basal medium produced higher cell yields, but Cu (0.1 mg) and V (0.1 mg) inhibited growth.     

Population dynamics of the freshwater dinoflagellate Ceratium hirundinella in the largest shallow lake of Central Europe, Lake Balaton, Hungary

SUMMARY.

• 1 Horizontal distribution, long-term (1933–82) and short-term (day-to-day) changes in abundance, vertical stratification and circadian rhythm of the freshwater dinoflagellate Ceratium hirtmdinella were studied in Lake Balaton, the largest shallow lake of Central Europe.
• 2 The lowest abundance was consistently found in those areas of the lake which had the strongest currents.
• 3 The density of C. hirundinella seemed to be, at least in those parts of the lake above the level of fertility considered oligotrophic, insensitive to changes in trophic conditions; only its relative contribution to total biomass decreased with increased enrichment.
• 4 During the day the bulk of the population stayed at a level in which the light intensity was between 126 and 440 μE m^-2 s^-1 PAR.

     

Modeling patterns of zooplankton diel vertical migration

Realized predation pressure, defined as the product of predationpressure and light intensity, expresses the mortality pressuredue to visual predation. The part of realized predation pressurewhich is sensed by organisms is here considered to be relatedto food level and temperature. This partly realized predationpressure is referred to as sensed predation pressure. We proposea possible control mechanism of diel vertical migration (DVM):organisms move vertically following the minimum change in sensedpredation pressure. To investigate this assumption, we presenta math ematical model of DVM. We assume that when predatorsare present, the food level is above a minimal level, and temperatureis higher than the tolerance of organisms to growth, prey organismsundertake DVM following the minimum change in sensed predationpressure. We examine how patterns of migration may be affectedby changes in water clarity, predation pressure, food leveland temperature. This work supports the assumption that minimizingchanges in sensed predation pressure can explain the wide variationin the vertical profile of zooplankton.     

Small-scale diel vertical migration of zooplankton in the High Arctic

Diel vertical migration (DVM) of zooplankton is considered less prominent at high latitudes where diel changes in irradiance are minimal during periods of midnight sun and polar night, leaving zooplankton without a temporal refuge and thus eliminating a key advantage of DVM. One of the shortcomings of previous DVM studies of zooplankton based on net sampling is that the depth resolution often has been too coarse to detect vertical migrations over short distances. We investigated DVM of zooplankton during August 2010 in drifting sea ice northeast of Svalbard (~81.5°N, ~30.5°E). Classical DVM behaviour (midnight rising, midday sinking) was observed between 20 and 80 m in young copepodite stages (CI–III) of Calanus finmarchicus and Calanus glacialis. The copepods Microcalanus spp., Pseudocalanus spp., Oithona atlantica, Oithona similis and Triconia borealis, alongside Eukrohnia hamata, Limacina helicina, and Fritillaria spp., all displayed signs of DVM. We conclude that zooplankton exhibit DVM in ice-covered waters over rather short distances to optimise food intake in the presence of predators.     

Temporal and spatial distribution of the dinoflagellate Ceratium hirundinella O.F. Müller within a small productive lake

The growth of Ceratium hirundinella in Esthwaite Water, a small productive lake, was investigated during 1975; the horizontal distribution of the alga was studied on four occasions over a 3-week period. Measurements of lake temperature, oxygen concentration, and vertical stratification of Ceratium at close intervals of depth, were also made. Lake population estimates from large samples at many stations were compared with small samples at the regular sampling station. On two occasions the means of these samples were significantly different (P<0·01). On one date, the estimate of Ceratium abundance in the lake from the large sample at many stations was more than twice the value obtained from the sample collected at the regular sampling station. The population of Ceratium was contagiously distributed in all the large samples. On 3 days the horizontal distribution showed an increase in Ceratium numbers towards the windward shore of the lake. Very large accumulations of Ceratium were found in the metalimnion, just above the anaerobic hypolimnion, during late afternoon. Possible mechanisms of horizontal pattern development are considered, based on the measurements of the vertical distribution of Ceratium, and meteorological factors. The ecological consequences for Ceratium of vertical and horizontal movements, and its spatial distribution in the lake, are discussed.     

Control mechanisms of diel vertical migration: theoretical assumptions

We explore control mechanisms underlying the vertical migration of zooplankton in the water column under the predator-avoidance hypothesis. Two groups of assumptions in which the organisms are assumed to migrate vertically in order to minimize realized or effective predation pressure (type-I) and to minimize changes in realized or effective predation pressure (type-II), respectively, are investigated. Realized predation pressure is defined as the product of light intensity and relative predation abundance and the part of realized predation pressure that really affects organisms is termed as effective predation pressure. Although both types of assumptions can lead to the migration of zooplankton to avoid the mortality from predators, only the mechanisms based on type-II assumptions permit zooplankton to undergo a normal diel vertical migration (morning descent and evening ascent). The assumption of minimizing changes in realized predation pressure is based on consideration of DVM induction only by light intensity and predators. The assumption of minimizing changes in effective predation pressure takes into account, apart from light and predators also the effects of food and temperature. The latter assumption results in the same expression of migration velocity as the former one when both food and temperature are constant over water depth. A significant characteristic of the two type-II assumptions is that the relative change in light intensity plays a primary role in determining the migration velocity. The photoresponse is modified by other environmental variables: predation pressure, food and temperature. Both light and predation pressure are necessary for organisms to undertake DVM. We analyse the effect of each single variable. The modification of the phototaxis of migratory organisms depends on the vertical distribution of these variables.     

Ceratium in Lake Erken: vertical distribution, migration and form variation

External morphological features and growth characteristics of the dinoflagellates Ceratium hirundinella and C. furcoides were investigated in relation to the environmental conditions in Lake Erken. Three distinct population maxima were distinguished, one in June, one in July, and one in September. C. hirundinella dominated the spring and summer populations. C. furcoides was rare in June, but it continuously increased and composed ca. 18% of the Ceratium-cetts in the autumn. The size of a C. hirundinella decreased during the investigation period and a form with a long horn disappeared in June. Ceratium was most numerous during the warmer periods in summer when a distinct thermocline appeared and before the turnover period in September. The alga preferred depths down to 3 m where the blue light dominated and the following parametric magnitudes could be measured: oxygen contents >5 mg 1^-1, pH >7, HCO₃, >1.7 meq. · 1^-1, and a specific conductivity of ca. 250 mS · cm^-1. The algal growth periods displayed doubling times of 2.63 and 4.04 days at surface temperatures of 19°C and 15°C, respectively. The water transparency decreased 3.8 m when Ceratium reached cell densities of 13 individuals · ml^-1 (0–10 m depth). Its vertical migration demonstrated a dial rhythm with accumulation of cells in the surface waters during the day. Complicated patterns of surface avoidance occurred in clear weather and under wind stress.     

Quantification of diel vertical migration by micronektonic taxa in the northeast Atlantic

Analyses of day/night changes in the bathymetric distribution of micronektonic biomass at 16 stations in the northeastern Atlantic, sampled between 1978 and 1994, provided quantitative estimates of the organic carbon fluxes associated with diel vertical migration of individual taxa of micronekton. Gelatinous taxa contributed 50–80% of the integrated standing crop by volume but, apart from tunicates, contributed relatively little to the active migratory fluxes when expressed in terms of carbon. Total micronektonic migratory fluxes into the upper 200 m ranged from 12.5 to 58 mgC per m². At 15 stations, fish and pteropods provided 50–80% of the fluxes into the upper 100, 200 and 400 m. At one station, tunicates (pyrosomes) contributed substantially. Wherever tunicates or the medusa Pelagia were swarming, migrations by other taxa appear to be suppressed. The mean proportions of the stock (in terms of biomass) of each of the dominant migratory taxa entering and leaving the upper 100 m were 23% for tunicates, 18% for fish, 22% for pteropods, 8% for decapod crustaceans and 23% for euphausiids. The maximum proportions for these five taxa were 90%, 60%, 75%, 25% and 75%, respectively. Similar estimates of the mean fluxes into and out of the upper 400 m were generally higher: 19% for tunicates, 39% for fish, 28% for pteropods, 49% for decapods and 55% for euphausiids; the respective maxima were 99%, 74%, 99%, 72% and 91%. It is estimated for fish that if these migrations occur throughout the year, they will result in an active carbon export (both POC and DOC) from the wind-mixed layer and immediate sub-thermocline depths of about 500% of the mean annual standing stock. If this estimate can be extended to other taxa, then the material fluxes resulting from these active migrations will be quantitatively similar to those resulting from the deposition of phytodetritus at temperate latitudes.     

Seasonal distribution and morphological changes of Ceratium hirundinella in two mediterranean shallow lakes

Hydrobiologia - Seasonal distribution and morphological changes in two forms of Ceratium hirundinella in the shallow karstic Mediterranean lakes, Ponikve and Njivice, during 1997/98 and 2000/01,...     

Fish predators, food availability and diel vertical migration in Daphnia

Diel vertical migration of zooplankton is a highly variableand complex behaviour which apparently cannot be explained byany single factor. We determined the relative importance offish predation, food availability and water depth in shapingthe migratory behaviour of Daphnia. A modified 2x2x2 factorialexperiment provided two levels of fish density (present/absent),food availability (ambient/high) and depth (4–10 m); shallowtreatments with fish were excluded. Triplicate 1.2 m diameterenclosures for each of the six treatments were held in an 18unit array in Peter Lake, Gogebic Co., MI, USA. Repeated measuresANOVA identified significant trends in daphnid density, migrationand fitness (determined by lipid-ovary-egg index, LOE) as wellas in chlorophyll a content of the water column for part ofa 4-week experiment in July 1988. In deep enclosures with fish,Daphnia performed significantly more intense migrations thanin fishless enclosures, save those in fishless ambient-foodenclosures. Daphnia in deep fishless enclosures without abundantfood at depth performed significantly reduced migrations. DaphnidLOE index was significantly influenced only by food content.Our results were consistent with the predator-avoidance hypothesisas well as with observations of greatest migrations where largevertical differences in food abundance exist. They support ahierarchical view of vertical migration, with presence of fishthe primary factor, and food availability the secondary factor.     

Partial diel vertical migration in an omnivorous macroinvertebrate,Mysis diluviana

Hydrobiologia - Partial migration, whereby only a portion of a population migrates, has just recently received attention in aquatic systems. Partial diel vertical migration (DVM) has received even...