Inhibitory effects of copper on marine dinoflagellates

The effect of copper on three species of marine dinoflagellates [Scrippsiella faeroense (Paulsen) Balech et Soares, Prorocentrum micans Ehrenberg, Gymnodinium splendens Lebour] was studied. It inhibited the growth of all species and was lethal to one species in batch cultures. The effect was more pronounced in semicontinuous culture than in batch cultures. Chlorophyll concentrations and rate of uptake of radioactive carbon by cells of S. faeroense were affected in a manner similar to cell numbers. Copper inhibited growth of cells, most probably either by arresting cell division or by penetrating inside the cell and affecting metabolism.     

Quantum yield,relative specific absorption and fluorescence in nitrogen-limited Chaetoceros gracilis

Decreases in cell-nitrogen quota resulted in changes in the carbon-based quantum yield of photosynthesis, the chlorophyll a-specific absorption coefficient, and in vivo fluorescence in the marine diatom Chaetoceros gracilis in laboratory experiments performed in 1983 and 1984. The three parameters were independently determined for the two spectral regions dominated by either chlorophyll a or fucoxanthin absorption. As cell-nitrogen quota decreased, the quantum yield for both pigments decreased; the specific absorption coefficient for chlorophyll a and the in vivo chlorophyll a fluorescence excited by each pigment increased. The observed increase in the in vivo fluorescence per chlorophyll a could be partially attributed to the increased specific absorption coefficient for chlorophyll a; the remainder of the fluorescence increase was related to a decline in photosystem activity. Energy transfer efficiency between light-harvesting pigments appeared to be maintained as cell-nitrogen quota decreased. The decrease in a fluorescence index [(F _DCMU-F _O)/F _DCMU] with nitrogen starvation suggested a decrease in Photosystem II activity. These results imply that decreases in reaction center and/or electron-transport system activity were responsible for the decline in rates of photosynthesis under conditions of notrogen deficiency.     

Chlorophyll a fluorescence,an alternative method for estimating primary production

The in vivo chlorophyll a fluorescence index (F_+DCMU-F_-DCMU/F_+DCMU) of natural waters was compared to the ¹⁴C-determined primary production, and the fluorescence intensity in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (F_+DCMU) was studied as a function of extracted and spectrophotometrically determined chlorophyll concentrations. Samples were taken every second week from May through October, 1979, at the station Systrarna situated in a coastal area of the Bottnian Sea. In addition, samples from the Archipelago Sea of the Baltic were collected on board the Finnish research vessel R/S Aranda during the September cruise 1979. The correlations between the fluorescence index and the ¹⁴C-determined primary production and between F_+DCMU and total chlorophyll concentration were good when samples taken over short time intervals were compared. The shortcomings of both the fluorescence and the ¹⁴C methods are discussed. It is concluded that the fluorescence method is useful if it is desirable to follow with high time resolution any changes in the potential for photosynthesis (or primary production) in a water mass over relatively short time periods; e.g. during an algal bloom. The fluorescence method can furthermore be technically developed for automatic monitoring with a high time resolution. Efforts are being made in our laboratory to develop the method further to give information about the in situ rates of photosynthesis rather than the potential for photosynthesis in a photoplankton population.     

Zooplankton growth rates: the influence of female size and resources on egg production of tropical marine copepods

Egg production was measured in 17 species of copepods from the genera Acartia, Calanopia, Centropages, Clausocalanus, Corycaeus, Eucheata, Euterpina, Oithona, Oncaea, Paracalanus, Parvocalanus, Temora and Undinula in Jamaican waters. At the high local temperatures (∼28 °C), mean egg production ranged from 3.2 to 88 eggs female^–1 d^–1, and instantaneous female growth (g, as egg production) ranged from 0.04 to 0.87 d^–1. Female growth was positively related to ambient chlorophyll concentration (r ² = 0.44) and negatively to female body size (r ² = 0.29). Together these two variables explained 60% of the variation in growth. When quadratic terms for chlorophyll and a term for interaction of body size and chlorophyll were introduced, 82% of the variance in growth rate was explained. Egg production rates represent an extension of the resource and size-dependent relationship established for copepodites. In smaller species (<3.5 μg), egg production was comparable to prior copepodite somatic growth; in larger species (>3.5 μg), egg production is compromised at lower resource concentrations than copepodite somatic growth. Thus, it appears that egg production in tropical copepods may be frequently limited by resources in a size-dependent manner. Under conditions where growth is resource limited, we caution against the application of egg production rates for the calculation of total copepod production. Received: 30 May 1997 / Accepted: 13 May 1998     

Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters

Phytoplankton growth and microzooplankton grazing were measured in two productive coastal regions of the North Pacific: northern Puget Sound and the coastal Gulf of Alaska. Rates of phytoplankton growth (range: 0.09–2.69 day⁻¹) and microzooplankton grazing (range: 0.00–2.10 day⁻¹) varied seasonally, with lowest values in late fall and winter, and highest values in spring and summer. Chlorophyll concentrations also varied widely (0.19–13.65 μg l⁻¹). Large (>8 μm) phytoplankton cells consistently dominated phytoplankton communities under bloom conditions, contributing on average 65% of total chlorophyll biomass when chlorophyll exceeded 2 μg l⁻¹. Microzooplankton grazing was an important loss process affecting phytoplankton, with grazing rates equivalent to nearly two-thirds (64%) of growth rates on average. Both small and large phytoplankton cells were consumed, with the ratio of grazing to growth (g:μ) for the two size classes averaging 0.80 and 0.42, respectively. Perhaps surprisingly, the coupling between microzooplankton grazing and phytoplankton growth was tighter during phytoplankton blooms than during low biomass periods, with g:μ averaging 0.78 during blooms and 0.49 at other times. This tight coupling may be a result of the high potential growth and ingestion rates of protist grazers, some of which feed on bloom-forming diatoms and other large phytoplankton. Large ciliates and Gyrodinium-like dinoflagellates contributed substantially to microzooplankton biomass at diatom bloom stations in the Gulf of Alaska, and microzooplankton biomass overall was strongly correlated with >8 μm chlorophyll concentrations. Because grazing tended to be proportionally greater when phytoplankton biomass was high, the absolute amount of chlorophyll consumed by microzooplankton was often substantial. In nearly two-thirds of the experiments (14/23), more chlorophyll was ingested by microzooplankton than was available for all other biological and physical loss processes combined. Microzooplankton were important intermediaries in the transfer of primary production to higher trophic levels in these coastal marine food webs. Received: 12 November 1999 / Accepted: 4 October 2000     

Une approche vers l'estimation de la production potentielle du phytoplancton par analyse des cinétiques d'induction de fluorescence

In vivo chlorophyll fluorescence is particularly interesting ot ecologists because of various concepts (biomass, productivity, physiological state) associated with it. Using a modified spectrophotofluorometer, we have studied the kinetics of fluorescence in unialgal cultures and in a natural population of marine phytoplankton. Our apparatus did not achieve satisfactory results with cell suspensions having a chlorophyll concentration less than 10 g l^-1. We have also tested a method for estimating kinetics of diluted cultures and marine phytoplankton using cells collected on glass-fibre filters. For unialgal cultures in the exponential growth phase, the method proved satisfactory, and results obtained from both cell suspensions and filters were in good agreement. However, for aged cultures (principally diatoms) and natural marine phytoplankton the method proved unsuitable. The kinetics of fluorescence induction vary according to taxonomic position of the cells, light intensity of the measuring excitation beam and productiveness of the culture medium. The importance of the kinetics of fluorescence induction for characterization of phytoplankton activity is discussed.     

Lethal and sublethal effects of naphthalene and 1,2-dimethylnaphthalene on the marine copepod <Emphasis Type="Italic">Paracartia grani</Emphasis>

Here we evaluate the effects of two quantitatively very important components of the water soluble fractions of fuel oils (naphthalene and 1,2-dimethylnaphthalene, hereafter NAPH and C2-NAPH, respectively) on the survival, feeding and egg production rates, and viability of eggs of the coastal copepod Paracartia (Acartia) grani. Acute toxicity responses resulted in lethal concentrations (LC50) of 2,535 and 161 μg l⁻¹ for NAPH and C2-NAPH, respectively, with no evidence of narcotic effects. Hydrocarbon-specific differences in the toxicity response indicate that sublethal effects (EC50) on feeding by C2-NAPH were likely driven by induced mortality, whereas NAPH has direct negative effects on feeding. Sublethal effects on egg production rates followed a similar detrimental pattern to the one exhibited by feeding rates, suggesting that the lower egg production rates were mediated by the decrease in feeding rates. At the exposure time tested (24 h), the 50% reduction effective concentrations (EC50) determined for sublethal effects were relatively high in comparison with hydrocarbons’ concentrations found under natural circumstances. Long exposure (4 days) of P. grani adults to the tested hydrocarbons at concentrations well below the recorded EC50, however, had no significant effects on feeding, egg production and hatching rates. The viability of the eggs was either not affected or only slightly influenced when healthy eggs were incubated under very high concentrations (up to 6,400 and 700 μg l⁻¹ NAPH and C2-NAPH, respectively). The significance of the effects of oil spills on marine zooplankton communities is discussed in light of the results presented in this study.     

The biological degradation of arginine and glutamic acid in seawater in relation to the growth of phytoplankton

The responses of natural summer coastal plankton communities to low-level additions (10^-5 to 10^-7 M) of arginine and glutamic acid has been followed by in vivo measurement of chlorophyll fluorescence. This technique is capable of detecting a response to a 10^-6 M enrichment under most conditions. The time sequence of the response varied with the amino acid used and with the enantiomeric form of the amino acid. Ammonia and carbon dioxide were liberated before the increase in chlorophyll fluorescence occurred. Liberation of ammonia in a dark bottle from L-arginine was from 75 to 85% of the theoretical yield. Microautoradiography using ¹⁴C L-arginine or L-glutamic acid at 10^-7 M showed heavy labeling associated with fecal pellets and detrital aggregates. Phytoplankton cells were not appreciably labeled. The evidence suggests that bacteria are important in the cycling of these compunds.     

Growth rates of summer nanoplankton (<10 μm) populations in lower Narragansett Bay,Rhode Island,USA

Growth rates of summer (June–September) phytoplankton assemblages and constituent species were measured in 30 diffusion culture experiments. Size-fractionated (<10 m) phytoplankton assemblages were incubated in situ or under simulated in-situ conditions in outdoor tanks connected to a running seawater system. Doubling rates of important species and groups (such as microflagellates) were compared to community biomass doubling rates estimated from ¹⁴C uptake and changes in chlorophyll a concentrations. Division rates of dominant diatom species generally equalled or exceeded community biomass doubling rates, while those of flagellates and non-motile ultraplankters were slower. Maximum division rates of sixteen common diatom species exceeded 2.1 divisions d^-1, while nine had maximum division rates in excess of 3 d^-1. Mean division rates of 12 diatom species exceeded 1 d^-1. Maximum division rates of flagellated species, uncharacterized microflagellates and non-motile ultraplankton assemblages were 2.1, 1.5 and 1.4 d^-1, respectively. Microflagellate and non-motile ultraplankton assemblage doubling rates were less than 0.5 d^-1 in over half of all growth experiments.     

Fluorescence properties of natural phytoplankton populations

The cellular fluorescence of chlorophyll a in natural phytoplankton was measured during vertical profiling in marine coastal waters. The ratio of in situ fluorescence to chlorophyll a concentration, which was considered as an index of cellular fluorescence, varied over a wide range, with large changes occurring both within the water column and between profiling sites. The variations were caused in part by an inhibition in the fluorescence of cells exposed to intense sunlight. The inhibition, which occurred at irradiances exceeding 0.15 langley (ly)/min, led to diel fluctuations in the fluorescence of those phytoplankton near the sea surface. The remaining variations were independent of changes in temperature, but were unexplained. Both light-dependent and light-independent variations in cellular fluorescence will affect the accuracy of the continuous, fluorometric measurement of in vivo chlorophyll.     

Growth interactions between marine dinoflagellates in multispecies culture experiments

The growth interactions between the marine dinoflagellates Scrippsiella faeroense (Paulsen) Balech et Soares, Prorocentrum micans Ehrenberg and Gymnodinium splendens Lebour were investigated in batch and continuous-culture combinations. Generation times were 1.3±0.2 days for S. faeroense; 1.6±0.1 days for P. micans and 1.8 ± 0.2 days for G. splendens. In mixed batch cultures, growth depended strongly on the ratio between cell numbers of the two species inoculated at the start of the experiments. In various inocula, the more abundant species prevailed and suppressed the competitor even during exponential growth. Total cell production of the suppressed forms was lowered drastically; initial generation time, however, remained more or less unaffected. In equal inocula, S. faeroense dominated over G. splendens, P. micans over S. faeroense and G. spendens over P. micans. In continuous cultures, the species grew independently of each other during the exponential stage; cell number was regulated only by generation times. Competitive inhibition did not occur until maximum cell densities of the dominating forms had been reached. Filtration experiments indicated inhibiting effects mainly in filtered culture liquids of stagnating cultures: reinoculated cells of all three test populations showed a somewhat reduced total cell production. Short initial lag phases were indicated in filtered culture liquids of P. micans and G. spendens; following this period, generation times of the test population remained unaffected, however. The experiments show that growth in multispecies cultures is regulated during the exponential stage mainly by nutrient competition, while at maximum cell densities an additional effect of inhibiting metabolic products is involved. Whether this effect is caused by toxic algal excretions or by bacterial decomposition products of dead cells could not be determined. Sexual stages occurred in aged cultures of S. faeroense and G. splendens both in monocultures and in multispecies combinations and influenced the equilibrium of the competing species. The results are discussed in the light of the findings of other authors.This paper was presented at a poster presentation of the Second International Conference on Toxic Dinoflagellate Blooms, held in Key Biskayne, Florida, USA, 1978.     

砷胁迫对不同烟草品种光合色素和叶绿素荧光特性的影响

为了研究不同浓度砷(As)对烟草光合色素和叶绿素荧光特性的影响,首先将3个烟草品种翠碧1号、K326和云烟-87幼苗种植在从0到100 mg·kg-1亚砷酸钠(Na As O2)的6个浓度组中进行盆栽试验,并定期进行烟草受害症状的观测,测定叶片的光合色素含量、叶绿素荧光参数。结果表明:烟草在As胁迫下的反应因As胁迫浓度、胁迫时间和烟草品种而异。烟草光合色素含量、叶绿素荧光参数均表现为低浓度下有促进效应和高浓度下有抑制效应,同时3种烟草在40 mg·kg-1As浓度处理下出现生长受阻,且浓度越高胁迫症状越明显。K326和云烟-87表观症状较明显,对As毒害的敏感性高于翠碧1号。随着As胁迫时间的延长,烟草的耐性增强,对As胁迫的敏感性减弱。     

Effects of ethyl 2-methyl acetoacetate (EMA) on the growth of Phaeodactylum tricornutum and Skeletonema costatum

We investigated the effects of ethyl 2-methyl acetoacetate (EMA) on growth of the marine diatom algae Phaeodactylum tricornutum (P. tricornutum) and Skeletonema costatum (S. costatum). Growth of P. tricornutum was significantly inhibited by the minimum concentration (3.5 mmol·L ^?1) of EMA at lower initial algal densities (IADs) (3.6×10⁴ and 3.3×10⁵ cells·mL ^?1). However, at the highest IAD, significant growth inhibition was found at above 7 mmol·L ^?1 of EMA exposure. In S. costatum, EMA concentrations of 10.5 mmol·L ^?1 or more significantly inhibited growth at lower IAD (3×10⁴ and 1.8×10⁵ cells·mL ^?1); at the highest IAD, only EMA concentrations above 14 mmol·L ^?1 obviously inhibited the growth of S. costatum. Changes in specific growth rates and pigment were consistent with algal growth, but only at higher EMA concentrations or lower IAD values was the ratio of chlorophyll a (Chla) to carotenoid significantly lower than the control. Medium effective concentration (EC ₅₀) values were in the order 4.07, 8.03 and 12.27 mmol·L ^?1 for P. tricornutum and 7.48, 11.92 and 17.22 mmol·L ^?1 for S. costatum. All these results show that the effect of EMA on the growth of algae was species specific and mainly depended on IAD, which might be an important factor to influence algal growth.     

Relationships between nucleic acid concentrations and primary production in the Catalan Sea (Northwestern Mediterranean)

We explored the relationships between classical estimators of autotrophic biomass and primary production, such as chlorophyll a concentration and ¹⁴C-fixation rates, and biochemical indices based on DNA and RNA determinations, which have been proposed as indicators of physiological state in natural plankton populations. The measurements were made during two cruises across the Catalan Front, carried out in May 1989 and February 1990, corresponding respectively, to periods of stratification and moderate mixing. DNA and RNA concentrations (measured by a double-staining fluorimetric technique) were significantly correlated with chlorophyll a in February 1990, but not in May 1989, when a marked deep chlorophyll maximum was present. Significant positive correlations between RNA concentration and primary production and between RNA: DNA and primary production were found during both surveys, probably reflecting both higher RNA concentrations per cell and enhanced bacterial and microheterotrophic growth in high primary production situations. The results support the potential usefulness, in biological oceanography, of biochemical indicators based on DNA and RNA concentrations.     

Continuous measurement of the DCMU-induced fluorescence response of natural phytoplankton populations

The effect of 3x10^-6 M DCMU [3-(3,4-dichlorophenyl)-1, 1-dimethylurea] on in vivo chlorophyll a fluorescence was observed in nearshore waters of the Southern California Bight. We compared fluorescence readings in the presence and absence of this inhibitor using parallel flow-through fluorometers. The increase in fluorescence induced by DCMU is expressed as the FRI (fluorescence response index). Theory and laboratory studies on batch cultures of phytoplankton suggest that the FRI is correlated with photosynthetic efficiency and/or physiological state, but other studies have produced results in apparent conflict with this interpretation. Although sufficient information does not exist to justify the use of fluorescence response as a precise physiological indicator in the field, we suggest that very low FRI values are a manifestation of photosynthetic debility in a sample. Vertical profiles showed a wide range of the fluorescence response index. At a station close to shore, low FRI values were observed well below the 1% light level, but the fluorescence response of the phytoplankton throughout the euphotic zone was similar to that of growing cultures. Farther offshore, the FRI was depressed near the surface, but increased in the enhanced nutrient conditions of the lower euphotic zone. The patterns observed were strong, and consistent with hypotheses which relate low values of the FRI to diminished photosynthetic capacity.     

Metallothionein induction inMytilus edulis exposed to cadmium

The exposure of mussels,Mytilus edulis, collected from Whitsand Bay, southwest England, in August 1988, to sublethal concentrations of cadmium (400µg l^–1) for 65 d resulted in the induction of metallothionein (MT) synthesis in the soft tissues. In cadmium-exposed mussels, metallothionein concentrations, measured by differential pulse polarography, increased by a factor of three, from 2 to 3 mg g^–1 to a maximum of 9 mg g^–1 after 30 d. No significant changes could be detected in controls. Cadmium accumulated in the soft tissues of mussels correlated significantly with metallothionein concentrations and can be described by the relationship: MT (mg g^–1)=0.045 Cd (µg g^–1)+3.03 (r=0.803,P<0.001). Gel chromatography of heat-treated cytosolic extracts showed that the accumulated cadmium is bound principally to the newly formed metallothioneins. Copper and zinc were also analysed in the whole soft-tissues and in subcellular fractions of cadmium-exposed mussels. Although copper concentrations were not affected by cadmium-exposure, zinc levels were significantly reduced. The results demonstrate that the induction of metallothioneins inM. edulis is a quantifiable biological response to sublethal levels of cadmium exposure.     

Effect of epibionts on the microdistribution of chlorophyll in corals and its detection by fluorescence spectral imaging

The spatial distribution of chlorophyll in three coral species carrying invertebrate symbionts was determined using spectral imaging techniques. From each pixel of the image, full fluorescence spectral data was obtained as well as comparative ratios of fluorescence. The multipixel fluorescence map and the relative-intensity fluorescence ratios demonstrated a high concentration of chlorophyll a next to the pits of Cryptochirus coralliodytes in Favites halicora. Spectral similarity maps of Goniastrea retiformis infested with Lithophaga lessepsiana and of Millepora dichotoma infested with Savignium milleporum revealed relatively higher chlorophyll concentrations in these two corals next to the symbionts. We hypothesize that the invertebrate symbionts fertilize their immediate surroundings with their excreta, enhancing algal growth. The spectral analysis system used in this study made it possible to distinguish such changes by spatial quantitation of the fluorescence emitted from small surface areas.     

铀胁迫对两种蓝藻生长及抗氧化酶活性的影响

研究了不同浓度铀(0.1、1.0、10.0和30.0mg·L-1)胁迫对满江红鱼腥藻(Anabaena azollae)和爪哇伪枝藻(Scytonemaj avanicum)生长及抗氧化酶活性的影响。结果表明,低浓度铀(0.1和1.0mg·L-1)条件下,两种蓝藻的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性及丙二醛(MDA)含量均无明显变化;叶绿素a含量和可溶性蛋白质含量均较对照上升,表明低浓度铀对A.azollae和S.javanicum均未形成明显胁迫,对生长表现为刺激和促进作用。10.0mg·L-1浓度的铀对A. azollae的生长影响不大,对S. javanicum却产生了明显的抑制作用。30.0mg·L-1铀胁迫下,两种蓝藻中的MDA显著增加,抗氧化酶系统受到破坏,生长严重受阻。实验结果显示,A. azollae和S. javanicum的耐铀极限分别在10.0～30.0mg·L-1和1.0～10.0mg·L-1之间,A. azollae的抗铀性比S. javanicum强。     

Pigment content and photosynthetic rate of the fronds of Macrocystis pyrifera

The Macrocystis pyrifera (L.) C. Ag. frond is here described in terms of chlorophyll a, fucoxanthin, chlorophyll c and photosynthetic rate. Pigment concentrations increased back from the apical meristem reaching a maximum after 2 to 3 m. Pigment concentrations were then generally constant throughout most of the length of the frond, finally decreasing again in the oldest parts of the frond with the exception of the sporophylls. Pigment ratios remained relatively constant throughout. Maximum net photosynthetic rates on a given frond showed a decrease with tissue age on both an area basis (1040 down to 463 nmol O₂ cm^-2 h^-1) and on a chlorophyll a basis, which was shown as half-saturation constants (quantum irradiance) which dropped on an area basis from 85 mol m^-2 sec^-1 at 4.5 m above the holdfast to 26 mol m^-2 sec^-1 at 15.5 m. Young sporophytes transplanted from the sea floor to the surface (12 m) tended to decrease pigment content, while those transplanted to the bottom tended to increase all pigments, but especially fucoxanthin. Photosynthetic rates, however, changed little on a unit area basis. The results of these data are considered in the light of recent work on photosynthetic units, tissue age effects and general adaptations of the M. pyrifera frond to its light environment.     

Photosystem II photoinhibition and altered kinetics of photosynthesis during nutrient-dependent high-light photoadaptation in Gonyaulax polyedra

Gonyaulax poledra Stein was transferred at different cell densities from increasingly nutrient-limited low-light (LL, 80 E m^-2 s^-1) batch-cultures to high-light (HL, 330 E m^-2 s^-1) growth conditions. Several age-dependent differences in HL-adaptation strategies were apparent. Short-term (3h) susceptibility to photosynthetic photoinhibition increased with culture age, with light-limited rates of photosynthesis exhibiting greater photosuppression than light-saturated rates at all stages of growth. These shortterm changes were not accompanied by photobleaching of chlorophyll but were directly related to age-dependent photoinactivation of Photosystem II electron-transport rates. The capacity of electron transport by Photosystem I was only slightly affected. Prolonged exposure of LL log-phase cells to HL conditions did induce photobleaching of chlorophyll associated with increased cell volume, a transient decrease of organic carbon and nitrogen content, enhanced cellular-, carbon-and chlorophyll-based rates of light-saturated photosynthesis (P _max) and suppressed cellular rates of light-limited photosynthesis. As a result, the density of LL log-phase cells doubled and their cellular photosynthetic performance nearly tripled within 1 d of HL exposure while cellular respiratory demands remained unchanged. By contrast, prolonged HL incubation of LL stationary populations induced a transitory burst in cell division and a large reduction in cell volume, leading to a short-term increase in volume-based organic carbon and nitrogen content. Despite reduced cell volume and lowered carbon demand, the cellular-, carbon-and chlorophyll-based rates of P _max in nondividing populations fell by 64, 48 and 27%, respectively, over a 4 d exposure to HL, while light-limited rates were almost fully suppressed within 1 d and chlorophyll a content was reduced by 56%. As a result, the photosynthetic performance of LL-aged cells declined immediately under HL conditions. Addition of inorganic nutrients to LL stationary cultures at the time of HL transfer led to immediate and complete suppression of photosynthesis and cell lysis within 1 d. Addition of nutrients following transfer to HL induced cell responses intermediate to those described for LL log and aged cells exposed to HL. Results support the view that declining nutrient-status impairs HL photoadaptive responses in phytoplankton populations and that the rate and pattern of photoadaptive responses may be used as physiological growth indicators in field studies. The study was conducted from March 1981 to May 1983.