Seasonal variations in salt-march macroalgae photosynthesis. II. Fucus vesiculosus and Ulva lactuca

Photosynthesis in whole plants of the salt-marsh algae Fucus vesiculosus and Ulva lactuca was evaluated by ¹⁴C-uptake under a variety of light intensities at approximately mately monthly intervals during a 15-month study. Photosynthetic capacity in both species was closely related to seasonal irradiation patterns and changes in field biomass. Maximum photosynthesis occurred in the spring and summer months. Photosynthesis on a dry weight basis was higher in U. lactuca, while photosynthesis on a chlorophyll a basis was equal in both species. Photosynthetic capacity was inversely related to pigment content. Maximum chlorophyll a concentrations occurred during the winter. Frond profile studies in F. vesiculosus indicated that apices always exhibited greatest photosynthetic capacity. Uptake of ¹⁴C into ethanol-soluble and insoluble fractions was different in each species. F. vesiculosus showed greater activity in the ethanol-soluble fraction while U. lactuca exhibited greater activity in ethanol-insoluble fractions.This research was supported by Research Grant AG-375 from the National Science Foundation and, in part, by the State University of New York Research Foundation and the Energy Research and Development Administration (ERDA).     

Seasonal variations in salt-marsh macroalgae photosynthesis. I. Ascophyllum nodosum ecad scorpioides

Photosynthesis in whole plants of the intertidal alga Ascophyllum nodosum ecad scorpiodes was evaluated by measuring ¹⁴C-uptake under a variety of light intensities and approximately monthly intervals during a 15 month study. Photosynthetic rates were determined in terms of dry weight, pigment content and uptake into ethanolsoluble and insoluble fractions. The specimens, naturally acclimated to in situ light intensities and temperatures, exhibited photosynthetic responses to light intensity which differed with time of year. Maximum photosynthetic potential occurred during the spring months and minimum potential occurred during late summer and winter months. Variations in photosynthetic potential were closely related to seasonal changes in field biomass. Both photosynthetic potential and biomass were inversely related to growth patterns of the salt-marsh phanerogam Spartina alternilora.This research was supported by Research Grant AG-375 from the National Science Foundation and, in part, by the State University of New York Research Foundation and the Energy Research and Development Administration (ERDA).     

Effects of light intensity on photosynthesis and dark respiration in six species of marine phytoplankton

Using an oxygen polarographic electrode, the shapes of photosynthetic curves and the effects of light on dark respiration in 6 species of marine phytoplankton wer examined. The species used were Skeletonema costatum, Ditylum brightwellii, Cyclotella nana (Thalassiosira pseudonana) (all Bacillariophyceae), Dunaliella tertiolecta (Chlorophyceae), Isochrysis galbana (Haptophyceae), and Gonyaulax tamarensis (Dinophyceae). A hysteresis was observed in all species examined with respect to increasing and decreasing light. Compensation light intensities varied by over 4 orders of magnitude, suggesting that the 1% light depth is an ambiguous measure of the euphotic zone. The data suggest that dark respiration accounts for ca. 25% of gross photosynthesis, but is species-dependent. In addition, respiration versus cell size does not describe an inverse exponential function over the size scales examined.This research was performed under the auspices of the United States Energy Research and Development Administration under Contract No. EY-76-C-02-0016.     

Action spectra and spectral quantum yield of photosynthesis in marine macroalgae with thin and thick thalli

Net photosynthesis at 10mol photons m^-2 s^-1 in each of 24 wavelengths was measured in absolute units by an O₂-electrode and corrected for dark respiration to construct action spectra for gross photosynthesis in nine species of algae, which included plants with thin and thick thalli from each of four major pigment groups. The photosynthesis of green and brown algae with thin thalli decreased in green light, but species with thick thalli from these two groups had action spectra which were almost flat, and matched the optical blackness of the thalli but did not reflect the pigment differences between the species. Among the red algae, on the other hand, there was little difference between the action spectra for thin and thick algae. Only wavelengths absorbed by the phycobilin pigments were effective in photosynthesis, even in species (e.g. Chondrus, Phyllophora) which absorbed all visible wavelengths strongly. Maximal quantum yields of 0.10 to 0.12 O₂ molecules per absorbed photon were recorded for thin green and brown algae, but thicker algae in these two groups had lower values. Red algae exhibited maximal values close to 0.10 O₂ molecules per absorbed photon, irrespective of thallus thickness or phycocyanin content, but the quantum yields of phycoerythrin-rich species in the 600 to 650 nm waveband were lower than those of phycocyanin-rich species.     

Photosynthesis,photorespiration, and dark respiration in eight species of algae

The rates of photosynthesis and dark respiration for 7 marine algae and 1 fresh-water alga were measured and compared. The dinoflagellates Glenodinium sp. and zooxanthellae have high dark respiration rates relative to photosynthetic rates, which may decrease their net growth rates. Photorespiration in the 8 algal species was studied by examining the effects of the concentration of oxygen on the rates of photosynthesis, on the incorporation of ¹⁴CO₂ into the photorespiratory pathway intermediates glycine and serine, and on the postillumination burst of carbon dioxide production and oxygen consumption. A combination of these results indicates that all the algae tested can photorespire, but that Glenodinium sp., Thalassiosira pseudonana, and zooxanthellae either have a photorespiratory pathway different from that proposed for freshwater algae (Tolbert, 1974), or an additional pathway for glycolate metabolism.     

The ecology of temperate salt-marsh fucoids. II. In situ growth of transplanted Ascophyllum nodosum ecads

Growth, in terms of length, weight, and number of branches and/or dichotomies, in transplanted specimens of Ascophyllum nodosum ecad scorpioides in a temperate salt marsh is described. The ecad scorpioides, when transplanted from its characteristic habitat on the mid-intertidal, Spartina alterniflora-dominated, marsh flats to a location near mean low-water developed characteristics normally associated with A. nodosum ecad mackaii. The growth of these plants was more rapid than those in the mid-intertidal region and was not affected by the shading of algal fronds by S. alterniflora. Unusually high temperatures and light intensities during the winter and spring months were major factors affecting growth in plants that were subjected to relatively long periods of tidal exposure. The presence of S. alterniflora during the summer months may act in a protective capacity for mid-intertidal ecad populations.This research was supported by research grants AG-375 and BO 38018 from the National Science Foundation and, in part, by the State University of New York Research Foundation and the Energy Research and Development Administration (ERDA).     

Phytoplankton photosynthetic adaptation to high frequency light fluctuations simulating those induced by sea surface waves

In order to test the ability of phytoplankton to adapt to the high frequency light fluctuations induced by sea surface waves, the green alga Dunaliella tertiolecta was grown under both steady and fluctuating (0.1, 1.0 and 10 Hz) illuminations. The latter conditions reproduced those fluctuations experienced by phytoplankton in the upper photic layer. For each culture, photosynthesis versus irradiance were measured under four incubation frequencies (steady, 0.1, 1.0 and 10 Hz fluctuating illuminations). Results indicated that growth rates were similar for algae grown under steady light and 10 Hz fluctuating light (0.26–0.33 d^–1). Cells grown at 0.1 and 1.0 Hz showed lower growth rates (0.17–0.26 d^–1). Chlorophyll a and b were significantly higher under 0.1 and 10 Hz frequencies than under steady illumination; at 1.0 Hz, there were no significant differences with steady light. No changes in carotenoids were evidenced at any frequency tested. Photosynthetic measurements showed that algae grown under steady illumination had higher photosynthetic efficiency and capacity when incubated under steady and 0.1 Hz fluctuating light. Photosynthetic characteristics of algae grown under 0.1 Hz illumination did not show any clear responses to fluctuating light. Algae grown under 1.0 or 10 Hz had higher photosynthetic efficiency and capacity than those grown under steady illumination, when incubated under 1.0 and 10 Hz light. This suggests that microalgae grown under high frequency illumination (1.0 and 10 Hz) can adapt their photosynthetic characteristics to the rapidly fluctuating light regime experienced during growth, and that algae grown under steady conditions respond better to steady or slowly fluctuating (0.1 Hz) light. Such an adaptation provides a means of probing the photosynthetic responses of phytoplankton to vertical mixing.Contribution to the program of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

Symbiont photosynthesis increases both respiration and photosynthesis in the symbiotic sea anemone Anemonia viridis

Dark respiration of the symbiotic sea anemone Anemonia viridis (Forskäl) was observed to increase by 34% when anemones were exposed to hyperoxic sea water (150% oxygen saturation) overnight, and by 39% after exposure to 6 h in the light at a saturating irradiance of 300 E m^-2 s^-1 at normoxia (100% oxygen saturation). No increase due to light stimulation was observed in aposymbiotic control anemones. In darkness, the oxygen concentration of the coelenteric fluid was hypoxic. However, within 10 min of anemones being illuminated, coelenteric fluid was hyperoxic, and it remained elevated throughout a 12 h light period. When measured over a 24 h period (12 h light: 12 h dark), the dark respiration rate increased gradually over the first 6 h of the light period until it was 35% above the dark night-time resting rate. It remained elevated throughout the remaining light period and for 2 h into the following dark period, after which it fell back to the resting rate. Gross photosynthesis (P ^gross) increased significantly when anemones were exposed to either hyperoxia (150% oxygen saturation) or 300 E m^-2 s^-1 at normoxia. This increase was not observed when symbiotic anemones were illuminated at a low-light intensity of 100 E m^-2 s^-1. The results of this study suggest that respiration in the dark is limited by oxygen diffusion and that normal respiration is restored in the daytime by utilisation of the oxygen released by photosynthesis. Furthermore, it appears that the increased respiration following exposure to high-light intensities provides a CO₂-rich intracellular environment which further enhances the photosynthetic rate of the zooxanthellae.     

Photosynthetic characteristics of Prochloron sp./ascidian symbioses

The prokaryotic green alga Prochloron sp. (Prochlorophyta) is found in symbiotic association with colonial didemnid ascidians that inhabit warm tropical waters in a broad range of light environments. We sought to determine the light-adaptation features of this alga in relation to the natural light environments in which the symbioses are found, and to characterize the temperature sensitivity of photosynthesis and respiration of Prochloron sp. in order to assess its physiological role in the productivity and distribution of the symbiosis. Colonies of the host ascidian Lissoclinum patella were collected from exposed and shaded habitats in a shallow lagoon in Palau, West Caroline Islands, during February and March, 1983. Some colonies from the two light habitats were maintained under conditions of high light (2 200 E m^–2 s^–1) and low light (400 E m^–2 s^–1) in running seawater tanks. The environments were characterized in terms of daily light quantum fluxes, daily periods of light-saturated photosynthesis (H_sat), and photon flux density levels. Prochloron sp. cells were isolated from the hosts and examined for their photosynthesis vs irradiance relationships, respiration, pigment content and photosynthetic unit features. In addition, daily P:R ratios, photosynthetic quotients, carbon balances and photosynthetic carbon release were also characterized. It was found that Prochloron sp. cells from low-light colonies possessed lower chlorophyll a/b ratios, larger photosynthetic units sizes based on both reaction I and reaction II, similar numbers of reaction center I and reaction center II per cell, lower respiration levels, and lower P_max values than cells from high-light colonies. Cells isolated from low-light colonies showed photoinhibition of P_max at photon flux densities above 800 E m^–2 s^–1. However, because the host tissue attenuates about 60 to 80% of the incident irradiance, it is unlikely that these cells are normally photoinhibited in hospite. Collectively, the light-adaptation features of Prochloron sp. were more similar to those of eukaryotic algae and vascular plant chloroplasts than to those of cyanobacteria, and the responses were more sensitive to the daily flux of photosynthetic quantum than to photon flux density per se. Calculation of daily minimum carbon balances indicated that, though high-light cells had daily P:R ratios of 1.0 compared to 4.6 for low-light cells, the cells from the two different light environments showed nearly identical daily carbon gains. Cells isolated from high-light colonies released between 15 and 20% of their photosynthetically-fixed carbon, levels sufficient to be important in the nutrition of the host. Q₁₀ responses of photosynthesis and respiration in Prochloron sp. cells exposed briefly (15–45 min) to temperatures between 15° and 45°C revealed a discontinuity in the photosynthetic response at the ambient growth temperatures. The photosynthetic rates were found to be more than twice as sensitive to temperatures below ambient (Q₁₀=3.47) than to temperatures above ambient (Q₁₀=1.47). The Q₁₀ for respiration was constant (Q₁₀=1.66) over the temperature range examined. It appears that the photosynthetic temperature sensitivity of Prochloron sp. may restrict its distribution to warmer tropical waters. The ecological implications of these findings are discussed in relation to published data on other symbiotic systems and free-living algae.     

Rehydration of desiccated intertidal brown algae: Release of dissolved organic carbon and water uptake

The release of dissolved organic carbon (DOC) by Ascophyllum nodosum (L.) Le Jol. and Fucus vesiculusus L. during rehydration was investigated after desiccation under experimental conditions. During 30 min of rehydration of plants which had lost up to 70% of their water, A. nodosum released about 2 to 10 mg C/100 g dry weight, while F. vesiculosus released 10 to 50 times more. When dried to water losses exceeding 70%, plants of both species yielded similar amounts of DOC, approximating 2 g C/100 g dry weight. Considerable variance in the amounts of DOC released by individual plant of both species was observed over the whole range of water losses tested. Among the DOC released, the portion of carbohydrate-C was O to 5% with A. nodosum but 2 to 47% with F. vesiculosus. This difference was most pronounced when less than 100 mg C/100 g dry weight were released. A. nodosum regained a smaller percentage of its original weight than F. vesiculosus after 30 min of rehydration when more than 30% of fresh weight were lost during desiccation. Curves were obtained which enable the estimation of water losses in naturally desiccated specimens within 30 min.     

Effects of ambient levels of solar ultraviolet radiation on zooxanthellae and photosynthesis of the reef coral Montipora verrucosa

Paired flat plates of the hermatypic coral Montipora verrucosa from Kaneohe Bay, Oahu, Hawaii, were acclimated to photosynthetically active radiation (PAR) only and to full sunlight (PAR+UV) for several weeks in the summer of 1990. After the acclimation period, photosynthesis, both in PAR-only and PAR+UV as well as dark respiration were measured. Levels of the UV-absorbing compounds, S320, density of zooxanthellae, and chlorophyll a concentration were determined. Corals acclimated in PAR+UV had higher levels of the UV-protective compounds and lower areal zooxanthellae densities than corals acclimated in PAR-only. Chlorophyll a per unit volume of coral host and per algal cell did not differ between corals from the two acclimation treatments. Corals acclimated to PAR+UV displayed higher photosynthesis in full sunlight than corals acclimated to PAR-only, but when photosynthesis was measured in the light regime to which the corals had been acclimated, there were no differences in photosynthesis. Dark respiration was the same for corals from the two acclimation treatments regardless of the light quality immediately preceding the dark period.Contribution No. 902 HIMB     

Questions on the mechanism of temperature adaptation in marine phytoplankton

The rate of light-saturated photosynthesis in 3 marine algae [Phaeodactylum tricornutum Bohlin, Nitzschia closterium (Ehrenberg) Smith and Dunaliella tertiolecta Butcher] varies during growth in batch culture. The photosynthetic rare declines most rapidly during growth at the higher temperatures. Because of these changes in photosynthesis rate, the previously reported enhanced photosynthetic abilities caused by growth at lower temperatures (generally interpreted as evidence for higher enzyme levels) can only be observed when measurements are made late in the exponential phase or after the onset of the stationary phase of growth. When allowance is made for the earlier peak of photosynthetic ability in cultures growing at higher temperatures, there is no evidence for adaptation to lower temperatures being caused by increased levels of the enzymes required for carbon-dioxide fixation. When the changes due to growth in batch culture are taken into account, certain effects of temperature can be recognized. the dry weight: chlorophyll ratio of all 3 algae increases with decreasing growth temperatures. For P. tricornutum and N. closterium, growth at lower temperatures reduces the cellular content of chlorophyll a, but has little effect on the chlorophyll content of D. tertiolecta. The dry weight: cell-number ratio of D. tertiolecta and P. tricornutum increases with lower growth temperatures, but growth temperature has little effect on the cell mass of N. closterium. Growth of the 3 algae at lower temperatures does not increase their ability to photosynthesize at these lower temperatures. Rather, it reduces their ability to assimilate carbon dioxide at the higher temperatures.     

Hydrocarbons in benthic algae from the eastern Gulf of Mexico

Thirty-six samples of benthic algae were collected from the continental shelf along the eastern Gulf of Mexico. The algae contain 82.8±143 ppm aliphatic hydrocarbons by dry weight and 11.8±22.7 ppm aromatic and polyolefinic hydrocarbons. The aliphatic constituents of red algae are composed almost entirely of n-C₁₇ (70 to 95% of aliphatic weight); green algae have varying amounts of n-alkanes in the range of n-C₁₅ to n-C₁₉, with homologous series of odd carbon number n-alkenes. Phytadienes occur as high as 740 ppm dry weight in the green algae and do not appear to be related to time or place of collection or to presence of any petroleum pollutants. The single brown algal species contains predominantly n-C₁₅. About 30% of the samples have hydrocarbons resembling degraded petroleum residues, but no petroleum pollution of recent origin was detected in any specimen.     

Photosynthetic response to temperature and desiccation of the intertidal alga Mastocarpus papillatus

When exposed to air during low tide, intertidal macroalgae experience a terrestrial environment and often encounter extreme levels of heating and desiccation. Two aspects of photosynthesis may be influenced by this increase in temperature and decrease in water content during exposure to air: (1) the rate of aerial photosynthesis itself, and (2) the rate at which aquatic photosynthesis recovers upon immersion in water at high tide. This laboratory study examines the effect of air temperature and desiccation on photosynthesis of the intertidal macroalga Mastocarpus papillatus Kützing. Plants were collected at Hopkins Marine Station, California, USA (36°37N; 121°54W) between July and December 1990. When apical tips were exposed to 15 to 25°C air for 2 h, photosynthesis was rapidly recovered upon reimmersion in seawater. Recovery was delayed, but complete, when tissue was exposed to 30°C air, but did not occur after exposure to 35°C air. Desiccation did not influence either the rate or the ultimate level of recovery upon reimmersion. Photosynthesis in air generally decreased with increasing desication, with no net photosynthesis occurring below 25% relative water content. Net photosynthesis of hydrated thalli increased with air temperature from 15 to 30°C, then decreased at 35°C. Dark respiration of hydrated thalli increased over the entire temperature range. This study indicates that thallus heating and desiccation during periods of exposure to air can potentially influence the total carbon budget of M. papillatus.     

Daily photosynthesis,respiration, and carbon budgets in a tropical marine jellyfish (Mastigias sp.)

From measured diel photosynthesis and respiration rates, using oxygen electrodes, estimates of carbon flux between symbiotic algae (zooxanthellae) and host animal are presented for the marine scyphomedusan Mastigias sp. from a marine lake in Palau, Western Caroline Islands, during February and March 1982. The carbon budgets calculated for these lake medusae indicate that carbon fixed photosynthetically by zooxanthellae and made available to the host may satisfy up to 100% of the host's daily metabolic carbon demand (CZAR). The stable carbon isotope (¹³C) signature of the mesogleal carbon of lake Mastigias sp. was close to that of the zooxanthellae, supporting the interpretation that while these medusae may feed holozoically, some of their carbon comes from their symbionts. The diel photosynthesis, respiration, and preliminary estimates of carbon budgets of three individuals of another ecotype of Mastigias sp. collected from nearby oceanic lagoons are also given. Photosynthesis of lagoon medusae was generally greater than that for lake medusae of similar size, and lagoon medusae were phototrophic with respect to carbon, with commensurately greater CZAR values. Carbon translocated from the symbiotic algae also may contribute to the growth requirements of both lake and lagoon medusae. From carbon flux data, the lake jellyfish were estimated to contribute about 16% to the total primary productivity of their marine lake habitat.     

Photosynthetic rates of benthic marine algae in relation to light intensity and seasonal variations

The effect of light intensity on rate of photosynthesis was measured at irregular intervals over a 12-month period for 22 benthic marine algae in the western Baltic Sea. In most species photosynthesis (mg O₂·g dry weight^-1·h^-1) was highest in spring and summer, corresponding to the seasonal growth pattern of the algae. In winter all the species showed adaptation of the light compensation point. Highest productivity was shown by algae which are: short-lived annual species rather than perennials, eulittoral rather than sublittoral, and which possess sheet-like or filamentous thalli rather than coarsely branched forms. These factors are clearly inter-related.This research was carried out while one of us (R.J.K.) was an Alexander von Humboldt fellow at the University of Kiel, and is part of the programme Sonderforschungsbereich 95, Wechselwirkung Meer-Meeresboden, Universität Kiel.     

The concept of light intensity adaptation in marine phytoplankton: Some experiments with Phaeodactylum tricornutum

The historical background on adaptation of algae to various light intensities is analysed. It is argued that there is little evidence to suggest that previous growth at low light intensities enhances the ability of an alga to utilize these low light levels. Rather, the published evidence suggests that the most general response to growth at sub-optimal light intensities is a reduced ability to utilize saturating levels. The present experiments with Phaeodactylum tricornutum Bohlin have tested this concept of light intensity adaptation. Changing photosynthetic abilities during batch growth depended on the light intensity used for growth and these changes affected interpretations of the data. When measurements were made intensities appeared to photosynthesize (at all intensities) better than did those grown at higher light levels. When the changes during batch growth were taken into account, or when the alga was grown in turbidostat cultures, a different picture was obtained. Growth at reduced light intensities was accompanied by (a) increased chlorophyll content, (b) decreased rate of light-saturated photosynthesis expressed on a chlorophyll, cell number or cell protein basis, and (c) decreased activity of RuDP carboxylase. One result suggested that growth at a suboptimal light intensity did enhance the ability to utilize lower light levels. The light-saturation curve of cells grown in batch culture at 0.7 klux showed higher slopes at the low light intensities than did those grown at 12 klux. This was most marked when photosynthesis was expressed per cell, but was also apparent when it was put on a per chlorophyll basis.     

Ethologie alimentaire d'invertébrés benthiques filtreurs (ascidies). II. Variations des taux de filtration et de digestion en fonction de l'espèce

Rates of filtration and digestion of 4 species of ascidians (Clavelina lepadiformis), Müller, Ciona intestinalis (Linné, 1767), Halocynthia papillosa (Linné, 1767) and Microcosmus sabatieri (Roule, 1885) from a rocky shore at banyuls-sur-Mer, France have been studied using the unicellular algae Monochrysis lutheri as food and the methods previously applied to Phallusia mammillata (Fiala-Médioni, 1973). Eleven experiments of 24 h each were performed under constant conditions of temperature, pH, salinity, oxygen and food concentration. No recognizable feeding rhythm emerged; filtration is irregular, varying around a mean value. Observed filtration rates averaged 2489 ml/h/g organ dry weight in Clavelina lepadiformis, 3515 in Ciona intestinalis, 6349 in Halocynthia papillosa and 6909 in Microcosmus sabatieri. The higher rates are related to larger size and higher complexity of the gills. No pseudo-faeces are formed; a very small part of the faecal material is discharged within 24 h. The mean rates of digestion, in mg albumin equivalent/24 h/g organ dry weight, are: Clavelina lepadiformis, 3.05 mg; Ciona intestinalis, 4.74 mg; Halocynthia papillosa, 9.25 mg; Microcosmus sabatieri, 10.41 mg. The amount of digested algae corresponds to 83–92% (mean=85%) of algae filtered. This high percentage indicates good assimilation of Monochrysis lutheri by ascidians.

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Ethologie alimentaire d'invertébrés benthiques filtreurs (ascidies). II. Variations des taux de filtration et de digestion en fonction de l'espèce

     

Time-course of photoadaptation in the photosynthesis-irradiance relationship of a dinoflagellate exhibiting photosynthetic periodicity

Cultures of the marine dinoflagellate Glenodinium sp. were light-shifted and rates of photoadaptation determined by monitoring changes in cell volume, growth rate, pigmentation, parameters of the photosynthesisirradiance (P-I) curves and respiration. To approximate physiological conditions of field populations, cells were cultured on an alternating light-dark cycle of 12hL:12hD, which introduced a daily periodicity of photosynthesis. One result of the present study was to demonstrate how specific parameters of the P-I relationship influenced by periodicity of the light: dark cycle are distinguished from photosynthetic parameters influenced by changes in light level. Under steady-state conditions, rates of both light-saturated (P_max) and light-limited photosynthesis changed in unison over the day; these changes were not related to pigmentation, and displayed their maxima midday. This close relationship between P_max and the slope (a) of the cellular P-I curves in steadystate conditions was quickly adjusted when growth illumination was altered. Rates of light-limited photosynthesis were increased under low light conditions and the periodicity of cellular photosynthesis was maintained. The short-term responses of the P-I relationship to changing light level was different, depending on (1) whether the light shift was from high to low light or vice versa, and (2) whether the high light levels were sufficient to promote maximal photosynthesis rates. Major increases in the photosynthetic carotenoid peridinin, associated with a single type of light-harvesting chromo protein in the chloroplast, was observed immediately upon shifting high light cultures to low light conditions. Following pigment synthesis, significant increases in rates of light-limited photosynthesis were observed in about one-tenth the generation time, while cellular photosynthetic potential was unaffected. it is suggested that general results were consistent with suggested that general results were consistent with earlier reports that the major photoadaptive strategy of Glenodinium sp. is to alter photosynthetic unit (PSU) size. Photoadaptive response times to high light were light-dependent, but appeared to be shower than photoadaptive responses to low light. If light intensities were bright enough to maximize growth rates, photosynthetic response times were on the order of a generation period and pigmentation fell quickly as cells divided at a faster rate. If light-intensities were not sufficient to maximize growth rates, then pigment content did not decline, while rates of light-limited photosynthesis declined quickly. In all cases, photoadaptation was followed best by monitoring fast changes in half saturation constants for photosynthesis, rather than fluctuating changes in pigmentation. Results compared well with time-course phenomena reported for other groups of phytoplankton. Overall, results suggest phytoplankton can bring about photo-induced changes in photosynthesis very quickly and thus accommodate widely fluctuating light regimes over short periods of time.     

Effect of phosphate and ammonium levels on photosynthetic and respiratory responses of the red alga Gracilaria verrucosa

Gracilaria verrucosa (Hudson) Papenfuss exposed to nutrient enriched media (0.1 mM PO₄; 1.0 mM NH ₄ ⁺ ) by pulse feeding 2 h every third day for a period of 5 wk at 20°C and 25–30 salinity showed significantly higher rates of photosynthesis regardless of photon flux density correlated with increased pigment levels. Algae in nonenriched media showed significantly higher levels of soluble carbohydrates and decreased levels of phycoerythrin and chlorophyll a. Photosynthetic and respiratory responses to temperature 15°, 25°, 30°C and salinity (15, 25, 30 S) combinations indicate broad tolerances by both nutrient enriched and non-nutrient enriched algae. Photosynthetic and respiratory rates were highest at the high temperatures. Pulse-fed algae had significantly higher photosynthetic rates than non-nutrient enriched plants at all temperature and salinity combinations. Non-nutrient enriched algae had significantly higher respiratory rates than nutrient enriched algae at only 30°C and 15. The respiratory rates of both nutrient enriched and non-nutrient algae decreased under combinations of higher temperatures and salinities. G. verrucosa, grown without nutrients, has lower tolerances to environmental stresses.