Seasonal variation in phytoplankton primary production in relation to light and nutrients in Lake Awasa,Ethiopia

The biomass and primary production of phytoplankton in Lake Awasa, Ethiopia was measured over a 14 month period, November 1983 to March 1985. The lake had a mean phytoplankton biomass of 34 mg chl a m^–3 (n = 14). The seasonal variation in phytoplankton biomass of the euphotic zone (mg chl a m^–2 h^–1) was muted with a CV (standard deviation/mean) of 31%. The vertical distribution of photosynthetic activity was of a typical pattern for phytoplankton with light inhibition on all but overcast days. The maximum specific rates of photosynthesis or photosynthetic capacity (Ø_max) for the lake approached 19 mg O₂ (mg chl a)^–1 h^–1, with high values during periods of low phytoplankton biomass. Areal rates of photosynthesis ranged between 0.30 to 0.73 g O₂ m^–2 h^–1 and 3.3 to 7.8 g O₂ m^–2 d^–1. The efficiency of utilisation of PhAR incident on the lake surface varied from 2.4 to 4.1 mmol E^–1 with the highest efficiency observed corresponding to the lowest surface radiation. Calculated on a caloric basis, the efficiency ranged between 1.7 and 2.9%. The temporal pattern of primary production by phytoplankton showed limited variability (CV = 21 %).     

Phytoplankton primary production in a eutrophic cooling water pond

The seasonal variation of phytoplankton photosynthesis was measured with ¹⁴C-method in a warmed ice-free pond in central Finland. Simultaneously with in situ measurements the photosynthesis was also measured in an incubator with different water temperatures and constant light (ca. 16 W m^–2). The total annual photosynthesis was 57.2 C m^–2 a^–1. The portion of the winter and spring production of the annual photosynthesis was 18.4%, that of the autumn production ws 17.4%. Thus 64.3% of the total annual phytoplankton photosynthesis occurred in the three summer months. The range of the daily integrated photosynthesis per unit area was 1.9—563 mg C m^–2d^–1. The photosynthetic rate per unit chlorophyll a varied in situ from 0.94 to 33.1 mg C (mg chl. a)^–1 d^–1. The highest value was measured in the beginning of July and the lowest in mid-January. The photosynthetic rate increased in situ exponentially with increasing water temperature. In the incubator the highest photosynthetic rate values were also found in July and August (at+20 °C) when the phytoplankton population was increasing and the minimum values occurred after every diatom maximum both in spring and autumn. Light was a limiting factor for photosynthesis from September to Mid-January, low water temperature was a limiting factor from late January through May. The efficiency of the photosynthesis varied between 0.1 and 0.7% of P.A.R. According to the incubator experiments the Q₁₀ values for the photosynthesis were 2.45 and 2.44 for the winter population between 1 and 10° C and for the summer population between 5 and 15° C, respectively, but the Q₁₀ values decrease at the higher temperatures. The main effect of the warm effluents on the yearly photosynthesis was the increase of production in spring months due to the lack of ice cover. However, the increase of total annual phytoplankton photosynthesis was only ca. 10–15%, because the water temperature was during the spring months below 10° C.     

Impacts of seabird-derived nutrients on water quality and diatom assemblages from Cape Vera,Devon Island,Canadian High Arctic

Relationships between key phytoplankton attributes including Chl a-specific light absorption, pigment composition and concentration, photosynthesis, primary production and community structure were studied in two open shallow nutrient-poor coastal systems receiving similar amounts of sewage water. Both systems were significantly nitrogen limited. However, differences in wastewater treatment (primary vs secondary) and sewage dilution (50%) between the two systems caused a greater difference between systems than locally around the outflows. For both systems, water at the outlet had significantly lower water transparency caused by a 20% higher absorption by coloured dissolved organic matter. Nutrient concentrations were also elevated, gradually decreasing with distance north (governing current) of the outflows, causing higher abundance of nano-sized phytoplankton, higher content of carotenoid pigments, 20–50% higher Chl a-specific absorption coefficients and higher photosynthetic capacity. Although maximum rates of Chl a-normalised photosynthesis were strongly related to nitrate availability, no effects were found on the derived areal primary production or algal biomass suggesting that photosynthetic and optical parameters are more sensitive indicators of nutrient enrichment than biomass or productivity. Handling editor: Tasman Peter Crowe     

Some aspects of photosynthetic characteristics in a set of perennial irrigation reservoirs located in five river basins in Sri Lanka

Phytoplankton primary productivity of eleven irrigation reservoirs located in five river basins in Sri Lanka was determined on a single occasion together with light climate and nutrient concentrations. Although area-based gross primary productivity (1.43–11.65 g O₂ m^–2 d^–1) falls within the range already established for tropical water bodies, net daily rate was negative in three water bodies. Light-saturated optimum rates were found in water bodies, with relatively high algal biomass, but photosynthetic efficiency or specific rates were higher in water bodies with low algal biomass, indicating nutrient limitation or physiological adaptation of phytoplankton. Concentrations of micronutrients and algal biomass in the reservoirs are largely altered by high flushing rate resulting from irrigation release. Underwater light climate and nutrient availability control the rate of photosynthesis and subsequent area-based primary production to a great extent. However, morpho-edephic index or euphotic algal biomass in the most productive stratum of the water column is not a good predictor of photosynthetic capacity or daily rate of primary production of these shallow tropical irrigation reservoirs.     

Phytoplankton biomass and production in northern South China Sea during summer: Influenced by Pearl River discharge and coastal upwelling

Chlorophyll a and primary production were studied in northern South China Sea during summer from 2007 to 2008. Microplankton dominated total phytoplankton biomass in the coast, while picoplankton dominated in the offshore. Algae bloom caused by Thalassionema nitzschioides was found at the subsurface of upwelling regions (D2, C2) in 2008, and maximum of phytoplankton abundance reached 1.58 × 10⁶ ind L^?1. Integrated primary production ranged from 189.3 to 976.2 mg m^?2 d^?1 in 2007, and ranged from 652.1 to 6601 mg m^?2 d^?1 in 2008. PP showed positive relationship with IPP (p < 0.01) and negative relationship with SST (p < 0.05). Coastal upwelling and Pearl River discharge sustained high PP, and played important role in regulating the phytoplankton biomass and production.     

Phytoplankton biomass and production in northern South China Sea during summer: Influenced by Pearl River discharge and coastal upwelling

Chlorophyll a and primary production were studied in northern South China Sea during summer from 2007 to 2008. Microplankton dominated total phytoplankton biomass in the coast, while picoplankton dominated in the offshore. Algae bloom caused by Thalassionema nitzschioides was found at the subsurface of upwelling regions (D2, C2) in 2008, and maximum of phytoplankton abundance reached 1.58 × 10⁶ ind L^?1. Integrated primary production ranged from 189.3 to 976.2 mg m^?2 d^?1 in 2007, and ranged from 652.1 to 6601 mg m^?2 d^?1 in 2008. PP showed positive relationship with IPP (p < 0.01) and negative relationship with SST (p < 0.05). Coastal upwelling and Pearl River discharge sustained high PP, and played important role in regulating the phytoplankton biomass and production.     

Phytoplankton biomass and production in shelf waters off NW Spain: spatial and seasonal variability in relation to upwelling

Summary Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m^–2 and 86.9 ± 44.0 mg C m^–2 h^–1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower.     

Theory of the Upper Limit to Phytoplankton Production per Unit Area in Natural Waters

Using the maximum quantum yield of photosynthesis, the maximum daily integral of photosynthetically active radiation (PAR) and the euphotic zone depth as a basis, general formulae for the upper limits to gross and net carbon fixation in natural waters are derived by theoretical considerations. The results are compared with a set of extremely high production data published by independently working authors, including data from algal mass cultures, oxidation ponds, freshwater and salt lakes, reservoirs, rivers and canals, coastal and other marine waters, including upwelling areas. The comparison reveals a quite surprising degree of agreement and suggests that the derived formulae represent a new, theoretically sound general approach to phytoplankton production. In particular, it can be shown that the upper limit to phytoplankton production in natural waters is about three times higher than earlier estimates in the literature. The maximum energy efficiency is of the same order of magnitude as in terrestrial plant communities.     

22 Nutrient use efficiency and coastal productivity: comparative perspectives on ecosystem structure and mechanisms of control

Net primary production in marine ecosystems ultimately reflects the inputs of nutrients and the efficiency with which nutrients are acquired and used by phytoplankton in growth. In contrast to our understanding of the linkages between nutrient loading and production, the influence of nutrient use efficiency (NUE) on cross-system variations in coastal productivity remains unclear. Nutrient use efficiency at the ecosystem scale is the product of the per capita efficiency of nutrient use in phytoplankton growth and the efficiency with which phytoplankton communities are able to assimilate limiting nutrient(s). We measured the relative dominance of ecosystem N pools by phytoplankton biomass as an index of NUE across 56 inner-shelf sites. These sites were distributed across a strong geographic range of upwelling intensity and productivity along the coasts of Oregon, California and New Zealand. We also compiled an extensive dataset of published NUE values in coastal and oceanic sites in order to assess cross-system patterns and differences in NUE. Our results indicate that exceptional rates of productivity in inner-shelf upwelling systems arise as a consequence of near dominance of ecosystem N pools by phytoplankton biomass. Elevated rates of NUE nevertheless appear to be a transient phenomenon in marine systems. Cross-shelf transects across upwelling fronts off the Oregon coast reveal a temporal pattern of intense phytoplankton blooms and decline that reflects the eventual dominance of ecosystems N pools by detrital and dissolved organic N pools. Our findings suggest that NUE may play a central role in governing the productivity of marine ecosystems.     

不同CO2浓度下大豆叶片的光合生理生态特性

CO₂是光合作用的原料和底物,影响着光合作用的进程和光合产物的数量.利用Li-6400-40B同时测量大豆叶片在不同CO₂浓度(300、400、500和600 μmol·mol^-1)下的光合电子传递速率和光合作用对光的响应曲线,并用构建的光合作用对光响应机理模型拟合这些光响应曲线,获得大豆叶片一系列的光合参数、生理生态参数和捕光色素分子的物理参数.结果表明: 电子利用效率、最大电子传递速率和最大净光合速率随CO₂浓度的升高而增加;光补偿点和暗呼吸速率随CO₂浓度的升高而下降;光能利用效率和内禀(瞬时)水分利用效率随CO₂浓度的升高而增加,不同CO₂浓度下的最大光能利用效率和最大内禀(瞬时)水分利用效率之间存在显著差异,但不同CO₂浓度下的最大羧化效率的差异不显著.CO₂浓度的大小对光合作用中原初光反应存在一定程度的影响,即高CO₂浓度有利于减小捕光色素分子处于最低激发态的最小平均寿命,以提高光能传递的速度及增加大豆光合电子流的利用效率.     

不同CO2浓度下大豆叶片的光合生理生态特性

CO₂是光合作用的原料和底物,影响着光合作用的进程和光合产物的数量.利用Li-6400-40B同时测量大豆叶片在不同CO₂浓度(300、400、500和600 μmol·mol^-1)下的光合电子传递速率和光合作用对光的响应曲线,并用构建的光合作用对光响应机理模型拟合这些光响应曲线,获得大豆叶片一系列的光合参数、生理生态参数和捕光色素分子的物理参数.结果表明: 电子利用效率、最大电子传递速率和最大净光合速率随CO₂浓度的升高而增加;光补偿点和暗呼吸速率随CO₂浓度的升高而下降;光能利用效率和内禀(瞬时)水分利用效率随CO₂浓度的升高而增加,不同CO₂浓度下的最大光能利用效率和最大内禀(瞬时)水分利用效率之间存在显著差异,但不同CO₂浓度下的最大羧化效率的差异不显著.CO₂浓度的大小对光合作用中原初光反应存在一定程度的影响,即高CO₂浓度有利于减小捕光色素分子处于最低激发态的最小平均寿命,以提高光能传递的速度及增加大豆光合电子流的利用效率.     

Polymixis and algal production in a tropical lake: latitudinal effects on the seasonality of photosynthesis

SUMMARY. 1. Phytoplankton production was measured during 1981–82 in Bahia de Puno. a large polymictic system that is part of LakeTiticaca in the tropical Andes (Peru-Bolivia), Photosynthesis followed aweak seasonal pattern through each 12-month cycle but the largestvariations occurrud between years. 2. The large temporal variations in productivity appeared to becontrolled by biological events rather than by the direct effeets ofseasonal or aseasonal physical processes. Major shifts in production overthe 2-year period were attributable to the proportional abundance andactivity of N₂-fixing blue-green algae. Production was uncorrelated withthe seasonal radiation cycle. 3. In vivo fluorescence and photosynthetic assays revealed largechanges in phytoplankton community structure over time and depth.The shifts in vertical structure were associated with changes in transparency and water column stabilily.Physiological as well as floristiceffects dictated the variations in fluorescence per unit chlorophyll a. 4. An analysis of twenty-seven primary productivity data sets fromdifferent latitudes shtiwed that Bahia dc Puno resembled other tropicallakes in its relatively weak coupling between algal photosynthesis andseasonal variations in light. Productivity in the temperate zone correlated with the annual cycle of incoming radiation while the tropicalproduction data did not. For many of the tropical lakes, but fewtemperate lakes, the between-month variance in primary production wassignificantly higher than the between-month variance for incomingradiation. There was a significant positive relationship between maximum production variance explained hy light (maximum r² for each dataset) and latitude. 5. As in many tropical lakes. Bahia de Puno experiences moderatelylarge variations in algal photosynthesis.The muted seasonal cycle of light explains only a small portion of the total variation In productivity, and other factors such as weuther-related events are disproportionately important.     

模拟水流条件下初级生产力及光动力学参数

为探讨水动力作用及其他物理因子改变对湖泊初级生产力的影响 ,1999年 5月 8日～ 6月 2 4日在中国科学院太湖湖泊生态系统研究站大型生态实验槽内进行模拟水动力实验 ,分 3种水流状态 2种光强测定初级生产力及其他相关参数。分析了初级生产力、光合速率的垂直分布 ,光合速率随光强的变化 ,并借助光动力学模型拟合得到光动力学参数。结果表明 ,在静止状态下 ,当水表面光强大于 5 0 0μmol/ (m2 · s)时 ,0～ 0 .4 m处存在光抑制现象 ,最大初级生产力出现在 0 .4～ 0 .6 m,此后由于动力作用使水体悬浮物增加 ,改变了水下光照条件 ,致使最大初级生产力呈向上移动的趋势 ,出现在 0～ 0 .2 m间 ;光合速率在静止状态下随深度递减缓慢 ,而到大水流状态则递减极为迅速 ,大水流状态下的平均光合速率明显低于静止状态和小水流状态 ;基于 2种类型的光动力学模型进行非线性拟合得到的 P- I曲线相关性很好 ,2种模型模拟的结果比较接近 ,基本上能够反映太湖光合速率随光强变化的实际情况 ;在太湖这种大型浅水湖泊 ,水动力的作用使得水体中悬浮物增加 ,造成光强的迅速衰减 ,这可能会大大降低湖泊的初级生产过程     

Influence of Sediment Inflow on Phytoplankton Primary Productivity in Lake Tahoe (California-Nevada)

Light, nutrient concentrations and phytoplankton photosynthesis were studied in a Lake Tahoe sediment plume during maximum spring runoff. They were compared with conditions in clear lake waters not influenced by inlets. In the plume, nutrient concentrations increased in proportion to sediment density whereas light transmission of water was reduced with little effect on the spectral composition except for red light. Light inhibition of photosynthesis at the lake surface was less pronounced in the plume than in clear water and light limitation occurred more rapidly in deeper layers. Evidence from both lake experiments and laboratory bioassays suggests that iron had the greatest stimulatory effect on both photosynthetic activity and biomass growth at maximum sediment densities near the stream inlet. Because of less surface inhibition, photosynthetic light energy utilization efficiency was usually higher in the sediment plume which occurred in relatively shallow areas near the shore. In order to estimate overall effects of enhanced turbidity associated with nutrient loading on Lake Tahoe's primary productivity, profiles taken in shallow areas near the lakeshore were extrapolated to the maximum depth of photosynthesis. Light limitation would cause decreasing productivity, but nutrient stimulation would make this effect less pronounced. The overall effect would depend on the extent of sediment loading relative to nutrient loading.     

Seasonal variations in upwelling and in the grazing impact of copepods on phytoplankton off A Coruña (Galicia, NW Spain)

The impact of grazing by copepods on phytoplankton was studied during a seasonal cycle on the Galician shelf off A Coruña (NW Spain). Grazing was estimated by measuring the chlorophyll gut content and the evacuation rates of copepods from three mesh-size classes: 200-500 (small), 500-1000 (medium), and 1000-2000 μm (large). Between February 1996 and June 1997, monthly measurements of water temperature, chlorophyll concentration, primary production rates, and copepod abundance, chlorophyll gut content, and evacuation rates were taken at an 80-m-deep, fixed shelf station. Additionally, the same measurements were collected daily during two bloom events in March and in July 1996. Small copepods were the most abundant through the seasonal cycle. The highest grazing impact, however, was due to the medium and large size classes. Grazing by small copepods exceeded grazing by medium and large copepods only during phytoplankton spring blooms. The impact of copepod grazing (considering all size fractions) was generally low. On average, 2% of the phytoplankton biomass and 6% of the primary production were removed daily by the copepod community. Maximum grazing impact values (9% of the phytoplankton biomass and 39% of the primary production) were found in mid-summer. These results suggest that most of the phytoplankton biomass would escape direct copepod grazing in this upwelling area.     

Limnological studies on freshwater ponds of Hyderabad — India

Seasonal abundance of phytoplankton has been discussed in three tropical ponds of Hyderabad, India during two years of investigation. The observed patterns have been characterized as seasonal maxima and minima during summer, monsoon and winter. The tropical patterns observed in the study ponds were typical but different from those observed in temperate regions. Most of the maxima were observed in winter and the minima during the monsoon or rainy season. Diatomeae dominated the phytoplankton of all the ponds in all seasons. An inverse relationship between Diatomeae and Cyanophyta, and Diatomeae and Euglenineae was observed. The phytoplankters have been grouped as perennial, summer, monsoon and winter species.     

Seasonal Dynamics of Planktonic Community Metabolism in Newly Constructed Tropical Ponds in a Swampy Area

Studies on community metabolism in newly constructed ponds on a swampy area were made over a period of twenty-four months from November, 1981 to October, 1983. The fluctuations in the gross and net primary productions, photosynthetic efficiency and assimilation efficiency are discussed. The productivity of ponds was apparently influenced by the physico-chemical and biological environment of the water. pH, secchi disc transparency, phosphate and nitrate-N were negatively correlated with gross primary productivity, while temperature, conductivity, total alkalinity and ammonium-N showed positive correlation. The phytoplankton also exhibited positive correlation with primary production. The P/R ratio ranged between 1.79 and 2.91, indicating a high degree of self maintenance of the system. The solar energy conversion efficiency through photosynthesis ranged between 0.17 % and 1.08 % in the first year and 0.09 % and 0.05 % in the second year. Annual average assimilation efficiency ranged between 37.32 % and 56.58 %.     

Hydrography and characteristics of the phytoplankton in shelf and oceanic waters off southeastern Brazil during winter (July/August 1982) and summer (February/March 1984)

The physical and chemical environment, and the phytoplankton primary production of southeastern Brazil were studied in relation to the general oceanographic structure during two research cruises (winter and summer). In each cruise, a total of 91 stations were occupied. Data were collected on the spatial distribution of nutrients, phytoplankton biomass and photosynthetic capacity over the coastal, shelf and oceanic areas off São Paulo, Paraná and Santa Catarina States.During wintertime, the mixing processes between tropical warm waters of the Brazil Current and subantarctic waters of the Malvinas Current formed strong environmental gradients. The drainings of Rio de La Plata and Lagoa dos Patos are transported northwards by coastal currents, enriching the shelf waters off Santa Catarina State with inorganic nutrients and consequently increasing the chlorophyll a to the highest concentrations (> 3.5 mg m ^–3) measured during the two cruises. In slope waters chlorophyll values were always low (0.05–0.45 mg m ^–3). The chlorophyll within the euphotic layer varied from 8.8–36.7 and 1.2–18.5 mg m^–2 during winter and summer, respectively.The surface photosynthetic rates during winter and summer cruises ranged respectively from 0.21–9.17 and 0.66–19.60 mgC/mgChl.a/h. The mean rates were higher in nearshore waters and decreased seaward.The thermal structure of the water column affected the vertical distribution of chlorophyll a and photosynthesis within the euphotic zone; During unstratified periods (winter) they were uniformly distributed but the occurrence of subsurface peaks of chlorophyll and strong photosynthetic inhibition of low light adapted cells in deeper layers are associated to the seasonal thermocline. Occasionally, upwelling of deep waters from shelf break enriched the deeper euphotic layers in offshore areas. Intensive upwelling was observed off Paranagua Bay (Parana State) and the mechanisms of its formation are discussed.     

Response of Phytoplankton Photophysiology to Varying Environmental Conditions in the Sub-Antarctic and Polar Frontal Zone

Climate-driven changes are expected to alter the hydrography of the Sub-Antarctic Zone (SAZ) and Polar Frontal Zone (PFZ) south of Australia, in which distinct regional environments are believed to be responsible for the differences in phytoplankton biomass in these regions. Here, we report how the dynamic influences of light, iron and temperature, which are responsible for the photophysiological differences between phytoplankton in the SAZ and PFZ, contribute to the biomass differences in these regions. High effective photochemical efficiency of photosystem II (/ 0.4), maximum photosynthesis rate (), light-saturation intensity (), maximum rate of photosynthetic electron transport (1/), and low photoprotective pigment concentrations observed in the SAZ correspond to high chlorophyll and iron concentrations. In contrast, phytoplankton in the PFZ exhibits low / ( 0.2) and high concentrations of photoprotective pigments under low light environment. Strong negative relationships between iron, temperature, and photoprotective pigments demonstrate that cells were producing more photoprotective pigments under low temperature and iron conditions, and are responsible for the low biomass and low productivity measured in the PFZ. As warming and enhanced iron input is expected in this region, this could probably increase phytoplankton photosynthesis in this region. However, complex interactions between the biogeochemical processes (e.g. stratification caused by warming could prevent mixing of nutrients), which control phytoplankton biomass and productivity, remain uncertain.     

Effect of Mesodinium rubrum (= Myrionecta rubra) on the action and absorption spectra of phytoplankton in a coastal marine inlet

This study, carried out at a single station in the Bedford Basin(Nova Scotia, Canada), examined time-dependent changes in thephysical and chemical conditions of the waters with associatedchanges in species composition and some photosynthesis propertiesof phytoplankton. The sampling period covered late summer months(August and September) and fall months (October to December).Changes in the water conditions were found to influence speciescomposition, which in turn had an effect on the shapes and amplitudesof the action and absorption spectra of phytoplankton, and onthe maximum quantum yield of photosynthesis. The most remarkablechange was observed in October during a bloom of Mesodiniumrubrum, a ciliate harbouring photosynthetic endosymbionts richin phycobilins. The presence of M. rubrum yielded atypical shapesof the measured photosynthetic action spectra; furthermore,other photosynthesis properties changed significantly. Theseresults demonstrate that the presence of certain pigments inthe water column may be associated with a marked shift fromwhat may be considered typical (representative) photosynthesisproperties of phytoplankton.