F. Xavier Niell

BIOMASS AND DYNAMICS OF GROWTH OF ULVA SPECIES IN PALMONES RIVER ESTUARY1

During the last decade, the Palmones River estuary has undergone severe eutrophication followed by a green tide episode; two species of Ulva, rotundata Blid. and Ulva curvata (Kütz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P)of Ulva species, as well as some physicochemical variables in the estuary. Maximum biomass (up to 375 g dry wt·m−2 in some spots, corresponding to a thallus area index of nearly 17 m2Ulva·m−2 sediment) were observed in June and December. However, the biomass varied among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates observed. Growth rates were estimated directly in the field. The rates were generally higher in Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The difference between both estimates was used to quantify the importance of the processes causing loss of biomass, which were attributable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme self‐shading. Maximum chlorophyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water. However, the absolute concentrations of tissue N and P were always higher than the critical levels for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estuary. In addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass.

The Feasibility of industrial production of Spirulina (Arthrospira) in Southern Spain

The viability of the industrial production of three strains of Spirulina platensis was tested in Malaga, Southern Spain. In a pre-industrial trial using raceway ponds from laboratory-scale to 450 m2, all three strains displayed satisfactory growth. In a 10-month industrial trial in 450 m2 ponds, production was equivalent to 30–32 metric tons of dry powder per hectare per annum. In conclusion, intensive industrial production of Spirulina is viable in certain Mediterranean climates, a region previously thought to be outside its geographic limits.

Non-photosynthetic enhancement of growth by high CO2 level in the nitrophilic seaweed Ulva rigida C. Agardh (Chlorophyta)

Abstract. The effects of increased CO2 levels (10,000 μl l−1) in cultures of the green nitrophilic macroalga Ulva rigida C. Agardh were tested under conditions of N saturation and N limitation, using nitrate as the only N source. Enrichment with CO2 enhanced growth, while net photosynthesis, gross photosynthesis, dark respiration rates and soluble protein content decreased. The internal C pool remained constant at high CO2, while the assimilated C that was released to the external medium was less than half the values obtained under ambient CO2 levels. This higher retention of C provided the source for extra biomass production under N saturation. In N-sufficient thalli, nitrate-uptake rate and the activity of nitrate reductase (EC 1.6.6.1) increased under high CO2 levels. This did not affect the N content or the internal C:N balance, implying that the extra N-assimilation capacity led to the production of new biomass in proportion to C. Growth enhancement by increased level of CO2 was entirely dependent on the enhancement effect of CO2 on N-assimilation rates. The increase in nitrate reductase activity at high CO2 was not related to soluble carbohydrates or internal C. This indicates that the regulation of N assimilation by CO2 in U. rigida might involve a different pathway from that proposed for higher plants. The role of organic C release as an effective regulatory mechanism maintaining the internal C:N balance in response to different CO2 levels is discussed.

Relationship between physicochemical variables and productivity in open ponds for the production of Spirulina: a predictive model of algal yield

Spirulina is one of the most extensively used microalgae for animal and human nutrition; its main interest is centered in its high protein content, 60–65% on a dry weight basis. In this study, Spirulina was grown in open raceway ponds, and several physicochemical (e.g., pH, dissolved oxygen concentration, temperature, conductivity and irradiance) and biological (e.g., biomass concentration and yield) variables were studied. The variables were correlated in order to implement a mathematical model to predict algal yield. Dissolved oxygen concentration in the cultivation ponds ranged between 10mg l 1 in winter (115% ofO2saturation) and 30mg l 1 in summer (375% of O2saturation); a clear decrease of biomass concentration was found when dissolved oxygen was >25 mg l 1 . Neither biomass concentration nor productivity was saturated at the maximum temperature achieved in the open pond during this study (approximately 28 jC). The pH seemed to control both the maximal algal density in the pond and the productivity that were found to be maximum at pH values below 10.5. Finally, all the variables were positively correlated with irradiance. Principal component analysis (PCA) allowed recognition of different sets of samples characterized by a combination of temperature, dissolved oxygen concentration, pH, biomass, productivity, irradiance and conductivity. This method helpedtopredictasignificantlossofproductivityintheopenpondsinmid-summerduetohighpHand high-dissolved O2 concentration. D 2003 Elsevier Science B.V. All rights reserved.

External carbonic anhydrase and affinity for inorganic carbon in intertidal macroalgae

Abstract Sixteen intertidal macroalga species from the Gibraltar Strait (Southern Spain) have been examined for both their external carbonic anhydrase activity (CA; 4.2.1.1.) and their affinity for inorganic carbon (C i ). Information on the ability to use HCO 3 − was obtained by measuring the effect of increasing seawater pH on the photosynthesis and by examining the O 2 evolution curves vs. C i concentration. The species exhibited a range of characteristics of C i utilisation: the green macroalgae were saturated at seawater C i concentration with K m ranging from 250.0 to 493.3 mmol m −3 and the photosynthetic O 2 production, expressed as conductance for CO 2 ranging from 432.8 to 16.1×10 −6 m s −1 . Only three out of the eleven tested red and brown macroalgae were saturated at C i concentration of seawater and for these algae HCO 3 − use was clearly indicated by the high initial slope of the O 2 evolution rate vs. C i curve. The most efficient HCO 3 − users were species from the high intertidal habitats and rockpools. Two methods were used to infer the presence of external CA: standard method (direct enzyme assay) and use of acetazolamide (AZ), a non-permeant inhibitor of CA, in assays of photosynthetic rate. Some discrepancies between the two methods were found and we obtained indications that the use of AZ could be a more sensitive method to detect external CA. It so, we suggest that external CA might be present in all the macroalgae examined. There appeared to be no correlation between the ability to use HCO 3 − and the presence of external CA. Therefore, the presence of external CA was not a strong indication for an efficient use of HCO 3 − , although some dependence between the requirement for external CA and habitats was found.

Effects of different levels of CO2 on photosynthesis and cell components of the red alga Porphyra leucosticta

Photosynthesis and cell composition of Porphyraleucosticta discs grown at low (< 0.0001% in air), current (control) and high (1% CO2 in air)inorganic carbon (Ci) concentrations were analyzed. Carbohydrate content in discs grown at high Ci increased (15.1 mg g-1 FW) with respect to the control (6.4 mg g FW-1), whereas soluble protein content decreased to one-third (5.6 to2.1 mg g-1 FW). Carbohydrate content was unaffected and soluble protein slightly increased in discs grown at low Ci. As a consequence of these changes, a lower C/N molar ratio (8.6) was found in the discs grown at low compared to high Ci(12.4). Nitrate reductase activity increased at high Ci from 0.3 ± 0.2 to 1.7 ± 0.4 μmolNO2- g-1 FW h-1indicating that reduction and assimilation of nitrate were uncoupled. The response of photosynthesis to increasing irradiance, estimated from O2evolution vs. irradiance curves, was affected by the treatments. Maximum quantum yield (Φ O2°) and effective quantum yield (Φ O2) at 150 μmol photon m-2s-1 decreased by 20% and 50%, respectively, at low Ci. These differences could be due to changes in photosynthetic electron flow between PSII and PSI. Treatments also produced changes in maximal (Fv/Fm) and effective (ΔF/Fm′)quantum yield for photosystem II charge separation.

Soil nitrogen availability and nitrification in Mediterranean shrublands of varying fire history and successional stage

The short-term effect of a single fire, and the long-term effect of recent fire history and successional stage on total and mineral N concentration, net nitrogen mineralization, and nitrification were evaluated in soils from a steep semi-arid shrubland chronosequence in southeast Spain. A single fire significantly increased soil mineral N availability and net nitrification. Increasing fire frequency in the last few decades was. associated with a sharp decrease in surface soil organic matter and total N concentrations and pools, and with changes in the long-term N dynamic patterns. The surface-soil extractable NH4+:NO3− ratio increased throughout the chronosequence. All net mineralized N in laboratory incubations from all sites was converted to nitrate, suggesting that allelochemic inhibition of net nitrification is probably not important in this system. Net nitrification in samples during incubation increased through the sere. The maximum rate of net nitrification (kmax) increased through the first three stages of the sere. A linear relationship was found between total soil N and N mineralization, and both kmax and net nitrification for the first three stages of the sere, suggesting that total N and ammonification are likely to be the control mechanisms of nitrification within the sere. The oldest site exhibited the lowest specific kmax and the highest, potential soil respiration rate suggesting that a lower N quality and increasing competition for ammonium might also limit nitrification at least in the long-unburned garrigue site.

Red and blue light regulation of growth and photosynthetic metabolism in Porphyra umbilicalis (Bangiales, Rhodophyta)

Thallus discs 9 mm in diameter of Porphyra umbilicalis were cultivated for 4 weeks in either blue or red light at 50 μmol m-2 s-1 and 12h light per day. Growth rate, in terms of weight and area, carbon content and dimensions of intercellular matrix, was higher in thalli grown in red light, while concentrations of soluble protein and photosynthetic pigments (chlorophyll, phycocyanin and phycoerythrin in particular), package effect and cell volume were higher in thalli grown in blue light. The slower growth rate in blue light was ascribed mainly to low efficiency of light absorption (high package effect) and low photosynthetic efficiency (in terms of total photosynthetic pigments) due to little overlap of photosystem I and photosystem II pigments in this red alga in blue light.

Effects of increased atmospheric CO2 and N supply on photosynthesis, growth and cell composition of the cyanobacterium Spirulina platensis (Arthrospira)

The consequences of the addition of CO2 (1%) in cultures of S. platensis are examined in terms of biomass yield, cell composition and external medium composition. CO2 enrichment was tested under nitrogen saturating and nitrogen limiting conditions. Increasing CO2 levels did not cause any change in maximum growth rate while it decreased maximum biomass yield. Protein and pigments were decreased and carbohydrate increased by high CO2, but the capability to store carbohydrates was saturated. C:N ratio remained unchanged while organic carbon released to the external medium was enhanced, suggesting that organic carbon release in S. platensis is an efficient mechanism for the maintenance of the metabolic integrity, balancing the cell C:N ratio in response to environmental CO2 changes. CO2 affected the pigment content: Phycocyanin, chlorophyll and carotenoids were reduced in around 50%, but the photosynthetic parameters were slightly changed. We propose that in S. platensis CO2 could act promoting degradation of pigments synthetised in excess in normal CO2 conditions, that are not necessary for light harvesting. Nitrogen assimilation was significantly not affected by CO2, and it is proposed that the inability to stimulate N assimilation by CO2 enrichment determined the lack of response in maximum growth rate.

Photosynthetic adaptation of Zostera noltii Hornem.

Abstract The study of Zostera noltii Hornem. under stressed conditions in an estuary in southern Spain gives evidence that this seagrass can tolerate high light intensities without damage to its pigment pool. Therefore, photosynthesis at high light intensities remains as intense as at saturation point and it is sustained principally by Photosystem I. The existence of a short-term pigmentary response (60 min) was evidenced and the relationship between assimilation rates and the pigment pool was established. Comparisons made with Z. marina L. and between the respective environmental characteristics of both plants suggests that the special adaptive photosynthetic performance of Z. noltii can be supported by a C 4 -type metabolism.