Juan J. Vergara

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.

Effects of light availability on growth, architecture and nutrient content of the seagrass Zostera noltii Hornem

The growth vs. irradiance response of the seagrass Zostera noltii from Cadiz Bay Natural Park (southwestern Spain) was characterised. Plants were exposed along 14 days to different light treatments (1%, 7%, 42% and 100% surface irradiance, SI), using shade screens in an outdoor mesocosm. Growth at 100% SI (1.6 mg DW plant(-1) day(-1)) was lower than that at 42% SI (2.4 mg DW plant(-1) day(-1)), suggesting photo inhibition. The minimum light requirement estimated was 0.8 mol photons m(-2) day(-1) (2% SI). Light availability affected the pattern of plant development and the overall plant growth. The contribution of the apical shoots to the aboveground production was nearly constant (c.a. 1.13 cm plant(-1) day(-1)) regardless of the light level (except at 1% SI). In contrast, recruitment and growth of lateral shoots arising from the main rhizome axes accounted for the observed differences in aboveground growth, Rhizome branching was only observed at 42% SI. The possibility of a light threshold for rhizome branching could explain the seasonality of shoot recruitment, as well as the observed decrease in shoot density along depth (or light) gradients in seagrass meadows. Carbon demands at low irradiances (1% and 7% SI) were partially met by mobilization of carbohydrate reserves (sucrose in belowground and starch in aboveground parts). Plant nitrogen content decreased with increasing light, especially in belowground parts, reaching critical levels for growth. [KEYWORDS: branching, C/N ratio, growth rate, light, nonstructural carbohydrates, plant architecture, seagrass]

Biofiltering efficiency in removal of dissolved nutrients by three species of estuarine macroalgae cultivated with sea bass (Dicentrarchus labrax) waste waters 1. Phosphate

The potential of three estuarine macroalgae (Ulvarotundata, Enteromorpa intestinalis andGracilaria gracilis) as biofilters for phosphate ineffluents of a sea bass (Dicentrarchus labrax) cultivationtank was studied. These seaweeds thrive in Cádiz Bay and were alsoselected because of their economic potential, so that environmental andeconomicadvantages may be achieved by future integrated aquaculture practices in thelocal fish farms. The study was designed to investigate the functioning of Pnutrition of the selected species. Maximum velocity of phosphate uptake (2.86μmol PO4 g−1 dry wth−1) was found in U. rotundata.This species also showed the highest affinity for this nutrient. At low flowrates (< 2 volumes d−1), the three species efficientlyfiltered the phosphate dissolved in the waste water, with a minimum efficiencyof 60.7% in U. rotundata. Net phosphate uptake rate wassignificantly affected by the water flow, being greatest at the highest rateassayed (2 volumes d−1). The marked decrease in tissue P shownby the three species during a flow-through experiment suggested that growth wasP limited. However, due to the increase in biomass, total P biomass increasedinthe cultures. A significant correlation was found between growth rates and thenet P biomass gained in the cultures. A three-stage design under low water flow(0.5 volumes d−1) showed that the highest growth rates (up to0.14 d−1) and integrated phosphate uptake rates(up to 5.8 μmol PO43− g−1dry wt d−1) were found in E.intestinalis in the first stage, with decreasing rates in thefollowing ones. As a result, phosphate become limiting and low increments oreven losses of total P biomass in these stages were found suggesting thatphosphate was excreted from the algae. The results show the potential abilityofthe three species to reduce substantially, at low water flow, the phosphateconcentration in waste waters from a D. labrax cultivationtank, and thus the quality of effluents from intensive aquaculture practices.

DIEL PERIODICITY OF NITRATE REDUCTASE ACTIVITY AND PROTEIN LEVELS IN THE MARINE DIATOM THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYCEAE)

The diel variation and regulation of the enzyme nitrate reductase (NR) were examined in the diatom Thalassiosira weissflogii (Gru.) Fryxell et Hasle. NR was purified, and polyclonal antibodies were raised to a 98‐kD polypeptide. The antibodies cross‐reacted only with proteins from closely related diatom species, suggesting significant epitopic variation of this enzyme within algal divisions. Neither NR enzymatic activity nor protein was detected in cells grown with ammonium as the sole nitrogen source; the addition of ammonium to cells growing on nitrate decreased both protein levels and enzyme activity by 40% within 2 h. In cells grown on a 12:12 h LD cycle, NR activity and NR protein levels were highly correlated, with a peak at midday, a decrease toward the end of the photoperiod, and an increase in activity beginning near the end of the dark period. The addition of actinomycin D (an inhibitor of RNA synthesis) and cycloheximide (an inhibitor of protein synthesis) affected NR activity and NR protein levels identically, strongly suggesting that this nuclear‐encoded protein is regulated primarily at a transcriptional level. The diel pattern of NR protein and activity ceased immediately following transfer to continuous light, indicating that the periodicity is not directly controlled by a circadian rhythm. Time‐lagged cross‐correlation analysis revealed a 6‐h phased difference between the minimum enzyme activity or protein levels and the maximum cellular carbon pool. On the basis of the experimental results, we develop a model proposing that (1) NR activity is regulated primarily by transcriptional regulation of NR synthesis and that (2) the level of expression of the enzyme during a given day is correlated with the integrated pool of organic carbon accumulated during the preceding photoperiod.

Biochemical responses and photosynthetic performance of Gracilaria sp. (Rhodophyta) from Cádiz, Spain, cultured under different inorganic carbon and nitrogen levels

Photosynthetic acclimation and the interactions between carbon (C) and nitrogen (N) metabolism have been studied in the red macroalga Gracilaria sp. from Cadiz, Spain, cultured under different inorganic C and N levels. The use of chemostats and buffered medium allowed continuous restoration of the alkaline reserve and constancy of pH during the experiments. The N:C ratios and phycobiliprotein, chlorophyll a and soluble protein contents decreased when Gracilaria sp. was grown at low N levels. Algae grown in a high inorganic C concentration (5% CO2) displayed a higher soluble carbohydrate concentration and maximum photosynthesis rates but a lower photosynthesic affinity for inorganic C, and lower phycobiliprotein and Rubisco contents, than those cultured at low inorganic C levels (air CO2). The inorganic C enrichment also affected the N uptake and assimilation in Gracilaria sp., causing a decrease in the N uptake rate even under conditions of N sufficiency. These results reflect the significant influence of...

Morphological and physiological differences between two morphotypes of Zostera noltii Hornem. from the south-western Iberian Peninsula

Abstract The morphological and physiological differences between two morphotypes of Z. noltii Hornem. were studied in the intertidal meadows on the south-western Iberian Peninsula (Palmones river estuary and Ria Formosa). A small-leaved morphotype (SM) grows mainly at high intertidal sites, meadow edges or in recently deposited sandbanks, whereas a large-leaved morphotype (LM) generally thrives in well-structured beds or in deeper places. This study deals with the morphological, biochemical and physiological differences between these morphotypes as well as the ecological implications of the occurrence of different morphotypes in the same meadow. Shoot length, leaf width, rhizome internode length, roots per node, root length, leaf nutrient and pigment contents, and photosynthetic rates of both morphotypes were compared. The below-ground architecture (root and rhizome complex) of both morphotypes was more developed in sites characterized by higher hydrodynamics and/or a lower nitrogen content in sediments. Both morphotypes showed similar values for photosynthetic efficiency, dark respiration rate and compensation irradiance. On the other hand, the net photosynthetic capacity was much greater (5-fold) for the SM. This difference could explain the greater growth rate and faster leaf turnover rate of the SM compared with the LM. The occurrence of the SM in newly settled areas (and in the meadow edges) could be explained on the basis of its higher growth rate, which would allow a faster spreading of the meadow and/or better recovery after burial resulting from stormy weathers.

Integrated outdoor culture of two estuarine macroalgae as biofilters for dissolved nutrients from Sparus auratus waste waters

An integrated outdoor cultivation of two macroalgal species: Ulva rotundata (Chlorophyta) and Gracilariopsis longissima (Rhodophyta) was designed. The macroalgae were cultured in effluents from an intensive marine culture (growout phase) of gilthead seabream Sparus aurata. The biomass evolution of the algal tanks followed a logistic curve, where the approach to the maximum stocking density of seaweeds was governed by thalli self-shading, as nutrient limitation in the cultivation tank was unlikely. The maximum stocking density of the system was approximately 27.8 g U. rotundata L−1 (16.7 Kg m−2) and 11.9 g G. longissima L−1 (7.12 Kg m−2). Yield was more than 3 times higher in U. rotundata than in G. longissima. Overall, U. rotundata removed a greater percentage of phosphate (8.9%) and total dissolved inorganic nitrogen (54%) flowing into the algal tanks than G. longissima. The latter species biofiltered approximately 3.2% of phosphate and 17% of the total dissolved inorganic nitrogen input. However, mean nutrient uptake rates on wet weight basis were usually higher in G. longissima than in U. rotundata. The production of total oxidised nitrogen in the algal tanks, considered as being the nitrification rate occurring on the algal fronds by nitrifying bacteria, was less than half of the ammonium uptake by the macroalgae, suggesting that seaweeds competed efficiently for ammonia against the nitrifyers. The biofiltration during a diel cycle showed that mean phosphate biofiltration was lower than 4.5% in the two species whereas ammonium was biofiltered efficiently (up to 67%), especially in U. rotundata. The metal and heavy metal content in the algal tissue at the end of the monitoring period suggested no metal contamination of tissues so that both macroalgal species could be used in the food industry. The study reveals the value of ecological engineering techniques in reducing the dissolved nutrient content in effluents from the fish farm, with the prospect of a better management practises, based on integrated mariculture designs, being developed by the local farmers.

Acclimation Responses of Gracilaria sp. (Rhodophyta) and Enteromorpha intestinalis (Chlorophyta) to Changes in the External Inorganic Carbon Concentration

Abstract The acclimation responses of two intertidal macroalgae, Gracilaria sp. and Enteromorpha intestinalis, to different dissolved inorganic carbon (DIC) levels were investigated under laboratory conditions. The effect of DIC availability on growth rate, biochemical composition (C, N, pigments and Rubisco) and on the degree of inhibition of external and total carbonic anhydrase activities (by acetazolamide and 6-ethoxyzolamide, respectively), and of a putative HCO3 − exchanger protein (sensitive to the inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulfonate, DIDS) was species-specific. Pigment and Rubisco contents co-varied negatively with DIC availability in Gracilaria sp. However, no such pattern was observed in Enteromorpha intestinalis. The mechanisms of DIC uptake were also modulated by the external DIC concentration. Under limiting DIC conditions, the induction of mechanisms for CO2 acquisition above the diffusive rate was observed in Gracilaria sp., while a repression of the DIDS-sensitive mechanism was obtained for Enteromorpha intestinalis. The results revealed the plasticity of these intertidal macroalgae to acclimate to different ambient DIC levels, and indicate the important role of DIC as a factor controlling biochemical and physiological processes.

SEASONAL VARIATION OF PHOTOSYNTHETIC PERFORMANCE AND LIGHT ATTENUATION IN ULVA CANOPIES FROM PALMONES RIVER ESTUARY1

The primary production of Ulva populations relies on their photosynthetic performance, which is dependent on the light availability under natural conditions. This study concerns the light attenuation characteristics in Ulva canopies and the seasonal photosynthetic performance of two different species (Ulva rotundata Blid., Ulva curvata (Kütz.) De Toni) blooming in the Palmones river estuary. Light within canopies differed from that reaching the surface. Light availability was reduced through the water column (at high tide) and Ulva canopies. In addition, light was spectrally filtered. As a result, the photosynthetically usable radiation (PUR) was further attenuated through Ulva canopies, increasing the photosynthetically active radiation/PUR ratio. The muddy sediment deposited on and between the Ulva thalli also drastically restricted the light availability. Thick Ulva mats are frequently found covering the intertidal mudflats, and therefore, thalli within these mats may be subjected to steep light gradients. As a consequence, individual Ulva growth rates cannot be extrapolated to estimate the primary production of Ulva canopies. Interspecific differences were observed for light‐saturated photosynthetic rates (Pmax) and light compensation points (LCP), with Ulva curvata generally displaying higher values than did U. rotundata. For both species, maxima were recorded in winter for Pmax, quantum yield, chlorophyll content, and absorptance, whereas minima were found in summer. Dark respiration (Rd) was not seasonally affected, and a maximum LCP was found in summer. To extrapolate these data to field situations, the temperature dependence of photosynthesis should be considered. The Q10 values were 2.44 for Rd and 1.79 for Pmax, whereas the photosynthesis rate at subsaturating light levels was unaffected. The Q10 values showed an enhanced respiratory rate in summer and a minimum in winter, whereas the seasonal differences on Pmax were damped.

Patch distribution and within-patch dynamics of the seagrass Zostera noltii hornem. in los Toruños Salt-Marsh, Cádiz Bay, Natural Park, Spain

Abstract Patch distribution and small-scale (i.e., within-patch) temporal variability in plant morphology, biomass, shoot density, tissue nutrient content and growth were studied in the intertidal seagrass Zostera noltii at Los Toruāos salt-marsh (Cádiz, Spain). The area covered by Z. noltii was 7.3%, and decreased exponentially with depth. The lack of recruitment from seedlings largely explained the normal patch size distribution observed. Overall, lower biomass, shoot density, above-ground to below-ground biomass ratios and higher leaf elongation rates were recorded at the patch edge, where biomass dynamics were primarily controlled by recruitment and mortality processes. In contrast, temporal variation in above-ground biomass in the patch centre depended largely on changes in shoot leaf number and size. There was no correlation between total biomass and shoot density in the patch centre suggesting that below-ground biomass may be space-limited. Low aboveground biomass and shoot elongation rates were recorded in May, regardless of position within the patch, and were coincident with the abundance of Ulva sp. mats. Light reduction by Ulva canopies also resulted in a mobilization of carbohydrate reserves. Such resource reallocation may represent an important short-term survival strategy, maintaining leaf and rhizome elongation capacity.