Raquel Carmona

Evaluation of the bioremediatory potential of several species of the red alga Porphyra using short-term measurements of nitrogen uptake as a rapid bioassay

Rates of inorganic nitrogen uptake by three Northeast US and three Asian species of Porphyra were compared in short-term incubations to evaluate potential for longer term and larger scale examination of bioremediation of nutrient-loaded effluents from finfish aquaculture facilities. The effects of nitrogen (N) species and concentration, temperature, acclimation history, and irradiance were investigated. Uptake rates increased ca. nine-fold from 20 to 150 μM N. Nitrate and ammonium uptake occurred at similar rates. Irradiance had a strong effect, with uptake at 40 μmol photons m−2 s−1only 55% of uptake at 150 μmol photons m−2 s−1. N-replete tissue took up inorganic nitrogen at rates that averaged only 60% of nutrient-deprived tissue. Although there were species (P. amplissima > (P. purpurea = P. umbilicalis)) and temperature effects (10 °C>5 °C>15 °C), interactions among factors indicated that individual species be considered separately. Overall, P. amplissima was the best Northeast US candidate. It took up ammonium at faster rates than other local species at 10 and 15 °C, two temperatures that fall within the expected range of industrial conditions for finfish operations.

IS THERE AN ECOPHYSIOLOGICAL EXPLANATION FOR THE GAMETOPHYTE–TETRASPOROPHYTE RATIO IN GELIDIUM SESQUIPEDALE (RHODOPHYTA)?1

In the fall, when 61% of the fronds of the Gelidium sesquipedale (Clem.) Born. et Thur. population located in Albufeira (southern Portugal) were reproductive, about 90% of these fronds were tetrasporophytes, whereas an equal percentage of female and male gametophytes was found (5%). The comparison of physiological performances of the reproductive phases (males, females and tetrasporophytes) did not reveal a physiological advantage of tetrasporic fronds. There were no significant differences either in the photosynthesis, nitrogen uptake, nitrate reductase activity, or biochemical composition of adult fronds. On the other hand, vegetative recruitment and spore production in the laboratory were significantly different. The re‐attachment to calcareous substrate and the subsequent rhizoidal growth were faster in tetrasporophytes. Particular levels of temperature, rather than irradiance, had an important effect on the phase differences in the spore release, attachment, and germination rates. Significant results were the higher release of carpospores at all irradiances at 17°C, and the higher attachment percentage of carpospores at 13°C versus tetraspores. Under higher temperatures (21°C), tetraspores showed higher attachment rates while carpospores germinated more. G. sesquipedale cystocarps released carpospores for 2 months, while tetrasporangia stopped shedding tetraspores after 1 month, resulting in a 3‐fold higher production of carpospores than tetraspores. Results showed that vegetative and spore recruitment may explain the low gametophyte–tetrasporophyte ratio of the studied population of G. sesquipedale as opposed to the physiological performance of phases.

BRYOZOANS INCREASE AVAILABLE CO2 FOR PHOTOSYNTHESIS IN GELIDIUM SESQUIPEDALE (RHODOPHYCEAE)

A possible benefit of the presence of the epiphytic bryozoan Electra pilosa (L.) for the red macroalga Gelidium sesquipedale (Clem.) Thuret et Bornet is described. Absorption spectra and photosynthetic parameters of O2 evolution vs. irradiance curves were determined for both epiphytized and nonepiphytized thalli. The absorptance of G. sesquipedale thalli for PAR was not modified by the presence of the epiphyte. Gross photosynthetic rates at saturating light were approximately doubled in epiphytized thalli. Photosynthesis by G. sesquipedale was enhanced when CO2 concentration was increased in the medium by a decrease in pH. On the other hand, an increase in pH from 8.1 to 8.7 produced a significant reduction of the O2 evolution rates indicating that G. sesquipedale has a very low capacity to use HCO3−. The decrease in photosynthesis at high pH was higher in nonepiphytized thalli than in epiphytized ones, suggesting that the amount of available CO2 is higher in the presence of E. pilosa. This positive effect was attributed to the CO2 released by respiration of the epiphyte.

Light quality affects morphology and polysaccharide yield and composition of Gelidium sesquipedale (Rhodophyceae)

Morphology and polysaccharide characterization of Gelidium sesquipedale (Clem.) Bornet et Thuret were studied in cultures grown under various light qualities. White light (WL), blue light (BL) and red light (RL) (all at photon fluence rate of 40 μmol m-2 s-1) were used for the study of morphological characteristics, and in addition yellow light (YL) for polysaccharide characterization. RL and BL induced a proliferating growth, which resulted in bushy plants under RL. Cortical cells of BL-grown plants were smaller and presented a higher density per unit area, whereas those of WL- and RL-grown alga were larger. Medullary cells followed the inverse pattern. Light quality also affected polysaccharide yield and composition, with the yield being higher under BL, RL or YL than WL. Most of the polysaccharide was extracted in distilled water at 100 °C, while a low amount was solubilized at 22 °C and 120 °C. Extracts from BL-grown alga presented the highest galactan content. The starch concentration was lower in extracts from RL-, BL- and YL-cultivated alga than in those from the initial plants. The degree of substitution with methoxyl groups and precursor was very low in all the agar fractions, but fractions extracted from BL- and WL-grown alga were more substituted by precursor. The highest sulfate content was reached under BL (about 9% w/w) and the highest 2-O-methyl-3,6-anhydro-L-galactose and 6-O-methyl-D-galactose content were found in extracts from alga grown under YL.

Affinity for inorganic carbon of Gracilaria tenuistipitata cultured at low and high irradiance

Abstract. Regulation by irradiance level of the mechanism for dissolved inorganic carbon (DIC) acquisition was examined in the red macroalga Gracilaria tenuistipitata Zhang et Xia. For this purpose, affinity for external DIC, carbonic anhydrase (CA; EC 4.2.1.1) activity and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were determined in thalli grown at 45 and 500 μmol photons m−2 s−1. Oxygen evolution rates declined by 50% when the medium pH was changed from 8.1 to 8.7, and the pH compensation point attained was ca. 9.2. These characteristics were unaffected by the light treatments. In contrast, photosynthetic conductance for DIC at pH 8.7 was doubled in thalli grown at high irradiance compared with those grown at low irradiance (to 0.74 × 10−6 from 0.33 × 10−6 m s−1). Photosynthetic rates at saturating DIC concentration were also higher by 60% in thalli grown at high irradiance. These differences could not be attributed to changes in the use of external DIC, since external CA activity did not vary. Although the irradiance level did not modify the pool size of Rubisco, Rubisco content expressed on a chlorophyll a basis was almost doubled at high irradiance. These results likely indicate that the internal transport of DIC towards the active-site of Rubisco, rather than the external use of DIC, is enhanced in the thalli grown at high irradiance.

Differential nutrient uptake by two segregated red algae in an estuarine intertidal zone

SÁnchez de Pedro R., Niell F.X. and Carmona R. 2013. Differential nutrient uptake by two segregated red algae in an estuarine intertidal zone. Phycologia 52: 461–471. DOI: 10.2216/13-147.1 Bostrychia scorpioides (Rhodophyta: Ceramiales) and Catenella caespitosa (Rhodophyta: Gigartinales) were segregated but slightly overlapping in the narrow intertidal of the Palmones River Estuary (Southern Spain). This study investigated whether there were interspecific differences in nutrient uptake capabilities and how meaningful these were to zonation. Uptake kinetics of ammonium, nitrate, and phosphate were measured over successive time intervals across a range of environmentally realistic concentrations. The interactions between ammonium and nitrate in mixed N source uptake were also tested. Using internal N and P content, turnover rates were calculated for each species for periods of emersion and submersion. Nutrient uptake kinetics were saturable for almost all nutrients except for ammonium in B. scorpioides, which showed surge uptake responses through linear kinetics. Vmax and affinity progressively decreased over 3 h for all nutrients in C. caespitosa and only for phosphate in B. scorpioides. At high dissolved inorganic nitrogen concentrations both species exhibited greater uptake rates for ammonium than nitrate; although, similar N uptake rates were obtained at the low ones. Ammonium contributed to the total N uptake in B. scorpioides to a greater extent; whereas, in C. caespitosa, this only occurred at high N concentrations. In mixed N source uptake experiments, ammonium and nitrate uptake rates by B. scorpioides decreased when the other N source was equimolarly supplied, while in C. caespitosa these interactions were absent. Catenella caespitosa showed a Vmax and affinity for phosphate fourfold higher than for B. scorpioides, with greater interspecific differences than those found for N uptake. Catenella caespitosa renewed internal nutrients faster and was more dependent on the external nutrient supply than B. scorpioides, which can withstand longer periods without nutrient supply due to its slower nutrient turnover rate. Different capabilities for nutrient acquisition in the two species suggested an adaptation to the nutrient availability at each intertidal position.

Assessing global range expansion in a cryptic species complex: insights from the red seaweed genus Asparagopsis (Florideophyceae)

The mitochondrial genetic diversity, distribution and invasive potential of multiple cryptic operational taxonomic units (OTUs) of the red invasive seaweed Asparagopsis were assessed by studying introduced Mediterranean and Hawaiian populations. Invasive behavior of each Asparagopsis OTU was inferred from phylogeographic reconstructions, past historical demographic dynamics, recent range expansion assessments and future distributional predictions obtained from demographic models. Genealogical networks resolved Asparagopsis gametophytes and tetrasporophytes into four A. taxiformis and one A. armata cryptic OTUs. Falkenbergia isolates of A. taxiformis L3 were recovered for the first time in the western Mediterranean Sea and represent a new introduction for this area. Neutrality statistics supported past range expansion for A. taxiformis L1 and L2 in Hawaii. On the other hand, extreme geographic expansion and an increase in effective population size were found only for A. taxiformis L2 in the western Mediterranean Sea. Distribution models predicted shifts of the climatically suitable areas and population expansion for A. armata L1 and A. taxiformis L1 and L2. Our integrated study confirms a high invasive risk for A. taxiformis L1 and L2 in temperate and tropical areas. Despite the differences in predictions among modelling approaches, a number of regions were identified as zones with high invasion risk for A. taxiformis L2. Since range shifts are likely climate‐driven phenomena, future invasive behavior cannot be excluded for the rest of the lineages.

Size structure and dynamics of an invasive population of lineage 2 of Asparagopsis taxiformis (Florideophyceae) in the Alboran Sea

In this study, we present basic population data of the red macroalga Asparagopsis taxiformis, widely recognized as invasive in the Mediterranean Sea. A 13‐month field study was carried out on a population located in southern Spain, addressing its phenology, population dynamics and demography. We further tested whether biomass variations were related to environmental variables at the study site. Gametophytes were present year‐round while tetrasporophytes were only found in spring and summer. Recruitment capacity and vegetative growth of the gametophytes are discussed as important modulators for the population structure and enhancers of its persistence. Thallus size‐time histograms revealed a high prevalence of small shoots that showed high mortality that was not related to self‐thinning. Biomass of A. taxiformis was higher from March to July. Vegetative growth was the main way the gametophyte population was maintained, although the presence of tetrasporophytes and fertile gametophytes in the field confirms that sexual reproduction also occurs. Its continuous and high recruitment, in terms of the number of smallest shoots, makes this southern population of A. taxiformis a source of future invasive populations due to the intensive maritime traffic in the region.

Reproductive ecology of an invasive lineage 2 population of Asparagopsis taxiformis (Bonnemaisoniales, Rhodophyta) in the Alboran Sea (western Mediterranean Sea)

Abstract Can the reproductive traits of Asparagopsis taxiformis contribute to its success as an invader? We present the reproductive phenology of a population located in southern Spain and a quantitative study of gametophyte reproductive structures. Reproductive allocation (the proportion of biomass allocated to reproductive tissue) in different size classes was analysed to investigate whether the shoot size influences the reproductive output of this population. Gametophytes were found to be reproductive in spring, autumn and the beginning of winter, whereas fertile tetrasporophytes were never observed. High reproductive performance was recorded in July, when reproductive allocation was surprisingly low (12.74±4.79%). Reproductive allocation of each size class varied over the study period, ensuring a continuous reproductive yield. The shoot size for reproduction ranged between 4–6 cm and 24–26 cm. An analysis of reproductive and vegetative volume suggested that reproductive allocation decreases with shoot size, which, as intermediate size classes are the most abundant and most persistent in the field throughout the year, optimizes the reproductive output. Reproduction in gametophytes was independent of environmental conditions in the study area. The yearly persistence of gametophytes together with the abundance of tetrasporophytes makes this population a donor source for future invasive populations.

Understanding the intertidal zonation of two estuarine red macroalgae from ex situ photoacclimative responses

This study investigated the influence of light on the distributional limits of Bostrychia scorpioides and Catenella caespitosa within a low amplitude intertidal zonation in the Palmones estuary, Spain. Changes in photosynthesis- and growth-irradiance curves and pigment content were examined ex situ at irradiances found in their natural habitat (10–230 µmol photons m−2 s−1). The highest maximum photosynthesis rate (Pm) and photosynthetic efficiency (α) were found between 20–40 µmol photons m−2 s−1 in both species. Bostrychia scorpioides, the uppermost intertidal species, had a higher Pm, α, dark respiration rate and light compensation point (Ec) than C. caespitosa at all acclimation irradiances. Net photosynthetic rates measured at their respective acclimation irradiances showed photosynthetic responses of B. scorpioides to be maximized at high irradiances, while in C. caespitosa they did not change. Higher growth rates were obtained in C. caespitosa than in B. scorpioides, which may be related to its lower thallus specific carbon content. When irradiance decreased, the chlorophyll a content of B. scorpioides increased whereas in C. caespitosa R-phycoerythrin increased. Ec for growth of B. scorpioides coincided with the irradiance at its lower distributional limit in the estuary, below which this species showed losses in biomass. However, in C. caespitosa the sustained growth ex situ at saturating irradiances contrasts with its absence from the upper intertidal zone, where similar light regimes occur. We demonstrated that while light clearly restricts the growth of B. scorpioides to the uppermost intertidal zone, this environmental factor would not prevent C. caespitosa from growing at higher levels.