Ecotypes of <Emphasis Type="Italic">Gracilaria caudata</Emphasis> (Gracilariales,Rhodophyta): physiological and morphological approaches considering life history phases

On the Brazilian coast, the red alga Gracilaria caudata J. Agardh is exploited for agar production. In view of its economic importance for potential mariculture, this work aimed to elucidate and characterize ecotypes along an extended Brazilian coastline by evaluating the effects of irradiance (70 and 150 μmol photons m^?2 s^?1) on the number of differentiated branches, growth rates (GRs), photosynthesis parameters, and pigment content of female gametophytes and tetrasporophytes from three distinct geographical areas: Ceará State (CE), Bahia State (BA), and São Paulo State (SP). Compared to low irradiance, high irradiance promoted higher GRs and a greater number of differentiated branches, as well as maximum electron transport rate (ETR_max) and maximum photosynthesis (P _max) in both phases. However, irrespective of population or irradiance, tetrasporophytes had higher ETR_max (3.30 μmol e^? m^?2 s^?1) than gametophytes (2.54 μmol e^? m^?2 s^?1), corroborating the hypothesis that tetrasporophytes have better physiological performance than gametophytes, implicating correspondingly better adaptive abilities. Under high irradiance, regardless of the period of cultivation (14 or 28 days), strains from CE presented the highest GR (15% day^?1) when compared to strains from SP (14% day^?1) and BA (13% day^?1). CE strains also had the highest number of differentiated branches and P _max. Based on these results, we suggest that CE strains are the best candidates for future experimental mariculture tests. Importantly, overall differences in physiological performance among the strains from different populations give evidence of intraspecific diversity, thus supporting the hypothesis of ecotypic differentiation and allowing this study to define different G. caudata ecotypes.     

Differential responses of tetrasporophytes and gametophytes of Mazzaella laminarioides (Gigartinales,Rhodophyta) under solar UV radiation

The effects of solar UV radiation on mycosporine‐like amino acids (MAAs), growth, photosynthetic pigments (Chl a, phycobiliproteins), soluble proteins (SP), and C and N content of Mazzaella laminarioides tetrasporophytes and gametophytes were investigated. Apical segments of tetrasporophytes and gametophytes were exposed to solar radiation under three treatments (PAR [P], PAR+UVA [PA], and PAR+UVA+UVB [PAB]) during 18 d in spring 2009, Punta Arenas, Chile. Samples were taken after 2, 6, 12, and 18 d of solar radiation exposure. Most of the parameters assessed on M. laminarioides were significantly influenced by the radiation treatment, and both gametophytes and tetrasporophytes seemed to respond differently when exposed to high UV radiation. The two main effects promoted by UV radiation were: (i) higher synthesis of MAAs in gametophytes than tetrasporophytes at 2 d, and (ii) a decrease in phycoerythrin, phycocyanin, and SPs, but an increase in MAA content in tetrasporophytes at 6 and 12 d of culture. Despite some changes that were observed in biochemical parameters in both tetrasporophytes and gametophytes of M. laminarioides when exposed to UVB radiation, these changes did not promote deleterious effects that might interfere with the growth in the long term (18 d). The tolerance and resistance of M. laminarioides to higher UV irradiance were expected, as this intertidal species is exposed to variation in solar radiation, especially during low tide.     

Effects of short-term exposure to ultraviolet-B radiation on photosynthesis and pigment content of red (wild types), greenish-brown,and green strains of Gracilaria birdiae (Gracilariales,Rhodophyta)

Based on physiological characteristics, our hypothesis was that different strains of Gracilaria birdiae from two distinct geographical areas of the Brazilian coast, 2,500 km apart, would respond differently to short-term exposure to UV-B radiation. These sites present diverse environment conditions, i.e., one is a warmer area in Ceará State (CE), northeast Brazil, whereas the other is a colder area in Espirito Santo State (ES), southeast Brazil. To test the hypothesis that the northeastern population is more resistant to the stress caused by UV-B than the southeastern, red (RD _CE , RD _ES ), green (GR _CE ), and greenish-brown (GB _CE ) strains were cultivated in the laboratory under two different treatments, viz., control (PAR) and artificial UV-B (PAR + UV-B), for 5 h each. Except for the RD _CE strain, the effective quantum yield decreased after exposure to UV-B. The photosynthesis recovery observed only for the GR _CE strain suggests dynamic photoinhibition. The phycoerythrin/phycocyanin ratio was also higher for the RD _CE strain, thereby favoring phycobilisomes acclimatization to changes in irradiance. The absence of alterations in chlorophyll a and carotenoid contents indicated there to be no damage to the photosynthetic apparatus. Results support the notion that the northeastern population, through adapting to higher irradiation, had thus become more resistant to increase UV-B. Furthermore, among the different strains, both the GR _CE and RD _CE strains appear to be more resistant to this radiation.     

Physiological comparison between gametophytes and tetrasporophytes of Gelidium canariensis (Gelidiaceae: Rhodophyta)

The physiological performances of tetrasporophytes and gametophytes of Gelidium canariensis (Grunow) Seoane-Camba were compared to estimate whether the field predominance of tetrasporophytes is due to lower fitness of gametophytes. No significant differences between tetrasporophytes and gametophytes were detected for calorific content, protein and pigment concentrations, NADH-Diaphorase, alkaline phosphatase and glucose-6-phosphate dehydrogenase activities and photosynthesis and respiration at 15, 20 and 25 °C, and pH 6.5, 8.2 and 9.2. Our results indicate that these physiological characteristics are not responsible for the scarcity of gametophytes in the field populations of G. canariensis.Abbreviations ALP = Alkaline phosphatase - G6PDH = glucose-6-phosphate dehydrogenase - DIA = NADH-Diaphorase - TRIS = Tris[hydroxymethyl]-aminomethane - PVPP = Polyvinylpolypyrrolidone     

Spatial and temporal variations of Chondrus crispus (Gigartinaceae, Rhodophyta) carrageenan content in natural populations from Galicia (NW Spain)

Qualitative and quantitative differences in carrageenan composition of gametophytes and tetrasporophytes of Chondrus crispus were observed in this study. Carrageenans in gametophytes belong to the kappa family (κ-, ι-, ν- and μ-carrageenan). The dominant fractions were κ- and ι-carrageenan (more than 50% of the total carrageenans). In tetrasporophytes, the presence of λ-carrageenan was confirmed. Carrageenan content in gametophytes (37.4?±?1.68% DW) was higher than in tetrasporophytes (29.13?±?0.76% DW). Spatial and temporal variation in carrageenan content in both life cycle phases appears to be related mainly to seawater and air temperatures, insolation, water movement and desiccation. The highest values of carrageenan content were recorded in those localities where higher values of precipitation, wind speed or water movement occurred. A bimodal temporal pattern on carrageenan content was observed. Fronds showed a high carrageenan content in spring and autumn. During these seasons, the content was over 40% in gametophytes and 30% in the tetrasporophytes. In summer and winter, these values down in both life cycle phases below 30%. In general the highest carrageenan contents were related to highest seawater temperatures. On the contrary, high air temperature and high insolation appeared to be unfavourable for carrageenan production. GLM models were obtained to predict carrageenan production from natural C. crispus populations, along Galician coast.     

Effects of elevation, wave exposure, and year on the proportion of gametophytes and tetrasporophytes in Mazzaella parksii (Rhodophyta, Gigartinaceae) populations

We investigated the effects of elevation, wave exposure, and year on the proportion of gametophytes and tetrasporophytes in populations of the intertidal red seaweed Mazzaella parksii (= M. cornucopiae, Gigartinaceae) from the Pacific coast of Canada. In July 2002, we determined the life-history phase of 864 frond samples from four populations from Barkley Sound, using the resorcinol-acetal test. For these populations, gametophytes were significantly more numerous than tetrasporophytes, and the proportion of gametophytes was significantly higher at higher elevations. The proportion of gametophytes varied directly (although less markedly) with the degree of wave exposure, but significance could not be assessed for this factor. All of these patterns were spatially consistent, as they held for two different rocky points with similar physical characteristics. One of these points had also been surveyed in 1994-1995, which allows us to conclude that the population-wise gametophyte predominance and the positive relationship between elevation and the proportion of gametophytes are stable features of this species in this area. However, the average proportion of gametophytes was similar between the studied levels of wave exposure in 1994–1995; such a difference revealed as non-significant when data were combined with those for 2002. This suggests that wave exposure is not important in determining the proportion of life-history phases for this species. Comparisons with other species are done in search of general patterns for the Gigartinaceae.     

PHOTOSYNTHETIC RESPONSES TO LIGHT AND TEMPERATURE OF THE HETEROMORPHIC MARINE ALGA MASTOCARPUS PAPILLATUS (RHODOPHYTA)1

Physiological differentiation of the heteromorphic life-history phases of the red alga Mastocarpus papillatus (C. Agardh) Kützing was assessed. Photosynthetic responses to light and temperature of the erect, foliose gametophyte were compared to those of the crustose tetrasporophyte. Plants of both phases were collected from four locations on the Pacific coast of Baja California, Mexico, and California, USA, between 32–4l° N latitude. Within each location, the chlorophyll-specific, light-saturated photosynthetic rates of gametophytes were generally five times greater than those of tetrasporophytes. Initial slopes of photosynthesis: irradiance curves were greater for gametophytes than for tetrasporophytes. The crust and the blade from each location were similar with respect to dark respiration rates. For tetrasporophytes from all locations, the photosynthetic temperature optima were between 12–15° C. The photosynthetic temperature optima for gametophytes ranged from 15–17° C for plants from Trinidad Head (41° N) to 22–25° C for plants from Punta Descanso (32° N). Both gametophytes and tetrasporophytes from the northernmost location had significantly higher photosynthetic rates than the same phase from the other three locations. The photosynthetic responses to light support models for the life history in which life history phases have different ecological roles. The gametophyte, thought to be specialized for rapid growth and competition, may allocate more resources to photosynthetic machinery, hence the higher maximum photosynthetic rates. The tetrasporophyte, thought to be specialized for resistance to herbivores, may allocate more resources to structural or chemical defenses in preference to photosynthetic machinery. Consequently, the tetrasporophyte has lower photosynthetic capacity.     

A simulation model for an Iridaea splendens (Gigartinales,Rhodophyta) population in Vancouver,Canada

Populations of Iridaea splendens at Brockton Point, Stanley Park, Vancouver, Canada were observed to alternate in dominance between the gametophytic phase in summer and tetrasporophytic phase in winter. The mechanism regulating this alternation is not clear. Using a matrix projection model to simulate population growth, we show that this alternation is possible if there are differential survival and recruitment rates of the two phases in summer and winter. Sensitivity and elasticity analyses indicate the relative importance of perennation vs. recruitment. Recruitment from tetrasporophytes and from gametophytes both contribute about 25% to the population growth. Perennation among gametophytes is more important than among tetrasporophytes. The implication of this is that if this population is to be harvested, more tetrasporophytes can be harvested than gametophytes without resulting in the depletion of the resource. This is simulated in the matrix model by comparing the relative effects on population growth of increasing the mortality rate of the perennation phase of tetrasporophyte and gametophyte by 50 to 75%, and increasing recruitment rate in either phase, from summer to winter or from winter to summer.Dedicated to Dr T. Bisalputra of the University of British Columbia on the occasion of his retirement.     

Chemical races in the red alga Laurencia nipponica (Rhodomelaceae, Ceramiales)

Genetic variation in the synthesis of halogenated secondary metabolites in the Japanese marine red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) has been investigated in laboratory crossing experiments and chemical analyses, F₁ tetrasporophytes and F₁ gametophytes resulting from crosses within chemical races produced major metabolites characteristic of these races. F₁ tetrasporophytes derived from reciprocal interracial crosses produced: (i) both parental types of secondary metabolites; (ii) either of the parental types; or (iii) a further major compound in addition to both parental types or in addition to either of the parental types. The latter cases suggest that hybrid-specific products were formed by the combined enzymatic complements of the parents, as F₁ gametophytes derived from these interracial F₁ tetrasporophytes yielded one or other of their parental products in an approximate 1:1 ratio. The population structure was analyzed at localities in Hokkaido, where two of the chemical races occur sympatrically. At Usujiri (Minami-kayabe), where the prepacifenol race and the laureatin race were sym-patric, hybrid gametophytes (recombination type) were found in high frequency in addition to hybrid tetra sporophytes, which strongly suggests that a new, pre-pacifenol/laureatm race is beginning to be produced by natural hybridization and recombination. By contrast, at Oshoro Bay, where the laurencin race and the epi-lauraliene race grew together, the interracial hybrids were rare: only a few tetrasporophytes (probably F₁ generation) were found, suggesting that racial integrity may be retained by habitat segregation and/or the absence of recombination-type gametophytes.     

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.     

Biomass variation and reproductive phenology of Gracilaria gracilis in a Patagonian natural bed (Chubut, Argentina)

The biomass variation and the reproduction of the natural Gracilaria gracilis bed in Bahía Bustamante (Patagonia, Argentina) were analyzed for 2 years, with the aim of determining the present situation of the population for an updated status overview; establishing the relevant features of the temporal variation in both biomass and reproductive states in relation to environmental factors, epiphytes and associated algae; and assessing carpospore availability for future spore-culture development. Field measurements and sampling were performed monthly between March 2006 and February 2008. In both years, G. gracilis biomass presented marked seasonal variations, with a minimum in winter and a maximum in late spring and in summer. During both years, coexistence of the three life-cycle phases was found, with dominance of tetrasporophytes. Two data sets from individuals originated from sexual reproduction (tetraspores and carpospores) and from asexual reproduction by thallus fragmentation were analyzed separately. In the fragmentation fraction, tetrasporophyte frequencies remained higher than those for gametophytes. However, in the spore-originated fraction, a generation ratio close to 0.5 was observed. Female gametophytes bearing cystocarps were always present, with a maximum in summer and autumn. Biological data were related to environmental factors by means of canonical correspondence analysis (CCA). The first year was characterized by higher biomass values of G. gracilis and Undaria pinnatifida, lower epiphytism, larger Gracilaria thalli and greater proportion of mature tetrasporophytes and gametophytes. The second year was characterized by a high proportion of Gracilaria vegetative thalli and high epiphyte density. The best time to obtain spores from cystocarpic thalli would be in summer and early autumn.     

Trypauchen vagina (Bloch & Schneider, 1801) a new established species in the Southwestern Atlantic

Trypauchen vagina (Bloch & Schneider, 1801) is a goby that lives burrowed into the substrata feeding on small invertebrates. It is native to the Indo-pacific region, ranging from Kuwait to China. Recently, this fish has been reported outside the original range of distribution, being found in the Mediterranean Sea, and more recently in the northeastern Brazilian coast. The Mediterranean reports are usually associated with Lessepsian migration, while the reports from Brazil are possibly related to ballast water transportation. In the present work, we provide eight new records from southeastern Brazilian coast, all made in São Paulo state, far from the first record. These additional records raised concern since the presence of an alien species could implicate in environmental and economic losses. Thus, we decide to model the environmental suitability for this goby in the Brazilian coast, specially focusing on major ports, usually places with high ballast water propagule pressure. In addition, an analysis of the suitability in the Red Sea was also made, to verify the hypothesis of Lessepsian migration. The results revealed that temperature and primary productivity are among the most important parameters for the presence of T. vagina, also indicating a high environmental suitability for this species in the Red Sea and Brazilian coast, especially in southeastern region, where the new records were made. Due to the number of collected individuals, it is hard to affirm that this taxon presents a self-sustaining population in Brazilian waters, but the several registers, in different locations and different life stages point to an establishment of the species in this new region. This population status allied with a high environmental suitability is alarming and should motivate new studies concerning T. vagina in Brazilian waters.     

Differential ecological responses to environmental stress in the life history phases of the isomorphic red alga Gracilaria chilensis (Rhodophyta)

In order to better understand the alternation of generations that characterizes haploid–diploid life cycles, we assessed the existence of ecological differences between the two phases (haploid gametophyte and diploid tetrasporophyte) in Gracilaria chilensis, a rhodophyte with a typical Polysiphonia-type life cycle. We investigated the effect of light intensity and salinity on viability and growth of both phases at different ontogenetic stages: juveniles and adults. In our study, the survival of juvenile gametophytes (n) was higher than the survival of juvenile tetrasporophytes (2n) despite culture conditions; however, low salinity had greater effect on carpospores (2n) than on tetraspores (n). On the other hand, a complex interaction between salinity and light intensity within each life history phase generated observed differences between juvenile growth rates. Low light was shown to trigger early onset of alteration of the holdfast growing pattern. In addition, adult tetrasporophytes showed, despite the conditions, a faster vegetative growth than female and male gametophytes. These differences between phases could have led to the complete dominance of tetrasporophyte fragments of fronds observed in G. chilensis farms. We hypothesize that Chilean fishers could have unknowingly selected for tetrasporophyte thalli during domestication of the species, thus enhancing the natural trend of tetrasporophytes dominance already present in estuarine natural populations of free-floating plants.     

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.     

DIVERSITY OF HALOGENATED SECONDARY METABOLITES IN THE RED ALGA LAURENCIA NIPPONICA (RHODOMELACEAE,CERAMIALES)1,2

Many morphologically similar, but chemically distinct, populations have been found in the marine red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) growing in Japan. Each chemical type is characterized by a specific end-product of halogenated secondaly metabolite synthesis: chamigrane-type sesquiterpenoids such as prepacifenol and halochamigrene epoxide and C₁₅ bromoethers such as laurencin, laureatin, isoprelaurefucin, epilaurallene, and kumausallene. These seven types of secondary metabolite syntheses remained the same in the wild and under various culture conditions. Because bromoethers and terpenoids are probably synthesized by different metabolic pathways, it is virtually certain that different sets of enzymes participate in their synthesis. Prepacifenol- and laureatin-producing populations were selected as representatives of terpenoid and bromoether groups, respectively. F₁ tetrasporophytes derived from crosses between reciprocal, female and male gametophytes of prepacifenol- and laureatin-producing strains bore both types of metabolites, suggesting that the genes Producing these enzyme systems are encoded by nuclear genomes. The F₁ gametophytes resulting from the reciprocal crosses produced either prepacifenol or laureatin, and the four individuals derived from spore tetrads (a set of tetraspores derived from a single tetrasporangium) produced either prepacifenol or laureatin in a 1:1 ratio, indicating that genes participating in terpenoid synthsis and those participating in bromoether synthesis are on different loci of homologous chromosomes and are segregated at meiosis (tetrasporogenesis). One individual of this interpopulational F₁ gamtophyte produced both parental types of metabolite, perhaps indicating the occurrence of a recombination type. Natural hybrid individuals, including such recombination-type gametophytes, were found in a sympatric locality at which these two chemical types occur. F₁ tetrasporophytes derived from crosses between respective prepacifenol- and laureatin-producing strains and their F₁ gametohytes produced only parental-type metabolite-producing plants. These results indicate that the diverse chemical types can be referred to as races (chemical races).     

Effects of UV-B radiation on growth rates,pigment content and ultrastructure of red (wild type), greenish-brown and green strains of Gracilaria birdiae (Gracilariales,Rhodophyta)

Based on physiological characteristics, we hypothesized that different strains of Gracilaria birdiae from two distinct geographical areas of the Brazilian coast (2500 km apart) would have different responses to long-term exposure to UV-B radiation (UV-B). The locations differ in their environmental conditions: one is a warmer area, Ceará State (CE), closer to the equator; the other is a colder area, Espirito Santo State (ES), closer to the Tropic of Capricorn. To test the hypothesis that the CE population is more resistant to UV-B than the ES population, apical segments of the red (RD_CE, RD_ES), green (GR_CE) and greenish-brown (GB_CE) strains were cultivated in the laboratory under two treatments: control (PAR) and artificial UV-B (PAR + UV-B). Algal performance was evaluated by considering growth rates, pigment content and ultrastructural analysis. Compared with the control, all strains showed a decrease in growth rates after exposure to UV-B. Of all strains, RD_ES showed the greatest sensitivity to UV-B. However, a decrease in growth rate and morphological changes were observed to a lesser extent in the RD_CE strain. Moreover, exposure to UV-B resulted in a decrease in the concentrations of phycobiliproteins in the RD_CE strain. The GB_CE strain showed an increase in phycoerythrin (PE)/allophycocyanin (APC) and phycocyanin (PC)/allophycocyanin (APC) ratios after exposure to UV-B, suggesting this strain had a higher tolerance to the radiation. No differences in the chlorophyll a and carotenoid content were found between the control and UV-B treated samples for all strains. Ultrastructural changes, such as damage to chloroplasts and mitochondria, were present in all strains after exposure to UV-B. In summary, our findings support the hypothesis that the population from Ceará State has adapted to the higher irradiation and is thus more resistant to increased UV-B. Additionally, of the strains tested, the GB_CE and RD_CE strains appear to be more resistant to this radiation.     

Initial description of the phylogeography,population structure and genetic diversity of Atlantic spotted dolphins from Brazil and the Caribbean,inferred from analyses of mitochondrial and nuclear DNA

We provide initial information regarding the population structure and genetic diversity of Stenella frontalis from the Caribbean and southeastern Brazil from analyses of mitochondrial control region sequences and sequences from the first intron of the α-lactalbumin gene. Comparisons with previously described S. frontalis sequences showed a high number of haplotypes shared between populations throughout their distribution range. High diversity was found for southeastern Brazil and Caribbean samples, and population structure analyses indicate significant differentiation among population units at the F_ST level, but not at the Φ_ST level. Significant differentiation at the F_ST level was found between the Caribbean population unit and all other populations units. These results suggest historical or present connectivity between the Azores and Madeira and the southeastern Brazil groups and population differentiation between the Caribbean and southeastern Brazil, supporting the notion of two separate stocks in the waters around the Atlantic coast of South America.     

Effect of nutrients and light intensity on growth of Mallomonascaudata (Synurophyceae)

We used batch cultures of three strains of the unicellular synurophyte Mallomonascaudata to investigate the effects of nitrate, phosphate, silicate and light intensity on population growth and growth rate. The three strains were isolated from three different reservoirs in Kyungpook Province, Korea. For all three strains, we observed high population growth under all nutrient concentrations studied, except at nitrate concentration below 0.8 μM. The maximum growth rate (μ_max) occurred at 8.2 μM or 16.5 μM nitrate, depending on the strain, and at 11.5 μM phosphate. Silicate concentration had no effect on growth rate. With respect to light intensity, the maximum population growth and maximum growth rates (μ_max) occured between 42 and 104 μmol m^?2 s^?1 depending on strain and culture temperature. Population growth of these three strains under batch culture occurred over a wide range of nutrient and light intensities, but there seemed to be strain‐specific differences that may represent adaptations to local environments.     

Growth responses and photosynthetic characteristics of wild and phycoerythrin-deficient strains of <Emphasis Type="Italic">Hypnea musciformis</Emphasis> (Rhodophyta)

The phycoerythrin-deficient strain (green phenotype) of Hypnea musciformis (Rhodophyta) originated from a green branch, which had arisen as a spontaneous mutation in a wild plant (brown phenotype) collected from the Brazilian coast. The present study describes the growth responses to irradiance, photoperiod and temperature variations, pigment contents, and photosynthetic characteristics of the brown and green strains of H. musciformis. The results showed that growth rates increased as a function of irradiance (up to 40 μmol photons m⁻² s⁻¹) but, with further increase in irradiance (from 40 to 120 μmol photons m⁻² s⁻¹), became light-saturated and remained almost unchanged. The highest growth rates of the brown and green strains were observed in temperatures of 20–25°C under long (14:10 h LD) and short (10:14 h LD) photoperiods. The brown strain had higher growth rates than the green strain in the short photoperiod, which could be related to the high concentrations of phycobiliproteins. Phycoerythrin was not detected in the green strain. The brown strain had higher concentrations of allophycocyanin and phycoerythrin in the short photoperiod while the green strain had higher concentrations of phycocyanin. The brown strain presented higher photosynthetic efficiency (α), and lower saturation parameter (I_k) and compensation irradiance (I_c) than the green strain. The brown strain exhibited the characteristics of shade-adapted plants, and its higher value of photosynthetic efficiency could be attributed to the higher phycoerythrin concentrations. Results of the present study indicate that both colour strains of H. musciformis could be selected for aquaculture, since growth rates were similar (although in different optimal light conditions), as the green strain seems to be adapted to higher light levels than the brown strain. Furthermore, these colour strains could be a useful experimental system to understand the regulation of biochemical processes of photosynthesis and metabolism of light-harvesting pigments in red algae.