Temporal and spatial variation in agar from a population of Pterocladia capillacea (Gelidiales,Rhodophyta) from Brazil

Pterocladia capillacea forms dense intertidal belts in southeastern Brazil, on moderately exposed rocky coasts. The studied population extends along a gradient of water exposure, where slightly different morphotypes can be recognized. Specimens were collected monthly from 3 points along the exposure gradient of its distribution (lower, medium and higher exposure), and analyzed for agar, sulfate and 3,6 anhydrogalactose content. Agar varied from 5–32% of dried seaweed with lower yields in the winter, and higher yields in late spring/early summer. Specimens from the surf side of the distribution had a consistently higher agar content throughout the year. Sulfate varied from 1–5%, and 3,6 AG from 27–48% of dried agar, without a clear variation among the sites.     

Resource biology of Pterocladia capillacea (Gelidiales,Rhodophyta) populations in Brazil

Pterocladia capillacea has been already exploited in Brazil and Uruguay, but exploitation was discontinued due to source depletion. Our attempts to cultivate this species in the sea, or in tanks, gave poor results. In this communication we present some ecological data as a contribution to evaluate the possibility of a production increase in natural beds on the southeast coast of Brazil.Our results show that: (i) the populations are perennial varying from 323 (i.c._0.05 = 51) to 600 (i.c._0.05 = 78) g dry weight throughout the year; (ii) horizontal distribution is affected by irradiance, with higher biomass in shaded areas and by water movement, with higher biomass in intermediate sites; (iii) vertical distribution is limited above by desiccation and below by herbivores — sea urchins removal increases cover by 20–50%; (iv) Sargassum vulgare is the main competitor for space, and its removal on areas of contact between both populations increases coverage of P. capillacea by ca 80%.     

Spore Adhesion and Cell Wall Formation in Gelidium Floridanum (Rhodophyta, Gelidiales)

The attachment of spores to a substratum is essential for their germination and, therefore, to the completion of the life cycle of the red algae. In most red algae, spores are liberated without a cell wall, within a sheath of mucilage which is responsible for their primary attachment. Utilizing fluorescent-labeled lectins, we identified carbohydrate residues and their locations in the mucilage and cell walls of spores of Gelidium floridanum. Cell wall formation and mucilage composition were studied with calcofluor, toluidine blue (AT-O), alcian blue (AB) and periodic acid-Schiff (PAS). In the mucilage we identified α-D mannose, α-D glucose, β-D-galactose, N-acetyl-glucosamine and N-acetyl-galactosamine. The first two sugar residues were not found in the cell wall of the germ tube but they were present on the rhizoid’s cell wall indicating their importance to substrate adhesion. A cell wall is produced soon after the spore’s attachment, beginning with a polar deposition of cellulose and its gradual spread around the spore as indicated by calcofluor. The cell wall matrix was positive to AB and metachromatic to AT-O, indicating acidic polysaccharides, while cellulose microfibrills were positive to PAS. A polar disorganization of the cell wall triggers the process of germination. As spores are the natural form of propagation of Gelidium, the understanding of the mechanisms of spore attachment may contribute to the cultivation of this valuable seaweed.     

Intrageneric differences in cystocarp structure in Gelidium and Pterocladia

Unilocular cystocarps, with ostioles opening to one frond surface, have traditionally distinguished Pterocladia from Gelidium, described as having bilocular cystocarps, with ostioles opening to both surfaces; however, unequally developed locules have been described in Pterocladia and differences in cystocarpic architecture between Pterocladia capillacea and the type species of the genus, P. lucida, have been recently found. As heterogeneity in cystocarp architecture raises questions of basic intergeneric distinction, a survey of reproductive morphology of species in both genera is presented in this study. Six morphologically-different types of cystocarps are distinguished among the five species of Pterocladia and the seven species of Gelidium examined.     

Agars from Gelidium rex (Gelidiales,Rhodophyta)

Gelidium rex grows in the rocky intertidal of central Chile. Extraction of vegetative G. rex with water at 95 °C yielded 17.9% of agar with a gel strength value of 590 g cm^–2. The gel strength increased up to 1272 g cm^–2 when the alga was treated with alkali prior to extraction. Cystocarpic and tetrasporic thalli of G. rex were extracted with distilled water at 95 °C, affording soluble polysaccharides in 36.0% and 15.7% yield respectively. Polysaccharides of both life history phases were fractionated by chromatography on DEAE Sephadex. Elution with distilled water gave fractions devoid of sulfate; the fraction from cystocarpic plants contained 45.5% of 3,6-anhydrogalactose whereas the neutral fraction from tetrasporic plants contained 40.0% of 3,6-anhydrogalactose. Further elution with 0.1, 0.4, 0.8 and 1.5 molar aqueous solutions of KCl afforded four fractions for each polysaccharide. Chemical analysis of these fractions showed that the agars from cystocarpic and tetrasporic Gelidium rex are mixtures of related polysaccharides that range from neutral polymers to highly sulfated galactans.     

Field and culture studies of species of Gelidium (Gelidiales,Rhodophyta) from their northern limit of distribution in Europe

Two species of Gelidium, provisionally referred to as G. pusillum and G. latifolium, are included in the Scandinavian flora and reach their northern limit of distribution on the Norwegian west coast. Small frond sizes due to adverse growth conditions, extreme phenotypic variability and lack of sexual reproduction make identification of specimens very difficult. Both species were isolated into unialgal culture and were compared with cultured strains referable to G. pusillum from Ireland and France. Temperature and salinity requirements and tolerance ranges were determined and discussed in view of distribution along the Norwegian coast. Little or no growth occurs below 9 °C, corresponding to a northern summer growth limit. On the Norwegian Skagerrak coast, low winter temperature rather than reduced salinity is the limiting factor.     

New and old problems in the taxonomy of the Gelidiales (Rhodophyta)

The order Gelidiales includes over 140 agar-producing taxa. Many species are taxonomically confused; the boundaries of one family and all but four genera recently have been contested, and the controversy over ordinal status has lasted for over 25 years. This study reviews recent developments in the taxonomy of the group and suggests future areas for studies. The order cannot be defined by a few exclusive characters, as intended in the past, but it shows a unique combination of characters. Additional studies on Gelidiella and Acanthopeltis seem advisable to clarify family limits. The segregation of Onikusa and Pterocladiastrum is doubtful. Only three of six characters discriminate Gelidium from Pterocladia. None allows complete generic segregation and all need variability studies. Analysis of nomenclatural types in the light of morphological variation would permit an understanding of species limits in Gelidium and Pterocladia. Similar studies are needed in Gelidiella and Ptilophora.     

The effect of phosphate concentration on growth and agar content of Gelidium robustum (Gelidiaceae,Rhodophyta) in culture

Phosphate concentration of the growth medium was found to affect the growth rate and agar yield of a clone of Gelidium robustum grown in the laboratory. To study differences in growth we used phosphate concentrations from 0 to 200 µM. To determine the effect of phosphate on agar yield and its properties we used concentrations from 0 to 20 µM. Growth rates generally increased with increasing phosphate concentration, with the highest growth rate (21% d^–1) obtained at 150 µM. Agar yield as percentage of fresh weight was highest (10%) in the algae grown with low phosphate concentrations, but agar yield as percentage of dry weight was highest(43%) at 20 µM of phosphate. Gel strength increased with phosphate concentration with a maximum of 160 g m^–2 for 0.75% gels for the cultures at 20 µM. Melting and gelling temperatures of the gels were also affected by phosphate concentration of the growth medium. Starch yield was highest in algae grown in low phosphate concentrations.     

Vegetative propagation by fragmentation of Gelidium sclerophyllum (Gelidiales,Rhodophyta)

Results of the first phase of production of "seed" for a project of marine culture of species of Gelidiales are presented. Vegetative fragments of different sizes and from different parts of the thallus of Gelidium sclerophyllum from the Mexican tropical Pacific coast were cultured under nine treatments with different N and P concentrations. In treatments without N all fragments died; good vegetative growth was present in all remaining treatments. Growth in length and branch production were favored in medial fragments, and rhizoid production was favored in apices. Growth in length and biomass increase were stimulated by high N concentrations (2–3 mM), and branch and rhizoid production were stimulated by high P concentrations (100–150 µM).     

Protoplasts of Gelidium robustum (Rhodophyta)

Viable protoplasts were isolated from apices of the agarophyte Gelidium robustum (Gardn.) Hollenb. & Abb. using a combination of commercial cell-wall degrading enzymes and extracellular wall-degrading enzymes isolated from a marine bacterium. The protoplasts were approximately 8–15 µm in diameter, liberated mainly from the surface cell layers and from cells at the distal ends of medullary filaments. The bacterial enzyme alone was not sufficient to liberate significant numbers of protoplasts. Maximum yield was 9 × 10⁵ protoplasts/g tissue (wet wt.). Optimum osmolality occurred between 1750–1950 mOs kg^–1; yield and viability were severely diminished at osmolalities less than 1350 mOs kg^–1. Viability, as determined by flurorescein diacetate staining and Evans Blue exclusion 1 hr after removal from the enzyme solution, was approximately 80–95%. Roughly 80% of the cells did not show Calcofluor fluorescence, while 40% stained positively for the presence of sulfated polysaccharides. Cell wall regeneration was observed with inconsistent reproducibility, and no cell division was observed when the protoplasts were placed in culture medium.Dedicated to the memory of Professor Michael Neushul.     

Fecundity,spore recruitment and size in Gelidium sesquipedale (Gelidiales,Rhodophyta)

Gelidium sesquipedale fecundity was quantified by counting tetrasporangial sori and cystocarps per meter squared and by estimating the number of spores contained inside them. These were obtained by regression on a size metric of reproductive structures. Tetrasporangial sori length and cystocarp thickness were the best estimators of spore number. To assess spore recruitment, 12 pottery tiles were fixed to the bottom, and the appearance of small fronds was monitored.No clear seasonal pattern of reproduction was found. Tetraspore production peaked in March 1990 with 10.4 × 10⁶ spores m^–2, whereas the carpospore peak was lower, 4.9 × 10⁵ spores m^–2 in July 1989. Recruitment followed tetraspore peaks. The probability of a G. sesquipedale tetraspore making the transition to a recruit was 4.7 × 10^–5. Frond length was significantly related to tetrasporangial sori number, while cystocarp number was only related to frond branching order. Minimum size for reproduction was 6.9 cm for gametophytes and 5.4 cm for tetrasporophytes; very rarely were cystocarpic fronds smaller than 9 cm, while tetrasporic fronds were often longer than 15 cm. Cystocarpic fronds were significantly shorter and had more branches than tetrasporic fronds.     

Reassessment of the taxonomic status of Gelidium subfastigiatum (Gelidiales, Rhodophyta)

The taxonomic relationship between Gelidium elegans Kützing and Gelidium subfastigiatum Okamura, two morphologically similar species of the red algal genus Gelidium (Gelidiaceae) growing in the north‐western Pacific, was critically re‐examined. Gelidium subfastigiatum has been distinguished from G. elegans by its more robust thalli, which have antrorse tooth‐like branches, although their distinction has been said to be often difficult or impossible. We determined the nuclear encoded internal transcribed spacer 1 (ITS1) for 14 samples from eight populations of this G. elegans/ G. subfastigiatum complex, and two types of ITS1 sequences were found. Analysis of seasonal variations of subterminal portions of major branches revealed that this complex includes two groups: one possessing the type 1 ITS1 sequence and antrorse tooth‐like branches that are subterminally thickened and widened during only colder months, and another possessing the type 2 ITS1 sequence and thin and narrow branches throughout the year. These groups should be recognized as separate species; the former is assigned to G. subfastigiatum and the latter to G. elegans.     

Advances in cultivation of Gelidiales

Currently, Gelidium and Pterocladia (Gelidiales) are collected or harvested only from the sea. Despite several attempts to develop a cultivation technology for Gelidium, no successful methodology has yet been developed. Initial steps towards developmental efforts in Portugal, Spain, South Africa and Israel have been published. More developments have probably been performed but have not been published. Two different technological concepts have been tested for Gelidium cultivation: (1) the attachment of Gelidium fragments to concrete cylinders floating in the sea, and (2) free-floating pond cultivation technology. These vegetative cultivation technologies might be partially optimized by controlling physical, chemical and biological growth factors. The pond cultivation technology is the much more controllable option. The effects of all factors are discussed in detail in this review. It seems that the main difficulty with cultivation of Gelidium is its low growth rate. The claimed yields of the two technologies are far from being economically attractive at this stage of their development. It seems that in order to introduce Gelidium into commercial cultivation, major efforts in genetic improvement through selection or genetic engineering will be required. Only high yield strains will have the potential to compete economically with the present harvesting tradition. However, accumulated experience with genetic improvement of other useful seaweed species suggests that this is possible.     

Two new species of Gelidium (Rhodophyta, Gelidiales), Gelidium tenuifolium and Gelidium koshikianum, from Japan

Two new marine red algae, Gelidium tenuifolium sp. nov. and Gelidium koshikianum sp. nov. (Gelidiales, Gelidiaceae) are described from Japan. Gelidium tenuifolium with large‐sized thalli (up to 30 cm tall) is distinguished from other species with such thalIi by the production of wide, flattened and thin branches (up to 2 mm wide and 60–80 urn thick), the presence of an apical depression and simple determinate branches. Gelidium koshikianum with middle‐sized thalli (5–8 cm tall) is distinguished from other species with such thalli by having wide axes (up to 2.5 mm wide) and short (2.0–3.2 mm), unbranched, second‐ and third‐order branches issuing at short intervals (0.8–1.4 mm). In phylogenetic analyses of rbcL sequences, four Gelidium species that are chiefly distributed in Japan including G. tenuifolium were clustered together with 99% bootstrap value (Japanese Gelidium‐complex clade). Gelidium linoides Kützing came to the position of the sister group to G. tenuifolium with 99% bootstrap value. There were four substitutions (0.3% divergence) between G. linoides and G. tenuifolium sequences. Gelidium koshikianum and Gelidium allanii Chapman were clustered together with 100% bootstrap value and they came to the position of the sister group to the Japanese GeIidium‐complex clade with 83% bootstrap value. There were six substitutions (0.4% divergence) between G. koshikianum and G. allanii sequences.     

Production of plantlets of the red alga of Gelidium genus (Rhodophyta) from thallus fragments

Experimental research on production of plantlents from fragments of thallus of the alga Gelidium were carried out. The best results on development of plantlets without rhizoids were achieved with cultivation of fragments of subapical parts of the plant. Thus, the average growth rate of plantlets in the last for 4 weeks of rearing was 6.7 ± 1.2% a day. Gelidium plantlets with rhizoids were grown from the top branches of plants in an intensively stirred culture with shading of the lower parts of the branches. It is suggested to use the same method for obtaining planting material during bottom rearing of Gelidium in the sea as that for intensive culture in tanks.     

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     

Physiological basis for the cultivation of the Gelidiaceae

An understanding of the physiological factors important to growth and agar production of the Gelidiales would be useful for successful mariculture of these commercially valuable plants. Several environmental factors, including light, nitrogen, carbon, temperature and water motion, have been shown to have potential significance for growth rates, reproduction and carbon partitioning in defining optimal conditions for cultivation. Limiting and optimal growth conditions, where known, are presented, and evaluation of data reported in the literature is addressed.     

Population modelling of Gelidium sesquipedale (Rhodophyta, Gelidiales)

A matrix population model of Gelidium sesquipedale, a commercial agarophyte from the Northeast Atlantic, was developed based on demographic data obtained during two years in a commercial stand of Cape Espichel, Portugal. G. sesquipedale individuals were classified into categories such as life cycle phase, spores, juveniles and adult frond size, because the species vital rates, fecundity, fertility, survival, growth and breakage depend on them. We also exemplify the use of a user-friendly modelling software, Stella, to develop a structured-population model. This is the first time this software has been used to model the demography of seaweed populations. The Stella model developed here behaved very similarly to the matrix model, because of its particular construction, which causes the forcing functions to be discrete rather than continuous. The relative importance of spore recruitment and vegetative growth of new fronds in both population growth and population structure was investigated. Elasticity analysis suggests that vegetative recruitment is the most important demographic parameter controlling population growth together with survival and transitions between juveniles (1–6 cm fronds) and class 1 fronds (6–9 cm fronds). On the other hand, sexual reproduction may, by itself, efficiently control the relative proportion of gametophytes and tetrasporophytes in the population, even though its contribution to recruitment is extremely small. A 40% difference in the growth rates of gametophyte and tetrasporophyte submatrices resulted from natural differences in spore recruitment rates. This revised version was published online in June 2006 with corrections to the Cover Date.     

Taxonomic review of the species of Pterocladia (Gelidiales, Rhodophyta)

Segregating Pterocladiella from Pterocladia stimulated new taxonomic studies of the species originally assigned to Pterocladia. A total of 28 species are ascribed to the genus, one of them with doubts. Thirteen of the 27 names are synonyms. Three of the remaining 14 species belong with Gelidium, including G. americanum, G. mcnabbianum (Dawson) comb. nov. and G. musciformis. Seven other species belong with Pterocladiella, including P. bartlettii (Taylor) comb. nov., P. bulbosa, P. caerulescens, P. caespitosa (Kylin) comb. nov., P. caloglossoides (Howe) comb. nov., P. capillacea and P. melanoidea. Two species are retained in Pterocladia, the type P. lucida and P. rectangularis. Two others, P. heteroplatos and P. media are placed in incertae sedis as additional studies of fertile materials are needed to determine their generic status. The genus Pterocladia now appears to include two large-sized species restricted to Australia-New Zealand. Pterocladiella has 8 small-sized species (including P. minima), mainly inhabiting tropical and subtropical waters. Future research documenting sexual reproduction in Gelidiella and solving the presently recognized heterogeneity in Gelidium will help to trace the relationships between Pterocladiella and these two genera. This revised version was published online in June 2006 with corrections to the Cover Date.