Seasonal variations in sterol composition of Delesseria sanguinea (Ceramiales,Rhodophyta)

On Normandy coasts, the red alga Delesseria sanguinea perennates by its stipe; fronds grow in January and disappear in June. Seasonal variations in sterol composition in relation to the biology of D. sanguinea are reported. Sterols in cellular membranes are free or conjugated by esterification with fatty acids, heterosides or lipid complexes like phospholipids. Both kinds of sterols were analyzed by GC-MS. The major sterol (80%) found in fronds was cholesterol whereas in stipes, cholesterol was also the major sterol in spring, but in September, an important reduction in cholesterol yield was noted with proportional increase in sitosterol content. It appears that cholesterol is synthesized in fronds in spring, then transferred to the stipe, which loses an important amount of cholesterol with loss of the blades.     

Experimental tank cultivation of Gracilaria sp. (Gracilariales,Rhodophyta) in Ecuador

This paper describes experiments to grow a local and still unidentified species of Gracilaria in shrimp hatcheries in Ecuador. The experiments used outdoor tanks of 1 and 18 m³ capacity, with continuous aeration and water renewal every two and five days, respectively. The sea water (salinity 34 ppt) was enriched with Guillard's f/2 medium; light and temperature were monitored but not controlled. One kg of fresh seaweed, inoculated into each tank, produced a biomass of ca. 3 kg in a period of 35 days in the 1 m3 tank and 18 kg in 43 days in the 18 m³ tank. We therefore believe that it is technically feasible to use the large infrastructure of existing shrimp hatcheries in Ecuador to produce Gracilaria.     

A model of seaweed growth in an outdoor culture in Israel

The agarophyte red seaweed Gracilaria conferta was used as a model plant to study the relationship between growth and environmental factors. This species was cultured in small outdoor tanks with continuous seawater supply during three years. Seaweeds were kept under constant density by weekly thinning and were also pulse-fed weekly with nitrogen and phosphate. Water temperature and underwater irradiance increase had opposite effects on the weekly growth rate in two seasons: negative in summer and positive in non-summer. Therefore, a dichotomic separation between summer (June–August) and non-summer (September–May) seasons was utilized in the proposed linear model. The linear model, of the analysis of covariance type, accounted for an explained percentage of total variation (R²) of 0.567, with significant coefficients of all variables included. A standardized model showed that season was the dominant variable, with its coefficient being twice that of temperature in summer, and zero in the non-summer season. Water temperature affected the growth rate twice as much as irradiance, and epiphytes showed a significant negative effect on growth only in the summer. This model aids in the prediction of growth on a seasonal basis under local conditions.     

Sulfated galactans from the red seaweed Nothogenia fastigiata (Nemaliales,Rhodophyta)

Fractionation of the cetrimide salts of the sulfated polysaccharides of Nothogenia fastigiata led to the isolation of a complex galactan sulfate. This product showed compositional and molecular weight heterodispersion together with composition-, temperature-, time-, and conformation-dependent molecular associations. In this sense, the behavior of the galactan sulfate is similar to that of the mannan sulfate previously isolated from the same seaweed.Formerly classified as Chaetangium fastigiatum.     

Seaweed production: overview of the global state of exploitation,farming and emerging research activity

ABSTRACT

The use of seaweeds has a long history, as does the cultivation of a select and relatively small group of species. This review presents several aspects of seaweed production, such as an update on the volumes of seaweeds produced globally by both extraction from natural beds and cultivation. We discuss uses, production trends and economic analysis. We also focus on what is viewed as the huge potential for growing industrial-scale volumes of seaweeds to provide sufficient, sustainable biomass to be processed into a multitude of products to benefit humankind. The biorefinery approach is proposed as a sustainable strategy to achieve this goal. There are many different technologies available to produce seaweed, but optimization and more efficient developments are still required. We conclude that there are some fundamental and very significant hurdles yet to overcome in order to achieve the potential contributions that seaweed cultivation may provide the world. There are critical aspects, such as improving the value of seaweed biomass, along with a proper consideration of the ecosystem services that seaweed farming can provide, e.g. a reduction in coastal nutrient loads. Additional considerations are environmental risks associated with climate change, pathogens, epibionts and grazers, as well as the preservation of the genetic diversity of cultivated seaweeds. Importantly, we provide an outline for future needs in the anticipation that phycologists around the world will rise to the challenge, such that the potential to be derived from seaweed biomass becomes a reality.     

An evaluation of species relationships in the Porphyra perforata complex (Bangiales,Rhodophyta) using starch gel electrophoresis

Traditional morphological features have formed the basis for distinguishing species of Porphyra. Among these features are number of cell layers, number of chloroplasts per cell, arrangement of reproductive structures on the thallus, and overall morphology. Chromosome number and chromosome morphology have helped corroborate some species identities. A survey of northeast Pacific species of Porphyra using starch gel electrophoresis of 15 soluble proteins has shown that electrophoretic banding patterns provide a reliable diagnostic tool for species identification. Data from starch gel electrophoresis are presented to confirm the identities of species formerly associated with the Porphyra perforata species-complex in British Columbia and northern Washington. Porphyra abbottae, P. fallax, P. kanakaensis, and P. torta are recognized as distinct species, and Porphyra sanjuanensis is synonymized with P. perforata.     

Carbon nutrition of seaweeds: Photosynthesis,photorespiration and respiration

Techniques are described for measuring gas exchange in seaweeds held in moist air (air suspension). In the species we have examined, oxygen has little or no effect on photosynthesis except at very low (50 μ1·1^?1) CO₂ concentration. Photorespiration could not be detected unless the seaweeds were treated simultaneously with high O₂ and low CO₂ or with the carbonic anhydrase inhibitor, diamox. However, sporulating and meristematic tissues exhibit oxygen-insensitive light respiration (CO₂production in light not associated with photorespiratory metabolism). Elevated pH in the surface water of seaweeds also caused light respiration. Oxygen-sensitive wound respiration was observed that could easily be mistaken for photorespiration. C₄ photosynthesis could not be detected. On the basis of several experimental approaches it was concluded that these seaweeds normally absorb bicarbonate rather than CO₂ from sea water. High CO₂ concentrations are required in gas streams aerating seaweed cultures in air or water suspension to maintain the bicarbonate concentration at levels normally found in sea water and to support normal levels of photosynthesis.     

Annual variations of the biochemical composition of Gelidium latifolium (Greville) Thuret et Bornet

Agar, floridean starch, protein, ash and water content in Gelidium latifolium from nature were followed monthly over one year. Comparison of variations in these contents, algal growth and cytological observations enable us to establish a cycle for agar synthesis. In autumn, after reproduction of alga, there is an active algal growth period with agar synthesis and utilization of floridean starch. In winter, synthesis is shifted toward protein accumulation while there is a partial agar hydrolysis. In spring another active growth period of the alga occurs with accumulation of floridean starch and synthesis of agar. In summer and during reproduction, there is a depletion of thalli nitrogen content while the agar synthesis pauses.     

Restriction enzyme analysis of variation and taxonomy in the kelp genus Laminaria (Laminariales,Phaeophyta)

High levels of phenotypic variation in kelp species necessitate the use of taxonomic markers that are independent of morphology. Restriction fragment length polymorphism (RFLP) analysis of nuclear DNA can provide such markers. In this paper we present the results of an RFLP analysis of cytoplasmic ribosomal DNA (rDNA) in three Laminaria species (L. agardhii, L. digitata, L. groenlandica). Comparison of the restriction maps of the nontranscribed spacer (NTS) in the rDNAs suggests that this method should be useful for the differentiation of these taxa. These results are discussed, as are the applications of RFLP mapping to the identification of field-collected, morphologically variable plants.     

Seasonal changes in the chemical and gelling characteristics of agar from Gracilaria verrucosa collected in Turkey

The chemical and gelling properties of agar from G. verrucosa collected from Izmit bay in Turkey at different months of the year were studied. Purification of agar was performed by using amylase treatment and isopropyl alcohol precipitation. The phycocolloid content was between 24.0–43.0% of the algal dry weight and was maximum in summer collected algae. Relative total sulfate and 3,6-anhydrogalactose content in the agar were determined from the ratios of infrared spectroscopy band intensities at 1250/2920 cm^–1 and 930/2920 cm^–1, respectively. 3,6-anhydrogalactose and sulfate contents were the highest in agar from algae collected from June until November and January until July, respectively. The gel strength of native agar were the highest from in autumn collected algae and increased to about 1250 N m^–2 after alkali treatment. Thus, this study demonstrated that G. verrucosa from Turkey produces an agar with optimal chemical and gelling properties after alkali-treatment in fall and winter collected algae and may be used for industrial agar production.     

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.     

The introduced alga Undaria pinnatifida (Laminariales,Alariaceae) in the lagoon of Venice

Since its appearance in 1992 in the lagoon of Venice, the brown algae Undaria pinnatifida (kelp) has gradually expanded along the banks of canals both at Chioggia and Venice, becoming the dominant species in the local algal community chiefly from February to July. In Chioggia Island, where another brown seaweed (Sargassum muticum) is present since 1992, the spreading of Undaria reaches a plateau. In Venice Island, instead, the colonisation process is still in progress. During 1999, the kelp has colonised the main canals (e.g. The Grand Canal) and, subsequently, the small inner ones. In order to evaluate the dynamics of substrate re-colonisation by Undaria, two mechanical eradications were carried out during (March) and after the fertile period (July) of the algae. Such experimental manipulations provided evidence of the fast re-colonisation potential of the algae mainly attributable to its efficient reproductive system. Eradication made during the fertile period, in fact, permitted the kelp development during the following year, while re-colonisation has started 2 years later where eradication was performed after the reproductive period. A significant decrease in the surface covered by other species has been observed both in shallow (Ulva rigida, Enteromorpha spp., Antithamnion pectinatum, Chondracanthus acicularis) and deeper areas (Rhodymenia ardissonei) during the period of maximum development of U. pinnatifida. On the basis of the results of this study, the following conclusions can be drawn: (1) the alga U. pinnatifida is continuously expanding in lagoon environments of Venice; (2) in order to limit its spreading, mechanical eradications would be done on a large spatial scale and before the zoospores release; (3) there is suggestive evidence of competition between Undaria and the remaining indigenous algae.     

Canopy characteristics of the brown alga Sargassum muticum (Fucales,Phaeophyta) in Lake Grevelingen,southwest Netherlands

The present distribution of the invasive brown alga Sargassum muticum in the southwest Netherlands is updated. Populations of the alga were found to remain at their 1985 level in Lake Grevelingen, with a small eastward expansion into the Eastern Scheldt estuary. A new population for the brackish, non-tidal Lake Veere is reported. Within Lake Grevelingen S. muticum forms a persistent, extensive canopy of 100% cover (4,442.5 ± 525.6 g fresh wt m^–2, 640.3 ± 75.8 g dry wt m^–2) that has a marked effect upon the penetration of photosynthetically active radiation (PAR) (reduced by 97% at 0.1 m). Surface sea water temperatures can be elevated by 2.7 °C above water not associated with a Sargassum canopy; furthermore, the dense canopy shades and hence reduces water temperatures below 0.1 m depth. Productivity studies indicate that assimilation occurs in the upper levels of the canopy (57.09 µg C mg dry wt^–1 m^–2 at a mean PAR rate of 106.7 J cm^–2 h^–1). Self-shading and a resultant decrease in the rate of assimilation was evident below the canopy.     

Biological basis for the management of ‘lugs negra’ (Sarcothalia crispata Gigartinales,Rhodophyta) in southern Chile

The present paper describes growth dynamics in a natural bed of the resource luga negra (Sarcothalia crispata) in Guapilinao, southern Chile (41°57 S, 73°31 W). This resource is currently harvested and exported as raw material for the production of carrageenan. Seasonal variation in biomass, frond size, density and phenology was determined by periodic sampling. Natural recruitment was evaluated on different substrata added to the field; at the same time, substrata were inoculated under greenhouse conditions. Results showed that luga negra has seasonal growth: biomass increased from a minimum in spring to a maximum in mid to late summer. On the other hand, density was minimal in winter (200 ind. m^–2) and increased to 2000 ind. m^–2 in late spring. Peak abundance of mature tetrasporic fronds occurred in late summer, whereas that of cystocarpic fronds occurred in winter. Recruitment began in summer and extended into winter. Survival on different substrata were compared. Gametophytes had better survival rates on clam shells and 5 mm rope while tetrasporophytes had the best survival rate on clam shells and secondarily on boulders.