Free sterols of the red alga Gigartina skottsbergii

The free sterols of the red alga Gigartina skottsbergii have been identified by means of GC and GC/MS analyses. The mixture contained saturated and unsaturated C²⁷, C²⁸ and C²⁹ sterols. The major component was cholest-5-en-3β-ol. Cholesta-5,24-dien-3β-ol (desmosterol) was present in low proportion but no side chain hydroxylated components were detected.     

Healing and regeneration responses in Gigartina skottsbergii (Rhodophyta, Gigartinales): optimization of vegetative propagation for cultivation

The red alga Gigartina skottsbergii is becoming increasingly valuable as a resource to providing the raw material for the carrageenan industry established in Chile and elsewhere. As a result, wild stocks of the species are subject to intense harvesting by local fishermen. With the current levels of harvesting, it seems likely that natural stands of G. skottsbergii will soon collapse. Although cultivation seems an alternative, knowledge regarding the biology of the species is exceedingly limited. This study reports the first attempt to determine the optimal conditions for vegetative propagation of this species in the laboratory. For this purpose, the processes of wound healing and regeneration of frond fragments and haptera were studied under controlled conditions of temperature, light, and media strength. Our results demonstrated that excised tissues of G. skottsbergii were able to seal the exposed areas in approximately 20 days, by a wound healing process characterized by a re-differentiation of medullary cells into a normal cortex. Our data also demonstrated that frond fragments are better than haptera for propagation purposes. The development of new cortical tissue at the cut surface is followed, within 60 days, by localized blade-like outgrowths along the repaired area. Furthermore, the healing and regenerative responses in both frond fragments and haptera differed in efficiency according to the various combinations of factors, with optimum of 10–15 °C, 5 ?mol m^?2 s^?1 and plain seawater or standard SFC medium for the fronds. The two types of responses were negatively affected by seawater enriched with a double concentration of nutrients.     

Phenology of Gigartina skottsbergii (Gigartinaceae,Rhodophyta) in Ancud Bay,southern Chile

This study reports the variations in biomass and reproductive phenology in a natural bed of Gigartina skottsbergii over a period of a year and correlates these variations with the abiotic factors solar radiation, number of daylight hours, water temperature and salinity. The results obtained show an annual production cycle with maximum biomass values in spring-summer, correlated with high solar radiation and to a lesser extent with salinity. Sexual reproduction was maximum in autumn-winter, correlated with low temperature and short-day conditions. The population showed a large gametophytic dominance according to size and biomass, which suggests that there is not ecological equivalence between the life history phases of the species. Finally, based on the results, a restriction of harvesting to spring-summer is suggested.     

Seasonal variation of carrageenan yield,gel strength and viscosity in Sarcopeltis (ex Gigartina) skottsbergii from Southern Chile

Chile is one of the top carrageenan producers worldwide, and Sarcopeltis (ex Gigartina) skottsbergii one of the topmost exploited carrageenophytes from the wild in the world. Total yield, gel strength and viscosity from two contrasting environments Calbuco and Ancud (Inner and Outer Sea, Chile) were estimated monthly in approximately 2 years for this species. While carrageenan yields did not show differences between localities, gametophytes in spring–summer had 15% higher, compared to tetrasporophytes. Sizes (frond surface) normally did not affect carrageenan yields. Gametophytes showed clear differences in gel strength between seasons, but not between localities, with maximum peaks during winter–spring months in Calbuco and autumn-winter months in Ancud. Seasonal variations in viscosity were also significant. While gametophyte viscosity did not exceed 120 cPs, tetrasporophytes reached 1400 cPs in Calbuco and 1000 cPs in Ancud. More remarkably, a positive correlation between viscosity and gel strength was found in S. skottsbergii gametophytes, which is significantly different between both localities. These results suggest that selective harvesting in spring–summer should be preferred to optimize cost–benefit of harvesting activities and subsequent carrageenan productivity.     

Field trials to optimise timing and frequency of pruning for cultivation of a New Zealand carrageenophyte, Gigartina atropurpurea

The endemic New Zealand red alga Gigartina atropurpurea has been identified as a candidate for aquaculture because of its high quality and value carrageenan and its broad-bladed morphology. As G. atropurpurea has not so far been exploited commercially, trials were conducted to investigate the effect of timing and frequency of pruning on the growth of plants in the wild and explants on ropes, in spring, and autumn. Plants were monitored monthly by measuring the length of the two longest blades (a proxy for biomass) and wet weights of all plant material retrieved. The results suggested five broad conclusions: (1) spring growth was much greater than autumn growth; (2) regardless of season, maximal growth rates were achieved 4–6 weeks post pruning; (3) pruning accelerated growth; (4) pruning plants twice during spring generated up to four times more biomass than when plants were pruned only once, and (5) there was no difference in the response of farmed and wild plants to pruning treatments. Based upon these preliminary trials, plant material from wild tetrasporic and female G. atropurpurea could be harvested up to three times during the growth period (August–December). However, further research on the feasibility of G. atropurpurea aquaculture is justified.     

Growth of the commercial carrageenophyte Sarcothalia crispata (Rhodophyta, Gigartinales) on suspended culture in central Chile

Laboratory and field studies on growth of Sarcothalia crispata, whichis one of the most important carrageenophytes of Chile, were made in toassess its viability and growth in a system of suspended culture. Invitro experiments on the survival of the germlings and on the effect oftemperature and irradiance on its growth allowed to determine the besttemperature and irradiance for seeding polypropylene culture ropes inindoors conditions. The growth of plants developed on ropes at threedepths in Coliumo Bay (central Chile) supports the idea that it is feasiblebiologically to manage the resource via aquaculture. Fouling and epiphyteswere the main problem at the experimental site. The results suggest thatmaintaining the cultures in deeper water during summer could minimize thisproblem.     

Vegetative propagation and spore-based recruitment in the carrageenophyte Chondracanthus chamissoi (Gigartinales, Rhodophyta) in northern Chile

In the present study we compared vegetative and spore‐based propagation for Chondracanthus chamissoi (C. Agardh) Kützing. Monthly field observations were made over a 1‐year period at Puerto Aldea, Tongoy Bay, Chile. Data were collected both outside and within a bed of C. chamissoi. Vegetative propagation was assessed via attachment of drifting fronds to shell‐encrusted concrete blocks at both sites. Germination of spores was recorded on the same shell substrates. Substrate re‐adhesion varied seasonally between sectors. Highest averages occurred within the algal bed between January 1997 and March 1997. The number of sporelings showed two peaks of maximal recruitment in spring and summer months (January‐March 1997 and September 1997‐January 1998). Spore‐based propagation is an important mechanism of seasonal regeneration of biomass in the C. chamissoi bed; however, re‐attachment of fronds may have been important in maintaining production of the bed during the period of maximum biomass accumulation.     

The effects of different light intensities on the culture of Gigartina skottsbergii (Rhodophyta,Gigartinales) tetrasporophytes and gametophytes in the Magellan region,Chile

Gigartina skottsbergii is a red seaweed used as raw material for extracting carrageenans, constituting an important economic resource for Chile. In 2009, extraction in the Magellan region reached 15,064 t. The growing demand has adversely affected the sustainability of natural beds, creating an interest in the culture of this resource. In order to provide information relevant to the culture and regeneration of this seaweed, the present study addresses the effects of different light intensities on the growth of G. skottsbergii gametophytes and tetrasporophytes during the early stages of development. Mature reproductive fronds were induced to release spores in the laboratory by a drying process. Gametophytes cultured at different light intensities showed an increase in diameter, which reached 519.13?±?108.95 μm with 4 μmol photons m^?2 s^?1, while tetrasporophytes showed a greater increase in diameter, reaching 714.11?±?116.45 μm with 8 μmol photons m^?2 s^?1. Results indicate that both stages of the reproductive cycle are influenced by different light intensities within a limited range. Therefore, both phases require different and specific ranges of light intensity.     

Cultivation of Gigartina skottsbergii (Gigartinales, Rhodophyta): Recent advances and challenges for the future

This study integrates landings statistics and biological studies of the red algaGigartina skottsbergii Setchell & Gardner. The analysis of the landings and carrageenan production in Chile suggeststhat this resource will suffer a strong harvesting pressure during the nextyears. Biological results on sporulation, germination, sporeling growth and survivorship in laboratory,indoor tanks and field conditions, indicated that cultivation of this species istechnically feasible, as spores can be seeded on ropes and other substrata. Vegetative propagation of this species through tissue fragmentationis also possible. Vegetative fragments of this carrageenophyte have 20 to30% higher growth rates than whole fronds in suspended culture systems. Protoplast production can be also explored for bypassing restrictions inspore availability. Major advantages that encourage the cultivation of G. skottsbergii include its gel quantity and quality, its pathogen-freecondition, a high reproduction potential and its regeneration capacity. Onthe other hand, the major constraints are related to its relatively slowgrowth as compared to other carrageenophytes, limited availability ofspores and high mortality during juvenile stages.     

A sulfated galactan with antioxidant capacity from the green variant of tetrasporic Gigartina skottsbergii (Gigartinales, Rhodophyta)

The water soluble polysaccharide produced by the green variant of tetrasporic Gigartina skottsbergii was found to be composed of D-galactose and sulfate groups in a molar ratio of 1.0:0.65. (1)H and (13)C NMR spectroscopy studies of the desulfated polysaccharide showed a major backbone structure of alternating 3-linked β-D-galactopyranosyl and 4-linked α-D-galactopyranosyl units, and minor signals ascribed to 3-O-methyl-substitution on the latter unit. Ethylation analysis of the polysaccharide indicated that the sulfate groups are mainly located at position O-2 of 4-linked α-D-galactopyranosyl residue and partially located at positions O-6 of the same unit and at position O-2 of 3-linked β-D-galactopyranosyl residue, and confirmed the presence of 3-O-methyl-galactose in minor amounts (4.4%). The sulfated d-galactan presents a similar structure to λ carrageenan but with much lower sulfation at position O-6 of the α-residue and at position O-2 of β-residue. The antioxidant capacity of the sulfated d-galactan was evaluated by the peroxyl radicals (ORAC method), hydroxyl radicals, chelating activity, and ABTS(+) assays. Kinetic results obtained in these assays were compared with those obtained for the commercial λ carrageenan. The antioxidant activity toward peroxyl radicals was higher for commercial λ carrageenan, this agrees with its higher content of sulfate group. The kinetics of the reaction of both polysaccharides with hydroxyl and ABTS(+) radicals showed a complex mechanism, but the antioxidant activity was higher for the polysaccharide from the green variant of tetrasporic Gigartina skottsbergii.     

Economic valuation of the commercial aquaculture of Sarcopeltis skottsbergii in Southern Chile

In this study we analyze the economic feasibility of commercial cultivation of Sarcopeltis skottsbergii, a red seaweed endemic in southern Chile with commercial interest as a source of carrageenan. To this end, a dynamic bioeconomic model was built that comprises three submodels, namely, a biological, a technical, and an economic one. The cultivation was by using a method where they are hung in the sea, with juveniles attached to lines. The site is located in the Bay of Ancud, in the Los Lagos Region of southern Chile. The sensitivity analysis showed that cultivation is profitable for a private investor when the price and growth of the biomass are substantially higher than the parameters established for the baseline model. The results suggest that greater technological development is required to make a culture of this type profitable and, thus, reduce the extractive pressure that is currently exerted on natural habitats.

     

Culture of Gigartina Skottsbergii (Rhodophyta) in Southern Chile. A Pilot Scale Approach

In the last 10 years studies on the management and exploitation of Chilean carrageenophytes have proliferated in response to the increasing development of the local processing industry. One of the most important sources of raw material for Chilean carrageenan, Gigartina skottsbergii Setchell et Gardner, was the subject of an intensive study to design a commercial cultivation technique which could be an alternative to wild harvest. In this context this pilot study reports the first successful attempt to culture G. skottsbergii from spores to harvestable plants. A three-step farming approach was developed: (i) seeding of spores onto scallop shells followed by a two-month nursery period in a greenhouse (until the development of initial upright thalli from the discoid crust occurred), (ii) outplanting juvenile plants on shells in the sea on a long-line system (until thalli attained 3–4 cm diameter) and (iii) detachment of fronds from the shells, fixing of individuals to vertical ropes and growth until commercial size was reached. Additional experiments to compare bottom and suspended growth, cultivation by fragmentation and whole fronds and meristematic activity of different zones of the fronds were performed. This study shows the technical feasibility of culturing G. skottsbergii from spores, complemented with growth of vegetative fragments, in order to optimize the management of the culture. In the future, therefore, it may be possible to replace the heavy exploitation of wild beds in southern Chile with farming activities.     

Growth and survival performance of the gametophyte of Gigartina skottsbergii (Rhodophyta, Gigartinales) under defined nutrient conditions in laboratory culture

Gigartina skottsbergii is a commercially important carrageenan producer that has been suffering severe extraction pressure in Chile’s Magellan Region and Cape Horn Archipelago since 1998. In order to create baseline information for its cultivation and repopulation, we studied the effects of agricultural fertilizers on growth of G. skottsbergii early developmental stages. The culture media utilized were: a) seawater + Bayfoland, b) seawater + Superphosphate, c) seawater + Urea, d) seawater + Provasoli and e) seawater as a control. The culture conditions were: a) 12L:12D photoperiod; b) temperature 8 ± 1°C and c) irradiance at 45 μmol photons m⁻² s⁻¹. After 60 days, higher relative growth rates between treatments were observed; the treatments that included Bayfoland and Provasoli showed greater growth (382 ± 55 and 378 ± 50 μm, respectively,) compared to Superphosphate (88 ± 16 μm), control (78 ± 10 μm) and Urea (70 ± 11 μm) treatments, after 81 days. The Urea treatment and the control had inhibitory effects on G. skottsbergii germlings growth and survival, as evidenced by progressive loss of pigmentation and death after 60 days. These results showed that Bayfoland was an excellent alternative to develop cultures.     

Utilization of holdfast fragments for vegetative propagation of Macrocystis integrifolia in Atacama, Northern Chile

We attempted to propagate Macrocystis integrifolia (giant kelp) by fragmentation and regeneration of holdfasts, which consist of creeping stolons with lateral haptera. Stolons from a natural kelp population in Bahia Chasco (Atacama, North Chile) were cut into fragments, each containing one or more lateral stipe and frond initials. Fragments were attached to longlines with elastic bands. We used two additional types of inoculants as controls: (1) natural recruits from the local parent population and (2) laboratory-cultured young sporophytes. Length, reproductive phenology, and mortality were determined monthly. Our results confirmed the feasibility of M. integrifolia propagation by reattachment of stolon fragments, and we obtained up to eight new individuals from one parent holdfast. Individuals from holdfast regeneration formed sporangial sori 3 months earlier than control specimens from recruits and laboratory culture, while all three types gave similar values for mortality. Holdfast morphology of regenerates differed strongly depending on their origin: stolon fragments continued growth and developed new haptera except in the cut surfaces, natural recruits formed typical M. integrifolia holdfast morphs, and sporophytes originating from laboratory culture produced minor stolons with many haptera. Implications of our results on ecology, repopulation, and aquaculture are discussed.     

Richness,systematics, and distribution of molluscs associated with the macroalga Gigartina skottsbergii in the Strait of Magellan,Chile: A biogeographic affinity study

Knowledge about the marine malacofauna in the Magellan Region has been gained from many scientific expeditions that were carried out during the 19th century. However, despite the information that exists about molluscs in the Magellan Region, there is a lack of studies about assemblages of molluscs co-occurring with macroalgae, especially commercially exploitable algae such as Gigartina skottsbergii, a species that currently represents the largest portion of carrageenans within the Chilean industry. The objective of this study is to inform about the richness, systematics, and distribution of the species of molluscs associated with natural beds in the Strait of Magellan. A total of 120 samples from quadrates of 0.25 m² were obtained by SCUBA diving at two sites within the Strait of Magellan. Sampling occurred seasonally between autumn 2010 and summer 2011: 15 quadrates were collected at each site and season. A total of 852 individuals, corresponding to 42 species of molluscs belonging to Polyplacophora (9 species), Gastropoda (24), and Bivalvia (9), were identified. The species richness recorded represents a value above the average richness of those reported in studies carried out in the last 40 years in sublittoral bottoms of the Strait of Magellan. The biogeographic affinity indicates that the majority of those species (38%) present an endemic Magellanic distribution, while the rest have a wide distribution in the Magellanic-Pacific, Magellanic-Atlantic, and Magellanic-Southern Ocean. The molluscs from the Magellan Region serve as study models for biogeographic relationships that can explain long-reaching patterns and are meaningful in evaluating possible ecosystemic changes generated by natural causes or related to human activities.     

A pilot-scale study of total volatile fatty acids production by anaerobic fermentation of sewage in fixed-bed and suspended biomass reactors

A comparative study of a fermentation process for total volatile fatty acids (TVFA) production using pilot-scale fixed-bed (FAS) and suspended biomass (FER) reactors in which similar operational conditions was carried out. The influence of the changes of ambient temperatures at fixed operational conditions was also studied. Oxidation–reduction potential (ORP) increased and effluent pH decreased as the hydraulic retention time (HRT) decreased, which was favourable for TVFA production. Equations describing the ORP and pH variations with the HRT were obtained. ORP variation with HRT for FAS and FER reactors followed a logarithmic function with a regression coefficient, R², equal to 0.98. The variations of pH with HRT followed polynomial functions with regression coefficients of 0.96 and 0.98 for FAS and FER reactors, respectively. Hydrolysis process increased with the experiment duration. At the beginning of the experiment, effluent soluble COD (SCOD) decreased with respect to the influent but further effluent SCOD increased showing higher values compared to the influent. Cold temperatures were more favourable than summer temperatures for the accumulation of TVFA at the liquid effluent. The FAS reactor was more effective in the production of TVFA than the FER reactor. The maximum yields of TVFA were obtained at an organic volumetric loading rate (B_V) of 1.9 g COD/l per day, corresponding to an HRT of 3.4 h, for both reactors. A maximum increase of ammonia and phosphorus was observed at the maximum value of HRT coinciding with an increase of pH and a decrease of ORP, as could be previously observed. The average P/SCOD ratio for the influent and effluent were 0.06 and 0.05, respectively, for FAS and FER reactors. The average Ammonia/SCOD ratio for the influent and effluent were 0.15 and 0.14, respectively. These results demonstrate that effluent quality was improved by the treatment employed in case a further process of nutrient removal is carried out.     

植被过滤带对悬浮固体净化效果的模拟

数学模型是进行植被过滤带(VFS)设计的重要工具.本研究通过分析植被过滤带对径流中悬浮固体的净化机理,采用植被过滤带田间尺度机理模型VFSMOD和修正的土壤侵蚀模型MUSLE耦合,对植被过滤带的悬浮固体净化效果进行模拟,并利用野外小区试验数据对该耦合模型进行了验证.结果表明,植被过滤带出流悬浮固体浓度模拟值与实测值的偏差多在±20％以内,其模拟值与实测值的判定系数R2为0.98,该模型具有较高的精度,且优于VFSMOD模型,可用于我国植被过滤带的规划设计.