Quantitative Sustainability Assessment of Seaweed Biomass as Bioethanol Feedstock

Since terrestrial biomass-based ethanol has environmental and economic vulnerability, seaweed-based bioethanol is emerging as a new biofuel. To investigate the sustainability of seaweeds as bioethanol feedstock, this study quantitatively assesses the energy, freshwater, and fertilizer requirements; land-related carbon balance; and bioethanol productivity of seaweed biomass through comparison with terrestrial biomass. Also, the metal resource potential of seaweeds is assessed because valuable metals can be recovered from seaweed fermentation residue. Compared to corn grain and stover, seaweeds exhibit competitive energy requirements and ethanol productivity. Seaweed cultivation does not incur carbon debt derived from land use change and requires less freshwater than corn grain but more than switchgrass in cultivation and fermentation. Seaweed cultivation also does not require fertilizer application despite the high content of nitrogen and phosphorus. Seaweeds exhibit high resource potential for gold and silver. Therefore, seaweed biomass has high potential as a sustainable bioethanol feedstock.     

Sustainable harvesting of wild seaweed resources

Abstract

Macroalgae have played an important role in coastal communities for centuries. In the past, they have been harvested and gathered from shorelines around the world for traditional uses such as food, animal feed and a crude fertilizer (marine manure). Today, seaweeds are used in a multitude of applications with expanding global industries based on hydrocolloids, cosmetics and food supplements, and also as a potential biofuel source. However, of the approximately 10?000 algal species reported to exist, only a small number are commercially utilized. While representing only a small fraction of total global seaweed production, harvesting and gathering ‘wild’ seaweeds has had, and continues to have, an integral role in many coastal societies, often being intrinsically linked to the cultural identity of those coastal communities. Today, 32 countries actively harvest seaweeds from wild stocks, with over 800?000 t harvested annually from natural beds. It is vitally important that seaweeds are utilized sustainably and that natural resources are effectively managed by coastal communities with vested interests around the world. As the popularity of seaweeds increases and the use of less traditional species with novel applications comes to the fore, it is critically important to make certain that the sustainability of the resource is ensured given the increased pressures of harvesting. Issues exist regarding ownership of the resource and its over-exploitation, and the implementation of environmentally damaging harvesting techniques must be avoided. Resource scientists, managers, conservationists, governments, and other stakeholders need to be proactive in the sustainable management of these vulnerable, yet valuable, resources.     

Seaweed biogeochemistry: Global assessment of C:N and C:P ratios and implications for ocean afforestation

Algal carbon-to-nitrogen (C:N) and carbon-to-phosphorus (C:P) ratios are fundamental for understanding many oceanic biogeochemical processes, such as nutrient flux and climate regulation. We synthesized literature data (444 species, >400 locations) and collected original samples from Tasmania, Australia (51 species, 10 locations) to update the global ratios of seaweed carbon-to-nitrogen (C:N) and carbon-to-phosphorus (C:P). The updated global mean molar ratio for seaweed C:N is 20 (ranging from 6 to 123) and for C:P is 801 (ranging from 76 to 4102). The C:N and C:P ratios were significantly influenced by seawater inorganic nutrient concentrations and seasonality. Additionally, C:N ratios varied by phyla. Brown seaweeds (Ochrophyta, Phaeophyceae) had the highest mean C:N of 27.5 (range: 7.6–122.5), followed by green seaweeds (Chlorophyta) of 17.8 (6.2–54.3) and red seaweeds (Rhodophyta) of 14.8 (5.6–77.6). We used the updated C:N and C:P values to compare seaweed tissue stoichiometry with the most recently reported values for plankton community stoichiometry. Our results show that seaweeds have on average 2.8 and 4.0 times higher C:N and C:P than phytoplankton, indicating seaweeds can assimilate more carbon in their biomass for a given amount of nutrient resource. The stoichiometric comparison presented herein is central to the discourse on ocean afforestation (the deliberate replacement of phytoplankton with seaweeds to enhance the ocean biological carbon sink) by contributing to the understanding of the impact of nutrient reallocation from phytoplankton to seaweeds under large-scale seaweed cultivation.     

Sequential inorganic chemical analysis of a core from Slapton Ley,Devon, UK

Numerous species of seaweed have been successfully cultivated in the sea for commercial purposes. Although considerable experimental work has been done on on-shore cultivation systems, none of these has yet proved to be economically viable on a sustained basis; nevertheless, such cultivation systems offer the potential for productivities greater than can be achieved in other systems. In on-shore systems, factors other than light can be controlled and provided at saturation levels. As density of biomass is controllable, all the light entering the cultivation system is absorbed. This results in efficient conversion of light energy to biomass when only light is limiting; moreover, density, rather than growth rate, is the major factor determining productivity. As growth of seaweeds in on-shore systems is only vegetative, there is no interruption for reproduction or maturation of the plants, and all of the net production can be recovered. Seaweeds have, though, relatively low percentage carbon composition, compared with terrestrial plants, and this may result in apparent high productivities based on dry matter.     

Seaweed micropropagation techniques and their potentials: an overview

The seaweed industry worldwide uses 7.5–8.0 million tonnes of wet seaweeds annually with a majority of it derived from cultivated farms, as the demand for seaweed based-products exceeds the supply of seaweed raw material from natural stocks. The main advantage of cultivation is that it not only obviates overexploitation of natural populations but also facilitates the selection of germplasm with desired traits. To enhance the economic prospects of seaweed cultivation, varied practices, such as simple and cost effective cultivation methods, use of select germplasm as seed stock coupled with good farm management practices, etc., are adopted. Nevertheless, in vitro cell culture techniques have also been employed as they facilitate development and propagation of genotypes of commercial importance. There are more than 85 species of seaweeds for which tissue culture aspects have been reported. Although the initial aim of these techniques focuses mostly on genetic improvement and clonal propagation of seaweeds for mariculture, recently the scope of these techniques has been extended for use in bioprocess technology for production of high value chemicals of immense importance in the pharmaceutical and nutraceutical sectors. Recently, there has been a phenomenal interest in intensifying seaweed tissue and cell culture research to maximize the add-on value of seaweed resources. This paper deals with the status of seaweed micropropagation techniques and their applications in the context of the marine biotech industry. Further, it also provides an analysis of the problems to be resolved for removing the barriers that are impeding the true realization of potentials offered by these techniques for sustainable development and utilization of seaweed resources.     

Prospects and challenges for industrial production of seaweed bioactives

Large‐scale seaweed cultivation has been instrumental in globalizing the seaweed industry since the 1950s. The domestication of seaweed cultivars (begun in the 1940s) ended the reliance on natural cycles of raw material availability for some species, with efforts driven by consumer demands that far exceeded the available supplies. Currently, seaweed cultivation is unrivaled in mariculture with 94% of annual seaweed biomass utilized globally being derived from cultivated sources. In the last decade, research has confirmed seaweeds as rich sources of potentially valuable, health‐promoting compounds. Most existing seaweed cultivars and current cultivation techniques have been developed for producing commoditized biomass, and may not necessarily be optimized for the production of valuable bioactive compounds. The future of the seaweed industry will include the development of high value markets for functional foods, cosmeceuticals, nutraceuticals, and pharmaceuticals. Entry into these markets will require a level of standardization, efficacy, and traceability that has not previously been demanded of seaweed products. Both internal concentrations and composition of bioactive compounds can fluctuate seasonally, geographically, bathymetrically, and according to genetic variability even within individual species, especially where life history stages can be important. History shows that successful expansion of seaweed products into new markets requires the cultivation of domesticated seaweed cultivars. Demands of an evolving new industry based upon efficacy and standardization will require the selection of improved cultivars, the domestication of new species, and a refinement of existing cultivation techniques to improve quality control and traceability of products.     

Spatial and seasonal variation of macroalgal biomass in Laguna Ojo de Liebre, Baja California Sur, Mexico

Laguna Ojo de Liebre is part of El Vizcaíno Biosphere's Reserve, one of the largest protected natural areas in the world. The contribution of seaweeds to the lagoons' total biomass had not been previously quantified. The purpose of this study was to evaluate the spatial and temporal variations of seaweed biomass in the lagoon. Seaweed samples were taken every season during 1995 at six sampling stations distributed throughout the lagoon. Total specific biomass of seaweeds was at its peak in the summer, and minimum in spring. The highest total annual biomass was found at Isla Brosa in the lagoon's central portion, and the lowest in El Dátil at the head. The seasonal and spatial variation of biomass in the lagoon is related with species richness and environmental parameters. Potentially important species in terms of biomass, wide spatial and temporal distribution, and potential use were: Spyridia filamentosa, Entheromorpha clathrata, Dasya baillouviana, Hypnea valentiaeand Sargassum sinicola .Using PCA three groups of stations were defined: one chiefly at the lagoon's mouth, another comprised the islands in the central portion, and the last in the lagoon's head.     

On-land cultivation of functional seaweed products for human usage

Worldwide, there has been much interest in the development and commercialization of human functional products from seaweeds. Novel seaweed compounds with potential applications as bioactive ingredients in natural health products are being isolated in a number of active research programs on this topic. The majority of these research programs do not include cultivation as a critically important component in scaling the discoveries up to commercialization (i.e., economies of scale realized). Many of these seaweeds of interest with potential as functional human products are diminutive in size, sparse in density, and seasonal in occurrence and bioactive efficacy, making commercialization by resource management and harvesting economically challenging and the application of traditional ocean-based production methods risky. Human functional products will require sustainable production coupled with quality assurance and standardized, consistent efficacy. Since humans are the consumers of these types of functional seaweed products, traceability and security of supply are of the utmost importance to successful commercialization. On-land cultivation is essential for commercial success in the development of human functional products from seaweeds at industrial scales. On-land cultivation allows the highest levels of control over quality, efficacy, traceability, and security. On-land cultivation represents the most environmentally acceptable method for the production of biomass from natural resources that could not be economically or sustainably developed any other way. However, on-land cultivation has many associated barriers to development, including high costs associated with capital, operations, maintenance, and cultivar development, and these demands limit industrial scale development of seaweed functional products for human consumption.     

Cultivation of red seaweeds: a Latin American perspective

The Latin American seaweed industry plays an important role at a global scale as 17 % of all seaweeds and 37 % of red seaweeds for the phycocolloid industry comes from this region. Increased market demand for algal raw materials has stimulated research and development into new cultivation technologies, particularly in those countries with economically important seaweed industries such as Argentina, Brazil, Chile, México, and Peru. The marine area of Latin America includes almost 59,591 km² of coastline ranging in latitude from 30ºN to 55ºS and encompasses four different oceanic domains: Temperate Northern Pacific, Tropical Eastern Pacific, Temperate South America, and Tropical Atlantic. Commercial cultivation of red seaweed in Latin America has been basically centered in the production of Gracilaria chilensis in Chile. Attempts have been made to establish seaweed commercial cultivation in other countries, going from experimental research-oriented studies to pilot community/enterprise based cultivation trials. Some genera such as Kappaphycus and Eucheuma have been studied in Brazil and Mexico, Gracilaria species in Argentina and Brazil, Gracilariopsis in Peru and Venezuela, and Chondracanthus chamissoi in Peru and Chile. In this short review, we address the Latin America perspective on the status and future progress for the cultivation of red seaweeds and their sustainable commercial development, and discuss on the main common problems. Particular emphasis is given to the needs for comprehensive knowledge necessary for the management and cultivation of some of the most valuable red seaweed resources in Latin America.     

Seaweeds: an opportunity for wealth and sustainable livelihood for coastal communities

The European, Canadian, and Latin American seaweed industries rely on the sustainable harvesting of natural resources. As several countries wish to increase their activity, the harvest should be managed according to integrated and participatory governance regimes to ensure production within a long-term perspective. Development of regulations and directives enabling the sustainable exploitation of natural resources must therefore be brought to the national and international political agenda in order to ensure environmental, social, and economic values in the coastal areas around the world. In Europe, Portugal requires an appraisal of seaweed management plans while Norway and Canada have developed and implemented coastal management plans including well-established and sustainable exploitation of their natural seaweed resources. Whereas, in Latin America, different scenarios of seaweed exploitation can be observed; each country is however in need of long-term and ecosystem-based management plans to ensure that exploitation is sustainable. These plans are required particularly in Peru and Brazil, while Chile has succeeded in establishing a sustainable seaweed-harvesting plan for most of the economically important seaweeds. Furthermore, in both Europe and Latin America, seaweed aquaculture is at its infancy and development will have to overcome numerous challenges at different levels (i.e., technology, biology, policy). Thus, there is a need for regulations and establishment of “best practices” for seaweed harvesting, management, and cultivation. Trained human resources will also be required to provide information and education to the communities involved, to enable seaweed utilization to become a profitable business and provide better income opportunities to coastal communities.     

Biochemical characteristics of cellulose and a green alga degradation by Gilvimarinus japonicas 12-2T,and its application potential for seaweed saccharification

ABSTRACT

Cellulose is one of the major constituents of seaweeds, but reports of mechanisms in microbial seaweed degradation in marine environment are limited, in contrast to the multitude of reports for lignocellulose degradation in terrestrial environment. We studied the biochemical characteristics for marine cellulolytic bacterium Gilvimarinus japonicas 12-2^T in seaweed degradation. The bacterial strain was found to degrade green and red algae, but not brown algae. It was shown that the bacterial strain employs various polysaccharide hydrolases (endocellulase, agarase, carrageenanase, xylanase, and laminarinase) to degrade seaweed polysaccharides. Electrophoretic analysis and peptide sequencing showed that the major protein bands on the electrophoresis gel were homologous to known glucanases and glycoside hydrolases. A seaweed hydrolysate harvested from the bacterial culture was found useful as a substrate for yeasts to produce ethanol. These findings will provide insights into possible seaweed decomposition mechanisms of Gilvimarinus, and its biotechnological potential for ethanol production from inedible seaweeds.     

Potential products from the highly diverse and endemic macroalgae of Southern Australia and pathways for their sustainable production

Macroalgae provide a substantial and renewable resource that can be sustainably utilized for economic and social benefit. A US$7 billion global industry already exists for macroalgae, but the huge majority of this is based on the production of species belonging to approximately six genera, within eight countries, for the manufacture of foods, industrial biomaterials and agricultural products. However, seaweed-derived functional products spanning numerous chemical classes have been identified with valuable therapeutic and industrial applications. This review focuses on the breadth of valuable bioproducts that could be produced from the seaweeds of Southern Australia—a hotspot for seaweed diversity, and the pathways available for their sustainable commercial production. This region contains among the highest level of recorded macroalgal diversity and endemism in the world, with approximately 1,200 described species, of which 62 % are considered endemic. Whilst a number of these species have been shown to be rich sources of higher-value functional products, and most of them still await exploration in this field, the seaweed industry of Southern Australia is largely limited to the harvest of beach-cast biomass for the manufacture of lower-value commodities such as fertilizer and animal feed. There is potential for the development of a substantial industry based on human functional products from seaweeds in Southern Australia. However, a number of challenges and knowledge gaps—including environmental, technological, agronomic, political, and cultural factors—are identified in this review, which must be addressed before sustainable expansion can be achieved. Furthermore, numerous strategic approaches and areas of suggested foci are underscored for research bodies and industry alike. Particular emphasis is given to the need for comprehensive surveying and bioprospecting of the resource; a focus on advanced downstream processing capabilities for improving production efficiency and enhancing product value; the use of biorefinery approaches to improve utilisation efficiency; and pursuing means of improving the sustainability of supply chains.     

Seaweed research and utilization in Chile: moving into a new phase

Two phases have been distinguished classically in the history of Latin American phycological research: the explorer phase characterized by the taxonomic work of mainly European and North American scientists, and the diversification phase marked by the establishment of resident scientists in the area and the training of a new generation of phycologists in subjects other than taxonomy. Over the last 15 years, Chile has entered a third phase, characterized by a significant increase in scientific and economic activity centered around seaweeds. Seaweed cultivation has been commercialized; raw materials are now locally processed and economic returns have more than tripled. In addition, some groups of opportunistic seaweed gatherers have become farmers. Loosely correlated with the above developments has been a significant increase in the number of scientific and technological studies related to seaweeds, in the number of professional phycologists and in the specialization of the various groups. This study first describes these new developments and the conceptual advances achieved in farming and resource management. It also emphasizes some socio-economic differences with seaweed farming in other countries and explores the level of interaction between the local scientific and productive sectors in view of future developments.     

Seaweed cultivation: Methods and problems

This paper presents an overview of the state of the art in global seaweed cultivation. It describes methodological approaches and main cultivation methods and discusses different problems arising during the application of these methods. One of the major problems is the negative effect of large-scale monoculture of seaweeds on natural benthic biocenoses. We express our views on how to tackle the most acute problems of macroalgal farming on the basis of our own data and data from other authors. The sustainable use of natural monodominant seaweed communities is shown to be preferable to mariculture. A detailed analysis is given of various mariculture models and the latest achievements in the integrated farming of seaweeds, fish, crustaceans, and mollusks.     

Application of the functional-form model to the culture of seaweeds

Selecting the most appropriate species or strains is an important first step in the development of most algal cultivation systems and is usually a tedious, time-consuming, and expensive step. The functional-form model, first developed to synthesize the adaptive significance of easily assessed thallus-form attributes relative to the productivity and survival of benthic macroalgae, is applicable to the culture of seaweeds and can expedite species or strain selection. The production ecology aspects of the model are useful particularly for applications where the desired product is not species-specific, e.g., systems in which the emphasis is on algal production, such as algal biomass farms and wastewater treatment. A thallus-form with a high surface area: volume ratio is more suited for rapid production and nutrient uptake. The utility of this model to strain selection is demonstrated with the red alga Gracilaria tikvahiae, a species that has been considered a maricultural candidate for a number of utilizations. A continuum of surface area: volume ratios for eight clones of G. tikvahiae showed that this ratio decreased as morphological complexity increased and was a good predictor of both short-term photosynthesis and long-term growth rate. Clones near opposite ends of the surface area: volume ratio spectrum had significant differences for both photosynthesis and growth. Each clone of G. tikvahiae possesses concomitant combinations of benefits as well as costs, which should be carefully evaluated for the cultivation application of interest. Knowledge of functional-form relationships in seaweeds can significantly expedite their successful cultivation.     

Phycological research in the development of the Chinese seaweed industry

The term seaweed industry is employed in a broad sense and includes production both of commercial seaweeds such as Laminaria and Porphyra by phycoculture and of processed seaweed products, such as algin, agar and carrageenan.Before the founding of the People's Republic, China had a very insignificant seaweed industry, producing small quantities of the purple laver Porphyra and the glueweed Gloiopeltis by the primitive rock-cleaning method and the kelps Laminaria and Undaria by the primitive stone-throwing method, both aiming at enhancing the growth of the wild seaweeds. Also, a small quantity of agar was manufactured by the traditional Japanese method of gelling, freezing, thawing and drying the product. The small production was not sufficient to meet the demand of the Chinese people who for ages have appreciated seaweeds and their products for food. Therefore, large quantities of seaweeds and seaweed products had to be imported from various countries, for instance, Eucheuma and Gracilaria from Indonesia and other southeastern Asian countries, Laminaria and agar from Japan, even Porphyra from the USA. Annual Laminaria import from Japan generally amounted to over 10 000 tons and in some years approached 20 000–30 000 tons. Some quantities of the glueweed Gloiopeltis and the vermifuge weed Digenea simplex were exported, mainly to Japan.Since the founding of the People's Republic of China in October, 1949, China has exerted efforts to build up a self-supporting seaweed industry. Now after a lapse of 30-some years, a sizable seaweed industry has been developed. China is now able to produce by phycoculture more than one million tons of fresh seaweeds, including Laminaria, Undaria, Porphyra, Eucheuma, Gracilaria etc. and several thousand tons of seaweed extracts, including algin, agar, carrageenan, mannitol and iodine. At present, China still imports some quantities of seaweeds and seaweed products from various countries but is able to produce sufficient quantities to meet the people's need and even to export some quantities of the seaweeds Laminaria, Undaria and Porphyra and the seaweed products algin and mannitol.At the Tenth International Seaweed Symposium, I presented a paper on the Marine Phycoculture of China, in which I emphasized on the methods of cultivation (Tseng 1981b). Therefore I would like to take this opportunity to supplement the last lecture by presenting a paper on the role of phycological research in the development of China's seaweed industry.     

Evidence for the presence of plant growth regulators in commercial seaweed products

Although seaweeds and various seaweed products have been utilized in agricultural practices for many years, the precise mechanism by which they elicit their beneficial growth responses is still not fully understood. The amount of mineral nutrients in commercial preparations cannot account for the magnitude of the responses. Some other factor, such as the presence of endogenous plant growth regulators is, therefore, thought to be involved. This paper reviews the literature supporting evidence for the occurrence of plant hormones in commercial seaweed preparations.abbreviations SWC seaweed concentrate - PGR plant growth regulator - GC-MS gas chromatography/mass spectrometry - ¹H-NMR proton nuclear magnetic resonance - HPLC high performance liquid chromatography     

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.     

Dietary exposure and risk assessment to trace elements and iodine in seaweeds

IntroductionSeaweeds are a rich source of elements such as iodine, and are also able to accumulate contaminants such as trace elements.MethodsThe aim of this study was to assess the dietary exposure as well as the risk from iodine and trace elements in edible seaweeds for the French population using current consumption data. The contribution of seaweeds to overall dietary exposure to trace elements and iodine was evaluated, and for those substances with minimal contribution to overall dietary exposure, simulations were performed to propose increased maximal limits in seaweeds.ResultsCadmium, inorganic arsenic and mercury in seaweeds were very low contributors to total dietary exposure to these contaminants (0.7 % 1.1 % and 0.1 % on average, respectively). Dietary exposure to lead via seaweed may contribute up to 3.1 % of total dietary exposure. Dietary consumption of iodine via seaweed may contribute up to 33 % of total exposure to iodine, which makes seaweeds the strongest contributor to iodine in diet.DiscussionNew maximal values in seaweeds are proposed for the very low contributors to total dietary exposure: 1 mg/kg dw for cadmium, 10 mg/kg dw for inorganic arsenic and 0.3 mg/kg dw for mercury.