James S. Craigie

Seaweed extracts as biostimulants of plant growth and development.

Marine algal seaweed species are often regarded as an underutilized bioresource, many have been used as a source of food, industrial raw materials, and in therapeutic and botanical applications for centuries. Moreover, seaweed and seaweed-derived products have been widely used as amendments in crop production systems due to the presence of a number of plant growth-stimulating compounds. However, the biostimulatory potential of many of these products has not been fully exploited due to the lack of scientific data on growth factors present in seaweeds and their mode of action in affecting plant growth. This article provides a comprehensive review of the effect of various seaweed species and seaweed products on plant growth and development with an emphasis on the use of this renewable bioresource in sustainable agricultural systems.

Evaluation of phytoplankton as diets for juvenile Ostrea edulis L.

Of 16 phytoplankton species tested as juvenile oyster diets, those superior to the reference diet Isochrysis galbana clone T-iso emerged with the following descending ranking: Chaetoceros gracilis Schutt, C. calcitrans Takano, Skeletonema costatum (Grev.) Cleve, Chaetoceros simplex Ostenfeld, Rhodomonas sp., and Thalassiosira pseudonana Hasle & Heimdal. The daily oyster growth rate with Chaetoceros gracilis was 1.5 to 1.8 times that with Isochrysis galbana clone T-iso. Biochemical analysis on some of the good and poor algal diets provided insight into the nutritional requirements of Ostrea edulis (L.) juveniles. Level of the essential fatty acids 20: 5ω3 and 22: 6ω3 and carbohydrate level are important factors in a good algal diet for O. edulis juveniles. Variation in the amino-acid composition among the seven algal diets analysed was small and did not explain the observed differences in oyster growth response with the diets. There was no clear trend between the protein level of the diet and the growth response of the oysters.

Growth of juvenile Ostrea edulis L. fed Chaetoceros gracilis Schütt of varied chemical composition

The chemical composition of Chaetoceros gracilis Schutt was altered by varying the nutrient conditions of the culture. The protein content of cells cultured in the complete f/2 nutrient medium (control) and the silicate-limited medium was similar, but cells from the nitrogen-limited medium contained ≈ 60% less protein. There was little change in amino-acid composition of cells from the three culture regimes. The lipid content of silicate-limited cells was more than twice that of either the control or the nitrogen-limited cells. The predominant fatty acids in the cells from all three nutrient treatments were 14:0, 16:0, 16:1ω 7, and 20:5ω3. The content of the essential fatty acid, 22:6ω3, in the control, silicate-limited, and nitrogen-limited cells was 0.23, 0.08, and 0.10 μg · (106 cells)−1, respectively. The carbohydrate levels of the silicate-limited and nitrogen-limited cells were, respectively, 1.6- and 3.2-fold higher than the control. The growth responses of Ostrea edulis (L.) juveniles fed the three cultures of Chaetoceros gracilis were a function of feeding ration. At high feeding ratios the highest oyster growth rates were obtained with the control C. gracilis diet. The relatively high level of the 22:6ω3 fatty acid in this diet is suggested as a possible explanation. At the lowest feeding rations, C. gracilis grown under silicate-limited conditions yielded the highest oyster growth rate of all three diets. When the growth responses of juvenile oysters fed various mixtures of the three C. gracilis cultures were examined, the highest oyster growth rates were obtained when 25% of the control algal cells was replaced with an equal number of nitrogen-limited cells. The results indicate that higher oyster growth rates are possible with additional carbohydrate, provided that adequate protein and essential fatty acids are supplied.

Carrageenans in the gametophytic and sporophytic stages of Chondrus crispus

SummaryThe morphologically similar sporophytic and gametophytic plants of Chondrus crispus Stackhouse were examined and it was shown that the former contain λ-carrageenan. The gametophytes contain ϰ- and two additional carrageenans which are KCl-soluble and may comprise up to 25% of the total carrageenan. After alkaline modification, these KCl-soluble components were separated into a gel and a soluble carrageenan. The gel was indistinguishable from ϰ-carrageenan and presumably was derived from μ-carrageenan while the KCl-soluble fraction possessed a unique infrared spectrum easily distinguished from alkali-modified λ-carrageenan. This appears to represent a third carrageenan in the gametophytes.Our observations suggest that the biologically separate plants of C. crispus exhibit distinctive patterns of sulfation of their galactans. The sporophytes add SO42- at C2 of the precursor, whereas the gametophytes appear to add it principally at the available C4 positions. Both types of plant are capable of sulfating at C6 of the 4-linked galactose unit.

Algae as nutritional and functional food sources: revisiting our understanding

Global demand for macroalgal and microalgal foods is growing, and algae are increasingly being consumed for functional benefits beyond the traditional considerations of nutrition and health. There is substantial evidence for the health benefits of algal-derived food products, but there remain considerable challenges in quantifying these benefits, as well as possible adverse effects. First, there is a limited understanding of nutritional composition across algal species, geographical regions, and seasons, all of which can substantially affect their dietary value. The second issue is quantifying which fractions of algal foods are bioavailable to humans, and which factors influence how food constituents are released, ranging from food preparation through genetic differentiation in the gut microbiome. Third is understanding how algal nutritional and functional constituents interact in human metabolism. Superimposed considerations are the effects of harvesting, storage, and food processing techniques that can dramatically influence the potential nutritive value of algal-derived foods. We highlight this rapidly advancing area of algal science with a particular focus on the key research required to assess better the health benefits of an alga or algal product. There are rich opportunities for phycologists in this emerging field, requiring exciting new experimental and collaborative approaches.

STUDIES ON THE ALGAL CUTICLE1

A chemically resistant cuticle fraction was isolated from 5 phaeophycean, 1 rhodophycean, and 11 chlorophycean marine algae using acid treatment alone, or acid treatment followed by leaching in cupra‐ammonium. In Cladophora rupestris and Chaetomorpha melagonium this fraction consists of several alternate microfibrillar and amorphous layers similar in appearance to those seen in innermost carbohydrate‐rich regions and amount to about 1/10 or more of the cell wall thickness. In Porphyra umbilicalis and Padina vickersiae it is a single layer less than I μ thick, accounting for 1/50–1/100 of the cell wall in Porphyra, and 1/5–1/10 of the cell wall in Padina. The cuticle fractions of all 4 algae contain surprisingly large amounts of protein (about 70% in Cladophora and 80% in Porphyra). Similarities in the behavior of cuticles obtained from the other 12 species studied suggest that they may have a similar protein‐rich composition.

ANTIALGAL ACTIVITY OF SOME SIMPLE PHENOLS1

The antialgal activity of a number of simple phenols was examined for their effect on the growth of 7 species of unicellular marine algae. The 3 knoiun algal phenols, 5‐bromo‐3,4‐dihydroxybenzaldehyde; 2,3‐dibromo‐4,5‐dihydroxybenzylalcohol, and 3,4‐dihy‐droxyphenylethylamine, were highly toxic as were other ortho dihydroxy compounds. Monohydroxy compounds were notably less toxic. Skeletonema costatum and Olisthodiscus sp. were the most sensitive organisms examined and Dunaliella tertiolecta was the most resistant. Possible ecological implications of these results are discussed.

NITRATE UPTAKE BY LAMINARIA LONGICRURIS (PHAEOPHYCEAE)1,2

Laminaria longicrucis De la Pylaie took up exogenous nitrate under both summer and winter conditions. During July and August no NO3‐ was detected in the ambient water or in algal tissues although it was present in both in February. Discs (2.3 cm diam.) of thin blade tissue were incubated with NO3‐ at four temperatures, with and without illumination. Similar values Jor NO3‐ uptake were found for both summer and winter collected plants when measured in light at 0 C. An apparent K of 4–6 μM was recorded for both types of plants; the Vmax ranged from 7 to 10 μmol h‐1 g‐1 dry wt measured in ca. 1800 μW cm‐2 of cool‐white fluorescent light. Uptake rates at 5 C were 66%, and at 0 C 30% of those for controls run at 15 C. The alga scavenged NO3‐ from solutions <0.5 μM. Ammonia did not inhibit NO3‐ uptake. Antibiotic pretreatment reduced NO3‐ uptake by a maximum of 12%. Nitrite uptake was inhibited in proportion to the concentration of NO3‐ in the medium.

CHEMICAL COMPOSITION AND STRUCTURE OF THE CELL WALLS OF THE CONCHOCELIS AND THALLUS PHASES OF PORPHYRA TENERA (RHODOPHYCEAE)1,2

Purified cell walls were prepared from both the conchocelis and thallus phases of Porphyra tenera (Kjellm.). The nitrogen content of cell walls from the conchocelis was significantly greater than that for the thallus cell walls, being 3.35 ± 0.26% and 2.39± 0.03%, respectively. Amino acid analysis revealed important differences. The conchocelis cell wall hydrolyzates were richer in aspartic acid, glutamic acid, methionine, and basic amino acids. The thallus cell wall hydrolyzates, however, contained much more glycine and alanine than did those of the conchocelis. Hydroxyproline was not detected in cell walls of either phase. The neutral sugar content of cell wall hydrolyzates from the thallus was more than double that from the conchocelis being 83.6% and 34.5%, respectively. The former contained predominantly mannose which accounted for 72.2% of the neutral sugars while the latter was principally galactose (49.9%) and glucose (36.4%). Methylation analysis confirmed the presence of cellulose microfibrils in the conchocelis in contrast to xylan microfibrils in the thallus. The results establish that the conchocelis and thallus phases of P. tenera differ markedly in the structure and composition of the cell walls.

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.