Determination of the Biomass and Phycocolloid Contentsof some Marine Algae from Eritrea

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Determination of the Biomass and Phycocolloid Contents of some Marine Algae from Eritrea

Y.M.H. YOUNIS1, ^*S. TECLEAB, T. GHEZA and I.H. RAHAMA 1Department of Chemistry, University of Asmara, Asmara, Eritrea

ABSTRACT. Specimens of five marine species of the brown (Cystosei- ra myrica, Sargassum torvum and Turbinaria ornata) and red (Graci- laria cortica and Gracilaria crassa) algae collected from the Red Sea coast of Eritrea were analyzed for their content of biomass and phycocolloids. Sargassum torvum was found to be the dominant species of a maximum biomass. Among the brown species, Turbinaria ornata was distinctive for its high content of alginic acid. Amount of agar did not fluctuate greatly in Gracilaria species.

Introduction

Marine algae provide a rich and adverse source of raw materials for the produc- tion of seaweed gums and polysaccharides. The major application of seaweeds is the extraction of alginic acid, alginate salts and agar. These extracts, which are called phycocolloids, have wide application in world industry (Round, 1973;

Sharma, 1986; Durairatnum et al., 1990). Alginic acid occurs, naturally on the cell wall of most of brown algae. It is a complex carbohydrate polymer consist- ing of D-mannuronic acid and L-guluronic acid residues linked by 1-4 posi- tions. The ratio of these two residues in the alginic acid polymer causes variation in the type of alginic acid produced (Othmex, 1954; Whistler, 1959;

Saddington, 1969; Dawes, 1981). Alginic acid is capable of absorbing water 10 to 20 times its molecular weight (Tresslen & Lemon, 1951).

There is a belief that large quantities of seaweed species are available in tropical waters and the great demand for phycocolloids in the world market will help to develop industries in such areas (Durairatnum et al., 1990; Yarish &

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*Present address: Department of Chemistry, King Faisal University, P.O. Box 1759, Hofuf 31982, Saudi Arabia. E-mail: [email protected].

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Wawukoya, 1990). However, seaweeds of Eritrea have, to a large extent, es- caped the attention of phycologists. Eritrea does not have a history of tradition of seaweed utilization. In this work, results of the studies on biomass, alginic acid and agar contents of some marine species from Eritrea are present.

Materials and Methods

The Study Sites

The selected sites for the study are Ghorgassum, Shaikh Saeed Island and Reisi medri. Khorgassum (15º37′N, 39º28′E) is located 12 km north of Mas- sawa, the seaport of Eritrea. Sheikh Saeed island (15º35′N, 39º28′E) is located south of Massawa. Reisi Medri (15º36′N, 38º29′E) is located east of Massawa.

The three sites share common characteristics. They have rocky intertidal area that can provide a suitable substratum for seaweeds attachment. However, they differ in wave action and possibly other environmental parameters that can af- fect algal growth.

Samples of Sargassum torvum, Cystoseira myrica, Turbinaria ornata (Phaeo- phyta), Gracilaria cortica and Gracilaria crassa (Rhadophyta) were collected from Shaikh Saeed island, Khorgassum and Reisi Medri on the Red Sea coast of Eritrea.

All plants were washed with seawater, freshwater, air-oven dried at 60ºC for 12 hr and powdered mechanically.

Abundance was studied using a transect-quadrate method. The quadrate used was 1 meter square in area (1 m × 1 m), and it was laid at intervals of 10 meters.

The wet and the dry weights of the seaweeds were measured. Statistical analysis was performed using three-way anova to determine the abundance of different species in terms of biomass, Table 1. The brown algae; C. myrica, S. torvum and T. ornata were examined for their alginic acid content. Two extraction methods were adopted in this work. On acidification, the resulting alginate salts were converted into alginic acid.

Extraction of Alginic Acid

a – The Sodium Alginate Method: (Dawes, 1987)

The dried ground samples (5 g each) were washed with acidulated water and digested with soda ash (150 ml) in a water bath for 20 minutes. The hot material was then filtered by suction. Concentrated hydrochloric acid (150 ml) was add- ed portion wise with continuous stirring. The precipitated alginic acid was filtered through Buchner funnel, dried and weighed. It was qualitatively tested (Criddle & Ellis, 1976), Table 2.

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TABLE 1.Biomass content of the selected species of Eritrean marine algae. January 1997March 1998 Red algaeBrown algaeRed algaeBrown algae Site Parameter Shaikh SaeedTran length (m)––– 60 35 60– 20 60 35 islandNo. of quard––– 03 03 03– 02 03 03 Wet weight–––6655087475–15725474438 Dry weight–––– 551 72– 260145 515 KhorgassumTran length (m) 30 30– 30 25 30 30– 30 25 No. of quard 03 03– 03 03 03 03– 03 03 Wet weight6501106–1877059570698–4506605 Dry weight141 118– 29 962 94131–111 923 Reisi MedriTran length (m)–– 30–––– 25 20 33 No. of quard–– 03–––– 02 02 03 Wet weight––1040––––27354801227 Dry weight–– 128–––– 455119 202 Turbinaria

ornata Cystoseira myrica Sargassum torvum Ciracilaria crassa Caracilaria cortiea Turbinaria ornata Cystoseira myrica Sargassum torvum

Caracilaria crassa Caracilaria Cortiea

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b – The Calcium Alginate Method: (Dawes, 1981)

The dried ground samples (5 g each) were digested with sodium carbonate solution (5%, 100 ml), for 12 hr and filtered. Soluble sodium alginate in the fil- trate was converted into calcium alginate by the addition of calcium chloride solution (5%). The isolated calcium alginate was dried and weighed, Table 2.

Extraction of Agar

The two species of Gracilaria were examined for their agar content. Extrac- tion of agar was conducted as described by Pickering et al. (1990). The dried seaweeds (10 g each) were washed with distilled water, extracted with sodium hydroxide solution (5%) at autoclave (120ºC) for 3 min. and filtered. The fil- trates were allowed to gel. The gels were dissolved in water and oven dried at 60ºC, Table 2.

Results and Discussion

The biomass of Cystoseira myrica, Sargassum torvum and Turbinaria ornata (Phaeophyta), Gracilaria cortica and Gracilaria crassa (Phadophyta) growing on the Red Sea coast of Eritrea has revealed clear variation in their abundance (Table 1). It was observed that, Sargassum formed dense strands, a criteria that have been reported for tropical species of Sargassum (Dawes, 1987). It could also be seen that Sargassum was also found to be the dominant species in all sites, particularly in Khorgassum site. Cystoseira has an even gradient distribution within the three sites. Turbinaria was completely absent in Khorgassum, but was the dominant species in Reisi medri. Comparatively, red algae have shown minimum distribution within the three sites. They are completely absent in Reisi Medri. In Shaikh Saeed Island, Gracilaria crassa was the only red algal

TABLE 2. Amounts of alginic acid and agar in some marine algae of Eritrea (Data are means of 6 determinations).

Algae species Alginic acid Agar

Sodium alginate method Calcium alginate method

Sargassum torvum 1.75 g (35%) 3.22 g (64.5%) – – Cystoseira myrica 0.69 g (13.8%) 3.31 g (66.2%) – – Turbinaria ornate 1.52 g (30.4%) 3.68 g (73.6%) – – Ciracilaria crassa – – – – 1.58 g (15.8%) Ciracilaria cortica – – – – 1.77 g (17.7%)

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species to be detected; but with the lowest abundance compared to brown algal species found on the same site. Both species, Gracelaria crassa and G. cortica are found in good abundance during the two sampling periods in Khorgassum (Table 1).

The biomass of Cystoseira and Sargassum species of Shaikh Saeed Island and Khorgassum (Table 1), are statistically different. The site effect could be due to physico-chemical differences (Lapointe & Tenore, 1981; El-Naggar, 1994), or to the extent of site exposure to wave action (McQuaid & Brach, 1984). No significant difference was revealed in biomass between the two sampling methods. This could be due to the reason that the Red Sea seaweeds are in their active growth period during low water temperature (October-April). The slight reduction in the biomass of Sargassum was attributed to the observed reduction of drifted piles. This is usually appearing at the end of the active growth period (Table 1). It could be observed that significant interactions occur between site and species. Interactions between site, period and species are of no statistical importance.

Utilizing the sodium alginate and calcium alginate extraction methods, the percentage yield of alginic acid in Turbinaria ornata, 30.4%, 73.6% was found to be the highest, compared to Sargassum torvum, 35%, 64% and Cystoseira myrica 13.6%, 66.2% respectively. Comparatively, the calcium alginate method gave higher percentage yield of alginic acid, (64.4%-73.6%) than the sodium alginate method (13.6%-35.0%) depending on the species. The results also con- firm the findings that Sargassum was found to be the best alginic acid produc- ing marine algal species in tropical waters (Dawes, 1987).

The agar content, in the red algae, Gracilaria crassa and G. cortica, does not fluctuate much and was found to be 15.8% and 17.7% respectively.

Since the Eritrean seaweed resources are still untouched, calls on an intensive study and wise utilization of such resources should be put into focus and consid- eration. It could be recommended that there is a need for a general biomass study of seaweed resources to determine the maximum sustainable yield and also to study the possible means of artificial propagation, processing methods in relation to seasonality. Such studies would synchronize with other ongoing ef- forts, on neighboring countries, to unveil the Red Sea rich resources.

Acknowledgement

The authors acknowledge the Swedish International Science Program (ISP), Sweden for the research grant. Thanks are due to Prof. Lars Bohlin, Department of Pharmacognosy, University of Uppsala, for his informative help.

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References

Criddle, W.J. and Ellis, G.E. (1976) Spectral and Chemical Characterization of Organic Com- pounds. John Wiley & Sons, London, UK.

Dawes, C.J. (1981) Marine Botany. John Wiley and Sons, Inc., New York.

Dawes, C.J. (1987) The biology of commercially important marine algae. The Development of Aquaculture and Fisheries Sciences, 16: 155, 190.

Durairatnam, M., Medeires, T.M.P. and Sena, A.N. (1990) Studies on yield and gel strength of agar from Gracilaria domingensis following the addition of calcium. Hydrobiologia 204/

205, 551-553.

El-Naggar, M.E.E. (1994) Effect of different environmental factors on the major chemical con- stituents of some marine algea. J. King Abdulaziz Univ., Mar. Sci., 5: 91-105.

Lapointe, B.E. and Tenore, K.R. (1981) Experimental outdoor studies with Ulva faciata- interaction of light and nitrogen on nutrient uptake. J. Exp. Mar., Bil. Ecol., 53: 135-152.

McQuaid, C.D. and Brach, G.M. (1984) Influence of sea temperature, substratum and exposure on rocky intertidal communities: Analysis of faunal and floral biomass. Mar. Ecol. Prog.

Ser., 19: 145-150.

Othmex, K. (1954) Algin. Encyclopedia of Chemical Technologies. Interscience Publishers, pp. 343-353, New York.

Pickering, T.D., Gordon, M.E. and Tong, L.J. (1990) Seasonal growth, density, reproductive phonology and agar quality of Gracilaria sordida at Mokomotko inlet, New Zealand. Hy- drobiologia, 204/205, 253-262.

Round, F.E. (1973) The Biology of Algae. Edward Arnold (Publishers) Ltd., London.

Saddington, A.W. (1969) Alginates in kelp. The Encyclopedia of Marine Resources. Van Nas- trand Reinhold Company. Canada, 19-22.

Sharma, O.P. (1986) Textbook of Algae. Tata Publishing Company Ltd., New Delhi, India.

Tresslen, R.L. and Lemon, J.Mc.W. (1951) Marine Products of Commerce. Reinhold Publ. Co., New York.

Whistler, R.L. (1959) Industrial Gums. Academic Press, New York.

Yarish, C. and Wawukoya, G. (1990) Seaweeds of potential economic importance in Kenya. Hy- drobiologica, 204/205, 339-346.

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Determination of the Biomass and Phycocolloid Contentsof some Marine Algae from Eritrea