Showing papers on "Turbinaria ornata published in 2002"

Food selectivity of Tripneustes gratilla (L.) (Echinodermata: Echinoidea) in oligotrophic and nutrient-enriched coral reefs at La Réunion (Indian Ocean)

Abstract: Herbivorous echinoids can control algal populations and structure their composition in coral reef ecosystems. Food selectivity might play an important role in this structuration. The gut contents of a total number of 40 individuals of the edible sea urchin Tripneustes gratilla were analysed at two coral reefs of La Reunion. The sites differed in eutrophication level, one being oligotrophic, the other being nutrient enriched. Available algal food was quantified in each site and food selectivity of T gratilla in the field was determined by the use of an electivity index. The diet of T. gratilla relied mainly on algae. However, a significant proportion of detritus was found in the digestive tracts of individuals at both sites. A strong food selectivity of T gratilla was found at both sites. The tough leathery macroalga, Turbinaria ornata, was the most selected species at both sites. Calcareous algae were strongly avoided. Algal species were generally either highly selected, or highly avoided, and rarely consumed in proportion to their availability in the field. Significant differences in food selectivity were found between sites, some species being selected/ avoided at one site but not at the other. These differences might be linked to the nutrient contents of algae at both sites and/or related to different levels of herbivory between sites.

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

Abstract: Specimens of five marine species of the brown (Cystoseira myrica, Sargassum torvum and Turbinaria ornata) and red (Gracilaria 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 production 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 consisting of D-mannuronic acid and L-guluronic acid residues linked by 1-4 positions. 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 & 19 J. KAU: Mar. Sci., vol. 11, pp. 19-25 (1420 A.H. / 2000 A.D ) *Present address: Department of Chemistry, King Faisal University, P.O. Box 1759, Hofuf 31982, Saudi Arabia. E-mail: yelhassan@kfu.edu.sa. Y.M.H. Younis et al. 20 Wawukoya, 1990). However, seaweeds of Eritrea have, to a large extent, escaped 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 Massawa, 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 affect algal growth. Samples of Sargassum torvum, Cystoseira myrica, Turbinaria ornata (Phaeophyta), 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 added 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. Determination of the Biomass and Phycocolloid