Cultivation Characteristics and Biological Responses of Agarophytic Seaweed, Gracilaria fisheri (Rhodophyta), in Southern Thailand.

Abstract

The study about cultivation characteristics and biological responses of Gracilaria fisheri aimed to contribute data for the future cultivation. The study was done in two parts: the first was investigation on cultivation environments and the second was investigation on optimal conditions for seedling propagation. The first part was conducted at three provinces, Pattani, Songkhla and Surat Thani. The samples including water and sediment were collected from four cultivating ponds of each province for the analysis. The parameters of light intensity, salinity, pH, water depth and transparency were directly measured at the ponds. Agar yield, moisture content, contaminants of the seaweed and pigment constituents including carotenoids, chlorophylls, r-phycoerythrin, mineral and heavy metal contents were analyzed in the laboratory. The amounts of Ca, Mg, K, Cu, Mn, Zn, Fe, Ni, Cr, Cd and Pb in seaweed, water and sediment were determined. The seaweed in Songkhla provided the significant higher (p<0.05) yield than other provinces with 58 ton FW ha-1 year-1. However, the agar yield from Songkhla province showed lower than those in the other two provinces. There was no significant difference (p>0.05) on color and pigment content of the seaweed in three provinces. The major elements: Ca, Mg, K and Na in the water were much higher than those in the sediment and seaweed whereas trace elements and heavy metals in the sediment and seaweed were higher than those in the water. The percentage of sand and silt of soil sediment, water depth and transparency of water showed the positive relation to Cu amount in the seaweed. The amount of Cu and Cr in the sediment and water hardness related absolutely to the amount of Mn in the seaweed. The amount of Fe in the seaweed showed positive relation with Cu and Mn in the sediment. The major elements in seaweed showed in order of Mg>K>Ca>Na with the amounts of 9.52, 12.13, 9.64 and 2.96 mg g-1 DW, respectively and trace elements in the seaweed showed in the order of Mn>Fe>Zn>Cu with the amounts of. 0.62, 0.55, 0.03 and 0.02 mg g-1 DW, respectively. The amounts of K and Na in the seaweed at Pattani showed significantly higher (p<0.05) than those at the other two provinces. The sequence of Cr, Pb and Cd in the seaweed showed the same pattern of Pb>Cr>Cd in the water and sediment. Heavy metal in the seaweed of Ni>Pb>Cr>Cd showed slightly different sequence with Pb>Ni>Cr>Cd in water. Besides, the amount of Pb in G. fisheri was found as high as 11.53 mg g-1 DW; however, it fluctuated among the provinces and ponds. In this study, it was found that the amount of Cd in the seaweed relates inversely to salinity in the water. Cd concentration in the sediment ranged from 1.0 to 1.2 µg L-1 DW. The seaweed yield inversely related to K, Na, Zn, phosphate-phosphorus and nitrate-nitrogen in the water. Agar yield of the seaweed showed positive relation with concentration of Mn in the water. The chlorophyll a related positively with Mg in the water. For major elements, the concentration of K and Na in the seaweed showed the positive relation with the concentration of Mg, Zn, phosphate-phosphorus and nitrate-nitrogen in the water. Besides, Mn, Ni, Fe, organic carbon, organic matter, percentage of sand and silt in the sediment provided positive relation to the amount of K in the seaweed. For optimal conditions of seedling propagation, the study was done under indoor and outdoor conditions. In indoor condition, seedling of G. fisheri was conducted in four selected influential factors: fragment length, salinity, part of thallus and propagule density. Each experiment was subsequently done with three replications and used the best result in the next study. The experiment on fragment length was conducted from 1 to 5 cm of sub-apical segments. The study on different salinity levels was done in the range of 15-35 ppt with 5 ppt of the interval. Different zones of tissues were selected apical, sub-apical and basal fragments for the next study. The study on density was conducted from 1 to 8 g L-1 with doubling of the prior and 6 g L-1. Each experiment was done for 40 days, under 25 µmol m-2 s-1 of light intensity and 12L:12D of photoperiod at temperature of 25±2ºC. The result showed that optimal conditions for G. fisheri tissues were at 2 cm of segment length under 20 ppt salinity and part of tissue from apical zone and 1 g L-1 density. Under optimal condition, the relative growth rate of G. fisheri tissues was 31.0 % day-1 and the final biomass was increased 12.4 times comparing to the initial biomass. New finding on physical performance of G. fisheri tissue was found that only apical tissues grew with apicobasal polarity. The number and length of branch were 7 branches per cm and 0.1 cm, respectively. Gracilaria fisheri sporeling and tissue propagation was conducted to investigate the optimal shading color for the cultivation. The study was conducted with two experiments: 1) indoor experiment under different shading colors: white, green, blue and red of tissue and sporeling and 2) outdoor experiment on tissue culture under different Saran colors of hoop house: green, blue and black and PVC window screen in white color. For indoor experiment, fluorescent lights were used and wrapped by different PVC color sheets. All treatments were set in the average light intensity of 20 µmol m-2 s-1. Sub-apical cleaned tissues of 2 cm were stocked and eight-week age sporelings were carefully cleaned and cultured at 0.3 g L-1 in 3 L spherical bottles. Other conditions were maintained under 12L:12D of photoperiod, 25±2ºC temperature and 20 ppt salinity for indoor experiments for 40 days Outdoor experiment was conducted in four plastic tanks of 0.8x0.5x0.3 m3 under different colors of hoop houses with 2 m high and the maximum light intensity of 110 µmol m-2 s-1. The excised tissues which were chopped into 2 cm length and then stocked at the density of 250 g∙m2 under conditions of 26.0±2.5ºC temperature, 20 ppt salinity. The experiment was conducted for 8 weeks with 4 replications. The highest growth rate of G. fisheri tissues and spores were found under red light with 1.4 and 2.8 % day-1, respectively. There was no significant difference (p>0.05) on pigment content of tissues indoor; whereas it was found that chlorophyll a concentration of the sporelings under green light was significant higher (p<0.05) with 348 µg g-1 fresh weight. However, under green Saran house, tissues showed the highest growth rate 2.9 % day-1with the relative high pigment content of 32.6±1.1 µg g-1 FW chlorophyll and 25.4±4.8 µg g-1 FW carotenoids. Besides, the study found that G. fisheri cultivation was less impacted by epiphytes under back Saran house with 15%. The yield of G. fisheri depended on nutrient in water while heavy metal accumulation in seaweed mainly depends on water characteristics. Seedling from tissue of G. fisheri expressed as a stenohaline species that was rather affected by salinity than the other factors. Light shading strongly influenced on growth of G. fisheri sporelings and tissues but little affected on pigment constituents. Red light is more effective light for the growth of G. fisheri tissues and spores in laboratory condition. The study showed the feasible and successful cultivation for G. fisheri sporelings and tissues.