Seasonal change of ingredient on the seagrass in Okinawa Japan

Transcription

1 Seasonal change of ingredient on the seagrass in Okinawa Japan Takuji Hirayama a, Go Ogura a, Hiroshi Mukai b and Noriyuki Otaishi c a University of the Ryukyus, 1-Senbaru, Nishihara-machi, Okinawa-prf, Japan, Nishihara, Japan b Association for protection of Marine Communities, 23-1 Higashi Hirai-machi, Kyoto, Japan c The Hokkaido University Museum, 10-8 Sapporo city, Hokkaido, Japan donald@agr.u-ryukyu.ac.jp In our investigation the seasonal change of covering percentage, growth rate and ingredient of seagrass was taken in the Kayo bay, Okinawa Island, southwest Japan. The species composition, covering percentage and ingredient of seagrass were examined six times (at intervals of two months) during the May (2003) to March (2004). The fixed 5 points regions of seagrass bed were examined every time using GPS data. The covering percentage was measured following the percent cover standard in 3 quadrats (50cm X 50cm each). These quadrats were launched at random in the point area, from 1 m high. And measuring the covering percentage was a value at the average of each measured value by three persons. The classification of species composition of seagrass was investigated by sampling. Samplings of seagrass were taken at low tide the ebb; the plants with rhizomes and roots were collected by dive. Sampling plants were immediately decided the species composition at boat or on land. The growth rate was measured by number of shoot and number of apex. Ingredient item was fiber content and protein content. In this investigation, the target species of seagrass was as follows (7 species); Halophila ovalis, Thalassia hemprichii, Cymodocea serrulata, Cymodocea rotundata, Syringodium isoetifolium, Halodule uninervis and Halodule pinifolia. The covering percentage of seagrass was highest at May, and then slowly decreased after July with the decline of sea water temperature. Seasonal change of number of shoot was observed different between species. Fiber content and protein content was observed different at season and species. Keywords; Dugong, Okinawa Island, Seagrass Introduction Tropical seagrass is known as a feeding ground of turtles, dugong and other plant-eating animals. Moreover, these seagrass ground are known as living space of fry, cucumber and other crustacean (Kikuchi and Peres, 1977; McRoy and McMillan, 1977). Therefore, chemical composition of the seagrass is most important for animal s nutrient and maintenance of ocean ecological system. Seagrass is a plant that produces seeds. There is 2 family, 12 genus and 55 species in the word seagrass (Larkum, 1989). Two family, 8 genus and 16 species of seagrass among them are growing

2 in southern west Japan (Kuo et al, 1995). And 2 family, 7 genus and 10 species of seagrass among them are growing in Ryukyu Islands (Amami Island to Okinawa Islands) (Kuo et al, 1995, 2006). Seagrass distributions in Okinawa Islands, Ishigaki Island, and Iriomote Island are particulars examined (Miki, 1932, 1933 and 1934; Hartog, 1970; Walker, 1954; Tsuda and Kamura, 1990; Kuo et al, 1995). The nutrient content of seagrass was different the ground plants (Aketa et al, 2001). And moreover, the growing field was affected the chemical composition of seagrass (Aragones et al, 1996). Thus it is suggested that chemical composition and amount is effected by sea water condition as follows; sea water temperature, depth, tide, illumination and solute nutriment in sea water. Therefore it thought that chemical composition of seagrass is influenced by seasonal change. The aim of this study was to investigate the seasonal change of nutrient content on the tropical seagrass. Materials and Methods Samples as in our study were taken in the kayo-bay, Okinawa Island, southwest Japan (Figure 1). Okinawa Island belong the subtropical insular climate. The temperature of sea water is about 20 at the lowest in winter season and about 34 in summer season. There are a lot of coves, and this Island is shallow to a considerable distance from the shore at most coasts. This Island is caught in the Kuroshio Current. The species composition, covering percentage and ingredient of seagrass were examined six times (at intervals of two months) during the May (2003) to March (2004). The fixed 5 points regions of seagrass bed were examined every time using GPS data. The covering percentage was measured

3 following the percent cover standard in 3 quadrats (50cm X 50cm each). These quadrats were launched at random in the point area, from 1 m high. And measuring the covering percentage was a value at the average of each measured value by three persons. The classification of species composition of seagrass was investigated by sampling. Samplings of seagrass were taken at low tide the ebb; the plants with rhizomes and roots were collected by dive. Sampling plants were immediately decided the species composition at boat or on land. The growth rate was measured by number of shoot and number of apex. Ingredient item was fiber content and protein content. Results and Discussion In this investigation, the target species of seagrass was as follows (7 species); Halophila ovalis, Thalassia hemprichii, Cymodocea serrulata, Cymodocea rotundata, Syringodium isoetifolium, Halodule uninervis and Halodule pinifolia. The covering percentage of seagrass and sea water temperature was shown figure 2. The covering percentage of seagrass was highest at May, and then slowly decreased after July with the decline of sea water temperature. Seasonal change of number of shoot was observed different between species. This result was generally changing phenomenon as sea water temperature and seagrass bed extent because year of this investigation was not occur the special natural phenomenon in Okinawa Japan. Fiber content of leaf and stem at each seagrass was shown figure 2. Fiber content was observed different at season and species. In Halodule uninervis, changing width of fiber content in season was narrow and flat. But in the Halodule pinifolia, fiber content was increased May to Nov. Other seagrass was decreased May to Nov in especially at Halophila ovalis. And these tendencies were observed in part of root. These results were suggested that period or season of growth activity is

4 different with seagrass species. In protein content of root, leaf and stem, all of seagrass species was similar changing with season. Therefore it will be another function in the body with fiber and protein. We were reported that chemical composition of seagrass was different in growth field with species. We have to consider at detail in these changing nutrient composition. References Aketa K. A. Kawamura (2001) Digestive functions in sirenians (Review). The Bulletin of the Faculty of Bioresources, Mie University, 27: Den Hartog C (1970) The seagrasses of the world. North Holland Pub., Amsterdam, 275pp. Go O, Hirayama T. Sudo K. Otaishi N. Mukai H. Kawashima Y (2005) Investigation of the Northern Limit of Dugong Habitat in Tokara Islands and Amamiohshima in the Ryukyu archipelago, Japan. Wildlife Conservation Japan. 9(2): Kikuchi T. Peres J (1977) Consumer ecology of seagrass beds. In: Seagrass Ecosystems; Eds. C. P. McRoy and C. Kuo J, Z. Kanamoto T. Toma, M. Nishihira (1995) Occurrence of Halophila decipiens Ostenfeld (Hydrocharitaceae) in Okinawa Island, Japan. Aquatic Bot., 51: Larkum AW. D. C. den Hartog (1989) Evolution and biogeography of seagrass. Biology of Seagrass, edited by A. W. D. Larkum, A. J. McCombo and S. A. Shepard, Elsevier, McRoy C. McMillan C (1977) Production ecology and physiology of seagrass. In: Seagrass Ecosystems; eds. C. P. McRoy and C. Helfferich, pp Marcel Dekker, Inc., New York and Basel.

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