2. LITERATURE REVIEW

Transcription

1 2. LITERATURE REVIEW 2.1. General remarks of seaturtle Overall, there are seven living species of seaturtles distributed worldwide (Marquez-M, 1990). They are Green turtle (Chelonia mydas), Hawksbill turtle (Eretmochelys imbricata), Leatherback turtle (Dermochelys coriacea), Loggerhead turtle (Caretta caretta), Olive ridley (Lepidochelys olivacea), Kemp s ridley turtle (Lepidochelys kempii) and Flatback turtle (Natator depressa). The latter two species are the only species which are not exist in Indonesia (Nuitja, 1992 and Dermawan and Adnyana, 2003). Green turtle (C. mydas) is the most common species in Indonesia (Dermawan and Adnyana, 2003). Observed species in this research will be Green turtle (C. mydas) (Figure 1). Seaturtles are widely spread from tropical to subtropical areas. They have been known as long migrating animals which are capable of migrating as far as hundreds kilometer (Bustard, 1972; Rebel, 1974; Marquez-M, 1990). However, their existence is threatened as the population is declining drastically over the last decades. The Convention on International Trade in Endangered Species of Flora and Fauna (CITES) lists all seaturtles on Appendix 1. The World Conservation Union (IUCN) lists the green, loggerhead, and ridley as Endangered, the leatherback, kemp s ridley and hawksbill are listed as Critically Endangered and the flatback is listed as data deficient, means there is insufficient data for determining its satus (PERSGA/GEF, 2004). Figure 1 Green turtle (Chelonia mydas)

2 Biological aspects Species identification Standard species identification key is based on carapace scutes, head scale and coloration pattern of the body (Figure 2). Green turtle (C. mydas) has five central scutes, four pairs of lateral scutes, and 12 pairs marginal scutes on its carapace. The head scales consist of one pair of prefrontal scales. On the upper side, the general appearance varies from pale to very dark from combination of yellow, brown and greenish tones. In juvenile, there is a clear narrow and yellowish margin at the head and upper side flippers scales (Marquez-M, 1990). Classification of Green turtle (C. mydas) based on Linnaeus (1758): Kingdom : Animalia Sub Kingdom : Metazoa Phylum : Chordata Sub Phylum : Vertebrata Super Class : Tetrapoda Class : Reptilia Sub Class : Anapsida Ordo :Testudinata Sub Ordo : Cryptodira Family : Cheloniidae Genus : Chelonia Species : Chelonia mydas (Linnaeus, 1758)

3 5 pf pf LS LS CS Figure 2 Green turtle (C. mydas) identification key (PERSGA/GEF, 2004). pf: prefrontal, CS: Central Scutes; LS: Lateral Scutes and MS: Marginal Scutes. MS Body size The size of turtles is principally related to the carapace length, which considered a reliable measure of overall size (Marquez-M, 1990). There are two standard methods to measure size such as Straight Carapace Length-Width (SCLW) and Curve Carapace Length-Width (CCLW) (Marquez-M, 1990; PERSGA/GEF, 2004) see Figure 3. Figure 3 Morphometric measurement of seaturtle carapace. Using Straight Carapace Length and Width (above) and Curved Carapace Length and Width (below)

4 6 Most of body size measurements for adult turtle come from the nesting females because they are more accessible than males. Marquez-M (1990) suggested that mean size of nesting female and hatchling shows wide variation from place to place. A size of cm CCL was recorded from the Comoro Islands and 81.2 cm SCL recorded from Guyana (Marquez-M, 1990). Green turtle body weight can be range from 89.8 kg to as heavy as 186 kg. Marquez-M (1990) also noted that green turtle (C. mydas) hatchling s size ranges from mm and body weight ranges from 18.4 to 35 g Habitat Nesting habitat There is more understanding about the ecology of nesting habitat because of its accessibility. But the fact is, seaturtle spend most of their life at sea (Bjorndal, 1999). Nesting habitat takes place at beach. Different species have their own preferences. Green turtle prefers small cove to large beaches (Pritchard and Mortimer, 1999) which usually are dominated by Sea Pandanus vegetation (Nuitja, 1992). In general, nesting habitat of green turtle (C. mydas) is consist of three different materials, coral sand is predominant, which sometime mix with roots of beach vegetation and shells fragments (Nuitja and Uchida, 1983). Sand grain size composition is related to accessibility for seaturtle to dig eggs cavity. Green turtle (C. mydas) was responsive to medium grained size sand (Nuitja and Uchida, 1983). Incubation period of eggs is related to temperature and humidity (Marquez- M, 1990). Warm weather usually results to short period of incubation while cool weather will make the incubation period to be longer. In general, green turtle eggs incubation period extends from 48 to 70 days. Incubation period of green turtle eggs at Pangumbahan beach extend from 52 to 71 days (Anwari, 1986). The latter data obtained from eggs which incubated at natural nest (not relocated). Ewert (1979) suggested that the suitable sand temperature for embryo development ranged between 25 C and 32 C Near shore habitat Sea turtles spend most of their lives at sea (Diez and Ottenwalder, 1999). They spend more than 90% of their lifetime there (Bjorndal, 1999). Foraging and

5 7 mating are located at sea. Different species has its own preference of foraging habitat (Bustard, 1972; Rebel, 1974; Marquez-M, 1990) while mating ground usually takes place near shore (Miller, 1997). Foraging habitat of green turtle is in seagrass beds. However, pelagic habitat for early stage turtles (juvenile) remains unclear. High priority must be given to the early pelagic stage that occurs in most sea turtle species. There is still less knowledge about the ecology of seaturtle s pelagic habitat, including green turtle Feeding Habit Green turtle is an herbivorous species, however, in early ages, they are carnivorous. (Bustard, 1972; Rebel, 1974 and Marquez-M, 1990). Marquez-M (1990) stated that the juvenile s diet consist of small molluscs, sea urchins, sea squirts and crustacean whereas most of the adult s diet is seagrass leaves. Stomach content investigation also showed that green turtle feed on seaweed (Rebel, 1974; Bjorndal, 1980; Marquez-M, 1990 and Lopez-Mendilaharsu et al., 2006). They feed during daytime at shallow waters. Specific genera of the feeding type are listed below (Table 1). Table 1 Green turtle diet Genera Seagrass: Zostera, Cymodocea, Thalassia and Halophila Source Rebel (1974) Seagrass: Thalassia testudinium Bjorndal (1980) Seagrass: Zostera, Cymodocea, Thalassia, Syringodium, Diplantera, Halodule, and Halophila Seaweed: Gelidium, Gracillaria, Gracilliaropsis, Hypnea, Caulerpa, Vidalia, Bryothamnion, Cryptonema, Agardiella Marquez-M (1990) Marquez-M (1990) Seaweed: Codium amplivesiculatum, Gracilaria textorii, Ulva lactuca, Chondria nidifica, Gracilaria pacifica, Caulerpa sertularoides, Aspagaropsis taxiformis, Amphiroa sp., Laurencia pacifica Lopez-Mendilaharsu et al., (2006)

6 Temperature role Sea turtles are poikilotherm organisms, which body activity is dependent upon environment temperature (Rebel, 1947). Hence, it holds an important role for each stage of sea turtle lives. They spend almost their life at sea, but the adult female will come back to their natal beach to lay eggs (Miller, 1997). Incubation temperature influence eggs incubation period and hatchlings sex determination (Miller, 1997; Broderick et al., 2000). Although incubation temperature range may differ by species and region, in general, higher temperature will result in a shorter eggs incubation period (Marquez M, 1990). Higher temperature will produce female individual whereas lower temperature will produce male (Limpus, 1985; Miller, 1997). High temperature plays important role in early gonadal differentiation (Barlian, 1987). Our knowledge of pelagic habitat temperature of green turtle is still limited, no data yet for hatchlings.