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SPC/Inshore Fish. Res./WP.ll 29 February 1988 ORIGINAL : ENGLISH SOUTH PACIFIC COMMISSION WORKSHOP ON PACIFIC IHSHORE FISHERY RESOURCES (Noumea, New Caledonia, 14 - 25 March 1988) BIOLOGY OF THE GREEK SHAIL (TURBO MARMORATUS) AMD ITS RESOURCE MANAGEMENT Document presented by Dr Nasachi Yamaguchi Professor of Marine Sciences University of the Ryukyus Okinawa, Japan INTRODUCTION The green snail is the largest species of its family Turbinidae, growing over 20 cm in diameter and 2 kg in weight. Its nacreous shell is highly prized for inlay material of lacquerware and jewellery, etc. This snail has been exploited by many tropical nations in the Pacific, such as Vanuatu, Solomons, and Papua New Guinea, as well as by the Southeast Asian countries, such as Indonesia, Malaysia and Philippines. Owing to the warm Kuroshio current, the green snail populations occur along the coral-reefs in the Ryukyus, up to ca. 29 degrees North latitude. This resource has been exploited extensively for its meat and shell throughout the Ryukyus. In recent years, it became evident that stocks of green snail had diminished from the most part of the Ryukyus, because of unchecked over- exploitation and illegal harvesting by divers equipped with air-breathing apparatus and powerful boats. There were numbers of diver-fishermen who harvested sedentary resources, including green snail, using goggles only, at each local villages. They have retired mostly without successors because of decimated stocks which can no longer support such fishermen. In order to restore and re-establish the resource itself and to develop ideas of its management in the mind of fishermen, it would be meaningful to implement marine ranching programs, by producing large numbers of juvenile green snails that would be released on the reefs by fishermen for them to harvest after careful management. 226/88 SPC/Inshore Fish. Res./WP.ll Page 2 RESOURCE Btomgy (A) Ta*PPOwy The green snail Turbo.marmoratus L. belongs to family Turbinidae in the order Archaegastropoda, subclass Prosobranchia of class Gastropoda. Other important members of this family in the tropical Pacific are Turbo setosus and T, argvrostomus. (B) gepKrapfrj-cal flj-smbution As already noted, the green snail is commercially exploited in the Indo- Malayan sub-region of the Indo-West Pacific. It may be rare or does not occur in New Caledonia and the Great Barrier Reef because it is not reported as being exploited in these areas. Cernohorsky (1972) stated that Turbo.marmoratus was moderately uncommon and that it ranged from the Fiji Islands westward. It has not been reported from Micronesian islands (Demond, 1957). (C) Habitat Juvenile green snails smaller than ca. 3 cm shell diameter have not been found in the field. Reef gleaners collect larger juveniles and subadults from reef crest areas, within crevices made by burrowing sea urchins Eehjppmetra mathaei. at Tokunoshima in the northern Ryukyus (Honma, 1988). Adults are found along the seaward reef slopes down to 15 meters, usually well-hidden inside holes and crevices in the daylight hours. (D) Feeding preferences Adults and juveniles of the green snail graze on epibenthic microalgae from surfaces of limestone substrates. They also ingest macroalgae in aquaria. The animal can hold blades of soft algae between two halves of the frontal part of its foot, so that it may be able to pick up and eat algal fronds deposited on the bottom of an aquarium. The snail in general prefers green and red algae to brown ones. Among the greens, Enteromorpha, Monostroma and soft varieties of Ulva are readily consumed. However, those with harder textures and consistency, such as {Uva cipnglpib,ai;a, ?. reticulata, CladophQrppgjs and Pictyosphaeria are not taken. Perhaps the most favoured algal genus is Gelidium which encrusts over substrates as short turfs. As long as this genus is available, the green snail in aquariums would not go for other algae. Other favoured red algae are Gracilaria, Hypnea and Eucheuma, all of which are agar-producing genera as is Gelidium. Dasya and some other conspicuous but bitter-tasting species are not accepted as food. SPC/Inshore Fish. Res./WP.ll Page 3 The author tested several species of dried algae, available from grocery stores for human consumption. All browns (kelps, Bizjkia and Undaria) tested were not consumed. Dried Enteromorpha did not appear to stimulate the appetite of the snail. Only dried GracilarJa and Eucheuma were consumed, but only slowly by starved animals. It was possible to feed the green snail with blocks or films of agar jelly processed from commercial agar that originated from Gelidium, when fresh alagal food was not available. Manufacturing artificial food for juvenile production may be benefitted by this fact, because something in the agar appeared to stimulate feeding response of the snail in the aquarium. Reproductive biology Breeding season In the Ryukyu islands, where significant seasonal fluctuations in water temperatures and other environmental parameters exist, tropical animals tend to breed in summer months. Ripe specimens are found during much of the warmer period of the year. However, there appeared to be peak breeding activities of this snail in early and late summer when animals with spent gonads increased after a high level of ripeness in the population. It is not clear whether or not a single animal would breed repeatedly in one year. Size at sexual maturity Devambez (1961) estimated that the green snail might become sexually mature in the individuals larger than 15 cm diameter in the New Hebrides (now Vanuatu). The smallest snail having well developed female gonads was ca. 13 cm diameter at Tokunoshima in the Ryukyus. There may be individual variations in attaining mature sizes but there has not been a sufficient quantity of materials for determination of this aspect. It might be postulated that the adulthood of the green snail would be detected by the presence of a continuous rib formed on the upper whorl. This rib is a continuation of a series of intermittent knobs in the juvenile shell. Fecundity in relation to size This is still being studied on gonad specimens collected. SPC/Inshore Fish. Res./WP.ll Page 4 Spawning and its induction Sexes are separate in the green snail and gametes of both sexes are freely released in the water column. Eggs and sperm were ejaculated intermittently with contractions of the snail body into the shell, lasting for less than half an hour. Spawned eggs are slightly heavier than sea water, so that they settle on the bottom of a container if kept still. However, slight agitation would keep the eggs suspended and they are likely dispersed at the mercy of water movements in the sea. Spawning was induced twice in the green snail at Iheya Island, near Okinawa. A few dozens of adult snails were kept in a 3-ton stainless steel tank together with a few hundred Trocbus njloticus. Those snails were collected from the nearby reefs for a mark-and-recapture experiment to study their growth rates. The sea water in the tank had been aerated overnight and became fouled with accumulated feces and mucus, etc. Then, the fouled water was drained out and fresh sea water was poured in. This procedure worked accidentally in the green snail for the first time in June 1986 and it was repeated to induce spawning of the green snail and trochus shells in November 1986. The latter was successful for the two species at the same time. The same method was effective in induction of spawning in another turban T> argyrostpmus. (F) Early life, history and morphogenesis Fertilized eggs of the green snail developed into trochophores to hatch out in about 22 hours (21-23 C) in November and little longer than 12 hours (at 25 C) in June. During the first few days after hatching, trochophores and later veligers swarmed near the surface in containers. Pediveligers are formed on day 3 and the majority of larvae settled on day 4, in June. Larvae were allowed to settle on coral rubble in glass jars and then moved to a small glass aquarium equipped with a subsand re-circulating filter system. The early juveniles were too small for the naked eyes to observe, so that their well-being was not ascertained until they grew to large enough sizes in about one month. As for the second spawning in November, most larvae perished while they were being transported from Iheya Island to the laboratory in the University of the Ryukyus, because a typhoon approaching at that time disrupted the ferry boat schedule. SPC/Inshore Fish. Res./WP.ll Page 5 Juveniles were fed with epibenthic microalgae covering on coral rubble and other available substrates such as plastic plates submerged in the sea for several weeks, etc. Feeding substrates were renewed weekly. As they grew, the juveniles were transferred to a larger aquarium with subsand recirculating system. After about six months old, juveniles were given freshly algae such as small pieces of Qelidjum and MonoStroma etc. for food. During the winter months, juveniles stopped feeding when water temperature fell below 18 C in an aquarium which was kept in the laboratory without heating facilities. Shell structure of the juvenile green snail showed a series of stepwise transformations as it grew. Just after settling, the first whorl after the transparent protoconch was extended with only slight distention of aperture size, so that the juvenile appeared as a disc with series of knobs along the outer corners of the shell. The juvenile body retained the light green colour of the embryonic stages and its shell was opaque white. Then, the second whorl started to expand in the aperture diameter. Two series of dark brown blotches which were interspaced with knobs appeared in this.

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