The Larval Development and Juvenile Growth of the Silver Mouth Turban, Turbo Argyrostomus
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The Larval Development and Juvenile Growth of the Silver Mouth Turban, Turbo argyrostomus. Item Type Thesis/Dissertation Authors Kimani, Edward Ndirui Publisher University of the Ryukyus, Japan Download date 28/09/2021 18:53:19 Link to Item http://hdl.handle.net/1834/7409 The Larval Development and Juvenile Growth of the Silver Mouth Turban, Turbo argyrostomus A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF THE RYUKYUS IN PARTIAL FULFILLMENT FOR THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MARINE SCIENCES August 1996 by Edward Ndirui Kimani Adviser: Masashi Yamaguchi ------ • • ":' We certifY that we have read this thesis and found it satisfactory in scope and • content for the degree of Master of Science in Marine Sciences • • Thesis committee •I I J • J Masashi Y • j ] 52;2~¥H ~ - Shigemitsu Shokita ....J ., · I :..J ~i~~ ~ l I Tetsuo Yoshino ..J J ] ] ] ] ~ ] 11 ] l .] .J .J Dedication .J I dedicate this report to my dear wi fe Sarah, and son Kirnani, for their .J patience and understanding during this work. J ] J ] ] ] } ] ] ] ] ] ] J 111 ] J ~ J ] Abstract ] The si lver mouth turban, Turbo argyrostomus L. 1758, is an ] archeogastropod widely distributed throughout the Indo-Pacific regIon. It is an important marine resource, harvested for food, ] marIne souvenirs and ornamental items. Mass seed production J techniques for Turbo marmoratus and T. argyrostomus, based on the techniques developed for Trochus niloticus in Palau, are J currently being developed in the Okinawa prefecture, Japan, to J replenish the declining populations of these commercial turbinids. Here, I report on the larval development, metamorphosis and the J effect of diet on growth and shell characters of silver mouth turban ] juveniles, raised in the laboratory. ] I studied the larval developlnent, metamorphosis and juvenile ] growth of T. argyrostomus between August 1995 and July 1996. ] Adults collected from Komesu, southern Okinawa Island, were induced to spawn by packing and UV sterilised seawater treatment ] on 9 August 1995. The green eggs (180-190 Jlm in diameter) ] hatched within 18 hours, underwent torsion a few hours later and metamorphosed in 3-4 days after fertilization in the presence of ] metamorphosis inducing cues. Forty-eight percent of 200 ] competent veligers spontaneously metamorphosed in the absence of metamorphosis inducing cues between 7 days and 21 days after ] J J l fertilization without feeding. The protoconch, 170-185 J.!rn diameter, was colorless and globose in shape with irregular articulations. The juveniles grew to a mean shell length of 3.7 mm in 5 months (mean growth rate of 0.7 mm per month) feeding on microalgae growing on coral rubble and the sides of the aquaria, and grew to 11.5 mm in 9 months (mean growth rate of2.7 mm per .~ " month) feeding on macroalgae. Small juveniles of mean shell length 3.9 mm, reared on a small fleshy red algae, Gelidiella acerosa, grew approximately 2 times faster than those reared on the green algae, VIva purtusa, over 18 ,.; weeks. The combined diet of these two algae species gave higher growth rates than either algae individually, but did not improve ,..J growth significantly in large juveniles with an initial shell length of i J 5.8 mIn. Percentage survival after 18 weeks was higher for ] juveniles reared on red algae (92.2 oj(,) compared to green algae (81.] 0/0). The shell color of the snails depended on the algal diet. J The shells ofjuveniles collected from the reef were heavier, for the ] same size, than those reared in the laboratory. The juveniles reared on mixed algae growing on coral rubble, collected from the reef, J and the green algae had higher mean shell weights than snails 'I J reared on red algae alone or on a combination of green and red algae. ] ] 2 ] l J ] Introduction ] ] Large turbinids are conspicuous members of the shallow coral reef habitats where they graze on detritus film and algae. They are J valued ornamental and food items in the Indo-Pacific region. The ] shells of turbinids are used in 'Raden', a traditional Japanese craftwork dating back to the 600 A. D. Consequently the ] population of the green snail, Turbo marmoratus, the largest (25 ] cm diameter) and most valued turbinid, has been depleted in the Ryukyu Islands (Yamaguchi 1993). In an attempt to restore the ] population of the commercial turbinids, mass seedling production ] techniques are being developed in the Ryukyu Islands (Murakoshi ] et al. 1993) based on the techniques developed for raising juveniles i] of the top shell, Trochus niloticus (Heslinga 1980). The silver mouth turban, Turbo argyrostomus is widely distributed between j - the intertidal zone and 3 m depth throughout the Indo-Pacific I ] region. Although it is a target species for the reef seeding program I ] in the Ryukyu Islands, little is known of the larval development and juvenile growth of T argyrostomus. I ] ] I Larval development and reproductive biology are central to understanding the biogeography, ecology and evolution of fossil I ] and present marine benthic communities. Gene flow between I ] 3 I ] ] I 1 J '] shallow water populations by means of pelagic larvae is dependent OJ on the length of larval life and the number of larvae produced by OJ the parent ° population (Scheltema ]971). These factors also determine the possibilities of successful colonization and re OJ colonization of depleted habitats, and therefore the geographic ] distribution and evolution of shallow water species. The larval development of T. marmoratus has been described by Murakoshi et 'J al. (1993). Grange (1976) reared the larvae of Lunella smaragda, a I) small turbinid, up to the veliger stage. Experimental larval and I) juvenile rearing of T. argyrostomus have been conducted by the Okinawa Prefectural Sea Farming Center (Murakoshi and J Yamamoto 1991) but details of larval and juvenile growth are J lacking. J The gastropod larval life is divided into two parts: the pre ] competent period during which the larvae cannot be induced to metamorphose to the sedentary form and the competent period J when metamorphosis can be induced by providing some chemical ] and/or physical cues of the adult environment (Hadfield 1977, Crisp 1974, Scheltema 1974). The dispersal potential of larvae is ] therefore a function of the rate of development to metamorphic ] competence and the maxinlum length of time that metamorphosis can be delayed in absence of a suitable substrate. Temperature and ] ] 4 ] 1 .J I J I the related rates of growth and differentiation are principle factors J in delaying metamorphosis of gastropod larvae (e.g. Pechenik I J 1984, Lima and Pechenik 1985). The potential for delaying I metamorphosis, and therefore the fate of the larvae of J lecithotrophic species, depends on temperature and is limited by ] the amount of yolk in the eggs. Despite widespread occurrence and obvious ecological importance of the ability of larvae to delay ] metamorphosis, delaying capabilities are so far unknown for most ] specIes. ] The mode of larval development in prosobranch gastropods is ] related to the morphology and ornamentation of the larval shell ] (Thorson 1950). Species with plantotrophic larvae have a small protoconch I and a clearly demarcated protoconch II reflecting J planktonic existence. Species with non-planktotrophic larvae have ] large eggs and a large protoconch I (larval shell) with little or no protoconch II reflecting the short time, if any, spent in the ] plankton. The 'Apex Theory' developed by Thorson (1950) and · ] later expanded by Shuto (1974) is based on the observation that I most shells with narrow, high protoconchs and pointed apices are I ] those of species with planktotrophic development, whereas those I ] with globose, low protoconchs and blunt apices are those of species I .. with non-planktotrophic development. Shuto (1974) observed that ] I 5 I ] I ] I 1 J ] protoconchs with distinct reticulation and close axial sculpture '] generally had planktotrophic larvae. To infer larval development ] accurately from shell morphology, the protoconchs of a given I • species should be compared with those of congenerics or 'J confamilial species of known larval development. Few records of , ] larval shell morphology of gastropods exist to pennit such comparIsons. ] ] Mass seed production techniques of the top shell, Trochus niloticus, were developed in Palau, Caroline Islands (Heslinga ] 1980, Heslinga and Hillmann 1981). Juveniles of the green snail ] have been raised to seed coral reefs in the Okinawa prefecture ] based on the spawning and juvenile rearing techniques developed for the top shell (Murakoshi et at. 1993). The sessile diatoms, -J Navicula ramosissima, grown on corrugated PVC plates are used J to feed the juveniles for the first 3 to 4 lTIonths. Fresh green algae, VIva pertusa, is then used until release of the 1 to 1.5 years old ] juveniles on the reefs. Diet determines growth rate (Uki et at. 1986, ] Murakoshi et al. 1993) and the shell coloration of gastropods (Ino 1949, Ino 1952, Olsen 1968, Murakoshi et al. 1993). Red, brown ] and green algae were found to progressively attract young top ] shell, Batillus cornutus (Fuj ii et al. 1988). Although species of Enteromolpha, Monostroma and soft varieties of VIva are taken ] ] 6 ] 1 J 1 by T marmora/us juveniles, red algae with soft tissues such as ] Hypnea, Gelidium, Graci/aria, Eucheuma, which are carrangeenan ] or agar producing genera, are preferred (Yamaguchi 1993). Comparative studies on diet preference and growth of juveniles J have economic relevance in reef seeding programs. ] Despite the recent advances in larval and juvenile rearing of coral J reef gastropods, outgrowing success on the reefs has been very J liJnited. The main problem is poor survival after release on the reef. Predation and dispersion by strong waves were the main j causes of poor survival of T marmora/us juveniles (Nakamura • J 1992). Many factors may lead to high predation rates of released gastropod juveniles.