FISHERIES SCIENCE 2001; 67: 596–605

Original Article

Radula development in abalone Haliotis discus hannai from larva to adult in relation to feeding transitions

Tomohiko KAWAMURA,*1a Hideki TAKAMI,1 Rodney D ROBERTS2 AND Yoh YAMASHITA1

1Tohoku National Fisheries Research Institute, Shiogama, Miyagi 985-0001, Japan and 2Cawthron Institute, Private Bag 2, Nelson, New Zealand

ABSTRACT: The radula morphology of Haliotis discus hannai was examined by scanning elec- tron microscope from the larval to the adult stage. The radula of competent larvae contained 11Ð13 transverse rows of teeth after 6Ð7 days at 20¡C. The number of rows increased to 25Ð30 during the first several days after settlement, but then remained approximately constant throughout the post- larval period, increasing again in abalone larger than 4 mm in shell length (SL). In post-larvae <~1 mm SL, only two pairs of lateral teeth (L1, L2) were present in the larval radula. An additional three pairs of lateral teeth (L3ÐL5) were added progressively as post-larvae grew from 0.9 mm to 1.9 mm SL. Marginal teeth were added steadily from one pair in larvae to 30Ð40 pairs at 3Ð4 mm SL, 70Ð80 pairs in 30Ð40 mm juveniles, and 70Ð90 pairs in 90Ð100 mm adults. The serrations on the working edges of the rachidian (R) and lateral teeth became less pronounced as the abalone grew. Nearly all serrations disappeared from the rachidian (R) and inner lateral teeth (L1, L2) by ~2 mm SL, and from the outer lateral teeth (L3ÐL5) by 20 mm SL. For abalone larger than 1.5 mm SL, the L3ÐL5 teeth became longer and more pointed, which increased the space between adjacent rows of teeth. Post-larvae < 1 mm SL had highly curved teeth with clearance angles of approximately or less than zero, whereas larger abalone had positive clearance angles. These radula developments appear to be related to transitions in feeding habits from microbial to macroalgal diets.

KEY WORDS: abalone, development, diet, feeding, larvae, postlarvae, radula.

INTRODUCTION diatom diets (sensu Kawamura et al.2 and grow more rapidly on efficiently digested diatom strains Feeding habits in the early life stages of abalone (the second transition). The final transition is at have been studied in detail in recent years1–8 and approximately 5–10 mm SL, from a diatom- three major transitions in feeding have been iden- dominated diet to a macroalgae-dominated diet. tified.9 The first is the transition from lecithotrophy The ingestion and digestion of diatoms appear to particle feeding around the time of metamor- to be affected by the action of the radula. The phosis. Benthic diatoms are a principal food for ability of post-larvae to ingest large diatom cells post-larval abalone after metamorphosis, and increases as post-larvae grow.7,8 Physical rupturing post-larvae smaller than approximately 0.8 mm of diatom cells, which directly affects digestibility, shell length (SL) grow at similar rates regardless of frequently results from the action of the radula.2 diatom strain, provided they receive an adequate Radula morphology is also important when ju- supply of biofilm material. Post-larvae bigger than venile and adult abalone graze macroalgae,10,11 but this size become responsive to the ‘digestibility’ of information on the action of the abalone radula during grazing macroalgae is limited. We previously observed the morphological *Corresponding author: Tel: 81-3-5351-6499. Fax: 81-3-5351- changes in the radula of a New Zealand abalone 6498. Email: [email protected] aPresent address: Ocean Research Institute, The University of Haliotis iris during the post-larval period, and Tokyo, 1-15-1, Minamidai, Nakano, Tokyo 164-8639, Japan. showed that post-larval radula developments are Received 14 April 2000. Accepted 15 December 2000. consistent with preparation for the transition from Radula development in abalone FISHERIES SCIENCE 597

microbial to macro-algal diets.12 It was suggested older post-larvae and young juveniles (~1–15 mm that the teeth of post-larvae < 1 mm SL probably SL) for radula observations. The main food source function as ‘scoops’ that slide across the surface for the abalone on the pregrazed plates was the collecting small diatoms and other fine, loose par- diatom film, which was dominated by Cocconeis ticles. Radulae of post-larvae > 1 mm SL became spp. more suitable for collecting larger particles and gouging feeding substrata. That paper is the first report to describe the progressive development of Radula observation the abalone radula throughout the post-larval period.12 Other reports present only limited infor- Samples of post-larvae and young juveniles were mation about the abalone radula, often at a single preserved in 5% seawater formalin at intervals point of larval or post-larval development.4,13–17 of 4–17 days from 6 to 109 days post-settlement. Larval and post-larval radula development has Competent larvae after 6–7 days at 20°C were also been studied only for polyplacophorans, apla- preserved in the same manner for observing the cophorans and pulmonates.18 larval radula. Radulae of these larvae, post-larvae In the present paper, changes in radula mor- and young juveniles were removed with a pipette phology of abalone Haliotis discus hannai from and an inverted microscope following dissolution larva to adult are described. We focus on radula of tissues by soaking in sodium hypochlorite (0.6% development in relation to transitions in feeding, Cl concentration; Wako Pure Chemical Industries and compare these developments with those of Ltd, Osaka, Japan) for several minutes. Radulae H. iris. were then serially pipetted through several distilled water baths to remove residual sodium hypochlo- rite. This procedure was selected after we con- MATERIALS AND METHODS firmed that the structure of radula teeth was not changed by the procedure. Post-larval and juvenile Abalone rearing SL (the longest shell dimension) were measured individually before dissolution. Radulae of older Larval abalone were hatched in May 1997 at the juveniles and adult abalone (~15–98 mm SL) were Iwate Sea Farming Association (Iwate, Japan) or dissected from fresh animals obtained from Iwate in October 1997 at the Akita Prefectural Hatchery Sea Farming Association and reared at TNFRI in a Center (Akita, Japan) using the procedures running seawater tank at 20∞C and fed brown alga described by Uki and Kikuchi.19 Four days after fer- Laminaria japonica. tilization at 20°C, the veliger larvae from Iwate were Radula length, width, number of transverse rows transported to Tohoku National Fisheries Research of teeth (Fig. 1a), and gap between rachidian teeth Institute (TNFRI, Miyagi, Japan) within 4 h. of adjacent rows (only for older juveniles and Five-day-old larvae from Iwate reared at 20°C, adult) were determined using an inverted micro- which were competent to metamorphose,20 were scope and video micrometer. Radulae were then transferred to plastic water tanks (diameter 28 cm, transferred to scanning electron microscope (SEM) height 14 cm), the inside of which were covered stubs, laid flat with the teeth upwards, and allowed with a mono-cultured benthic diatom Cocconeis to air dry before sputter coating with gold for SEM scutellum that had been pregrazed overnight observations. by juvenile abalone (2 cm SL). Cocconeis scutel- The length and width of the rachidian tooth, lum coated with trail mucus of juvenile abalone lengths of the L3 teeth and the gap between the has a high potential for the induction of settle- rachidian teeth of adjacent transverse rows ment/metamorphosis of larvae and provides a (Fig. 1b) were measured using SEM photographs. suitable food source for all stages of post-larval The clearance angle of rachidian and lateral teeth abalone.5 The metamorphosed animals were (Fig. 1c) of post-larval radula was also measured as maintained as a source of young post-larvae described elsewhere.12 The clearance angle of teeth (<~1.5 mm SL) for radula observations by being fed was defined by Padilla, who suggested that it pro- C. scutellum, as described elsewhere.21 vides information on the function of radula teeth.11 Four-day-old competent larvae from Akita were Rake angle (Fig. 1c) was also suggested to be settled on pregrazed plates and reared continu- important in the function of radula teeth,11 but ously in running seawater at 20°C at the hatchery. we could not measure it directly on most teeth Seven days after settlement, post-larvae were because of their shape and orientation in the SEM transported to TNFRI on the plates in a water tank preparations. We did not measure the clearance within 5 h. These post-larvae were reared on the and rake angles of juvenile and adult radula plates in running seawater at 20°C as a source of because accurate measurements were difficult 598 FISHERIES SCIENCE T Kawamura et al.

Fig. 1 Scanning electron micro- scope photographs showing terms used in the text to describe radula morphology. (a) An entire radula showing length and width. (b) Transverse rows of radula teeth. R, rachidian tooth; L1–L5, lateral teeth 1–5; M, marginal teeth; G, gap between rachidian teeth of adjacent transverse rows; WR, width of rachidian tooth; LR, length of rachidian tooth; LL3, length of L3 tooth. (c) Side view of a row of radula teeth showing individual teeth. CA, clearance angle (positive); TTA, tooth tip angle; RA, rake angle. even on the outside laterals because of obstruction by the overhanging marginal teeth. Measurements of the angles of rachidian tooth and inner lateral teeth of juveniles and adults were impossible because of their positions behind the lengthened outer laterals. These measurements were done for several teeth rows located in the middle part of the whole radula.

RESULTS

Changes in radula length and width from larva to adult

The overall length of radula increased linearly with abalone SL, reflecting increases in the gap between adjacent rows of teeth, the length of teeth (indi- cated by rachidian in Fig. 2), and the number of transverse rows of radula teeth (Fig. 2). The number of rows of teeth, however, was relatively constant during the post-larval period and started increasing only above shell lengths of 4–5 mm (Fig. Fig. 2 Increase in radula length with abalone shell 2). The width of the radula also increased linearly length, from post-larva to adult. Graphs plot factors con- as the abalone grew (Fig. 3). This increase in width tributing to the change in radula length: number of was caused mainly by the increase in width of transverse rows of radula teeth, gap between rachidian the individual teeth (illustrated by the width of teeth in adjacent transverse rows, and the length of the rachidian teeth in Fig. 3). The increase in the rachidian teeth. Radula development in abalone FISHERIES SCIENCE 599

Fig. 3 Increase in radula width and the width of rachi- dian teeth with abalone shell length from post-larva to adult.

number of lateral and marginal teeth per row con- tributed to the increase in radula width for young post-larvae, but not for juveniles and adults (dis- Fig. 4 Relationship between abalone shell length (SL) cussed later). Most of the important morphologi- and factors relating to radula length for abalone < 5mm cal developments occurred in abalone measuring SL. (a) Total radula length and number of transverse rows less than approximately 4 mm SL, as will now be of radula teeth. (b) Length of rachidian and L3 teeth, and discussed. the gap between rachidian teeth in adjacent transverse rows. Data points show the mean ± SE (n = 3).

Radula development in abalone < 4 mm shell length width for shell lengths smaller than 2 mm partly Length of the radula increased linearly with reflected an increased number of lateral teeth (Fig. abalone shell length during the post-larval period 5b). The larval radula appeared to contain the (Fig. 4a). The competent larval radula contained rachidian tooth (R), two pairs of lateral teeth (L1 11–13 rows of teeth, and the number of rows and L2), and one or two pairs of marginal teeth per increased rapidly during the first several days after row (Fig. 6a), although lateral and marginal teeth settlement. At 6 days post-settlement, post-larvae were not differentiated clearly. Post-larvae smaller (458 ± 10 mm SL; mean ± SE) had 20–26 rows of than ~1 mm SL contained only the two pairs of teeth in the radula. The number of rows remained lateral teeth (L1 and L2) present in the larval radula between 25 and 30 (with two exceptions) from ~500 (Fig. 6b). An additional three pairs of lateral teeth mm to ~4 mm SL (Fig. 4a). The increase in radula (L3–L5) were added progressively as post-larvae length during the post-larval period reflected both grew from ~0.9 mm to ~1.9 mm SL (Fig. 5b). Thus, increased length of the rachidian and lateral teeth, the adult complement of five pairs of lateral teeth and an increased gap between adjacent rows of was completed early in the abalone’s life. For teeth (Fig. 4b). For abalone larger than ~2 mm SL, abalone larger than 1.9 mm SL, radula width the gap between rows of teeth also increased as increased mainly as a result of the widening of differentiation of the L3–L5 teeth developed individual teeth (Fig. 5a). The number of marginal (discussed later). teeth per row also increased from one pair in com- Width of the radula also increased with post- petent larvae to 30–40 pairs at 3–4 mm SL, 70–80 larval shell length (Fig. 5a). The increase in radula pairs in 30–40 mm juveniles, and 70–90 pairs in 600 FISHERIES SCIENCE T Kawamura et al.

tions on their edges (Fig. 6d,e). All serrations disappeared from L3–L5 teeth by approximately 20 mm SL (Fig. 6f). The L3–L5 teeth became longer than R, L1 and L2 as abalone grew larger than ~1.5 mm SL (Fig. 6d,e). This differentiation of the lateral teeth accompanied an increase in the gap between adjacent rows of teeth (Fig. 4b). The L3–L5 teeth became pointed, similar to canine teeth, while the tip of R and L1 teeth became flat, similar to spades (Fig. 6f), during the juvenile and adult stages. The L2 teeth of adults were almost the same size as R and L1 and much shorter than L3–L5, but more pointed at the tip than R and L1. Marginal teeth retained their comb-like shape and fine serrations from larval stage to adult abalone. The tip of marginal teeth, however, became more round as abalone grew to become juveniles. The serrations became less pronounced near the tip of marginals for abalone measuring approximately 30–40 mm SL, but even adult mar- ginal teeth retained serrations on their edges. The size of individual marginal teeth relative to the rachidian and lateral teeth became smaller as abalone grew. The clearance angle of the rachidian and lateral teeth was variable within and between radulae, but generally increased as the post-larvae grew. Post-larvae smaller than 1 mm SL had strongly curved rachidian and lateral teeth (Fig. 7a) with Fig. 5 Relationship between abalone shell length and clearance angles of approximately or less than zero factors relating to radula width for abalone 5 mm SL. < (Fig. 8). Larger post-larvae > 1 mm SL had much (a) The widths of radula and rachidian teeth. Data points higher clearance angles of 5–35° (Figs 7b,8). for the width of rachidian teeth show the mean ± SE ~ (n = 3). (b) Number of pairs of lateral teeth in each trans- Because the angle across the tooth tip was about verse row. 10–20∞, the rake angle in post-larvae > 1 mm SL was about 35–75° (90∞ – Tooth tip angle – Clearance angle). adults measuring 90–100 mm SL (Fig. 6c–e). This increase in marginal teeth contributed to an in- DISCUSSION crease in the radula width of young post-larvae, but contributed little to older animals, as adjacent The development of the radula of H. discus hannai rows of marginals lay one upon another. shown in the present study is remarkably similar to that of H. iris.12 The two species show the same changes in the shape of specific radula teeth (size, Changes in the morphology of individual teeth clearance angle, differentiation, serrations) and the same features contributing to an increase in radula The serrations on the working edges of the rachid- length (discontinuous increase in number of ian and lateral teeth changed as abalone devel- rows of teeth, increased tooth size, increasing oped. R, L1 and L2 teeth initially had long, pointed spacing between adjacent rows of teeth) and serrations (Fig. 6a,b). For abalone larger than width (increased width of teeth, delayed addition ~1 mm SL, these serrations became progressively of L3–L5, steady increase in number of marginals). shallower, first on R, and later on L1 and L2 as Moreover, these developments took place in the L3–L5 developed. By approximately 2 mm SL, same sequence, and at nearly identical abalone when the adult complement of lateral teeth was sizes in the two species. Genetically these two completed, nearly all serrations had disappeared abalone species are not close,22 but their feeding from R, L1 and L2 teeth, but L3–L5 retained serra- habits and growth patterns are similar.9 Radula development in abalone FISHERIES SCIENCE 601

Fig. 6 Scanning electron micro- socope photographs of the radula showing developmental stages. Radula formulae represent num- bers of teeth in a transverse row as follows: M + L + R + L + M.32 Abbre- viations for tooth types are ex- plained in Fig. 1. (a) Competent larva of 280 mm SL after 6 days at 20°C, radula formula: 1 + 2 + R + 2 + 1. (c) Post-larva of 470 mm SL at day 6 post-settlement, 3 + 2 + R + 2 + 3. (c) Post-larva of 1145 mm SL at day 17, 8 + 2 + R + 2 + 8. A valve of a diatom (Cocconeis scutellum) is caught by R and L1 teeth. (d) Post- larva of 1890 mm SL at day 49. Dif- ferentiation of the lateral teeth has started, ~15 + (2+2) + R + (2+2) +~15. (e) Post-larva of 3240 mm SL at day 63. L3–L5 teeth are larger and longer than R, L1 and L2. ~30 + (3+2) + R + (2+3) +~30. Marginal teeth are not all visible. (f) Juvenile of 29.9 mm SL. L3–L5 teeth are much longer and more pointed than central teeth (R, L1, L2). Marginals are not visible. 70–80 + (3+2) + R + (2+3) + 70–80.

The morphology of radula teeth in abalone first transition in feeding from lecithotrophy to species is generally similar, but Haliotis asinina particle feeding. Post-larvae begin feeding within a and Haliotis ovina have many more marginals23 day of the velum being shed, but they can grow up and longer L2 teeth as adults than H. discus hannai to ~400 mm SL without food.26,27 Abalone may need and H. iris. The two tropical species, H. asinina to develop the radula immediately after settlement and H. ovina, have slight but obvious differences to establish an effective feeding organ. The rapid between them in their radular structures and increase in the number of rows of teeth in larvae shapes.23 and early post-larvae probably indicates the active Changes in radula morphology that were formation of new rows of teeth before they start observed in H. discus hannai (present study) and shedding worn teeth at the anterior end during H. iris12 are probably related to changes in feeding feeding. The relatively constant number of rows habit, as suggested by Nybakken for carnivorous during the post-larval period suggests that the rate gastropods of the genus Conus24 and by Warén for of formation of new rows was almost same as the Trochoidea.25 The number of transverse rows of rate of loss by shedding teeth. radula teeth increased rapidly during the first There is conflicting evidence concerning the several days after settlement ~< 500 mm SL). When time at which diatoms are first ingested by post- larger than this size, the number of rows of teeth larval abalone. Haliotis iris efficiently ingest a small remained relatively constant for the remainder of diatom strain by two days after settlement induc- the post-larval period. This early increase in the tion (larvae were 10 days old at 16°C when settled). number of rows of teeth seems to be related to the Norman-Boudreau et al. first found diatoms in the 602 FISHERIES SCIENCE T Kawamura et al.

Fig. 8 Relationship between clearance angle of teeth and post-larval shell length. Each data point shows the mean ± SE of 9–12 teeth on one radula.

phosis. Moss reported that Haliotis australis larvae showed characteristic feeding movements soon after being exposed to a film, and apparently ingested diatoms after 7 days.17 By this time the larval radula had developed 16–17 rows of teeth, but the larvae retained their velum.17 The mouth and gut of Japanese abalone are reported to form only during metamorphosis20 but developmental sequences may vary between abalone species, or if metamorphosis is delayed. Post-larvae 1 mm SL had clearance angles of Fig. 7 Scanning electron microscope photographs < showing side views of post-larval radula. (a) Strongly approximately or less than zero. Padilla suggested curved rachidian and lateral teeth of post-larvae of that clearance angles of zero may result in the 720 mm SL at day 11 post-ettlement, with clearance tooth sliding across the surface rather than cutting angles of approximately or less than zero. (b) Radula it.11 The curved radula teeth of post-larvae < 1mm teeth with positive clearance angles on a 3240 mm post- SL probably function as scoops, which are suitable larva at day 63. for collecting biofilm components such as extra- cellular secretions. Positive clearance angles and relatively high rake angles for larger post-larvae > 1 mm SL would allow them to ‘cut’ rather than just guts of post-larval abalone 2–6 days after settle- slide across the substratum. Post-larvae approxi- ment,28 whereas Moss found them only after 7 mately > 0.8 mm SL require high levels of absorp- days,17 and Kitting and Morse observed no inges- tion of diatom cell contents for rapid growth, tion of ‘cellular solids’ from coralline surfaces in whereas smaller post-larvae grow at similar rates the first 10 days post-settlement.16 This variation is regardless of whether they feed on diatom strains probably partly related to the nature of the diatoms that have a high or low digestibility.9 Very tightly present. Small, loosely attached cells are most attached diatoms such as Cocconeis spp., which are easily ingested by small post-larvae,8,28 which is often dominant on crustose coralline algae (CCA) consistent with the observations of early radula (see Kawamura et al.9) where abalone larvae pref- (present paper and Roberts et al.12) The number of erentially settle in the natural environment (e.g., rows of teeth in the larval radula increases rapidly Saito,29 Morse and Morse30), often have a high if metamorphosis is delayed,12,17 hence, the age of digestibility for older post-larvae resulting in rapid larvae at settlement may also affect the diatom growth.2,5,7,8 Tightly attached diatoms require con- feeding ability of the radula soon after metamor- siderable force to be detached from substrata and Radula development in abalone FISHERIES SCIENCE 603

are usually ruptured if dislodged. Small post-larvae rhipidoglossan gastropods eat CCA.10 The radula of are not able to efficiently detach Cocconeis cells, H. discus hannai is not highly mineralized and it is but by approximately 0.8 mm SL post-larvae can considered that they are not able to erode a rock ingest Cocconeis cells efficiently.5,8 The increase in surface.34 However, CCA fragments have been clearance angle in abalone measuring approxi- observed in the guts of 5–10 mm SL abalone.35,36 mately 1 mm SL could contribute to the post- The cuticle and epithelial cell contents of CCA are larva’s ability to detach Cocconeis cells. However, considered to be food sources for even post-larval the hardness and flexibility of radula teeth should abalone,14,37 but it appears that the food sources also be considered because the teeth of post-larval from CCA themselves are not adequate to support abalone could be soft and flexible. Teeth’s hardness the rapid growth of post-larvae (e.g. Kitting and and flexibility may affect an abalone’s ability to Morse,16 Takami et al.6). Biofilm components such ingest tightly attached diatoms and other firm sub- as diatoms and their extracellular products on CCA strata such as CCA or elastic macroalgae.11 The data surfaces seem to be the main nutrition sources for obtained in the present study on the clearance post-larval abalone.6,9 The radula developments angle of radula teeth are based on radulae removed that occur by 4 mm SL, especially the differentia- from post-larvae and prepared for SEM observa- tion of the cutting L3–L5 teeth, appear to enable tion, and we do not know how relevant these juvenile abalone to efficiently utilize CCA tissue. measurements are to the real attack angles of the The number of transverse rows of teeth remained teeth of the live animals during feeding. Thus, the relatively constant during post-larval period, but earlier discussion on the increasing clearance angle started increasing again at 4–5 mm SL. In the can only be conjectural until more is known about experiments of the present study, the diet did not the position of radula teeth during feeding.12 alter during this transition, so the increased During feeding movements, the radula protrudes number of rows of teeth is unlikely to be caused by around the tip of the supporting cartilages.11,31,32 a reduction in the rate of loss of teeth. Rather, it However, the action of the teeth and their clear- appears that the addition of further rows of teeth is ance angle at the point of contact with food will developmentally programmed and independent of depend on various factors, including the shape of diet. The reasons for an increased number of rows the radula when it protrudes for feeding, the nature of teeth when abalone are larger than 4 mm SL are of the substrate, and the rotation and flexing of the not clear. They may relate to either tougher foods radula during the feeding stroke.11,31,32 Observa- causing a greater turnover of teeth, or an increase tions of clearance angles in the present study are in the relative size of the buccal apparatus. meaningful for a radula action such as that char- Haliotis discus hannai begin feeding on soft acterized for limpets by Padilla.11 Interpretation is algae such as Ulva spp. at approximately 4–5 mm much more difficult when the radula bend is sharp, SL, and on macroalgal fronds such as Laminaria and clearance angles are highly dynamic, as and Eisenia when larger than 13 mm SL.38 Juvenile described for some other gastropods.31,32 H. discus discus of 3–4 mm SL feed and grow well Detailed morphology of the cusp of teeth may on early juvenile macroalgae.39 Based on evidence be important in understanding feeding substrate from both natural habitats and hatcheries, a shift characteristics and dietary preferences, as sug- in the feeding habits of abalone from microalgal gested by Hickman.33 The reduction in tooth to macroalgal feeding seems to occur at approxi- serrations in H. discus hannai, which start at mately 5–10 mm SL.9 Data from the present study approximately 1 mm SL, could be related to change suggest that this transition in feeding is at least in food sources from very small items (such as partly because of the structural and functional small diatoms and bacteria) to larger foods. The changes in the radula during post-larval and ju- increase of the gap between teeth rows as the L3– venile stages. The structural changes in the radula L5 teeth differentiated appeared to make the observed in the present study and the transitions radula more suited to collecting larger food items. in feeding of H. discus hannai are summarized in Indeed, post-larval H. iris became more efficient at Table1. At the same abalone size that differentia- ingesting large diatom cells as they grew.7,8 tion of the L3–L5 teeth began, a marked increase The L3–L5 teeth of juveniles and adults are in the activity of macroalgal polysaccharide- sharply cusped and lack serrations. They appear to degrading enzymes was seen in H. discus hannai.21 be more suited to excavating tough substrata and Thus, abalone appear to prepare for digestive cutting tightly attached algae than just for scraping abilities before they start utilizing macroalgae. and sweeping food items from surfaces. Steneck The present study describes morphological and Watling considered that rhipidoglossan developments in a Japanese abalone that are radulae (including abalone) are less capable of remarkably similar to those observed in a New grazing very tough substrata, and stated that no Zealand abalone,12 which is ecologically similar but 604 FISHERIES SCIENCE T Kawamura et al.

not closely related. Study of radula development in a wider range of abalone, including species with very different habitat characteristics, will provide biofilm

juvenile an interesting comparison of the influence of + + 6 genetics and ecology on the evolution of abalone radulae. Further studies on the detailed functions 5 of the different types of abalone radula teeth (R and (Source of nutrition) (Source

4 L1, L2, L3–L5 and marginal teeth), the way they are

adult macroalgae used during feeding, and their hardness and flexi- +

ingested biofilm material bility during development are needed to more fully

+ understand the transitions in feeding and the food macroalgae sources of abalone throughout their life stages.

3 ACKNOWLEDGMENTS L3–L5 teeth develops, which makes radula more which makes radula L3–L5 teeth develops, We thank Mr S. Komatsu (Iwate Sea Farming

L3–L5, M material Association) and Mr K Saitoh (Akita Prefectural serrations Hatchery Center) for providing the larval abalone. This study was supported by the Ministry of 2 Agriculture, Forestry and Fisheries of Japan 0 R, L1–L5, M material Biofilm 0 R, L1–L5, M Yolk 0 R, L1–L5, M from yolk energy Residual < < < (BIOCOSMOS Project), and the Japan Science and 0–40 (R, L1, L2), cell contents Diatom 20–40 L3–L5, M cell contents Diatom angle

No dataNo (L3–L5), M Juvenile Technology Agency. spp. Loosely attached diatoms are easily ingested but are usually ‘indigestible’. usually easily ingested but are Loosely attached diatoms are spp. 1 REFERENCES – – – – + 1. Kawamura T, Takami H. Analysis of feeding and growth rate

Cocconeis of newly metamorphosed abalone Haliotis discus hannai fed on four species of benthic diatom. Fisheries Sci. 1995; 61: Radular morphology Radular 357–358. 2. Kawamura T, Saido T, Takami H, Yamashita Y. Dietary value of benthic diatoms for the growth of post-larval abalone Haliotis discus hannai. J. Exp. Mar. Biol. Ecol. 1995; 194:

<+ 189–199. ~ 40 3 40 3–8 1–2 3. Matthews I, Cook PA. Diatom diet of abalone post-larvae 8–16 ~ (Haliotis midae) and the effect of pre-grazing the diatom overstorey. Mar. Freshwater Res. 1995; 46: 545–548. and their transitions in feeding and their transitions 4. Daume S, Brand S, Woelkerling WJ. Effects of post-larval abalone (Haliotis rubra) grazing on the epiphytic diatom assemblage of coralline red algal surfaces. Mollusc Res. 1997;

5 18: 119–130. 5. Takami H, Kawamura T, Yamashita Y. Survival and growth rates of post-larval abalone Haliotis discus hannai fed lateral teethlateral teeth marginal teeth lateral H. discus hannai conspecific trail mucus and/or benthic diatom Cocconeis scutellum var. parva. Aquaculture 1997; 152: 129–138.

< 6. Takami H, Kawamura T, Yamashita Y. Contribution of

30 diatoms as food sources for post-larval abalone Haliotis

9 discus hannai on a crustose coralline alga. Mollusc Res. 1997; 18: 143–151. et al. 7. Kawamura T, Roberts RD, Nicholson CM. Factors affecting the food value of diatom strains for post-larval abalone < Haliotis iris. Aquaculture 1998; 160: 81–88. 2–4 25–30 5 16– 1–2 25–30 3–5 0.5–1 25–30 2 ~ 0.45 20–26 2 ~ 0.28 11–13 2 (mm) 8. Roberts RD, Kawamura T, Nicholson CM. Growth and 1 such as diatoms’ ‘digestible ingest tightly attached mm can effectively

> survival of postlarval abalone (Haliotis iris) in relation to 1 mm grow more rapidly on ‘digestible diatoms’, which they can access to the diatom cell contents. diatoms’, 1‘digestible on rapidly more mm grow

> development and diatom diet. J. Shellfish Res. 1999; 18: Structural changes in the radula of changes in the radula Structural 243–250. 9. Kawamura T, Roberts RD, Takami H. A review of feeding

Outer lateral teeth (L3–L5) become specialized cutting teeth. The gap between rows of teeth increases as differentiation of the as differentiation of teeth increases rows The gap between teeth (L3–L5) become specialized cutting teeth. lateral Outer than slide. will cut rather angle means radula clearance Increasing during the period. shallower become progressively edges of the teeth in parenthesis on the working Serrations Kawamura by Reviewed bacteria CCA, and conspecific abalone trails. mucus material diatoms, from Mainly Post-larvae and growth of postlarval abalone. J. Shellfish Res. 1998; 17: 1 2 3 4 6 5 Post-larva Juvenile 4 Table 1 Larva able to handle large particles. Post-larvae Stage length Shell rows No. pairs of No. pairs of No. of Differentiation Clearance with Teeth habit Feeding 615–625. Radula development in abalone FISHERIES SCIENCE 605

10. Steneck RS, Watling L. Feeding capabilities and limitation of 25. Warén A. Ontogenetic changes in the trochoidean herbivorous molluscs: A functional group approach. Mar. (Archaeogastropoda) radula, with some phylogenetic inter- Biol. 1982; 68: 299–319. pretations. Zool. Scripta 1990; 19: 179–187. 11. Padilla DK. The structural resistance of algae to herbivores: 26. Roberts RD, Lapworth C, Barker R. Effect of starvation on A biomechanical approach. Mar. Biol. 1985; 90: 103–109. the growth and survival of post-larval abalone (Haliotis iris). 12. Roberts RD, Kawamura T, Takami H. Morphological changes Aquaculture (in press). in the radula of abalone (Haliotis iris) during postlarval 27. Takami H, Kawamura T, Yamashita Y. Starvation tolerance of development. J. Shellfish Res. 1999; 18: 637–644. newly metamorphosed abalone Haliotis discus hannai. 13. Tong L. Paua larvae put under the microscope. Shellfish Fisheries Sci. 2000; 66: 1180–1182. Newsletter 1984; 11: 7. 28. Norman-Boudreau K, Burns D, Cooke CA, Austin A. A 14. Garland CD, Cooke SL, Grant JF, McMeekin TA. Ingestion of simple technique for detection of feeding in newly meta- the bacteria on and the cuticle of crustose (non-articulated) morphosed abalone. Aquaculture 1986; 51: 313–317. coralline algae by post-larval and juvenile abalone (Haliotis 29. Saito K. The appearance and growth of 0-year-old Ezo ruber Leach) from Tasmanian waters. J. Exp. Mar. Biol. Ecol. abalone. Nippon Suisan Gakkaishi 1981; 47: 1393–1400. 1985; 91: 137–149. 30. Morse ANC, Morse DE. Recruitment and metamorphosis 15. Dinamani M, McRae C. Paua settlement: The prelude. Shell- of Haliotis larvae induced by molecules uniquely available fish Newsletter 1986; 13: 9. at the surface of crustose red algae. J. Exp. Mar. Biol. Ecol. 16. Kitting CL, Morse DE. Feeding effects of post-larval red 1984; 75: 191–125. abalone, Haliotis rufescens (Mollusca: Gastropoda) on en- 31. Solem A. Patterns of radular tooth structure in carnivorous crusting coralline algae. Mollusc Res. 1997; 18: 183–196. land snails. Veliger 1974; 17: 81–88. 17. Moss GE. Factors affecting settlement and early post-settle- 32. Voltzow J. Gastropoda: Prosobranchia. In: Harrison FW, ment survival of the New Zealand abalone Haliotis australis. Kohn AJ (eds). Microscopic Anatomy of Invertebrates, Vol. 5, N.Z. J. Mar. Freshwater Res. 1999; 33: 271–278. Mollusca I. Wiley-Liss, Inc., New York. 1994; 111–252. 18. Eernisse DJ, Kerth K. The initial stages of radular develop- 33. Hickman CS. Gastropod radulae and the assessment of ment in chitons (Mollusca: Polyplacophora). Malacologia form in evolutionary paleontology. Paleobiology 1980; 6: 1988; 28: 95–103. 276–294. 19. Uki N, Kikuchi S. Regulation of maturation and spawning of 34. Okoshi K, Ishii T. Concentrations of elements in the radular an abalone, Haliotis (Gastropoda), by external environmen- teeth of limpets, chitons, and other marine molluscs. J. Mar. tal factors. Aquaculture 1984; 39: 247–261. Biotechnol. 1996; 3: 252–257. 20. Seki T, Kan-no H. Observations on the settlement and meta- 35. Tomita K, Tazawa N. On the stomach contents of young morphosis of the veliger of the Japanese abalone, Haliotis abalone Haliotis discus hannai Ino, in Rebun Island, discus hannai Ino, Haliotidae, Gastropoda. Bull. Tohoku Hokkaido. Sci. Rep. Hokkaido Fish. Exp. Stn. 1971; 13: 31–38. Reg. Fish. Res. Lab. 1981; 42: 31–39. 36. Shepherd SA, Cannon J. Studies on southern Australian 21. Takami H, Kawamura T, Yamashita Y. Development of poly- abalone (genus Haliotis) X. Food and feeding of juveniles. J. saccharide degradation activity in postlarval abalone Malacol. Soc. Aust. 1988; 9: 21–26. Haliotis discus hannai. J. Shellfish Res. 1998; 17: 723–727. 37. Shepherd SA, Daume S. Ecology and survival of juvenile 22. Lee Y-H, Vacquier VD. Evolution and systematics in Halio- abalone in a crustose coralline habitat in South Australia. In: tidae (Mollusca: Gastropoda): Inferences from DNA Watanabe Y, Yamashita Y, Oozeki Y (eds). Survival Strategies sequences of sperm lysin. Mar. Biol. 1995; 124: 267–278. in Early Life Stages of Marine Resources. A. A. Balkema, 23. Chitramvong YP, Upatham ES, Kruatrachue M, Sobhon P, Rotterdam. 1996; 293–313. Limthong V. Scanning electron microscope study of radulae 38. Seki T. Biological studies on the seed production of the in Haliotis asinina Linnaeus, 1758 and Haliotis ovina northern Japanese abalone, Haliotis discus hannai Ino. Bull. Gmelin, 1791 (Gastropoda: Haliotidae). J. Shellfish Res. 1998; Tohoku Reg. Fish. Res. Lab. 1997; 59: 1–71. 17: 755–759. 39. Maesako N, Nakamura S, Yotsui T. Food effect of brown and 24. Nybakken J. Ontogenetic change in the Conus radula, its green algae of early developmental stage and blue green form, distribution among the radula types, and significance algae for the growth of the juvenile abalone, Haliotis discus in systematics and ecology. Malacologia 1990; 32: 35–54. Reeve. Bull. Nagasaki Pref. Inst. Fish. 1984; 10: 53–56.