Aquacult. Sci. 63（3），273－282（2015）

Population characteristics of annulus (Linnaeus, 1758) (: ) from temperate to tropical areas

1 2,＊ Shiela VILLAMOR and Tomoko YAMAMOTO

Abstract: The aim of this study was to describe the population characteristics of (Linnaeus, 1758), including the density, abundance of different developmental stages, sex ratio, and size dimorphism between sexes, which are significant factors for resource management. We surveyed populations in the Philippines (tropical area) for comparison with populations in Japan (subtropical and temperate areas). The population density in the tropical area was interme- diate between that in the sub-tropical and temperate areas, although density varied among stations in the same geographical area. There was a low proportion or absence of immature in the habitat shared with adults, except for Nogas Island in the Philippines. Because marine protected areas (MPAs) include a nursery area, which is a protective area for immature cowries, further study was required to determine where juveniles are recruited and grow. We detected the sex of adult cowries by histological analysis and measured the length of each shell to distinguish sexual dimorphism. Females were larger than males in some sampling sites. When formulating fisheries guidelines, including controlling the collection of larger individuals, we should investigate the sex ratio and size dimorphism in each resource population to avoid a sex ratio that is biased toward males.

Key words: Monetaria annulus; Developmental stages; Sex ratio; Sexual size dimorphism

The Cypraeidae family (commonly known tropical countries around the Indian and Pacific as cowries) is widely distributed in the Indo- , where shells and shell craft products West Pacific from tropical to temperate areas. are continuously exported. Cowries are in high Monetaria annulus (Linnaeus, 1758) or the demand by shell collectors, and many tourists gold-ringed cowry is one of the most common buy the crafts as souvenirs, thereby providing in this family. These gastropods are a source of livelihood for the people in coastal usually found in the middle and lower intertidal fishing communities (Wells 1981; Newton et al. areas in shallow water, tide pools, under stones, 1993; Tiraa-Passfield 1996; Ponder and Grayson or among seagrasses. Their habitats include 1998; Floren 2003; Gossling et al. 2004; Oliver rocky, muddy and sandy shores (Orr 1959; Foin 2004). 1989). The northern limit of their distribution Research has identified habitat degrada- was observed in Boso, Japan (Irie 2006) and tion (Floren 2003; Huang et al. 2008; van der the southern limit in Algoa Bay, Meij et al. 2009) and overexploitation (Wells (Schilder and Schilder 1939). Cypraeid shells 1981; Newton et al. 1993; Tiraa-Passfield 1996; are beautiful, glossy and colorful, making them Floren 2003; Gossling et al. 2004) as reasons an economic commodity, mainly important in for a decrease in population numbers. Resource

Received 12 December 2014; Accepted 1 May 2015. 1 The United Graduate School of Agricultural Sciences, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-8580, Japan. 2 Faculty of Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890-0056, Japan. ＊Corresponding author: E-mail, [email protected] (T. Yamamoto). 274 S. Villamor and T. Yamamoto management based on scientific information with populations in Japan. is greatly required, particularly in the tropi- cal areas, where prolific collection of Cypraeid Materials and Methods shells occurs. A potential method of resource conservation is prohibiting collection during Fig. 1 shows the sampling sites and sta- the reproductive and recruitment seasons; tions in Japan and the Philippines. Sampling however, this practice appears to be difficult to stations were located in the intertidal area of implement in tropical and sub-tropical regions. each sampling site. The sampling sites in Japan In the tropical and sub-tropical areas, repro- included the southern part of Kyushu Island, duction and recruitment of larvae continues the coast of Hanase (with three neighboring throughout the year for these gastropods, and stations), the small islands at the southwest in particular for M. annulus (Frank 1969; Katoh part of Japan, including Tanegashima Island 1989). Another alternative method is to restrict (with five stations around it: Yanagihara, Iseki, the minimum harvest size. Through histologi- Ushino, Kamitateshi, and Shimoneshime), cal analysis, we found that in a temperate area a Amami Island (with one station at Hienhama bias toward females exists in the sex ratio, and in the west), and Tokunoshima Island (with size dimorphism between sexes where the shell three stations around it: Kanami, Shikaura, length of females were significantly larger than and Motokawa). In the Philippines, the sam- those of males (Villamor and Yamamoto 2015). pling sites were located in the central part of If size dimorphism is a general phenomenon the country, including Sulangan Island (Guiuan in this species, the limitation of the minimum Province) in the east, Nogas Island (Antique harvest size may result in a higher pressure on Province) in the west, and Olango Island (Cebu females than on males. Province) (with three stations around it: Sta. Establishing marine protected areas (MPAs) Rosa, Sabang, and Pangan-an) at the center. where egg masses and juveniles can be pro- Surveys in Japan and the Philippines were tected appears to be the most effective method conducted on different dates from 2010 to 2013. of fisheries management. Because egg masses Each sampling station was surveyed once, and brooding females have been observed in except at Hanase and Nogas Island. At Hanase the vicinity where adults were found (Natarajan Station 1 on Kyushu Island, surveys were con- 1957; Kay 1960; Frank 1969; Katoh 1989), it ducted every 2 months from June 2010 to June can be said that the spawning area comprises 2011, and all data were pooled. At Nogas Island almost the entire area of adult stage habitat. in the Philippines, surveys were conducted in However, there is little information regarding 2012 and 2013. The geographical coordinates nursery areas for this species. Katoh (1989) of the sampling sites, range and mean of sea identified both juveniles and adults in the field surface temperatures, and the sampling date at throughout the year but failed to mention the each sampling site are shown in Table 1. habitat difference between the two developmen- Survey areas at Hanase Station 1 in Japan and tal stages. Nogas and Olango islands in the Philippines The aim of this study was to describe the pop- were set at the wide range of the intertidal ulation characteristics of M. annulus, including zone. In each survey area, 2-3 transect lines the population density; abundance of juveniles, with a length of 50-100 m each were laid, and sub-adults and adult cowries occupying the all the individuals in every 1 × 1 m2 quadrat same habitat or fishery ground; sex ratio; and placed within 1 m of both sides of the transect size dimorphism between sexes, which are lines were sampled. At Hanase Stations 2 and significant factors for resource management. 3, all individuals in every 1 × 1 m2 quadrat Because this species is a high-valued resource in the designated survey area were sampled. in tropical areas, we conducted a survey on pop- At Tanegashima Island in Japan, all individu- ulations in the Philippines and compared them als collected at each coast were counted and Population characteristics of Monetaria annulus 275

Fig. 1. Location of sampling sites in (A) Japan and (B) the Philippines.

Table 1. Sampling sites of Monetaria annulus Sea surface Latitude Longitude Sampling date Area Sampling site and station temperature (㱥) (North) (East) (yyyy.mm) Range Mean Temperate Hanase Station 1 31°11' 130°30' a16.8-27.8 a21.9 c2010.06-2011.06 Kyushu Island Hanase Station 2 31°11' 130°30' 2011.06 Hanase Station 3 31°11' 130°30' 2011.08 Yanagihara 30°47' 131°04' Iseki 30°46' 131°04' Tanegashima Ushino 30°26' 130°51' b19.5-28.4 b23.7 2011.02 Island Kamitateshi 30°24' 130°51' Shimoneshime 30⁰21' 130°51' Sub-tropical Amami Island Hienhama 28°18' 129°23' a19.3-28.1 a23.3 2012.07 Kanami 27°52' 128°58' Tokunoshima Shikaura 27°41' 128°54' no data no data 2013.02 Island Motokawa 27°41' 128°59' Tropical Sulangan Island Sulangan Island 10°56' 125°49' b27.5-29.8 b28.8 2013.08 (Guiuan) Nogas Island Nogas Island 10°25' 121°55' 2012.11 b26.9-30.0 b28.6 (Antique) Nogas Island 10°25' 121°55' 2013.08 Sta. Rosa 10°16' 124°02' Olango Island Sabang 10°15' 124°03' b26.7-29.5 b28.4 2012.11 (Cebu) Pangan-an 10°13' 124°03' aSource: Kagoshima Prefectural Fisheries Technology and Development Center bSource: http://www.seatemperature.org cSampling was done every two months. 276 S. Villamor and T. Yamamoto measured. At Amami (62 quadrats) and from Hanase Station 1 (Villamor and Yamamoto Tokunoshima (5-32 quadrats) islands in Japan 2015). and Sulangan Island (20 quadrats) in the Philippines, 50 × 50 cm2 quadrats were set in Results the area where M. annulus was found, and all individuals were counted and measured. Densities of M. annulus in the Philippines and Two to four persons conducted the survey southern Japan at each sampling site within 1-2 h during the In the tropical area, Sulangan Island (8.4 ± low spring tide. Cowries were counted, and the 0.3 mean ± SD ind./m2, n = 42) showed the shell size (length, width, and height) of each highest mean density, followed by Nogas Island live gastropod was measured using digital cal- (4.4 ± 10.6 ind./m2, n = 111), while Olango ipers. The developmental stages of M. annulus Island (0.01 ± 0.003 ind./m2, n = 3) had the were also recorded and categorized as adult lowest mean density (Table 2). The standard (with developed teeth on the shell deviation of density in each quadrat was higher and a complete, bright orange-yellow ring on at Nogas Island than at Sulangan Island. The the dorsal surface of the shell), sub-adult (with highest density among surveyed quadrats was developing teeth on the shell aperture, and an at Nogas Island (46 ind./m2), which was higher indistinct yellow ring on the dorsal surface of than that at Sulangan Island (20 ind./m2). the shell), and juvenile (no teeth on the shell The densities of M. annulus were almost the aperture, instead of a yellow ring, a yellow or same at some stations of the sub-tropical area. brown line is found on the dorsal surface and At Tokunoshima Island, the highest density the shell is very thin) (Katoh 1989; Irie and among the quadrats was 52 ind./m2, while at Morimoto 2008). Amami Island, the density was 16 ind./m2. The Histological analysis was performed to deter- mean density in the quadrats where M. annulus mine the sex of the M. annulus samples that was found was 32.8 ± 1.3 ind./m2 (n = 41) at were randomly obtained from the three coasts. the smallest station at Tokunoshima Island and At Tokunoshima, 24 adult individuals were 6.0 ± 0.2 ind./m2 (n = 93) at Amami Island and collected during February 2013. At Nogas showed larger values than the mean density in and Olango islands, 30 adult individuals were the tropical area. collected from each island during November At Hanase, a temperate area, the mean and 2012. After measuring the shell length, the the highest densities were lower than those at samples were fixed in 10% formalin, each shell the Sulangan and Nogas islands, but higher than was cracked open, and the soft body was col- those at Olango Island. M. annulus was found lected. The gonads were cut off from the soft to be concentrated at Hanase Station 2, with a bodies, dehydrated in graded alcohol succes- density of 4.9 ind./m2, similar to that at Nogas sions, washed in xylene, and embedded in par- Island. However, the density was very low in all affin wax. Following this, histological sections the surveyed stations of Tanegashima Island. of 8μm were cut, stained with hematoxylin and eosin, and laid on slides for later examina- Abundance of different developmental stages tion under a microscope to determine the sex. All M. annulus individuals collected at These procedures were in accordance with Tokunoshima, Sulangan, and Olango islands Villamor and Yamamoto (2015). were in the adult stage (Fig. 2). Females sitting Fisher’s exact test was used to determine on egg masses were observed at Hanase (0.7% whether the sex ratio differed significantly from in average), Amami Island (1.1%), Sulangan 1 : 1. A Student’s t-test was used to compare the Island (16.7%), and Nogas Island (3.8%, during mean shell lengths between females and males. August 2013). The data of the sex ratio and shell length of The percentage of juveniles was found to be females and males were compared with those greater than 19% during August and November Population characteristics of Monetaria annulus 277

Table 2. Densities of Monetaria annulus at different sampling sites Total survey area Density Maximum no. of Area Sampling site and station (m2) (mean ± SD/m2) individuals/m2 Temperate Hanase Station 1 320 0.3±0.2 15 Kyushu Island Hanase Station 2 70 4.9 ＊ Hanase Station 3 150 0.4±1.0 7 Yanagihara ＊＊ Iseki ＊＊ Tanegashima Ushino aRandom ＊＊ Island Kamitateshi ＊＊ Shimoneshime ＊＊ Sub-tropical Amami Island Hienhama b15.5 6.0±0.2 16 Kanami b8 8.6±0.4 24 Tokunoshima Shikaura b1.25 32.8±1.3 52 Island Motokawa b3.25 9.2±0.5 24 Tropical Sulangan Island Sulangan Island b5 8.4±0.3 20 (Guiuan) Nogas Island Nogas Island (2012) 25 4.4±10.6 46 (Antique) Nogas Island (2013) 47 0.6±1.3 7 Sta. Rosa 300 0.01±0.003 0.01 Olango Island Sabang 300 0.07±0.01 0.04 (Cebu) Pangan-an 300 0.02±0.005 0.01 aWe sampled all individuals that we found because of very low density. bSampling was within quadrats where M. annulus were found. (Numbers indicated here are overestimated for their actual density.) ＊No quadrat was set.

1,14154 93 140 11142 26 32 (30.6% during November 2012 and 19.2% 100 during August 2013) at Nogas Island, while no

) juveniles were found along other coasts of the Philippines (Sulangan and Olango islands). In the temperate and sub-tropical areas, the 50 percentages of juveniles were much smaller ercentage (%

P than that at Nogas Island. The percentages of juveniles were on average 0.7% and 1.1% at Hanase and Amami Island, respectively, while 0

) juveniles were not found at Tanegashima and 8) 1 11) 1 08) 02) 07) 0 02) 08) ......

3 Tokunoshima islands. 12 012 0

2013 Sub-adults were found at similar percentages -2011 (2013 6 d(2 d 0

. in the sub-tropical (3.2%, Amami Island) and n and ( lan land (2011 l la

s tropical (3.6%; Nogas Island during November iIsland(2 sIs oIsland(2012 aIs aI a g

m 2012) areas; however, we did not observe sub- m m i a h m Nog s angan Island (201 Nogas Is adults at the Tokunoshima, Sulangan, and l Olan A aseHan (2010 Su

uno Olango islands. In the temperate area, the k o

Tanegashi percentages of sub-adults were greater than T Sampling site and date 1% (1.8% in average at Hanase and 5.6% at Tanegashima Island). Fig. 2. Percentages of the different developmental stages comprising the populations of Monetaria annulus at the Sex ratio and shell size dimorphism different sampling sites. , adult with eggs; , adult; , sub-adult; , juvenile. Numbers above the bars indicate Males were sampled more often than females the total number of samples. at Tokunoshima and Nogas islands, in contrast 278 S. Villamor and T. Yamamoto with Hanase Station 1, where more females The modes of the shell length distributions than males were found (Table 3). However, at were 24-25 mm for females and 23-24 mm Olango Island, the sex ratio was almost 1:1. In for males at Hanase Station 1, 26-27 mm all sampling sites, we did not find a statistically for females and 23-24 mm for males at significant difference in the sex ratio (P > 0.05; Tokunoshima Island, 20-21 mm for both Fisher’s exact test). females and males at Nogas Island and The ranges of the shell length of both sexes 21-22 mm for females and 18-19 mm for males overlapped widely in all sampling sites (Table at Olango Island (Fig. 3). 3). The mean shell length of females was sig- nificantly larger than that of males at Hanase Discussion Station 1 (23.5 ± 1.9 mm, n = 114 for females and 22.3 ± 1.9 mm, n = 81 for males) and Densities and resource levels of M. annulus in the at Olango Island (19.4 ± 1.7 mm, n = 15 for Philippines and southern Japan females and 18.0 ± 1.3 mm, n = 15 for males). Our results showed that the population den- While there was no significant difference in the sity of M. annulus in the tropical area (the shell lengths between females (20.6 ± 1.3 mm, Philippines) was intermediate of that in the n = 14) and males (20.5 ± 1.2 mm, n = 16) at sub-tropical and temperate (Japan) areas, Nogas Island as well as at Tokunoshima Island although the density varied among stations (24.0 ± 1.9 mm, n = 10 for females and 22.7 ± in the same geographical area. Future study 2.5 mm, n = 14 for males) (Table 3). should analyze whether these density data

Table 3. Sex ratios and shell lengths (mm) of female and male Monetaria annulus Sex ratio Range SL (mm) Mean ± SD SL (mm) Sampling sites (Female:Male) n % Female Male Female Male ＊Hanase Station 1 114:81 58:42 18-28 17-26 a 23.5±1.9 a 22.3±1.9 Tokunoshima Island 10:14 42:58 21-26 19-29 24.0±1.9 22.7±2.5 Nogas Island 14:16 47:53 19-23 19-23 20.6±1.3 20.5±1.2 Olango Island 15:15 50:50 16-22 15-20 b19.4±1.7 b18.0±1.3 ＊Data of every 2 months in Villamor and Yamamoto (2015) were pooled and analyzed. aP < 0.0001; Student’s t-test bP < 0.01; Student’s t-test

n n n n

n n n n No. of samples

Shell length (mm)

Fig. 3. Shell length (mm) of female and male Monetaria annulus at different sampling sites. Graphs at Hanase Station 1 were drawn using the data of Villamor and Yamamoto (2015). Population characteristics of Monetaria annulus 279 reflect the population abundance at each island difference of almost 100-fold in their densities. and geographical area. The very low density found at Olango Island Sampling surveys at each study site were could have been influenced by overexploitation conducted only once (except at Hanase and by humans. The island has a very dense human Nogas Island). If the population abundance of population and has many shell craft factories M. annulus is seasonally variable, we cannot in operation. Cowries are harvested by shell compare the data obtained over several sea- collectors using a push net or ‘sud-sud’, a tri- sons. Seasonal changes in the density of M. angle-shaped net supported by bamboo poles annulus can be the result of recruitment. M. pushed on the surface of a sandy-muddy sub- annulus has a very long reproductive season strate in shallow waters. This fishing gear is in the temperate area (Villamor and Yamamoto considered destructive because it has a very 2015), whereas in sub-tropical (Katoh 1989) fine mesh net that indiscriminately gathers very and tropical areas (Frank 1969), reproduction small shells. occurs all year round without detectable peaks. At Hanase, we observed that the density grad- Habitat difference between mature and immature ually increased from June to December 2010 M. annulus (highest density 0.7 ± 2.0 ind./m2, n = 230), In the present study, we found that juveniles dropped in February 2011 (lowest density 0.1 and sub-adults contributed a very low pro- ± 0.6 ind./m2, n = 46), and gradually increase portion or were absent within the same hab- again from April 2011 (Villamor unpubl. data). itat of adults, except for Nogas Island in the However, the difference between the highest Philippines. We suggest three hypotheses to and lowest density was approximately five-fold, explain these data: (1) the life cycle of this spe- while the density difference among stations or cies has a low recruitment rate but a high juve- areas was greater than ten-fold. Therefore, it nile survival rate; (2) the recruitment rate is can be said that the seasonal change in the den- high but they have short juvenile and sub-adult sity, if any, did not affect the varying densities in stages and a long adult stage and; (3) mature the present study. (adult) and immature (juvenile and sub-adult) Conversely, the varying densities may be a M. annulus individuals prefer different habitats. result of differences in the methodology of col- Hypothesis (1) proposes a life cycle that is lection. In the survey method used in Amami unusual for marine invertebrates. We observed and Tokunoshima islands, quadrats were set in that the percentage of juveniles and sub-adults the area where M. annulus was found. At the was very low at all the surveyed stations. other survey stations, except for Tanegashima However, we found that the percentage of juve- Island in Japan, the area in which quadrats niles was greater than 30% during November were set included areas devoid of M. annulus. 2012 at Nogas Island. Hence, we can disregard It can be expected that compared with tropi- this hypothesis. cal and temperate areas, the population den- Hypothesis (2) infers that juveniles and sub- sity was overestimated in the sub-tropical area. adults grow and mature rapidly. Katoh (1989) Conversely, we can compare the highest den- reported that juveniles need at least 6 weeks sity among geographical areas. The highest to reach the adult stage in Okinawa, Japan. density in the tropical area was similar to that in He evaluated that the growth rate in the shell the sub-tropical area and larger than that in the length of juveniles (approximately 1.0 mm temperate area. week－1) and sub-adults (approximately 0.1- The results indicated that the resource level 0.5 mm week－1) was much greater than that of of this species in the tropical area was slightly adults (0-0.1 mm week－1) in the field. Indeed, higher than that in temperate area, and it may juveniles and sub-adults of this species grow be lower than that in the sub-tropical area. Even rapidly. However, we think that this hypothesis among islands in the tropical area, we found a can be rejected for the same reason we rejected 280 S. Villamor and T. Yamamoto hypothesis (1). Sex ratio and sexual size dimorphism among pop- Hypothesis (3) presumes that juveniles and ulations sub-adults inhabit a different habitat from adult In the present study, we determined the sex M. annulus in the surveyed areas, except for of adult M. annulus by histological analysis and Nogas Island. In Okinawa, Katoh (1989) sam- measured the length of each shell to distinguish pled juvenile and sub-adult cowries in the same sexual dimorphism. We found more males than intertidal habitat as adults. However, juveniles females at two sampling sites (Tokunoshima were not found in the area that was completely and Nogas islands) and more females at one exposed during low tides at mid-day during site (Hanase Station 1), however, there were summer. If Hypothesis (3) is correct, it can be no statistically significant differences in the presumed that there were suitable habitats sex ratio at any of the sampling sites (P > 0.05; for juveniles within the sites surveyed only at Fisher’s exact test). In Okinawa, Katoh (1989) Nogas Island. However, we could not find any found a greater number of female M. annulus differences between the environmental con- individuals (n = 105) than males (n = 88). For dition of the survey area at Nogas Island and M. caputdraconis (Melvill, 1888) collected on that of the other survey areas, particularly at Easter Island, 60% (n = 365) were females, and Sulangan Island (Table 4). Because a slight dif- the difference was significant at various sites ference in topography may result in a change on various dates (Osorio et al. 1999). Schilder in the environmental condition during a cer- and Schilder (1961) found that the dominance tain season, future studies should be conducted of females (55%) of M. moneta and Erosaria over different seasons to determine the habitat helvola was statistically insignificant. There conditions preferred by juveniles. was a 1 : 1 female to male ratio of M. moneta at MPAs are essential for the management of Enewetak, Marshall Islands (Renaud 1976). this important resource. MPAs must include a Among populations of M. annulus, the mean nursery ground where immature cowries can body size varies widely, with females being be sheltered. Further study is required to deter- larger than males (Irie and Adams 2007; Irie mine the habitat suitable for juvenile recruit- and Morimoto 2008). Our samples revealed that ment and growth. the mean shell length of females was signifi- cantly larger than that of males in the temperate

Table 4. Characteristics of Monetaria annulus habitats in the intertidal shores of different sampling sites Habitat Fishery Human Area Sampling site Topography Substrate Vegetation pressure settlement cobbles Temperate Kyushu Island rocky irregular algae low absent boulders cobbles Tanegashima Island rocky flat algae unknown present boulders sand Sub-tropical Amami Island rocky flat cobbles algae unknown absent coral rubbles sand algae Tokunoshima Island rocky flat cobbles unknown absent seagrass coral rubbles sand algae Tropical Sulangan Island rocky flat high absent coral rubbles seagrass sand algae Nogas Island rocky flat high absent coral rubbles seagrass sand/mud algae Olango Island rocky flat very high present coral rubbles seagrass Population characteristics of Monetaria annulus 281 area at Hanase Station 1. In the sub-tropical Prof. Hiroshi Suzuki (Faculty of Fisheries, area at Tokunoshima Island, the mean shell Kagoshima University) for their support with length of females was not significantly larger laboratory facilities and valuable advice. We than that of males; however, the modes of the appreciate Dr. Gregory N. Nishihara (Institute shell length distributions were larger in females for East China Sea Research, Nagasaki than in males. Statistically, no significant dif- University) and the editor of Aquaculture ference was found between the shell lengths Science for their useful comments that helped of females and males because the sample size us improve our paper. This study was supported may be small in Tokunoshima Island. In the by Japan MEXT Scholarship. tropical area, there was no significant differ- ence in the mean shell lengths between sexes References at Nogas Island, while there was a statistically significant difference at Olango Island. In Floren, A. (2003) The Philippine Shell Industry with Special Focus on Mactan, Cebu. Coastal Resource Zanzibar, the shell length of adult females was Management Project, Department of Environment larger than that of adult males, although the and Natural Resources and United States Agency for difference was not compared statistically (Orr International Development, Cebu, Philippines, 50 pp. 1959). At the Ellice Islands, Marshall Islands in Foin, T. (1989) Significance of shell thickness in cowries (Mesogastropoda: Cypraeidae). Bull. Mar. Sci., 45, the central Pacific Ocean, and Mahé Island in 505-518. the in the , female M. Frank, P. (1969) Growth rates and longevity of some gas- annulus individuals were not significantly larger tropod mollusks on the coral reef at Heron Island. than males (Schilder and Schilder 1961). Oecologia, 2, 232-250. Gossling, S., T. Kunkel, K. Schumacher and M. Zilger In the present study and with the support of (2004) Use of molluscs, fish, and other marine taxa by the above mentioned studies, it was found that tourism in Zanzibar, . Biodivers. Conserv., 13, the size dimorphism between the sexes of M. 2623-2639. annulus varied among coastlines in different Huang, C., S. Zhu, J. Lin and Q. Dong (2008) Imposex of arabica on the south-eastern coast of China. geographical areas. When creating fisheries J. Mar. Biol. Assoc. U.K., 88, 1451-1457. guidelines, including controlling the collection Irie, T. (2006) Geographical variation of shell morphol- of larger individuals, we should investigate the ogy in annulus (Gastropoda: Cypraeidae). J. sex ratio and size dimorphism in each resource Molluscan Stud., 72, 31-38. Irie, T. and B. Adams (2007) Sexual dimorphism in soft population. This is because if shell gleaners body weight in adult Monetaria annulus (Family continue to collect larger shells, this practice Cypraeidae). Veliger, 49, 209-211. may lead to a higher pressure on females than Irie, T. and N. Morimoto (2008) Phenotypic plasticity on males, which will eventually result in a sex and sexual dimorphism in size at post-juvenile meta- morphosis: common-garden rearing of an intertidal ratio that is biased toward males. gastropod with determinate growth. Biol. Bull., 215, 126-134. Acknowledgments Katoh, M. (1989) Life history of the golden ring cowry Cypraea annulus (: Gastropoda) on Okinawa - The authors acknowledge the support of Island, Japan. Mar. Biol., 101, 227 233. Kay, A. (1960) The functional morphology of Cypraea Ms. Nonita Cabacaba (BFAR-Guiuan Marine caputserpentis L. and an interpretation of the relation- Fisheries Development Center), Mr. Boy ships among the Cypraeacea. Int. Rev. Ges. Hydrobiol., Saldaña (The Dive House, Nogas Island), 45, 175-196. and Dr. Filipina Sotto (University of San Natarajan, A. (1957) Studies on the egg masses and larval development of some prosobranchs from the Gulf of Carlos, Cebu City) for their logistics support Mannar and the Palk Bay. Proc. Indian Acad. Sci. B, in field surveys. We thank the undergradu- 46, 170-228. ate and post-graduate students of the Faculty Newton, E., V. Parkes and R. Thompson (1993) The effects of shell collecting on the abundance of gastropods on of Fisheries, Kagoshima University, for their Tanzanian shores. Biol. Conserv., 63, 241-245. assistance in collecting the samples. We thank Oliver, A. (2004) Guide to Seashells of the World. Prof. Yasuji Masuda, Prof. Tadahide Noro, and Publishing Group Ltd., London, 320 pp. 282 S. Villamor and T. Yamamoto

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温帯から熱帯におけるハナビラダカラ Monetaria annulus の 個体群特性

Shiela VILLAMOR・山本智子

熱帯から温帯まで幅広く分布し，主に熱帯域で重要な資源となっているハナビラダカラについて， 資源管理上重要な個体群の特性を調査した。調査は，熱帯に位置するフィリピン各地，亜熱帯の奄美 群島及び温帯に属する種子島や薩摩半島の潮間帯で行った。多くの海岸では成熟した個体に比べて未 成熟個体が極めて少なく，資源維持の観点から未成熟個体の生息環境を明らかにする必要性が示唆さ れた。雌雄比はいずれの個体群でもどちらかに有意に片寄ることはなく，いくつかの個体群では，雌 の殻長の方が有意に大きかった。工芸品として利用するため大型個体を選択的に採集する行動は雌へ の漁獲圧を高める可能性があり，長期的な資源管理において好ましくない結果をもたらす可能性があ る。以上の結果から，本種の繁殖に関する既存の研究も参考にして，資源の持続的利用のための漁業 管理の方向性を提案した。