Aquaculture Sci. 57（4），567－577（2009）

Juvenile Ecology of the Loxechinus albus in Chiloé Island, Chile

Sohei KINO

Abstract: The natural distribution of the juvenile Chilean sea urchin Loxechinus albus was investi- gated to understand the ecology of the juvenile period from May 1987 to February 1989 in eastern coastal waters of Chiloé Island, Chile. Searching for juveniles by scuba diving and observing sus- pended bivalve culture lines was conducted. Juvenile L. albus at 38.5 individuals/m2 were found in Linao in February 1989. This was the maximum density noted in this study, and the juvenile size was 2.8-7.8 mm in test diameter. The habitat of juveniles was at the tip of the peninsula, where tidal drift was optimal and the depth was less than 6 m. Moreover, the bottom was pebbles or rock bed, and shell detritus or gravel was found. On the other hand, juvenile L. albus were also found on the suspended culture lines for oysters in Linao and Hueihue. Especially in Linao, approximately 540000 juveniles of 3.5 mm in test diameter were observed attached to suspended oyster culture lines in December 1988. The possible predation of juvenile L. albus in natural waters by juvenile crabs was suggested. According to findings on juvenile ecology, a fishing bank formation mecha- nism was discussed.

Key words: Loxechinus albus; Juvenile sea urchin; Settlement; Recruitment

For basic studies on stock enhancement However, there are few reports on the juve- of the sea urchin, a grasp of the juvenile ecol- nile ecology of this species. To achieve stock ogy is one of the most important factors. In enhancement by releasing juveniles, it is essen- the Japanese sea urchin Strongylocentrotus tial to understand the juvenile ecology in natu- intermedius, natural seed collection has been ral waters. In northern Chile, juvenile L. albus developed (Kawamura 1984), and the release of are distributed in crevices with abundant shell artificial seeds is now the main method for stock detritus in the inter-tidal zone (Guisado and enhancement (Agatsuma et al. 1995; Sakai et al. Castilla 1987), but environmental parameters 2004). Artificial seeds of several species such as of the northern habitat of L. albus may differ Strongylocentrotus nudus, Tripneustes gratilla, from southern Chile (Vásquez 2001). Chile Pseudocentrotus depressus, and Hemicentrotus has a long coastline from north to south, and pulcherrimus are also used for stock enhance- the habitat of L. albus depends on the environ- ment in Japan (National Center for Stock ment of the region. Therefore, it is necessary to Enhancement 2008). In the Chilean sea urchin, grasp the regional characteristics of the habitat Loxechinus albus, artificial seed production was for juvenile L. albus. Since information on wild developed (Zamora and Stotz 1994; Cárcamo juveniles of L. albus was lacking in Chile, some 2004), and the replenishing of resources using investigations of them were carried out over artificial seeds is needed (Stotz et al. 1992; as wide an area as possible not only in east- Zamora and Stotz 1994). Moreover, juvenile set- ern coastal waters of Chiloé Island but also in tlement ecology using suspended artificial sub- coastal waters of the continent, because no site strates has been studied (Kino and Kani 2009). where abundant juveniles were observed nor Received July 8, 2009: Accepted September 2, 2009. NTEM Consulting, Inc., Nishi-shinjuku, Shinjuku-ku, Tokyo 160-0023, Japan. E-mail: [email protected]. 568 S. Kino they had recently grown was found in Chiloé ing predation, which will contribute to the stock Island. In this study, the natural distribution enhancement of this species. This is essential of juveniles was focused on in order to obtain information for the release of natural or artificial ecological information on juvenile L. albus, seeds. Additionally, the creation of a fishing bank such as on settlement and recruitment includ- of L. albus in the coastal waters was discussed.

Fig. 1. Localities and sites for investigating juvenile Loxechinus albus in eastern coastal waters of Chiloé Island and coastal waters of the continent, Chile. (●: scuba diving site, ○: inspection site of bivalve culture farm). Juvenile Ecology of Loxechinus albus 569

observation in large area was performed at the Materials and Methods sea bottom. The average depth was measured with diving depth gauge and the characteristic Field investigation sea bottom type was recorded. Although the Investigation localities and sites are shown in size of pebble is normally defined as 4-64 mm Figure 1, and natural waters (subtidal zone) and in diameter, in this study, substrate less than bivalve culture facilities were surveyed (Table approximately 100 mm which can be caught 1). The investigations were divided into three: by one hand was also recorded as pebble. On the first was a diving survey in the southern the other hand, on the third investigation, on part of Chiloé Island, the second was a diving the basis of the attachment of juvenile L. albus survey in continental waters, and the third to suspended oyster (Ostrea chilensis) cul- was a diving survey and inspection of bivalve ture lines in Linao, all the suspended culture culture farms. In the first and second investiga- lines of bivalves in Chiloé Island and Calbuco tions, the diving sites were determined based were investigated by lifting the lines to assess on the information from fisheries research- whether there were juveniles. Additionally, nat- ers and fishermen in this region. Scuba diving ural waters in Pichicolu and Linao were investi- surveys were performed by 2 divers, and the gated by scuba diving. Under artificial rearing diving time was approximately 20 minutes per conditions, L. albus grows to 18.5±3.7 mm in site, and daily diving involved 5 sites at the test diameter in 374 days (Zamora and Stotz maximum. In this survey, a square frame of 1994). Although juveniles are defined herein as 1 m or 50 cm square was used for the collec- individuals of 0 years old (<20 mm in test diam- tion of high-density juveniles, and a waterproof eter), a search for juveniles as small as possible, camera (Nikonos V, UW Nikkor 20 mm/F2.8 especially <5 mm in test diameter, was carried and Nikonos speed-light SB 103) was used to out considering recent recruitment. The sea take photographs of the natural attachment urchins collected were measured with a vernier substrate of the sea urchin. In each site, visual caliper to an accuracy of 0.1 mm.

Table 1. Contents of the investigation of juvenile Loxechinus albus in eastern coastal waters of Chiloé Island and coastal waters of the continent Investigation Period Locality Category Number of sites Measure 1st May 1987 South of Queilen Natural waters 16 Scuba diving June 1987 South of Quellón Natural waters 13 Scuba diving 2nd January 1988 Caicura Natural waters 1 Scuba diving Pichicolu Natural waters 5 Scuba diving February 1988 Talcán Natural waters 8 Scuba diving March 1988 Calbuco Natural waters 4 Scuba diving 3rd December 1988 Linao Oyster culture 1 Inspection January 1989 Pichicolu Natural waters 4 Scuba diving Calbuco Oyster culture 1 Inspection Hueihue Oyster culture 1 Inspection February 1989 Rilán Oyster culture 1 Inspection Quehui Oyster culture 1 Inspection Castro Scallop culture 1 Inspection Teupa Mussel culture 1 Inspection Compu Mussel culture 1 Inspection Detico Mussel culture 1 Inspection Huildad Mussel culture 1 Inspection Yaldad Mussel culture 1 Inspection Linao Natural waters 1 Scuba diving Oyster: Ostrea chilensis, Scallop: Agropecten purpuratus, Mussel: Mytilus chilensis. 570 S. Kino

Predation during diving surveys and its gastric contents Two species of juvenile crab, Pilumnoides were observed. perlatus (family Xanthidae) and Cancer seto- sus (family Cancridae), were found on the Results suspended collectors, and suggested to prey on juvenile L. albus (Kino and Kani 2009). Figure 2 shows the state of the sea bottom Therefore, a predation test was carried out and L. albus at principal diving sites (a-i), the with these juvenile crabs and L. albus collected suspended oyster culture lines in Linao ( j), and from suspended oyster culture lines in Linao the juvenile L. albus (juvenile Arbacia dufresnei on March 2, 1989. They were transported with also can be observed) attached to them (k and seawater to the laboratory in Hueihue and set in l). Table 2 shows the number and minimum size experiment tanks within 3 hours without feed- of juvenile L. albus collected by scuba diving with ing. Two 20-liter, transparent, acrylic plastic the sea bottom type and depth at each site in tanks were used for the experiment. Juvenile coastal waters of Chiloé Island and the continent. crabs of P. perlatus (13 individuals, 6.4-9.8 mm in carapace width) and C. setosus (6 individuals, The first investigation (May-June 1987) 13.2-23.7 mm in carapace width) were placed in In the south part of Queilen, L. albus was them, along with 15 juvenile L. albus of 4.6-5.8 found at many sites except sites 4, 6, 8, and 16. mm in test diameter, respectively. The experi- Juveniles were found at sites 3, 12, and 15. Site 3 ment lasted for six days (on March 2-7, 1989), was a rocky bed at a 15-m depth (Fig. 2-a), where and the conditions of each tank were as follows: 126 individuals of L. albus were collected, includ- seawater volume was 10 liters, initial seawater ing 30 (24%) juveniles, of which the size varied temperature and salinity were 13.5℃ and 33.0, from 11.3 to 90 mm in test diameter. Site 12 was respectively, one stone of approximately 10 cm a pebbled sea bottom of a 3-m depth, where only in diameter was set in the center at the tank one juvenile of 12.0 mm in test diameter was bottom as an attachment substrate for L. albus, found. Site 15 was also a pebbled bottom of a 3-m no aeration was set, approximately 90% of the depth (Fig. 2-b), where 4 juveniles (minimum seawater was exchanged only once on the third size: 12.0 mm) were found, and the sample size day, and an appropriate quantity of Ulva sp. was varied from 70 to 90 mm in test diameter. provided as food for L. albus. Juvenile L. albus In the south part of Quellón, L. albus was that climbed the tank walls were carefully put found at many sites excluding sites 18, 22, and back on the stone every morning with forceps, 23. Juveniles were found at only site 24 (Bajo avoiding any damage. The surviving number of Errázuriz), with a pebbled bottom of a 15-m L. albus was counted every day, and the number depth (Fig. 2-c, d), and the bottom was distinctly predated was calculated. The maximum and flat and the pebbles were covered with non- minimum seawater temperatures in 1986-88 in geniculate . L. albus was observed Hueihue were approximately 16℃ (January- on the bottom, forming variously sized groups. February) and 11℃ ( July-September), respec- The size of 3 groups was measured: group 1 was tively, however, the maximum in 1989 was lower 280 (major axis)×110 (minor axis) cm, within than those in former years showing approxi- which 213 individuals (ca. 88 indiv./m2) of L. mately 14℃ in February (Kino and Agatsuma albus were counted, including 7 (3.3%) juveniles; 2007). Consequently, this experiment (at 13.5℃ group 2 was 120×90 cm, containing 83 individu- in March) was carried out in high seawater tem- als (ca. 99 indiv./m2), including 4 (4.8%) juveniles; perature period suggesting high activity of crabs. and group 3 was 80×50 cm, with 46 individuals Except for crabs, as fish also prey upon L. albus (ca. 146 indiv./m2), including 4 (8.7%) juveniles. (Deppe and Viviani 1977), a suspected predator, The size of these juveniles varied from 9.8 to a fish of family Pinguipedidae Pinguipes chilensis, 18.2 mm, and each group contained various sizes noted in their vicinity was killed with a spear gun of individuals up to 80 mm in test diameter. Juvenile Ecology of Loxechinus albus 571

Fig. 2. Type of the sea bottom, Loxechinus albus presence at several diving sites in eastern coastal waters of Chiloé Island and coastal waters of the continent, and L. albus attached to the suspended oyster culture lines in Linao in 1987-89. a: South of Queilen site 3 (Chadmo), b: South of Queilen site 13 (Chaullin), c and d: South of Quellón site 24 (Bajo Errázuriz), e: Pichicolu site P5, f: Caicura, g and h: Talcán site T6 and T8, i: Calbuco site C2, j: Suspended oyster culture lines in Linao, k and l: L. albus attached to suspended oyster culture lines in Linao (k: with cement base and oyster, l: with only cement base).

The second investigation (January-March 1988) of 10.9 mm in test diameter. In Talcán, 8 sites In Pichicolu, sites P1, P3, P4, P5, and P6 (T1-T8) were investigated, and L. albus was were investigated, and L. albus was observed at observed at every site except T2. Juveniles every site, however, no juvenile was observed. were observed at sites T1, T6 (Fig. 2-g), T7, and Pichicolu site P5 was a rock bed of a 2-m depth T8 (Fig. 2-h), which were rock beds or pebbled with many Crepidula sp. (Fig. 2-e), and 17.5 bottoms of a 4-10-m depth with non-geniculate individuals/m2 of 25-30 mm in test diameter coralline algae. Here a total 119 individuals were found. Caicura was shell detritus bottom were collected, including 9 (7.6%) juveniles with of a 9-m depth (Fig. 2-f) and various sizes up to a minimum size of 12.3 mm in test diameter. In 60 mm in test diameter of L. albus were found. Calbuco, L. albus was observed in sites C2 (Fig. Seventy-eight individuals were collected, includ- 2-i) and C4, but there were no juveniles. ing 20 (25.6%) juveniles with a minimum size 572 S. Kino

Table 2. Juvenile Loxechinus albus collected by scuba diving, type of sea bottom, and depth at each site in eastern coastal waters of Chiloé Island and coastal waters of the continent Juvenile＊ collected Depth Locality Site Type of bottom Period (m) Number of Minimum test individuals diameter (mm) 1st investigation South of Queilen 3 Rock bed 15 30 11.3 May 1987 12 Pebbles 3 1 12.0 May 1987 15 Pebbles 3 4 12.0 May 1987 South of Quellón 24 Pebbles 15 15 9.8 Jun 1987 2nd investigation Caicura Shell detritus 9 20 10.9 Jan 1988 Talcán T1 Pebbles 10 2 12.6 Feb 1988 T6 Pebbles 4 2 12.3 Feb 1988 T7 Pebbles 4 2 12.5 Feb 1988 T8 Rock bed and pebbles 6 3 12.8 Feb 1988 3rd investigation Pichicolu P2 Pebbles 5 10.0/m2 3.0 Jan 1989 Linao Pebbles 3 15.0/m2 1.9 Feb 1989 Rock bed 6 38.5/m2 2.8 Feb 1989 ＊L. albus ＜20 mm in test diameter.

The third investigation (December 1988-February was very difficult to find them, but there was no 1989) juvenile under the pebbles. The attachment of juvenile L. albus was con- In Linao in February 1989, the eastern coast firmed to the suspended oyster culture lines in of the Linao peninsula was investigated, and Linao (Fig. 2-j) on December 27, 1988. There 15.0 individuals/m2 comprising juveniles of were 2576 suspended lines with oysters on a 1.9-3.7 mm in test diameter were found at a 3-m cement base (Fig. 2-k), and 2850 suspended depth on a pebbled bottom. Moreover, 38.5 lines with only a cement base (Fig. 2-l), of juveniles/m2 of 2.8-7.8 mm in test diameter which the length was approximately 2 m. were found slightly offshore at a 6-m depth on a Juvenile L. albus attached at rates of 171 and 35 rocky bed. Almost all of these juveniles camou- individuals per line, respectively. The total flaged themselves with algae such as Ulva sp. number attached in the facility was estimated These algae grew well, and easily drift under to be 540000 individuals. The average size of rough conditions. Juveniles of approximately juveniles was 3.5 mm in test diameter. On the more than 5 mm in test diameter attached to bottom (5-m depth) under the suspended cul- these algae. ture lines, small numbers of juveniles were found. Although only 2 juveniles were found Predation on Hueihue’s suspended oyster culture lines Table 3 shows the summary of a test of pre- excluding Linao, no juvenile was found in the dation on juvenile L. albus by two species of other bivalve culture farms. juvenile crab (P. perlatus and C. setosus). It was In Pichicolu in January 1989, sites P2, P3, apparent that these crabs preyed upon L. albus; P4, and P5 were investigated, and juveniles more than 50% of them were preyed on in six of 3.0-5.0 mm in test diameter were found at days. On daily observation, the movement of every site. Although there were very few juve- tube feet was very effective in individuals not niles at sites P3, P4, and P5, juveniles at 10.0 preyed upon, and no weak individual was noted. individuals/m2 were found at site P2 (pebbled In C. setosus, cannibalism was observed and two bottom, 5-m depth). These juveniles attached to juvenile crabs were preyed upon, while no can- the surface of pebbles, especially the sides or nibalism was noted in P. perlatus. gaps between pebbles, and covered their body The fish, P. chilensis, which inhabits rocky with shell detritus or small particles of gravel. It areas, preyed upon the juvenile L. albus. Juvenile Ecology of Loxechinus albus 573

Table 3. Summary of the experiment on the predation of Loxechinus albus in two acrylic 20-liter tanks by juvenile crabs Pilumnoides perlatus and Cancer setosus collected from the oyster culture lines in Linao (in March 1989) Tank A Tank B Juvenile crab: species Pilumnoides perlatus Cancer setosus carapace width 6.4-9.8 mm 13.2-23.7 mm number of individuals 13 6 Loxechinus albus: test diameter 4.6-5.8 mm 4.6-5.8 mm number of individuals 15 15 Number of L. albus preyed upon after 6 days 10 8 Number of crabs cannibalized 0 2

Although this fish showed no signs of the selec- L. albus, supporting the hypothesis of Dayton. tive predation of L. albus, it was verified that Consequently, the influence of freshwater or the gastric contents of this fish (approximately the sediment load should be considered for the 50 cm in total length) included the juvenile L. settlement of sea urchins. albus and A. dufresnei. Juvenile sea urchins were The natural habitat of juvenile L. albus in swallowed whole, although the size of juveniles central Chile is a cleft in a rock bed where depended on the mouth size of P. chilensis, the much shell detritus exists in the inter-tidal zone maximum size of L. albus was 12.0 mm in test (Guisado and Castilla 1987). However, there is diameter. Additionally, the predation of adult L. no detailed report on this in the coastal waters albus and A. dufresnei by an asteroid, of Chiloé Island, the former main fishing bank gelatinosus, was also observed. of L. albus in Chile. In this study, places where juvenile L. albus were at a high density (more Discussion than 10 individuals/m2) were searched for at more than 50 sites by scuba diving for about Settlement and recruitment of L. albus 3 years from 1987 to 1989. Finally, in January It is hypothesized that the absence of L. albus and February 1989, sites could be confirmed in protected areas in southern Chile has a rela- suggesting non-periodic recruitment. This sup- tionship with the unsuccessful settlement of ports the appearance of metamorphic larvae in larvae due to the low salinity and high sediment Hueihue in October 1988 (Kino 2009), and it load (Dayton 1985). In this study, the mass is the reason why juveniles were barely found attachment of juvenile L. albus to the artificial from May 1987 through March 1988, due to the substrate was observed only on the suspended fact that no metamorphic larva was observed in oyster culture lines in Linao, while a very low those periods in the study. level of juvenile attachment was observed on Places where many juveniles were observed the suspended oyster culture lines in Hueihue. were Pichicolu (10.0 individuals/m2) and Linao Although these two oyster culture sites are at (15.0 or 38.5 individuals/m2) in January or adjacent sites, the gathering and settlement of February 1989, respectively. These sites had metamorphic larvae in Hueihue were inferior the following characteristics: located at the tip to Linao because the culture site of Hueihue is of a peninsula, drift of the tide was optimal, the located in a slightly isolated place influenced depth of seawater was less than 6 m, the bottom by freshwater from a river. Juvenile were not was a pebble or rock bed, and shell detritus observed on suspended mussel culture lines. or gravel to conceal the juveniles was found. The surface of mussels was covered with These observations have a lot in common with shell epidermis, and sessile organisms were those of central Chile (Guisado and Castilla few, unlike with oysters. The accumulation of 1987). Consequently, metamorphic larvae sediment was observed at the site of mussel gather around places exhibiting these condi- attachment (byssus) on the line. These condi- tions, and settle. However, it is also a fact that tions are also unsuitable for the settlement of juveniles were found at a depth of 15 m, like 574 S. Kino at site 3 south of Queilen or site 24 south of Predation Quellón (Bajo Errázuriz), and so it is difficult From the observations in this study, juve- to precisely describe the settlement depth of niles of L. albus cover their body with small L. albus. The bottom at Bajo Errázuriz was gravel or shell detritus, or hide in algae up flat and made up of pebbles which were cov- to approximately 5 mm in test diameter. On ered with non-geniculate coralline algae, and the other hand, juveniles of more than 10 mm so it was so-called a coralline community, and in test diameter change their behavior, and other live algae were hardly found (Fig. 2-c, d). expose their body on rock or pebble surface The urchin-coralline pavement is covered with without hiding. It is believed that these dis- 90-100% of encrusting coralline algae in south- tinctive juveniles can be preyed upon easily ern Chile (54-46º S), and urchin barren pro- in natural waters. In northern Chile, the fish ceeds by the grazing of by Pimelometopon maculates and Oplegnathus L. albus (Dayton 1985). Non-geniculate coralline insignis prey upon L. albus (Deppe and Viviani algae secrete dibromomethane which induces 1977). The asteroid M. gelatinosus and south- the metamorphosis of sea urchin and abalone ern king crab Lithodes antartica also prey upon larvae, they offer a developmental niche for sea L. albus (Dayton 1985). In fact, the predation urchins, and maintain their domination utiliz- of juvenile L. albus (<12 mm in test diameter) ing the sea urchins as a grazer of other algae by the fish P. chilensis approximately 50 cm in (Taniguchi and Hasegawa 1999). From this total length and adults by the asteroid M. gela- point of view, Bajo Errázuriz exhibited favor- tinosus was observed in this study. However, able conditions for settlement, however, few since these two species were present in low juveniles were found (4-7 individuals) and their numbers according to visual observation during size was also large (9.8-18.2 mm in test diam- the diving survey, it is suggested that preda- eter), suggesting non-periodical recruitment. tion by these two species was not involved in Moreover, since the seawater current speed the decrease of L. albus in these waters. As was high (Kino and Kani 2009) and algae were for other predators, it was shown that two spe- hardly found, these conditions should seem to cies of juvenile crab, P. perlatus and C. setosus, be inappropriate for the settlement of metamor- preyed upon juvenile L. albus (<6 mm in test phic larvae and growth of post-metamorphosed diameter) in an experiment using a 20-liter tank, juvenile sea urchins. providing evidence that predation by these The growth curve of L. albus on artificial crabs could occur in natural waters. Regarding seed production indicates that it takes approxi- S. intermedius, the spider crab, Pugettia qua- mately 60 days to grow 3 mm in test diameter dridens and the bat star, Asterina pectinifera after metamorphosis (Zamora and Stotz 1994). are known to prey upon released juveniles in In the natural seed production of S. intermedius, Hokkaido, Japan, and some body parts are it takes 3 months to grow 4 mm in test diam- found at a high rate in the stomach of these 2 eter (Kawamura 1984). The size of juveniles that species after releasing juveniles (Kawai and were observed on the suspended oyster culture Agatsuma 1996). Although predation by crabs lines in Linao was 3.5 mm in test diameter on can be eliminated effectively using covering December 27, 1988. Therefore, it is suggested material such as plastic button and shell for that the settlement period of these juveniles was juvenile S. intermedius (Agatsuma 2001), the 2-3 months previous. Since 1.3 individuals/m3 of predation of juveniles has become a marked metamorphic larva were observed on October problem in natural waters. Additionally, it 3, 1988 in Hueihue situated next to Linao (Kino was shown in a tank based experiment that 2009), it was suggested that the same groups of P. quadridens also preys upon S. nudus, and it metamorphic larvae settled to the oyster culture is clear that juveniles of 10 mm in test diam- lines in Linao at the beginning of October 1988. eter are easier to be preyed upon than those of 20 mm (Shiraishi 1997). The results based on Juvenile Ecology of Loxechinus albus 575 observations in this study are very important tradictory phenomena: L. albus settles down in when considering the release site and the size shallow areas but distributes to deep areas, in of L. albus in natural waters. Making allowances spite of its behavior of being mostly sedentary. for predation by fish or crabs, the release size Namely, it is difficult to explain how juveniles should be more than 15 mm in test diameter, move this distance by themselves from a shal- but further studies on the appropriate release low to deep area according to growth in the size and period for L. albus are needed. waters. Rowley (1989) also doubts the long-dis- tance movement of juvenile sea urchins (5 mm Formation of fishing bank in test diameter). The key to this phenomenon L. albus has been found to live at depths of is drift algae. Many juvenile L. albus of approxi- 340 m (Larraín 1975). Moreover, their area of mately 5 mm in test diameter were found movement is very small, remaining mostly sed- attaching to free algae (not epiphytic Ulva sp. entary (Dayton 1985). On the other hand, in and M. pyrifera), and so they may easily drift northern Chile, settled juveniles in the inter-tidal on this substrate. These juveniles on the algae zone form a fishing bank, migrating from a tide could be transferred to deep areas by tidal cur- pool to a deeper site according to their growth rents along with the algae, settle in the deep (Stotz et al. 1992; Guisado and Castilla 1987). areas, and grow there. In other words, they In this study, the settlement depth of juveniles can move passively and distribute from shallow was estimated to be mainly <6 m. However, the to deep areas; additionally, if the sea bottom depth of some superior fishing banks of this spe- is appropriate for growth, containing rocks or cies had been formed at around 15-20 m such as pebbles, and if drift algae are found, they can Bajo Errázuriz, and sometimes more than 20 m inhabit the area irrespective of the depth. deep far from the coastline. There are thus con- Figure 3 shows a hypothetical bank formation

Fig. 3. A fishing bank formation mechanism of Loxechinus albus in eastern coastal waters of Chiloé Island. 576 S. Kino mechanism of L. albus according to the results method of stock enhancement of this species. of field observations in eastern coastal waters of The attachment of 540000 juveniles occurred on Chiloé Island. the suspended oyster culture system in Linao. (1) A superior bank is found up to 15-20 m This suggests that there still remains a natural deep. Spawning and fertilization occur method of stock enhancement, even in the face there. Echinopluteus larvae spend approxi- of the overexploitation of L. albus resources mately 1-2 months in a planktonic phase (Zamora and Stotz 1994; Palma and Arana 1996; (Kino 2009), and then metamorphic larvae Vásquez 2001). In consequence, methods for settle in shallow areas less than 6 m deep. stock enhancement must be considered that In a natural seed collection experiment, effectively employ this capacity. 99% of juvenile L. albus attached to collec- tors of less than 7 m in depth (Kino and Acknowledgements Kani 2009). (2) Since juveniles of 5 mm in test diameter This study is a part of international technical start to eat algae (Zamora and Stotz 1994), cooperation of Overseas Fishery Cooperation they attach to free algae surrounding them. Foundation between Japan and Republic of Chile. (3) The algae become drift algae with I sincerely thank Dr. Y. Agatsuma of Tohoku attached juveniles, and transport the juve- University and Dr. H. Nakagawa of Hiroshima niles to deeper sites based on the tidal University for their kind comments and sugges- current. Juveniles that are not transported tions for preparation of this manuscript. I am also by algae grow in the settlement area. grateful to Dr. K. Kawamura for his guidance and (4) At sites where there are many sea encouragement, to Mr. Ricardo Troncoso T. for urchins, algae with juveniles attached supporting the study, and to the bivalve culture become trapped by the sea urchins. farmers for permitting the inspection of their sus- (5) Juveniles settle in spaces between adult pended culture lines. sea urchins after the algae are grazed by the sea urchins. Herewith, recruitment to References deeper sites takes place. (6) Therefore, in a deep water fishing bank, a Agatsuma, Y. (1984) Stocking effect survey for artificial lack of “algae trap” occurs when sea urchins seed of Strongylocentrotus intermedius. Hokkaido Hakodate fisheries experimental station, Bulletin (1983), are over-harvested, and the chance of juve- pp. 160-167 (in Japanese). nile recruitment decreases. Consequently, Agatsuma, Y., Y. Sakai and T. Matsuda (1995) Manual for at sites where periodical recruitment is not artificial seeds stocking of the sea urchin shown, like Chiloé Island, when the density Strongylocentrotus intermedius. Hokkaido Central Fisheries Experimental Station, Hokkaido Kushiro of sea urchins decreases markedly, a vicious Fisheries Experimental Station and Hokkaido Hakodate cycle begins leading to difficulty in new Fisheries Experimental Station, 81 pp. (in Japanese). recruitment and the recovery of stock. Agatsuma, Y. (2001) Effect of the covering behavior of the In S. intermedius, released juveniles are juvenile sea urchin Strongylocentrotus intermedius on predation by the spider crab Pugettia quadridens. Fish. sometimes washed ashore attached to drift Sci., 67, 1181-1183. algae (Agatsuma 1984), and juveniles can move Cárcamo, P. (2004) Massive production of larvae and with the drift algae. Since juveniles moving seeds of the sea urchin Loxechinus albus. In “Sea with drift algae were not observed in L. albus, urchins. Fisheries and ecology” (ed. by J. M. Lawrence and O. Guzmán), EDStech publ., Lancaster, pp. 299-306. Figure 3 is no more than a hypothesis; however, Dayton, P. (1985) The structure and regulation of some it can be tested through the installation of some South American communities. Ecol. Monog., 55, artificial traps for drift algae at sites such as in 447-468. Figure 2-c. If a supply of juveniles along with Deppe, R. and C. A. Viviani (1977) La pesquería artesanal del erizo comestible Loxechinus albus (Molina) drift algae is confirmed by “algae trap”, this (Echinodermata, Echinoidea, Echinidae) en la región natural recovery capacity can be employed as a Juvenile Ecology of Loxechinus albus 577

de Iquique. Biol. Pesq. Chile, 9, 23-41. urchins (Strongylocentrotus spp.) in a sea-urchin Guisado, C. and J. Castilla (1987) Historia de vida, repro- barren ground and a kelp bed: are populations regu- ducción y avances en el cultivo del erizo comestible lated by settlement or post-settlement processes? chileno L. albus (Molina, 1782) (Echinoidea; Mar. Biol., 100, 485-494. Echinidae). In “Manejo y Desarrollo pesquero” (ed. by Sakai, Y., K. Tajima and Y. Agatsuma (2004) Stock enhance- P. Arana), pp. 59-68. ment of the short-spined sea urchin Strongylocentrotus Kawai, T. and Y. Agatsuma (1996) Predators on released intermedius in Hokkaido, Japan. In “Stock Enhancement seed of the sea urchin Strongylocentrotus intermedius and Sea Ranching. Developments, pitfalls and opportu- at Shiribeshi, Hokkaido, Japan. Fish. Sci., 62, 317-318. nity.” (ed. by K. M. Leber, S. Kitada, H. L. Blankenship Kawamura, K. (1984) Natural seed capturing, intermediate and T. Svasand), Bkackwell, Oxford, pp. 456-476. culture and repopulation of Japanese sea urchin Shiraishi, K. (1997) Effect of water temperature on the Strongylocentrotus intermedius. Hokusuishi-geppo, 41, predation of the sea urchin, Strongylocentrotus nudus. 270-315 (in Japanese). Suisanzoshoku, 45, 321-325 (in Japanese). Kino, S. (2009) Larval appearance of the sea urchin Stotz, W., S. González and C. López (1992) Siembra experi- Loxechinus albus in Chiloé Island, Chile. Aquaculture mental del erizo rojo Loxechinus albus (Molina) en la Sci., 57, 371-382. costa expuesta del centro-norte de Chile: efectos del Kino, S. and K. Kani (2009) Settlement ecology of the sea erizo negro Tetrapygus niger (Molina) sobre la perma- urchin Loxechinus albus using suspended collectors in nencia y crecimiento de los juveniles. Inves. Pesq. Chiloé Island, Chile. Aquaculture Sci., 57, 489-499. (Chile), 37, 107-117. Kino, S. and Y. Agatsuma (2007) Reproduction of sea Taniguchi, K. and M. Hasegawa (1999) Cyclic succession urchin Loxechinus albus in Chiloé Island, Chile. Fish. of marine algal communities in an infralittoral zone. In Sci., 73, 1265-1273. “The ecological mechanism of ‘Isoyake’ and marine Larraín, A. P. (1975) Los equinoídeos regulares fósiles y afforestation” (ed. by K. Taniguchi), Koseisha recientes de Chile. Gayana, Zoología, 35, 1-189. Koseikaku-120, pp. 25-37 (in Japanese). National Center for Stock Enhancement, Fisheries Vásquez, J. A. (2001) Ecology of Loxechinus albus. In Research Agency (2008), Seed production for stock “Edible Sea Urchins: Biology and Ecology” (ed. by J. M. enhancement, acquisition and releasing, sea urchin, Lawrence). Elsevier, Developments in aquaculture pp. 10-11 (in Japanese). and fisheries sceience-32, pp. 161-175. Palma, S. and P. Arana (1996) Méodo rápido de determi- Zamora, S. and W. Stotz (1994) Cultivo masivo en laborato- nación del sexo en el erizo comestible Loxechinus albus rio de juveniles de erizo Loxechinus albus (Molina, (Molina, 1782) y su aplicación en estudios biológico- 1782), (Echinodermata: Echinoidea). Invest. Pesq. pesqueros. Investig. Mar. Valparaíso, 24, 123-130. (Chile), 38, 37-54. Rowley, R. J. (1989) Settlement and recruitment of sea

チリ共和国チロエ島におけるチリウニ Loxechinus albus の 稚ウニの生態

城野草平

1987年から89年にかけてチロエ島東部海域においてチリウニ Loxechinus albus の稚ウニの分布を潜 水と貝類養殖施設調査により調べた。天然海域では Linao において1989年 2 月に38.5個体/m2 の稚ウ ニの生息が観察された。稚ウニの大きさは殻径2.8-7.8 mm であった。稚ウニの分布域は半島先端部の 潮通しのよい水深 6 m 以浅で，海底は玉石または岩盤で貝殻片や砂利が認められた。一方，Linao と Hueihue のカキ養殖連でも稚ウニが認められた。特に Linao では1988年12月に平均殻径3.5 mm の稚 ウニ54万個体の付着が観察された。Pilumnoides perlatus と Cancer setosus の稚カニによるチリウニの 食害が示唆された。稚ウニの生態から漁場形成の仕組みが議論された。