Effects of macroalgal type and water temperature on macroalgal consumption rates of the abalone Haliotis diversicolor Reeve.

ABSTRACT The Japanese abalone "tokobushi" (Haliotis diversicolor Reeve) supports a valuable fishery off Tanegashima Island, southern Japan. However, catches have been declining, probably caused by over harvesting and other factors. Understanding the effects of macroalgal type and water temperature on the consumption rates of tokobushi has applications for the management of its population such as to identify sites with appropriate quality and quantity of macroalgae and the favorable water temperature during stock enhancement. Under controlled conditions, the effects of macroalgal type and water temperature on the macroalgal consumption rates of tokobushi were evaluated. On a short-term basis (24-h feeding), consumption rates were higher on leathery brown algae (Sargassum fusiforme, Sargassum patens, Sargassum duplicatum, Sargassum alternato-pinnatum, Undaria pinnatifida and Laminaria japonica), corticated red algae (Acanthophora spicifera, Gracilaria gigas, Carpopeltis affinis and Ceramium sp.) and foliose green algae (Ulva pertusa and Enteromorpha intestinales) than on siphonous green algae (Codium spp.) and filamentous green algae (Chaetomorpha crassa and Cladophoropsis zollingeri). Averaged across 20 species of macroalgae, the mean consumption rate was 4.96 [+ or -] 0.27%[wet-TW.d.sup.-1] (wet alga and wet abalone; TW = total weight) or 1.37 [+ or -] 0.19%[dryTW.d.sup.-1] (dry alga and dry abalone). On a long-term basis (20 days feeding), tokobushi had higher consumption rates on the green alga Ulva pertusa and the brown alga Sargassum fusiforme than on the red alga Meristotheca papulosa. When presented with a choice of species (3 days feeding), tokobushi ate more of the brown alga Sargassum fusiforme and the red alga Gracilaria gigas than the green alga Codium cylindricum. Consumption rates generally increased with temperature. Generally, tokobushi prefer macroalgae with high percent dry weight composition, most of which are brown and red algae, and eat more at water temperatures around spring/fall (17[degrees]C, 21[degrees]C) and summer (27[degrees]C) in Kagoshima, Japan.

KEY WORDS: abalone, consumption rate, Haliotis diversicolor, macroalgae, temperature, tokobushi

INTRODUCTION

The abalone, Haliotis diversicolor Reeve, 1846, is a high-valued shellfish in Japan. Locally, it is called "tokobushi". Tokobushi supports a valuable fishery off Tanegashima Island, Kagoshima, Japan. However, catches have been declining steadily from 80 mt in 1980 to 6.5 mt in 2002 (Yamashita 1992, Tanegashima Fisheries Office 2002). At present, the fishery's cooperatives on the island are regulating the catch and releasing hatchery-raised juveniles in the fishing grounds to increase the wild population and hopefully boost catches. Aquaculture production is greatest in China (~4,500 mt) and Taiwan (~3,000 rot) (Gordon & Cook 2003). Farms depend mostly on cultured macroalgae for feeding stock (Chen 1989, Liao et al. 2002).

In addition to overfishing, other factors may have contributed to the declining catch observed in the tokobushi fishery. These factors include the quality and seasonality of macroalgal production and temperature changes during the different seasons.

When tokobushi feed, several macroalgal characteristics affect their consumption rate and consequently their growth. For example, the feeding rates of Haliotis discus hannai Ino and Haliotis rubra Leach are highly linked to the hardness or softness of algae (McShane et al. 1994, Corazani & Illanes 1998). Haliotis iris Martyn consumes more red algae than brown algae (Marsden & Williams 1996). Algal consumption by Haliotis midae Linnaeus and H. rubra are greatly affected by the nutritional value of the algae, and to some extent the presence of plant chemical defenses (Fleming 1995, Stepto & Cook 1996).

Being a subtropical species, tokobushi is exposed to water temperatures ranging from 5[degrees]C to 32[degrees]C (Chen 1989, pers. obs.). The behavior and overall physiology of tokobushi might be affected by these temperature fluctuations. Macroalgae that comprise the bulk of the abalone food are also subjected to similar fluctuations, causing seasonal oscillation in production (Day & Fleming 1992, Tegner et al. 2001). H. discus hannai grazing activity varies with season, with maximum intake occurring in April to June and minimum intake occurring in October to November (Hahn 1989).

This study was conducted to evaluate the influence of environmental factors (i.e., macroalgal type and temperature) on the macroalgal consumption rate of tokobushi. The findings will have application in the management of tokobushi populations, such as the need to identify stock enhancement sites with appropriate quality and quantity of macroalgae and optimal water temperature.

MATERIALS AND METHODS

In all experiments, tokobushi and macroalgae were weighed (TW) (Shimadzu EL-120 W/AC, Shimadzu Corporation, Japan), after removing excess water with a paper towel. The shell length (SL) and shell width (SW) of tokobushi were measured using a Vernier caliper. The following water quality parameters in the experimental tanks were measured daily or as indicated in the experimental protocol: temperature (mercury thermometer); pH (pH meter Yokogawa pH82, Yokogawa Electric Corporation, Japan); dissolved oxygen (DO) and salinity (oxygen meter YSI 85, YSI Incorporated, USA). All instruments were calibrated before taking the measurements.

Supply of Tokobushi

Experimental juvenile tokobushi ([congruent to] 2 years old), provided by the Kagoshima Prefecture Mariculture Association in Tarumizu City, Kagoshima, Japan, were maintained in floating net cages at the sea near the experimental station of the Faculty of Fisheries, Kagoshima University in Azuma-cho, Nagashima Island, Izumigun, Kagoshima, Japan.

Species of Macroalgae

Fresh macroalgal species collected from 4 sites in Kagoshima, Japan (Fig. 1) were maintained in indoor-lighted aerated aquaria, and used in feeding tokobushi. Their collections were as follows: (1) Sakurajima, Kagoshima Bay--Acanthophora spicifera (Vahl) Borgesen, Codium cylindricum Holmes, Codium contractum Kjellman, Codium divaricatum Holmes, Enteromorpha intestinalis (Linnaeus) Nees, Laurencia undulata Yamada, Sargassum duplicatum Bory, Sargassum fusiforme (Harvey) Setchell, Sargassum patens Agardh, Undaria pinnatifida (Harvey) Suringar; (2) Yojirogahama, Kagoshima Bay--Carpopeltis affinis (Harvey) Okamura, Chaetomorpha crassa (C. Agardh) Kuetzing, Ceramium sp., Gracilaria gigas Harvey, Hypnea charoides Lamouroux. Ulva pertusa Kjellman; (3) Azuma-cho, Nagashima Island--Laminaria japonica Areschoug, Meristotheca papulosa (Montagne) and (4) Nishino-omote, Tanegashima Island--Cladophoropsis zollingeri (Kuetzing) Reinhold, Sargassum thunbergii (Mertens ex Roth) Kuntze, and Sargassum alternato-pinnatum Yamada.

[FIGURE 1 OMITTED]

Based on their taxonomic and morphologic characteristics, the 20 species of macroalgae were classified into 5 groups (Lobban & Harrison 1994, Dawes 1998, Graham & Wilcox 2000): (1) green, soft and siphonous macroalgae--green algae with a delicate thallus and composed of big-multinucleated cells (Codium cylindricum, Codium divaricatum and Codium contractum); (2) green, soft and filamentous macroalgae--green algae with a delicate thallus and composed of uniseriate filaments (Cladophoropsis zollingeri and Chaetomorpha crassa); (3) green, soft and foliose macroalgae--green algae with a delicate thallus and composed of thin sheets of tissue (Enteromorpha intestinales and Ulva pertusa); (4) red, cartilaginous and corticated macroalgae--red algae with firm and flexible thallus with cortical cells (Gracilaria gigas, Hypnea charoides, Ceramium sp., Acanthophora spicifera, Laurencia undulata and Carpopeltis affinis); (5) brown, tough and leathery macroalgae--brown algae with strong, large and complex thallus and has many adaptations to its environment such as a bladder and large holdfast (Lamim japonica, Undaria pinnatifida, Sargassum fusiforme, Sargassum duplicatum, Sargassum patens, Sargassurn thunbergii and Sargassum alternato-pinnatum).

Experimental Protocols

Five experiments (2.3.1-2.3.5) were conducted to address two factors affecting the macroalgal consumption rates of tokobushi. All experimental tokobushi were acclimated to different macroalgal diets for at least a week before the feeding studies. A summary of the conditions in each experiment is given in Table 1.

Experiment 1.1

This experiment was conducted to determine the short-term macroalgal consumption rates of tokobushi. Experiment 1.1 used a glass aquarium (48 x 28 x 33 cm) supplied with recirculating-seawater passing through a filter system and cooler-heater system (REI-SEA LX-110 BX, Japan). Three polyvinyl chloride (PVC) pipes (10.7 x 17.0 cm) secured with a nylon mesh (~1 x 2 mm mesh) at both ends served as enclosures for the test macroalga and individual tokobushi.

The correction factor was the change in weight of the macroalga alone without tokobushi. Each trial, replicated three times, was performed on the rest of the species tested. Twenty species of macroalgae were individually tested in this experiment. The order of which macroalgal species to test was random, depending largely on the collected species from the wild.

Experiment 1.2

This experiment was conducted to investigate the consumption rates of tokobushi on a long-term basis. Eighteen 10-L plastic aquaria provided with sand-filtered seawater in a flow-through system at a rate of 1 L per minute, with moderate aeration, were used. Each aquarium was also provided with PVC gutter cut lengthwise as additional surface area. Five individuals were placed in each aquarium.

Tokobushi were fed with 3 macroalgal species, Ulva pertusa, Sargassum fusiforme and Meristotheca papulosa, representing the most common green, brown and red algae, respectively, in the locality. Each treatment was replicated three times. Every 3 weeks thereafter, water quality, weights of the remaining algae and TW of tokobushi were measured, after which the food was replenished. All macroalgal food lasted for 3 weeks in good condition, in control and in treated aquaria.

Experiment 1.3

This experiment was conducted to validate the preference on a particular macroalgal species as observed in the previous experiments by feeding tokobushi combinations of different macroalgal species. The treatments (T) were: T1 = Gracilaria gigas; T2 = Codium cylindricum + Sargassum fusiforme; T3 = Codium cylindricum + Gracilaria gigas; T4 = Sargassum fusiforme + Gracilaria gigas; T5 = Codium cylindricum + Sargassum fusiforme + Gracilaria gigas; and Treatment 6 = Control (all macroalgae). The three species were chosen randomly because they were one of the most abundant green (Codium cylindricum), brown (Sargassum fusiforme) and red (Gracilaria gigas) algae in the locality during the experiment.

Sixteen 10-L plastic aquaria, supplied with aeration and water of ambient temperature, were used. Five tokobushi were stocked in each aquarium, replicated three times. Macroalgae were measured and changed once every 3 days, along with cleaning and changing of the water.

Experiment 2.1

This experiment was conducted to investigate the effects of water temperature on short-term macroalgal consumption rate of tokobushi. Preliminary investigations showed that 15[degrees]C, 21[degrees]C and 27[degrees]C roughly represent the water temperature off Tanegashima Island during winter, spring/fall and summer, respectively. The rate of intake under natural conditions of different macroalgal species by tokobushi at these temperatures was compared according to the methodology outlined in experiment 1.1.

Experiment 2.2

This experiment was conducted to investigate the effect of water temperature on the long-term macroalgal consumption rates

by tokobushi. Nine aquaria were provided with heaters to elevate the water temperature to about 5[degrees]C higher than the ambient. The average temperature of the nine aquaria supplied with seawater of ambient temperature was 12[degrees]C ([+ or -] 2), whereas the average temperature of the nine aquaria supplied with the heaters was 17[degrees]C ([+ or -] 2). The same methodology outlined in experiment 1.2 was used in this experiment.

Determination of the Consumption Rate by Tokobushi

The differences of the initial wet weight from the final wet weight of macroalgae in relation to the correction factor from the no-abalone control at different sampling periods were used for computation of the rate of macroalgal consumption. To standardize and compare the consumption rate of each macroalga, dry weights of macroalgal species and tokobushi were determined. Five samples (5 g wet wt) of each macroalgal species were air- and sun-dried for 1 week, then oven-dried at 60[degrees]C for about 48 h until constant in weight. Ten individuals of tokobushi of different sizes, considered as samples for their cohort, were also dried following the same procedure. In all experiments, computation of the rate of macroalgal intake followed the following formulae:

correction factor (CF) = ([m.sub.1c] - [m.sub.2c])/[m.sub.1c] (1)

consumption [rate.sub.wet] (%[wetTW.d.sup.-l]) = {[([m.sub.1] - [m.sub.2] [+ or -] ([m.sub.2] x CF))]/(wetTW)} x 100/([d.sub.2] - [d.sub.1]) (2)

dry wt (%) = dry wt (g) x 100 / wet wt (g) (3)

consumption [rate.sub.dry] (%[dryTW.d.sup.-1]) = [(m x %drym)/(wetTW x %dryTW)] x 100 / ([d.sub.2] - [d.sub.1]) (4)

where: [m.sub.1c] = initial wet weight of macroalga in control (g); [m.sub.2c] = final wet weight of macroalga in control (g); [m.sub.1] = initial wet weight of macroalga in treatment (g); [m.sub.2] = final wet weight of macroalga in treatment (g); m = consumption of macroalgae in wet weight (g) or [([m.sub.1] - [m.sub.2] [+ or -] ([m.sub.2] x CF))]; wetTW = wet total weight of abalone (g); wet wt = wet weight of macroalga or abalone (g); dry wt = dry weight of macroalga or abalone (g); %drym = per cent dry weight of macroalga; %dryTW = per cent dry total weight of abalone; [d.sub.1] = day of initial measurement; and [d.sub.2] = day of final measurement.

Statistical Analysis

Differences in rates of macroalgal consumption by tokobushi in all experiments were analyzed using analysis of variance (ANOVA), or ANOVA on ranks when normality tests failed. Where differences were detected, pairwise multiple comparison procedures (Duncan's or Dunn's method, respectively) were conducted to compare means. Analyses were done using the SPSS and Sigmastat software (SPSS, Inc., Illinois, USA).

RESULTS

Effects of Macroalgal Type

Experiment 1.1

Tokobushi consumption of the different species of macroalgae varied with intake rates as low as (mean [+ or -] SE) 0.78 [+ or -] 0.23%[wetTW./d.sup.-1] (=0.28 [+ or -] 0.09%[dryTW.d.sup.-1]) for Chaetomorpha crassa, and as high as 7.32 [+ or -] 1.04%[wetTW.d.sup.-1] (=3.30 [+ or -] 0.47%[dryTW.d.sup.-1]) for Laminaria japonica. There was a significant difference in the consumption rates of tokobushi on different macroalgae (P < 0.001). Laminaria japonica and Undaria pinnatifida were taken in large amounts and significantly different from Co dium contractum, Chaetomorpha crassa, Codium cylindricum, Cladophoropsis zollingeri and Codium divaricatum, which were grazed in small amounts (Fig. 2). Most of the leathery brown, corticated red and foliose green algae had a higher percentage of dry weight (5.3% to 22.0%) than the siphonous green and filamentous green algae (2.5% to 15.3%) (Table 2). The overall mean rate of macroalgal intake by tokobushi was 4.96 [+ or -] 0.27%[wetTW.d.sup.-1] (= 1.37 [+ or -] 0.19%[dryTW.d.sup.-1]) calculated from 20 species of macroalgae).

[FIGURE 2 OMITTED]

Experiment 1.2

The rates of intake pooled across times by tokobushi of Ulva pertusa (mean [+ or -] SE; 3.19 [+ or -] 1.09%[dryTW.d.sup.-1]) were significantly different from Sargassum fusiforme (2.37 [+ or -] 0.16%[dryTW.d.sup.-1]), which was significantly higher than Meristotheca papulosa (0.44 [+ or -] 0.07%[dryTW.d.sup.-1]) (Fig. 3).

[FIGURE 3 OMITTED]

Experiment 1.3

The rates of intake of tokobushi on the combinations of Sargassum fusiforme + Gracilaria gigas and Codium cylindricum + Sargassum fusiforme + Gracilaria gigas were significantly higher than Codium cylindricum + Sargassum fusiforme. In addition, the treatments with Gracilaria gigas and Codium cylindricum + Gracilaria gigas were not statistically different from the previous three treatments (Table 3). Consumption rates were computed based on dry weights to eliminate the effects of varying water content of the macroalgae and tokobushi. In the different macroalgal combinations given to tokobushi during the culture experiment, Sargassum fusiforme (55.62%) was consumed in significantly greater quantities than Gracilaria gigas (40.03%), which was also consumed significantly more than Codium cylindricum (4.36%) (P < 0.001) (Fig. 4).

[FIGURE 4 OMITTED]

Effects of Water Temperature

Experiment 2.1

Overall, tokobushi fed significantly more at 21[degrees]C and 27[degrees]C thanat 15[degrees]C (P < 0.001) (Fig. 5). Macroalgal intake by tokobushi differed with temperature and the interaction between macroalgal species and temperature was significant (P < 0.001) (Fig. 6). At 15[degrees]C, there were significant differences in the consumption rates of tokobushi of the 20 species of macroalgae (P < 0.001). The highest grazing rates were on Ceramium sp., Undaria pinnatifida and Sargassum duplicatum. The lowest grazing rates were on Chaetomorpha crassa, Codium divaricatum and Codium contractum. At 21[degrees]C, a significant difference in the rate of intake among the 20 species of macroalgae (P < 0.001) was found. This was because of a significant difference in consumption of Laminaria japonica and Cladophoropsis zollingeri. The rates of intake of the other algal species were not statistically different. At 27[degrees]C, there were also significant differences in the rates of intake among the 20 species of macroalgae (P < 0.001). The macroalgae eaten most by tokobushi were Laminaria japonica, Undaria pinnatifida, Sargassum fusiforme, Gracilaria gigas and Ceramium sp., whereas the least taken were Codium cylindricurn, Cladophoropsis zollingeri, Chaetomorpha erassa, Codium contraetum, Codium divaricatum and Hypnea charoides.

[FIGURES 5-6 OMITTED]

Experiment 2.2

The long-term rates of macroalgal intake by tokobushi fed UIva pertusa, Sargassum fusiforme and Meristotheca papulosa were significantly different between 12[degrees]C and 17[degrees]C (P > 0.05). The rates of intake of each species were (mean [+ or -] SE) 2.54 [+ or -] 0.96, 1.88 [+ or -] 0.12 and 0.34 [+ or -] 0.04%[dryTW.d.sup.-1], respectively at 12[degrees]C and 3.83 [+ or -] 1.06, 2.87 [+ or -] 0.05 and 0.44 [+ or -] 0.10%[dryTW.d.sup.-1], respectively at 17[degrees]C.

DISCUSSION

In this study, the rates of macroalgal intake by tokobushi were probably affected by the individual characteristics of the different species of macroalgae including morphology and chemical composition. Tokobushi consumed greater quantities of brown leathery, red corticated and green foliose macroalgae in preference to green filamentous and green siphonous algae. This may be because the algal texture was easier for tokobushi to masticate and digest and so they could consume enough to meet their physiological needs. Moreover, brown and red algae contain polysaccharides like alginates, fucoidans, laminarans and galactans that make their cells mucilaginous, hence, absorbent to minerals and other nutrients (Giusti 2001, Hashim & Chu 2004, Lodeiro et al. 2005). Such condition may render the brown and red algae attractive, palatable and beneficial to herbivores like tokobushi.

Tokobushi also prefer macroalgae with a high percent dry weight as shown in high consumption rates of Laminariajaponica, Undaria pinnatifida, Sargassum spp., Ceramium sp., Carpopeltis affinis, Gracilaria gigas, Acanthophora spicifera, Hypnea charoides, Laurencia undulata, Enteromorpha intestinales and Ulva pertusa (see Table 2). Most of these macroalgae are also fed on by different Haliotis species in the wild and in culture (McShane et al. 1994, Mai et al. 1996, Serviere-Zaragoza et al. 1998, Tahil & Juinio-Menez 1999, Reyes & Fermin 2003). In addition, such macroalgae (e.g., Undaria and Laminaria) were (in this study) good food for abalone in terms of growth and food conversion efficiency (Sakai 1962a) and contained effective phagostimulants (Sakata & Ina 1992). These macroalgae may contain more nutrients and minerals as implied by its dry weight component. The higher ash content of brown algae (30% to 39%) than red algae (21%) (Ruperez 2002) may also explain why tokobushi prefer the former to the latter. Consumption rates of tokobushi were measured in wet weight and dry weight bases; however, all inferences were based on dry weights (e.g., Table 3). Dry weights turned out to be the more informative measure because estimates of macroalgal material content are not masked by water content.

Other studies showed that toughness could deter feeding of abalone (e.g., Chen 1989, Shepherd & Steinberg 1992, McShane et al. 1994). However, within the range tested, this study showed that relative toughness of macroalgae did not prevent tokobushi from feeding on brown leathery Laminaria japonica, Undaria pinnatifida and Sargassum spp. rather than the green filamentous Cha etomorpha crassa and Cladophoropsis zollingeri and the green siphonous Codium spp. (Fig. 2). The general functional-form classification of algae according to the difficulty gastropods having grazing them (Steneck & Watling 1982, Littler et al. 1983, Littler & Littler 1983) may not be applicable to tokobushi as shown by the results of this study; however, tokobushi may be classified as a general herbivore. Because algal toughness was not a major factor in the feeding of tokobushi, it is proposed that algal characteristics such as nutrient content and metabolites may be important. For instance, avoidance of some macroalgae by H. rubra seems to be related to phenolic content (Fleming 1995). The general macroalgal preference of tokobushi in this study is: brown algae > red algae > green algae. This is supported by the lower phenolic levels of the brown than the red algae (Steinberg 1985, Winter & Estes 1992), and that siphonous green algae have defensive compounds to deter herbivores (Hay 1988). In experiment 1.2, where tokobushi fed on the green foliose Ulva pertusa and the brown leathery Sargassum fusiforme but ate little of the red corticated Meristotheca papulosa, it is probable that something adverse was present or some essential nutrient was absent in Meristotheca papulosa. In this study, we measured long term consumption rates to see the sustainability of feeding by tokobushi on some macroalgae tested in short term trials. The results of the long-term experiments should have application to stock enhancement and culture management of tokobushi.

In nature, abalone may select from among the many available species of macroalgae. Some abalone prefer seaweeds that are most abundant in their habitat (Barkai & Griffiths 1986, Wood & Buxton 1996), such as Haliotis roei Gray, Haliotis laevigata Donovan, H. rubra, and Haliotis asinina Linnaeus that eat more red algae than brown and green algae because of their abundance (Shepherd & Steinberg 1992, Tahil & Juinio-Menez 1999). Similarly, the common foods for Haliotis fulgens Philippi are the seagrass Phyllospadix and the macroalgae Sargassum, Eisenia, Cryptoleura and Rhodymenia (Serviere-Zaragoza et al. 1998), whereas H. asinina feeds chiefly on benthic diatoms (Sawatpeera et al. 1998) because they are predominant in the area. In a similar study, when presented with a mixed diet H. discus hannai preferred Undaria pinnatifida (61.3%), followed by Ulva pertusa (21.3%) and then Grateloupia sparsa (Okamura) Chaing (17.4%), which Floreto et al. (1996) related to the fatty acid profile of the algae. Hatchery and grow-out rearing of tokobushi also rely heavily on fresh and dried macroalgae for food. In Japan, fresh Ulva pertusa and other species in season and dried Laminaria japonica are given to tokobushi in cages and tanks (pers. obs.). In Taiwan, Gracilaria sp. is provided to cultures in intertidal ponds (Chen 1989).

The 20 species of macroalgae with five broad morphologic classifications roughly characterize most of the macroalgae present in tokobushi's habitat. The three water temperatures represent the average seasonal temperatures in a subtropical area, like Tanegashima, where tokobushi inhabits. Therefore, an estimate of the quantity of macroalgae grazed by tokobushi in the wild can be inferred using the lumped data in this study and adjusted for temperature fluctuations. Accordingly, a population of 2-y-old tokobushi, with a collective TW of 1,000 kg, could consume 49.6 [+ or -] 0.27 kg wet wt of macroalgae daily or 18,104 [+ or -] 98.55 kg wet wt of macroalgae yearly. The seasonality of seaweeds may then be considered as a critical factor for a population of tokobushi to stay healthy and consequently produce offspring. Sakai (1962b) reported that abalone production was affected by fluctuation in algal production, which correlated to temperature and salinity changes. In Southern California, USA, the eventual demise of the red abalone (Haliotis rufescens Swainson) fishery was caused by the combined effect of overfishing, extreme climates (i.e., warm water El Nino) and reduced kelp (Macrocystis pyrifera (Linnaeus) C. Agardh) production (Tegner et al. 2001). The significant interaction of macroalgal species and temperature in this study implies that consumption rate of macroalgae by tokobushi was influenced by macroalgal type and water temperature.

Tokobushi seem to eat well from 17[degrees]C to 27[degrees]C but less from 12[degrees]C to 15[degrees]C. In the seas around Kagoshima, the former occur from late March to early December (spring, summer and fall), whereas the latter from late December to early March (winter) (unpublished data). The temperature range at which macroalgal consumption peaked in this study is similar to that reported for tokobushi in Taiwan, which was at 22[degrees]C to 27[degrees]C (Chen 1989). Further, H. iris had higher feeding activity in summer compared with other seasons (Allen et al. 2001). In spring, seaweeds are usually at their highest abundance and most dense growth (Hirata et al. 2001). During this season, water temperature and solar radiation, which are season-dependent factors, are favorable for seaweed production and consequently, the quantity and quality of food for abalone (Evans & Langdon 2000). It is recommended, therefore, that release of juvenile should be in early spring for stock enhancement of tokobushi.

CONCLUSION

Tokobushi prefers to feed on species of leathery brown algae, corticated red algae and foliose green algae than on filamentous and siphonous algae. Moreover, tokobushi consume more of the macroalgae with high percent dry weight. Water temperature also affects the macroalgal consumption rate of tokobushi. Macroalgal intake is lowest during winter and highest during spring to autumn. The findings of this study implied that areas with abundant brown and red macroalgae should support tokobushi population for stock enhancement and that hatchery-raised juvenile may be released in early spring.

ACKNOWLEDGMENTS

The authors thank the Kagoshima Prefecture Mariculture Association for providing the experimental tokobushi, Mr. Hiromori Shimabukuro for identifying most of the macroalgae, the Japanese Government Ministry of Education Science and Technology (Monbukagakusho) for a scholarship grant to the first author and Dr. Scoresby Shepherd and anonymous reviewers for input that improved the manuscript.

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LOTA B. ALCANTARA (1,3), * AND TADAHIDE NORO (2)

(1) The United Graduate School of Agricultural Sciences, Kagoshima University, Japan; (2) Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima 890-0056 Japan; (3) Western Philippines University, Sta. Monica, Puerto Princesa City, Palawan 5300, Philippines

* Corresponding author. E-mail: [e-mail]

TABLE 1.
Summary of conditions in different experiments conducted.

                                  Experiment 1

Experimental
conditions                         Expt 1.1

Temperature ([degrees]C)
Temperature ([degrees]C)        20 ([+ or -]1)
pH                            7.57 ([+ or -]0.4)
DO (mg * [L.sup.-1])          8.18 ([+ or -]0.5)
Salinity ([per thousand])     34.2 ([+ or -]0.3)
Total water exchange
  rate (1x/period)                /48 hours
Water flow                      recirculating
Macroalgae type                   20 species

Feeding frequency                 /24 hours
  (lx/period)
Abalone density
  (ab/[m.sup.-2]
   substrate area)                  15.13
Abalone TW (g)                    8.36-9.29
Abalone SL (mm)                   39.4-52.5
Abalone SW (mm)                   27.3-34.85
Duration of experiment            48 hr/run
Months conducted              April to September

                                 Experiment 1

Experimental
conditions                         Expt 1.2               Expt 1.3

Temperature ([degrees]C)
Temperature ([degrees]C)        15 ([+ or -]2)         25 ([+ or -]1)
pH                            7.20 ([+ or -]0.3)     8.6 ([+ or -]0.3)
DO (mg * [L.sup.-1])          6.26 ([+ or -]0.4)     6.5 ([+ or -]0.4)
Salinity ([per thousand])     35.1 ([+ or -]0.2)     33.5 ([+ or -]0.3)
Total water exchange
  rate (1x/period)                 /3 weeks               /3 days
Water flow                       flow-through              static
Macroalgae type                  U. pertusa,             G. gigas,
                                S. fusiforme,         C. cylindricum,
                                 M. papulosa            S. fusiforme
Feeding frequency                  /3 weeks               /3 days
  (lx/period)
Abalone density
  (ab/[m.sup.-2]
   substrate area)                  18.98                  17.70
Abalone TW (g)                    8.53-16.27             9.23-18.49
Abalone SL (mm)                   40.0-49.15            41.10-49.95
Abalone SW (mm)                    no data              26.95-34.35
Duration of experiment             88 days                53 days
Months conducted               January to April        June to August

                                            Experiment 2

Experimental
conditions                         Expt 2.1               Expt 2.2

Temperature ([degrees]C)
Temperature ([degrees]C)    15, 21, 27 ([+ or -]0)   12, 17 ([+ or -]2)
pH                            7.59 ([+ or -]0.3)     7.15 ([+ or -]0.3)
DO (mg * [L.sup.-1])          8.06 ([+ or -]0.3)     6.32 ([+ or -]0.3)
Salinity ([per thousand])     33.9 ([+ or -]0.2)     34.8 ([+ or -]0.3)
Total water exchange
  rate (1x/period)                 /48 hrs                /3 weeks
Water flow                      recirculating           flow-through
Macroalgae type                   20 species            U. pertusa,
                                                        S. fusiforme

Feeding frequency                 /24 hours               /3 weeks
  (lx/period)
Abalone density
  (ab/[m.sup.-2]
   substrate area)                  15.13                  18.98
Abalone TW (g)                    8.33-9.27              8.52-16.23
Abalone SL (mm)                   39.2-52.1              40.2-49.18
Abalone SW (mm)                   27.1-34.6               no data
Duration of experiment            48 hrs/run              88 days
Months conducted              April to September      January to April

([+ or -]SD. = standard deviation;
/ = every; lx = once; ab = abalone).

TABLE 2. Percent dry weight and consumption rates of macroalgae
in wet weight and dry weight by H. diversicolor (mean [+ or -]
SE; n = 3).

                                   Macroalgal
                                       dry
Species of macroalgae                weight

Green algae
  Enteromorpha intestinales     9.16 [+ or -] 0.10
  Ulva pertusa                  21.0 [+ or -] 0.40
  Codium divaricatum            5.72 [+ or -] 0.14
  Cladophoropsis
    zollingeri                 10.88 [+ or -] 0.53
  Codium cylindricum            2.48 [+ or -] 0.08
  Codium contractum             3.16 [+ or -] 0.23
  Chaetomorpha crassa          15.28 [+ or -] 0.31
Brown algae
  Laminaria japonica            18.8 [+ or -] 0.53
  Undaria pinnatifida          16.44 [+ or -] 0.57
  Sargassum fusiforme           12.2 [+ or -] 0.17
  Sargassum patens             17.56 [+ or -] 0.52
  Sargassum duplicatum          13.0 [+ or -] 0.52
  Sargassum
    alternato-pinnatum         17.04 [+ or -] 0.80
  Sargassum thunbergii         17.76 [+ or -] 0.25
Red algae
  Ceramium sp.                 22.04 [+ or -] 0.79
  Carpopeltis afiinis          17.96 [+ or -] 0.26
  Gracilaria gigas             10.04 [+ or -] 0.18
  Acanthophora spicifera        7.04 [+ or -] 0.07
  Hypnea charoides              7.08 [+ or -] 0.05
  Laurencia undulata            5.28 [+ or -] 0.29

                                          Consumption rate of
                                        macroalgae by tokobushi

                                     % wetTW                % dryTW
Species of macroalgae             x [d.sup.-1]            x [d.sup.-1]

Green algae
  Enteromorpha intestinales    7.46 [+ or -] 1.04    1.65 [+ or -] 0.23
  Ulva pertusa                 2.31 [+ or -] 0.34    1.16 [+ or -] 0.17
  Codium divaricatum           5.43 [+ or -] 1.65    0.74.[+ or -] 0.23
  Cladophoropsis
    zollingeri                 1.53 [+ or -] 0.52    0.40 [+ or -] 0.14
  Codium cylindricum           6.19 [+ or -] 1.47    0.37 [+ or -] 0.09
  Codium contractum            3.69 [+ or -] 0.80    0.28 [+ or -] 0.06
  Chaetomorpha crassa          0.78 [+ or -] 0.23    0.28 [+ or -] 0.09
Brown algae
  Laminaria japonica           7.32 [+ or -] 1.04    3.30 [+ or -] 0.47
  Undaria pinnatifida          7.37 [+ or -] 0.56    2.90 [+ or -] 0.22
  Sargassum fusiforme          7.84 [+ or -] 1.37    2.21 [+ or -] 0.39
  Sargassum patens             3.98 [+ or -] 0.93    1.68 [+ or -] 0.39
  Sargassum duplicatum         5.07 [+ or -] 0.88    1.58 [+ or -] 0.27
  Sargassum
    alternato-pinnatum         2.89 [+ or -] 0.72    1.18 [+ or -] 0.29
  Sargassum thunbergii         2.40 [+ or -] 0.42    1.02 [+ or -] 0.18
Red algae
  Ceramium sp.                 4.95 [+ or -] 0.44    2.61 [+ or -] 0.23
  Carpopeltis afiinis          3.49 [+ or -] 0.75    1.50 [+ or -] 0.32
  Gracilaria gigas             6.15 [+ or -] 1.69    1.48 [+ or -] 0.41
  Acanthophora spicifera       6.99 [+ or -] 1.34    1.17 [+ or -] 0.22
  Hypnea charoides             5.91 [+ or -] 0.85    1.01 [+ or -] 0.14
  Laurencia undulata           7.50 [+ or -] 1.35    0.96 [+ or -] 0.17

TABLE 3.
Wet weight and dry weight consumption rates by H. diversicolor in
culture given combinations of macroalgae (mean [+ or -] se; n = 15;
treatments having the same letter superscript do not
differ significantly).

Macroalgal Food    %wetTW x [d.sup.-1]     %dryTW x [d.sup.-1]

G. gigas           11.58 [+ or -] 0.72   2.62 [+ or -] 0.93 (ab)
C. cylindricum +
  S. fusiforme      8.85 [+ or -] 0.29   2.29 [+ or -] 0.50 (b)
C. cylindricum +
  G. gigas         12.43 [+ or -] 0.43   2.58 [+ or -] 0.70 (ab)
S. fusiforme +
  G. gigas         10.78 [+ or -] 0.64   2.77 [+ or -] 0.81 (a)
C. cylindricum +
  S. fusiforme +
  G. gigas         11.25 [+ or -] 0.48   2.77 [+ or -] 0.70 (a)