2002 recent advances in larval recruitment processes of scyllarid and palinurid lobsters in japanese waters

Recent Advances in Larval Recruitment Processes of Scyllarid and Palinurid Lobsters in Japanese Waters HIDEO SEKIGUCHI* and NARIAKI INOUE Faculty of Bioresources, Mie University, Kamiham

Journal of Oceanography, Vol 58, pp 747 to 757, 2002

Review

Keywords:

⋅ Larval recruitment,

⋅ phyllosoma,

⋅ puerulus,

⋅ nisto,

⋅Panulirus japonicus.

* Corresponding author E-mail: sekiguch@bio.mie-u.ac.jp

Copyright © The Oceanographic Society of Japan.

Recent Advances in Larval Recruitment Processes of

Scyllarid and Palinurid Lobsters in Japanese Waters

HIDEO SEKIGUCHI* and NARIAKI INOUE

Faculty of Bioresources, Mie University, Kamihama-cho, Tsu, Mie 514-8507, Japan

(Received 16 January 2002; in revised form 14 March 2002; accepted 16 March 2002)

Phyllosoma larvae collected to date in Japanese and Taiwanese waters have been

clas-sified into two genera (Linuparus, Panulirus) of the Palinuridae, four genera (Ibacus,

Parribacus, Scyllarides, Scyllarus) of the Scyllaridae, and one genus (Palinurellus) of

the Synaxidae However, phyllosoma larvae of three Scyllarus species (S bicuspidatus,

S cultrifer, S kitanoviriosus) are absolutely dominant among the larvae collected in

the waters Scyllarus larvae are abundant in coastal waters while those of Panulirus

are often collected in offshore/oceanic waters Based on previous and ongoing studies

dealing with spatial distributions of phyllosoma larvae in Japanese and Taiwanese

waters, it appears that phyllosoma and nisto larvae of the Scyllarus are retained within

coastal waters north of the Kuroshio Current On the other hand, the life history of

the Panulirus (particularly P japonicus) may be completed within the Kuroshio

Subgyre: their phyllosoma larvae may be flushed out from coastal waters into the

Kuroshio, then transported through the Counter Current south of the Kuroshio into

the water east of Ryukyu Archipelago and Taiwan where they attain the subfinal/

final phyllosoma or puerulus stages, once again entering the Kuroshio and dispersing

into coastal waters.

Compared to a variety of studies dealing with larval recruitment processes of two palinurid lobsters, the

west-ern Australian rock lobster Panulirus cygnus and New Zealand red rock lobster Jasus edwardsii (see Booth and

Phillips, 1994), little information had accumulated on the

early life history of P japonicus, the predominant

palinurid in Japanese waters, before 1985, when Sekiguchi (1985) advanced a hypothesis to explain the recruitment process of the species by putting together fragmentary information on its early life history and taking into ac-count water circulation within the Kuroshio Subgyre Twelve years latter, Sekiguchi (1997) examined and/or tested his hypothesis using evidence that had become available until 1997 Sekiguchi’s (1985, 1997) hypoth-esis was thereafter supported by direct evidence obtained

by Yoshimura et al (1999) and Inoue and Sekiguchi

(2001)

Our goal is to clarify the larval recruitment processes

by which P japonicus populations are maintained in

Japa-nese waters To do this, we must address several essen-tial issues, e.g (1) estimating the abundance and stock size of scyllarid and palinurid lobsters, (2) identifying phyllosoma and puerulus/nisto larvae, (3) examining the

1 Introduction

Lobsters belonging to three families (Palinuridae,

Scyllaridae, Synaxidae) pass through three phases of life

in their ontogeny: planktonic life for phyllosoma larvae,

a transition from planktonic to benthic life for puerulus/

nisto larvae, and benthic life for juveniles and adults The

phyllosoma is the long-lived, leaf-like, transparent,

plank-tonic zoea that is thought to be a poor horizontal

swim-mer but a strong vertical one The phyllosoma period

usu-ally lasts for at least several months for most scyllarid

lobsters while it is nine months and more (twenty-two

months in Jasus edwardsii) for most palinurid lobsters,

with the result that palinurid larvae can disperse over a

long distance from coastal to offshore/oceanic waters

(Booth and Phillips, 1994; Cobb, 1997) Moreover, the

puerulus is a short-lived megalopa, a strong horizontal

swimmer, which is a transitional stage between

plank-tonic phyllosoma larvae and benthic juveniles (Booth and

Phillips, 1994)

spatial distribution of the species composition and

abun-dance of the larvae as related with their behavior and

ecol-ogy, (4) advancing hypotheses to explain the larval

re-cruitment processes of the Scyllarus and the Panulirus,

particularly P japonicus, (5) examining spatial and

tem-poral variations in larval settlement and recruitment of

the lobsters, (6) understanding relationships between

lar-val recruitment strength and stock size of the lobsters,

and so on In this review, we deal mainly with the first

four issues, larval recruitment processes of Scyllarus and

Panulirus spp., particularly P japonicus Issues (5) and

(6) will be dealt with in a forthcoming paper

2 Scyllarid and Palinurid Adult Lobsters with a

Note on Geographical Distributions of Panulirus

Species

Marine fauna in Japanese and Taiwanese waters share

a wide variety of species because Ryukyu Archipelago,

southern Japan, and Taiwan belong to the subtropical/

tropical region in biogeographical terms, and are exposed

to the powerful influence of the Kuroshio Current,

flow-ing along the coasts of the Archipelago and Taiwan (Fig

1) A total of 39 adult species (31 and 33 species in

Japa-nese and TaiwaJapa-nese waters, respectively) have been

re-ported to date (Table 1) They belong to five genera

(Justitia, Linuparus, Palinustus, Panulirus, Puerulus) of the Palinuridae, six genera (Arctides, Ibacus, Parribacus,

Scyllarides, Scyllarus, Thenus) of the Scyllaridae, and one

genus (Palinurellus) of the Synaxidae However,

Panulirus species are absolutely dominant among the

palinurid lobsters and are also commercially important

to Japan and Taiwan, particularly P japonicus in Japan and three species (P japonicus, P longipes s l., P.

stimpsoni) in Taiwan (Ho and Yu, 1987; Huang et al.,

1988; Sekiguchi, 1988a) Total annual catch yields of palinurids over the last two decades have been ca 1000 tons and 200–300 tons in Japan and Taiwan, respectively

Scyllarus species may be abundant and dominant among

scyllarid lobsters, which has been supported by abundance data on phyllosoma larvae in Japanese and Taiwanese

waters (Sekiguchi, 1988a, b; Inoue et al., 2000, 2001).

However, scyllarids are not important commercially to

Japan or Taiwan, although Ibacus and Scyllarides

spe-cies are consumed locally

Until 1996, two subspecies of the commercially

im-portant Indo-West Pacific spiny lobster Panulirus longipes

were recognized (Holthuis, 1991): the western

spotted-legged form P longipes longipes and the eastern striped-legged form P longipes femoristriga Chan and Chu (1996) discussed the taxonomy of P longipes s l and

Fig 1 Current systems in the upper layer of Japanese and its neighboring waters (from Kawai, 1991), with notes on geographical

distributions of Panulirus japonicus and P longipes bispinosus (from Sekiguchi, 1988a) A, warm Kuroshio Current;

A ′ , Kuroshio-Counter Current; B, B ′ , B ″ , branches of the Kuroshio; C, cool Oyashio Current; D, warm Tsugaru Current;

E, warm Soya Current; F, warm Tsushima Current Areas with horizontal and vertical lines indicate geographical distributions

of P japonicus and P longipes bispinosus, respectively.

described a new species, P albiflagella, which they

be-lieved had previously been misidentified as P longipes

femoristriga Chan and Chu (1996) also argued that P.

longipes bispinosus was a junior subjective synonym of

P longipes femoristriga Based on the morphological

fea-tures of P longipes femoristriga specimens collected in

Japanese waters, including the Ogasawara Islands, and

also on the color patterns of their antennular flagella,

Sekiguchi (1991) divided these specimens into three

types: “Aka-ebi”, “Shirahige-ebi” and “Shironuke-ebi”

Of these types, “Shirahige-ebi” and “Shironuke-ebi” are

identical to P longipes bispinosus (=P longipes

femoristriga) and P femoristriga (P albiflagella),

respec-tively, according to Chan and Ng (2001) who examined

the nomenclature of the three species (P longipes

femoristriga, P longipes bispinosus, P albiflagella).

Thus, we believe another new Panulirus species name

will be given to “Aka-ebi” in the Ogasawara Islands (George and Sekiguchi, pers comm.)

P japonicus is confined to Japanese and Taiwanese

waters (Fig 1), though it is abundant in northern Taiwan-ese waters while it is meager in number in Cheju Island, southern Korea (Sekiguchi, 1997) But the species has not been reported from Ogasawara and Iou Islands, from

Ryukyu Archipelago where P longipes bispinosus

re-places it, and from the central to southern parts of

Tai-Table 1 List of lobster species belonging to the three families (Palinuridae, Scyllaridae and Synaxidae) reported to date in Japanese and Taiwanese waters.

This list is based on Chan and Yu (1986, 1992, 1995), Sekiguchi (1986b), Poupin (1994), Nomura and Sekiguchi (1995), Chan and Chu (1996), Nomura (1998) and Chan and Ng (2001).

Symbols + and * indicate the species reported from Japanese and Taiwanese waters, respectively.

1 J chani+

39 Pal wieneckii+

2 J japonica+

*

3 J longimanus+

21 I ciliatus+

*

*

4 L sordidus*

5 L trigonus+

23 Par antarcticus+

*

6 Pa unicornutus+

*

7 Pa holthuisi+

8 Pa waguensis+

25 Sc haanii+

*

26 Sc squamosus+

*

Panulirus

9 P japonicus+

10 P longipes bispinosus+

* 27 S aurora+

11 P longipes longipes+

* 28 S bicuspidatus+

12 P femoristriga+

13 P homarus homarus+

* 30 S bertholdii*

14 P ornatus+

*

15 P penicillatus+

*

*

18 P versicolor+

*

36 S martensii+

*

*

19 Pu angulatus+

*

Thenus

38 T orientalis+

*

wan, where it is replaced by P homarus homarus

How-ever, both P japonicus and P longipes bispinosus have

been reported to occur together in Amami-oshima,

Tanegashima and Yakushima Islands, and in northern

Taiwan (Huang et al., 1988; Sekiguchi, 1988a, 1988b,

1989) None of P longipes bispinosus nor P japonicus

occur on the coasts of the mainland China and Russia

along the East China, Yellow and Japan Seas, because

they can not survive the severe winter (Sekiguchi, 1988a,

b) In summary, the geographical distribution of P.

japonicus is confined to coastal waters north of the

Kuroshio Current What determines this geographical

dis-tribution of P japonicus remains unclear According to

recent studies by Sekiguchi (1988a, 1989, 1995), it is

probable that the presence of either coral or rocky reefs

determines the presence of P longipes bispinosus and P.

japonicus, respectively Coral reefs are common and are

developing in the Ryukyu Archipelago, but in Taiwan they

are confined to its southern tip The northern boundary

of coral reefs in Japanese (and neighboring) waters is the

Tokara Strait between Amami-oshima and Yakushima

Is-lands, the eastern boundary lying between Torishima and

Ogasawara Islands (Takahashi, 1988) Since P japonicus

has been found in waters without coral reefs but with

rocky reefs, it is assumed that the southern boundary of

the P japonicus distribution coincides with the northern

boundary of the coral reef distribution in the western

North Pacific and also with the northern boundary of the

Kuroshio Current (Sekiguchi, 1989) According to De

Bruin (1962) and George (1967, 1974), the two

subspe-cies of P longipes are typical inhabitants of coral reef

waters, though they prefer the waters outside of coral

ar-eas This is also true of P longipes bispinosus in the

Ryukyu (Shokita et al., 1984) On the other hand, P.

japonicus typically inhabits rocky reefs directly exposed

to the ocean (Sekiguchi, 1989)

3 Identification of Phyllosoma and Puerulus/Nisto

Larvae

3.1 Phyllosoma larvae

Phyllosoma larvae collected to date in Japanese and

Taiwanese waters have been classified into three genera

(Linuparus, Panulirus, Puerulus) of the Palinuridae, four

genera (Ibacus, Parribacus, Scyllarides, Scyllarus) of the

Scyllaridae, and one genus (Palinurellus) of the Synaxidae

(Sekiguchi, 1986a, b; Sekiguchi and Saisho, 1994; Inoue

et al., 2000, 2001; Inoue and Sekiguchi, 2001) However,

phyllosoma larvae of three Scyllarus species are

abso-lutely dominant among the larvae collected in the waters

(Sekiguchi, 1986a, b; Inoue et al., 2000, 2001): S.

bicuspidatus, S cultrifer and S kitanoviriosus, the last

of which is dominant in Taiwanese waters Scyllarus

phyllosoma are abundant in coastal waters, whereas

Panulirus ones are often collected in offshore/oceanic

waters (Inoue et al., 2000, 2001; Inoue and Sekiguchi,

2001) Based on previous studies, identification keys for

phyllosoma larvae of the Scyllarus and the Panulirus are

compiled in Tables 2 and 3

Based on specimens of late-stage phyllosoma larvae

of the Panulirus collected in Japanese waters, Murano

(1971) classified these specimens into five types (Forms A–E) and tentatively identified his Form A and further

Form F described by Oshima (1942) as P japonicus This

identification was supported by Sekiguchi (1986b), and also by Inoue (1981) who succeeded in rearing eggs and

in growing phyllosoma to the final stage phyllosoma in laboratory, deducing from Forms A and F, which have width ratios of the cephalon to the thorax similar to those

of P japonicus phyllosoma larvae reared in laboratory However, since the width ratios of P longipes s l (P.

longipes bispinosus and P femoristriga in this case)

over-lap those of P japonicus, it may be difficult to distin-guish phyllosoma larvae of P japonicus from the above

two species using the width ratios and the other

morpho-logical features (Table 3; Yoshimura et al., 1999; Inoue

and Sekiguchi, 2001) Thus, as indicated by Yoshimura

et al (1999) and Inoue and Sekiguchi (2001), we can

iden-tify phyllosoma larvae of P japonicus in Japanese and

Taiwanese waters based on the following facts: the final

stage phyllosoma larvae of P longipes s l develop into the puerulus in October and later while those of P.

japonicus do mainly in summer, and that the puerulus of

the former, settles in October to April, while those of the latter, in summer

3.2 Puerulus/nisto larvae

As referred to in Table 1, six Panulirus species are found in Japanese waters: P homarus homarus, P.

japonicus, P longipes s l., P ornatus, P penicillatus and

P versicolor, of which P japonicus is absolutely

domi-nant, though P longipes bispinosus is found commonly

in Ryukyu Archipelago while “Aka-ebi” is found in the

Ogasawara Islands where the other four Panulirus spe-cies except P japonicus are reported as well as in the Ryukyu (Sekiguchi, 1991) Another Panulirus species (P.

stimpsoni and P polyphagus) are reported from Taiwan

(Table 1)

P japonicus and P longipes s l are regarded as

sib-ling species to be classified as belonging to the P.

japonicus group (P cygnus, P japonicus, P longipes s.

l., P marginatus, P pascuensis) (George and Holthuis,

1965; George and Main, 1967) This indicates that it is

difficult to distinguish larvae of P japonicus from those

of P longipes s l However, we feel there is no problem

in distinguishing pueruli of P japonicus from those of P.

longipes s l based on their morphological features

(Tanaka et al., 1984; Tanaka, 1987; Inoue et al., 2002),

though it is difficult to distinguish between phyllosoma

larvae of the above two species as mentioned above (see

Inoue and Sekiguchi, 2001) Of the above six Panulirus

species in Japanese waters, morphological features of

pueruli of four species (P homarus homarus, P japonicus,

P longipes s l., P penicillatus) were compiled for

iden-tification by Tanaka et al (1984) and Tanaka (1987)

Al-though P japonicus pueruli are dominant among

Panulirus pueruli collected in Japanese waters (Ichiki et

al., 1976; Kanamori, 1982; Tanaka et al., 1984; Tanaka,

1987), pueruli of the other five Panulirus species are also

infrequently collected in coastal waters along the Pacific

coast of southern and central parts of Japan, because they

may be transported over a long distance through the

Kuroshio Current along Ryukyu Archipelago and Taiwan

Unfortunately, it is difficult to specifically identify

Scyllarus nisto larvae in Japanese waters because

infor-mation on their morphology is unavailable

4 Hypotheses to Explain Larval Recruitment

Proc-esses of Panulirus and Scyllarus Species, with Par-ticular Reference to P japonicus

4.1 Current systems in the upper layer

Coastal to offshore/oceanic processes affect larval recruitment processes, i.e long-distance dispersal and transport of the long-lived phyllosoma larvae and also the return of the late-stage phyllosoma and puerulus/nisto larvae to coastal waters (Phillips, 1986; Cobb, 1997) As

a background to recruitment processes of Scyllarus and

Panulirus species in Japanese and Taiwanese waters, we

describe current systems in the upper layer of the west-ern North Pacific

Current systems in the upper layer of Japanese and Taiwanese waters are illustrated in Fig 1 The Kuroshio Current located east of Taiwan enters the East China Sea after passing through the strait between northern Taiwan

Table 2 Identification key for the late-stage Scyllarus phyllosoma larvae collected in Japanese and Taiwanese waters.

This table was compiled based on Sekiguchi (1986b), Inoue et al (2000, 2001) and Inoue and Sekiguchi (2001)

Identifica-tion key for scyllarid genera has been compiled in Sekiguchi (1986b).

* 1S bicuspidatus is identical with Scyllarus sp a reported by Sekiguchi (1986b)’s key and also with S bicuspidatus by

Inoue et al (2000, 2001).

* 2Scyllarus sp d and sp e are reported from Taiwanese waters by Inoue et al (2001).

*3S cultrifer is identical with S bicuspidatus reported by Sekiguchi (1986b) that identified phyllosoma larvae according to

the identification key devised by Phillips et al (1981) for the larvae collected in western Australian waters, and also with S.

cultrifer by Inoue et al (2000, 2001).

* 4According to Sekiguchi (1986b)’s key, Scyllarus sp c was identified with S cultrifer But Inoue et al (2000) made clear that these larvae were identified erroneously as S cultrifer.

1 Cephalic shield more or less trapezoidal in shape (2)

3 Telson extending beyond uropod, with two prominent posteriorly

directed lateral spines projecting beyond uropod

(4)

4 Lateral process of antenna directed anteriorly S bicuspidatus*1

5 5th pereopod with coxal spine on the basal segment Scyllarus sp d*2

5th pereopod without coxal spine on the basal segment S cultrifer*3

6 Eyestalk longer than antennule; lateral process of antenna directed anteriorly S kitanoviriosus

Eyestalk much shorter than antennule; lateral process of antenna directed laterally Scyllarus sp e*2

Eyestalk nearly equal length to or shorter than antennule (7)

7 Lateral process of antenna directed laterally S rugosus

Lateral process of antenna directed anteriorly Scyllarus sp c*4

and the southern parts of the Ryukyu Archipelago After flowing along the continental shelf edge of the Sea and then separating off the Tsushima Current that flows in the water west of Kyushu and passes through Tsushima Strait between Japan and Korea to enter the Japan Sea, the Kuroshio Current passes through Tokara Strait be-tween Amami-oshima and Yakushima Islands and flows along the Pacific coast of the southern and central parts

of Japan

Recent oceanographic studies indicate that the North Pacific Subtropical Gyre is composed of three subgyres (Fig 2): from north to south, the Kuroshio-Counter rent Subgyre (=Kuroshio Subgyre), the Subtropical Cur-rent Subgyre and the North Tropical CurCur-rent Subgyre Thus, the Counter Current that is joined to the Kuroshio Current may consist mostly of the Kuroshio water, i.e forming the Kuroshio Subgyre (Hasunuma and Yoshida, 1978) These features are supported by recent studies

us-ing satellite-trackus-ing buoys (Fig 3; Ishii et al., 1982; McNally et al., 1983; Michida and Ishii, 1993) and also

sea surface height anomaly data acquired by TOPEX/ POSEIDON and ERS altimeters (Ebuchi and Hanawa, 2001; Ichikawa, 2001)

Table 3 Identification key for the late-stage Panulirus phyllosoma larvae collected in Japanese waters.

This table was modified in part from Sekiguchi (1986b) According to Inoue and Sekiguchi (2001), two Panulirus species (P japonicus and P longipes s l.) are difficult to distinguish from each other See text for further explanation Identification key for palinurid genera, including the Palinurellus, has been compiled in Sekiguchi (1986b).

* 1To include the following four species: P longipes longipes from Taiwan, P longipes bispinosus and “Aka-ebi” from Japan, and P femoristriga from Japan and Taiwan See text for further explanation.

* 2 In the gill/final stage, the 4th pereopod bears coxal spines.

* 3 In the gill/final stage, coxal spines are present on 2nd to 4th pereopods, but ventral spines are absent.

1 Cephalic shield slightly or distinctly narrow than thorax,

coxal and subexopodal spines absent on pereopods

P japonicus

P longipes s l.*1

Cephalic shield nearly as wide as thorax or slightly narrow than thorax (2)

2 Subexopodal spines absent on pereopods,

cephalic shield less oblong than in the above 2 species

P penicillatus

3 Coxal spines present on 3rd maxilliped and 1st to 4th pereopods,

though 3rd maxilliped and 1st pereopod with only ventral coxal spines

P versicolor

Coxal spines present on 3rd maxilliped and 3rd pereopod, though ventral coxal spines only on 3rd maxilliped.

Subexopodal spines present on 1st to 3rd pereopods

P ornatus*2

Dorsal coxal spines present on 2rd to 4th pereopods, while ventral coxal spines on 3rd maxilliped and 1st pereopod

P homarus*3

Fig 2 Long-term geopotential anomaly at the sea-surface

rela-tive to the 1000-db surface in dynamic meters (10j kg–1)

(from Hasunuma and Yoshida, 1978).

The Ryukyu Archipelago is located east of the

Kuroshio Current, while the Ogasawara Islands lie south

of the Counter Current According to Ishii (1981) who

examined trajectories of satellite-tracking buoys released

across the main axis of the Kuroshio, an anti-clockwise

mid-scale eddy has been detected in the water east of

Okinawa Islands where a buoy was retained for nearly

six months (see Sekiguchi, 1997) As referred to in Nitani

(1972) and Worthington and Kawai (1972), recent

stud-ies indicate that a northward or northeastward current

passes south and east of the Ryukyu Archipelago to

coa-lesce with the main Kuroshio current passing through

Tokara Strait (Ichikawa and Beardsley, 1993; Liu et al.,

1998; Yuan et al., 1998) There are three branches of the

Kuroshio east of Taiwan (Yuan et al., 1998): the Kuroshio

in the East China Sea comes from the main (1st) and 2nd

branches of the Kuroshio east of Taiwan, and the

eastern-most (3rd) branch of the Kuroshio flows to the northeast

in the water south and east of the Ryukyu Archipelago

Considerable westward or northwestward propagating

eddies are then found in the water east of Taiwan,

indi-cating leakage of the Kuroshio water to the southeast/

east of Ryukyu Archipelago (Yang et al., 1999; Fig 4).

4.2 Larval recruitment processes

According to the review by Booth and Phillips

(1994), the early life history of spiny lobsters can be

sum-marized as follows: phyllosoma larvae appear to be poor

horizontal swimmers but swim more strongly vertically

After early-stage phyllosoma larvae are flushed out from

coastal waters into offshore/oceanic waters, where they

develop for many months, some phyllosoma larvae re-turn towards the continental shelf edge where they de-velop into the puerulus stage Puerulus larvae are megalopic, transitional between planktonic phyllosoma larvae and benthic juveniles, and complete the oceanic phase as a stronger swimmer This is also true of scyllarid phyllosoma larvae, except that their early life history is completed within coastal waters due to a shorter larval periods as compared to that of palinurid lobsters and also

to their larval strategies, which differ from those of

palinurid ones (Phillips et al., 1981; Sekiguchi, 1986a; Baisre, 1994; Inoue et al., 2000, 2001).

Fig 3 Trajectories of nine buoys in the period from 14 January 1980 to 15 May 1981 (from Ishii et al., 1982) Buoys were

deployed at the main Kuroshio west of Okinawa Islands, southern Japan Numericals indicate the position at the first day of each month.

Fig 4 Trajectories of the WOCE/TOGA drifting buoys near

Taiwan in 1993 (from Yang et al., 1999).

In relation to coastal to offshore/oceanic processes,

some behavioral traits of phyllosoma larvae, such as a

long larval period, different vertical distribution and

mi-gration related to developmental stage and so on, may

affect the dispersal and transport of the larvae Scyllarus

phyllosoma larvae have a shorter larval period of several

months while Panulirus have a larval period of nine

months and more (Booth and Phillips, 1994) Based on

previous studies dealing with the vertical distribution and

migration of phyllosoma larvae, movements appear to be

confined to nocturnal vertical migration, focused in the

upper 150 m (Phillips et al., 1981; Yeung and McGowan,

1991; Booth, 1994; Minami et al., 2001) Patterns of

ver-tical distribution and nocturnal verver-tical migration are very

similar between phyllosoma larvae of the Scyllarus and

the Panulirus (Yeung and McGowan, 1991; Minami et

al., 2001) However, Rimmer and Phillips (1979) and

Phillips et al (1981) have stated that differences in the

vertical behavior of the larvae exist between the above

two genera

Before Yoshimura et al (1999) and Inoue and

Sekiguchi (2001), there was little information on the early

life history of P japonicus in Japanese waters It can be

summarized as follows (Sekiguchi, 1997): (1) the period

for phyllosoma larvae is nearly nine months according to

Fig 5 Distribution of subfinal/final stage phyllosoma of Panulirus japonicus in the waters south of the Kuroshio Current and

east of the Ryukyu and Taiwan (from Inoue and Sekiguchi, 2001) Solid circles: sampling stations, numericals with solid

squares and open triangles: individual number of the final and subfinal stage phyllosoma larvae of P japonicus, respectively, numericals with open circles: individual number of P penicillatus, dotted lines: isopleths of 200 m depth.

culture experiments (Kittaka and Kimura, 1989;

Yamakawa et al., 1989), (2) first stage phyllosoma

lar-vae, released in summer, have been collected in Japanese coastal waters where berried females have been found (Harada, 1957; Murano, 1967), (3) benthic populations exist in waters exposed to the powerful influence of the Kuroshio Current and its branches (Sekiguchi, 1985, 1997), (4) phyllosoma larvae in middle to late-stages have rarely been collected in Japanese coastal waters north of the Kuroshio (Sekiguchi, 1985, 1997), and (5) pueruli settle in Japanese coastal waters commonly and

abun-dantly in summer (Ichiki et al., 1976; Fushimi, 1978;

Kanamori, 1982) More recently, it was shown that late-stages phyllosoma larvae are found mainly in waters south

of Kyushu and also east of the Ryukyu Archipelago,

south-ern Japan (Yoshimura et al., 1999; Inoue and Sekiguchi,

2001) Putting together the fragmentary information on

the early life history of P japonicus as related to water

circulation of the Kuroshio Subgyre, Sekiguchi (1985, 1997) advanced a hypothesis to explain the larval

recruit-ment processes that maintain P japonicus populations in

Japanese waters Subsequently, Sekiguchi’s hypothesis

was supported by direct evidence of Yoshimura et al.

(1999) and Inoue and Sekiguchi (2001) as shown in Fig 5

Therefore, based on previous and ongoing studies

dealing with spatial distributions of phyllosoma larvae in

Japanese and Taiwanese waters, it is safe to say that

phyllosoma and nisto larvae of the Scyllarus may be

re-tained within coastal waters west and north of the

Kuroshio Current (Sekiguchi, 1985, 1986a; Inoue et al.,

2000, 2001; Inoue and Sekiguchi, 2001) Scyllarus

phyllosoma are usually abundant in coastal waters while

Panulirus ones are often found in offshore/oceanic

wa-ters (Phillips et al., 1981; Baisre, 1994; Chiswell and

Booth, 1999) On the other hand, as Sekiguchi (1985,

1997) and Inoue and Sekiguchi (2001) have indicated

(Fig 6), the life history of the Panulirus, particularly P.

japonicus, may be completed within the Kuroshio Subgyre

east and south Japanese Islands and also east of Taiwan,

so that it takes nearly one year from egg hatching to

set-tlement: their phyllosoma larvae may be flushed out from

coastal waters into the Kuroshio, be transported through

the Kuroshio-Counter Current south of the Kuroshio into

the water east of the Ryukyu Archipelago and Taiwan

where they may attain the subfinal/final phyllosoma and

puerulus stages, again entering the Kuroshio to then

dis-perse into the coastal waters Thus, individuals of P.

japonicus in both Japanese and Taiwanese waters may

belong to the same population that is sustained by a

com-mon pool of the larvae, as suggested by Sekiguchi (1985,

1997) and Inoue et al (2001).

Fig 6 Early life history of Panulirus japonicus within the Kuroshio Subgyre as related to its larval recruitment a, early stages

phyllosoma; b, middle to late stages phyllosoma; c, subfinal/final stage phyllosoma; d, puerulus Areas with vertical lines

indicate the geographical distribution of P japonicus This illustration is based on Sekiguchi (1985, 1997) and Inoue and

Sekiguchi (2001) See text for further explanation.

Based on the notion that Sekiguchi’s hypothesis

ex-plaining larval recruitment of P japonicus may be

sup-ported, the following three issues have to be explained in the near feature: (1) mechanisms by which early-stage phyllosoma larvae may be transported/flushed out into the Kuroshio from the coastal waters north of the Kuroshio, (2) mechanisms by which middle-stage phyllosoma larvae may transfer from the Kuroshio to the Counter Current, and mechanisms by which the final (subfinal) phyllosoma or pueruli may enter the Kuroshio from the waters east of Okinawa Islands and Taiwan Unfortunately, we have no information on issues (2) and (3) However, we have some information concerning

is-sue (1), i.e Panulirus phyllosoma larvae are transported into the Kuroshio while Scyllarus ones are retained within the coastal waters north of the Kuroshio (Inoue et al.,

2000, 2001), as related to the difference between larval periods of those two genera and also with no difference between the vertical distribution of these two genera

(Minami et al., 2001) Sekiguchi (1997) have predicted that most early-stage phyllosoma larvae of P japonicus

may be collected in the Kuroshio region around Hachijojima Island and neighboring waters east of the Island, so we may have a good chance to make clear the mechanisms by which the early-stage phyllosoma larvae are transported into Kuroshio from the coastal waters

We wish to express our sincere thanks to Drs J D

Booth and B F Phillips for their comments on the first

version of our manuscript

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