Nariaki Inoue

Population structure of Japanese spiny lobster Panulirus japonicus inferred by nucleotide sequence analysis of mitochondrial COI gene

The mitochondrial DNA sequence for the COI region was determined for 73 Panulirus japonicus individuals collected at three sample locations in Japan. Fifty-one haplotypes, including 69 polymorphic sites without insertion and deletion, were detected, of which three dominant haplotypes were shared among the three sample locations. The nucleotide and haplotype diversities at the three sample locations were in the ranges of 0.009–0.010 and 0.959–0.990, respectively. No significant population subdivision was detected among the sample locations based on the Fst value and net nucleotide substitution rate, and analysis of the molecular variance model (AMOVA). There was no characteristic geographic distribution pattern for these haplotypes. These results indicate there is no genetic differentiation between P. japonicus populations in Japan, and support the hypothesis that benthic individuals of P. japonicus are sustained from a population of a common pool of long-period phyllosoma larvae through long-distance larval transport within the Kuroshio Subgyre.

Distribution of late-stage phyllosoma larvae of Panulirus japonicus in the Kuroshio Subgyre

The present study was undertaken in waters south of the Kuroshio Subgyre to examine and/or test Sekiguchi’s (1985, 1997) hypothesis about the larval recruitment processes of Panulirus japonicus by which the benthic populations of the species are maintained in Japanese waters. A total of 61 Panulirus phyllosoma larvae were collected in early summer; 56 belonged to P. japonicus, of which 30 were in the final stage, 24 in the subfinal stage, and 2 were too heavily damaged to permit identification of the stage. Most of the final-stage phyllosoma larvae were found in the northern part of the waters east of the Ryukyu Archipelago, whereas the larvae in the subfinal stage were found in the southern part. The present study supports Sekiguchi’s hypothesis that late-stage P. japonicus phyllosoma larvae are transported by the Kuroshio Countercurrent into waters east of the archipelago and then again enter the Kuroshio Current.

Pearl Microstructure and Expression of Shell Matrix Protein Genes MSI31 and MSI60 in the Pearl Sac Epithelium of Pinctada fucata by In Situ Hybridization

Expression patterns of the shell matrix protein genes MSI31 and MSI60 in the pearl sac epithelium were examined by in situ hybridization 38 days after implantation, and related to pearl quality. A pearl sac that produced a nacreous pearl showed very weak expression of MSI31 and strong expression of MSI60. A pearl sac, which yielded a prismatic pearl, strongly expressed MSI31 and very weakly expressed MSI60. In a complex pearl, whose surface consisted of a mosaic of both nacreous and prismatic layers, the expression pattern of MSI31 and MSI60 similarly corresponded to the underlying surface structures of the pearl. A nacreous pearl whose pearl sac showed strong MSI31 expression had an entirely nacreous surface composed of a laminar structure with unusual tablet growth at the corresponding site. MSI31 and MSI60 are the major components of the shell matrix proteins of the nacreous and prismatic layers. Clearly, high expression of MSI31 does not always result in prismatic secretion. These observations cannot be explained solely on the basis of the expression patterns of MSI31 and MSI60. We propose that, in addition to the MSI genes that form the prismatic and nacreous layers, upstream from these genes there are regulatory master genes that determine whether a nacreous layer (aragonite) or a prismatic layer (calcite) is formed.

Spatial Distributions of Phyllosoma Larvae (Crustacea: Decapoda: Palinuridae and Scyllaridae) in Taiwanese Waters

Distributions and taxonomy of phyllosoma larvae were examined in Taiwanese waters, based on ichthyoplankton samples collected from May 1990 to July 1995. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae representing 6 genera and 13 species. Of the collected phyllosoma larvae, those of Scyllarus and Panulirus species were most abundant, forming 90% of total numbers. Early stage Scyllarus and Panulirus phyllosoma larvae were abundant in Taiwanese waters. Middle to late stages (except the final stage) of Panulirus phyllosoma larvae were absent from the waters throughout the year, while those of Scyllarus phyllosoma larvae were collected in the waters. This suggests that all stages of Scyllarus phyllosoma larvae may be retained in the northern part of the waters around northern Taiwan while middle to late stages of Panulirus phyllosoma larvae may be flushed out from the waters, the sub-final and final stages then possibly returning to the waters. An anticlockwise eddy existed in the waters off northeastern Taiwan, which may be closely related to flushing out and returning of Panulirus phyllosoma larvae through a much longer planktonic period.

Vertical Distributions of Phyllosoma Larvae of Palinurid and Scyllarid Lobsters in the Western North Pacific

Vertical distributions of phyllosoma larvae were examined in waters east of the Philippines or west of the Mariana Islands (18°56′ N to 19°04′ N; 129°10′ E to 129°35′ E) based on zooplankton samples collected with an Isaacs-Kidd Midwater Trawl on September 22–24, 1986. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae comprising 4 genera and 9 species. Of the collected phyllosoma larvae, those of Scyllarus cultrifer and Panulirus longipes were most abundant and showed similar vertical distributions: (1) both species were collected from the mixed layer at night but not in the day, (2) their vertical distributions did not change with their stages, and (3) the upper limit of their vertical distributions during the day accorded with the base of mixed layer. Furthermore, their vertical distributions were similar to those of lepthocephalus larvae which were collected using the same sampling stations and gear in the present study. Vertical distributions of phyllosoma larvae were discussed in relation to their horizontal distributions.

Comparison of Expression Patterns of Shell Matrix Protein Genes in the Mantle Tissues between High- and Low-Quality Pearl-Producing Recipients of the Pearl Oyster, Pinctada fucata

The production of a cultured pearl is the result of a complex interplay between the donor and recipient oysters. However, there is a paucity of information on the relationship between donor and recipient oyster gene expression patterns and pearl quality. Shell matrix proteins affect not only the formation of the shell, but also that of the pearls. We compared the gene expression patterns of five shell matrix proteins (msi60, nacrein, msi31, prismalin-14, and aspein) in the mantle edge (ME), which forms the prismatic layer, and the mantle center (MC), which forms the nacreous layer, between high- (HP) and low quality pearl- (LP) producing recipient oysters. After culturing for about two months, ME and MC tissues were collected from nine recipient oysters: four with HP, five with LP. In the ME, the average threshold cycle (&Dgr;CT) for aspein was higher in HP than in LP (t-test, p = 0.03). Additionally, in the MC, the average &Dgr;CT for msi60 was lower in HP than in LP (p = 0.06). This means the relative expression level of msi60 in the mantle of HP was higher than that of LP, and expression level of aspein in the mantle of HP was lower than that of LP. Pearl quality was closely related to the expression patterns of shell matrix protein genes of recipient oysters.

Can long‐term variation in catch of Japanese spiny lobster Panulirus japonicus be explained by larval supply through the Kuroshio Current?

Abstract Long‐term annual variation in the catch index (CI) of Japanese spiny lobster Panulirus japonicus was examined in relation to the Kuroshio Current index (KCI). We identified two clusters (A, B) of the regions (prefectures) located east (A) and west (B) of Shionomisaki at the southern tip of Kii Peninsula, Japan. There was a significant positive relationship between the KCI at year t and the CI at year t+2 (2 years later) for cluster A. This relationship suggests annual variation in P. japonicus catch may be determined by the variation in puerulus supply through the Kuroshio Current. Relationships between the CI of these two clusters varied depending on 3 periods, which corresponded to 3 regime shifts: years before 1976, from 1977 to 1988, and after 1989. Significant negative relationships were detected between the CI of clusters A and B from 1975 to 2001, whereas a positive but non‐significant relationship was found from 1965 to 1974. Annual variation in the CI of each cluster did not have a significant relationship with the presence/absence of the large‐meander path of the Kuroshio Current.