Isao Hayashi

若狭湾西端部海域 (丹後海) における小型マクロベントスの生物帯区分と種の多様性

Grab samples of the smaller macrobenthos (>1 mm, <1g wet weight) were obtained seasonally at fourteen stations along two transects in the shallow coastal waters of the westernmost part of Wakasa Bay. According to Morisitas similarity index (Ci, two faunal groups were recognized to be present throughout the year. The boundary between them was found to lie between depths of 10 and 20 m where the silt-clay fraction increased abruptly in the sediment, although the boundary was less obvious in summer. Statistics on community structure (species diversity, species richness, and evenness) also showed marked differences between the two assemblages. The change in faunal features was found to be roughly parallel to changes in sediment characteristics. On the nearshore sandy bottom, the influence of wave action is considered to be the major factor affecting the fauna as it results in a decrease in evenness and species richness. On the other hand, on the offshore muddy bottom, stagnant conditions cause the benthic fauna to decrease in density and to bear some resemblance to those of enclosed bays. The highest species diversity was found on the silty sand bottom (20 m deep). This can be understood as an edge effect of an ecotone.

Morphological analysis of a deep-sea whelk Buccinum tsubai in the Sea of Japan

Morphometrical analyses were performed on Buccinum tsubai, a deep-sea gastropod found in the Sea of Japan, and morphological differences were examined between the gender and among the four local subpopulations of Hokkaido, Yamagata-Toyama, the Yamato Bank, and San’in which are distinguished by mitochondrial DNA sequence analysis. As a result, sexual dimorphism of B. tsubai was found. Morphological differences were also recognized among four areas which may be related to genetic differences. They are also thought to be associated with the phenotypic plasticity in response to different environmental factors in each area. B. tsubai inhabits the the upper portion of the Sea of Japan Proper Water (UJSPW); and in the UJSPW of the Yamato Basin, nutrients are comparatively abundant and the dissolved oxygen content is low. Such environmental differences may be related to morphological differences among the four areas.

Temporal fluctuation in the abundance of a semelid bivalve, Theora fragilis (A. Adams) in Maizuru Bay, Sea of Japan

The population dynamics of a semelid bivalve Theora fragilis (A. Adams) were studied in Maizuru Bay, the Sea of Japan based on data obtained through weekly or bi-weekly sampling. A sharp increase in population abundance occurred from early February to early April. However, the benthic population had almost disappeared leaving only sporadic survivors by early August. Comparison of average growth between the central and the innermost stations showed that many juveniles recruited into adult size at the latter station, where high sedimentation of particulate organic matter (POM) was observed. At the central station, the mean POM sedimentation rate was 1/3 that of the former station, and few individuals recruited into adult size. The occurrence of small juveniles was comparable at both sites. It was concluded that nutritional input is important for both recruitment into adult size and resulting fecundity.

Osmo-responsive expression of oyster amino acid transporter gene and analysis of the regulatory region involved

To elucidate the involvement of amino acid transporter in osmotic adaptation of oysters, the expression of the amino acid transporter gene in response to environmental osmotic changes was investigated. As expected, the expression of the amino acid transporter gene was increased by hyper-osmotic stress, probably to elevate intracellular osmolality. Unexpectedly, the expression was also increased by hypo-osmotic stress, and the level of expression was higher than that induced by hyper-osmotic stress. To identify the region regulating the expression of the oyster amino acid transporter gene in response to changes in environmental osmolality, the 5′-flanking region of approximately 2.3 kb upstream from the translation start site was cloned. Expression vectors with luciferase as a reporter gene driven by 5′-flanking regions with different lengths were constructed and their promoter activities were compared. As a result, the osmo-responsive regulatory region responding to osmolality by both hyper- and hypo-osmolality was found within 132 bp from the transcription start site.

Expression of HSP70 in response to heat-shock and its cDNA cloning from Mediterranean blue mussel

Expression of HSP70 in response to heat-shock was investigated at the protein and mRNA levels in Mediterranean blue mussel. Western and Northern blot analyses revealed that HSP70 was expressed following heat-shock in the mantle at both protein and mRNA levels, suggesting that gene expression of HSP70 is implicated in the cellular response to heat-shock stress in mussel. It was then attempted to clone HSP70 cDNA in order to determine the primary structure of mussel HSP70. As a result, two full-length cDNA encoding HSP70 were isolated from a cDNA library prepared from the heat-shocked mantle. The isolated cDNA consist of single open reading frames of 2067 bp and 1911 bp which encode proteins of 689 amino acids and 637 amino acids, respectively. Both HSP70 cDNA encode an ATPase do main, and a substrate-binding do main in addition to a Glu-Glu-Val-Asp (EEVD) peptide motif that is specific for cytosolic HSP70. These findings suggest that the cDNA clones obtained in the present study encode cytosolic HSP70.

Scallop DMT functions as a Ca2+ transporter

We identified a DMT (divalent metal transporter) homologous protein that functions as a Ca2+ transporter. Scallop DMT cDNA encodes a 539‐amino‐acid protein with 12 putative membrane‐spanning domains and has a consensus transport motif in the fourth extracellular loop. Since its mRNA is significantly expressed in the gill and intestine, it is assumed that scallop DMT transports Ca2+ from seawater by the gill and from food by the intestine. Scallop DMT lacks the iron‐responsive element commonly found in iron‐regulatory proteins, suggesting that it is free of the post‐transcriptional regulation from intracellular Fe2+ concentration. Scallop DMT distinctly functions as a Ca2+ transporter unlike other DMTs, however, it also transports Fe2+ and Cd2+ similar to them.

Expression of taurine transporter in response to hypo-osmotic stress in the mantle of Mediterranean blue mussel

Expression of taurine transporter in response to osmotic stress was investigated at the protein level in the mantle of the Mediterranean blue mussel by using the specific antibody raised against the carboxy-terminal region of the deduced amino acid sequence of mussel taurine transporter. Immunohistochemical observation revealed that taurine transporter was expressed in the mantle and the expression was up-regulated in response to hypo-osmotic stress, while down-regulated in response to hyper-osmotic stress. Western blot analysis revealed major protein bands corresponding to 62 kDa and 65 kDa. In response to hypo-osmotic stress, the 62 kDa band became more intense, while it became less intense when the ambient osmolality was elevated. These results suggested that the 62 kDa taurine transporter would be implicated in hypo-osmotic adaptation.

Changes of the trophic position of the Japanese flounder Paralichthys olivaceus juvenile in a sandy sublittoral area in Wakasa Bay, Sea of Japan, examined by carbon and nitrogen isotope analyses

Hokkaido Wakkanai Fisheries Experimental Station, Wakkanai, Hokkaido 097-0001, Shimoda Marine Biological Station, College of Bioresource Science, Nihon University, Shimoda, Shizuoka 415-0014, Field Science Education and Research Center, Maizuru Fisheries Research Station, Kyoto University, Maizuru, Kyoto 625-0086, and Division of Applied Bioscience, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 606-8502, Japan

Sabellaria tottoriensis n. sp. (Annelida: Polychaeta: Sabellariidae) from Shallow Water off Tottori, the Sea of Japan

A new species of the genus Sabellaria Lamarck, 1812 (Annelida: Polychaeta: Sabellariidae), is described from shallow water off Tottori, the Sea of Japan. Sabellaria tottoriensis n. sp., is gregarious with tubes constructed of sand and shell debris. The new species is distinguished by the character combination of 1 or 2 pairs of nuchal spines, two forms (long and short) of opercular paleae in the middle row, with the slender blades of long ones recurved outward. Detailed morphological features of the species are described and compared with other Japanese and worldwide congeners.

Ecological distribution of macrobenthic animals on the level bottom in maizuru Bay-I

Macrobenthos were investigated at 77 stations on the level bottom of Maizuru Bay in the spring season in 1971. Among the animals collected in this survey, two animal groups,i.e. bivalves and polychaetes, predominated.Theora lubrica was the most predominant species, occupying 39 % of the total individuals collected. An apodan holothurian,Notomastus sp.,Prionospio ehlcrsi andLumbrineris longifolia also prevailed in number.According to the similarity of the composition of eight species common in the present area, the sampling stations were classified into four categories. As the stations belonging to each category are distributed in a peculiar portion of the bay, the bay can be divided into four areas, A–D, which are characterized as follows: Area A,Theora lubrica is highly predominant; Area B, an apodan holothurian and six common polychaetes (Notomastus sp.,Lumbrineris longifolia, Paraprionospio pinnata, Glycera chirori, Tharyx sp. andPolycirrus sp.) are relatively abundant; Area C, intermediate between Areas A and B; Area D, the above-mentioned eight species are scanty. These regional divisions of the bay correspond well with those based on the physico-chemical conditions on the bottom. Benthic feature of each area of the bay was discussed in connection with the bottom environment.Comparison of the present results with the previous data has revealed a considerable decrease of population density during the past 25 years in the area concerned.