Renewal of genetic composition of a lancelet, Branchiostoma belcheri, in the Seto Inland Sea, Japan

We studied renewal of genetic composition of a lancelet, Branchiostoma belcheri, at a station in the Seto Inland Sea, Japan, using random amplified polymorphic DNA (RAPD) technique. We detected a total of 49 DNA bands from 27 individuals of 5 seasonal samples. Among these, some were specific to individual or seasonal sample. There were no bands common to all individuals. We calculated the Band Sharing Index (BSI) values for each combination of individuals. BSI was in a wide range of 0.00-0.97 and the average BSI between the individuals of a sample was remarkably different from sample to sample (0.37-0.83). In cluster analysis on the basis of BSI, largely 3 clusters were constructed, which finally connected to a single cluster at as low as about 0.2 of BSI. Besides, many clusters were constructed exclusively by a seasonal sample. These results suggest a large gene pool of lancelets in this area, the remarkable differences in gene pool size among the samples and a seasonal renewal of genetic composition at a habitat.     

Larval development of the oriental lancelet, Branchiostoma belcheri, in laboratory mass culture

We are successfully maintaining a laboratory colony of the lancelet Branchiostoma belcheri bred in the laboratory. Based on living individuals in this mass culture, morphological characteristics from the seven-day larval to benthic juvenile stages have been studied. Most striking was that later larval development of B. belcheri showed great individual variation even in a rather stable culture environment. Metamorphosis first occurred on 60 days post fertilization (dpf) and was continuously observed throughout the present study up to 100 dpf. Morphological traits such as the number of primary gill slits and body size at the start of metamorphosis are apparently affected by culture condition. Body size measured in the largest individuals showed nearly linear growth at 0.087 mm/day. The variability found in larval development calls for caution when developmental stages and chronological ages are compared between populations. However, the developmental flexibility of this animal also raises the possibility that growth and sexual maturation could be controlled artificially in captivity.     

A histochemical study of the distribution of lectin binding sites in the developing oocytes of the lancelet Branchiostoma belcheri

The distribution of carbohydrate moieties in lancelet (Branchiostoma belcheri) oocytes has been studied at different stages of development, using a peroxidase-labeled lectin incubation technique, the PAS-reaction and Alcian Blue staining. Binding sites of 5 lectins, indicating the presence of different sugar moieties (Wheat germ agglutinin (WGA) for N-acetylglucosamine, Concanavalin A (Con A) for glucose/mannose, Helix pomatia agglutinin (HPA) for N-acetyl-D-galactosamine, Ricinus communis agglutinin (RCA-I) for galactose and Ulex europaeus agglutinin (UEA-I) for fucose), were identified and were shown to undergo considerable variation during oocyte development. In the previtellogenic stage, HPA, RCA-I and UEA-I were not identified on the oocyte surface, but WGA and Con A gave strongly positive reactions at this site. In the cytoplasm, 4 lectins (Con A, HPA, RCA-I and UEA-I) gave a weak or moderate reaction, and Con A was also observed in the perinuclear region. In vitellogenic oocytes, these 4 lectins were found to also bind to the nuclear envelope, karyoplasm and nucleolus, and, with the exception of Con A, could also be found in the nuclei of more mature stages. The cytoplasmic yolk granules and Golgi vesicles of the vitellogenic oocyte, were moderately positive for Con A, HPA, RCA-I and UEA-I, but HPA, RCA-I and UEA-I were only weakly bound at the oocyte surface. In mature oocytes, all 5 lectins bound moderately or strongly to yolk granules and cell surface. HPA, RCA-I and UEA-I bound moderately or strongly to various nuclear compartments. Thus, carbohydrate content varied with the development and maturation of the oocytes, and the PAS results were in agreement with the lectin-binding results. Charged carbohydrate residues were observed in the egg envelope and Golgi bodies.These results suggest that the appearence of Con A-, HPA-, RCA-I- and UEA-I-binding glycoconjugates in the nuclei of developing oocytes show a varying pattern indicating different phases of nuclear activity which correlate with different carbohydrate synthetic activities of the oocyte.     

Distribution,abundance, and food habits of the snailfishLiparis tanakai in the Suo Sea,Seto Inland Sea

In order to examine the distribution, abundance, and food habits of the snailfish,Liparis tanakai, in the Suo Sea, western Seto Inland Sea of Japan, experimental fishing surveys were made using trawl nets on the night (1930–0340 h) of 26 May and 2 and 3 June, 1986. The study area was subdivided into 18 areas, each sampled by one trawl tow of 35 min duration. A total of 190 fish was collected during the surveys, and most fish (78.9%) were obtained from muddy substrata ranging in depth from 30 to 40 m at the middle area of the Suo Sea. The total length of the fish in the samples ranged from 72 to 273 mm. The overall length-frequency distribution formed a unimodal curve, the mode occurring at the class of 100–130 mm in total length. Of 151 fish examined, 146 (96.7%) had stomachs full of food, including a variety of small crustaceans and fish. Shrimps, especiallyCrangon affinis, ranked highest in importance in the diet ofL. tanakai. These biological data are compared with those of conspecifics from Sendai Bay, northern Honshu of Japan.     

Biology of the amphioxus,Branchiostoma belcheri in the Ariake Sea,Japan I. Population structure and growth

We investigated the population structure and growth of the amphioxus Branchiostoma belcheri for four years in the southern Ariake Sea, Japan. We counted 62-66 myotomes and 251-310 dorsal fin-ray chambers, and these results support that this species is an intermediate form of B. belcheri and its subspecies B. belcheri tsingtauense. The ratio of females to males was 1:1.12. Males were more numerous than females among small individuals (< 40 mm body length), but we found no significant differences among large animals (50 mm body length). Spawning occurred from mid June to early July. Groups of newly settled young appeared from January to June of their second year. We observed a large fluctuation between years in the numbers of newly settled young. The estimated size of one-year-old individuals was 19.4 mm in body length; within the next 12 months, they reached 32.1 mm. Three- and four-year-old individuals measured 38.6 mm and 45.8 mm, respectively. Few grew beyond 60 mm; the largest specimen collected was a 64 mm male.     

Biology of the amphioxus,Branchiostoma belcheri in the Ariake Sea,Japan II. Reproduction

We investigated the reproduction of the amphioxus Branchiostoma belcheri in the southern Ariake Sea, Japan, from 1999 to 2002. Gonads were very small or almost absent from September to December and began to develop in January. Changes in the gonad length index indicated that spawning began in mid June, after the gonads had attained maximum size. Although most gametes were extruded during the first spawning, some remained in the gonads. Shrunken gonads were much smaller but contained gametes, and the second spawning occurred around 10 July. It was unclear whether all adults spawned twice, but a large proportion of individuals did. After the first spawning, both males and females lost 30% of their body weight. Most one-year-old individuals did not spawn, and the minimum size at maturity was ca. 20 mm. We found no termination of reproduction among very large individuals. The average number of gonads was significantly larger on the right side of the body (26.2 in males and 26.1 in females) than on the left side (24.0 in males and 23.5 in females). We found two hermaphrodites in a total of 11,184 specimens examined. Each had four or three ovaries among a total of 45 or 54 gonads.     

Carbon and nitrogen content of Noctiluca scintillans in the Seto Inland Sea, Japan

The carbon and nitrogen content of Noctiluca scintillans cellsfrom the Seto Inland Sea, Japan was investigated in order toestimate its biomass in natural samples. The carbon contentof N.scintillans ranged from 123 to 627 ng C cell^–1 witha mean value of 353 ng C cell^–1, or 1.12 to 2.67 fg Cµm^–3 with a mean value of 1.98 fg C µm^–3.The nitrogen content ranged from 36.0 to 232 ng N cell^–1with a mean value of 131 ng N cell^–1, or 0.499 to 0.910fg N µm^–3 with a mean value of 0.694 fg N µm^–3.Total cell carbon and nitrogen increased but the carbon andnitrogen per cell volume decreased with increasing cell volume.The C/N ratio of the cells ranged from 2.3 to 4.4, which wasrelatively low compared with the Redfield ratio. The carbonand nitrogen content was extremely low (91.2 ng C cell^–1,41.8 ng N cell^–1) for starved cells, whereas it was extremelyhigh (528 ng C cell^–1, 205 ng N cell^–1) for cellswhich had ingested the large diatom, Coscinodiscus wailesii.Our results suggest that the carbon and nitrogen content ofN.scintillans varies depending on its physiological conditionand the type of food that it has recently consumed.     

Effect of prey concentration on growth of piscivorous Japanese Spanish mackerel Scomberomorus niphonius larvae in the Seto Inland Sea, Japan

Japanese Spanish mackerel, Scomberomorus niphonius, larvae feed almost exclusively on fish larvae from the first‐feeding stage. The relationship between the growth of S. niphonius larvae and concentration of major prey organisms of the larvae, clupeid larvae, was investigated in the Sea of Hiuchi, the central Seto Inland Sea, Japan, from 28 to 29 May 1997. Water temperature, salinity, and the concentration of clupeid larvae had no significant effect on the S. niphonius larval concentration. Mean growth rate of S. niphonius larvae varied between 0.38 and 0.64 mm day^?1. The temperature and salinity had no significant effect on the mean larval growth rate while there existed prey concentration‐dependent growth at lower prey concentration. The relationship between the mean larval growth rate (G_m) and concentration of clupeid larvae (C_C) was expressed by a logarithmic equation: G_m = 0.037 log C_C + 0.441 (n = 16, r² = 0.519, P < 0.01).     

Clutch size and body size at first reproduction in Daphnia pulicaria at different levels of food and predation

Field data from seven alpine lakes in Serra da Estrela. Portugal.show that reproduction in Daphnia may be as efficiently controlledby fish predation and copepod predation on eggs in brood cavitiesas it is by food limitation. Body length and clutch size estimatesin Daphnia pulicaria revealed high inter- and intra-populationvariability in maturation size (body size at first reproduction).and in number of eggs per clutch. Daphnia at first maturationin lakes stocked with rainbow trout were half the size of thosefound in fishless lakes (body length of 0.86–0.95 and1.55–1.81 mm. respectively). The mean number of eggs perclutch was reduced to a similar degree by food limitation, predationby fish and copepod predation on eggs in brood cavities, butthe underlying mechanisms of this reduction were different.Food limitation caused smaller clutch sizes in all individuals,so variation remained the same. Fish predation caused the selectiveremoval of individuals with maximum clutches, so variation decreased.Copepod predation caused removal of eggs from brood cavitiesof randomly infested females, so that variation increased, particularlyat a high food level when non-infested females carried largeclutches of eggs.     

Effects of temperature on growth rate and body size in the Mediterranean Sea anemone Actinia equina

Actinia equina is the most common sea anemone in the rocky intertidal zone of the Mediterranean coast of Israel, yet little is known about its biology in this habitat. We examined variation in polyp growth at several temperatures within the local range. Under laboratory conditions, only polyps at low temperatures (15 and 20 °C) grew, whereas those at higher temperatures (25 and 30 °C) lost body mass. Seasonal monitoring of pedal disk diameter over 18 months at field sites showed that polyps shrank significantly during the summer when temperatures were high. We conclude that at summer seawater temperatures along the coast of Israel (28.7-29.5 °C), polyps of A. equina are unable to balance their metabolic requirements with energy input, resulting in a seasonal reduction in biomass. Polyps appear able to acclimate to high temperatures, but not sufficiently to avoid shrinkage of tissues.     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.     

Studies on pathogenic Vibrio parahaemolyticus during a warm weather season in the Seto Inland Sea,Japan

Vibrio parahaemolyticus is a potentially pathogenic bacterium, occurring naturally in estuarine and marine environments throughout the world. The incidence of this organism in an aquatic environment depends upon many ecofactors. Sea water and organic material were collected during the warm weather season from a coast of the Seto Inland Sea, Japan, and analysed to determine V. parahaemolyticus densities and the occurrence of pathogenic strains, defined as those possessing tdh and/or trh genes by polymerase chain reaction (PCR), using isolated DNA from enrichment culture of the samples. About 99% of samples were positive for V. parahaemolyticus with densities of 3 to >1400 cells per 100 ml of water or 10 g of organic samples by the most-probable-number (MPN)-PCR technique, but only 76.6% were positive by the conventional MPN culture technique, with densities ranging from 3 to >1400 cells per 100 ml of water or 10 g of organics. Furthermore, the tdh and trh genes were positive in 41.5% and 8.5% of samples, respectively, by the MPN-PCR technique. No tdh and trh gene-positive strains were isolated by the conventional MPN culture procedure. The difference in detection between the MPN culture and the MPN-PCR techniques appeared to be significant and may be attributed to different detection sensitivities and other factors.     

文昌鱼哈氏窝结构与功能研究进展

评述了最近20多年来,国内外学者用多种技术和方法证明文昌鱼哈氏窝能够分泌多种类似脊椎动物脑垂体激素,如促性腺激素、促甲状腺素、催产素和生长激素,为100多年前勒格罗（Legros）提出文昌鱼哈氏窝与脊椎动物脑垂体同源的推测提供了确凿可靠的证据,并进一步发现哈氏窝是调节文昌鱼性腺发育和成熟的内分泌中枢。     

Reproductive seasonality of the seaweed pipefish Syngnathus schlegeli (Syngnathidae) in the Seto Inland Sea, Japan

Latitudinal variations in fitness-related traits have been reported in a variety of organisms. Intraspecific comparison of such traits among populations living under different environmental conditions is an effective approach for elucidating the cause and consequences of such latitudinal variations. In the present study, population demography, seasonal changes in somatic and reproductive conditions, and the occurrence of egg-brooding males were investigated in the seaweed pipefish, Syngnathus schlegeli, collected monthly in the Seto Inland Sea, Japan, in order to estimate the reproductive season and mating pattern. The findings were then compared with those reported for a population in Otsuchi Bay, northern Japan. We found that the reproductive season is longer in the Seto Inland Sea population (March–November) than in the Otsuchi Bay population (May–October), although reproductive activity may temporarily cease during August in the Seto Inland Sea population. Males of the Seto Inland Sea population brooded eggs that were at the same developmental stage, suggesting that males mate with only one female in a single brooding episode (i.e., monogamy)—in contrast to the Otsuchi Bay population, where a portion of males brooded eggs consisting of multiple clutches at different developmental stages, suggesting that multiple females contribute to a single brood (i.e., polygamy). Additionally, we found that the standard lengths of both males and females are approximately 30?mm smaller in the Seto Inland Sea than in the Otsuchi Bay population. These results suggest that the multiple mating by males in a single brood and the larger body size in the Otsuchi Bay population are results of fecundity selection on life history and behavioral traits to adapt to the shorter reproductive season and lower reproductive efficiency in this relatively cold environment.     

Seasonal variation in the species composition of tintinnid cilates in Hiroshima Bay, the Seto Inland Sea of Japan

Seasonal changes in the species composition of tintinnid ciliateswere examined based on time-series samples taken at 2 week intervalsover a 3 year period in Hiroshima Bay, the Seto Inland Sea ofJapan. The maximum abundance of total tintinnids over the entireperiod was 5.7 x 10³ indi viduals l^– Among 32 speciesidentified, a consistent seasonal occurrence was recognizedin 22 species. The relationships between various environmentalfactors and the abundance of each species of tintinnids wereanalyzed using principal component analysis From this analysis,the abundance of many tintinnids was revealed to be associatedwith temperature, the <20 µm size fraction of chlorophylla and water column stability, but not with the <20 µmsize fraction of chlorophyll a, nor with salinity. From theseresults, tintinnid species were divided into five associationtypes: species whose abundance increased with increasing temperature,decreasing temperature, nanophytoplankton abundance, increasingwater column mixing, or increasing water stratification coupledwith low temperature.     

Ribosomal protein in E. coli: rate of synthesis and pool size at different growth rates

Summary Relative rates of ribosomal protein synthesis _r was determined by pulsechase labeling of cell protein followed by isolation of ribosomes by electrophoresis of complete lysates on agarose gels. The agarose gel fractionation of lysates is described in detail. Cells growing in acetate, glucose and enriched glucose media had _r values of 0.09, 0.16, and 0.24, respectively. Estimates of the free pool of ribosomal protein were obtained from the kinetics of pulse-chase labeling of ribosomal particles (including precursor particles) and gave maximal values of 1.1, 2.1, and 3.1% of total ribosomal protein at the three different growth rates. The kinetics indicate that the free concentrations in the cell are not the same for all ribosomal proteins.     

青岛胶州湾口海域秋季文昌鱼的分布及栖息环境的特征

为了准确掌握青岛胶州湾口海域文昌鱼(Branchiostoma belcheri)的分布特征,2009年11月作者选择了北沙海域和南沙海域,共设34个站位,采用箱式采泥器对文昌鱼资源及栖息环境进行了调查.在北沙海域发现了较为集中的文昌鱼栖息地,栖息密度为162 ind./m2,平均生物量为11.93g/m2;优势体长为...     

Photosynthetic property and primary production of phytoplankton in sublittoral sand bank area in the Seto Inland Sea,Japan

We investigated the photosynthesis–light intensity (P–I) relationships of phytoplankton collected from a sublittoral sand bank in the Seto Inland Sea, Japan, under different temperature conditions. In spite of low chlorophyll a concentration (<3 mg m⁻³), phytoplankton had considerably high photosynthetic potential (>10 mg C (mg chl a)⁻¹ h⁻¹) in the study area. Based on the P–I relationships, we conducted numerical simulation of areal primary production using published data on water temperature, chlorophyll a concentration, and irradiance. The areal primary production ranged between 159 and 187 g C m⁻² year⁻¹. This production was within the range of typical values reported previously in deeper areas of the Seto Inland Sea. The productivity in the sand bank area was discussed in relation to water current, allochthonous resource input, and fisheries.