The life history and vertical distribution of the chaetognath, Sagitta elegans, in Dabob Bay, Washington

Seasonal changes in the population structure and patterns ofvertical distribution and migration of the dominant chaetognath,Sagitta elegans, in a fjord off Puget Sound were determinedwith samples collected at approximately semi-monthly intervalsfrom November 1972 to November 1973. S. elegans bred continuouslyfrom March through August, with major recruitment in June andJuly. Seasonal changes in the vertical distribution of the populationand in the proportion of the population that vertically migratedreflected the stage of maturity and size of the individuals.Small chaetognaths were non-migratory and distributed in thetop 100 m. Stage II individuals were dispersed throughout thewater column; some did migration was evident. Breeding stageswere restricted to a layer between SO and 100 m during the dayand migrated to the surface layer at night, enhancing the probabilityof successful reproduction.     

Sperm emission in the chaetognath Sagitta crassa

Sagitta crassa which had just extruded a sperm ball, togetherwith a tube-like secretion, was obtained from Tokyo Bay forthe first time. The question of spermatophores in chaetognathsis discussed.     

Copulation in the neritic chaetognath Sagitta crassa

The number of spermatophores found attached to Sagitta crassa,the dominant chateognath in Tokyo Bay, ranged from one to four.Individuals with one spermatophore were most abundant, accountingfor 70% of chaetognaths with spermatophores (A). Using the meanminimum body length of chaetognaths with spermatophores (A),those without spermatophores were subdivided into two categories:those >7 mm (B) were considered to be mature animals, andthose <7 mm (C) to be immature. The ratio of chaetognathswith spermatopbores (A) to all chaetognaths (A+B+C) varied withtime, with high values from 0040 through 0120 h as in a previousstudy. Variations in the ratio of chaetognaths with spermatophores(A) to all adults (A+B) showed a pronounced peak at 0100 h.Thus, it was confirmed that copulation of S. crassa is a periodicactivity with a peak soon after midnight. Most of the chaetognathpairs exchange one spermatophore. The frequency of copulationis considered to be two times per night at most because thechaetognaths have a single pair of seminal vesicles. However,the presence of chaetognaths with 3–4 spermatophores suggeststhat occasionally a reciprocal exchange of spermatophores doesnot occur. This could be called false copulation. It is suggestedthat copulation in S. crassa including false copulation occursat most four times per night.     

Abundance, breeding and temporal size distribution of the chaetognath Sagitta setosa in the Kattegat

During a hydrographical survey in the northern Kattegat, 1975to 1977, vertical plankton hauls were taken monthly at fourstations between Göteborg and Frederikshavn. Hydrographicalparameters were measured at 10 stations along the transect.Sagitta setosa J. Mailer was by far the most dominant chaetognath(99% of individuals). Sagitta elegans Verrill and Eukrohniahamata Möbius occurred simultaneously with inflowing highsaline water during autumn and winter. The transport of S. setosaby currents was an important factor influencing the abundancesand the breeding period in the Kattegat. The abundance peakin 1977 was only one fifth of that found in 1975. The startand the duration of the breeding period (defined as presenceof stage 1 individuals <3 mm) varied between the three years.Breeding occurred between the middle of July and December witha peak in August and September. Changes in size distributionwere small during winter and spring, possibly due to low temperatures.S. setosa has probably a life span of one year in the Kattegat.Some earlier results regarding the number of breeding periodsof S. setosa per year are questioned. It is proposed that thenumber of generations per year of S. setosa and the start andthe duration of the breeding period(s) in western European watersshould be regarded as an open question until further informationis available.     

Early life history of a seahorse, Hippocampus mohnikei, in Tokyo Bay, Japan

The early morphological development, seasonal and spatial occurrence patterns, and food habits of a seahorse, Hippocampus mohnikei, in offshore waters of Tokyo Bay, central Japan, were studied on the basis of 206 juvenile and young specimens (6.0–65.3 mm TL) collected between August 1995 and January 1999. All the specimens were collected within the period from May to January, inclusive, each year. In the least developed specimen (6.0 mm TL), the number of dorsal, anal, and pectoral fin rays had attained the adult complement, whereas the minute caudal fin, consisting of two rays, was present in juveniles of 6.0–26.4 mm TL. Hippocampus mohnikei≧35 mm TL, being larger than settlement size (ca. 30 mm TL), had very low gut fullness index values (GFI = 0, >70% of specimens), whereas those of 15–29 mm TL had higher values (GFI = 2–4, >80% of specimens). In addition, larger individuals selectively fed on larger planktonic animals (species of Brachyura), which occurred naturally at low densities, although smaller food items, such as Oithona davisae and Penilia avirostris, occurred abundantly, being consumed by smaller H. mohnikei individuals (15–34 mm TL). These results indicated that food availability for H. mohnikei in offshore waters of Tokyo Bay is significant for individuals larger than settlement size, because their food preference would shift from smaller food items to larger food items, which would be scarce in their environments. Received: January 12, 2001 / Revised: May 13, 2001 / Accepted: June 14, 2001     

Seasonal variation and life history of the pelagic chaetognatha, Sagitta elegans Verrill, in Toyama Bay, southern Japan Sea

The seasonal variation and life history of the pelagic chaetognatha,Sagitta elegans Verrill, in Toyama Bay, southern Japan Sea,were investigated using a time series of 0–500 m verticalhauls with a Norpac net from 1 February 1990 to 30 January 1991.Nine species of one genus occurred in Toyama Bay throughoutthe year, including the cold-water species S.elegans. Therewas no remarkable variation in abundance throughout the year,although many individuals were collected in August. Juvenilesoccurred mostly in spring and summer, from late March to August.Adults (Stage 3) occurred in all seasons, except summer. Thebody length of adults ranged from 26 to 30 mm. There were twoprincipal spawning periods. One was in March-May and the otherwas in August. Life spans of both cohorts were 10–12 months.Copepods were major prey of S.elegans inhabiting Toyama Bay.The annual mean food-containing ratio (FRC) was 6.1%, but values>10% occurred in February, April, May, July and September.     

Vertical distribution and seasonal variation of eelgrass beds in Iwachi Bay,Izu Peninsula,Japan

The vertical distribution and population structure of eelgrass beds were surveyed in Iwachi Bay, along the Pacific coast of central Japan. Samplings were conducted from May through November 1977 by SCUBA. Eelgrass was distributed between 3 and 11 m in depth. The relative light intensity at 12 m depth was 11% at the lower range. The highest population density was 290 shoots/m² in September and the fresh weight of biomass was 888 g/m² in July at 7 m depth. The maximum mean leaf area index was about 3 at 10 m depth in July. The ratio of reproductive shoots to the total shoots was about 36% at 7 m depth in June. Eelgrass showed good growth at 7–10 m depth, which is comparatively deeper than other eelgrass habitations. The high values of water transparency and sunshine duration, as well as solar radiation compared with other localities was believed to contribute to the growth of eelgrass in deeper waters in Iwachi Bay.     

Visual observations on the process of digestion and the production of faecal pellets in the chaetognath Sagitta hispida Conant

The passage of food through the gut of Sagitta hispida Conant is described as a batch process and the formation of membranes which surround the faecal material is demonstrated photographically. The utility of such a peritrophic membrane system is considered in the light of the marine ecosystem as a whole.     

The liquid crystalline nature of the cytoskeleton in epidermal cells of the chaetognath Sagitta

The chaetognaths have a multilayered epidermis, which is not covered by cuticle, except in the head region. Two kinds of cells are found in the epidermis: the filament-rich cells, adjacent to the basement membrane, and superficial cells, which are filament poor. The filament-rich cells, which are linked by gap junctions and columnar junctions, are highly developed in the collarette region, which joins the head and the trunk. As elsewhere in the epidermis these cells are covered by the filament poor cells which are linked by zonulae adhaerentes, gap junctions and septate junctions. The filaments present in the inner cells of the collarette form a twisted fibrous arrangement, which shows parallel series of nested arcs when observed in oblique section. Such systems are well known in numerous skeletal materials and correspond to polymerized analogues of certain liquid crystals. The amount of connective tissue is extremely reduced in Sagitta. One can hypothesize that filament-rich cells are abundant in regions which undergo strong deformations. This is the case in the collarette, in contact with the basement membrane of the epidermis (which in turn is in contact with a myotendinous system), in a region where ingested prey must go through the general cavity where there is high internal pressure.     

Life history and population dynamics of the chaetognath Sagitta elegans in central Long Island Sound

One chaetognath species is found in Long Island Sound. Sagittaelegans. Individuals ranging in length from 1.5 to 22 mm werefound from March through August. Length at maturity ranged from13 to 22 mm. Maximum abundances. 67 ind m^–3 in 1982 and106 md m in 1983. occurred in early summer Two cohorts wereseen during both years, beginning as eggs produced in April-May.and in late June. The population is not endemic to Long IslandSound because temperatures during summer exceed 19C, whichseems to be lethal. The appearance of the first cohort in springis due to advection of animals from shelf waters. The secondcohort, however, is produced locally. The S. elegans populationin Long Island Sound is unique in two ways. First, the adultsare considerably longer than predicted by McLaren's (1963) Belhrdekfunction, and second, the total abundance of eggs, juvenilesand adults is at least two times higher than anywhere else.     

Modern dinoflagellate cysts in hypertrophic coastal waters of Tokyo Bay, Japan

A survey of dinoflagellate resting cysts in surface sedimentsamples was carried out in Tokyo Bay, Japan, to document theirhorizontal distribution. At least 21 different cyst types werefound. Dominant cyst types allowed the recognition of assemblageswhich form three different dinoflagellate cyst communities:the innermost part of the Bay, the central area and the moutharea. In all stations in Tokyo Bay, heterotrophic dinoflagellatecysts always occupied more than half of the cyst populations.Cysts of Polykrikos schwartzii/kofoidii are the most abundantheterotrophic species. These assemblages may reflect highlynutrient-enriched (hypertrophic) and turbulent water conditions.Among the cyst types found were probable ellipsoidal cysts ofAlexandrium tamarense. This is the first record of toxic Alexandriumspecies cysts in Tokyo Bay sediments.     

Vertical distribution of pelagic chaetognaths and feeding of Sagitta enflata in the Central Equatorial Pacific

The vertical distribution and feeding of pelagic chaetognathsat 5°S, 160°W in the Central Equatorial Pacific wereinvestigated using a series of 0–500 m vertical haulswith a VMPS net over a 24 h period between 6 and 7 October 1990.The total number of individuals per haul was between 370 and688. Fourteen species in four genera were found at this station.The most abundant species was Sagitta enflata which comprised32.4–61.1% of the individuals collected from the 0–500m layer. Mesopelagic species made up 9.3–15.1% of thetotal number of individuals. Sagitta enflata and Pterosagittadraco were found in the upper part of the thermocline both byday and at night. The fraction of the population containingfood items (FCF) of S.enflata in the 0–50 m layer variedbetween 4.8 and 12.5% (mean 10.8%) and feeding activity washighest between sunrise and noon. The percentages of Copepoda,Foraminifera, crustacean larvae, Chaetognatha, Pteropoda, Ostracoda,fish and unidentified material in the gut of S.enflata were51.9,6.7,3.8,2.9,1.9,1.9 and 30.9%, respectively. Sagitta enflataconsumed food organisms which were mainly between 0.5 and 1.0mm in length. The daily feeding rate of S.enflata was 1.81 preyper individual, which was equivalent to 8.06 mg C m^–2day^–1. This corresponded to     

Feeding rates in the chaetognath Sagitta elegans: effects of prey size, prey swimming behaviour and small-scale turbulence

The gut contents of Sagitta elegans were sampled twice daily(noon and midnight) during 9 days in October at an anchor stationin the northern North Sea. Observations of the ambient preyfield and of turbulent dissipation rates were collected simultaneously.The average number of prey per chaetognath was among the highestever recorded, 0.57 ± 0.10. Total gut content was independentof ambient prey concentration, suggesting that feeding ratewas saturated. Clearance rates were estimated from gut contentsand ambient prey concentrations and a literature-based estimateof digestion time. The clearance rate to prey size showed adome-shaped relationship. The maximum clearance rates, about100–300 ml h^-1, were observed for prey sizes correspondingto 6–10% of Sagitta length. Clearance rates varied notonly with prey size, but also with prey type. For example, copepodmales were cleared at rates up to an order of magnitude higherthan similarly sized females, probably owing to differencesin swimming behaviour. Sagitta elegans is an ambush predatorthat perceives its prey by hydromechanical signals. Faster swimmingprey generates stronger signals and is, hence, perceived atlonger distances. We develop a simple prey encounter rate modelby describing the swimming prey as a ‘force dipole’and assuming that a critical signal strength is required toelicit an attack. By fitting the model to the observations,a critical signal strength of 10^-2 cm s^-1 is estimated; thisis very similar to estimates for copepods that also perceiveprey by mechanoreceptory setae. Gut contents were independentof turbulent dissipation rate. Because feeding rates were saturated,we did not expect to see positive effects of turbulence. However,the strong wind-generated turbulent dissipation rates observedduring the study (10^-3–10^-1 cm² s^-3 in the upper mixedlayer) could lead to negative effects by interfering with preyperception. At a dissipation rate of 10^-2 cm² s^-3 a 10-mm longS. elegans would experience fluid signals of order 0.3 cm s^-1due to turbulence, 30 times stronger than the signal strengthfrom the prey. It is, therefore, suggested that S. elegans isable to separate prey signals from turbulence signals due totheir different spatial characteristics.     

The role of the chaetognath Sagitta gazellae in the vertical carbon flux of the Southern Ocean

Chaetognaths are among the most abundant predators in the Southern Ocean and are potentially important components in the biological carbon pump due to the production of large, fast-sinking fecal pellets. In situ S. gazellae abundance, fecal pellet production, sinking rates, carbon content, and vertical carbon fluxes were measured at the Lazarev Sea between December 2005 and January 2006. Sagitta gazellae produce fecal pellets that sink at speeds of 33–600 m day⁻¹ and have carbon contents of 0.01–0.8 mg C pellet⁻¹. Vertical carbon flux was later compared with the total carbon flux measured at 360 m depth at the study area. Rough estimates using published seasonal abundance of S. gazellae indicate that, at 360 m depth in the Lazarev Sea, this specie may contribute 12 and 5% of the total vertical carbon flux in winter (ice-covered) and summer (ice-free), respectively. Thus, the role of chaetognaths in the downward transport of organic matter may be far more important than previously thought.     

Effects of antibiotics on the life cycle ofNeurospora crassa

Some antibiotics and synthetic inhibitors affect, in several ways, the life cycle ofNeurospora crassa (germination of conidia → myceliar growth → formation of conidia). Bikaverin, cyanein, scopathrioin and phenethyl alcohol retard the germination of conidia, without inhibiting it completely. 5-Fluorouracil, ramihyphin A and zygosporin A (cytoohalasin D) do not inhibit the germination. Bikaverin brings about a thickening of the hyphae of growing mycelium. Ramihyphin A, cyanein, scopathricin and zygosporin A stimulate the ramification of hyphae while 5-fluorouracil and phenethyl alcohol do not affect the myceliar morphology apart from their inhibitory effect on growth. Actinomycin D, 5-fluorouracil, cycloheximide, ramihyphin A and partially also sodium iodoacetate inhibit to a different degree the photoinduced formation of conidia. The inhibition by 5-fluorouracil is very conspicuous when the agent is present during the photoinduction but considerably weaker when it is applied 2 h after the photoinduction.     

Characterization of microaerophilic bacteria isolated from the coastal waters of Tokyo Bay, Japan

Abstract A total of 84 strains of microaerophiles were isolated from the Edo River mouth, Tokyo Bay, Japan, and their morphological, physiological and biochemical properties and mole percent guanine-plus-cytosine contents (mol%) of DNAs extracted from them were examined. Eighty-eight to 100% of the strains, collected in summer, grew at 15–37°C but only 5% of the strains grew at 5°C. Seventy-seven to 100% of the strains, collected in winter, were able to grow at 10–25°C but 79% of the strains were unable to grow at 37°C. The shift in growth-range of bacteria strongly suggests that the microflora of estuarine microaerophiles changes seasonally. All the strains could grow at 50% seawater while 70 and 42% of the strains could not grow at 0 and 100% seawater, respectively.
On the other hand, 72 strains, out of the 84 strains, clustered into 9 phena using numerical taxonomy methods. The strains belonging to phena 1 through 9 were all Gram-negative, non-spore-forming rod-shaped organisms which were negative for susceptibility to vibrostatic agent O/129, H₂S production and acid from dulcitol, and the G + C contents of DNAs ranged from 29.8 to 56.6 mol%. However, almost all strains could not be identified and are suggested to be new species.     

Geographic distribution, seasonal life cycle, biomass and production of a planktonic copepod Calarms sinicus in the Inland Sea of Japan and its neighboring Pacific Ocean

The geographical distribution, seasonal life cycle, biomassand production of a copepod Calanus sinicus were investigatedin and around Kii Channel of the Inland Sea of Japan. The distributioncenter of the population was located in Kii Channel. The patternof the seasonal variation in abundance of copepodites and adultsdiffered geographically within the study area. In Kii Channel,for example, they were most abundant in June-July and leastabundant in October. Over the study area, the reproduction ofC.sinicus took place throughout the year, indicating the absenceof diapause phase. In adults, females usually outnumbered males.The prosome length of late copepodites and adults was inverselycorrelated with water temperature. The annual mean biomass washighest (4.87 mg C m^–3 or 231 mg C m^–2) in Kii Channel.The potential production rate of the population exhibited aseasonal variation more or less similar to that of the biomassand the annual potential production rate was 358 mg C m^–3year^–1 (14.1 g C m^–2 year^–1) in Kii Channel.Daily production and biomass (P/B) ratios in Kii Channel increasedfrom 0.11 at 11.8°C to 0.26 at 20°C.     

海洲湾强壮箭虫的生态学特征研究

根据海洲湾2006年8月—2007年11月的强壮箭虫(Sagitta crassa)调查数据,采用聚集强度指标、Iwao和Taylor模型分析了强壮箭虫的空间分布特征和丰度的时空变化。结果表明:强壮箭虫在调查海域呈聚集分布;强壮箭虫平均丰度的时空变化差异显著,空间上,中、北部海域的平均丰度高于南部海域,时间上,强壮箭虫春、冬季节的平均丰度明显高于夏、秋季节。