ULTRASTRUCTURE OF CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE): AUXOSPORE,RESTING SPORE AND VEGETATIVE CELL MORPHOLOGY1

The structure of the frustule of auxospores, resting spores and vegetative cells of Chaetoceros muelleri Lemm. are described with LM and SEM. Vegetative frustules are relatively small and lightly silicified, are not united into filaments, and appear unornamented under LM and SEM. The setae are circular to subcircular in transverse section with spines and puncta arranged in a spiral pattern. The resting spore and auxospore frustules are more silicified than the vegetative frustules and appear unornamented under LM and SEM. The auxospores of C. muelleri were previously unknown.     

Resting spore formation in the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo

Summary The resting spore morphology of the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo are described. Both species form endogenous resting spores. The spore valve of C. furcatus differ from those of the vegetative cells primarily by (i) a greater convexity and (ii) a coarser and more distinctly fasciculated areolation. This resting spore is identical to the diatom traditionally identified as C. stellaris var. symbolophorus (Grunow) Jørgensen in the Antarctic. The resting spore of T. australis differs from the vegetative cells by (i) a lack of clusters of strutted processes in a modified ring on valve face, (ii) a coarser areolation and tangential rows of areolae and (iii) a narrower and more simply structured girdle. The resting spore valve of T. australis has been described as belonging to a separate species, Actinocyclus excentricus Peragallo.     

Marine phytoplankton at the Weddell Sea ice edge: Seasonal changes at the specific level

Summary The Antarctic ice edge acts as a dynamic frontal system on the phytoplankton in the water column. Austral spring and autumn cruises to the Weddell Sea ice edge provided the opportunity to compare phytoplankton at the beginning of biological spring and at the end of biological autumn. The USCGC icebreakers Westwind (1983) and Glacier (1986) went into the sea ice, and the RV Melville (1983 and 1986) completed the transects in the adjacent open ocean. Field samples were observed alive on board ship to record different lifestages near the ice edge. In both seasons cell numbers were low under the ice, and single cells or short chains were the common growth habit. In spring in the open ocean, long chains of vegetative cells with large vacuoles and gelatinous colonies of diatoms and of prymnesiophytes dominated; in autumn in the open ocean close to the accreting ice edge, short chains, single cells, and resting spores were mostly packed with storage products. Enlarged cell diameters and auxospores also occurred near the ice cover in the autumn. Species from the following genera are included: the diatoms Leptocylindrus, Stellarima, Thalassiosira, Eucampia, Corethron, and Chaetoceros, the prymnesiophyte Phaeocystis, and the chrysophyte Distephanus.     

Resting spore formation ofLeptocylindrus danicus (Bacillariophyceae) during short time-scale upwelling and its significance as predicted by a simple model

Resting spore formation during short time-scale upwelling and its significance were investigated in the field and by a simple theoretical model. Field observations of spore formation ofLeptocylindrus danicus were made off Izu Peninsula, Japan. A rapid increase in ratio of resting spore to vegetative cell numbers indicated thatL. danicus formed resting spores quickly as a response to nutrient depletion in the upwelled water, although only a very low number of resting spores was found in the upwelling. A simple model was constructed to investigate the possible advantages of spore formation during short time-scale upwelling. This showed that there is a critical time-scale for resting spore formation to be advantageous. The nutrient depletion period of the upwelling off Izu was shorter than the critical time-scale determined by the model. Rapid-sinking of resting spores may increase further the critical time-scale, unless spores return with upwelling water. For short time-scale upwelling, the vegetative cell may be better suited than the resting spore for enduring a short period of nutrient depletion. Contribution from Shimoda Marine Research Center, University of Tsukuba, No. 475.     

Molecular variation of Spiranthes sinensis (Orchidaceae) in Japan, with special reference to systematic treatment of seasonally differentiated groups and a dwarf form, f. gracilis, from Yakushima Island

Molecular variations of Spiranthes sinensis Ames var. australis (R.Br.) H. Hara et Kitam. ex Kitam. in Japan were examined to evaluate the validity of the seasonally differentiated groups and a dwarf form of the species, which is endemic to Yakushima Island, Japan. Sequence differences in the plastid trnL-F locus clearly distinguished Japanese S. sinensis var. australis from S. sinensis var. sinensis collected from Ryukyu. In contrast, the trnL-F sequence of S. sinensis var. australis from Sabah, Malaysia, clearly differed from that of Japanese S. sinensis var. australis, suggesting genetic heterogeneity of Spiranthes sinensis var. australis in Asia. Moreover, a molecular analysis based on the sequences of nuclear ITS1 regions indicated that there are two major groups of S. sinensis var. australis in Japan, with a geographic distribution boundary on Kyushu Island. However, the trnL-F and ITS1 sequences did not support the genetic differentiation of the seasonally differentiated groups or the dwarf form from the other Japanese individuals. Based on these molecular data, the systematic treatment of physiological and morphological variations in the Japanese population of S. sinensis. var. australis is discussed.     

Life cycle of the ichthyotoxic dinoflagellate Cochlodinium polykrikoides in Korean coastal waters

Since 1995, blooms of the harmful dinoflagellate, Cochlodinium polykrikoides, have caused considerable mortality of aquatic organisms and economic loss in Korea. However, little is known about the life cycle of the species, except for the planktonic vegetative stage; therefore, the aim of this paper was to elucidate the life cycle of C. polykrikoides. Its life cycle has two morphologically different stages: an armored and an unarmored vegetative stage. Armored vegetative cells were found in seawater samples collected in late-November and developed into four-cell chained, unarmored vegetative cells under laboratory culture. In samples collected in late-May, both the armored and unarmored types (vegetative swimming stage) occurred; the former easily developed into an unarmored vegetative cell type, suggesting that the armoured–unarmored transition occurs as early as May. A presumptive resting cyst, round but folded at one side, was produced from armored type cells in laboratory conditions. It was also collected from natural bottom sediments, which suggests it is the dormant resting cyst of C. polykrikoides.     

Selection and viability after ingestion of vegetative cells, resting spores and resting cells of the marine diatom, Chaetoceros pseudocurvisetus, by two copepods

Feeding response of two copepods Neocalanus flemingeri and Calanus sinicus on cultures of three life-forms; vegetative cells, resting spores and resting cells, of Chaetoceros pseudocurvisetus was investigated. N. flemingeri fed heavily on the vegetative cells but scarcely responded to feed on the resting spores. C. sinicus showed significantly higher filtering rate on the vegetative cells and resting cells than on the resting spores. Survival of the three life-forms of C. pseudocurvisetus after gut passage of the copepods was also studied. The resting spores could germinate from fecal pellets of both N. flemingeri and C. sinicus; however, both the vegetative cells and the resting cells could not survive ingestion by the copepods. These results suggest that resting spore forming diatoms, such as C. pseudocurvisetus form spores which have a low nutritional value and during gut passage are largely indigestible due to the heavily silicified frustules and thus minimize the effects of grazing by copepods.     

Zur Lebensgeschichte der DiatomeeAchnanthes linearis und Bemerkungen über andereAchnanthes-Arten

Achnanthes linearis produces two auxospores from one cell pair by allogamic fusion of migratory and stationary gametes. Unusually little copulation jelly is produced. Pairing occurs by chance in regard to the heteropoly of the transapical axis. The orientation of the primary cells in relation to the substratum and to the mother cells is constant and characteristic. Variation of cell size is much larger than hitherto known; correspondingly the diagnosis is to be completed.—The position and orientation of vegetative cells and partner cells is strongly determined by the relief of the leaves ofFontinalis on which they are fixed with their raphe valve. The same is true for the cells ofA. minutissima which usually are fixed at one cell pole only, but exceptionally at both poles; this means that morphological heteropoly of apical axis is lacking, and that the function of the second holdfast-jelly producing structure usually is suppressed. The cells of both species normally creep by means of the raphe mechanism; the direction is very independent of the relief of theFontinalis leaves. After cell division the moving down of the upper daughter cell follows a different mechanism.A. linearis is the first to settle onFontinalis leaves, other epiphytes come much later.

     

Production and biomass of Tenagomysis tasmaniae Fenton, Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea: Mysidacea)

Annual production estimates were calculated for Tenagomysis tasmaniae, Anisomysis mixta australis and Paramedopodopsis rufa using the size-frequency and Petrovich methods. Annual production for T. tasmaniae was more than twice that for P. rufa and A. mixta australis. The P:B ratio was however , higher for a. mixta australis than T. tasmaniae and P. rufa. The P:B values for the three species are among the highest ratios reported for mysids.     

Diet and predators of Tenagomysis tasmaniae Fenton, Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea:Mysidacea)

The diets of three mysid species Tenagomysis tasmaniae Fenton, Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton were investigated together with a number of potential fish predators by gut contents and stable isotope analysis. Gut content analysis of the three mysis species revealed that all have an omnivorous diet, although the stomachs of P. rufa contained a greater percentage of crustacean remains, whereas the stomach contents of T. tasmaniae were largely composed of fragments of macroalgae. The stomach contents of A. mixta australis were composed mainly of fine particulate matter. Diel feeding rhythms were examined from mysids collected during a 24-hour sampling session in October. P. rufa appeared to be primarily a day-time feeder while T. tasmaniae fed more intensively at night. The results for A. mixta australis were inconclusive. Gut contents analysis of fish collected at the study site revealed predation on mysids by Arripis trutta (juveniles), Aldrichetta forsteri, Vincentia conspersa and Pseudolabrus fucicola. The mysid species most frequently eaten was Tenagomysis australis Fenton. The mysid species most frequently eaten was Tenagomysis australis Fenton.     

Survival, growth, and escape from herbivory are determined by habitat and herbivore species for three Australian woodland plants

To understand how plant communities are structured by herbivory it is essential to investigate the roles of different herbivores and the responses of a variety of plant species in different habitats. We examined the effects of mammalian herbivores on survival and growth of transplanted seedlings of two native trees (Eucalyptus albens and Callitris glaucophylla), and one native grass (Themeda australis) in white box (E. albens) woodlands in eastern Australia over 3 years. Herbivores were manipulated using four fencing treatments that successively excluded livestock, macropods, and rabbits from woodland and grassland (cleared pasture). Survival was highest in the absence of mammalian herbivores and in woodlands, and patterns differed among plant species. Survival of T. australis was low, especially in grasslands, and mortality by overgrowth was common in ungrazed treatments. All plant species were taller in fenced plots, and differences between treatments were greater in grassland. Rabbits and livestock had the greatest influence on C. glaucophylla, while T. australis and E. albens were most affected by livestock and macropods. We used field data to parameterize stage-classified matrix models to predict escape from herbivory (escape height >100 cm) for tree species. Reduced herbivory increased the proportion of individuals reaching escape height after 15 years. Rate of escape was greater in grassland, and this faster growth appeared to counteract much of the negative impact of herbivores. While T. australis was unable to escape herbivory, larger, ungrazed individuals were more likely to flower and therefore contribute to the maintenance of the population. Our results show that habitat and herbivore species strongly influence the effect of herbivory on vegetation.     

Interactions between mediterranean shrub species eight years after experimental fire

This paper is part of a wider study in which different combinations of species were assayed for the revegetation of experimentally burnt heathlands. In this particular case, we determined whether there was any interaction between the dominant species, Erica australis, which recovered by vegetative resprouting, and the only successful woody species sown, Cytisus sp., eight years after fire and seven years after sowing. A detailed study was carried out on each square metre of cover and height of both species in three 160 m² plots. Total cover exceeded 100% in all subplots sown with Cytisus, whereas it did not reach 65% in the others, when both species coexist together. There was an inverse correlation between the covers of both species and a positive correlation between the height of Erica australis and the cover and the height of Cytisus. There was no significant difference in Erica cover in plots sown with Cytisus and plots not sown. There could be some competition for light, but both species are capable of coexisting with high canopy overlap, for at least some time. Cytisus is expanding from the seeded subplots, suggesting that the dense cover of Erica australis does not impede the establishment of Cytisus. This revised version was published online in August 2006 with corrections to the Cover Date.     

Population dynamics of Tenagomysis tasmaniae Fenton,Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea:Mysidacea)

The population dynamics of a coastal mysid community was examined at One Tree Point in southern Tasmania over a 12-month period, including three 24-hour sampling sessions. Fourteen mysid species were recorded. Zonation patterns, life-history and diel activity of the three most abundant species, Tenagomysis tasmaniae, Anisomysis mixta australis and Paramesopodopsis rufa were examined. These three species were found in large numbers throughout the year associated with the macroalgal fringe on either side of the bay. Habitat partitioning within this zone of occurrence was evident. T. tasmaniae was the most abundant species (annual mean density 32.4 m^–3), followed by A. mixta australis (annual mean density 20.5 m^–3 ) and P. rufa (annual mean density 11.3 m^–3). The major peaks of abundance of these three species were temporally separate. Breeding was intensive for the three species from spring till late autumn. A cessation of breeding in winter was evident for A. mixta australis and to a lesser extent for P. rufa but T. tasmaniae bred throughout the year although at a reduced rate during winter. Examination of the diel behaviour identified peaks of abundance at sunrise and sunset for T. tasmaniae; P. rufa was caught in greater numbers at night, but no consistent pattern was observed for A. mixta australis.     

Lethality of chlorine, chlorine dioxide, and a commercial fruit and vegetable sanitizer to vegetative cells and spores of Bacillus cereus and spores of Bacillus thuringiensis

Chlorine, chlorine dioxide (ClO₂), and a commercial raw fruit and vegetable sanitizer (Fit powder) were evaluated for their effectiveness in killing vegetative cells and spores of Bacillus cereus and spores of Bacillus thuringiensis. The ultimate goal was to use one or both species as a potential surrogate(s) for Bacillus anthracis in studies that focus on determining the efficacy of sanitizers in killing the pathogen on food contact surfaces and foods. Treatment with alkaline (pH 10.5–11.0) ClO₂ (200 mg/mL) produced by electrochemical technologies reduced populations of a five-strain mixture of vegetative cells and a five-strain mixture of spores of B. cereus by more than 5.4 and more than 6.4 log cfu/mL, respectively, within 5 min. This finding compares with respective reductions of 4.5 and 1.8 log cfu/mL resulting from treatment with 200 mg/mL chlorine. Treatment with a 1.5% acidified (pH 3.0) solution of Fit powder product was less effective, causing 2.5-log and 0.4-log cfu/mL reductions in the number of B. cereus cells and spores, respectively. Treatment with alkaline ClO₂ (85 mg/mL), acidified (pH 3.4) ClO₂ (85 mg/mL), and a mixture of ClO₂ (85 mg/mL) and Fit powder product (0.5%) (pH 3.5) caused reductions in vegetative cell/spore populations of more than 5.3/5.6, 5.3/5.7, and 5.3/6.0 log cfu/mL, respectively. Treatment of B. cereus and B. thuringiensis spores in a medium (3.4 mg/mL organic and inorganic solids) in which cells had grown and produced spores with an equal volume of alkaline (pH 12.1) ClO₂ (400 mg/mL) for 30 min reduced populations by 4.6 and 5.2 log cfu/mL, respectively, indicating high lethality in the presence of materials other than spores that would potentially react with and neutralize the sporicidal activity of ClO₂.Published by permission of the International Association for Food Protection: Journal of Food Protection (2004) 60:1702–1708This revised version was published online in April 2005 with corrections to the text and the section heading.In section Preparation of treatment solutions the phrase 22-28°C was replaced by 22±2°C.     

In vitro spore formation and completion of the asexual life cycle of Neozygites parvispora, an obligate biotrophic pathogen of thrips

Capilliconidia, the asexual secondary spores of Neozygites parvispora (Zygomycetes, Entomophthorales) were produced in vitro either by entrapment of vegetative cells (hyphal bodies) in alginate pellets or after plating them onto water agar. Cultivation of the fungus for 3 days in a medium lacking hemolymph increased spore production 30 to 40-fold, and about 10% of the cells produced capilliconidia. The in vitro produced capilliconidia were infectious to Thrips tabaci and the fungus was reisolated from infected insects, thus completing its asexual life cycle under laboratory conditions. A decrease in capilliconidia production and a modification of the number of nuclei per spore were observed for isolates cultivated in vitro for more than 2 months, but subsequent host passages restored and increased sporulation efficiency without influencing the number of nuclei. Fungal cultures were stored at —80 °C for up to 7 months, and the capability to sporulate and infect T. tabaci was preserved. A bioassay procedure for infecting T. tabaci with N. parvispora is described, the first mycosed insects dying usually after 8 d of incubation.     

Optimization of inactivation of endospores of Bacillus cereus by antimicrobial lipopeptides from Bacillus subtilis fmbj strains using a response surface method

Bacillus subtilis fmbj can produce a lipopeptide antimicrobial substance, the main components of which are surfactin and fengycin. In this paper, the sensitivity of Bacillus cereus to antimicrobial lipopeptides from B. subtilis fmbj was observed, and the effect of the microstructure of antimicrobial lipopeptide on spores of B. cereus was investigated. At the same time, the optimization of the inactivation of antimicrobial lipopeptides to spores of B. cereus by a response surface methodology was studied. Results showed that B. cereus had high sensitivity to it, whose minimal inhibitory concentration was 156.25 μg/ml. It could result in the death of spores by destroying the structure of resting spores and sprouting spores, as was observed by transmission electron microscopy. The optimization result indicated that spores of B. cereus could be inactivated by 2 orders of magnitude when the temperature was 29.6°C, the action time was 7.6 h, and the concentration was 3.46 mg·ml⁻¹.     

Breeding biology of Tenagomysis tasmaniae Fenton,Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea: Mysidacea)

The number, size and developmental stage of young in the brood pouch of female Tenagomysis tasmaniae, Anisomysis mixta australis and Paramesopodopsis rufa was recorded throughout the year. Breeding was intensive from spring till the end of autumn for the three species. Calculation of the egg ratio for each species showed that their major reproductive peaks occurred during spring and summer. A winter depression in the breeding cycle was observed for T. tasmaniae and P. rufa, but A. mixta australis ceased breeding during winter. Seasonal variation in the length of gravid females and number of young carried was evident for these three species. Females were longer in spring and summer and carried more young than in autumn and winter. A linear relationship between female length and brood size was demonstrated for each species; annual and seasonal equations were calculated for females carrying each developmental stage. The seasonal equations showed that for a female of given length fecundity was greater during spring than any other season. Natality was estimated to be highest during late spring, summer and early autumn for the three species. No seasonal variation in the size of eggs was evident for the three species. The reproduction pattern of T. tasmaniae, A. mixta australis and P. rufa appears to be very similar to that reported for the majority of iteroparous coastal temperate mysids throughout the world.     

种间竞争对香蒲与芦苇生长的影响

为了探究种间竞争对香蒲（Typha domingensis）与芦苇（Phragmites australis）生长的影响,利用根系分隔盆栽试验研究了3种不同分隔方式条件下香蒲与芦苇的种间竞争特性,包括塑料膜分隔（根系完全分隔,无相互作用,无物质交换）、尼龙网分隔（根系部分分隔,无相互作用,有物质交换）和不分隔（根系完全相互作用,有物质交换）,分析了香蒲与芦苇根系形态和地上部生长的变化,探究香蒲与芦苇种间竞争的差异。结果发现（1）在尼龙网分隔和不分隔处理中芦苇具有明显的劣势。与塑料膜分隔处理相比,芦苇的总生物量、植株密度在尼龙网分隔和不分隔处理中分别减少了39.14%、49.41%和82.08%、79.22%,总根长、总根表面积、总根体积分别减少了40.53%、44.84%、62.52%和85.7%、82.45%、89.67%,且均具有极显著差异（P<0.01）;根系分隔方式也影响芦苇的株高、茎粗和叶片数,表现为不分隔 > 塑料膜分隔 > 尼龙网分隔。（2）与塑料膜分隔处理相比,香蒲总生物量在尼龙网分隔和不分隔中虽有增加,但差异不显著,植株密度和株高在尼龙网分隔和不分隔处理中都有增加且具有显著差异（P<0.05）,其总根长、总根表面积、总根体积在尼龙网分隔中分别增加了57.93%、26.5%、8.04%,但在不分隔处理中分别减少了11.57%、14.92%、11.39%（P<0.05）,虽然根系的相互作用对香蒲根系的生长具有促进作用,但植物种间根系相互作用越强,对两者的生长越不利。（3）在不同的分隔方式中,芦苇与香蒲间也存在明显变化。在不分隔处理中,香蒲的生物量和植株密度是芦苇的1.7倍和6.74倍,与塑料膜分隔处理相比增加了6倍,表明芦苇与香蒲根系的完全相互作用,显著削减了芦苇的繁殖生长,增加了香蒲的根系分蘖。（4）通过种间相互作用强度（RII值）分析也表明,尼龙网分隔和不分隔处理下芦苇表现为抑制作用（RII值为负值）,香蒲表现为促进作用（RII值为正值）。香蒲与芦苇互作对芦苇具有抑制作用,说明种间相互作用是能改变植物的适应性和植物群落的繁殖,同时也表明植物根系不仅在吸收土壤中的水和养分中起着关键作用,在种间关系中也起着重要作用。因此利用种间竞争控制植物生长,可以为保护生物多样性和生态系统的功能提供有效的技术支撑。     

Auxospore formation inLicmophora (Bacillariophyta)

InLicmophora gracilis var.anglica two auxospores are produced per pair of mother-cells, through the allogamic fusion of migratory and stationary gametes. Both active gametes are produced from the same mother-cell and hence both zygotes are formed in the other mother-cell. Pairing can occur between two stalked cells, or between a stalked cell and a detached cell; in the latter case the migratory gametes derive from the detached cell. The auxospores expand parallel to one another and to the apical axis of the donor mother-cell. Behavioural anisogamy of this kind, which may be termed thecis-type, seems to be characteristic of most araphid pennates and contrasts with thetrans-type exhibited byCymbella, Gomphonema and some other raphid taxa, where each mother-cell produces one migratory and one stationary gamete.     

Methods for sampling free-living Symbiodinium (zooxanthellae) and their distribution and abundance at Lizard Island (Great Barrier Reef)

The abundance and distribution of free-living dinoflagellates in the genus Symbiodinium have important implications for the ecology of coral reefs, determining both the symbionts available to newly recruited corals and symbiont types available for uptake by adult corals during environmental stress. However, little is known about where symbiotic dinoflagellates reside outside the host, due to the difficulty of capturing and detecting unicellular organisms in the marine environment. This study presents a successful protocol for sampling Symbiodinium from both the benthos and the water column. Comparisons of two detection methods for enumerating Symbiodinium indicated that conventional microscope analysis is accurate and more efficient when estimating Symbiodinium densities in sediment samples, while an automated particle counter (FlowCAM) was more efficient in detecting cells in the water column where densities are low. Symbiodinium densities were found to be relatively high (1000–4000 cells/mL) in sediment samples and much lower (up to 80 cells/mL) in the water column, indicating that the free-living form resides mainly in the benthos. Symbiodinium densities were found to be highly variable spatially, differing significantly between two reef locations. Within sites, elevated densities of Symbiodinium along reef margins combined with significant decreases in densities one meter away from the reef, suggest that cells aggregate within the reef habitat.