Thraustochytrid protists as a component of marine microbial films

Although ubiquitous in the marine environment, the presence and importance of thraustochytrid fungoid protists in primary film formation of freshly immersed surfaces in the sea have not been investigated. We isolated thraustochytrids from surfaces of glass, aluminium, mild steel and fibre glass panels immersed in sea water for 1 to 4 d, but not from those of copper and cupro-nickel. Microscopic examination of the primary film on glass surfaces revealed the presence of thraustochytrids. Thraustochytrids grew to varying population densities on surfaces of glass, aluminium and fibre glass in the laboratory. Scanning electron microscopy of the growth of Ulkenia profunda Gaertner, isolated from the primary film, on surfaces of glass and aluminium suggested that cells of the thraustochytrid attached directly to the surfaces, without producing copious extracellular polysaccharides. The presence of ectoplasmic net elements was not a prerequisite for attachment of cells to surfaces. Cell surface hydrophobicity of the thraustochytrid, as estimated by the MATH assay, might play an important role in adhesion. The presence of thraustochytrid cells on a polystyrene surface markedly induced settlement of barnacle larvae (Balanus amphitrite), as compared to barnacle extract and a control. Received: 26 July 1999 / Accepted: 21 January 2000     

Microalgal communities epibiontic on the marine hydroid <Emphasis Type="Italic">Eudendrium racemosum</Emphasis> in the Ligurian Sea during an annual cycle

The microalgal community associated with Eudendrium racemosum, a marine hydroid widely distributed in the Mediterranean Sea, was studied during an annual cycle, at monthly frequency, in a coastal station of the Ligurian Sea. Microalgae were represented mainly by diatoms, which exhibited higher abundance and biomass values between autumn and spring (max 46,752 cells mm⁻² and 1.94 μg C mm⁻², respectively), while during summer a significant decrease was observed (min 917 cells mm⁻² and 0.013 μg C mm⁻²). High levels of abundance of filamentous cyanobacteria were observed in summer. Spatial distribution of epibiontic microalgae showed a markedly increasing gradient from the basal to the apical part of hydroid colonies. Considering the growth forms of diatom communities, motile diatoms (mainly small naviculoid taxa) were the most abundant in all the periods. Adnate (Amphora and Cocconeis spp.) were distributed mainly in the basal and central part of hydroid colonies and showed two peaks (autumn and summer). Erect forms (mainly Tabularia tabulata, Licmophora spp., Cyclophora tenuis) were mainly distributed in the apical part of the colonies and showed their maximum densities in spring–summer. Tube-dwelling (Berkeleya rutilans, Parlibellus sp.) were observed at low densities throughout the study period, without any significant temporal or spatial variability. Comparing the microalgal communities on marine hydroid to those grown on mimic substrata placed in the sampling station during summer, significantly higher values of abundance were observed in the hydroid, suggesting that microalgae may benefit from the polyp catabolites. This fact was particularly evident for the adnate diatoms, whose temporal trend paralleled the cycle of hydroid host.     

To what extent does upright sessile epifauna affect benthic biodiversity and community composition?

Small-scale habitat complexity, including that caused by biological structures, is an important factor in structuring benthic communities and also sometimes in increasing biodiversity. The aim of this study was to determine if hydroid colonies have an effect on the composition of benthic communities in the Irish Sea, and if so, which components of the fauna are affected. Forty-six seabed core samples were taken by divers from two sites off Port Erin, Isle of Man, Irish Sea. Half of these were centred on hydroid colonies, half were not. All taxa retained by a 63-m sieve from the cores were identified and counted. Community composition and diversity were compared between hydroid and non-hydroid cores using multivariate and univariate methods. Benthic communities were significantly different between the two sample groups. This was almost entirely due to the presence of sessile and mobile epifaunal taxa in the hydroid cores. The tube-building amphipod, Ericthonius punctatus, was particularly abundant attached to the hydroid stems. Infauna was not significantly different between the two groups. Upright sessile epifauna may play a particularly important role in the Irish Sea as a settlement substrate for juvenile scallops (Pecten maximus and Aequipecten opercularis), which are an important fishery resource in this area. The 11-year closure of an area to dredging has not only enhanced scallop stocks but has had the added benefit of enhancing habitat complexity and biodiversity.Communicated by J.P. Thorpe, Port Erin     

The life cycle of Eutima commensalis sp. nov. (Eutimidae,Hydromedusae)

Developmental stages of the medusa Eutima commensalis sp. nov. were obtained from plankton collections made at 2 fixed stations, one at Fareway Buoy and the other at Aroor in the Cochin backwater system. Six stages were arbitrarily assigned and described. The hydroid and the medusa of this form were found to occur in these waters throughout the year, except during the monsoon months from June to September. The hydroid is endocommensalic on wood-boring molluscs such as Nausitora hedleyi, Teredo furcifera and Martesia striata.     

Ecology of the bivalve-inhabiting hydroid Eugymnanthea inquilina in the coastal sounds of Taranto (Ionian Sea,SE Italy)

The life history of the bivalve-inhabiting hydroid Eugymnanthea inquilina was investigated in two different hosts, the mussel Mytilus galloprovincialis (collected from 1989–1991 from the Ionian Sea, Italy) and the clam Ruditapes decussatus (collected from 1991–1992, Ionian Sea, Italy). Hydroids living in mussels revealed a size selection for hosts longer than 40 mm, being almost completely absent in mussels below this size. This might be controlled by signals linked to the sexual maturity of the bivalve. The proportion of molluscs inhabited showed a seasonal trend in mussels only, with a sharp decline at the onset of medusoid liberation. Production of medusoids was high in mussels, whereas medusoids were rare and often abortive in clams. This indicates a higher degree of fitness of E. inquilina in mussels than in clams. The hydroid life cycle was not completed in clams, which therefore were presumably supplied by planulae from medusoids produced by mussel-inhabiting hydroids. Mussels played a key role in the stability and persistence of E. inquilina populations in the studied area. Selective ingestion of trematode sporocysts by E. inquilina hydroids indicated a protective role of the hydroid against mussel parasites, leading to reconsideration of this symbiotic association as a possible mutualism rather than a simple inquilinism.     

Thraustochytrids as novel parasitic protists of marine free-living flatworms: <Emphasis Type="Italic">Thraustochytrium caudivorum</Emphasis> sp. nov. parasitizes <Emphasis Type="Italic">Macrostomum lignano</Emphasis>

The Labyrinthulomycota are a relatively poorly studied group of heterotrophic unicellular eukaryotes. They comprise three lineages, labyrinthulids, thraustochytrids, and aplanochytrids, which are all primarily marine organisms and considered to be important components of marine microbial communities. Recently a number of Labyrinthulomycota have been implicated as parasites of marine (but also terrestrial) plants and marine molluscs. Here we describe a new species of thraustochytrid, Thraustochytrium caudivorum sp. nov. that we have isolated from laboratory cultures of Macrostomum lignano (Rhabditophora, Macrostomorpha), a marine free-living flatworm. In these worms T. caudivorum can cause lesions, which start at the tip of the tail plate and which can lead to the dissolution of the posterior part of the animal. Although the worms can frequently cure these lesions and regenerate the lost parts, the lesions can also result in the complete dissolution of the animal. We describe this thraustochytrid based on pure agar cultures and infestations in the worm cultures. Moreover, we describe its pathological effects on the worms and its morphology using both light and electron microscopy. In addition, we report a phylogenetic analysis using a partial 18S rDNA sequence that allows us to place this new species within the thraustochytrids. Finally, we outline a protocol that allows to permanently remove the parasites from infested worm cultures. We conclude that thraustochytrids represent a novel group of parasites of free-living flatworms. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The biology of colonial hydroids. I. The morphology of the polyp of Eirene viridula (Thecata: Campanulinidae)

The colonial marine hydroid Eirene viridula Peron and Lesueur (Thecata, Campanulinidae) is readily maintained under laboratory conditions and reproduces in both vegetative and sexual modes. Polyps from these colonies displayed 4 distinct body regions, which were studied by comparison of light and electron micrographs of semi-thin and ultra-thin sections. Attention was directed chiefly to the epitheliomuscular and digestive muscle cells, found in all 4 regions and characterized by the presence of a central vacuole. Particular emphasis has been placed upon the coated vesicles and discoidal coated vesicles, which appear side by side in the digestive muscle cells of the stomach, and upon the central vacuoles typical of the muscle cells of the contractile parts of the body. The possible functional significance of these structures is discussed.This work was supported by the Deutsche Forschungsgemeinschaft.     

The marine bacterium Alteromonas espejiana induces metamorphosis of the hydroid Hydractinia echinata

The marine hydroid Hydractinia echinata develops into a primary polyp from a planula larva stage. The planula does not undergo metamorphosis in sterile filtered seawater. Metamorphosis is induced by certain bacteria occurring, as a rule, on the shells of molluscs inhabited by hermit crabs of the genus Eupagurus. Bacteria were isolated from shells occupied by H. echinata, and bacterial clones were selected which had a strong potency for inducing metamorphosis in planula larvae. One such clone was further subcloned for strong metamorphosis-inducing potency and finally investigated for inductive characteristics and for identification purposes. The bacterium is a motile, aerogen, gram-negative rod with a polar flagellum. It was identified on the basis of several physiological characteristics as a strain of the genus Alteromonas espejiana. The ability to induce metamorphosis might not be restricted to A. espejiana. The inhibitor of protein kinase C, sphingosine, inhibited metamorphosis induced by A. espejiana. The metamorphosis-inducing principle is likely to be a lipid, since upon lipid extraction and separation of different lipid classes by solid phase extraction on silica-aminopropyl columns a metamorphosis-inducing fraction was obtained.     

Morphology,nutrition and taxonomy of an Aplanochytrium sp. from the Sargasso Sea

Aplanochytrium sp. 2400/57 was isolated from samples of sargasso weed collected in the Sargasso Sea on April 4, 1979. The monocentric eucarpic thallus of this organism produced aplanospores by successive bipartitioning. The cell wall contained only 20% polysaccharide, composed of fucose, galactose, xylose, glucose, and galacturonic acid. The guanine+cytosine content of the DNA (mol% G+C) was 37.6%. L-isoleucine, L-leucine, and L-proline were utilized as nitrogen sources in synthetic media of defined composition.     

Starvation-induced barotolerance as a survival mechanism of a psychrophilic marine vibrio in the waters of the Antarctic convergence

Ant-300, a psychrophilic marine vibrio isolated from the Antarctic convergence, was tested for survival under conditions simulating those expected in situ for this organism. In particular, the organism's response to increased hydrostatic pressure was examined. Under a hydrostatic pressure of 250 atm, the viability of Ant-300 was reduced over 755 in growth media and under starvation conditions after 3 and 2 days, respectively. However, if the cells were starved for 1 week prior to pressurization of the starving suspension, 100% viability was maintained for over 6 weeks at the same pressure. After 10 weeks, the viability of a population of cells suspended for 1 week in natural or artificial seawater at a density of 10³ cells ml^–1 prior to pressurization of the suspension was 2 to 3 times greater than 1 atm controls. The data indicate that starvation conditions are a contributory if not the primary factor for the barotolerance of this organism in Antarctic waters. The data also indicate that under certain conditions, not unlike those expected in situ, hydrostatic pressure actually increases the survival of this organism under low nutrient conditions.Technical Paper No. 4907, Oregon Agricultural Experiment Station.     

Occurrence and detrimental effects of the bivalve-inhabiting hydroid <Emphasis Type="Italic">Eutima japonica</Emphasis> on juveniles of the Japanese scallop <Emphasis Type="Italic">Mizuhopecten yessoensis </Emphasis>in Funka Bay,Japan: relationship to juvenile massive mortality in 2003

In November 2003, we first observed prevalent occurrence of a hydroid, Eutima japonica, on soft body tissues of age zero Japanese scallop (Mizuhopecten yessoensis) juveniles cultured in large areas of Funka Bay, Hokkaido. The occurrence coincided with massive death of juvenile scallops. A major objective was to clarify ecological relationships between the symbionts, and to infer the relationship between symbiosis and the massive mortality. To do this, we investigated distributions of association rates of hydroids with juvenile scallops at 15–34 sites over 3 years (2003–2005), with age one adult scallops at 24 sites in 2003, and with mussels at 13 sites in 2004. We studied seasonal changes in association rates with juvenile scallops, and numbers of polyps per juvenile scallop at three sites from November 2003 to June 2004. We also quantified the hydroid impacts on juvenile scallop shell length growth and triglyceride accumulation in the digestive gland. The association rate of E. japonica polyps with juvenile scallops was high in large areas of Funka Bay in 2003, and overlapped the distribution of mussels bearing polyps. Association rates with age one adult scallops were very low in November 2003, even at the sites where polyps were very common on juvenile scallops. Levels of hydroid occurrence in juvenile scallops varies by year. We found that hydroids presence in juvenile scallops declined drastically in 2004 and 2005. The association rates with juvenile scallops, and numbers of polyps per juvenile scallop declined during winter, until they disappeared completely in the following June. Since polyps were rare in adult scallops, we believe that infection of juvenile scallops was probably initiated from the planulae produced by medusae released from polyps growing on Mytilus spp., especially M. galloprovincialis. Subsequently, the inhabitation spread intraspecifically and interspecifically. In juvenile scallops, inhabitation of polyps reduced shell length growth by 43%, and triglyceride accumulation in digestive glands by 24–47%. Inhabitation of E. japonica on juvenile scallop is best regarded as parasitism, rather than inquilinism or commensalism. Occurrence of polyps was probably not a direct lethal factor for juvenile scallops, because there were some sites where association rates were high, but mortalities were low. Massive mortalities in 2003 may have resulted from simultaneous impacts of heavy polyp load and stresses caused by the way in which the animals were handled (transferred from cages for pre-intermediate culture to cages for intermediate culture), because the massive mortality occurred within a month of the transfer. The presence of polyps in juvenile scallops does not affect the quality of the product in Funka Bay, because market size scallops are hydroid-free.     

Distribution and structure of heterotrophic protist communities in the northeast equatorial Pacific Ocean

The distribution and structure of heterotrophic protist communities and size-fractionated chlorophyll a were studied during the Korea Deep Ocean Study 98 (KODOS 98) research expedition (July 1998) in the northeast equatorial Pacific Ocean (5–11°N). Areas of convergence and divergence formed at the boundaries of the South Equatorial Current (SEC), North Equatorial Current (NEC), and North Equatorial Counter Current (NECC) during the expedition. Water column physicochemical characteristics significantly influenced the size structure of heterotrophic protist communities. Intense vertical mixing and high nutrient and chlorophyll a concentrations characterized SEC and NECC areas, which were affected by converging and diverging water masses, respectively. Nanophytoplankton dominated in SEC and NECC areas; both areas also had relatively high heterotrophic protist biomasses (average 743 µg C m^–2). NEC areas were characterized by a stratified vertical structure, low nutrient and chlorophyll a concentrations, and picophytoplankton dominance. The heterotrophic protist biomass in NEC areas averaged 414 µg C m^–2; nanoprotists (<20 µm) dominated the community. The nanoprotist biomass comprised 49–54% of the total heterotrophic protist biomass in SEC/NECC areas and 67–72% in NEC areas. The biomass of heterotrophic protists was higher in SEC/NECC areas than in NEC areas, but the relative importance of nanoprotists was greater in NEC areas than in SEC/NECC areas. Heterotrophic dinoflagellates were dominant components of the <20 µm and >20 µm size classes in both water columns. The biomass of heterotrophic protists significantly correlated with the net-, nano-, and picophytoplankton biomass in SEC/NECC areas and with the nano- and picophytoplankton biomass in NEC areas. Heterotrophic protists and phytoplankton also showed strong positive correlation in the study area. The size structure of the phytoplankton biomass coincided with that of heterotrophic protists; the heterotrophic protist biomass positively correlated with the protists prey source. These relationships suggest that the community structure of heterotrophic protists and the microbial food web depended on size classes within the phytoplankton biomass. Microzooplankton grazing and phytoplankton growth rates were higher in SEC/NECC areas than in NEC areas. In contrast, the potential primary production grazed by microzooplankton was relatively high in NEC areas (127.3%) compared with SEC/NECC areas (94.6%). Our results indicate that the relative importance and size structure of heterotrophic protists might vary according to two distinct water column structures.Communicated by T. Ikeda, Hakodate     

上海市典型污水处理厂污泥浸出液的化学和毒性评价

为了研究污水污泥在海洋环境中释放带来的生态风险,在分析上海7处典型污水处理厂污水污泥浸出液中重金属与溶解性有机碳的基础上,使用黑鲷,卤虫,三角褐指藻,纤细角毛藻和小球藻研究污水污泥浸出液对海洋生物的急性毒性作用和生长抑制作用。化学分析结果表明,所有样点的污水污泥浸出液中重金属总量均低于中国(GB5085.3-2007)与欧盟(EN12457.2-2002)关于危险废弃物的鉴别标准,但溶解性有机碳(DOC)含量超过欧盟标准1个数量级。毒性实验结果表明,黑鲷幼鱼对污水污泥浸出液的敏感性最强,其次是海洋微藻,卤虫无节幼体的敏感性较低;毒性综合分析结果表明,S2和S3点的污水污泥浸出液对海洋生物的综合生物毒性相对最高,而S4,S5的综合生物毒性最低,其中接纳污水为工业污水,且有机质与硫化物含量较低的污水污泥浸出液对海洋生物的综合生物毒性较低。     

Biochemical and cytological bases of metamorphosis in Hydractinia echinata

Larvae of the marine hydroid Hydractinia echinata Fleming are induced to settle and metamorphose by contact with bacteria of the genus Alteromonas espejiana (Leitz and Wagner 1992). In previous studies the biochemical mechanism for the activation of the larvae was found to include the signal transduction pathway via the phosphatidylinositol cycle and a role for a kinase C-like enzyme was established. In the present investigation laboratory-reared larvae were immunohistochemically stained with antibodies against kinase C and experiments were conducted to investigate protein phosphorylation during initial metamorphic events. A polyclonal antibody against a synthetic peptide derived from a conserved retion of kinases C binds to an antigen in neurosensory cells of the anterior part of the larvae and corresponding nerve fibres. The Western blot reveals major binding to a protein of M_r (relative molecular mass)=67 and two minor bands at M_r=66 and 48. Assays in vivo show that 3 to 25 min after induction of metamorphosis the phosphorylation of a protein with M_r=30 is enhanced. A hypothesis about the mechanism of induction at the cellular and biochemical level is presented which combines most of the ideas now available from our and other groups.     

Symbiosis within a symbiosis: Intracellular bacteria within the endosymbiotic protistNephromyces

The marine protistNephromyces Giard, 1888 is a chronic endosymbiont of molgulid tunicates. Ultrastructural and cytochemical studies of this protist, isolated from molgulid hosts collected from the Pacific, Atlantic and Gulf Coasts of the United States, indicate thatNephromyces is itself chronically infected with Gramnegative, intracellular bacteria. Molgulid tunicates are thus the locus of a nested,tripartite endosymbiosis. Intracellular bacteria are present in both trophic and reproductive stages ofNephromyces, suggesting that the bacterial-Nephromyces symbiosis is an hereditary association. The presence of endosymbionts inNephromyces raises the possibility that some ofNephromyces' metabolic characteristics, in particular its high urate oxidase activity, might be supplied not byNephromyces itself, but rather by its intracellular bacteria, possibly functioning as peroxisomal analogues.     

Occurrence and characteristics of unusual protistan symbionts from surgeonfishes (Acanthuridae) of the Great Barrier Reef,Australia

The occurrence of unusual symbiotic microorganisms was examined in the intestines of a range of fish from the Great Barrier Reef, Australia. The fish taxa examined included 26 species of the family Acanthuridae, as well as representatives of phylogenetically related and herbivorous taxa. The microorganisms, referred to as protists, were only found in herbivorous and detritivorous members of the Acanthuridae. Protists were not found in planktivorous acanthurids, nor in any members of the families Kyphosidae, Pomacentridae, Scaridae, Zanclidae, Siganidae and Bleniidae we examined. In addition, protists were absent from the herbivorous acanthurids A. xanthopterus and A. nigricans. A range of protist forms, characterized by differences in size (8 to 417 m), shape and mode of cell division (daughter-cell production and binary fission), was observed. The occurrence of these forms appeared to be correlated with host feedingecology. Large forms (>100 m) of the protists were only found in acanthurids which fed over hard-reef substrata. Smaller forms were found in sand-grazing and detritivorous species. One of the protist forms appears identical to protists previously reported from Red Sea acanthurids.     

A ciliate red tide at Barrow,Alaska

In September 1968 the first occurrence of extensive red water in the Arctic Ocean in the vicinity of Point Barrow, Alaska, was recorded. The organism causing this water discoloration was a fairly large (100 to 150 ) ciliated protozoan, with chlorophyll-containing endosymbionts. This ciliate, which is not identical to the commonly reported Mesodinium or Cyclotrichium species, is described in this paper, but cannot be identified with any organism described in the literature. Concentrations of dissolved inorganic nutrients and trace metals were determined on water samples obtained from the red water and also in the clear water adjacent to it. These data are discussed relative to the hydrographic conditions in the Chuckchi Sea around Point Barrow. A direct species' analysis by microscopic methods indicated that the plankton were quite similar in all the water samples except for the aforementioned red ciliate, which accounted for over 90% of the total cellular organic carbon in the samples from the red water. Chemical analyses indicated that the red tide ciliate contained approximately 51% protein, 33% lipid, 8% carbohydrate, 0.2% chlorophyll a, and 1.2% DNA.     

The life cycle ofClytia attenuata (calyptoblastea: Campanulariidae)

The life cycle of the hydroidClytia attenuata (Calkins) (Calyptoblastea: Campanulariidae) has been completed in the laboratory including development of the medusa, previously described asPhialidium lomae Torrey (Leptomedusae: Campanulariidae). Under laboratory conditions, the hydroid exhibits some morphological variation. Characteristic branching of the hydroid occurs at temperatures between 17° to 19°C. At 13° to 15°C the colonies are unbranched and cannot be distinguished fromClytia cylindrica L. Agassiz. Young medusae are similar to other young species ofPhialidium. Development to the adult form requires 25 to 30 days at 17° to 24°C. The adult medusae are 6 to 10 mm in diameter, watch-glass shaped, and have 20 to 28 tentacles. Based on the adult medusa,Clytia attenuata is maintained as a valid species.