Effects of symbiont elimination and reinfection on the life processes of the planktonic foraminifer Globigerinoides sacculifer

Laboratory experiments were carried out to determine the influence of symbiotic dinoflagellates (zooxanthellae) on the shell growth, longevity, and reproductive potential of Globigerinoides sacculifer (Brady). Its symbionts were eliminated by 72-h treatment with a photosynthetic inhibitor (DCMU). Symbiont elimination resulted in earlier gametogenesis (shortened survival time) and smaller shell sizes of G. sacculifer when compared to untreated foraminifera grown in sea water. Individuals kept in continuous darkness in untreated sea water also exhibited early gametogenesis, short survival times and small shell sizes. Aposymbiotic foraminifera formed on the average one or two chambers fewer per individual and their rate of shell size increase is slower than symbiont-bearing foraminifera. Symbionts were lysed within perialgal vacuoles of G. sacculifer when subjected to DCMU treatment or kept in continuous darkness. One DCMU-treated group was reinfected with symbionts from crushed G. sacculifer donors. Soon after reinfection, these foraminifera resumed a shell growth rate and exhibited developmental stages that were nearly equivalent to those of untreated individuals, as deduced from their shell size, frequency of sac-like chambers, rate of gametogenesis, and survival time. Our experiments indicate that the symbionts aid in calcification and that elimination of symbionts triggers gametogenesis, thus shortening the life span of the foraminiferal host. The results imply that shell growth in symbiont-bearing planktonic foraminifera occurs mainly in the euphotic zone and that they do not survive for long periods below it.     

Environmental factors affecting the standing crop of foraminifera in sublittoral and psammolittoral communities of a Long Island salt marsh

Representative samples from the epiphytic and psammolittoral communities were made during the summer of 1968 in North Sea Harbor, Southampton, Long Island, USA. In the epiphytic communities, the foraminifera were very patchy; 2.6% of the total samples accounted for 56.4% of the total foraminifera collected. The standing crop and species composition of the foraminifera changed throughout the summer. Two seasonal peaks were observed in the epiphytes. In early summer Protelphidium tisburyensis was the dominant form. In late July and August Elphidium incertum was dominant. Taken as a whole over the entire summer, the following species comprised the epiphytic foraminiferan community: Elphidium incertum (46.63%); Protelphidium tisburyensis (25.64%); Ammotium salsum (9.88%); Elphidium clavatum (6.74%); E. translucens (3.47%); Ammonia beccarii (2.83%); Ammobaculites dilatatus (2.08%); Trochammina inflata (1.8%); Elphidium advenum (< 1%); E. galvestonense (< 1%); E. gunteri (< 1%); Quinqueloculina lata (< 1%); Q. seminulum (< 1%) and Trochammina macrescens (< 1%). Although fewer species were found, many more foraminifera live in the benthos than in the epiphytic community. Taken as a whole, over the entire summer, the following species comprised the foraminifera in the psammolittoral community: Trochammina inflata (49.6%); Elphidium incertum (31.8%); Ammotium salsum (10.9%); Quinqueloculina seminulum (4.2%); Elphidium sp. (1.5); Protelphidium tisburyensis (0.9%); Ammonia beccarii (0.7%); Elphidium clavatum (< 0.1%); and E. translucens (< 0.1%). Three species, Ammotium salsum, Elphidium incertum and Trochammina inflata bloomed successively in the psammolittoral community. The distribution of the latter two species was correlated with the vertical and horizontal changes of grain size; Elphidium incertum distribution clustered around a median grain size of 0.1 mm, whereas Trochammina inflata clustered around a median grain size of 0.46 mm. The sediments were sampled both at high and low tide. No evidence was obtained to suggest migration of foraminifera through the sediments as a function of tidal cycle. Horizontal distribution of the foraminifera in the marsh was correlated with the flow patterns of very small rivulets in the study area. With respect to many species of foraminifera, the overlying epiphytic communities are not continuous with the psammolittoral communities below them in the water column. Protelphidium tisburyensis was an early summer dominant epiphyte, but was rare in the psammolittoral communities. Trochammina inflata, on the other hand, was dominant in the coarser, deeper sediments and was rare in the epiphytic community. Elphidium incertum is presumably a generalist species. It formed half the foraminiferan population throughout the water column. Ammotium salsum was also abundant in both communities.Supported by US AEC Contract AT (30-1) 3995. Ref. No. NYO 3995-16.Summarized from a thesis submitted by N. J. Matera in partial fulfillment of the requirements of Master of Arts at The City College of New York.University Institute of Oceanography of CUNY, Contribution No. 1.     

Onset of symbiosis and distribution patterns of symbiotic dinoflagellates in the larvae of scleractinian corals

The establishment of symbiosis in early developmental stages is important for reef-building corals because of the need for photosynthetically derived nutrition. Corals spawn eggs and sperm, or brood planula larvae and shed them into the water. Some coral eggs or planulae directly inherit symbiotic dinoflagellates (Symbiodinium spp.) from their parents, while others acquire them at each generation. In most species examined to date, the larvae without dinoflagellates (aposymbiotic larvae) can acquire symbionts during the larval stage, but little is known regarding the timing and detailed process of the onset of symbiosis. We examined larval uptake of symbiotic dinoflagellates in nine species of scleractinian corals, the onset of symbiosis through the early larval stages, and the distribution pattern of symbionts within the larval host, while living and with histology, of two acroporid corals under laboratory conditions. The larvae acquired symbiotic dinoflagellates during the planktonic phase in all corals examined which included Acropora digitifera, A. florida, A. intermedia, A. tenuis, Isopora palifera, Favia pallida, F. lizardensis, Pseudosiderastrea tayamai, and Ctenactis echinata. The larvae of A. digitifera and A. tenuis first acquired symbionts 6 and 5 days after fertilization, respectively. In A. digitifera larvae, this coincided with the formation of an oral pore and coelenteron. The number of symbiotic dinoflagellates increased over the experimental periods in both species. To test the hypothesis that nutrients promotes symbiotic uptake, the number of incorporated dinoflagellates was compared in the presence and absence of homogenized Artemia sp. A likelihood ratio test assuming a log-linear model indicated that Artemia sp. had a significantly positive effect on symbiont acquisition. These results suggest that the acquisition of symbiotic dinoflagellates during larval stages is in common with many coral species, and that the development of both a mouth and coelenteron play important roles in symbiont acquisition.     

Under-ice feeding and diel migration by the planktonic copepodsCalanus glacialis andPseudocalanus minutus in relation to the ice algal production cycle in southeastern Hudson Bay,Canada

The marine planktonic copepodsCalanus glacialis Jaschnov andPseudocalanus minutus (Kroyer) typically dominate the copepod biomass in spring under the ice in southeastern Hudson Bay, Canada. Females of both species exhibited significant diel feeding cycles, as measured by gut pigment content, throughout a bloom of ice algae at the ice-water interface in 1986. Periods of grazing correlated well with a nighttime vertical migration by females to within 0.2 m of the ice-water interface, suggesting that feeding took place at or just below the thermohaline boundary between seawater and the interfacial layer containing the ice algae. Seasonal melting of the ice bottom in mid-May resulted in freshening of the surface layer and release of the ice algae into the water column. FemaleC. glacialis andP. minutus responded by ceasing migration to the interface. Gut pigment content, and by reasonable assumption, feeding activity in the water column, increased substantially immediately after this event. In mid-May, the water column phytoplankton consisted of flagellates, sedimenting ice algal cells, and diatoms (Navicula pelagica andChaetoceros sp.) previously found at the interface and then growing in the water column. We conclude that algae growing at the ice-water interface, and sedimenting or actively growing algae derived from this interfacial layer, are a regular and principal source of nutrition for these pelagic copepods during and immediately after the ice algal bloom.     

The ecophysiological complex of Bathyporeia pilosa and B. pelagica (Crustacea: Amphipoda). I. Respiration rates

The metabolic rates of high and low shore estuarine populations of Bathyporeia pilosa Lindström and an open coast population of B. pelagica (Bate) have been determined over a range of temperatures during January and February, and June and July, 1968. Changes in oxygen uptake have also been measured monthly at 15°C. During the winter, oxygen uptake was in the order: high shore B. pilosa>low shore B. pilosa>B. pelagica. During the summer, high shore B. pilosa and B. pelagica had similar metabolic rates, but both were significantly higher than low shore B. pilosa. Both populations of B. pilosa had lower metabolic rates in summer than in winter, whereas the metabolic rate of B. pelagica remained much the same. Seasonal changes in metabolic rate are closely correlated with reproductive cycles. The possible influences of environmental parameters are discussed.     

Dietary study of the midwater polychaete Poeobius meseres in Monterey Bay,California

This study presents the first quantification of the diet of a gelatinous midwater organism on a temporal basis. Using the Monterey Bay Aquarium Research Institute's remotely operated vehicle Ventana, regular collections of the polychaete Poeobius meseres (Heath, 1930) over a 1 yr period (October 1990 to November 1991) in Monterey Bay yielded intact organisms for the study of feeding behavior and quantitative analysis of stomach contents. In situ observations showed P. meseres feeding in two different ways: (1) by deployment of a mucus web in the water column that passively collects particles for consumption; and/or (2) by grasping detrital material in the water column with its ciliated tentacles. Stomach-content analyses showed that P. meseres is primarily coprophagic, its diet being dominated by fecal pellets from euphausiids and copepods. These fecal pellets appear to provide P. meseres with essentially all its carbon. Although fecal pellets were the most important food item volumetrically, P. meseres also consumed large numbers of diatoms and small numbers of dinoflagellates, chrysophytes, radiolarians, foraminiferans and eggs. The diet of P. meseres appears to reflect primary productivity in the surface waters, with different food items predominant in the diet at different times of the year. Pennate diatoms were most abundant in the diet during the fall, centric diatoms were most abundant during the sumnier, and fecal pellets during the winter. The composition of P. meseres diet suggests that this and other midwater gelatinous organisms have a significant role in the remineralization of particles as they sink from the surface to the deep sea.     

Standing crop of foraminifera in sublittoral epiphytic communities of a Long Island salt marsh

During the summers of 1966 and 1967, 12 field trips were made to stations in North Sea Harbor, Southampton, Long Island (USA). From representative locations, 228 small samples of larger algae and their epiphytes (0.2 g dry weight) were taken aseptically. Enteromorpha intestinalis, the most widely distributed aquatic plant, was the most frequently collected. The large standing crop of Zostera marina and Zanichellia palustris was also sampled. Foraminifera were most abundant in epiphytic communities of Enteromorpha in early summer and later spread to Zostera, Zanichellia, Ulva, Polysiphonia, and Ceramium. Foraminifera were rarely found in epiphytic communities of Fucus or Codium. By summers' end Enteromorpha rarely had a standing crop of foraminifera. One of the most abundant foraminiferan species, Protelphidium tisburyensis, was found most frequently on Enteromorpha; Quinqueloculina spp occurring on Enteromorpha, less frequently. Ammonia beccarri and Elphidium spp were abundant in the environment, and showed little substrate preference. Patches of decaying Enteromorpha had the greatest standing crop of foraminifera and low species diversity index (0.581). Young green patches had a much higher species diversity index (0.94). Indices for Zostera, Zanichellia, Polysiphonia, Fucus, Ulva and Codium were, respectively, 0.82, 0.99, 0.86, 0.70, 0.77, and 0.196. No correlation was found between epiphytic community weight and total number of foraminifera recovered. The standing crop of epiphytes/g substrate dry weight was lower at some field stations; possibly explained by stronger current. Of the total samples, 50.4% were positive, with an average of 18 foraminifera/sample, or 40 foraminifera/g substrate plant and epiphytes. Twenty six samples were classified as bloom with 50 or more forams (57 to 425)/sample. Species diversity indices for these blooms ranged from 0.38 to 1.12. Ammonia beccarii was the dominant form in 18 blooms, Allogromia laticollaris and Protelphidium tisburyensis in 3; Elphidium incertum, Quinqueloculina seminulum and Trochammina inflata in 1 each.Supported by US AEC Contracts AT (30-1) 3396 and AT (30-1) 3995. Ref. numbers NYO 3396-17 and NYO 3995-2.Much of this study was carried out in the Living Foraminifera Laboratory, Department of Micropaleontology of the American Museum of Natural History.     

Role of bacteria in larval settlement and metamorphosis of the polychaete Hydroides elegans

The serpulid polychaete Hydroides elegans Haswell, 1883 is an early colonist of new substrata in Pearl Harbor, Oahu, Hawaii. When metamorphically competent, larvae of H. elegans will settle rapidly upon an acceptably biofilmed surface, but not on a clean surface. In this study we found the ability of larvae to respond selectively to inductive surfaces to be retained for at least 3 wk. Of a series of bacterial strains isolated from Hawaiian marine biofilms, 13 induced larval settlement, 11 gave moderate or mixed results, and 10 others did not stimulate the settlement of H. elegans. The amount of settlement induced by monospecific strains was rarely as great as with natural, multispecies films. Most of the isolated bacteria were motile Gram-negative rods, but Gram-positive strains were also present, and diverse metabolic types were represented in the study. Biofilms killed by treatment with heat, ultraviolet radiation or chemical fixatives were no longer inductive. Soluble, dialyzable, heat-stable bacterial products induced settlement and metamorphosis more slowly. The range of bacteria producing an inductive signal suggests either that there are multiple cues, or that the cue is common to many bacteria. Chemical signals characteristic of early microbial biofilms may indicate freshly available substrata with optimal potential for the growth and survival of H. elegans. Received: 30 January 1998 / Accepted: 12 September 1998     

Planktonic bioluminescence in the pack ice and the marginal ice zone of the Beaufort Sea

An icebreaker cruise into the Beaufort Sea in the fall of 1986 provided a unique opportunity for studying planktonic bioluminescence in ice fields and in the marginal ice zone. Bathyphotometer casts (bioluminescence intensity, seawater temperature, beam attenuation coefficient, and salinity) and biological collections were made to a depth of 100 m. A light budget, which describes the planktonic species responsible for the measured bioluminescence, and a dinoflagellate species budget were constructed from the mean light output from luminescent plankton and plankton counts. The vertical distribution of bioluminescence among the ice stations was similar. The maximum intensities were 2 to 8×10⁶ photons s^-1 cm^-3 in the upper 50 m of the sea-ice interface. The marginal ice zone station (MIZ) exhibited a maximum intensity of 2 to 3×10⁸ photons s^-1 cm^-3 between 5 and 30 m depth. At Ice Station 2, Metridia longa and their nauplii contributed approximately 80% of stimulable bioluminescence in the upper 10 m but, overall, Protoperidinium spp. dinoflagellates contributed most of the light to a depth of 100 m. In the MIZ, Protoperidinium spp. dinoflagellates contributed 90% of the light within the upper 10 m, decreasing to 43% of the contributed light at a depth of 40 m. Below 40 m, dinoflagellate bioluminescence decreased to a few percent of the total to a depth of 90 m. Metridia spp. copepods contributed more than 50% of the light at depths from 40 to 90 m. Ostracods, larvaceans, and euphausiid furcilia contributed <1% of all bioluminescence at all depths sampled. Correlation analyses between measured bioluminescence (photons s^-1 cm^-3), the number of bioluminescent dinoflagellates and the light budget for the MIZ indicated highly significant associations: r=0.919, p=0.001, and r=0.912, p<0.001, respectively (Student's two-tailed t-tests). Bioluminescence was negatively correlated with seawater salinity at all stations (p=0.001). Maximum bioluminescence was measured in the less saline surface waters at all stations.     

Prey size selection,feeding rates and growth dynamics of heterotrophic dinoflagellates with special emphasis on Gyrodinium spirale

The relationship between size and growth rate in heterotrophic dinoflagellates (collected from the Kattegat, Denmark during 1989 and 1990) was studied. In addition, prey size selection, feeding rates and growth dynamics were studied for the naked heterotrophic dinoflagellate Gyrodinium spirale Bergh. Heterotrophic dinoflagellates have growth rates which are approximately three times lower than that of their potential competitors, the ciliates. G. spirale requires a relatively high prey concentration in order to grow. Ingestion rate at the maintenance level is about half of that of maximum ingestion rate. Consequently, yield is lower than typically found for planktonic protozoa. When exposed to low prey concentrations, the dinoflagellate is able to reduce its metabolism and thus prolong survival. The optimum prey particle size for G. spirale, which feeds by direct engulfment, corresponds to its own size. The ability to ingest relatively large prey may explain why these organisms are competitive in nature.     

Studies of primary productivity in coastal waters of southern Long Island,New York

Phytoplankton productivity of the tidal estuaries and coastal waters of southern Nassau Country, Long Island, New York, USA was determined monthly at 28 stations during 1966. Diatoms alternated with dinoflagellates in dominating the standing crop in the coastal area. The estuaries were characterized by sustained blooms of green flagellates and dinoflagellates during the spring/summer period, 1966. Chlorophyll a ranged from 1.0 to 27.6 mg/m³ in the estuarine area, and 1.45 to 10.15 mg/m³ in adjacent coastal waters. Rate of phytosynthesis per unit weight chlorophyll a for surface samples in the region under study a veraged from 3.1 to 3.5 mgC/mg chlorophyll a/h. At light saturation, however, the ratio varied according to water temperature and species' composition. Primary productivity decreased seawards, with mean values for 1966 of 0.35, 0.22, and 0.16 gC/m³/d for the estuarine, nearshore and offshore areas, respectively.This study was carried out at the Lamont Geological Observatory of Columbia University Palisades; New York, USA.The study was conducted with financial assistance from Nassau County, New York, and the G. Unger Vetlesen Foundation.     

Marine fungi (Ascomycetes) within and on tests of Foraminifera

Fruiting bodies of higher marine fungi occur within and on tests of foraminiferans on tropical beaches of the Pacific (Australia, Hawaii) and Atlantic Ocean (Belize, Mexico). Ascocarps (fruiting bodies ) of five intertidal species or varieties of the genera Arenariomyces, Corollospora and Lindra colonize foraminiferans in the natural habitat and may contribute to the eventual breakup of the tests. Fungal fruiting structures, which are normally subglobose when developing in other substrates, adjust to the shape of the foraminiferan chambers when growing within the tests. Pure cultures of L. thalassiae var. crassa yielded the same type of irregular fruiting bodies when grown at 30° C on foraminiferan tests as the sole source of nutrients.Smithsonian Contribution No. 174 (Investigations of Marine Shallow-Water Ecosystems Program, Reef and Mangrove Study-Belize)     

Ultrastructural examination of chamber morphogenesis and biomineralization in the planktonic foraminiferOrbulina universa

Pre-sphere, trochospiralOrbulina universa (d'Orbigny) were hand-collected between June and September, 1982 to 1984, from surface waters of the Pacific Ocean ca. 2 km off Santa Catalina Island, California, USA. The formation of a spherical chamber by this planktonic foraminifer was studied with light and electron microscopy. Chamber morphogenesis is preceded by the secretion of a cytoplasmic layer rich in mitochondria. The layer expands away from the pre-existing foraminiferal shell surface in a spherical pattern. Full cytoplasm expansion is followed by the secretion of an organic matrix (OM) approximately 200 m above the original shell surface. Cytoplasm, mitochondria and/or vesicles may play a role in OM secretion. Calcification and chamber thickening, new spine growth and pore development are documented and continue for a period of 1–7 d. Approximately 24 h prior to gamete release, the foraminiferal spines are resorbed and a veneer of calcite is deposited on the shell surface. An extensive intracellular organelle unique to foraminifera, the fibrillar system, is examined and is hypothesized to play a role in the biomineralization process. The taxonomic and functional significance of theO. universa spherical chamber is discussed with respect to other foraminiferal species.     

Seasonal population structure,vertical distribution and migration of the chaetognath Sagitta elegans in the Celtic Sea

The biology of the chaetognath Sagitta elegans Verrill has been much researched, but detailed studies of population structure have generally been conducted in coastal water where dynamic tidal conditions may cause difficulty in interpretation of data. The resolution of sampling examining vertical distribution and diurnal migration has also been rather coarse. During a series of eight cruises to a seasonally thermally stratified sampling site in the Celtic Sea in 1978 and 1979, detailed vertical zooplankton profiles were taken to study the seasonal population structure, vertical distribution and migration of this species. The overwintering stock of S. elegans (22 to 52 individuals m^-2, 0 to 90 m) had a wide range of lengths (5 to 20 mm) and matured in 1978 from early March, spawning several times before dying out by late July. Young produced by the overwintering stock started to mature in July and population numbers reached their highest in August (2483 m^-2, 132.8 mg C m^-2) when sea temperature peaked (17.1°C). By October, the population of S. elegans declined (284 m^-2), which was thought to be due to a combination of lower sea-water temperature, competition for and availability of food, and predation. Because of the length range of the overwintering population (5 to 20 mm), it is assumed that reproduction continued at a low level over the winter, although eggs were not found in January and February, the coldest months of the year. In summer, the smallest S. elegans (2 to 6 mm) were found in the near-surface waters and did not migrate, but as their lengths increased they occupied deeper depth ranges and a portion of the population started to migrate diurnally. Individuals which did not migrate and stayed in the warmer surface waters, or those which migrated into it, matured faster than those remaining in the colder water below the thermocline. Migration to surface waters by mature individuals seemed to be stopped by high surface temperatures (17°C) and a sharp thermocline (3 C°). As sea temperature increased during the year from the winter minimum of 7.7°C, S. elegans matured at a progressively shorter length (14 mm in March 1978 to 10 mm in August). There are probably only three generations of S. elegans a year in the Celtic Sea.     

The early summer bloom of dinoflagellates in the North Sea,with special reference to 1971

The south-western quarter of the North Sea (between the Wash and the River Tyne) has been investigated for the presence of dinoflagellates. Extensive net surveys were carried out in March, May and June 1971 and a number of other collections were made in the area. North of Flamborough Head, the spring bloom of diatoms was succeeded by a considerable growth of dinoflagellates, of which Dinophysis norvegica was the most abundant organism. Maximum counts of over 28 million dinoflagellates per m³ were recorded. Distribution charts are given for the most common species. A total of 61 species was found during the course of the survey.     

GO通过氧化损伤激活秀丽线虫未折叠蛋白反应

以秀丽线虫为受试生物,探讨氧化石墨烯(GO)对秀丽线虫未折叠蛋白应答的激活及其与氧化应激的关系。将L4幼虫暴露于GO中24 h,通过检测活性氧(ROS)水平、乳酸脱氢酶(LDH)、丙二醛(MDA)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(GSH-Px)等指标评估GO对秀丽线虫所致氧化损伤;以hsp-4和hsp-6分别作为秀丽线虫内质网和线粒体未折叠蛋白反应(UPR)的报告基因评价GO对秀丽线虫UPR应答的激活;同时以谷胱甘肽(GSH)作为抗氧化剂探讨GO所致UPR应答与氧化应激的关系。研究结果显示,GO暴露后秀丽线虫体内ROS、LDH和MDA水平升高,抗氧化酶活性上升;内质网和线粒体UPR反应增强,GSH预处理可以降低内质网和线粒体UPR应答。研究表明,GO短期暴露可以诱导秀丽线虫机体氧化应激进而激活UPR应答,抗氧化保护可以降低UPR应答反应。     

Form and feeding mechanism of a living Planctosphaera pelagica (phylum Hemichordata)

We describe aspects of the anatomy and suspension-feeding mechanism of a single Planctosphaera pelagica captured from the plankton in June 1992 off Bermuda in the western Atlantic. We also describe several unusual features of the larva, including its occurrence in surface waters, unusually large size, and limited swimming ability. Our account of the form and feeding behavior of P. pelagica is the first based on observations of a specimen captured and observed alive. Our limited observations suggest that the planctosphaera may use a suspension-feeding mechanism much like that of the other feeding deuterostome larvae (the pluteus and bipinnaria larvae of echinoderms and the tornaria larva of enteropneust hemichordates) known to capture food particles using a single ciliated band. Although we could not observe cilia directly, the movement of dye streams and food particles and the structure of the ciliated band suggest that some particles may be captured at the ciliated band by the reversal of ciliary beat. The planctosphaera possesses many prominent mucous glands near the food grooves. This suggests an important role of mucus in the biology of the larva, but we were not able to observe directly any role of mucus in particle capture.     

Role of glutamine synthetase in ammonia assimilation by symbiotic marine dinoflagellates (zooxanthellae)

The dinoflagellate symbionts (zooxanthellae) present in many reef corals aid in the survival of the symbiotic unit in nitrogen deficient tropical waters by providing additional routes of nitrogen uptake and metabolism. The enzymatic pathway of ammonia assimilation from seawater and the re-assimilation of coral ammonium waste by zooxanthellae was studied by examining the affinity of glutamine synthetase for one of its substrates, ammonia. Glutamine synthetase activity was measured in dinoflagellates of the species Symbiodinium microadriaticum found in symbiotic association with various marine coelenterates. Michaelis-Menten kinetics for the substrate ammonia were determined for freshly isolated dinoflagellates from Condylactis gigantea (apparent NH₃ K_m=33 M) and for cultured dinoflagellates from Zoanthus sociatus (apparent NH₃ K_m=60 M). On the basis of the low apparent K_ms for NH₃, it appears that ammonia assimilation by these symbiotic dinoflagellates occurs via the glutamine synthetase/glutamate synthase pathway. Additionally, the uptake of exogenous ammonium by an intact coelenterate-dinoflagellate symbiosis was strongly inhibited by 0.5 mM methionine sulfoximine, and inhibitor of glutamine synthetase.     

Seasonal fluctuations in the abundance of populations of marine cladocerans and their resting eggs in the Inland Sea of Japan

Seasonal fluctuations in the abundance of resting eggs of four species of marine cladocerans, Penilia avirostris Dana, Podon polyphemoides (Leuckart), Evadne tergestina Claus and Evadne nordmanni Lovén, were investigated in association with their planktonic populations in the central part of the Inland Sea of Japan for a period of over two years. Most numerous were the eggs of P. avirostris, followed by those of the species in the aforementioned order. There was a marked seasonal fluctuation in the number of eggs that was closely correlated with the occurrence of the planktonic population for each species. The egg-number was highest just before the planktonic population disappeared from the water column, and gradually decreased thereafter until a minimum value was reached shortly before the new planktonic population appeared in the next season. The pattern of fluctuation in number was found to be very similar among all four species, indicating strongly that the cladoceran populations in this warm temperate sea may persist either as plankton in warmer seasons or as benthic resting eggs in colder seasons. The possible causes of the decrease in egg density in bottom sediments are discussed.     

Effects on larval crabs of exposure to algal toxin via ingestion of heterotrophic prey

We tested whether ingesting toxic algae by heterotrophic prey affected their nutritional value to crab larval predators, using toxic algal strains that are either ingested directly by larval crabs or rejected by them. Ingestion of toxic strains of the dinoflagellates Alexandrium andersoni and A. fundyense by the rotifer Brachionus plicatilis was confirmed. Rotifers having ingested either algal type for five days were fed to freshly hatched larvae of three crab species, with larval survival and stage durations determined. For both algal/rotifer treatments in all three crab species, larvae fed algae directly died during the first zoeal stage, while those fed rotifers that had been fed either algal strain survived to the experiment’s end (zoeal stage 3). Survival was lower, and stage duration longer, for larvae fed rotifers cultured on toxic algae when compared to those fed non-toxic algae. The role of toxic algae in the planktonic food web may be influenced by its direct or indirect ingestion by larval crabs.