First monospecific bloom of the harmful raphidophyte Chattonella antiqua (Hada) Ono in Alexandria waters related to water quality and copepod grazing

The massive red tide bloom of Chattonella antiqua that occurred in Alexandria waters during late August/early September 2006 was monospecific, of very high density, and of wide spatial distribution, and was accompanied by mass fish and invertebrates mortalities. During the bloom, surface water temperature ranged between 26.5 and 28.5 °C and salinity between 23 and 27 psu. The bloom started under very high nitrate and ammonia levels; where the uptake of ammonia seemed to be faster than that of nitrate, and the bloom seemed to avoid the copepod grazing. Mass fish and invertebrates mortality was observed. Few cells of Heterosigma species have been reported for the first time in the Alexandria waters. Several environmental constraints (including physical factors), nutrient loading, copepod grazing and comparison with other data for C. antiqua blooms in Alexandria waters are also discussed.     

Oxygen-radical-mediated toxic effects of the red tide flagellate Chattonella marina on Vibrio alginolyticus

Toxic mechanisms of the red tide flagellate, Chattonella marina, collected in 1985 from Kagoshima Bay, Japan, were studied at the subcellular level. C. marina was found to reduce ferricytochrome c at a rate related to the concentration of plankton cells. Ca. 50% of the cytochrome c reduction was inhibited by the addition of 100 U superoxide dismutase ml^-1. These results suggest that a part of the cytochrome c reduction was caused by a superoxide anion which was extracellulary released from C. marina. Moreover, a small amount of hydrogen peroxide was detected in the C. marina suspension using the fluorescence spectrophotometric assay method. The identity of the hydrogen peroxide was confirmed by its reaction with 500 U catalase ml^-1. It is thus proposed that C. marina produces harmful active oxygen radicals and therefore exhibits a toxic effect on surrounding living organisms. In agreement with these results, C. marina strongly inhibited the proliferation of marine bacteria, Vibrio alginolyticus, in a plankton/bacteria co-culture system. The growth inhibition of bacteria caused by C. marina was related to the density and the metabolic potential of C. marina. Ruptured plankton showed no toxic effect on the bacteria. Furthermore, the toxic effect of C. marina on V. alginolyticus was completely suppressed by the addition of catalase and superoxide dismutase. In addition to these radical-scavenging enzymes, a chemical scavenger, sodium benzoate, also had a protective effect. These results suggest that oxygen radicals are important in the toxic action of C. marina.     

Cyst formation of the noxious red tide flagellate Chattonella marina (Raphidophyceae) in culture

Cyst formation of the noxious red tide flagellate Chattonella marina (Raphidophyceae), cultured from a cyst in sediments of Suo-nada, Japan in 1986, was investigated by culture experiments. Nitrogen limitation was effective in inducing cyst formation. After incubation in N-limited medium at 25°C with 10000 lux on a 14 h light, 10 h dark photo-cycle, cultures were subjected to six different light intensities (0 10000 lux) in order to determine effects of light intensity on cyst formation. Cysts were formed under light intensities of 1000 lux or below, but not at 10000 lux. Cysts formed in culture displayed morphological characteristics quite similar to those natural cysts observed in sediments collected from the Inland Sea of Japan. Observations on nucleus, using diaminidinophenylindole (DAPI)-staining and epifluorescence microscopy, indicated that the majority of cysts formed in culture were uninucleate, a few were binucleate. Germination of cysts was observed under adequate conditions for germination (22°C, 3500 lux with a 14 h light, 10 h dark photo-cycle) even after storage at 11°C in the dark for more than 4 mo.     

Ultrastructural alterations on chloride cells of the yellowtail Seriola quinqueradiata,following exposure to the red tide species Chattonella antiqua

By means of scanning and transmission electron microscopy, the influence of the red tide species Chattonella antiqua was examined with respect to the surface ultrastructures of chloride cells of the yellowtail Seriola quinqueradiata. Conspicuous ultrastructural alterations occurred on the apical surface of these cells. The majority of chloride cells in the control gills showed an apical surface with numerous cellular extensions, while more than half the chloride cells affected by red tide organisms exhibited an apical surface with fewer and smaller extensions, a wrinkled apical surface, or a protruded apical surface. These ultrastructural alterations of chloride cell surface may be due to the partial disturbance of salinity by C. antiqua, and reflect the changes of the ion-transport function in yellowtail gills exposed to red tide water.     

Toxin accumulation and feeding behaviour of the planktonic copepod Calanus finmarchicus exposed to the red-tide dinoflagellate Alexandrium excavatum

The planktonic copepod Calanus finmarchicus is a dominant member of the zooplankton community in the lower St. Lawrence Estuary in eastern Canada. Blooms of the toxic marine dinoflagellate Alexandrium excavatum which produces high cellular levels of paralytic shellfish poisoning (PSP) toxins, occur during the period of high C. finmarchicus production in summer in this region. To study the feeding behaviour of C. finmarchicus in the presence of Alexandrium spp., experiments were conducted in which female adult copepods collected from the St. Lawrence Estuary between May and September 1991 were exposed under controlled conditions to two toxic isolates of A. excavatum (Pr18b and Pr11f) from the estuary and to a non-toxic control (PLY 173) of a closely related species, A. tamarense isolated from the Tamar Estuary, Plymouth, U.K. Clearance rates on non-toxic A. tamarense cells averaged 5.5 ml ind^-1 h^-1 but were nearzero with either toxic isolate. When presented with a mixture of A. excavatum and the non-toxic diatom Thalassiosira weissflogii in varying proportions, C. finmarchicus fed upon the diatom but avoided the toxic dinoflagellate. Although feeding rates on A. excavatum were very low, toxin analysis by high-performance liquid chromatography with fluorescence detection (HPLC-FD) revealed that the PSP toxins were accumulated in copepods exposed to toxigenic dinoflagellates.The toxin composition in copepods was similar to that of the toxic dinoflagellate, but not necessarily identical, particularly after short-term (2-h) exposure, when relatively elevated levels of N-sulfocarbamoyl toxins were detected. The evidence suggests that C. finmarchicus ingests toxic dinoflagellate cells, either mistakenly or during exploratory bouts of feeding, and accumulates PSP toxins in its gut system and perhaps in other tissues.     

Histological and histochemical changes in the gills of the yellowtail Seriola quinqueradiata exposed to the Raphidphycean flagellate Chattonella marina

The gills of the yellowtail Seriola quinqueradiata, exposed to Chattonella marina a red tide species, were examined histologically and histochemically. The pavement cells of primary lamellae were swollen in the exposed specimens. This presumably indicates that C. marina contains undetermined toxic substances. The number of mucous cells containing mucous decreased in proportion to the duration of exposure. The loss of the mucous substance in the cells is probably due to the ichthyotoxic stimulus caused by C. marina. A decrease of carbonic anhydrase activity in the secondary lamellae was confirmed, when mucous substances were lost in most mucous cells. Since the carbonic anhydrase usually exists in the epithelia of the secondary lamellae, it was presumably resolved by C. marina. The decrease of the carbonic anhydrase activity may cause certain physiological disadvantages to the fish exposed to C. marina.     

Impact of epibenthic predation on estuarine intertidal harpacticoid copepod populations

The extent to which energy is transferred directly from benthic meiofauna to epibenthic predators was investigated on an intertidal sand-flat in the Exe estuary, southwest England, during 1981–1982 and compared with data obtained from an intertidal mud-flat in the Lyhner estuary, also in south-west England, between 1978 and 1981. Two species of flatfish (Pleuronectes platessa L. and Platichthys flesus L.), two species of goby [Pomatoschistus microps (Krøyer) and P. minutus (Pallas)], brown shrimp (Crangon crangon L.) and shore crabs (Carcinus maenas L.) are the most common epibenthic predators feeding on the benthic invertebrates in these locatites. Harpacticoid copepods are the only component of the meiofauna to form a significant part of the diet of early juvenile stages of these predators, particularly the invertebrates. Harpacticoids are a more important source of food for predators feeding over the sand-flat than for those feeding on the mud-flat because in the sand-flat alternative prey of suitable size, such as small annelids, are absent. Moreover, the impact of predation on the mud-flat is spread over the whole harpacticoid species spectrum whereas on the sandflat it is confined almost entirely to a single species, Asellopsis intermedia (T. Scott). Flatfish, gobies and shrimp consume daily an estimated 0.01 to 0.1% of the standing stock of A. intermedia and account for between 12 and 22% of the observed reduction in the population of this species between July and October. Therefore, only a very small proportion of total meiofauna biomass is transferred directly to higher trophic levels.     

Estimation of Arctic copepod grazing rates in vivo and comparison with in-vitro methods

Gut evacuation rates were measured in Calanus hyperboreus and C. glacialis from two stations in Jones Sound, Northwest Territory (NWT) and one station in an Ellesmere Island Fjord during late summer of 1984. Gut content decreased exponentially with a rate constant, that, for Stage V C. glacialis at least, was independent of food type and time of day. Gut filling rates were measured in Stage V C. glacialis in the light and in the dark, at noon and midnight. Nighttime gut filling rates were very similar for both light intensities, and also similar to the daytime rate in the dark, whereas the daytime rate in the light was much lower. Ingestion rates were calculated for these latter experiments, including a rate term for defecation, and these results were compared to the values obtained from the observations of gut filling rates in vivo as reported in Head et al. (1985) and from long-term (2–3 d) bottle incubations as reported in Head et al. (in press). The following points were made: (1) in-vivo and in-vitro ingestion rates were very close if appropriate in-vitro experimental conditions were used with respect to light intensity and time of day; (2) copepods could fill their guts at a rate apparently higher than their normal nocturnal ingestion rate; and (3) the calculated rations were dependent on the shape of the observed diurnal feeding patterns.     

In situ grazing rate of the copepod population in the western subarctic North Pacific during spring

Time series sampling with a multi-layer plankton sampler was carried out in the western subarctic North Pacific during spring 1991. Neocalanus cristatus, N. flemingeri and Eucalanus bungii dominated and accounted for 88.5% of the copepod population in volume. Neocalanus spp. were distributed in the upper mixed layer, while E. bungii was mainly distributed between 120 and 300 m throughout the day and night. In contrast, Metridia pacifica, Pleuromamma scutullata and Gaetanus simplex showed clear diel vertical migration. Grazing activities were estimated simultaneously by gut fluorescence. Nocturnal grazing was observed for diel migrating species. Neocalanus spp. did not have a diel feeding rhythm and had relatively low gut fluorescence. E. bungii was considered to be dormant during the observation period. The estimated grazing rate of the copepod population on phytoplankton was 1.4 to 2.0% of the primary production while the metabolic requirement was 8.3 to 12.4% of the primary production. These facts suggest that the copepod population was unimportant as primary consumers and that microzooplankton plays a much more important role in sustaining low standing stock of phytoplankton and a high nutrient concentration in the western subarctic Pacific Ocean.     

Possible involvement of the glycocalyx in the ichthyotoxicity of Chattonella marina (Raphidophyceae): immunological approach using antiserum against cell surface structures of the flagellate

Although the ichthyotoxic mechanism of Chattonella marina is still unknown, several lines of evidence suggest that the reactive oxygen species (ROS), such as superoxide anion (O₂^-), hydrogen peroxide (H₂O₂)_, and hydroxyl radical (·OH), produced by C. marina are involved in the mortality of fish exposed to this flagellate. Recently, we found that the cell-free supernatant prepared from C. marina, which is considered to contain the glycocalyx, showed NADPH-dependent O₂^- generation. In this study, we prepared antiserum against the crude glycocalyx of C. marina. Using indirect immunofluorescence, it was confirmed that the antiserum specifically reacted with C. marina cells. In addition to C. marina, the antiserum also reacted with other raphidophycean flagellates such as Heterosigma akashiwo, Olisthodiscus luteus, and Fibrocapsa japonica, whereas no reactivity was observed against six other flagellate species tested. These results suggest that raphidophycean flagellates have common epitopes recognized by the antiserum. Interestingly, immunohistochemical analysis of paraformaldehyde-fixed gill lamellae from yellowtail exposed to C. marina revealed that the antiserum stained the surface of gill lamellae, while no such staining pattern was observed in control gill lamellae. These results suggest that the glycocalyx may be discharged when C. marina cells are inhaled into the fishes' mouths and then come into contact with the gill surface. Based on the present results, together with our previous findings, we propose that continuous accumulation of the discharged glycocalyx on the gill surface occurs during C. marina exposure, which may be responsible for the ROS-mediated severe gill tissue damage leading to fish death.     

氯氰菊酯对海洋卡盾藻的毒性效应

为了解拟除虫菊酯农药对海洋生态系统以及海洋初级生产力的影响,研究了氯氰菊酯对重要赤潮藻类海洋卡盾藻(Chattonella marina)的生长及生化指标的影响.结果表明,低浓度(≤10μg·L-1)的氯氰菊酯对海洋卡盾藻生长具有明显的促进作用,而高于50μg·L-1则产生较明显的抑制效应,但暴露后期会出现一定的超补偿效应.藻细胞内叶绿素a(Chl.a)、可溶性糖和可溶性蛋白含量及超氧化物歧化酶(SOD)活性在暴露初期变化较剧烈,24h或48h后趋于平稳.随着培养(暴露)时间的延长,低浓度暴露组以上指标均呈现先促进后恢复趋势,而高浓度暴露组则呈现先抑制后恢复趋势,丙二醛(MDA)含量随培养(暴露)时间的延长呈先促进后恢复趋势且随氯氰菊酯浓度升高而明显升高.在实验设计浓度下,氯氰菊酯对SOD活性和MDA含量的最低作用剂量为10μg·L-1,而对其他生长和生化指标的最低抑制浓度为50μg·L-1,SOD和MDA可作为监测环境中氯氰菊酯污染的敏感指标.     

Occurrence of large numbers of carcasses of the large,grazing copepod Calanus cristatus from the Japan Sea

Carcasses of Calanus cristatus were discovered in plankton samples collected from the Japan Sea throughout the year from 1970 to 1985. Many carcasses of copepodite Stages IV and V occurred in the layer between 15 and 300 m below a distinct thermocline. The number of copepodite Stage V carcasses also peaked in the layer between 1 500 and 2 000 m. The highest density of copepodite Stages IV and V carcasses was 169 individuals per 1 000 m³ and 1 573 individuals per 1 000 m³, respectively. Carcasses of adults occurred at depths below 500 m and numbers of males and females per 1 000 m³ were 1 to 16 and 1 to 42, respectively. Living males were larger in catch number than living females, but the relationship for carcasses was the opposite. Weight of carcasses was 15 to 25% of living C. cristatus. Carcasses contained about 51% carbon and 8% nitrogen by weight. Carcasses may have been drifting for more than one year in the epipelagic layer under the thermocline because of their slow decomposition rate.     

Impact of cattle grazing on the occupancy of a cryptic, threatened rail

Impacts of livestock grazing in arid and semiarid environments are often concentrated in and around wetlands where animals congregate for water, cooler temperatures, and green forage. We assessed the impacts of winter-spring (November-May) cattle grazing on marsh vegetation cover and occupancy of a highly secretive marsh bird that relies on dense vegetation cover, the California Black Rail (Laterallus jamaicensis coturniculus), in the northern Sierra Nevada foothills of California, U.S.A. Using detection-nondetection data collected during repeated call playback surveys at grazed vs. ungrazed marshes and a "random changes in occupancy" parameterization of a multi-season occupancy model, we examined relationships between occupancy and habitat covariates, while accounting for imperfect detection. Marsh vegetation cover was significantly lower at grazed marshes than at ungrazed marshes during the grazing season in 2007 but not in 2008. Winter-spring grazing had little effect on Black Rail occupancy at irrigated marshes. However, at nonirrigated marshes fed by natural springs and streams, grazed sites had lower occupancy than ungrazed sites. Black Rail occupancy was positively associated with marsh area, irrigation as a water source, and summer vegetation cover, and negatively associated with marsh isolation. Residual dry matter (RDM), a commonly used metric of grazing intensity, was significantly associated with summer marsh vegetation cover at grazed sites but not spring cover. Direct monitoring of marsh vegetation cover, particularly at natural spring- or stream-fed marshes, is recommended to prevent negative impacts to rails from overgrazing.     

Release of ultraviolet-absorbing compounds by the red-tide dinoflagellateLingulodinium polyedra

We tested the hypothesis that ultraviolet-absorbing compounds known as mycosporine-like amino acids (MAAs) are not only synthesized but also excreted by marine phytoplankton. An experiment was performed with cultures of the marine dinoflagellateLingulodinium polyedra (previously known asGonyaulax polyedra) exposed to visible (photosynthetically available, PAR, 400 to 700 nm) and ultraviolet (UV, 290 to 400 nm) radiation. Absorption properties of both particulate and dissolved organic matter pools (POM and DOM, respectively) showed maxima in ultraviolet absorption at 360 nm. Chromatographic analysis confirmed the presence of MAAs in both pools. Release of organic matter byL. polyedra, as measured spectrophotometrically by changes in UV absorption in the surrounding medium, showed a differential increase at 360 nm in cultures exposed to UV-B + PAR radiation. The changes in absorption in the DOM fraction were inversely proportional to intracellular UV absorption. Photodegradation experiments in which the DOM fraction was exposed to visible and UV-B radiation showed a decrease in absorption with dose. First-order photooxidation decay rates varied between – 0.005 and – 0.26 m² (mol quanta)^–1 and were also a function of the initial optical density (OD). These results indicate that UV-absorbing compounds synthesized by phytoplankton, such as certain dinoflagellates, may be a component of the DOM pool in surface waters of the ocean and contribute to the attenuation of UV radiation in the water column. Photooxidation consumes only 3 to 10% of the daily production of the DOM absorbing between 280 and 390 nm (including MAAs). This suggests that MAAs dissolved in seawater may contribute to the decrease of UV transmission through the water column on a time scale representative of phytoplankton growth (days) and bloom development (weeks).     

Effect of copper on volume regulation in the marine flagellate Dunaliella marina

The marine flagellate Dunaliella marina responds to hypotonic media in the same way as animal cells: an initial phase of osmotic swelling occurs, followed by a second, more prolonged phase of cell shrinkage — the volume-regulation phase. D. marina also volume-regulates in hypertonic media. This does not usually occur in animal cells exposed to normal concentrations of K⁺. Copper concentrations of 2 ppm and higher inhibit regulation of cell volume in D. marina transferred to hypotonic media. This is probably due to reduced cell-membrane permeability to K⁺ and/or Cl^- and not to an interference with the Na⁺/K⁺ exchange pump. These findings suggest that volume regulation is functionally independent of the Na⁺/K⁺ exchange pump. The method described herein appears to be a suitable biotest for pollutants, providing specific information on their effects on the permeability of cell membrane.     

营养盐对海洋卡盾藻生长与产毒的影响（Effect of Some Nutrients on the Growth and Haemolytic Toxins Production of Chattonella marina）

海洋卡盾藻(Chattonella marina)是我国南方重要的有害赤潮原因种,其产生的溶血毒素、活性氧等可能是造成鱼类死亡的重要原因.在实验室条件下,研究了氮、磷和铁等营养盐对海洋卡盾藻生长及产毒的影响,以期为阐明海洋卡盾藻溶血毒素生成机制奠定基础.研究结果发现:在铁、氮、磷盐三因素四水平正交实验条件下,铁盐和氮盐是影响海洋卡盾藻生长的显著因子;氮盐和磷盐是影响海洋卡盾藻产毒的显著因子;铁盐浓度0.492mg·L-1、氮盐浓度375mg·L-1、磷盐浓度5mg·L-1时海洋卡盾藻的比生长速率最大;铁盐浓度0mg·L-1、氮盐浓度375mg·L-1、磷盐浓度0.5mg·L-1时海洋卡盾藻的产毒能力最强,即高氮、低磷条件下有利于海洋卡盾藻溶血毒素的合成.     

Photosensitivity of the calanoid copepod Acartia tonsa

The light intensity and spectral sensitivities of the calanoid copepod Acartia tonsa Dana were determined by measuring phototactic responses. Adult females displayed only positive phototaxis. The dark-adapted copepod, which possesses a single naupliar eye, perceived light at intensities as low as 2.8x10¹¹ photons m^-2 s^-1. The action spectrum for positive phototaxis had no clear maxima but rather showed a broad range of greatest sensitivity from 453 to 620 nm. This sensitivity encompassed those wavelengths that are maximally available at the depth where the copepod is found during the day. This spectral overlap, coupled with the finding that the copepod requires light cues for nocturnal vertical miration, suggests that broad spectral sensitivity is an adaptive mechanism to maximize light intensity sensitivity during migration.     

Mating system of the intertidal copepod Tigriopus californicus

Male Tigriopus californicus clasp immature females (copepodid stages II–V) for a period of up to a week prior to the female's terminal molt; upon maturation (stage VI) the female is inseminated and released. While females can mate anytime after their terminal molt, experiments using electrophoretically-detected genetic markers indicate that each mates only once in her lifetime. No evidence of sperm displacement was observed. Hence, male mating behavior can be interpreted as pre-copulatory mate guarding, a strategy employed to assure that a potential mate has not been previously inseminated. Males minimize the time investment required to insemiate a single female successfully by preferentially choosing to clasp more developmentally-advanced females; males clasped to stage III females will release them in order to clasp stage V females if the latter are present. Since males are capable of multiple mating, under most conditions of population sex ratio, this mating system results in low availability of unclasped, developmentally-advanced females; consequently, males must clasp successively younger (i.e. developmentally less-advanced) females in order to obtain a successful insemination.     

Reproductive biology of the planktonic copepod Temora stylifera

Laboratory studies on the reproductive cycle of the planktonic copepod Temora stylifera, collected from the Gulf of Naples between October 1987 and March 1988, showed that females oscillated between a light and dark gonadal condition. Histological preparations indicated that the dark condition corresponded to a ripe stage of oogenesis as compared to the light or unripe maturation state of primary oocytes. The number of eggs released within 24 h was strongly dependent on the reproductive status of the female at the time of incubation. Light unfed females rarely reverted to a dark or ripe condition and egg deposition in such cases was almost always zero. Dark females produced eggs within 24 h under all experimental food conditions, reverting from dark to light soon after egg deposition. Successively, the length of the interclutch period was strongly dependent on the type of food present. A high percentage of infertile eggs was almost always present. We suggest that short-term studies, not taking into consideration the condition of gonads at the time of incubation, will underestimate potential egg production rates. Females maintained for longer than three or four days produced mainly infertile eggs. After remating, females reinitiated the production of fertile eggs but egg viabilities never reached 100% hatching success, indicating poor efficiency in the fertilization of mature oocytes. We hypothesize a possible cause and effect relationship between egg viabilities and seasonal fluctuations in population densities.Died tragically at sea during a cruise     

Transfer of radioactive carbon within the copepod Temora longicornis

Standard autoradiographic techniques have been used to describe the temporal pattern in the transfer of radioactive carbon from the chlorophyte Tetraselmis suesica (Kylin) to females of the neritic copepod Temora longicornis (Müller, 1792). After 4 and 6 h exposure to labelled phytoplankton, silver grains were deposited only in the cells of the gut-wall. After 24 h exposure, grains were deposited in most tissues, with highest concentrations in cells of the gut-wall and in oocytes within the ovary. Experiments with Centropages typicus (Krøyer), Centropages hamatus (Lilljeborg), and Labidocera aestiva Wheeler demonstrated that much of the assimilated label was not turning over rapidly and that the amount of label assimilated was correlated with known food preferences of these species.