Oxygen dependent sulfide detoxification in the lugwormArenicola marina

The lugwormArenicola marina L. oxidizes entering sulfide to thiosulfate. After 8 h of normoxic incubations with sulfide concentrations of 0.2 to 1.0 mmoll^-1 thiosulfate in the coelomic fluid amounted up to about 4 mmoll^-1 whereas sulfite concentrations were 100-fold lower and no accumulation of sulfate in the coelomic fluid was found. The sulfide oxidation was highly oxygen dependent. An increase of oxygen partial pressure ( ) in the medium was followed by enhanced thiosulfate production and by a decrease of sulfide concentration in the coelomic fluid. Under normoxia, the sulfide oxidation rate was sufficient to compensate the influx of sulfide into the coelomic fluid when the sulfide concentration in the medium was below 0.33 mmoll^-1. When external sulfide was raised beyond this level, sulfide up to 5 moll^-1 in the coelomic fluid appeared. Succinate in the body wall tissue was low as long as no sulfide appeared in the coelomic fluid, indicating the maintenance of an aerobic metabolism. The oxidation of sulfide to thiosulfate was localized in the mitochondria of the body wall tissue. The oxygen consumption of mitochondria was stimulated by the addition of sulfide. The mitochondrial sulfide oxidation rate depended on the amount of mitochondrial protein and followed a Michaelis-Menten kinetic. An apparentK _m of 0.68±0.29 moll^-1 and aV _max of 41.9±22.3 nmol min^-1 mg^-1 protein was calculated. Sulfide was stoichiometrically oxidized to thiosulfate with 1 mol sulfide consuming 1 mol oxygen. Sulfide oxidation was not inhibited by sulfide concentrations as high as 100 moll^-1. At low concentrations of cyanide or azide, when respiration without sulfide was already inhibited, sulfide oxidation could still be stimulated, tentatively indicating the existence of an alternative terminal oxidase. Specimens examined in the present study were collected near St. Pol de Leon, France, from 1989 to 1992.     

Sulfide-oxidizing bacteria in the burrowing echinoid,Echinocardium cordatum (Echinodermata)

Symbiotic filamentous bacteria thrive in the intestinal caecum of the deposit-feeding echinoid Echinocardium cordatum. Specimens of E. cordatum were collected at Wimereux (Nord Pas-de-Calais, France) in 1991. Their symbiotic bacteria build nodules by forming multilayered mats around detrital particles that enter the caecum. The morphological features of the bacteria are those of Thiothrix, a sulfide-oxidizing genus. The filaments, which may form rosettes, are sheathed and made by a succession of hundreds of rod-shaped bacteria which store elemental sulfur in the presence of external sulfide. Live bacteria are restricted to the outer layers of the nodules. Their sulfide-oxidizing activity was investigated, using a Biological Oxygen Monitor, by measuring the O₂-consumption when reduced sulfur compounds are provided. They oxidize thiosulfate and sulfide. Optimal sulfide oxidation occurs at intermediary pO₂ (100 to 160 M O₂l^-1). Spectrophotometry has confirmed that the sulfur content of the filamentous symbiotic sulfideoxidizing bacteria depends on the presence of external sulfide. This is the first report of symbiotic intradigestive Thiothrixspp.-like bacteria; it lengthens the list of symbioses between sulfide-oxidizing bacteria and invertebrates from sulfide-rich habitats.     

The bacterial symbiont from the hydrothermal vent tubewormRiftia pachyptila is a sulfide specialist

We have investigated the metabolic adaptations of the chemolithotrophic bacterial symbionts ofRiftia pachyptila. Specimens of the tubeworm were collected by submersible from depths of 2600 m at 13°N on the East Pacific Rise in 1987, and 2450 m at the Galápagos Rift in 1988. Isolated bacteria utilize sulfide, but not thiosulfate or sulfite, as their sole reduced-sulfur energy source. The bacteria rapidly oxidize a wide range of sulfide concentrations (5µM to 2 mM), with maximal respiration rates at concentrations >1 mM, and unlike many sulfur-oxidizing bacteria, show no inhibition in oxygen consumption at sulfide concentrations up to 2 mM. Incubations of freshly homogenized trophosome tissue or isolated bacteria with sodium [³⁵S] sulfide and subsequent analysis of sulfur products by high-performance liquid chromatography and flow-through scintillation counting showed that sulfide disappeared almost completely within 1 min. Both soluble and insoluble products of sulfide oxidation were produced. The soluble fraction contained sulfate and polysulfides, with no thiosulfate produced. However, the majority of the radioactivity was in the water-insoluble fraction, mostly as elemental sulfur. Whole-worm experiments under pressure showed a rapid removal of³⁵S-sulfide from the incubation water, with sulfide, sulfate, and polysulfides appearing in the blood within 4 h. There was no utilization of thiosulfate by the whole worms, freshly homogenized trophosome tissue, or isolated bacteria.     

Effects of sulfide exposure history and hemolymph thiosulfate on oxygen-consumption rates and regulation in the hydrothermal vent crab Bythograea thermydron

The hydrothermal vent crab Bythograea thermydron is exposed to high environmental concentrations of sulfide and low levels of oxygen for extended periods of time. It has previously been shown that hydrogen sulfide is oxidized to the relatively non-toxic thiosulfate (S₂O ₃ ^2– ), which accumulates in the hemolymph. Hemolymph thiosulfate levels in freshly captured crabs vary significantly among crabs from different hydrothermal vent sites as well as between crabs from different microhabitats within the same site. Hemolymph thiosulfate concentrations were not significantly different between crabs captured at the same site 6 mo apart. Hemolymph thiosulfate concentrations ranged from 66 mol 1^–1 in a crab captured at a site with relatively low sulfide venting, to 3206 mol 1^–1 in an individual that was netted from an active smoker vent with much higher sulfide exposure. The differences in hemolymph thiosulfate between sites and the stability of hemolymph thiosulfate in crabs captured at the same site at different times suggest that sulfide exposure is significantly different between sites and that this exposure may not vary significantly over the course of a few months. B. thermydron experimentally exposed to sulfide had high levels of thiosulfate in their hemolymph and increased abilities to regulate oxygen consumption in conditions of low oxygen. This enhancement of regulatory abilities suggests that the previously demonstrated increased hemocyaninoxygen (Hc–O₂) affinity due to elevated thiosulfate may be adaptive in vivo. Average oxygen-consumption rates were much higher in crabs experimentally exposed to sulfide than in unexposed crabs. Crabs injected with isosmotic thiosulfate did not have increased oxygen-consumption rates as did the sulfide-exposed individuals, but did show a similar reduction in P _c (the critical partial pressure of oxygen at which crabs can no longer regulate oxygen consumption). This suggests that it is the sulfide exposure and/or detoxification rather than the elimination of thiosulfate that causes the increase in metabolic rate. Thiosulfate diffuses into dead crabs and into live crabs exposed to 15 mmol S₂O ₃ ^2- l^–1, indicating substantial permeability, and yet live crabs are able to eliminate thiosulfate when incubated in sea water containing 1.5 mmol S₂O ₃ ^2- l^–1, suggesting a process that has an active component.     

Tolerance to low oxygen and sulfide in Amphiura filiformis and Ophiura albida (Echinodermata: Ophiuroidea)

The brittle stars Amphiura filiformis (Müller) and Ophiura albida (Forbes) were exposed to different oxygen saturations (100, 10, 5, 3, and <1% oxygen saturation) and to physiological anoxia (<1% oxygen saturation) at different total sulfide concentrations (0, 2, 20, 200 μM). The mortality was followed during experiments and the median survival time (LT₅₀) was determined. The infaunal A. filiformis had a significantly higher tolerance to both hypoxia and sulfide than did the epibenthic O. albida. After exposure to 10% oxygen saturation for a month, only 2.0% A. filiformis and 0% O. albida were dead. In oxygen saturations <1% A. filiformis and O. albida had a LT₅₀ of 7.5 and 2.5 d, respectively. The presence of even very small concentrations of sulfide decreased the survival significantly. Sulfide is shown to be the key factor for the survival of the two species. Received: 11 October 1996 / Accepted: 12 November 1996     

The gill symbiont of the hydrothermal vent mussel Bathymodiolus thermophilus is a psychrophilic,chemoautotrophic, sulfur bacterium

Certain hydrothermal vent invertebrates, e.g. Riftia pachyptila and Calyptogena magnifica, are clearly established as harboring dense populations of chemoautotrophic sulfur bacteria in specialized tissues. By contrast, the physiological characteristics of the abundant intracellular gill symbiont of the vent mussel Bathymodiolus thermophilus have been questioned. The low activities of enzymes diagnostic for CO₂ fixation (Calvin cycle) and for sulfur-driven energy generation, as measured by other investigators, have been attributed to bacterial contamination of the gill surface. Based on research at the Galápagos Rift hydrothermal vents in 1988 and subsequent laboratory experiments, the current study confirms that the B. thermophilus symbiont is a psychrophile for which thiosulfate and sulfide stimulate CO₂ fixation. It strongly indicates that the symbiont is a chemoautotroph by establishing the following: (1) Sulfide and thiosulfate can stimulate CO₂ fixation by partially purified symbionts by up to 43-fold and 120-fold, respectively; (2) the ribulose-1,5-bisphosphate carboxylase/oxygenase activity of the symbiont is sufficient to account for its sulfide- or thiosulfate-stimulated CO₂ incorporation; (3) the symbiont's molar growth yield on thiosulfate, as judged by CO₂ incorporation, is indistinguishable from that of free-living chemoautotrophs. Due to the high protein-degrading activity of B. thermophilus gill lysate, it is also suggested that host lysis of symbionts plays a more important role in the nutrition of the vent mussel than in R. pachyptila or C. magnifica, for which no comparable protein-degrading activity was found.     

Predation on penaeid prawns by fishes in Albatross Bay,Gulf of Carpentaria

Fishes were trawled from Albatross Bay, on the west coast of Cape York, north Queensland (12°45S; 141°30E) during 4 yr, from August 1986 to April 1989. Penaeids were the first or second most important prey item by dry weight in 14 of the 34 penaeid-eating fish species, and in 12 of the species by frequency of occurrence. Eighteen species of Penaeidae were identified in fish stomachs. The five commercially important species comprised over 70% by dry weight of all the penaeids eaten by all the fishes;Metapenaeus ensis, Penaeus semisulcatus andP. merguiensis comprised 22, 28 and 11%, respectively. Commercially unimportant penaeids comprised 85% by numbers of all penaeids eaten. Larger fishes ate larger penaeids, mainly commercially important species, while smaller fishes ate smaller penaeids, mainly commercially unimportant species. All penaeid-eating fishes also ate some teleost prey and many were primarily piscivorous. Most penaeid-eating fish species took more benthic prey than bentho-pelagic and pelagic prey combined. The fishes with the strongest predation impact on commercially important penaeids wereCaranx bucculentus and four species of elasmobranchs. The highest impact on commercially unimportant penaeids was made by several species of smaller but abundant fishes. An overall annual estimate of 2950 t yr^–1 of commercially important penaeids is eaten by all fishes, a much higher figure than the average 870 t yr^–1 taken by the fishery. This study highlights the need for accurate measurement of the abundance of penaeid predators as well as analyses of their diets when assessing the impact of predators on prawn stocks.     

Phenotypic variations in the gills of the symbiont-containing bivalve Lucinoma aequizonata

The marine bivalve Lucinoma aequizonata (Lucinidae) maintains a population of sulfide-oxidizing chemoautotrophic bacteria in its gill tissue. These are housed in large numbers intracellularly in specialized host cells, termed bacteriocytes. In a natural population of L. aequizonata, striking variations of the gill colors occur, ranging from yellow to grey, brown and black. The aim of the present study was to investigate how this phenomenon relates to the physiology and numbers of the symbiont population. Our results show that in aquarium-maintained animals, black gills contained fewer numbers of bacteria as well as lower concentrations of sulfur and total protein. Nitrate respiration was stimulated by sulfide (but not by thiosulfate) 33-fold in homogenates of black gills and threefold in yellow gill homogenates. The total rates of sulfide-stimulated nitrate respiration were the same. Oxygen respiration could be measured in animals with yellow gills but not in animals with black gills. The cumulative data suggest that black-gilled clams maintained in the aquarium represent a starvation state. When collected from their natural habitat black gills contain the same number of bacteria as yellow gills. Also, no significant difference in glycogen concentrations of the host tissues was observed. Therefore, starvation is unlikely the cause of black gill color in a natural population. Alternative sources of nutrition to sulfur-based metabolism are discussed. Denaturing gradient gel electrophoresis (DGGE) performed on the different gill tissues, as well as on isolated symbionts, resulted in a single gill symbiont amplification product, the sequence of which is identical to published data. These findings provide molecular evidence that one dominant phylotype is present in the morphologically different gill tissues. Nevertheless, the presence of other phylotypes cannot formally be excluded. The implications of this study are that the gill of L. aequizonata is a highly dynamic organ which lends itself to more detailed studies regarding the molecular and cellular processes underlying nutrient transfer, regulation of bacterial numbers and host–symbiont communication. Received: 1 September 1999 / Accepted: 1 February 2000     

Buoyancy function of the enlarged fluid-filled cranium in the deep-sea ophidiid fish Acanthonus armatus

Acanthonus armatus Günther (family Ophidiidae) is a slightly negatively buoyant (mean weight in surface seawater =0.58% of air weight) benthopelagic fish without a swimbladder that has reduced tissues and components (muscle, bone, brain, gills, lipids) and a massive head. This species has an enlarged cranial cavity (10% of head volume) filled, except for the very small brain, with a low-density (specific gravity 1.008) fluid. The fluid provided static lift of about 0.30 g each for 4 specimens whose weights in water ranged from 1.0 to 2.6 g. Osmotic concentrations of the cranial fluid averaged 294 mOsm 1^-1 in 4 specimens and , in 2 specimens for which comparisons were possible, were 43 to 45% lower than the concentrations of the plasma and perivisceral fluid. Similarly, Na⁺ and K⁺ concentrations of the cranial fluid were lower than those of the plasma or perivisceral fluid. A. armatus has highly reduced heavy tissues and an increased content of dilute fluid, with a localization of even more highly dilute fluid in the enlarged cranium which partially offsets the relatively dense tissues of the head. Information on the morphology, behavior and ecology of the fish supports the interpretation of the buoyancy and chemical data. The conclusion is consistent with the hypothesis that obtaining and conserving energy and reducing predation are the important selective factors affecting the evolution of deep-sea fishes and that these factors have greatly influenced the chemical composition of the fishes.     

六溴环十二烷(HBCD)对斑马鱼发育早期能量代谢及软骨、肌肉和鱼鳍发育的影响

六溴环十二烷(hexabromocyclododecane, HBCDs)是一种添加型阻燃剂,在环境中广泛存在。由于具有持久性、生物蓄积性和毒性等特征,HBCD很可能在水生生物体内富集并对其生长发育产生影响。将斑马鱼胚胎暴露于不同浓度的HBCD(0.1、0.5和1 mg·L^-1),通过油红O和阿尔新蓝染色观察幼鱼发育状况,并通过能量代谢及发育相关基因探讨可能的作用机制。结果表明,HBCD暴露影响了幼鱼对卵黄囊内生脂肪的吸收,并对幼鱼躯干骨骼肌、头部软骨和鱼鳍的发育产生损害。进一步研究发现,暴露组幼鱼体内ATP含量降低,ATP合成酶及电子呼吸链中还原性辅酶Ⅰ(NOX)和细胞色素C氧化酶(COX)等的活性显著降低;同时,早期发育相关基因如骨形成蛋白bmp、肌肉决定因子myod以及sox9a和wnt等基因的转录水平均受到显著抑制(P<0.05)。上述结果表明,HBCD会影响早期发育阶段的斑马鱼对卵黄囊营养物质的吸收,干扰体内能量代谢,导致能量供应不足,并通过bmp-sox9和wnt-myod等信号通路影响软骨组织、鱼鳍和骨骼肌的正常发育。     

饵料加标研究二甲苯麝香在鱼体内的蓄积和清除能力

二甲苯麝香(musk xylene,MX)是一种人造麝香,具有强烈的麝香气,可用作化妆品香精和皂用香精等的定香剂。由于其持续不断地输入环境,它们在水、土壤、大气中的浓度逐渐升高,并且在动物和人体组织中产生了蓄积,其蓄积效应相当于有机氯农药(organochlorine pesticides,OCPs)等持久性有机污染物,因而研究MX在鱼体内的蓄积特征是十分必要的。本文用含浓度为50 mg·kg-1和100 mg·kg-1的MX的饵料投喂斑马鱼(Danio rerio)和稀有鮈鲫(Gobiocypris rarus)14 d,继而进入为期28 d的清除实验。通过快速溶剂萃取(accelerated solvent extraction,ASE)、凝胶渗透色谱(gel permeation chromatography,GPC)、气相色谱-质谱联用法(gas chromatography-mass spectrometry,GC-MS)测定斑马鱼和稀有鮈鲫体内MX的浓度,继而评估鱼对MX的清除能力。结果表明,饵料中MX浓度越高,鱼体内MX的蓄积水平越高,100 mg·kg-1浓度组的蓄积水平为50 mg·kg-1浓度组的蓄积水平的2~3倍。在整个试验阶段的不同时间点分析鱼的体重和脂肪与鱼体内MX浓度的关系,数据显示,MX在鱼体内的蓄积水平与鱼的体重存在正线性关系,而与鱼体内脂肪含量的关系还有待进一步研究。经28 d的清除,鱼体内的MX残留量接近于零,说明斑马鱼和稀有鮈鲫对MX的清除能力较强。     

Ultrastructure and anaerobic metabolism of mitochondria in the marine oligochaete Tubificoides benedii : effects of hypoxia and sulfide

It has often been suggested that ultrastructural properties of mitochondria are correlated with oxygen and sulfide levels from the environment, although careful analyses of this question are rare. In this study the ultrastructure and distribution of mitochondria in Tubificoides benedii, a marine oligochaete from sulfide-rich sediments, were investigated after a series of oxic, hypoxic and hypoxic–sulfidic (200 μM H₂S) incubations up to 24 h. Succinate, one of the key endproducts of an anaerobic metabolism, was used as an indicator of mitochondrial anaerobiosis. Consistent differences in mitochondrial ultrastructure were not observed in any of the incubations, even after 24 h. Stereological parameters of mitochondria (volume density, surface density of the outer mitochondrial membrane, and specific surface) in epidermal and intestinal tissues of T. benedii were not affected by hypoxia or sulfide either. On the other hand, succinate concentrations increased significantly within 24 h under hypoxic and hypoxic–sulfidic conditions. Thus, experimental hypoxia and sulfide clearly caused mitochondrial anaerobiosis without affecting ultrastructure or distribution of mitochondria in T. benedii. Distinct differences in ultrastructural and stereological parameters were common between different tissues and between individuals, showing that different forms of mitochondria can occur within one species. Our results imply that a mitochondrial ultrastructure specific to thiobiotic animals does not appear to exist. Received: 4 August 1996 / Accepted: 20 September 1996     

Diets of the demersal fishes on the shelf off Iwate,northern Japan

Diets of demersal fishes were determined on the shelf (ca. 130 m deep) off Iwate, Japan. Samples were taken in three different types of habitat, an artificial reef (AR) site, a natural reef (NR) site, and sandymud bottom (SB) site, from May 1987 to September 1991, mostly every two months. A total of 67 prey items were recognized in the stomachs of 45 predator fish species. The most important preys were the pelagic fishes Sardinops melanostictus and Engraulis japonicus, which comprised 37% wet wt of the overall stomach contents. The percentage of pelagic fishes was highest at AR site, where fish density was highest. The dominant ten species could be divided into five feeding types. The pelagic fish feeders Physiculus maximowiczi and Gadus macrocephalus fed mainly on S. melanostictus. The dietary breadth of P. maximowiczi was wide, while that of Gadus macrocephalus was narrow. The pelagic crustacean feeder Theragra chalcogramma mostly consumed Themisto japonica and euphausiids and showed the least dietary overlap with other fishes. Benthic fish feeders were Hemitripterus villosus and Liparis tanakai. The benthic crustacean feeders Alcichthys alcicornis and Hexagrammos otakii consumed benthic crustaceans as well as pelagic and benthic fishes and showed the largest dietary breadth. The benthic invertebrate feeders Gymnocanthus intermedius, Dexistes rikuzenius and Tanakius kitaharai fed mainly on polychaetes and benthic crustaceans. But Gymnocanthus intermedius consumed a significant proportion of pelagic fishes. Ontogenetic dietary shift was recognized for these fishes. Pelagic fishes were consumed more intensively by larger individuals, especially true of A. alcicornis, Theragra chalcogramma and Gadus macrocephalus. Predominancy of the two most adundant species, P. maximowiczi and A. alcicornis, may be supported by their wide dietary breadth and the significant proportion of pelagic fish in their diets. Interspecific dietary overlap was low in most cases suggesting that food resources were well partitioned, although some high overlap was observed among the pelagic fish feeders, A. alcicornis, and Gymnocanthus intermedius, and among the benthic invertebrate feeders. Interspecific competition seemed more likely in the benthic invertebrate feeders than in the pelagic fish feeders partly because of superabundance of the pelagic prey S. melanostictus.     

Burrow environment and coelomic fluid characteristics of the echiuran worm Urechis caupo from populations at three sites in northern California

The burrow microhabitat and physiology of the echiuran worm Urechis caupo at a high-density site (Elkhorn Slough, California, USA), were investigated from 1987 to 1990 to determine physical and chemical conditions, worm density and distribution, and coelomic fluid characteristics such as heme composition, pO₂, pH, and coelomocyte volume. During tidal exposure, worm burrows at this site exhibited, on average, 52% air-saturated water, 11M burrow-water sulfide, 85 g/mg wet weight sediment sulfide, and salinity and osmolalities similar to those of seawater. These conditions are compared to those of another California site, Bodega Bay, which had slightly lower oxygen concentrations, but higher water and sediment-sulfide levels. A more limited comparison to a third site, Princeton Harbor, California, is included. Worms from Bodega Bay, the higher sulfide site, had greater concentrations of hematin, a non-globin heme compound contained in the coelomocytes, and exhibited a greater tolerance to sulfide in the laboratory. These data are consistent with the hypothesis that hematin is a sulfide-detoxifying agent that may enhance survival of U. caupo in the sulfide-rich mudflat environment.     

Sponge-feeding fishes of the West Indies

In an analysis of the stomach contents of 212 species of West Indian reef and inshore fishes, sponge remains were found in 21 species. In eleven of these, sponges comprised 6% or more of the stomach contents; it is assumed that these fishes feed intentionally on sponges. Sponges comprise over 95% of the food of angelfishes of the genus Holacanthus, over 70% of the food of species of the related genus Pomacanthus, and more than 85% of the food of the filefish, Cantherhines macrocerus. Lesser quantities of sponges are ingested by the remaining fish species. Fishes that feed on sponges belong to highly specialized teleost families, suggesting that this habit has evolved in geologically late time. The small number of fish species that concentrate on sponges as food suggests that the defensive characters of sponges—mineralized sclerites, noxious chemical substances, and tough fibrous components—are highly effective in discouraging predation. The two sponges most frequently eaten by fishes have a low percentage of siliceous spicules relative to organic matter, but among the 20 next most frequently consumed species no striking correlation occurs with respect to spicule content. Color and form of the sponge show no special correlation with frequency of occurrence in fish stomachs. Three species of fishes appear to concentrate on one species of sponge, but in these cases over 60% of the food taken consists of a variety of other organisms. Those fishes, more than half of whose diet consists of sponges, tend to sample a wide variety of species. No strong evidence is provided by our data that fish predation is a significant factor in limiting sponge distribution in the West Indian region.     

DNA barcoding of Pacific Canada’s fishes

DNA barcoding—sequencing a standard region of the mitochondrial cytochrome c oxidase 1 gene (COI)—promises a rapid, accurate means of identifying animals to a species level. This study establishes that sequence variability in the barcode region permits discrimination of 98% of 201 fish species from the Canadian Pacific. The average sequence variation within species was 0.25%, while the average distance separating species within genera was 3.75%. The latter value was considerably lower than values reported in other studies, reflecting the dominance of the Canadian fauna by members of the young and highly diverse genus Sebastes. Although most sebastids possessed distinctive COI sequences, four species did not. As a partial offset to these cases, the barcode records indicated the presence of a new, broadly distributed species of Paraliparis and the possibility that Paraliparis pectoralis is actually a species pair. The present study shows that most fish species in Pacific Canadian waters correspond to a single, tightly cohesive array of barcode sequences that are distinct from those of any other species, but also highlights some taxonomic issues that need further investigation.     

Population structure and feeding deterrence in three shallow-water antarctic soft corals

Alcyonium paessleri and Clavularia frankliniana are numerically abundant soft corals in the nearshore (12 to 33 m depth) benthic communities of eastern McMurdo Sound. They are much less abundant in western McMurdo Sound where a third species, Gersemia antarctica, co-occurs in low numbers. The body tissues of these three species are comprised mainly of organic material (53 to 70% dry wt), which is primarily dervied from NaOH-soluble protein and refractory material. The energetic contents of the whole-body tissues of A. paessleri, C. frankliniana and G. antarctica are 15.9, 17.3, and 14.5 kJ g^-1 dry wt, respectively. The mean biomass per individual is 1.81, 0.008, and 45 g dry wt for each respective species. Based on population densities of 7.3, 1337.3, and 0.04 soft corals m^-2 for A. paessleri, C. frankliniana and G. antarctica, respectively, the population energetic densities are estimated to be 210.1, 185.1, and 26.1 kJ m^-2. Despite the relatively rich energetic content of the tissue and apparent vulnerability to predators, very little predation occurs on these soft corals. Two potential predators, the antarctic sea stars Perknaster fuscus and Odontaster validus, exhibited significant chemotactic defensive tube-foot retractions to hexane, chloroform, methanol, and aqueous methanol extracts of each soft coral. In addition, wholebody tissue of each soft coral was rejected by the demersal fish Pseudotrematomus bernacchii and the cryopelagic fish Pagothenia borchgrevinki. In contrast, whole soft-coral tissues sequentially extracted in four increasingly polar solvents were readily ingested by these antarctic fishes, indicating that sclerites do not play a significant role in deterring predators. Our results indicate that these antarctic soft corals contain bioactive compounds which deter common predatory seastars and fishes.     

Comparison of cellular and molecular cytotoxic mechanisms of Cochlodinium polykrikoides in isolated trout and rat hepatocytes

Harmful algal blooms produced by the marine ichthyotoxic dinoflagellate Cochlodinium polykrikoides are responsible for mass mortalities of wild and farmed fish globally. This study compared the cytotoxic mechanisms of C. polykrikoides total extract on both trout and rat liver hepatocytes. Trout hepatocytes were more sensitive than rat hepatocytes against C. polykrikoides extract. The effective concentration 50 after 3 hour incubation (EC50_3hr) concentrations found for C. polykrikoides extract in trout and rat hepatocytes (i.e., 50% membrane lysis in 3 hr) were Eq. 1 cell/ml and Eq. 240 cell/ml, respectively. C. polykrikoides extract exposure in both isolated trout and rat hepatocytes resulted in membrane lysis, reactive oxygen species formation, glutathione depletion, collapse of mitochondrial membrane potential, ATP depletion, increase in adenosine diphosphate (ADP)/adenosine triphosphate (ATP) ratio, cytochrome c release into the hepatocyte cytosol, and activation of caspases cascade. Trout hepatocyte toxicity was also associated with lysosomal membrane injury. Mitochondrial permeability transition in both trout and rat hepatocytes produced cytochrome c release from the mitochondrial intramembrane space into the cytosol. Thus, the cytochrome c release triggered activation of caspase-3 and apoptosis. Finally, data demonstrated that C. polykrikoides extract may induce more apoptotic phenotype in rat than trout hepatocytes, which in the latter favored predominantly necrotic mode of cell death.     

Comparison of the food of Triphoturus mexicanus and T. nigrescens,two lanternfishes of the Pacific Ocean

Prey (chiefly euphausiids and copepods) eaten by two myctophids (lanternfishes) are compared from incidence in fish stomachs and from abundance in the environment. One lanternfish species, Triphoturus mexicanus, lives in the California Current, and the other, T. nigrescens, lives in the central Pacific Ocean. Although these two environments are very different physically and biologically, the feeding habits of the two lanternfishes are surprisingly similar. Prey biomass is 94% euphausiids, 3% copepods, and 3% other organisms for T. mexicanus and 88% euphausiids, 4.5% copepods, and 7.5% other organisms for T. nigrescens; the difference between the fish species is not significant when tested statistically. The two fishes resemble one another in frequency distributions of ingested copepod individuals, copepod species, euphausiid individuals, and euphausiid species. During a single diurnal feeding period, both fishes eat a variety of copepod species but tend to eat only a single species of euphausiid. T. mexicanus grows to twice the length of T. nigrescens and eats proportionally larger euphausiids; however, both fishes eat copepods having the same median size. The frequencies of euphausiid species in the diets of both fishes differ from the frequencies in the environment. The chief differences between the feeding habits of the two lanternfishes are that T. nigrescens, in comparison to its congener, eats a greater variety of organisms during one diurnal feeding period and captures smaller euphausiids. The feeding patterns for each lanternfish species are consistent over distances of hundreds of kilometers and over many years of sampling.     

Etude des eaux rouges dues à la prolifération des bactéries photosynthétiques sulfo-oxydantes dans l'étang du Prévost,lagune saumâtre méditerranéenne

Dystrophic crises or malaígues with red water, were observed in summer, in Mediterranean brackish lagoons near Montpellier, France. During July 1976, the photosynthetic sulfide-oxidizing bacteria causing this phenomenon were isolated from the Prévost lagoon. The most important genera isolated from this red water wereChromatium, Thiocystis andThiocapsa (Chromatiaceae): the predominant species wasThiocapsa roseopersicina. Water and sediment samples from the same lagoon were collected during the winter season (October 1976 and January 1977) and were enriched with organic matter. The samples were incubated in aquaria under artificial light (800 to 1000 lux) at room temperature (ca. 22°C). Eight to 10 days later, red water developed which was similar to that observedin situ in summer. These red waters develop under conditions of anaerobiosis and H₂S production. Such conditions are necessary for the growth of Chromatiaceae. Excessive deposists of organic matter in the lagoon water lead to increased oxygen consumption and overproduction of hydrogen sulfide, which can be oxidized by photosynthetic sulfideoxidizing bacteria. This bacteria bloom (causing the red water) removes the hydrogen sulfide, thus re-establishing aerobiotic conditions in the water of the Prévost lagoon.