Lipid profiles of Nematocarcinus gracilis a deep-sea shrimp from below the Arabian Sea oxygen minimum zone

Specimens of the deep-sea benthic shrimp Nematocarcinus gracilis were collected from 900 m to 1000 m in the Arabian Sea, close to where the permanent oxygen minimum zone meets the sea floor. Lipid profiles, encompassing total lipid, lipid class and fatty acid composition, were compared with previously reported crustacean lipid assays and provided an insight into the life history of the species. The major storage lipid in N. gracilis was triglyceride, supporting the supposition that this species exists in benthic regions. Neutral lipid levels were commensurate with N. gracilis being an opportunistic feeder. Fatty acid composition was typical of an organism with a diet based on an ultimately photosynthetic source of organic carbon, but also reflected the reduction in the availability of labile organic carbon (in the case of lipid, highly unsaturated fatty acids) in the deep sea.     

Living benthic foraminifera of the Okhotsk Sea: Faunal composition, standing stocks and microhabitats

Live (Rose Bengal stained) benthic foraminifera were investigated in surface sediment samples from the Okhotsk Sea to reveal the relationship between faunal characteristics and environmental parameters. Live benthic foraminifera were quantified in the size fraction > 125 µm in the upper 8 cm of replicate sediment cores, recovered with a multicorer at five stations along the Sakhalin margin, and at three stations on the southwestern Kamchatka slope. The stations are from water depths between 625 to 1752 m, located close or within the present Okhotsk Sea oxygen minimum zone, with oxygen levels between 0.3 and 1.5 ml l^- 1. At the high-productivity and ice-free Kamchatka stations, live benthic foraminifera are characterized by maximal standing stocks (about 1700-3700 individuals per 50 cm²), strong dominance of calcareous species (up to 87-91% of total live faunas), and maximal habitat depths (down to 5.2-6.7 cm depth). Vertical distributions of total faunal abundances exhibit a clear subsurface maximum in sediments. At the Sakhalin stations, which are seasonally ice-covered and less productive, live benthic foraminifera show lower standing stocks (about 200-1100 individuals per 50 cm²), lower abundance of calcareous species (10-64% of total live faunas), and shallower habitat depths (down to 2.5-5.4 cm depth). Faunal vertical distributions are characterized by maximum in the uppermost surface sediments. It is suggested that 1) lower and strongly seasonal organic matter flux, caused by the seasonal sea ice cover and seasonal upwelling, 2) lower bottom water oxygenation (0.3-1.1 ml l^- 1), and 3) more pronounced influence of carbonate undersaturated bottom water along the Sakhalin margin are the main factors responsible for the observed faunal differences. According to species downcore distributions and average living depths, common calcareous species were identified as preferentially shallow, intermediate and deep infaunal. Foraminiferal microhabitat occupation correlates with the organic matter flux and the depth of the oxygenated layer in sediments.     

The second species of Gromia (Protista) from the deep sea: its natural history and association with the Pakistan margin oxygen minimum zone

We describe a gromiid protist Gromia pyriformis sp. nov., from bathyal depths on the Pakistan margin (NE Arabian Sea), an area characterised by a well-developed Oxygen Minimum Zone (OMZ). The new species is smaller (length usually <1 mm) than the only other described deep-sea gromiid species (Gromia sphaerica) or the well-known coastal species Gromia oviformis. Its identification as a gromiid is based on the test-wall ultrastructure. This includes (i) an outer wall (165-300 nm thick) limited by an electron-opaque layer and perforated by pore structures which typically extend through its entire thickness, and (ii) inner "honeycomb membrane" structures which form a discontinuous sheet (18-20 nm thick) lying parallel to the outer wall. An outermost glycocalyx (approximately 75 nm thick), not observed in other gromiid species, is also present and imparts a finely granular appearance to the outer test surface, as seen by Scanning Electron Microscopy (SEM). Numerous rod-shaped prokaryotes are attached to the exterior of the glycocalyx. Gromia pyriformis sp. nov. typically occurs above the sediment-water interface, attached to the large arborescent foraminiferan Pelosina sp. It is confined to a very narrow bathymetric zone (approximately 1000 m water depth) in the lower portion of the OMZ, where bottom-water oxygen concentrations are approximately 0.2 ml l(-1).     

Paleoceanographic implications of smaller benthic and planktonic foraminifera from the Eocene Pazin Basin (Coastal Dinarides,Croatia)

Summary Smaller benthic and planktonic foraminifera from the clastic sediments of the Pazin Basin (Istria, Croatia) were studied in order to obtain more data about paleoceanographic conditions that existed in the Middle Eocene Dinaric foreland basin. The succession investigated corresponds to the Middle Eocene planktonic foraminiferal zones Globigerapsis kugleri/Morozovella aragonensis (P11), Morozovella lehneri (P12), and Globigerapsis beckmanni (P13). Benthic foraminiferal assemblages from the clastic succession are dominated by epifaunal trochospiral genera suggesting oligotrophic to mesotrophic conditions and moderately oxygenated bottom waters. Planktonic foraminiferal assemblages indicate mesotrophic to eutrophic conditions of the surface waters, with increased eutrophication in the upper part of the section. Water depth, based on the ratio between planktonic and epifaunal benthic foraminifera and on the recognized species of cosmopolitan benthic foraminifera, was estimated to have been between about 900 and 1200 m. The basin was elongated and open to marine currents on both sides allowing good circulation and ventilation of the bottom water.     

Palaeoenvironments of deposition of Neogene laminated diatom mat deposits from the eastern equatorial Pacific from studies of benthic foraminifera (sites 844, 849, 851)

Massive sedimentation of mats of the diatom Thalassiothrix longissima forming laminated diatom mat deposits (LDM) occurred intermittently in the equatorial Pacific throughout the Neogene from at least 15 to 4.8 m.y. ago. The background deposition was otherwise calcareous nannofossil diatom ooze (NO). Benthic foraminifera have been used to reconstruct the benthic environment of deposition and the role of both surface waters (as a source of food) and bottom waters (including their corrosivity) during LDM deposition. Three LDM events were studied: Site 844 (11.4 Ma, early Tortonian), Site 849 (4.8 Ma, early Zanclian and 6.6–6.8 Ma, early Messinian). A control section of NO spanning the 4.8 Ma event was studied from Site 851. In addition, the carbonate high NO immediately preceding the 4.8 Ma event was examined in Site 849. From the foraminiferal evidence it can be shown that the LDM was deposited under conditions of normal oxygenation because infaunal taxa are present throughout and there was an increase in epifaunal taxa such as Cibicides spp. However, there was a reduction in test size probably because only those smaller than 250 μm were able to move through the restricted sediment pore spaces caused by the diatom mat meshwork. The rate of accumulation of tests is highest in LDM interval and may reflect reduced predation from macrofaunal endobenthos. Among the epifaunal taxa, Nuttallides spp. show a decrease in abundance in the LDM and even immediately preceding it. This may be linked to a greater influence of corrosive AABW. Species known to feed opportunistically on phytodetritus (Epistominella exigua and Alabaminella weddellensis) are common in both NO and LDM. The increased relative abundance of A. weddellensis in the LDM may be due to this species being smaller than E. exigua and better able to exploit the food resource within the restrictive mat meshwork. The foraminiferal results corroborate the previous interpretation that preservation of lamination in the LDM is due to the physical exclusion of macro endobenthos rather than oxygen depletion of the bottom waters.     

The spatial and vertical distribution of living (stained) benthic foraminifera from a tropical,intertidal environment,north Queensland,Australia

We investigated the distribution of living (stained) benthic foraminifera across a tropical, intertidal shoreline adjacent to Cocoa Creek, Queensland, Australia for the purpose of better understanding the nature of test production and ultimately fossil assemblage development within such environments. Short cores (up to 1 m) were collected during the wet and dry season, along an elevational gradient comprising non-vegetated intertidal mudflat and higher-intertidal mangrove forest environments. The distribution of stained specimens can be broadly delineated into assemblages characterising ‘upper mangrove’ (2.64–2.91 m above Lowest Astronomical Tide (LAT)) and ‘low mangrove-mudflat’ (1.62–2.18 m above LAT) environments. Agglutinated species were generally limited to upper mangrove stations. Calcareous species occurred within all of the intertidal environments examined but differ in their composition between upper and lower intertidal settings. Upper mangrove faunas were characterised by the agglutinated species Arenoparrella mexicana, Haplophragmoides wilberti, Miliammina fusca, Miliammina obliqua and Trochammina inflata and the calcareous species Helenina anderseni. Live (stained) assemblages at lower intertidal elevations were dominated by the calcareous species Ammonia aoteana, as well as Rosalina spp., Elphidium oceanicum, Triloculina oblonga, Ammonia pustulosa and Shackoinella globosa.     

Carbon and oxygen isotope geochemistry of live (stained) benthic foraminifera from the Aleutian Margin and the Southern Australian Margin

Comparisons of ambient bottom-water geochemistry and stable isotopic values of the tests of living (stained) calcareous benthic foraminifera from the North Pacific (on the Aleutian Margin, water depth 1988 m) and Murray Canyons group in the Southern Indian Ocean (Australian Margin, water depths 2476 m and 1634 m) provide modern environmental analogs to calibrate paleoenvironmental assessments. Consistent with the hypothesis that microhabitat preferences influence foraminiferal isotopic values, benthic foraminifera from both margins were depleted in ¹³C with respect to bottom-water dissolved inorganic carbon (DIC). The carbon isotope values of deep infaunal foraminifera (Chilostomella oolina, Globobulimina pacifica) showed greater differences from estimates of those of DIC than shallow benthic foraminifera (Bulimina mexicana, Bolivinita quadrilatera, Pullenia bulloides). This study provides new isotopic and ecological information for B. quadrilatera. The mean Δδ¹³C value, defined as foraminiferal δ¹³C values minus estimated ambient δ¹³C values from the Aleutian Margin, is 0.97‰ higher for G. pacifica than the mean from the Murray Canyon. This difference may result either from genetic or biological differences between the populations or from differences in environmental isotopic influences (such as pore water differences) that were not accounted for in the equilibrium calculations. These analyses provide calibration information for the evaluation of bottom water conditions and circulation patterns of ancient oceans based on fossil foraminiferal geochemistry.     

Nitrite oxidation in the upper water column and oxygen minimum zone of the eastern tropical North Pacific Ocean

Nitrogen (N) is an essential nutrient in the sea and its distribution is controlled by microorganisms. Within the N cycle, nitrite (NO₂⁻) has a central role because its intermediate redox state allows both oxidation and reduction, and so it may be used by several coupled and/or competing microbial processes. In the upper water column and oxygen minimum zone (OMZ) of the eastern tropical North Pacific Ocean (ETNP), we investigated aerobic NO₂⁻ oxidation, and its relationship to ammonia (NH₃) oxidation, using rate measurements, quantification of NO₂⁻-oxidizing bacteria via quantitative PCR (QPCR), and pyrosequencing. ¹⁵NO₂⁻ oxidation rates typically exhibited two subsurface maxima at six stations sampled: one located below the euphotic zone and beneath NH₃ oxidation rate maxima, and another within the OMZ. ¹⁵NO₂⁻ oxidation rates were highest where dissolved oxygen concentrations were <5 μM, where NO₂⁻ accumulated, and when nitrate (NO₃⁻) reductase genes were expressed; they are likely sustained by NO₃⁻ reduction at these depths. QPCR and pyrosequencing data were strongly correlated (r²=0.79), and indicated that Nitrospina bacteria numbered up to 9.25% of bacterial communities. Different Nitrospina groups were distributed across different depth ranges, suggesting significant ecological diversity within Nitrospina as a whole. Across the data set, ¹⁵NO₂⁻ oxidation rates were decoupled from ¹⁵NH₄⁺ oxidation rates, but correlated with Nitrospina (r²=0.246, P<0.05) and NO₂⁻ concentrations (r²=0.276, P<0.05). Our findings suggest that Nitrospina have a quantitatively important role in NO₂⁻ oxidation and N cycling in the ETNP, and provide new insight into their ecology and interactions with other N-cycling processes in this biogeochemically important region of the ocean.     

基于GAM模型的阿拉伯海鲐鱼渔场分布与环境关系

基于2016-2017年中国印度洋围拖网生产数据以及同期的海表温度、叶绿素、表层海流和海面高度数据,采用广义加性模型(Generalized Additive Model,GAM)建立了围网单位捕捞努力量渔获量(catch per unit effort,CPUE)对海洋环境的非线性响应模型,分析了阿拉伯海鲐鱼(Scomber australasicus)渔场分布与海洋环境关系.结果表明:空间因子和环境因子对阿拉伯海鲐鱼渔场有显著影响,GAM模型的方差解释率为30.1%;印度洋季风对鲐鱼CPUE影响大,鲐鱼CPUE在印度洋东北季风高,在夏季季风低;全年阿拉伯海鲐鱼围网渔场主要分布在60°E、13°N-15°N斜向椭圆区域;模型表明,鲐鱼渔场适宜海表温度为26~28℃,叶绿素浓度0.2~0.5 mg·m^-3,海面高度0.2~ 0.4 m;影响鲐鱼渔场的因子按重要性依次为海面高度、经纬度、海表温度和叶绿素浓度.     

Distribution of living planktonic foraminifera in the Ross Sea and the Pacific sector of the Southern Ocean (Antarctica)

In order to determine the factors controlling the distribution of planktonic foraminifera as a proxy for reconstruction of paleoenvironments, we present data on live assemblages collected in the Southern Ocean. Plankton tows and hydrographic measurements were taken in the upper 400 m of the water column at different sites in the Ross Sea (site B) and at the Polar Front of the Pacific Ocean (site O) during austral summers from 1998 to 2003.Based on qualitative micropaleontological observations we discriminated between Neogloboquadrina pachyderma dextral (dex) and N. pachyderma sinistral (sin). In addition for N. pachyderma (sin) we distinguished four morphs: the first one (1) has a thickened test and depressed sutures; the second morph (2) is represented by specimens characterized by a subspheric and heavily encrusted test; the third morph (3) has a thin and lobate walled test; the fourth one (4) represent the juvenile stage of N. pachyderma (sin) and is characterized by a smaller average size.The microfauna collected in the Ross Sea (site B) is characterized by the dominance of N. pachyderma (sin) (morphs 1 and 2), whereas low occurrences of Turborotalia quinqueloba, N. pachyderma (dex) and Neogloboquadrina dutertrei were noted in the first 50 m of the water column. The water column at this station is characterized by a marked and shallow stratification and a marked thermocline during the sampling season.At the ocean station (site O), the assemblage shows increasing diversification: T. quinqueloba, G. bulloides, N. pachyderma (dex) and few specimens of Globigerinita uvula characterize the planktonic microfauna. There is a predominance of non-encrusted morphs and juvenile specimens (3 and 4). At this station the mixed surface layer is deeper than in the Ross Sea (60–70 m), the pycnocline and the thermocline less marked.The depth and the intensity of the Deep Chlorophyll Maximum (DCM) influence foraminiferal distribution: N. pachyderma (sin) shows abundance peaks at or just below the DCM while G. bulloides peaks above the DCM. Coiling direction of N. pachyderma seems to be not controlled exclusively by Sea Surface Temperature (SST): probably the two coiling types are genetically different.Results document that diversity of planktonic foraminifera, number of specimens and variations in test morphology are related to regional differences in water properties (temperature, salinity, and DCM depth).     

Bottom water oxygenation history in southeastern Arabian Sea during the past 140 ka: Results from redox-sensitive elements

The concentrations of multiple redox-sensitive elements such as Re, U, Mo, Cd, V, Sb, and Tl were determined in sediments from the southeastern Arabian Sea (9°21′N: 71°59′E) to understand the bottom water oxygenation history throughout the past 140 ka. The enrichment of redox-sensitive elements (Re, U, Cd and Sb) above average crustal abundances suggests that the Last Glacial Maxima (17.48 ka), stadials of Marine Isotope Stage (MIS)-5 (5b and 5d) and Glacial Termination (GT)-II (133 ka) were associated with suboxic bottom water conditions. Sediments deposited during these suboxic conditions show the highest Re content (up to 54 ppb normalized to a carbonate free basis) which is highly enriched over average continental crust (0.4 ppb) and these sediments appear to be the major sink for the global mass balance estimation. Marine Isotope Stages 1, 3, 4 and interstadials of MIS-5 (5a, 5c & 5e) were all associated with near-oxic conditions. Overall, the lack of enrichment of Mo and V above crustal abundance, and a high Re/Mo (ppm/ppm) ratio (avg. 18.2 × 10^− 3) suggest that sediments of the southeastern Arabian Sea never contained free H₂S during the last 140 ka. These changes in the bottom water oxygen content can be related to the oceanic circulation pattern during this time and in part are reflected in relationships between the timing of redox changes and paleoproductivity proxies.     

Establishment of the western Pacific warm pool during the Pliocene: Evidence from planktic foraminifera, oxygen isotopes, and Mg/Ca ratios

This study presents new evidence of when and how the Western Pacific Warm Pool (WPWP) was established in its present form. We analyzed planktic foraminifera, oxygen isotopes, and Mg/Ca ratios in upper Miocene through Pleistocene sediments collected at Deep Sea Drilling Program (DSDP) Site 292. These data were then compared with those reported from Ocean Drilling Program (ODP) Site 806. Both drilling sites are located in the western Pacific Ocean. DSDP Site 292 is located in the northern margin of the modern WPWP and ODP Site 806 near the center of the WPWP. Three stages of development in surface-water conditions are identified in the region using planktic foraminferal data. During the initial stage, from 8.5 to 4.4 Ma, Site 806 was overlain by warm surface water but Site 292 was not, as indicated by the differences in faunal compositions and sea-surface temperature (SST) between the two sites. In addition, the vertical thermal gradient at Site 292 was weak during this period, as indicated by the small differences in the δ¹⁸O values between Globigerinoides sacculifer and Pulleniatina spp. During stage two, from 4.4 to 3.6 Ma, the SST at Site 292 rapidly increased to 27 °C, but the vertical thermal gradient had not yet be strengthened, as shown by Mg/Ca ratios and the presence of both mixed-layer dwellers and thermocline dwellers. Finally, a warm mixed layer with a high SST ca. 28 °C and a strong vertical thermal gradient were established at Site 292 by 3.6 Ma. This event is marked by the dominance of mixed-layer dwellers, a high and stable SST, and a larger differences in the δ¹⁸O values between G. sacculifer and Pulleniatina spp. Thus, evidence of surface-water evolution in the western Pacific suggests that Site 292 came under the influence of the WPWP at 3.6 Ma. The northward expansion of the WPWP from 4.4 to 3.6 Ma and the establishment of the modern WPWP by 3.6 Ma appear to be closely related to the closure of the Indonesian and Central American seaways.     

Desmotersia levinae, a new genus and new species of free-living nematode from bathyal oxygen minimum zone sediments off Callao, Peru, with discussion on the classification of the genus Richtersia (Chromadorida: Selachinematidae)

Desmotersia levinae gen. n., sp. n. is proposed, based on material found in bathyal oxygen minimum zone sediments off the coast of Peru. Desmotersia closely resembles Richtersia in the animals’ general appearance and in spiny ornamentation of the body cuticle, but clearly differs in stoma structure and by the presence of a dorsal tooth. The systematic positions of the two genera are discussed, since Desmotersia apparently forms a link between Selachinematidae and Desmodoridae. Desmotersia levinae is characterized by a variety of spiny ornamentations anteriorly formed by bipartite spines arranged into a fin-like picket fence, by a head with an asymmetrical cephalic capsule, presence of two closely spaced ventral longitudinal rows of copulatory thorns, and by 2-4 ventral thorns in mid-tail positions on the male. The interaction between the new species and its habitat is discussed.     

Genetic diversity in strains of the genus Anabaena isolated from planktonic and benthic habitats of the Gulf of Finland (Baltic Sea)

Late summer cyanobacterial blooms in the Baltic Sea contain Anabaena sp. together with Nodularia spumigena and Aphanizomenon flos-aquae. Although Anabaena is common especially in the Gulf of Finland, very little is known about its genetic diversity. Here we undertook a molecular phylogenetic study of 68 Anabaena strains isolated from the brackish Gulf of Finland. We sequenced the 16S rRNA genes from 54 planktonic and 14 benthic Anabaena strains, and rbcL and rpoC1 genes from a subset of these strains. Phylogenetic trees showed that Anabaena strains, from both planktonic and benthic habitats, were genetically diverse. Although the Anabaena strains were morphologically diverse, in our study only one genetically valid species was found to exist in the plankton. Evolutionary distances between benthic Anabaena strains were greater than between planktonic strains, suggesting that benthic habitats allow for the maintenance of greater genetic diversity than planktonic habitats. A number of novel lineages containing only sequences obtained in this study were compiled in the phylogenetical analyses. Thus, it seemed that novel lineages of the genus Anabaena may be present in the Baltic Sea. Our results demonstrate that the Baltic Sea Anabaena strains show surprisingly high genetic diversity.     

Linking denitrifier community structure and prevalent biogeochemical parameters in the pelagial of the central Baltic Proper (Baltic Sea)

The oxic-anoxic interface of the water column of the Gotland Basin (central Baltic Sea) is characterised by defined biogeochemical gradients and is hypothesised to be a zone of pronounced denitrification. Our aim was to analyse the composition and distribution of pelagic denitrifying microorganisms in relation to the physico-chemical gradients in the water column. PCR-amplified nirS genes--coding for dissimilatory nitrite reductase--were analysed as functional markers by terminal restriction fragment length polymorphism and cloning. The overall nirS diversity was low, with the lowest levels found at the oxic-anoxic interface. Only a few terminal restriction fragments dominated the denitrifier communities throughout the water column, and these could be assigned to several new Baltic Sea clusters that were revealed by phylogenetic analysis. The novel clusters were separated in two groups corresponding to the oxygen concentrations within specific layers of the water column. Gradients of prevalent biogeochemical parameters (H(2)S, NH(4) (+), NO(3) (-) and O(2)) largely determined the composition of the nirS-type denitrifier communities within the water column of the Gotland Basin.     

Energy metabolism of Chironomus anthracinus (Diptera: Chironomidae) from the profundal zone of Lake Esrom,Denmark, as a function of body size,temperature and oxygen concentration

The profundal zone of Lake Esrom, Denmark has a dense population of Chironomus anthracinus, which survives 2–4 months of oxygen depletion each summer during stratification. The metabolism of 3rd and 4th instar larvae was examined in regard to variation in biomass and temperature. Respiration at air saturation was described by a curvilinear multiple regression relating oxygen consumption to individual AFDW and temperature. At 10 °C and varying oxygen regimes the O₂ consumption and CO₂ production of 4th instar larvae were almost unaltered from saturation to about 3 mg O₂ l^–1, but decreased steeply below this level. The respiratory quotient increased from 0.82 at saturation to about 3.4 at oxygen concentrations near 0.5 mg O₂ l^–1. This implied a shift from aerobic to partially anaerobic metabolism. At 0.5 mg O₂ l^–1 the total energy production equalled 20% of the rate at saturation of which more than one third was accounted for by anaerobic degradation of glycogen. This corresponded to a daily loss of 12 µg mg AFDW^–1 or approximately 5% of the body reserves. At unchanged metabolic rate the glycogen store would last three weeks, but long term oxygen deficiency causes a further suppression of the energy metabolism in C. anthracinus.     

Relationship between biofouling and growth of the pearl oyster pinctada fucata (Gould) in Kuwait,Arabian Gulf

Results are presented from a three-year investigation of the relationship between accumulations of marine fouling organisms and growth of the pearl oyster Pinctada fucata (Gould). Estimates are provided of the diversity of the foulers, and data on certain hydrological features of the experimental site are also given.There was an inverse correlation between growth of the pearl oyster and diversity of the biofouling assemblages, whatever depth. Growth curves did not follow seasonal variations in the environmental factors very exactly. It was also observed that the polychaete, Polydora vulgaris Mohammad, preferred the oysters planted on the bottom to those suspended near the surface. Bottom oysters suffered the highest mortality, but definite evidence of a relationship between mortality and infestation by the polychaete was not apparent. Percentages of both infestation and mortality were higher among the fouled oysters than those cleaned periodically.     

Genus Alexandrium Halim, 1960 (Dinophyta) from the Pacific coast of Russia: Species composition, distribution, and dynamics

At present 8 species of Alexandrium genus have been found in seas and adjacent waters of Russia: A. acatenella, A. catenella, A. insuetum, A. margalefii, A. ostenfeldii, A. pseudogonyaulax, A. tamarense, and A. tamutum. The distribution and population density of Alexandrium species varied within the surveyed area of the Pacific: in the Sea of Japan and Sea of Okhotsk, 7 species were recorded; 3 species were recorded along the Pacific coast of Kamchatka; and 2 species were found in the Bering Sea. A. tamarense was the most widespread and abundant species over the area. A. insuetum was recorded only in the Sea of Japan, and A. catenella, in the Sea of Okhotsk (Terpeniya Bay). The highest concentration of Alexandrium spp. (2–7 million cells/l) was recorded along the Pacific coast of Kamchatka and in the Bering Sea; in the Sea of Okhotsk, a rather high concentration (51000 cells/l) was registered in Aniva Bay; in the Sea of Japan, the highest concentration was recorded in Peter the Great Bay (6000 cells/l). The distribution of cysts (spores) in surface sediments of the Pacific coast of Russia as a whole reflected the pattern of distribution of vegetative cells of Alexandrium. Cysts of Alexandrium cf. tamarense prevailed all over the area, with the maximum concentration along the Pacific coast of Kamchatka. Beyond that type of cysts, insignificant numbers of cysts of Alexandrium cf. minutum were recorded in Peter the Great Bay and Aniva Bay. Analysis of seasonal dynamics revealed that cells of Alexandrium spp. occurred in Peter the Great Bay from June up to September, and along the Pacific coast of Kamchatka from April to October. In the first region, the maximum density was recorded in August; it was provided by A. pseudogonyaulax (59% of the total density of Alexandrium), A. tamarense (35%), and A. insuetum (6%). In the second region, it was recorded in July, thanks only to development of A. tamarense.     

Leptonemella species (Desmodoridae, Stilbonematinae), benthic marine nematodes with ectosymbiotic bacteria, from littoral sand of the North Sea island of Sylt: taxonomy and ecological aspects

Leptonemella species represent a dominant element of the nematode fauna in sulfidic, deep sediment layers on the sandy shore of Sylt. Based on collections sampled here in 1991–1999, a taxonomic treatise is presented on the three co-existing species, Leptonemella aphanothecae Gerlach, 1950, the closely related L. vicina sp. nov., and L. gorgo Gerlach, 1950. The high incidence of pseudohermaphrodites in the material, mostly functional females with a male copulatory apparatus, is remarkable. The highest population densities of Leptonemella spp. (up to 73 individuals/10 ml sand) were found near polychaete burrows. Because of the great spatial and temporal variations in the oxygen/sulfide regime of these microhabitats, and because of the strong adhesive capabilities of Leptonemella spp., which can anchor themselves firmly to sand grains using caudal glands, we propose that a hemisessile life strategy is employed by these nematodes to fulfill the metabolic needs of their sulfide-oxidizing ectosymbionts. Communicated by K. Reise