Ecological investigations of the marine nematode Metoncholaimus scissus

Significant concentrations of the large oncholaimid Metoncholaimus scissus Wieser and Hopper (1967) (>7000 animals/24 cm² area or 2.68x10⁶ specimens/m²) have been noted in soft-bottom turtle grass communities. Activities of the nematode frequently show an indirect relationship to blooms of the benthic diatom Pleurosigma balticum. Analysis of biomass data for M. scissus (as much as 28 g wet weight/m²) demonstrate the importance of microsite activity and sensitivity of the species to small significant changes in the benthic environment.This work was supported by grant GM 12824 from the National Institutes of Health to the Institute of Marine and Atmospheric Sciences, University of Miami. Contribution No. 1188 from the Institute of Marine and Atmospheric Sciences, University of Miami and from the Entomology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa.     

Some direct observations on the ecology and behaviour of the Norway lobster Nephrops norvegicus

A detailed investigation of a small area of sea bed occupied by the Norway lobster Nephrops norvegicus (L.) was carried out by diving and television observations at depths of 30 m in Loch Torridon, Scotland. The density of burrows was 1/2 m², but only a proportion of these were occupied by N. norvegicus. Although about 70% of the larger burrows were occupied by N. norvegicus, giving a density of 1 lobster/8 m², very few juveniles (carapace length less than 30 mm) were found in the area. Many of the small burrows were occupied by the gobiid fish Lesueurigobius friesii (Collett). There was evidence that N. norvegicus frequently change their burrows, and fighting for burrows was observed. N. norvegicus remain within their burrows during the day, emerge around sunset to forage for food during the night, and then return to their burrows at dawn. This, and other aspects of their burrowing behaviour, have a marked effect on the commercial trawl catches of N. norvegicus which show large seasonal and diurnal variations in size and sex composition.     

NADP+-dependent glutamate dehydrogenase from Acropora formosa: purification and properties

As an initial step in our study of nitrogen metabolism in the coral/algal symbiosis we have purified glutamate dehydrogenase (EC 1.4.1.4) to homogeneity from polyp tissue of the staghorn coral Acropora formosa collected from Magnetic Island (North Queensland) in 1985–1986. The purified enzyme had a specific activity of 78 U mg^-1. The native enzyme had a relative molecular weight, M _r, of 360 000 (±20 000), and appears to be a hexamer with subunits of M _r=56000 (±3 000). Like the enzyme from other coelenterates, the coral glutamate dehydrogenase (GDH) was absolutely specific with respect to the coenzyme substrate (NADP⁺/NADPH), and was insensitive to allosteric regulation by nucleotides; unlike other coelenterate GDHs, the coral enzyme was absorlutely specific for ammonium as amino group donor in the reductive amination reaction, and major differences in kinetic properties were apparent. Linear Michaelis-Menten kinetics were observed for the substrates a-ketoglutarate, NADPH and NADP⁺, the K _m values being 0.93, 0.11 and 0.03 mM, respectively. However glutamate dehydrogenase displayed biphasic kinetics with respect to l-glutamate and ammonium, indicating two apparent K _m values (18 and 81 mM for l-glutamate and 9.2 and 416 mM for ammonium). The enzyme also exhibits Scatchard plots, Hill coefficients and cooperativity indices characteristic of enzymes displaying negative cooperativity.     

Life history of the sandy-beach amphipod Neohaustorius schmitzi (Crustacea: Haustoriidae)

Neohaustorius schmitzi Bousfield, the dominant macroscopic invertebrate on sandy beaches in North Carolina, USA, is strictly intertidal, and distributed from mean low tide to high tide, with an average density of 790/m². Location of greatest densities within the intertidal zone is dependent upon season and sex. An aggregated distribution is shown. N. schmitzi has 2 generations/year: a winter generation which lives about 8 months, and a summer generation which lives about 4 months. The reproductive season extends from February through October, with spring and summer peaks. Each female appears to produce only 1 brood of young. The number of young ranges from 2 to 14, depending upon the length and generation of the female.     

Seasonal growth and productivity ofMacrocystis integrifolia in British Columbia,Canada

The seasonal growth rates and nitrogen and carbon fluxes were estimated for two subtidalMacrocystis integrifolia Bory kelp forests in British Columbia, Canada from changes in population structure through time. Mean relative growth rates of the forests varied from a high of 4.3% d^-1 to a low of-3.6% d^-1. Mean net assimilatioon rates of carbon (a photosynthesis analog) varied from a high of 0.66 g C m^-2 of foliage d^-1 to a low of-0.87 g C m^-2 d^-1. The leaf area index ranged from 0.3 to 11.9. Annual carbon input on a foliage area basis was calculated at 250 g C m^-2 yr^-1. Annual carbon input to the forest was estimated at 1 300 g C m^-2 of ocean bottom yr^-1. The yearly nitrate nitrogen input to the forest was estimated at 60 g N m^-2 of ocean bottom yr^-1. The net ecosystem production varied from-520 to +31 g C m^-2 of ocean bottom yr^-1. The intra-forest, inter-forest and seasonal variabilities of these productivity parameters are discussed.     

On the ecology of a North Adriatic benthic community: Distribution,standing crop and composition of the macrobenthos

The boundaries as well as the macro-epibenthic biomass distribution and composition of a North Adriatic benthic community, dominated by the brittle star Ophiothrix quinquemaculata (D.Ch.), the sponges Reniera ssp., and the ascidians Microcosmus ssp. were determined. Transects totalling more than 80 km (i.e., a recorded area of approximately 150 000 m²) were taken by means of a combined TV- and photocamera sled. The observations, TV-recordings, and photos, together with 392 diver-collected quantitative samples were evaluated. The biomass values were used to establish isobenths. Within the community, the mean biomass, measured as wet weight, amounted to 370 (±73) g/m² with maxima of more than 1000 g/m². 64% of the biomass was due to the designating group Ophiothrix-Reniera-Micrcosmus, 87.5% were represented by filter- and suspension-feeding species alone. The mean biomass in the peripheral areas was evaluated at 166 (±62) g/m². Biomass distribution and composition is examined, and the ecological function and meaning of the observed patterns is discussed.This investigation was carried out within the frame of a joint programme between the Lehrkanzel für Meeresbiologie, University of Vienna, and the Marine Biological Station, Portoroz, University of Ljubljana.     

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. I. Zonation and biomass of seaweeds

An intertidal and underwater survey of the zonation of seaweed in St. Margaret's Bay, NovaScotia, Canada showed 8 major zones as one proceeded away from shore: (1) Fucus and Ascophyllum; (2) Chorda with filamentous browns; (3) Chondrus crispus; (4) Zostera marina; (5) Laminaria digitata with L. longicrusis; (6) Laminaria longicruris; (7) L. longicruris with Agarum cribrosum; (8) Agarum cribrosum with Ptilota serrata. Zostera occurred at the same level as O. crispus but replaced it in sheltered water. Ascophyllum was more abundant in sheltered water. L. digitata was confined to the more exposed, steeper shore. The average horizontal extent of the seaweed zone was 369 m, and the greatest depth of significant amounts of seaweed 20 to 30 m. Laminaria longicruris contributed 36% of the total biomass, and Laminaria spp. and Agarum together constituted 83%, while intertidal seaweeds contributed less than 10% of the biomass. The estimated average total biomass per m of shore line was 1,481 kg fresh weight, 326 kg dry weight, 98 kg carbon, or 980x10³ kcal. When averaged over the whole area of the bay, the corresponding figures were 1.38 kg/m² fresh weight, 0.30 kg/m² dry weight, 91 g/m² carbon or 912 kcal/m². Dry matter of Laminaria was 15 to 27% of fresh weight in blades, 10 to 12% in stipes. The dry matter content of blades was least in spring and highest in autumn, but carbon content and calorific value of dry matter showed little difference with species or season.Contribution to the International Biological Programme CCIBP 108.Bedford Institute Contribution BI 249.     

Effect of ionizing radiation on haemoglobin of marine lamellibranchs

The effect of ionizing radiation on the iron-linked protein (haemoglobin) of the marine lamellibranchs Anadara granosa (Linn.) and Cardita antiquata (Lam.) from Bombay waters, India is discussed. Purified haemoglobin solutions were exposed to a ⁶⁰Cobalt source delivering a dose of about 4,600 rad/min, at the sample irradiation point. Radiation damage or degradation was measured spectrophometrically by studying changes in the absorption spectra following irradiation in the presence and absence of oxygen. Exposure to ionizing radiation in general caused a decrease in absorption of both haemoglobins, irrespective of location, viz extra-versus intracellular, at Soret (412 m), (540 to 42 m) and (574 to 76 m) peaks, and an increase in absorption at 510 and 630 m. Upon exposure to a higher dose, O₂Hb of C. antiquata showed an increase in absorption at the protein peak (280 m); exposure to a lower dose, however, resulted in decreased absorption. Furthermore, the changes following irradiation were dependent upon the initial state of the pigment. Oxyhaemoglobin, when exposed to radiation, oxidized to hemiglobin, and hemiglobin reduced to oxyhaemoglobin. The extracellular haemoglobin of high molecular weight (3x10⁶) of the false cockle C. antiquata was found to be extremely radio-resistant, whereas intracellular haemoglobin of low molecular weight (74,000) of the arcid clam A. granosa was highly radiosensitive, since it could not be exposed to doses exceeding 18,000 r.     

Annual abundance and biomass of aloricate ciliates in tropical neritic waters off Kingston,Jamaica

The daily abundance of aloricate ciliates at Lime Cay, Jamaica, a shallow neritic site, ranged from 29 to 118 × 10⁶ m^–2 (0.97 to 3.93 × 10⁶ m^–3) between November 1985 and November 1986. Biomass was converted to kilojoules (1 kcal=4.1855 kJ) assuming 42% carbon, 20.15 kJ (g dry wt)^–1, and 20% cell shrinkage. Biomass ranged from 0.40 to 3.00 kJ m^–2 (13.3 to 100 J m^–3; 0.28 to 2.08µg C l^–1) with an annual mean of 1.11 kJ m^–2 (36.8 J m^–3; 0.764µg C l^–1). Nanociliates (<20µm equivalent spherical diameter, ESD) dominated abundance, but microciliates (> 20µm ESD) dominated biomass.Strombidium, Strobilidium, Tontonia andLaboea species were conspicuous taxa. Annual production estimates of the aloricate assemblage, based on literature growth rates, ranged from 404 kJ m^–2 yr^–1 (37 J m^–3 d^–1) to 1614 kJ m^–2 yr^–1 (147 J m^–3 d^–1). A compromise estimate of 689 kJ m^–2 yr^–1 (i.e., 63 J m^–3 d^–1) is comparable to other estimates from tropical and subtropical regions. A model of annual energy flow through 11 planktonic compartments suggests the total ciliate assemblage (aloricates and tintinnines) to be as productive as metazoan herbivores and metazoan carnivores.     

Community structure of the benthos in Scottish sea-lochs. I. Introduction and species diversity

The diversity of the macrobenthos was measured, using the rarefaction method of Sanders (1968), from bottom samples from Loch Etive, Loch Creran and the Firth of Lorne (Scottish west coast). Each sample (representing 1.6 m² of bottom area) was accumulated as a series of separate hauls taken consecutively in a systematic pattern with a van Veen grab. Two habitats were considered: soft mud and muddy sand. Within-habitat comparison of species diversity clearly indicates that diversity is lower in Loch Etive than in Loch Creran or the Firth of Lorne. The reasons for this are probably connected with the relatively high freshwater runoff into Loch Etive, possibly limiting the survival of planktonic larval stages of the benthos. The values of species diversity measured for the soft-mud areas in Loch Creran and the Firth of Lorne are thought to be representative for this habitat along the west coast of the British Isles. They agree well with the diversity predicted by Sanders for such a boreal inshore area, where a maritime climate prevails, on the basis of his time-stability hypothesis and the results of his sampling elsewhere.     

Macroinfauna of a Southern New England salt marsh: seasonal dynamics and production

The animal-habitat relationships and seasonal dynamics of the benthic macroinfauna were investigated from November 1986 to October 1988 in the Great Sippe-wissett salt marsh (Massachusetts, USA). Total macrofaunal abundance varied seasonally, displaying a peak in late spring and early summer, then declining sharply during late summer and recovering briefly in fall before collapsing in winter. Three macroinfaunal assemblages were found in the marsh, distributed along gradients of environmental factors. These included a sandy non-organic sediment assemblage, a sandy organic sediment assemblage and a muddy sediment assemblage. The species groups characteristic of unstable sandy non-organic sediments included the polychaetes Leitoscoloplos fragilis, Aricidea jefreyssi, Magelona rosea and Streptosyllis verrilli, the oligochaete Paranais litoralis, and the crustacean Acanthohaustorius millsi. Sandy organic sediments were characterized by the polychaetes Marenzelleria viridis, Capitella capitata, Neanthes succinea, N. arenaceodonta, Polydora ligni and Heteromastus filiformis, the oligochaete Lumbricillus sp., and the mollusc Gemma gemma. In muddy sites, the polychaete Streblospio benedicti and the oligochaetes Paranais litoralis and Monopylephorus evertus were the dominant species. Secondary production of benthic macroinfauna in each of these habitats was estimated. The highest values of biomass and production were recorded in the sandy organic sediments. Secondary production was estimated to be 1850 kJ m^-2 yr^-1 in sandy organic areas, but only 281 kJ m^-2 yr^-1 in sandy non-organic areas and 113 kJ m^-2 yr^-1 in muddy areas. This results in an area-weighted average production of 505 kJ m^-2 yr^-1 for the unvegetated areas of the marsh. The Great Sippewissett salt marsh has an area of 483800 m², the total secondary production of the macroinfauna for the whole unvegetated area of the marsh was estimated as 4651 kg dry wt yr^-1, expressed as somatic growth. This production value seems consistent with production data obtained for other intertidal North Atlantic environments.     

Fish Responses to Experimental Fragmentation of Seagrass Habitat

Abstract: Understanding the consequences of habitat fragmentation has come mostly from comparisons of patchy and continuous habitats. Because fragmentation is a process, it is most accurately studied by actively fragmenting large patches into multiple smaller patches. We fragmented artificial seagrass habitats and evaluated the impacts of fragmentation on fish abundance and species richness over time (1 day, 1 week, 1 month). Fish assemblages were compared among 4 treatments: control (single, continuous 9‐m² patches); fragmented (single, continuous 9‐m² patches fragmented to 4 discrete 1‐m² patches); prefragmented/patchy (4 discrete 1‐m² patches with the same arrangement as fragmented); and disturbance control (fragmented then immediately restored to continuous 9‐m² patches). Patchy seagrass had lower species richness than actively fragmented seagrass (up to 39% fewer species after 1 week), but species richness in fragmented treatments was similar to controls. Total fish abundance did not vary among treatments and therefore was unaffected by fragmentation, patchiness, or disturbance caused during fragmentation. Patterns in species richness and abundance were consistent 1 day, 1 week, and 1 month after fragmentation. The expected decrease in fish abundance from reduced total seagrass area in fragmented and patchy seagrass appeared to be offset by greater fish density per unit area of seagrass. If fish prefer to live at edges, then the effects of seagrass habitat loss on fish abundance may have been offset by the increase (25%) in seagrass perimeter in fragmented and patchy treatments. Possibly there is some threshold of seagrass patch connectivity below which fish abundances cannot be maintained. The immediate responses of fish to experimental habitat fragmentation provided insights beyond those possible from comparisons of continuous and historically patchy habitat.     

Effect of food location and quality on recruitment sounds and success in two stingless bees,<Emphasis Type="Italic"> Melipona mandacaia</Emphasis> and<Emphasis Type="Italic"> Melipona bicolor</Emphasis>

It is unclear whether stingless bees in the genus Melipona (Hymenoptera, Apidae, Meliponini) can reliably encode the distance to a food source through recruitment sounds produced inside the nest, in part because the sound features correlated with distance also vary with food quality. We therefore trained marked foragers of two species, Melipona mandacaia and M. bicolor, to feeders at different distances and to different sucrose concentrations at the same distance. In both species, foragers successfully recruited to a rich 2.5-m food source and produced pulsed recruitment sounds in which pulse duration was significantly and positively correlated with distance to the rich food source. When returning from poorer food sources (0.6–1.5 m), foragers of both species decreased sound production, producing shorter sound pulses and longer sound interpulses than they did for 2.5 m food located at the same distance. Thus the temporal structure of M. mandacaia and M. bicolor recruitment sounds varies with distance and food quality. However, nestmates were not recruited by performances for poorer food sources (0.6–1.5 m), whose sucrose concentration was sufficiently low to affect recruitment sounds. Surprisingly, the interphase (the time between behavioral phases that communicate location) also increases with decreasing food quality in the closely related honeybees (Apis), suggesting a potential homology in the effect of food quality on the recruitment systems of Apis and Melipona. We explore the evolutionary implications of these similarities.Communicated by M. Giurfa     

Symbiosis in sacoglossan opisthobranchs: functional capacity of symbiotic chloroplasts

It has been previously reported that many species of the order Sacoglossa (Mollusca: Opisthobranchia) contain algal chloroplasts within the cells of their digestive gland and maintain them in a symbiotic condition. In the present study, two species, Elysia hedgpethi Marcus and Placobranchus ianthobapsus Gould, were compared as to their abilities to retain functional chloroplasts in their tissues. Animals were starved for varying lengths of time, and the functional capacity of the plastids was ascertained at intervals. The chlorophyll content of whole animals, and the ability to incorporate ¹⁴CO₂ were used as the assay for functional capacity. E. hedgpethi decreased in chlorophyll content during starvation until the tenth day, when no chlorophyll was detectable spectrophoto-metrically. Incorporation of ¹⁴CO₂ paralleled the decline in chlorophyll, and was at control levels by the tenth day. P. ianthobapsus showed no decline in chlorophyll content over 27 days starvation, although the ability to incorporate ¹⁴CO₂ showed a decrease.     

Factors affecting the distribution of rock-lobster larvae (Panulirus longipes cygnus), with reference to variability of plankton-net catches

One of the major problems in the quantitative study of the distribution of larvae of the western rock lobster Panulirus longipes cygnus George, is the high variability in planktonnet catches taken at night, even when replicate hauls are made at a single station. Some of the possible causes of this variability are considered. The density of early and late-stage phyllosoma larvae caught at the surface at night showed no direct relationship to either temperature or salinity. Early-stage phyllosoma larvae were equally well represented at the surface under all light conditions encountered at night. In contrast, the density of late-stage phyllosoma larvae at the surface was, on an average, four times greater on dark nights than on bright moonlight nights. The mean density for all phyllosoma stages decreased rapidly with depth, i.e., from 0.70/1000 m³ at the surface to 0.04/1000 m³ at 25 to 35 m, indicating that the vertical movements at night are not very extensive. The density of early-stage phyllosoma larvae in the surface at night showed no relationship to micronekton biomass (measured as wet weight). Density of late-stage phyllosoma larvae at the surface at night increased slightly, but significantly, with increase of micronekton biomass, possibly indicating similar behavioural responses to light or some other factor(s). The distribution of cast exuviae of final-stage phyllosoma larvae indicated that metamorphosis to the puerulus phase can occur more than 100 miles (161 km) from shore. Moreover, 80% of the puerulus larvae caught were within 80 miles (129 km) of the shore. Mean densities of puerulus larvae taken at and below the surface at night were 0.04/1000 m³ and 0.10/1000 m³, respectively, although total numbers were low. This evidence indicates that, after metamorphosis, the puerulus larvae return to the coastal environment at some subsurface depth.     

城市社区农贸市场空气微生物及抗生素抗性基因研究

社区农贸市场活禽交易区是城市重要的人畜交叉感染区域,区内高存量的微生物和抗生素抗性基因(antibiotic resistance genes,ARGs)可通过粪便、冲洗水、空气等介质传播扩散。而空气介质中通过微生物气溶胶形式的传播途径,因其隐秘性、持久性的特点而对社区居民健康构成严重威胁。本文研究了深圳市某典型社区农贸市场内空气微生物及抗生素抗性基因。结果表明,活禽交易区可培养细菌浓度高达105CFU·m-3,远高于一般室内区域(103CFU·m-3),其中PM2.5精细颗粒物(0.65~3.3μm)中所含菌量占总菌量42%以上;活禽交易区空气介质中,抗生素抗性基因tet G、tet W、sul1和sul2检出率达70%以上,其绝对浓度在10~4~10~9copies·m-3之间;周边环境空气样品中,随着与活禽交易区距离的增加,空气微生物及抗生素抗性基因含量呈显著下降趋势。结果表明,农贸市场活禽交易区是微生物和抗生素抗性基因的一个重要储存库,活禽交易区空气会严重影响农贸市场及其外周边空气质量。     

Effects of mussel aquaculture on the nitrogen cycle and benthic communities in Kenepuru Sound,Marlborough Sounds,New Zealand

Nitrogen pools and transformations and benthic communities at a Perna canaliculus farm and a nearby reference site without direct influence of marine farming in Kenepuru Sound, New Zealand, were compared on four dates between September 1982 and May 1983. The organic nitrogen pool in the top 12 cm sediment was 7.4 to 10.8 mol m^-2 at the mussel farm and 6.1 to 8.9 mol m^-2 at the reference site. The nitrate and nitrite pools were similar in both sediments, but the ammonium pool in the mussel farm sediment was about twice as high as in the reference sediment. In January, the sediment ammonium concentrations ranged from 418 nmol cm^-3 (surface) to 149 nmol cm^-3 (12 cm depth) at the mussel farm and from 86 to 112 nmol cm^-3 at the reference site. The molar C:N ratio of the sediment organic matter was 6.2 to 7.2 at the mussel farm and 7.9 to 10.0 at the reference site. The molar N:P ratio of the sediment organic matter was 4.3 to 7.2 and 3.3 to 6.1 at mussel farm and reference site, respectively. The total nitrogen mineralisation rate in the top 12 cm sediment ranged from 21.7 to 37.1 mmol m^-2 d^-1 at the mussel farm and from 8.5 to 25.0 mmol m^-2 d^-1 at the reference site. Ammonium excretion by mussels was about 4.7% (January) and 7.4% (May) of the combined nitrogen mineralisation by mussels and sediment. The sediment-denitrification rate was 0.7 to 6.1 mmol m^-2 d^-1 at the mussel farm and 0.1 to 0.9 mmol m^-2 d^-1 at the reference site. In January, 76 and 93% of the nitrate reduced in the sediments were denitrified at the mussel farm and reference site, respectively. The denitrification rate on the mussel lines (determined on detritus-covered mussels) was twice the mussel farm sediment-denitrification rate and 10 times the reference sediment-denitrification rate. Total denitrification at the mussel farm was 21% higher than at the reference site. The loss of nitrogen through mussel harvest and denitrification was 68% higher at the mussel farm. The surface layers of both sediments contained about 75 mg m^-2 chlorophyll a. Sediment phaeophytin levels were 52 mg m^-2 at the reference site and 137 mg m^-2 at the mussel farm. While the benthic infauna of the mussel-farm sediment consisted only of polychaete worms, the reference sediment contained also bivalve molluscs, brittle stars and crustaceans.     

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O₂ m⁻² h⁻¹ (~11.7 mg C m⁻² h⁻¹) while from the sediment it was 6.08 mmol O₂ m⁻² h⁻¹ (~70.8 mg C m⁻² h⁻¹). When the ice was present O₂ export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)⁻¹ h⁻¹ while those from the benthos were up to 1.53 mg C (mg Chl-a)⁻¹ h⁻¹. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.     

Zooplankton biomass in the ice-covered Weddell Sea,Antarctica

Zooplankton was sampled by a Rectangular Midwater Trawl (RMT 1 + 8) in Weddell Sea surface waters (0 to 300 m) between 66 and 78°S during austral summer (February – March 1983). Sixty-nine taxa including different developmental stages were considered and divided into 16 size classes between <1 and >39.5 mm length. Biomass was determined by taxon and size class for three different meso- and macroplankton communities in the oceanic region, on the northeastern shelf and on the southern shelf of the Weddell Sea. The highest biomass of 11.2 mg DW m^–3 (3.4 g DW m^–2) was found in the northeastern shelf community (70 to 74°S), where juvenile and adultEuphausia crystallorophias accounted for 3.7 mg DW m^–3 (1.1 g DW m^–2). Although not quantitatively sampled, early copepodite stages (CI to CIII) ofCalanoides acutus andCalanus propinquus ranked second with 2.7 mg DW m^–3 (0.8 g DW m^–2). Biomass in the northeastern shelf community was concentrated in the size ranges 1 to 4 mm and 19.5 to 39.5 mm. The oceanic community of the central Weddell Sea was dominated by copepods smaller than 5 mm, which made up half of the total oceanic biomass. The tunicateSalpa thompsoni (7.0 to 8.5 mm) was the dominant single species with 1.6 mg DW m^–3 (0.5 g DW m^–2). Euphausiids, mainly juvenile and adult krillEuphausia superba, comprised 1.2 mg DW m^–3 (0.4 g DW m^–2). Total standing stock in the oceanic community was 9.4 mg DWm^–3 (2.8 g DW m^–2). Lowest biomass values were found in the southern shelf community (south of 75°S) with 4.0 mg DW m^–3 (1.2 g DW m^–2), concentrated in the 1 to 4 mm and 14.5 to 34.5 mm size classes. Abundant species were the pteropodLimacina helicina (1 to 2 mm; 0.7 mg DW m^–3; 0.2 g DW m^–2) andE. crystallorophias (24.5 to 39.5 mm; 0.9 mg DW m^–3; 0.3 g DW m^–2). The data reveal that it is essential to distinguish among subsystems in the Southern Ocean. This leads to a better understanding of the structure and function of those pelagic food webs which represent alternatives to the paradigmatic krill-centered system.     

UV- and salinity-induced oxidative effects in the marine diatom <Emphasis Type="Italic">Cylindrotheca closterium</Emphasis> during simulated emersion

The diatom Cylindrotheca closterium was exposed to transient light- and osmotic conditions as occur during its tidal emersion. The objective was to analyze how this simulated emersion contributes to the production of active oxygen species (AOS) and via this, to oxidative cell damage. Light- and salinity conditions were varied in factorial combination: low light (no UVB) or high light (unweighted UVB-dose rates of respectively 0.01; 0.07; 0.24; 1.03 W m⁻²) at normal (30 psu) or high salinity (60 psu). UVB (0.01–0.24 W m⁻²) and high salinity had a significant, negative effect on the photosynthetic efficiencies ΔF/F _m’ (steady-state quantum yield) and F _v/F _m (maximum yield). UVB at 1.03 W m⁻² (15 kJ m⁻² d⁻¹) almost arrested electron transport. At ecologically relevant UVB levels, i.e. below 0.24 W m⁻² (≈3.4 kJ m⁻² d⁻¹) with UVB:PAR<0.4:100 (PAR photosynthetically active radiation) only dynamic photoinhibition was observed (protection via heat dissipation). Non-photochemical quenching was positively correlated with the de-epoxidation of diadinoxanthin (DD) to diatoxanthin (DT). A decreasing ratio DT/(DD+DT) after 4 h of UVB at >0.07 W m⁻² and at 60 psu indicated a reversal of the diatom xanthophyll cycle (diminished photoprotection) which may be caused by an enhanced AOS production. Oxidative stress and -damage to C. closterium cells were assessed applying fluorescent indicator dyes, via confocal microscopy and quantitative image analysis. AOS production rates (cellular DCF fluorescence) were stimulated by UV, and were ~50% higher at 60 psu. AOS production decreased with an increasing pre-exposure (0–4 h) to normal UVB (0.24 W m⁻²), which indicated a stimulation of the antioxidative defence. Non-protein thiols (indicator CMF) and glutathione pools (HPLC-analyzed) decreased with UVB-dose rates (0.01–0.24 W m⁻²), most likely due to AOS-mediated thiol oxidation. Hypersalinity (60 psu) and UVB (0.01–0.24 W m⁻²) caused membrane depolarization (dye DIBAC₄(3)) and phospholipid hydrolysis (phospholipase A₂ dye: bis-BODIPY FL-C₁₁-PC). AOS production may have diminished the membrane polarity, and peroxidized the membrane lipids (HPLC-analyzed malondialdehyde) which enhanced PLA₂ activity. The dyes indicated an increased oxidative (lipid) damage at a 15% inhibition of photosynthesis in this diatom, at UVB levels and salinities that can be expected in situ during its periodic tidal emersion.