Living conditions, abundance and biomass of under-ice fauna in the Storfjord area (western Barents Sea, Arctic) in late winter (March 2003)

The under-ice habitat and fauna were studied during a typical winter situation at three stations in the western Barents Sea. Dense pack ice (7–10/10) prevailed and ice thickness ranged over <0.1–1.6 m covered by <0.1–0.6 m of snow. Air temperatures ranged between –1.8 and –27.5°C. The ice undersides were level, white and smooth. Temperature and salinity profiles in the under-ice water (0–5 m depth) were not stratified (T=–1.9 to –2.0°C and S=34.2–34.7). Concentrations of inorganic nutrients were high and concentrations of algal pigments were very low (0.02 g chlorophyll a l^–1), indicating the state of biological winter. Contents of particulate organic carbon and nitrogen ranged over 84.2–241.3 and 5.3–16.4 g l^–1, respectively, the C/N ratio over 11.2–15.5 pointing to the dominance of detritus in the under-ice water. Abundances of amphipods at the ice underside were lower than in other seasons: 0–1.8 ind. m^–2 for Apherusa glacialis, 0–0.7 ind. m^–2 for Onisimus spp., and 0–0.8 ind. m^–2 for Gammarus wilkitzkii. A total of 22 metazoan taxa were found in the under-ice water, with copepods as the most diverse and numerous group. Total abundances ranged over 181–2,487 ind. m^–3 (biomass: 70–2,439 g C m^–3), showing lower values than in spring, summer and autumn. The dominant species was the calanoid copepod Pseudocalanus minutus (34–1,485 ind. m^–3), contributing 19–65% to total abundances, followed by copepod nauplii (85–548 ind. m^–3) and the cyclopoid copepod Oithona similis (44–262 ind. m^–3). Sympagic (ice-associated) organisms occurred only rarely in the under-ice water layer.     

Diurnal vertical distribution of rotifers (Rotifera) in the Chara zone of Budzyńskie Lake,Poland

Diurnal vertical distribution of rotifers was investigated in the Chara bed and the water immediately above it in the shallow region (ca. 1 m depth) of Budzyskie Lake (Wielkopolski National Park, Poland) in early September 1998. Eighty one rotifer species were identified – 71 among Chara and 59 in the open water. Significant differences in rotifer densities were observed in the Chara, with highest numbers during the day (2316 ind. l^–1) and lowest numbers early morning (521 ind. l^–1) and at dusk (610 ind. l^–1). Above the Chara, the numbers of rotifers did not change significantly (615–956 ind. l^–1). Littoral- or limnetic-forms differed in their diel vertical distribution between both zones. One group of littoral species was characterized by increased densities in the Chara in the daytime, while a second group increased in density during the night. The densities of limnetic species, which were much higher in open water, decreased in the morning or daytime in this zone. These differences in the diel behaviour of particular groups of rotifers may be dependent on microhabitat and may also be related to different kinds of predation, the exploitative competition for shared food resources between rotifers and crustaceans, as well as typical adaptation to littoral or limnetic life.     

Vertical distribution of organic constituents in an Antarctic lake: Lake Fryxell

Vertical distribution of organic constituents, i.e. total organic carbon (TOC), hydrocarbons, fatty acids and hydroxy acids in water and sediment samples from Lake Fryxell (77° 35 S, 163° 15 E) of southern Victoria Land, Antarctica were studied to elucidate their features in relation to stratification of the lake waters and likely distribution of microorganisms. The TOC content of the surface water (5.0 m; just below the ice cover of 4.50 m thickness) was 1.4 mg l^–1. It increased markedly with depth and attained a maximum value of 21.7 mg C l^–1 at a depth of 17.5 m, but decreased to the bottom (13.3 mg C l^–1). The high TOC content of the anoxic bottom layers (> 15 m) is attributable to the concentration of refractory organic substances over long periods following the degradation of labile organic constituents. Hydrocarbons were not found in the water column, but the major constituent of the bottom sediment was n-C_{29 : 2} alkene. Total concentrations of fatty acids in the oxic layers ( 10 m) were highest at 10.0 m and much higher than those in the anoxic layers (> 10 m), probably reflecting the phytoplankton population. The content of branched (iso and anteiso) fatty acids and 3-hydroxy acids in the anoxic layers were much greater than those in the oxic layers which would seem to reflect the distribution of bacterial abundance. The differences of organic composition between the water column and sediments imply that sinking dead organisms were quickly degraded in the lake bottom. Also, the composition of microorganisms in the water column must be very different from that in the sediments.     

High sympagic metazoan abundance in platelet layers at Drescher Inlet, Weddell Sea, Antarctica

The metazoan fauna of platelet layers was investigated at Drescher Inlet, Weddell Sea, Antarctica in the late summer of 1995. Twenty-eight species were found, many of them new to science. The most abundant subclass was the Copepoda, of which almost 90% of the individuals belong to only three species: Drescheriella glacialis, Stephos longipes and Paralabidocera antarctica. Among copepods, Harpacticoida was the largest group, represented by 16 species. Total abundance varied between 40 and 120 individuals l⁻¹. Abundances and population structure were comparable to other especially porous sea-ice habitats. Results indicate competitive exclusion among the three dominant species. The finding of a profuse meiofauna in platelet layers may explain enigmatic concentrations of ammonium and phosphate commonly detected there. Accepted: 5 February 1999     

Observations on the relationship between the Antarctic coastal diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen and sea ice concentrations during the late Quaternary

The available ecological and palaeoecological information for two sea ice-related marine diatoms (Bacillariophyceae), Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen, suggests that these two species have similar sea surface temperature (SST), sea surface salinity (SSS) and sea ice proximity preferences. From phytoplankton observations, both are described as summer or autumn bloom species, commonly found in low SST waters associated with sea ice, although rarely within the ice. Both species form resting spores (RS) as irradiance decreases, SST falls and SSS increases in response to freezing ice in autumn. Recent work analysing late Quaternary seasonally laminated diatom ooze from coastal Antarctic sites has revealed that sub-laminae dominated either by T. antarctica RS, or by P. glacialis RS, are nearly always deposited as the last sediment increment of the year, interpreted as representing autumn flux. In this study, we focus on sites from the East Antarctic margin and show that there is a spatial and temporal separation in whether T. antarctica RS or P. glacialis RS form the autumnal sub-laminae. For instance, in deglacial sediments from the Mertz Ninnis Trough (George V Coast) P. glacialis RS form the sub-laminae whereas in similar age sediments from Iceberg Alley (Mac.Robertson Shelf) T. antarctica RS dominate the autumn sub-lamina. In the Dumont d'Urville Trough (Adélie Land), mid-Holocene (Hypsithermal warm period) autumnal sub-laminae are dominated by T. antarctica RS whereas late Holocene (Neoglacial cool period) sub-laminae are dominated by P. glacialis RS. These observations from late Quaternary seasonally laminated sediments would appear to indicate that P. glacialis prefers slightly cooler ocean–climate conditions than T. antarctica. We test this relationship against two down-core Holocene quantitative diatom abundance records from Dumont d'Urville Trough and Svenner Channel (Princess Elizabeth Land) and compare the results with SST and sea ice concentration results of an Antarctic and Southern Ocean Holocene climate simulation that used a coupled atmosphere–sea ice–vegation model forced with orbital parameters and greenhouse gas concentrations. We find that abundance of P. glacialis RS is favoured by higher winter and spring sea ice concentrations and that a climatically-sensitive threshold exists between the abundance of P. glacialis RS and T. antarctica RS in the sediments. An increase to > 0.1 for the ratio of P. glacialis RS:T. antarctica RS indicates a change to increased winter sea ice concentration (to >80% concentration), cooler spring seasons with increased sea ice, slightly warmer autumn seasons with less sea ice and a change from ~ 7.5 months annual sea ice cover at a site to much greater than 7.5 months. In the East Antarctic sediment record, an increase in the ratio from <0.1 to above 0.1 occurs at the transition from the warmer Hypsithermal climate into the cooler Neoglacial climate (~ 4 cal kyr) indicating that the ratio between these two diatoms has the potential to be used as a semi-quantitative climate proxy.     

Nitrogen uptake in the Weddell Sea during late winter and spring

Summary Uptake rates of ammonium, nitrate and urea were measured during the EPOS leg 1 cruise to the Weddell Sea in October–November 1988 using the isotope ¹⁵N. Nitrate was the most important nitrogen source both for ice algae (f-ratio 0.88) and for phytoplankton in the water column (f-ratio 0.85). Indications of a gradual decrease in % new production with time were found in the outer marginal ice zone. Nitrogen uptake rates in ice algae from the sub-ice assemblage were light-limited at in situ irradiances. Significant regeneration of ammonium was found in ice algal samples only.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Faecal pellet production by Arctic under-ice amphipods – transfer of organic matter through the ice/water interface

The underside of Arctic sea ice is inhabited by several autochthonous amphipod species (Apherusa glacialis, Onisimus spp., Gammarus wilkitzkii). The amphipods graze on ice-bound organic matter, such as ice algae, detritus and ice fauna, and release faecal pellets into the underlying water column, thus forming a direct link between the sea ice and the pelagic ecosystems. Experiments on faecal pellet production rates showed species-specific differences, which were related to size of the animals. The smallest species, A. glacialis, produced the highest mean number of pellets (15.4 pellets ind.^-1 d^-1), followed by Onisimus spp. (2.7 pellets ind.^-1 d^-1) and the largest species, G. wilkitzkii (1.1 pellets ind.^-1 d^-1). Relative carbon content of the pellets was very similar in all species (21.2–22.6% dry mass). Juvenile amphipods (Onisimus spp., G. wilkitzkii) produced more pellets with less POC than adults. Based on field determinations of the POC concentration in the lowermost 2 cm of the sea ice (mean: 36.4 mg C m^-2) and mean amphipod abundances (A. glacialis: 33.8 ind. m^-2, Onisimus spp.: 0.5 ind. m^-2, G. wilkitzkii: 9.4 ind. m^-2) in the Greenland Sea in summer 1994, the amount of POC transferred from the ice to the water by faecal pellet production was estimated (0.7 mg C m^-2 d^-1 or almost 2% of ice-bound carbon). Since this process probably takes place in all ice-covered Arctic regions as well as during all seasons, grazing and pellet production by under-ice amphipods contributes significantly to matter flux across the ice/water interface.     

Temporal variability in abundance and biomass of ciliates and copepods in the eutrophicated part of Kaštela Bay (Middle Adriatic Sea)

Seasonal variations in abundance and carbon biomass of ciliated protozoa and micrometazoa were studied from May 1998 to November 1999 in the eutrophicated area of Katela Bay (Middle Adriatic Sea). Ciliates showed peaks in spring and autumn, primarily due to changes in the abundance and biomass of tintinnines, which participated in total ciliate abundance and biomass with 40.48 and 60.02%, respectively. The highest tintinnine density was 4,278 ind. l^–1, while their average biomass varied from 0.611 to 26.557 gC l^–1 . Maximal average density and biomass of non-loricates were 1,430 ind. l^–1 and 3.925 gC l^–1, respectively. The micrometazoa community was dominated by copepod nauplii, especially during the summer and autumn. The copepod biomass ranged between 3.47 and 26.75 gC l^–1 . High abundance and biomass values of the investigated zooplankton groups point to an important role of these organisms in the secondary production in the Bay, indicating that they may be (1) a crucial factor in controlling the populations of nano-/pico-phytoplankton and heterotrophic nanoflagellates, and (2) a significant prey for larger micrometazoans.     

Build-up and decline of summer phytoplankton biomass in the eastern Weddell Sea,Antarctica

The seasonal development and decline of phytoplankton was investigated in the eastern Weddell Sea during summer and fall 1991. During the first half of the study (15 Jan–13 Feb) in an area off Vestkapp, favourable irradiance/mixing regimes initiated net phytoplankton growth in ice-free waters on the shelf and in stretches of open water over the partially ice-covered deep ocean. Chi a concentrations in the upper water column were moderate (0.2–0.8 g l^–1), but significantly above winter values. Later in the season (16 Feb–11 March), a phytoplankton bloom with surface Chl a concentrations ranging from 1.6–2.3 g l^–1 was encountered in an area further to the east. We suggest that the upper water column must have been stratified in this region for time scales of weeks to faciliate bloom development. Bacterial biomass and productivity generally paralleled the seasonal development of the phytoplankton. Nitrate concentrations in the upper mixed layer were substantially lower than would be expected from the existing phytoplankton standing stock, suggesting that heterotrophic consumption of organic matter by bacteria and zooplankton removed a large fraction of the primary production. The shallow seasonal pycnocline was eventually eroded by the passage of a storm, resulting in a homogeneous distribution of phytoplankton biomass over the entire water column, followed by sedimentation and deposition of phytodetritus on the sea floor. After the storm induced destratification, bacterial productivity was particularly high, amounting to more than half of the primary production (range: 10%–120%) in the upper water column. Subsequently, phytoplankton biomass in the upper water column decreased to values <1 g Chl a l^–1. The combination of low incident irradiances and incessant deep mixing prevented the phytoplankton biomass to increase again. During the last week of the investigation, extensive new-ice formation was observed. A major fraction of the residual surface plankton was incorporated into new sea ice, thus terminating the pelagic growth season of the phytoplankton in the eastern Weddell Sea.     

Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica)

The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 g l^–1 . Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 mol l^–1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation.     

Zooplankton boom and ice amphipod bust below melting sea ice in the Amundsen Gulf, Arctic Canada

Early summer in the Arctic with extensive ice melt and break-up represents a dramatic change for sympagic–pelagic fauna below seasonal sea ice. As part of the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL), this investigation quantified zooplankton in the meltwater layer below landfast ice and remaining ice fauna below melting ice during June (2008) in Franklin Bay and Darnley Bay, Amundsen Gulf, Canada. The ice was in a state of advanced melt, with fully developed melt ponds. Intense melting resulted in a 0.3- to 0.5-m-thick meltwater layer below the ice, with a strong halocline to the Arctic water below. Zooplankton under the ice, in and below the meltwater layer, was sampled by SCUBA divers. Dense concentrations (max. 1,400 ind. m⁻³) of Calanus glacialis were associated with the meltwater layer, with dominant copepodid stages CIV and CV and high abundance of nauplii. Less abundant species included Pseudocalanus spp., Oithona similis and C. hyperboreus. The copepods were likely feeding on phytoplankton (0.5–2.3 mg Chl-a m⁻³) in the meltwater layer. Ice amphipods were present at low abundance (<10 ind. m⁻²) and wet biomass (<0.2 g m⁻²). Onisimus glacialis and Apherusa glacialis made up 64 and 51% of the total ice faunal abundance in Darnley Bay and Franklin Bay, respectively. During early summer, the autochthonous ice fauna becomes gradually replaced by allochthonous zooplankton, with an abundance boom near the meltwater layer. The ice amphipod bust occurs during late stages of melting and break-up, when their sympagic habitat is diminished then lost.     

Occurrence of cyclopoid copepods and faecal material in the Halley Bay region,Antarctica, during January–February 1991

Faecal material and cyclopoid copepods were collected during the expedition ANT IX/3, in the Halley Bay area (Weddell Sea, Antarctica), between January and February 1991. Faecal material comprised pellets produced by krill, copepods, ostracods and appendicularians. Cyclopoid copepods were represented by two genera, Oithona and Oncaea. In the Halley Bay area, higher concentrations of krill faecal material (420.9 mm³ m^–2) and chl.-a (39.3 mg m^–2) were found within the upper 200 m of the water column of the polynya than in ice-covered open-ocean areas (58.2 mm³m^–2 and 25.5 mg m^–2, respectively). At an ice-drift station, high concentrations of krill faecal strings under fest-ice were found. In addition, similarities between diatom assemblages in the pack-ice algae and krill faecal strings contents suggest an active utilization of ice-algae by krill populations. Sedimented material collected at 50 m depth by a sediment trap was dominated by krill faecal strings. Contents of small oval pellets (of probable cyclopoid copepod origin) resemble those of krill faecal pellets suggesting that coprophagy was involved. This suggestion is supported by: (1) The small quantity of food particles (other than krill faecal matter) available in the water column (< 0.3 g chl.-al^–1). (2) The negative in situ correlation between krill faecal strings and cyclopoid copepods. (3) The structure of cyclopoid copepod buccal appendages, which are more adapted for raptorial feeding.     

Production and fate of faecal pellets during summer in an East Antarctic fjord

The abundance of small faecal pellets is high in marine waters. Little is known, however, about the processes governing their production and fate in the water column. We investigated faecal pellet production and flux in relation to the phytoplankton and copepod assemblages present in Ellis Fjord, Antarctica. Results show that the phytoplankton community shifted from a dominance of diatoms to that of a cryptomonad species during late January. This coincided with an increase in abundance of the small copepods Paralabidocera antarctica and Oithona similis, although Oncaea curvata was still the dominant species. The mean faecal pellet flux was 9943 pellets m^–2 d^–1. Only 37% of the faecal pellet flux at 5 m sedimented to 10 m depth, 15% to 20 m, and 12% to 40 m depth. Our results suggest that recycling of faecal pellets by copepods contributes to this decreased flux with increasing depth, which concurs with results from large scale oceanic studies. Additionally, we propose that the summer ice melt changes the physical characteristics of the water column and the phytoplankton species abundance and distribution; both of which potentially impact on the distribution and abundance of copepods, thereby regulating faecal pellet flux.     

Dynamics of coexisting Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus populations in a high-Arctic fjord

We studied the population dynamics of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in Billefjorden, Svalbard (78°40N). All three species reproduced in the fjord with different timing. The maximum abundance of Calanus spp. copepodite stages peaked on the 11th of July (29,000 ind m^–2). C. glacialis was the dominant species accounting for 60–80% of the total Calanus abundance. C. finmarchicus appear to thrive in the fjord despite the low temperatures (–1.86°C to 5°C) and accounted for 20–30% of the total population. C. hyperboreus contributed less to the total abundance (5–20%). A 1-year life cycle is suggested for C. finmarchicus and C. hyperboreus in the fjord, C. glacialis has a 1- to 2-year life cycle. Highest mortality rates were observed for copepodite stage CV in C. finmarchicus and C. glacialis (0.09 and 0.075 d^–1, respectively) and for females in C. hyperboreus (0.149 d^–1). Mortality of copepodite stages was substantially lower in C. glacialis than in the other species. This is particularly obvious in the early and numerous copepodite stages (CI + CII) during the period of recruitment to these stages. This suggests that differences in secondary production in Arctic pelagic ecosystems are controlled partly by population loss rates.     

Abundance, biomass and small-scale distribution of cryopelagic amphipods in the Franz Josef Land area (Arctic)

Arctic sea ice is inhabited by several amphipod species. Abundance, biomass and small-scale distribution of these cryopelagic (=ice associated) amphipods were investigated near Franz Josef Land in summer 1994. The mean abundance of all species was 420 ind./m²; the mean biomass was 10.61 g ww/m². Gammarus wilkitzkii was the dominant species, whereas Apherusa glacialis, Onisimus nanseni and O. glacialis were only scarcely found. Amphipods were concentrated at the edges of ice floes and were less frequent in areas further away under the ice. The relationship between the distribution and ecological/physiological requirements of cryopelagic amphipods, as well as the small-scale morphology of Arctic sea ice, are discussed. Received: 14 January 1998 / Accepted 14 April 1998     

The spring-time abundance and feeding ofEurytemora affinis (Poppe) in Volkerak-Zoommeer,a newly-created freshwater lake system in the Rhine delta (The Netherlands)

Eurytemora affinis, a calanoid copepod, has been encountered in Volkerak-Zoommeer (Rhine delta region, S.W. Netherlands) both before this lake system was isolated in 1987 from the estuarine influence, and after. It was the main particle-feeding crustacean at all the 3 sampling stations in March–April 1990 when it reached densities of up to 215 ind.l^–1. Its decline from mid April onwards, and low densities through summer, coincided with increase in cladocerans, especiallyDaphnia spp. (D. pulex andD. galeata), a decrease in seston (<33m) and chlorophyll concentrations and in primary production rates. The clearance rates (CR) ofEurytemora measured in the spring period varied enormously (0.6–24 ml.ind^–1.d^–1) depending mainly on size (0.44–1.06 mm), food concentration (0.8–2.2 mg C.l^–1), and the water temperature which varied only narrowly (8.0–9.0°C). Mean ingestion rates of the animals measuring 0.68±0.02 mm during the study was 6.7±3.2 gC.ind^–1.d^–1; and assimilation efficiency varied between 27 and 53% (mean: 41±9%). The weight specific CR (SCR) varied between 0.96 and 6.4 litre.mg^–1 body C.d^–1. Pooled regression of SCR on the animal's body weight at the 3 study stations revealed a significant inverse relationship. Also daily ration and specific assimilation ofE. affinis varied greatly and inversely with the body weight. This calanoid contributed from about 50 to 100% to the zooplankton community grazing rates and assimilation rates, the former often exceeding the phytoplankton primary production.     

Phytoplankton distribution in relation to sea ice,hydrography and nutrients in the northwestern Weddell Sea in early spring 1988 during EPOS

Summary Phytoplankton biomass and distribution of major phytoplankton groups were investigated in relation to sea ice conditions, hydrography and nutrients along three north-south transects in the north western Weddell Sea in early spring 1988 during the EPOS Study (European Polarstern Study), Leg 1. Three different zones along the transects could be distinguished: 1) the Open Water Zone (OWZ) from 58° to 60°S with high chlorophyll a concentrations up to 3.5 g l^–1; 2) the Marginal Ice Zone (MIZ) from 60° to about 62.5° with chlorophyll a concentrations between 0.1 and 0.3 g l^–1, and 3) the closed pack-ice zone (CPI) from 62.5° to 63.2°S with chlorophyll a concentrations below 0.1 gl^–1. Nutrient concentrations increased towards the south showing winter values under the closed pack-ice. Centric diatoms such as Thalassiosira gravida and Chaetoceros neglectum forming large colonies dominated the phytoplankton assemblage in terms of biomass in open water together with large, long chain forming, pennate diatoms, whereas small pennate diatoms such as Nitzschia spp., and nanoflagellates prevailed in ice covered areas. Fairly low concentrations of phytoplankton cells were encountered at the southernmost stations and many empty diatom frustules were found in the samples. The enhanced phytoplankton biomass in the Weddell-Scotia-Confluence area is achieved through sea ice melting in the frontal zone of two different water masses, the Weddell and the Scotia Sea surface waters.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Influence of medium composition and aeration on the synthesis of biosurfactants produced by Candida antarctica

Candida antarctica synthesised surface-active mannosylerythritol lipids at 46 g l^–1 by adding 80 g soybean oil l^–1 to the medium and maintaining the pO₂ at 50% with an air flow rate 1 vvm. Two-stage culturing of C. antarctica avoided medium foaming but the yield of biosurfactants synthesis was 28 g l^–1. The biosurfactants decreased the surface tension of water to 35 mN m^–1.     

Crustacean assemblage and environmental characteristics of a man-made solar saltwork in southern France,with emphasis on anostracan (Branchiopoda) population dynamics

Physical and chemical variables, anostracan populations (Artemia parthenogenetica and Branchinella spinosa) and other biota were studied during 1996–1997 in a Camargue saltern (max. depth 1 m). The taxonomic composition and density of macroinvertebrates were investigated twice monthly, based on benthic substrate and water column samples. Fauna was composed of three groups in terms of numerical importance. The benthic macroinvertebrates were represented only by nematodes (< 50 ind. m^–2 to > 500 ind. m^–2 in November–December and May respectively). The zooplankton was dominated by crustaceans, one cladoceran, Moina salina (ranging from 670 to 2350 ind. m^–2 in spring), two anostracans, Artemia parthenogenetica (< 50 ind. m^–2 in autumn), and Branchinella spinosa (max. 190 ind. m^–2 in December to absent in April), and two copepods, Cletocamptus retrogressus (max. density 2000 ind. m^–2 in November), and Eurytemora velox (max. density 650 ind. m^–2 in February–March). Insects (Chironomidae, Culicidae) were rare, with mean densities < 1 ind. m^–2. The phenology of each crustacean population is discussed in relation to physical and chemical water variables. Salinity appeared to be of greatest importance regulating the population abundance.     

Estimation of bottom ammonium affinity in the New Caledonia lagoon

Ammonium affinity of New Caledonia lagoon benthic communities was measured during the course of 33 in situ enrichment experiments, in order to estimate the contribution of benthos to ammonium fluxes. Ammonium chloride was injected into enclosures pushed into the sediment, in order to obtain a concentration of 20–22 mol l^-1 in the enclosed water which approximated the interstitial water content. Ammonium kinetic uptake was then followed for two hours. Grey-sand bottom displayed the highest affinity for ammonium, but white-sand and muddy bottom affinity was of the same order of magnitude. Macrophytes, and microphytes (when macrophytes are absent), account for the bulk of ammonium bottom uptake. As a result, grey-sand bottoms with their dense macrophyte cover represent a sink for water column nitrogen and play a key role in nutrient cycling of the lagoon. Correspondence to: G. Boucher