Population structure, growth and production of the surf clam Donax hanleyanus (Bivalvia: Donacidae) from northern Argentinean beaches

The surf clams Mesodesma mactroides Reeve, 1854 and Donax hanleyanus Philippi, 1847 are the two dominating species in macrobenthic communities of sandy beaches off northern Argentina, with the latter now surpassing M. mactroides populations in abundance and biomass. Before stock decimation caused by exploitation (during the 1940s and 1950s) and mass mortality events (1995, 1999 and 2007) M. mactroides was the prominent primary consumer in the intertidal ecosystem and an important economic resource in Argentina. Since D. hanleyanus was not commercially fished and not affected by mass mortality events, it took over as the dominant species, but did never reach the former abundance of M. mactroides. Currently abundance and biomass of both surf clams are a multiple smaller than those of forty years ago, indicating the conservation status of D. hanleyanus and M. mactroides as endangered. Therefore the aim of this study is to analyse the population dynamics (population structure, growth and reproductive biology) of D. hanleyanus and M. mactroides, and to compare the results with historical data in order to detect possible differences within surf clam populations forty years ago and at present.

Bacterial production in the eastern Mediteranean Sea in October 2008 during SES_GR2

The HCMR_SES_LAGRANGIAN_GR2_ MICROBIAL PARAMETERS dataset is based on samples collected in the framework of the project SESAME, in the North Aegean Sea during October 2008. The objectives were to measure the standing stocks and calculate the production of the microbial compartment of the food web, describe the vertical distribution pattern and characterize its structure and function through the water column as influenced by the BSW. Bacterial production was estimated by the 3H-leucine method (Kirchman et al. 1986, Kirchman 1993). At each depth, duplicate samples and a control were incubated with 20 nM L-[4,5 3H]-leucine. Samples were incubated in the dark, at in situ temperature.

Bacterial production in the eastern Mediterranean Sea in March and April 2008 during SES_GR1

The dataset is based on samples collected in the framework of the project SESAME, in the Ionian, Libyan and Aegean Sea during March- April 2008. The objectives were to measure the standing stocks and calculate the production of the microbial compartment of the food web, describe the vertical distribution pattern and characterize its structure and function through the water column. Bacterial production was estimated by the 3H-leucine method (Kirchman et al. 1986, Kirchman 1993). At each depth, duplicate samples and a control were incubated with 20 nM L-[4,5 3H]-leucine. Samples were incubated in the dark, at in situ temperature.

Laboratory investigation of flow structure and resistance of high- and low-angle dunes

A prominent control on the flow over subaqueous dunes is the slope of the downstream leeside. While previous work has focused on steep (~30°), asymmetric dunes with permanent flow separation, little is known about dunes with lower lee-slope angles for which flow separation is absent or intermittent. Here, we present a laboratory investigation where we systematically varied the dune lee-slope, holding other geometric parameters and flow hydraulics constant, to explore effects on the turbulent flow field and flow resistance. Three sets of fixed dunes (lee-slopes of 10°, 20° and 30°) were separately installed in a 15 m long and 1 m wide flume and subjected to 0.20 m deep flow. Measurements consisted of high-frequency, vertical profiles collected with a Laser Doppler Velocimeter (LDV). We show that the temporal and spatial occurrence of flow separation decreases with dune lee-slope. Velocity gradients in the dune leeside depict a free shear layer downstream of the 30° dunes and a weaker shear layer closer to the bed for the 20° and 10° dunes. The decrease in velocity gradients leads to lower magnitude of turbulence production for gentle lee-slopes. Aperiodic, strong ejection events dominate the shear layer, but decrease in strength and frequency for low-angle dunes. Flow resistance of dunes decreases with lee-slope; the transition being non-linear. Over the 10°, 20° and 30° dunes, shear stress is 8%, 33% and 90 % greater than a flat bed, respectively. Our results demonstrate that dune lee-slope plays an important, but often ignored role in flow resistance.

Pigments, phytoplankton and its production parameters in the Obskaya Guba and adjacent Kara Sea in the latest September 2007

Material was collected in the Ob River estuary and the adjacent shallow Kara Sea shelf between 71°14.0'N and 75°33.0'N at the end of September 2007. Latitudinal zonation in phytoplankton distribution was demonstrated; this zonation was determined by changes in salinity and concentration of nutrients. Characteristic of the phytocenosis in the southern desalinated zone composed of freshwater diatom and green algae species were high population density (1500000 cells/l), biomass (210 ?g C/l), chlorophyll concentration (4.5 ?g/l), and uniform distribution in the water column. High primary production (~40 ?g C/l/day) was recorded in the upper 1.5 m layer. The estuarine frontal zone located to the north had a halocline at depth 3-5 m. Freshwater species with low abundance (250000 cells/l), biomass (24 ?g C/l), and chlorophyll concentration (1.5 ?g/l) dominated above the halocline. Marine diatom algae, dinoflagellates, and autotrophic flagellates formed a considerable part of the phytocenosis below the halocline; community characteristics were two-fold lower as compared with the upper layer. Maximal values of primary production (~10 ?g C/l/day) were recorded in the upper 1.5 m layer. The phytocenosis in the seaward zone was formed by marine alga species and was considerably poorer as compared with the frontal zone. Assimilation rates of carbon per chlorophyll a at the end of the vegetation season within the studied area were low, average 0.4-1.0 ?g C/?g Chl/hour in the upper layer and 0.03-0.1 ?g C/?g Chl/hour below the pycnocline.

On the fine structure of oxygen distribution in surface water layers in the area between Iceland and Faroe Islands

During the international "Overflow-Expedition'' 1973 on R.V. "Meteor" oxygen concentrations in surface layers were measured in order to determine the oxygen gradients within the first two meters and to add some informations to the mechanisms of oxygen exchange at the air-sea interface. These investigations may be interesting also with regard to longterm- observations of the oxygen distribution in the Atlantic, especially the problem of the A.O.U. (apparent oxygen utilization) determination. To measure oxygen gradients a special sampler was built which is able to take water samples each 20 cm of the first 2 meters. These data were supplemented by further samples down to 150 m, taken by conventional water samplers, from which samples were also taken to measure N2/O2-relations. By comparing these relations with theoretical relations in air-saturated water the influence of biological production and consumption on the oxygen contents in water could be estimated. A simple glass apparatus was built to extract gas from the water samples, and hereafter the N2/O2-relations were determined by mass spectrometry. Most distributions of the oxygen anomaly show a negative oxygen balance which varies largely, probably due to strong mixing processes in the Iceland-Faroe ridge area. The distribution of surface oxygen saturation values are of two different types. The values of the stations 260, 262 and 270 stem from mixed water and show homogeneous supersaturations, as can be found instantly when whitecaps appear. The values of 9 other stations are from water, sampled during calm periods which has been mixed and supersaturated before. They show a decreasing oxygen saturation towards the sea surface and often undersaturation in the upper decimeters up to 98 % and even 91 %. So at the air-sea interface even less initial oxygen saturation than 100 % can be found after supersaturation during heavy weather periods.

Berry production, shoot growth and biomass of E. hermaphroditum, V. vitis-idaea and V. myrtillis at Abisco ANS

Extreme weather events can have strong negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme, short-lived, winter warming events in the Arctic rapidly melt snow and expose ecosystems to unseasonably warm air (for instance, 2-10 °C for 2-14 days) but upon return to normal winter climate exposes the ecosystem to much colder temperatures due to the loss of insulating snow. Single events have been shown to reduce plant reproduction and increase shoot mortality, but impacts of multiple events are little understood as are the broader impacts on community structure, growth, carbon balance, and nutrient cycling. To address these issues, we simulated week-long extreme winter warming events - using infrared heating lamps and soil warming cables - for 3 consecutive years in a sub-Arctic heathland dominated by the dwarf shrubs Empetrum hermaphroditum, Vaccinium vitis-idaea (both evergreen) and Vaccinium myrtillus (deciduous). During the growing seasons after the second and third winter event, spring bud burst was delayed by up to a week for E. hermaphroditum and V. myrtillus, and berry production reduced by 11-75% and 52-95% for E. hermaphroditum and V. myrtillus, respectively. Greater shoot mortality occurred in E. hermaphroditum (up to 52%), V. vitis-idaea (51%), and V. myrtillus (80%). Root growth was reduced by more than 25% but soil nutrient availability remained unaffected. Gross primary productivity was reduced by more than 50% in the summer following the third simulation. Overall, the extent of damage was considerable, and critically plant responses were opposite in direction to the increased growth seen in long-term summer warming simulations and the 'greening' seen for some arctic regions. Given the Arctic is warming more in winter than summer, and extreme events are predicted to become more frequent, this generates large uncertainty in our current understanding of arctic ecosystem responses to climate change.

Bacterial production in the eastern Mediteranean Sea in August and September 2008 during SES_GR2

The SES_GR2_MICROBIAL PARAMETERS dataset is based on samples collected in the framework of the project SESAME, in the Ionian, Libyan and Aegean Sea during August-September 2008. The objectives were to measure the standing stocks and calculate the production of the microbial compartment of the food web, describe the vertical distribution pattern and characterize its structure and function through the water column. Bacterial production was estimated by the 3H-leucine method (Kirchman et al. 1986, Kirchman 1993). At each depth, duplicate samples and a control were incubated with 20 nM L-[4,5 3H]-leucine. Samples were incubated in the dark, at in situ temperature.

Nutrient concentrations and primary production in the Bering Sea in June 1992

Calculations of new production (NP) are made based on hydrochemical characteristics, recycling production (RP) is assessed on the basis of recycling of phosphorus and nitrogen. Photosynthesis, coupling with uptake of nutrients and development of minimum of silicate and maximum of oxygen, at the lower chlorophyll maximum in the pycnocline is discussed. In situ determination of production by C-14 and oxygen and vertical scanning of chlorophyll A have permitted to calculate assimilation numbers for all the biohydrochemical areas and to map primary production (PP) distribution in the Bering Sea. The total PP in the Bering Sea has been assessed as 6.4x10**8 t C/yr.

Bacterial production in the Aegean Sea in April 2008 during SES_GR1

The HCMR_SES_LAGRANGIAN_GR1_ MICROBIAL PARAMETERS dataset is based on samples collected in the framework of the project SESAME, in the North Aegean Sea during April 2008. The objectives were to measure the standing stocks and calculate the production of the microbial compartment of the food web, describe the vertical distribution pattern and characterize its structure and function through the water column as influenced by the BSW. Bacterial production was estimated by the 3H-leucine method (Kirchman et al. 1986, Kirchman 1993). At each depth, duplicate samples and a control were incubated with 20 nM L-[4,5 3H]-leucine. Samples were incubated in the dark, at in situ temperature.