Dyfamed-benthos time series observations

In 1990, a benthic component to the DYFAMED (dynamics of fluxes in the Mediterranean) program, the DYFAMED-BENTHOS survey, was established to investigate the possible coupling of benthic to pelagic processes at a permanent station in >2700 m water depth, 52 km off Nice, France. Surface sediment was first sampled at different periods of the year to assess the importance of the biological compartment (particularly metazoan meiofauna) and its relation to seasonally varying particulate matter input to the sea floor (estimated by measuring surface sediment particle size and porosity, as well as chloroplastic pigments, organic carbon, nitrogen and calcium carbonate contents). Beginning in 1993, surface sediment was sampled at an average interval of 1.4 months for over five consecutive years using multicorers. Biogeochemical techniques such as deployments of a free-vehicle benthic respirometer and a near-bottom sediment trap, along with analyses of sediment vertical profiles for dissolved oxygen, nutrients and dissolved metals in the porewater, were developed in conjunction with more extensive biological analyses to characterize the recycling of organic matter, and ultimately increase our understanding of the oceanic carbon cycle. This article provides the scientific background and motivation for the development of the on-going DYFAMED-BENTHOS survey, the general characteristics of the benthic site, as well as a detailed description of the sampling design applied from late 1990-2000.

The distribution of macrobenthos in surface sediments at Fladen Ground stations, North Sea

A general study of structure, biomass estimates and dynamics on the macrofauna was carried out in August 1975 and March 1976 during PREFLEX (1975) and FLEX (1976), the Fladen Ground Experiment. On the basis of these data an attempt was made to estimate macrobenthic production expressed as minimum production (MP). The macrobenthic production is discussed together with meiobenthic annual production and with indirectly estimated microbenthic production in relation to an energy input from the water column of about 25 g C m**-2 year**-1. From the production estimates of the three benthic components a rough energy budget is proposed. Sampling was performed at five stations for endofauna twice during the time of investigation and for epifauna once. At each station two replicate box core samples (30 X 20 cm) were taken for endofauna. Epifauna was sampled with an Agassiz trawl once at each station. The total numbers of endofauna increased from station 1 to 5. This was valid as well for August 1975 (4,233-12,166 individuals per m**2 and 10 cm sediment depth) as for March 1976 (1,008-2,925 individuals). The polychaetes were the dominant organisms with a share of 33 to 62 %. The densities for the endofauna decreased from August 1975 to March 1976 by a mean factor of 2.8. Abundances of epifauna amounted to values between 11 and 102 individuals per 1000 m**2. The biomass dry weights (DWT) for macrobenthic endofauna varied between 0.97 g DWT m**-2 and 6.42 g DWT m**-2 in August 1975 and between 0.27 g DWT m**-2 and 2.64 g DWT m**-2 in March 1976. The mean amounted to 1.74 g DWT m**-2. Dry weights of epifauna biomass gave values between 4.9 and 83.1 g DWT * 1000 m**-2. The minimum production for the total macro-endofauna at Fladen Ground amounted to 1.43 g DWT m**-2 yr**-1 or 0.82 g C m**-2 yr**-1. This resulted in a minimum turnover rate (P/B) of 0.8. The share produced by the polychaetes amounted to 1.06g DWT m**-2 yr**-1 or 74 %.

Distribution of deep-sea meiobenthos in surface sediments off North Carolina

Observations on the ecology and distribution of meiofauna occurring on the outer continental shelf and continental slope at depths from 50 to 2500 m in the region where the Blake Plateau cuts across the North Carolina slope are reported. Total numbers of meiofauna ranged from 151/100 cm**3 of sediment at 400 m to 1196/100 cm**3 of sediment at 250 m. Sediments of the upper region (50-500 m) consisted of medium-sized calcareous sands with relatively low organic carbon contents, while the deeper sediments (600-2500 m) consisted of sandy silts and silts with organic carbon contents 6-10 times that of the shallower sediments. Two basic faunas appear to be present in the areas investigated; a shallow-water fauna extending from 50 to 500 m and a deep-water fauna from 800 to 2500 m. The shallow-water fauna consists of nematodes (the dominant taxon) and relatively large numbers of harpactacoid copepods, ostracods, benthic foraminifera, polychaetes, gastrotrichs and several other groups, while below 500 m only nematodes and foraminifera are present in large numbers, the latter being especially abundant between 800 and 2000 m. A major change in the meiofauna occurs on the Blake Plateau between the depths of approximately 400-500 m and 600-750 m where the composition of the sediment changes from sand to silty sand. From 50 m to 400-500 m gastrotrichs, turbellaria, tardigrades, kinorhynchs, halicarids, hydrozoans, gnathostomulids, lamellibranchs and cumaceans are commonly encountered; these groups are absent below 500 m. In addition, there are significant reductions in the numbers of harpactacoids, ostracods, nemerteans and polychaetes below 500 m. Examination of the nematode population also show faunal differences between the shallower sediments (50-500 m) and the deeper sediments (600-2500 m). High indices of affinity exist among the faunas between 50 and 500 m and among the faunas between 800 and 2500 m; the fauna at 600-750 m represents a transition between these two regions, but it is more closely related to the deep-water fauna. Changes in the distribution of both the total meiofuna and also the nematodes are highly correlated with changes in sediments composition and bottom water temperatures. It is suggested that changes in grain size and accompanying changes in sources of nutrition, which are the results of Gulf Stream and other current activity, are the dominant environmental factors influencing the meiofauna of the area.

Antarctic sympagic meiofauna in winter

This study of Antarctic sympagic meiofauna in pack ice during late winter compares communities between the perennially ice-covered western Weddell Sea and the seasonally ice-covered southern Indian Ocean. Sympagic meiofauna (proto- and metazoans > 20 µm) and eggs > 20 µm were studied in terms of diversity, abundance and carbon biomass, and with respect to vertical distribution. Metazoan meiofauna had significantly higher abundance and biomass in the western Weddell Sea (medians: 31.1 * 10**3/m**2 and 6.53 mg/m**2, respectively) than in the southern Indian Ocean (medians: 1.0 * 10**3 /m**2 and 0.06 mg/m**2, respectively). Metazoan diversity was also significantly higher in the western Weddell Sea. Furthermore, the two regions differed significantly in terms of meiofauna community composition, as revealed through multivariate analyses. The overall diversity of sympagic meiofauna was high, and integrated abundance and biomass of total meiofauna were also high in both regions (0.6 - 178.6 * 10**3/m**2 and 0.02 - 89.70 mg/m**2, respectively), mostly exceeding values reported earlier from the western Weddell Sea in winter. We attribute the differences in meiofauna communities between the two regions to the older first-year ice and multi-year ice that is present in the western Weddell Sea, but not in the southern Indian Ocean. Our study indicates the significance of perennially ice-covered regions for the establishment of diverse and abundant meiofauna communities. Furthermore, it highlights the potential importance of sympagic meiofauna for the organic matter pool and trophic interactions in sea ice.

Coastal plankton communities under elevated CO2: community barcoding results, link to data files in FASTA format

The acidification of the oceans could potentially alter marine plankton communities with consequences for ecosystem functioning. While several studies have investigated effects of ocean acidifications on communities using traditional methods, few have used genetic analyses. Here, we use community barcoding to assess the impact of ocean acidification on the composition of a coastal plankton community in a large scale, in situ, long-term mesocosm experiment. High-throughput sequencing resulted in the identification of a wide range of planktonic taxa (Alveolata, Cryptophyta, Haptophyceae, Fungi, Metazoa, Hydrozoa, Rhizaria, Straminipila, Chlorophyta). Analyses based on predicted operational taxonomical units as well as taxonomical compositions revealed no differences between communities in high CO2 mesocosms (~760 µatm) and those exposed to present day CO2 conditions. Observed shifts in the planktonic community composition were mainly related to seasonal changes in temperature and nutrients.

Distribution of meiobenthos in sediment samples of the northeastern Atlantic

The meiofauna of the deep sea areas (800 - 5500 m) between Madeira and Lisbon was quantitatively investigated during "Meteor" cruises in 1970 and 1971. With respect to numbers and biomass the meiofauna (especially nematodes and harpacticoid copepods) of the investigated areas is relatively poor averaging about 66,000 individuals per m**2 and 34 mg per m**2 wet weight biomass (polychaetes and foraminifera excluded). Regional differences are more pronounced in the investigated areas than differences due to depth. A comparison with the results of other authors from other areas confirms the regional variations in the meiofauna abundance of the deep sea.