Articles

Keywords: Alexandrium; antibody; oligonucleotide; physiology; probe; rRNA

The toxic dinoflagellate Alexandrium fundyense Balech was grown under temperature- and nutrient-limited conditions, and changes in labeling intensity on intact cells were determined for two probe types: an oligonucleotide probe targeting rRNA and a monoclonal antibody (MAb) targeting a cell surface protein. In nutrient-replete batch culture, labeling with the rRNA probe was up to 400% brighter during exponential phase than during stationary phase, whereas MAb labeling did not change significantly with growth stage at the optimal growth temperature. In cultures grown at suboptimal, low temperatures, there was a significant difference between labeling intensity in stationary versus exponential phase for both probe types, with exponential cells labeling brighter with the rRNA probe and slightly weaker with the MAb. The decrease in rRNA probe labeling with increasing culture age was likely due to lower abundance of the target nucleic acid, as extracted RNA varied in a similar manner. With the MAb and the rRNA probes, slower growing cultures at low, nonoptimal temperature labeled 35% and 50% brighter than cells growing faster at warmer temperatures. Some differences in labeling intensity per cell disappeared when the data were normalized to surface area or volume, which indicated that the number of target antigens or rRNA molecules was relatively constant per unit area or volume, respectively. Slow growth accompanying phosphorus and nitrogen limitation resulted in up to a 400% decrease in labeling intensity with the rRNA probe compared to nutrient-replete levels, whereas the MAb labeling intensity increased by a maximum of 60%. With both probes, labeling was more intense under phosphorus limitation than under nitrogen limitation, and for all conditions tested, labeling intensity was from 600% to 3600% brighter with the MAb than with the rRNA probe. Thus, it is clear that significant levels of variability in labeling intensity can be expected with both probe types because of the influence of environmental conditions and growth stage on cellular biochemistry, cell size,rRNA levels, and the number or accessibility of cell surface proteins. Of the two probes tested, the rRNA probe was the most variable, suggesting that in automated, whole-cell assays, it can be used only in a semiquantitative manner. For manual counts, the human eye will likely accommodate the labeling differences. The MAb probe was less variable, and thus should be amenable to both manual and automated counts.

Using microscopic and biochemical approaches, the relative contribution of the main groups of pelagic microorganisms (bacteria, heterotrophic nanoflagellates, phytoplankton and ciliates) and detritus (<150m) to total particulate protein and DNA was investigated at two stations of the Catalano-Balearic Sea (NW Mediterranean) during the stratified period. The two stations, one located in the shelf break front (S) and the other in the open sea, above the central divergence zone (D), were sampled twice in early summer 1993. Both of them showed a well-developed deep chlorophyll maximum (DCM). Maximum DNA concentrations were observed close to the DCM, while protein concentrations were fairly homogeneous from the surface to 60 m depth in all samplings. In general, the microorganism distribution showed maximum concentrations at or near the DCM depths. At both stations, bacteria were the most important contributors to living particulate DNA (22.5-32.6%), while phytoplankton and heterotrophic nanoflagellates were the main contributors to living particulate protein (3.8-24.4 and 2.9-29.1%, respectively). In addition, an important amount of detrital DNA and protein was estimated to occur at both stations. Detrital DNA accounted for 23.9-42.9% of the particulate DNA, while detrital protein represented from 63.5 to 84.7% of the particulate protein. Because both protein and DNA contain nitrogen and DNA is also a phosphorus source, these results indicate that heterotrophic organisms and detrital particles play an important role in the nitrogen and phosphorus cycles in the open sea waters of the NW Mediterranean.

Straits in the Mediterranean Sea form an important network from which one can determine the characteristics of the water exchange between all the constituent sub-basins. This includes the definition of water masses and water transport and their time variability. From 1994, all the major straits in the Mediterranean Sea (Gibraltar, Sicily, Otranto, Balearic Sea Straits, Cretan Arc Straits and Corsica) were subject to long term observations as part of various research projects. Besides adding new elements to the knowledge of internal strait conditions, the data sets collected allow us to propose a fairly consistent representation of the Mediter- ranean circulation and budgets in key points within the basin. The amplitude of the annual water transport measured at these straits was about 1 Sv and it appears to be modulated by a significant low-frequency and seasonal variability. For the first time, a seasonal component was identified at Gibraltar, thus raising new questions on the actual state of the Mediterranean. Also, the very likely existence of a significant interannual component was documented. In the Corsica Channel, this component was found to be related to the interannual variability of the North Atlantic Oscillation. The observations in the Cretan Arc Straits have provided a more comprehensive representation of the recent changes in the Eastern Mediterranean thermohaline cell. It is noteworthy that the effects of these changes have been observed both in the Otranto and Sicily Straits, and are now affecting the adjacent sea regions. The presence of a stream of Modified Atlantic Water in the Balearic Sea Channels indicates that part of the Atlantic inflow may be diverted directly into the northern region of the Western Mediterranean. Finally, data gathered in the Sardinia Channel indicate that the central Mediterranean region plays a critical role in controlling exchanges between the Eastern and the Western Mediterranean, while it is emphasized that the Tyrrhenian Sea area plays a role in strongly modifying some of the water masses that contribute to the large scale basin circulation. Their mixing creates new water types which modify the currently known pattern and composition of the Mediter- ranean circulation.

Keywords: current; channel of Sardinia; PRIMO-1

The channel of Sardinia is one of the less-known areas of the Western Mediterranean sea. The paths of the Levantine Intermediate Water ŽLIW., the Tyrrhenian Dense Water ŽTDW. and the Western Mediterranean Deep Water ŽWMDW. mainly, in this wide passage, are still debated. Two major aims of the PRIMO-1 ŽProgramme de Recherche International en Mediterrane ́e Occidentale. experiment were to specify the mean circulation paths of these intermediate and deep waters there and to verify hypotheses about the migration of mesoscale eddies from Algeria to Sardinia and their effect on the circulation paths of all the water masses. Despite an important loss of moored instruments, current time series have been collected from November 1993 to October 1994 at four different locations and two CTD cross-sections have been performed. Current meters on the Sardinian slope indicate, during 1 year, an almost permanent alongslope flow toward the northwest in the intermediate and deep layers. Currents recorded on the African slope are always directed alongslope eastward down to 2500 m. Coherently, in the mid-western part of the channel, the bottom flow is northward along the isobaths, while the 200-m flow is southward due to the influence of anticyclonic eddies. At the bottom in the central part of the channel, the current is low and changing: episodes of northeast current along the orientation of the deepest channel axis alternate with westward flows. No seasonal variations have been clearly detected, but the mesoscale variability is large and has a deep signature in the western part of the channel.

The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen. The ranges of DOC and DON concentrations were 4495 μM-C and 2.86.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.50.4, and the mean POC : PON ratio was 8.60.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break. It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material

Mesoscale distribution of chaetognaths in the South Scotia Sea was studied in January 1994. Three transects (ice margin to Elephant Island, ice margin to the Weddell-Scotia Confluence, and the Drake Passage) and a station grid in the East Bransfield Strait were laid out, seeking the greatest possible heterogeneity in hydrographic conditions. Six species were collected, with the most abundant species, Eukrohnia hamata, accounting for 83% of the total number of individuals, followed by Sagitta gazellae (9.7%). High spatial variability was observed both along the transects and over the mesoscale station grid. The station grid allowed two assemblages to be distinguished on the basis of species abundance and demographic population structure. Both assemblages were distributed through areas with distinct hydrographic characteristics. Use of a smaller sampling scale and a more detailed definition of development stages than in earlier studies revealed a higher level of spatial heterogeneity than previously suggested for chaetognaths in the Southern Ocean.

SMOS, a European satellite mission, will provide for the first time global coverage of Sea Salinity for climàtic and general circulation studies from year 2005. The measurement will be done by low frequency microwave radiometry, and the data are expected to have a resolution similar to the standard climatilogies presently used for other ocean variables

A recurrent, prolonged and singular bloom of Alexandrium taylori Balech in an open beach (La Fosca, Spain, NW Mediterranean) is described. Alexandrium taylori appears at several places along a wide area of the NW Mediterranean (Costa Brava) during the summer, reaching concentrations up to 105 cells l–1, but it only proliferates persistently, massively (densities >106 cells l–1) and recurrently during August in La Fosca beach. The A.taylori bloom can be considered a manifestation of large-scale proliferation in a restricted area, where coupling between resting cysts in the sediment and bloom outbreak is not a major factor compared to the interaction of local environmental conditions with the planktonic organism\'s life history. From observations of environmental conditions (the environmental window) and the multiscale spatio-temporal distributions and life history of A.taylori, we describe the bloom dynamics and answer some critical questions about the different phases of the bloom. Some of these answers are: (i) the source of the A.taylori population is widespread offshore and is not located directly at the beach; (ii) high cell densities are reached and maintained with a moderate in situ growth and low loss rates; (iii) temporary cysts act as a reserve of the population.

The circulation and upwelling processes that control the phytoplankton distribution in the Alboran sea (western Mediterranean) are examined from a climatological perspective for the first time. To characterize the annual cycle of the near-surface phytoplankton patterns, we analyze the monthly distributions of pigments from the Coastal Zone Color Scanner (CZCS). Two regimes occur: a fall-to-winter bloom occurs. The newest ocean color data set available today from the Sea-viewing Wide Field-of-view Sensor (SeaWiFs) and the Ocean Color and Temperature Scanner (OCTS) fall within this annual progression. The combined interaction of seasonal stratification, coastal and gyre-induced upwelling, and horizontal advection control the near-surface pigment distribution in Alboran, while light availability does not determine the seasonal cycle of pigments.

The objective of this work is to evaluate the patterns of the ocean-atmosphere coupling in the Mediterranean sea using the statistical analysis of the time series of the three satellite measured variables: wind stress curl computed from the surface wind velocities measured by the European Remote Sensing Satellite-ERS1, sea level anomalies from the emerged ERS1-TOPEX/POSEIDON altimetric data and the sea surface temperature from the NOAA/NASA Pathfinder AVRR Oceans Project. This study examines the ocean-atmosphere coupling patterns in time and space through a canonical correlation analysis of the fields. The wide and exhaustive coverage of the oceanic and atmospheric fields from satellites (such as TOPEX/POSEIDON and ERS1) allow a potential detailed inspection of the coupling. In this study we assess the role of the wind stress and/or sea surface temperature space/time variations as forcing mechanisms of the sea level variability for the total 440 day duration (from October 1992 to December 1993) of the three satellite data sets in the different Mediterranean sub-basins. The linear barotropic vorticity equation is computed in order to estimate id the Mediterranean Sea level response to wind forcing is barotropic. Results indicate that except for the Strait of Sicily and the Adriatic Sea the barotropic response is not dominant. From the canonical correlation analysis, a correlation of 0.57 for the first mode between the sea level anomaly and the wind stress curl indicates a significant local coupling between them, especially in areas of the Eastern Mediterranean. Two uncoupled annual cycles are found in the sea surface temperature data.

This paper addresses the problem of motion estimation in sequences of remotely sensed images of the sea. When the temporal sampling period is low the estimation of the velocity field can be done by finding the correspondence between structures detected in the images. The scale space aproximation of these structures using the wavelet multiressolution is presented. The correspondence is solved using a simulated annealing technique which assures the convergence to high quality solutions.

Keywords: CO2 production rates · O2 consumption rates · Isocitrate dehydrogenase · Respiratory electron transfer system · ETS · Marine bacterium

Physiological rates of CO2 production and O2 consumption, and the activities of isocitrate dehydrogenase (IDH) and the electron transfer system (ETS) were studied in the marine bacterium Pseudomonas nautica growing on acetate. In exponential growth, IDH and ETS activities were well coupled with CO2 production and O2 consumption rates, but in senescence they were uncoupled. Our results clearly show that under starvation conditions, IDH and ETS activities remained high even though their corresponding respiration rates dropped. The respiratory metabolism in the different physiological states of the acetate-grown cultures was compared with previous observations made in pyruvate-grown cultures. Time profiles of CO2 production and O2 consumption rates showed completely different respiratory fingerprints associated with the different carbon sources. Acetate-grown cultures showed an increase of respiratory quotients (RQ) in the senescence phase whereas in pyruvate-grown cultures it stayed close to 1.0. On both carbon sources, respiration to respiratory capacity ratios were constant in exponential phase and decreased to almost zero after carbon source exhaustion. Our results clearly show the impact of physiological state and carbon sources on bacterial respiration rates.

The Mediterranean Sea has been investigated intensively since the early nineties, using modern techniques and collaborative approaches. This overview summarizes some of the resulting advances that were made concerning the physical oceanography of the western Medit- erranean. The water mass formation processes are now much better understood and have been quantified to a large extent. The boundary conditions of the system in terms of surface fluxes and strait transports can be determined with improved accuracy, thus enabling future investi- gation of interannual variability. The dynamics of the surface and intermediate layers have revealed a variety of eddy and mesoscale processes that are important for the circulation and spreading of water masses. The deep circulation is being investigated with Lagrangian tech- niques (tracers and floats). First results show a large component of the deep water originating from the Tyrrhenian Sea and intense cyclonic and anticyclonic eddy flows.