Structure et variabilité de I'ichtyofaune d'une zone rocheuse protégée en Méditerranée (Pare national de Port-Cros, France)

Abstract. A Mediterranean fish assemblage has been visually censused over a period of two years from two permanent, rocky, infralittoral stations (10–15 m) which display a high habitat complexity and are located in a protected area. Six home-range categories were defined for a better understanding of the community structure which was analyzed through qualitative and quantitative data. The respective roles of different sources of variability in species composition and numerical abundance were evaluated.     

Contribution a l'etude chimique du materiel dissous et particulaire de l'estuaire de la riviere rimouski

Temperature, pH, total alkalinity, dissolved oxygen, silicate, nitrate, phosphate and the Mn, Fe and Al contents of suspended particulate matter (SPM) were measured in the Rimouski River estuary as functions of chlorinity during the period May—September 1980.At any given time, total alkalinity (TA) is conservative within the estuary with respect to chlorinity. However, the total alkalinity (TA) of the freshwater is related to river flow. This is attributed to dilution of the river water with bicarbonate-poor rainwater.Generally, pH follows the same pattern observed for TA in freshwater. Dissolved oxygen is usually more concentrated in freshwater and decreases linearly with increasing chlorinity. Freshwater is always saturated or supersaturated with respect to O₂. Seasonal fluctuations are attributed to temperature variations.There is no evidence for removal of soluble silicate from the freshwater entering the sea. The concentration of silicate in the freshwater is strongly influenced by rainfall. Soil leaching, conditioned by high rainfall increases the concentration of soluble silicate in freshwater. Nitrate behaves similarly whereas phosphate is complicated by the presence of sewage.Analysis of the Mn, Fe and Al contained in the SPM indicates dilution of river-borne particles rich in Mn by others less rich in this element. A decrease in Mn content with increasing chlorinity and SPM concentration as well as increasing concentrations of SPM with increasing chlorinity indicate that the composition is controlled primarily by physical mixing of material from two sources rather than by chemical processes. Within the analytical precision the Fe/Al ratio does not vary with the chlorinity.     

Incidence de la cinetique de decroissance de la temperature apres le choc thermique sur les modifications d'activite des esterases et les possibilites de survie de Scolelepis (malacoceros) fuliginosa (annelide polychete)

Scolelepis fuliginosa reared in the laboratory at 13°C were put through 10-min thermal shocks at 16°C and 18°C and were then submitted to either a slow or a rapid temperature reduction. After the thermal shock, a posterior fragment of each specimen was cut off at intervals, until six days. Samples were submitted to electrophoresis on polyacrylamide gel, esterase activity being determined with α-naphthyl acetate.Enzymograms show that thermal shocks act on esterases in decreasing the activity of the main fractions. Immediate effects result in a very precocious enzymic response; more long-term effects depend on the maximum temperature, the animal's sex and the kinetics of the post-shock thermal reduction.Females are more sensitive than males. For a given Δt, esterase changes are greater and more long-lasting. After a 16°C Δt, a rapid decrease in temperature prevents the loss of activity of the middle and fast fractions in males and delays, by about 10 h, the alteration of female esterases. After 18°C ΔT, loss of activity of the middle and fast fractions occurs in less than 1 h, independently of the thermal kinetics, but survival is only possible—solely for males—with a rapid decrease in temperature which also delays females' deaths by between 24 and 48 h.In conclusion, a rapid decrease in temperature gives organisms a better resistance to thermal shock, as determined by esterase activity and controls the lethality of a high Δt.     

Evolution à Long terme (1978–1986) des populations d'Amphipodes des sables fins de la pierre noire (baie de morlaix, manche occidentale) aprs̀s la catastrophe de l'Amoco Cadiz

Greatly reduced in 1978 by the Amoco Cadiz oil spill, the amiphipod populations of the fine sand community of Pierre Noire in the Bay of Morlaix have not yet fully recovered 8 years after the pollution. The sublittoral sandi-mud benthic communities in the western part of the English Channel show a discontinuous distribution, occurring in isolated zones which are localized in estuaries and bays. The amphipods, which are characteristic of these communities and lack a pelagic larva, form insular populations. This insular distribution delays their re-introduction to the fine sand community of Pierre Noire. Moreover, the biological and demographic characteristics of the species entail limited periods of recolonisation and increase in population.     

Quaternary evolution of the Ría de Vigo, Spain

The seismic analysis of the sedimentary infill of the Ría de Vigo reveals that the infill comprises of a fifth order sequence (18 ky) bounded by a major discontinuity surface. Within the Holocene sequence, several seismic units have been identified; the oldest one originated after the Würm glaciation and the origin of its top discontinuity was eroded during the regression (sea level at − 120 m) of this last glacial episode (isotopic stages 2 to 4), 18 ky B.P.

In some places below this ría infill, another sequence can be identified. This older sequence is associated with the pre-existing faults and troughs in the deepest parts of the ría, and it was deposited during the Würm glaciation (Miocene–Pleistocene). Eroded sediments were moved from the rías area to deeper zones, where they accumulated in the lowstand system tract. The next sea level rise occured in two steps, producing two transgressive units separated by an hiatus surface. This cycle was interrupted by the next sea level fall (to − 55 m) marked on the seismic records by another recognizable boundary. The next sea level rise took place in several steps (back-stepping) with some stillstands, generating another transgressive system tract in the ría. From that time on, the relative sea level continued rising, depositing the most recent unit which represents the highstand system tract. Separating the highstand system tract and the transgresive unit below there is a consensed section.

The analysis of 29 cores provides groundtruthing for our hypothesis. The identified main lithologic units show a transgressive sequence: a granitic rock base, an overlying second unit-locally wedge shaped- and most recently, a marine muddy unit covering the present ría seafloor.     

Concentration du chrome dans deux profils de l'ocean pacifique

Determination of total chromium on two profiles and chromium III on four samples of equatorial Pacific Ocean water have been carried out using coprecipitation of chromium from sea water with hydrous iron oxides, followed by ion-exchange separation and isotope dilution mass spectrometry. Results for two Pacific profiles show increasing total chromium concentration from surface to 250 m. The Cr concentration appears to be different below 1,000 m, with nearly homogeneous concentrations for the first profile and regularly increasing Cr concentrations from 0.330 to 0.550 μg/l at 3,900 m for the second one. Results for Cr(III) show that trivalent species are dominant in these samples.     

Distribution des terres rares dans les fractions de sediments et nodules de Fe et Mn associes en l'ocean Indien

The REE distribution in size fractions of sediments and associated ferromanganese nodules from the Indian Ocean was studied. Bulk-sample patterns of sediments result from the combination of coarsest fractions depleted in Ce and fine fractions enriched in Ce. Ce depletion of the coarsest fractions is related to biogenic silica; on the contrary, REE distribution patterns of fine fractions are closely similar to those of associated ferromanganese nodules. The Ce excess in fine fractions is probably of continental origin, but it could also be derived from submarine weathering of volcanic glass or related to Ce oxydation in the marine environment. In fine fractions Ce is probably in its tetravalent state, hence it can easily be scavenged by fine clays and oxyhydroxydes. Trivalent REE can be incorporated in nodules, partly by occlusion of fine clays or oxyhydroxydes and partly by surface to surface transfer as was proposed by Ehrlich (1968). Comparison between REE patterns of fine-sized fractions, nodules and seawater also supported adsorption as a possible mechanism governing the incorporation of REE of sediments and nodules from seawater. Light REE are probably incorporated as oxyhydroxyde complexes, whereas heavy REE are markedly fractionated with increasing atomic number. This fractionation reflects the complexed form of the heavy REE in seawater.     

La Réponse aux Couleurs chez Dicentrarchus labrax (Moronidae), Placé en Situation de «Self-feeding>>, et de Choix Multiple: Response to Colours in Dicentrarchus labrax (Moronidae), in a Self-Feeding and Multiple Choice Condition

Abstract. A population of sea-bass, housed under semi-natural and self-feeding conditions, was presented with six different coloured levers. Their choices tended to favour more colour-contrasted levers and were greatly affected by environmental conditions such as stress factors, circadian period, season, and thermal fluctuations. A correlation was observed between increases in instrumental acitivity, indicating an increase in energetic requirements, and a widening of choices in the exploitation of the coloured levers.
Consequences of these behaviours were considered in relation to predator pressure that the fish imposes on potential prey populations in the natural environment, and in relation to the initiation of feeding activity when the fish are maintained in captivity and under self-feeding conditions.     

Resultats de dragages et essai de stratigraphie des bancs de Galice,et des montagnes de Porto et de Vigo (marge occidentale Iberique)

Dredged samples have been studied to establish the stratigraphy as well as the probable paleogeographic evolution of the sedimentary cover of Galicia Bank, and Vigo and Porto Seamounts. The sedimentation appears to have been neritic up to the Late Jurassic. These structural features evolved separately from the Iberic continental margin in Late Jurassic to Early Cretaceous times. Part of the sediments is made of calpionellid limestones, which is indicative of open marine conditions in this area of the Atlantic at that time. This also suggests the establishment of marine connections between this area and the “Mésogée”. These open marine conditions would have persisted since the Early Cretaceous.     

Direction de croissance des eperons sur le front d''un recif barriere — L''exemple du Grand Recif de Tulear (Madagascar)

A study has been made of the orientation of the spurs of the outer front of a barrier coral-reef tract in the Bay of Tuléar on the southwest coast of Madagascar. All types of coral reef tracts are present: outer or barrier reefs, lagoon reefs and coral banks. The orientation of the spurs was studied as a function of the direction of the swell crests which are either parallel or oblique to the alignment of the reef front of the “Grand Récif” which extends over 18 km. When the swell is oblique, the spurs are not, as is generally held, perpendicular to the crests of the swell. The orientation of the spurs is a resultant direction between the direction of the swell orthogonals and the direction of the slope of the outer reef flat. From aerial photographs one can determine the directions of the spurs and of the slope of the outer reef flat. It is easy to obtain the direction of the crests of the swell and then to construct the wave diagram. The morphological aspects and the distribution of the deposits on the inner flat of the coral reef tract depend on the orientation of the swell.

Résumé

L'étude de l'orientation des éperons d'un front récifal externe a été réalisée dans la baie de Tuléar sur la côte sud-ouest de Madagascar. Dans ce secteur, tous les types d'édifices récifaux sont présents: récifs barrières externes, récifs de lagon et bancs coralliens. Nous avons étudié l'orientation des éperons en fonction de la direction de la houle qui est soit parallèle, soit oblique par rapport au front récifal du Grand Récif qui s'étend sur 18 km. Quand la houle est oblique, les éperons ne sont pas — comme on le dit généralement — perpendiculaires à la houle, mais leur orientation est une direction résultante entre la direction de propagation de la houle et celle de la pente du platier récifal au point considéré. Sur les photographies aériennes, on détermine la direction des éperons et celle de la pente. Une construction simple permet d'obtenir la direction de la crête des vagues et de construire le plan de vagues. Toute la morphologie et la répartition des dépôts du platier d'un édifice récifal sont sous la dépendance de l'orientation de la houle.     

Spatial patterns of ichthyoplankton assemblages in the Río de la Plata Estuary (Argentina–Uruguay)

Two oceanographic surveys were conducted across the salinity gradient of the Río de la Plata Estuary during austral late spring and summer. Ichthyoplankton was dominated by families Sciaenidae, Clupeidae, Engraulidae, Cynoglossidae and Carangidae. The distribution of larval fish assemblages was strongly associated to the salinity structure. Oceanographic conditions were characterized by a large salt wedge (180 km long and a vertical salinity gradient up to 10 units per meter). During both sampling periods each ichthyoplankton assemblage was related to the same region of the salt wedge: the fresh water environment, the bottom salinity front, the mixohaline zone and the outer portion (surface salinity front) of the estuary. Larval assemblages were not related to the thermal structure. Reproductive activity of fishes inside the Río de la Plata Estuary is relatively common (60% of the teleosts sampled use this estuary as a nursery ground). Moreover, the high incidence of pelagic eggs spawners (75% of the species present in the ichthyoplankton) in the Río de la Plata contrasts to the vast majority of estuaries, where this reproductive strategy is poorly represented. Estuarine dynamics plays a dominant role in allowing this reproductive style in this estuary. Spring–summer wind pattern should generate a retentive environment which could minimize advective losses of eggs and larvae to the adjacent ocean.     

Alteration de la fonction de reproduction chez Idotea balthica basteri (Crustacea,Isopoda) soumis a l'effet chronique d'un détergent non ionique

Reproduction is greatly affected when the crustacean isopod Idotea balthica basteri is exposed to detergents, maturation being considerably delayed. Adults suffer a significant decrease in fecundity, either through females failing to produce eggs or miscarrying, and so producing fewer juveniles. This decrease of fecundity is accompanied by hormonal changes. Many juveniles from animals exposed to detergents are malformed.     

Importations et remaniements de thanatofaunes dans les sables de la plate-forme profonde des approches occidentales de la Manche

Macro- and micro-faunas are reported from six gravity cores collected at a mean depth of 150 m in the surficial deposits of the Kaiser sand bank in the Southern Western Channel Approaches. These are bivalves (mainly), gastropods, echinids, crustaceans and foraminifers. These fauna present a very rich association of numerous, well preserved species from various ecological settings. Such an association is commonly reported from the continental shelf of the last transgressive cycle. In addition, the sediment comprises two imported faunal associations. The first one corresponds to thanatocaenoses of Pliocene/lowermost Pleistocene and Weichselian age, reworked respectively from the underlying celtic incised valley fills and the Celtic Sand Banks. The absence of Quaternary fauna prior to the Weichselian suggests that the introduction of Pliocene sources occurred during the last climatic cycle. The second stage of importation took place after the last transgression in the Western Channel, and corresponds to the enrichment of the sediment in coastal fauna derived from western Brittany by the the predominant ebb tidal current. The variations of taxonomic diversity from core to core suggest a sediment transport around the bank that matches the one deduced from the study of tidal bedforms. At the present day, the wave action is highlighted by accumulation of species of the same shape, size and density inside storm beds. However, the survival within these beds of very small, juvenile shells indicate that each storm reworking was short in duration.     

Structure de la marge continentale Norvégienne au débouché de la mer de Barentz

Reconstructions of the continents prior to the opening of the Norwegian sea indicate an overlap between the Greenland and the Norwegian continental margins just west of the Barentz sea and imply that the basement of this area is of oceanic origin. Seismic profiling shows an oceanic-type basement covered by thick Tertiary sediments. The sedimentary supply is related to the geological history of the Barentz sea where only little unconsolidated sediments are known. Further south the structures of the present margin are directly related to the early opening of the Norwegian sea.