Jean-Claude Romano

Organic matter composition and pollutant enrichment of sea surface microlayer inside and outside slicks

Abstract Surface microlayer samples were collected with a rotating device at eight stations in a coastal area, and examined, with their related bulk waters, for their organic matter composition. At each station, sampling operations were conducted inside and outside slicks. With the exception of pigments, all the examined groups of compounds, particularly hydrocarbons and anionic detergents, exhibit accumulation in surface microlayer; enrichment is higher in samples collected inside slicks than outside. A decrease of the surface tension measurements is linked to the accumulation of organic matter in the slicks. In surface microlayers, the major part of the identified organic fraction, consists of carbohydrates and proteinaceous compounds rather than lipids. As far as could be deduced from an estimation of lipid, sugar- and protein-carbon, half the recorded particulate organic carbon weight is of an unidentified complex form. The study of hydrolysis kinetics of the carbohydrate particulate fraction shows that the organic matter is in a less condensed form in surface microlayers than in bulk water samples. A close relationship appears between pollutant accumulation and the lowering of surface tension in slicks. This has a direct consequence: the dampening effect on waves which smooths the surface of the sea, making slicks observable features of pollutant accumulation.

Temperature Anomalies and Mortality Events in Marine Communities: Insights on Factors behind Differential Mortality Impacts in the NW Mediterranean

Two large-scale mass mortality events (MMEs) of unprecedented extent and severity affecting rocky benthic communities occurred during the summers of 1999 and 2003 along the coasts of the NW Mediterranean Sea. These mortality outbreaks were associated with positive thermal anomalies. In this study, we performed an analysis of inter-regional and inter-annual differences in temperature (T) conditions associated with MMEs of the red gorgonian Paramuricea clavata by analyzing high resolution T time series (hourly records for 3 to 8 years) from four regions of the NW Mediterranean with differing hydrological conditions and biological impacts. High resolution records allowed a detailed analysis using classical and new descriptors to characterize T anomalies. We were able to determine that the MMEs were triggered by two main types of positive thermal anomalies, with the first type being characterized by short periods (2 to 5 days) with high Mean T reaching more than 27°C in some regions and being associated with high intra-day and intra-period variability, while the second type of anomaly presented long duration (near one month) at warm T (24°C) with low intra-period variability. Inter-regional patterns arose; some regions displayed both types of anomalies, while others exhibited only one type. The results showed that T conditions should be considered as the main factor that explains the observed inter-regional and inter-annual differences in mortality impacts. In explaining these differences, the late timing of T anomalies, in addition to their magnitude was found to be determinant. Finally, by combining thermotolerance experimental data with the maximal T stress conditions observed in the four regions, we were able to determine the differential risk of mass mortality across regions. We conclude that expanding high resolution T series is important for the development of sound management and conservation plans to protect Mediterranean marine biodiversity in the face of climate change.

Sea-surface slick occurrence in the open sea (Mediterranean, Red Sea, Indian Ocean) in relation to wind speed

Abstract The frequency, occurrence and extent of sea-surface slicks were studied in open seas during a ship crossing from the eastern Mediterranean to La Reunion Island (Indian Ocean), via the Red Sea, by taking sea-surface photographs every 1 min 45 s and relating them to wind speed and direction records. During 10% of the recording time, slicks covered from 20% to 80% of the observed sea surface, and they covered the entire photographic field during 1% of the recording time. Slicks were observed only at wind speeds below 5 m/s, but in some cases, they were absent at lower wind speeds. Conversely, slicks were never observed at wind speeds higher than 6 m/s. Compared to that in coastal waters, the frequency of occurrence of slicks was lower (11% against 30%) at the surface of the open sea, mainly as a consequence of persistent bad weather (southwest monsoon period). Nevertheless, the records provide evidence that slicks are not rare in the open sea and that slick-forming meteorological conditions found in coastal areas are similar to those of open seas. These include the upper wind speed limit and the percentage of the sea surface covered by slicks in relation to wind speed. The daily rhythm of slick formation in coastal waters, due to diurnal changes in wind speed and direction, is absent in the open ocean.

Biogeochemical impact of a dilution plume (Rhone River) on coastal sediments: comparison between a surface water survey (1996–2000) and sediment composition

The Rhone River is the major source of nutrients and particulate matter to the Mediterranean basin. Its influence on coastal sediments was investigated by searching for the presence of continental markers. The composition of coastal sediments situated in the area influenced by the Rhone River inputs was compared with surface water salinity time-series records (five years bi-monthly survey). Sediment samples were analysed for grain-size, total and organic carbon and nitrogen, pigments, trace metals, carbohydrates, protein and lipid content. Comparisons show that changes in sediments are associated with the mean extension of the dilution plume of the river. The organic carbon content of sediments does not exhibit spatial changes related to the variations in the overlying water column. A large amount of inorganic carbon is discharged into the sea by the river and results in dilution of the organic carbon in the deposited material. The CaCO3 fraction of the total carbon of sediments is influenced by the river inputs with lower values in front of the river mouth. Changes in the composition of organic matter are linked with the inputs of the Rhone River and associated with variations of concentrations of the chlorophyll b as a marker of the terrestrial origin of the organic matter. Chlorophyll b content of sediments showed statistically significant negative correlation with the five-year bi-monthly mean surface salinity values (slope=−0.0233, R2=0.9437, n=22, p<0.001). Other parameters such as Mn content of sediments exhibit significant positive correlation with chlorophyll b and negative correlation with mean surface water salinity. Labile carbon fraction (carbohydrates, lipids and protein) shows significant correlation both with chlorophyll b and salinity. In the area influenced by the Rhone River dilution plume, there is enrichment in labile organic matter. The amounts of insoluble carbohydrates and phaeopigments suggest that this enrichment is mainly due to detritic organic matter of terrestrial origin. This twofold approach associating a long-term survey of the surface water with analysis of the sediments located beneath seems suitable for achieving a better knowledge of the environment at the sea–continent interface.

HPLC determination of chlorophylls and breakdown products in surface microlayers

Abstract Chlorophyll and its breakdown product contents were determined by both high pressure liquid chromatography (HPLC) and the fluorimetric method in surface microlayer and related bulk water samples collected in the western Mediterranean Sea. Differences in chlorophyll α measurements between the two methods are enhanced in highly loaded organic matter water samples such as surface microlayers. In several samples, pheophytins, which are commonly reported to be present in surface microlayers, were detected by the fluorimetric method, but not by HPLC. In most cases, the accumulation processes of pigments can be recorded in surface microlayers, but with small differences in pigment composition when compared with that of related bulk waters. Enrichment factors for chlorophyll are often higher than those of its degradation products. On the other hand, the low reported values of phytoneustonic productivity provide evidence for an inhibition of phytoplankton organisms transported to the sea-air interface; these organisms should be stressed but alive. These results also support the hypothesis that pigments could be actively photo-oxidized by the high level of solar radiation prevailing in surface microlayers.

Seasonal and interannual variations (1996–2000) of the coastal waters east of the Rhone river mouth as indicated by the SORCOM series

Between 1996 and 2000, 79 cruises have been achieved following always the same transect between Marseilles and the Rhone river’s mouth. While cruising, salinity, temperature and fluorescence of surface waters (1.5 m) were recorded every minute, in association with precise GPS position. The whole set of data (i.e. 128 measured points per cruise) constitutes the Sorcom series whose synthetic results are presented here. Despite the high spatial and temporal variability encountered between two successive cruises, the regularity and duration of the sampling strategy permitted to define coherent spatial zonation and temporal evolutions. In the Cape Couronne vicinity the dynamic of the eastern extension of the dilution plume clearly changes. Westward, waters are frequently under its influence, but more sporadically to the east, with a less pronounced gradient. In few cases, salinity lowering has been measured up to the gulf of Marseilles. In these two areas, which can be divided in two sub zones, seasonal evolutions are different. In the eastern area (Cape Couronne–Marseilles), the classical rhythm prevailing over marine waters is observed but with earlier phytoplanktonic bloom than usually reported. In the western part, and as getting closer to the Rhone river mouth, a weaker seasonal variability is observed for the phytoplanktonic biomass then salinity and temperature differences remain high. The better knowledge of the eastern dilution plume is of important socio-economical concern due to the numerous population living on this coast and the presence of pollutants in the river waters.

Monosaccharide composition of particulate hydrolysable sugar fraction in surface microlayers from brackish and marine waters

Abstract Twenty-nine sea-surface microlayer samples, associated with their related bulk water, were collected in coastal waters of the northwestern Mediterranean Sea, and examined for the concentration and composition of their particulate sugar fraction. The monosaccharide content was assayed by high-performance liquid chromatography (HPLC) and fluorescence detection after dansylhydrazine precolumn derivatization. Samples were collected in both marine areas influenced by fresh water. As compared with bulk waters, accumulation of particulate organic matter in the surface microlayer was higher in marine than in brackish waters (about three-fold higher for particulate organic carbon (POC) and ten-fold higher for sugars). However, in brackish bulk waters, the concentrations of organic compounds (POC, particulate organic nitrogen (PON), chlorophyll a and sugars) were higher than in marine bulk waters. In all the samples the sugar content appeared to be directly linked to POC. All the surface microlayers were enriched in bacteria but phytoplanktonic pigments were less represented in microlayers than in other particulate organic fractions. In brackish waters, chlorophyll a concentrations were correlated with the percentage of monosaccharide carbon in POC, but the microbiomass could explain only a small part (5–10%) of the sugar concentrations recorded in surface microlayers. In all cases, glucose was the major monosaccharide form. In brackish waters, no change was noted in monosaccharide composition of the sugar fraction in surface microlayers as compared with their related bulk waters. In marine samples, a slight but significant depletion of glucose was recorded in the microlayers, and three forms (mannose, arabinose and rhamnose) exhibited higher percentages (+4%, +4% and +15%, respectively) in marine sea-surface microlayers. During mild acid hydrolysis of the particulate organic matter, the release of the ·Dubois-reactive compounds’ was faster in marine microlayer samples than in related bulk waters, and the relative concentration of glucose increased with time of hydrolysis in the two types of water. When hydrolysis was not complete, a compound which eluted at the beginning of the chromatogram and remained at a constant level throughout the hydrolysis, was detected.

Influence of some coral reef communities on the calcium carbonate budget of Tiahura reef (Moorea, French Polynesia)

The calcium carbonate budget of coral reefs is the result of the interaction of the processes of calcification and biological degradation, and is reflected in the chemical properties of the seawater overlying the reefs. A series of experiments at Moorea Island (French Polynesia) in 1988 monitored the diurnal and nocturnal variations in the chemical properties of seawater under field and laboratory conditions. Our results revealed that in the study area (Tiahura barrier reef flat), the calcium carbonate budget varied over space and time as a function of location in the water current. Two in-situ sites were investigated; one was situated 100 m from the algal crest of the barrier reef, the other 300 m further downstream. As a result of cumulative upstream events, the daily net calcification was ten times higher at the downstream (5.22 gm-2 d-1) than at the upstream (0.45 gm-2 d-1) site. The carbonate uptake by in situ Porites lobata in enclosures (8 kgm-2 yr-1) was ten times higher than the uptake by the whole community in the surrounding water (0.8 kgm-2 yr-1) and five times higher than that recorded for P. lobata in laboratory experiments (1.4 kgm-2 yr-1), where illumination levels were 10% of in situ levels. In laboratory experiments, the planktonic fraction of the seawater had no perceptible influence on the calcium carbonate budget. In the absence of bioeroders, living coral totally depleted the carbonate content of the seawater (3.7 gm-2d-1). Bioerosive organisms played an important role in restoring this calcium carbonate; e.g. sea urchins grazing on algal turf covering dead coral ingested CaCO3 and released this as a carbonate powder (1.26 gm-2d-1); a form of carbonate which is extremely accessible to chemical dissolution.

Occurrence frequencies of sea-surface slicks at long and short time-scales in relation to wind speed

Abstract For 2 years photographic records of the sea surface were taken in a coastal area. These were used, in conjuction with records of the wind speed and direction, to determine the frequency of formation of slicks as an index of surface microlayer presence. Parallel collection of sea-surface samples provided evidence for a relation between the pictures and accumulation processes of organic matter in surface microlayers. Results show that slicks are present for more than 25% of the recording time; this frequency may reach more than 60%, depending on the hour and season. Slick formation is dependent on wind speed and slicks never exist at wind speeds greater than 7 m s −1 ; below this upper limit the highest probability of slick formation corresponds with wind speed values between 2 and 4 m s −1 , but in many cases, no slicks are formed under low wind speed conditions. (Slicks were found to require considerable time to form, following a decrease in wind speed, and to disperse, following an increase in wind speed. This dependence explains most of the seasonal and diurnal variations in slick occurrence.) Slicks are more frequent in the morning, and less frequent at midday and afternoon, because of wind induced by heat flux between the sea and continent in coastal areas. Despite the fact that it was not possible to take photographic records during the night, a high probability of slick formation during the night can be deduced from the recorded decrease in wind speed.

Caractéristiques du feutrage algal des récifs coralliens de Polynésie française soumis à différentes intensités de bioérosion

Abstract This study deals with the colonisation of experimental Porites blocks by epilithic and endolithic algal community in two atoll lagoons and two high-island lagoons in French Polynesia, exposed to different environmental conditions during a 5-year period. A qualitative analysis of the community (cyanobacteria and micro-algae) was carried out, and the relationship between the epilithic and endolithic strata observed. HPLC analysis of chlorophyll pigments was used to quantitatively determine the plant biomass, which was then compared to that of the algal turf of neighbouring reefs. The results show that these blocks are colonised according to two factors: the reef structure (atoll or high-island) and the degree of human disturbance. The epilithic and endolithic population dynamics differ. The density of the epilithic algal community and the species diversity increase with the degree of eutrophication and the amount of borers (sea-urchins, parrotfish), while the proportion of endolithic species remains low (34 %–59 %). This is especially marked in the high-island lagoons, where leaching has caused enhanced nutrient levels. An extreme case is the station at Faaa, a highly polluted harbour, where increased sea-urchin levels (44 ind. m −2 ) meant that the blocks disappeared completely in less than five years due to bioerosion. In the oligotrophic waters of the atoll lagoons, the losses of CaCO 3 by bioerosion do not exceed 35 % per block, and the algal community is made up mainly of endolithic species (66 %–85 %). The algal biomass is lowest in the Takapoto atolls (10–11 μg cm −2 ) and maximum in Tikehau atoll (23 and 56 μg cm −2 ). The first microborers to settle in the ecological succession of the community are the cyanobacteria. These are gradually replaced by Ostreobium (Chlorophyceae borers), which become dominant in the blocks exposed to the lowest bioerosion rate. The richness and the density of the algal turf reflect the convergence of many ecological factors: it seems that the covering of epilithic algae or the richness of endolithic flora could be used as a global indicator of the quality and the health of a reef.