Molecular polymorphisms (allozyme and amplified fragment length polymorphisms (AFLP)) were investigated in the mullet specie's Liza ramada and Liza saliens to determine levels of genetic variability and assess possible correlations between the population genetic structure and the specie's adaptability to shallow water environments. The thinlipped (L. ramada) and the sharpnose (L saliens) mullets are diadromous species-that enter coastal lagoons during early life stages to complete growth previous to sexual maturation. Bi-monthly samples (n = 30-50) were collected in the period 2000-2002 in different sites of the Sacca di Goro (Po river delta) and a nearby aquaculture lagoon (Valle Bertuzzi). Biochemical analyses were carried out by means of starch gel electrophoresis (SGE) on 24 genetic loci corresponding to 15 gene-enzyme systems. In addition, molecular species-specific AFLP (15 primer combinations) were obtained by means of capillary electrophoresis. The degree of allozyme variability determined at three polymorphic loci, GPI-A, GPI-B and G3PDH in L. saliens and L ramada (polymorphic loci P = 0.08; mean heterozygosity H = 0.010-0.022) and AFLP diversity (P = 0.110-0.430), seems lower than the one reported in the literature for ecologically similar teleost species. The identification of diagnostic alleles at GPI-A, G3PDH, AK-2, CK-A, CK-B, AAT, IDH, PGM-1, PGM-2 loci in the two mullet species was used for the taxonomic classification of L. saliens and L. ramada. Molecular taxonomy (allozyme and AFLP) demonstrated that the presence of small individuals inside the lagoons previously identified according to morphological characters has often been misinterpreted. The results are discussed in relation to the adaptive role of genetic variation and the migratory characteristics of Mugilidae. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
The sessile hard bottoms zoobenthos community was studied in three northern Adriatic lagoons (Venice, Caorle and Grado-Marano). On the basis of previous researches (1993-1994 in Venice; 1997 in Grado-Marano), these lagoons had been subdivided into ecological sectors. The time consistency of such a subdivision has been assessed. The largest number of species was found in the lagoon of Venice, showing a high heterogeneity of environments and an intense shipping traffic, coupled with aquaculture activities that favoured the arrival of exotic species. A very poor community of obligate oligohaline species was found in Caorle. The natural and stable environment of Grado-Marano lagoon, with its large area of freshwater influence, hosted an intermediate number of species. The multi-dimensional scaling ordination plot of 27 representative stations from the three lagoons (samples of July 2000) clearly distinguished a cluster of "estuarine" sites from the remaining ones, that could be classified as "inner lagoon" sites, "vivified lagoon" sites and "lagoon mouth" sites. When compared with past results by Anosim test and Simper analysis, a lesser degree of discrimination between clusters of sites could be observed. In the following year (samples of July 2001), a larger number of sampling stations was considered in Venice and Grado-Marano. The multi-dimensional scaling plot for the community data of Grado-Marano showed fairly recognisable clusters, that substantially repeated those defined in 1997. As far as Venice is concerned, about 25% of the examined stations had shifted towards a different group, compared with those identified in 1993-1994; in particular, the "urban", "inner lagoon" and "estuarine" sectors and their peculiar assemblages survived only in small areas with unique features of harsh environmental conditions. The progressively enhanced marine influx in all the lagoon sectors (but the ones directly affected by the outflow of the only river still discharging into the lagoon) has, on the one hand, reduced the most evident effects of eutrophication and urban pollution, and on the other, led to a banalisation of the lagoon communities. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
In the central Ligurian Basin, Western Mediterranean Sea, dense water formation occurs in winter so that near-surface stratification displays a marked seasonality. Consequently, kinetic energy spectra from the surface to intermediate depths are entirely different in summer and winter. In summer, the spectra show a peak near the local inertial frequency (f). The polarization of currents in the internal gravity wave frequency (sigma) band (f < sigma < N, N the buoyancy frequency) resembles internal wave theory (for N >>f). In winter, however, no significant near-inertial (or any other) spectral peak is observed and motions are not polarized at any frequencies, whatever the observation depths. With respect to the energy levels observed in summer, those in winter are enhanced at all frequencies (except near f). The seasonal pycnocline determines the summertime development of near-inertial and higher frequency internal waves, also at great depths (similar to 1100 m at least). In winter, no near-surface pycnocline does exist and no (gravity nor gyroscopic) near-inertial internal waves occur; the observed currents are associated with strong mesoscale activity and dense water formation, not with local N. For the 'internal wave band' this implies a lack of scaling of horizontal kinetic energy with N that is reflected in changes of the spectral slope. In the coastal zone of the Ligurian Basin, especially near Corsica, where the alongslope circulation and an almost permanent stratification prevail, near-inertial currents are found yearlong, with only moderate changes in amplitude in the near-surface layer. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
A study of the sediment bedload in the Mont-Saint-Michel bay is presented here. It combines the use of a 2DH numerical model and a pattern of sediment bedload transport established on the analysis of the statements of sidescan imagery combined with a dense groundwork of sedimentary grab samples. Results show the role of tidal currents asymetry in the realistic bioclastic sand transfert from the subtidal environment to the coast and the divergence of sedimentary dynamic between the maritime bay to the West and the tidal delta to the East. This in-shore transfer is responsable of the Holocene prism construction. The model reproduces tidal sedimentary dynamics with the immediate surroundings of the Mont-Saint-Michel. It shows the interest of the modeling of bedload flows in the reconstitution of the sedimentary processes in the filling bays of Manche-Atlantic coast. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. Tous droits reserves.
The low tidal range of the Mediterranean Sea and the high sediment load of the Rhone induce the formation of an important submarine delta. The Cs-137 inventory in sediment on a 480 km(2) area near the Rhone mouth reached 19.6 TBq in 1990. The spatial distribution of both sediment accumulation rates and (CS)-C-137 concentrations in this area confirm the existence of a spatially well-delimited zone, i.e. the prodelta, where both parameters are the highest. Thus, 40% of the total amount of Cs-137 stored in this 480 km(2) area was found within the prodelta (30 km(2)) in the close vicinity of the river mouth. This attests to the efficiency of the (CS)-C-137 trapping by the prodelta sediments. A study on the part the different (CS)-C-137 sources in the Mediterranean Sea play in contributing to this inventory has been carried out. These sources are (i) direct deposition from both global fallout and the Chernobyl accident, (ii) indirect inputs arising from the erosion of surface soils of the Rhone catchment area that were also contaminated by the previous fallout, (iii) liquid effluents from the nuclear industry into the Rhone waters. Assuming that direct deposition is evenly distributed over the study area (480 km(2)) and that the particulate Cs-137 input from the Rhone is entirely trapped in this same area, these sources account for about 50% of the inventory. These hypotheses are unlikely in a coastal area subject to various physical disturbances but they are conservative enough to assess the lower limit of the nuclear liquid releases contribution to this inventory to be 50%. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
The spatial variability of oxygen and dissolved nutrient exchanges across the sediment-water interface was studied on the continental shelf in the Gulf of Lions (NW Mediterranean Sea). Replicate sediment cores were sampled at nine stations (64-162 m depth) along two lines parallel to the coast during two cruises in March and June 1998. Sediment-water exchanges were measured using the core incubation technique. Surficial sediments, bottom water and interstitial water characteristics were also described. Fluxes of oxygen (3.72-8.83 mmol m(-2) d(-1)), nitrate (0.026-0.283 mmol m(-2) d(-1)), ammonium (-0.022 to 0.204 mmol m(-2) d(-1)), nitrite (-0.034 to 0.002 mmol m(-2) d(-1)), phosphate (-0.007 to 0.029 mmol m(-2) d(-1)) and silicate (0.504-1.656 mmol m(-2) d(-1)) were generally quite low. This has to be related to the oligotrophy of the Mediterranean Sea. Fluxes showed a weak spatial variability, and a significant correlation could be established between oxygen fluxes and the organic carbon content of surficial sediments. A general increase in ammonium, nitrate and phosphate release was also observed towards the coast and the mouth of the Rhone River. Nitrite uptake and silicate release showed high variability between cruises, and the change in silicate fluxes depended mainly on the location on the eastern or western part of the continental shelf.Over the whole continental shelf, calculated sediment mineralization rate represents 342 kt a(-1) of organic carbon. The annual release from the sediments approximates to 14.1 kt dissolved inorganic nitrogen, 2.9 kt P, and 165 kt dissolved silica, which represent, respectively, an amount close to 5%, 7% and 28% of the nutrient requirements for primary production. When compared to nutrient inputs from the Rhone River, sediments appear to play a significant role in the biogeochemical cycles of the Gulf of Lions system, mainly for inorganic phosphorus and dissolved silica. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
The first evaluations of the daily ration and population food consumption of four Sciaenid fish, under natural conditions for the Brazilian south-western Atlantic shelf (23degrees35'S, 45degrees00'W) are presented. The average daily ration ranged from 4.38 to 12.92 % body mass (90% confidence interval) for the juvenile shortfin corvina (Isopisthus parvipinnis), from 0.41 to 5.52 % body mass (90% confidence interval) for the juvenile shorthead drum (Larimus breviceps) and from 3.14% to 3.15% body mass for the juvenile whitemouth croacker (Micropogonias furnieri). Juveniles of the banded croacker (Paralonchurus brasiliensis) showed higher estimates (2.58-2.60% body mass) than those for the adults (1.2-1.84% body mass). The mean food consumption rate of the population was estimated at about I I and 8 year I, respectively, for the whitemouth croacker, and banded croacker, corresponding to a gross efficiency of 13 and 10%. The estimates of daily ration were related to the feeding habits as well as to size of the fish, and probably to their specific energy budget. Estimates of population food consumption are related to population structure. (C) 2003 Edition scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
For a given species in a particular environment, the success and the harmlessness of transmitter attachment appear to be highly specific. As no information was available for the tagging of the strepie, Sarpa salpa, a suitability study of attachment techniques was needed. Two types of transmitter attachments were investigated: (1) externally, placed on the back of the fish below the dorsal fin by means of two threads sutured through the dorsal musculature, and (2) internally, in the peritoneal cavity. Twenty-five fish were monitored over a 14-d period for survival, surgical healing, injury occurrence and post-tagging behaviour. Even though we observed a 100% survival rate for both groups, with no noticeable buoyancy or swimming alteration, findings from this study indicate that both groups of tagged fish were affected by the presence of the transmitter in different ways. Fish with an external transmitter were chronically affected, incurring physical impact, whereas the surgically-implanted fish exhibited short-term tagging effects (less than 36 h), attributable to surgery effects, and were not subject to fouling on transmitter or wound chafing. Moreover, they appeared to recover quickly with no indication of long-term effects. Based on the findings of this study. the use of the surgical implantation method for Sarpa salpa is recommended. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
Many studies in marine coastal lagoons have focused on the marine-to-terrestrial gradient as a main source of variation for the structure of assemblages. In this paper, the magnitude of differences among locations arranged along the marine-to-terrestrial gradient of the western lagoon of Orbetello (Grosseto, Italy) was contrasted with the amount of spatial variability occurring among sets of locations that were not positioned along this axis. We propose that if the most important processes influencing assemblages were those associated with the external-internal gradient of the lagoon, as usually supposed, then assemblages should differ more among these locations than among any other locations. To test the above proposition, four locations arranged along the two major axes of the lagoon were established in November 2000. Each location was sampled three times (November 2000, April 2001, August 2001) to test for temporal consistency in spatial patterns. At each time of sampling, three replicate sites were established in each location. This design enabled estimates of spatial variability to be obtained at three scales: among locations hundreds of meters apart, among sites tens of meters apart and among quadrats hundreds of centimeters apart. Non-metric multidimensional scaling (nMDS) ordination plots on abundance data revealed differences among assemblages hundreds of meters apart. Assemblages in the inner part of the lagoon were separated from those closer to the sea inlet, depending on the marine-to-terrestrial gradient. In addition to this pattern, differences also occurred among assemblages hundreds of meters apart, but positioned at a similar distance from the sea. Multifactorial Anovas on abundance of the most common taxa showed significant differences in mean values at the scales of location and site, with patterns changing over time. These results indicated that spatial structure in assemblages was not a distinctive feature of locations arranged along the marine-to-terrestrial gradient in the lagoon of Orbetello. Similar differences also occurred among other sets of locations at the scale of hundreds of meters, regardless of their position in the lagoon. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
The Medusae of Tunis Gulf (25 species) are qualitatively the third zooplanktonic group after Tintinnids and Copepods. Anthomedusae (eight species), Trachymedusae (five species) and Leptomedusae (four species) represent the major part among the 20 species of Hydromedusae identified during our study (December 1993-November 1995). However, the Limnomedusae (two species) and the Narcomedusae (one species) are poorly represented. In the Bay of Tunis, Obelia spp., the most common and dominant species, command the quantitative fluctuations of Hydromedusae and reach exceptionally the density of 25 800 ind. m(-3). Within the Scyphomedusae (five species), Pelagia noctiluca is the most common species which outbreaks in winter and autumn. Tunis Gulf seems to be, composed of two jellyfish communities; the first one is composed of endogenous species showing a constant period of blooming like Olindias, Cladonema, Aurelia, Cotylorhiza and Rhizostoma and sometimes permanent like Obelia spp. and Clytia spp.; the second. is represented by exogenous species considered as "visitors" like Velella, Sminthea or Pelagia whose presence on the coast is dependent on local and particular winds and currents. (C) 2003 Publie par Editions scientifiques et medicales Elsevier SAS.
Coastal lagoons are highly variable and dynamic systems that have been rarely investigated in terms of benthic microbial loop. We present here the results of a comparative study aimed at investigating factors and benthic processes potentially affecting microbial loop functioning in three lagoon systems (Goro, Lesina and Marsala lagoons). The three lagoons were characterised by different geo-morphological, trophic and ecological features. We determined organic matter quantity and biochemical composition, exo-enzymatic activities, bacterial biomass and bacterial carbon production together with heterotrophic nanoflagellate and meiofauna biomass. These variables allowed providing estimates of biomass ratios between different benthic compartments and gathering information on C transfer in different systems. The results of this study indicate that organic matter composition played a primary role on microbial loop ability of channelling C-biomass to higher trophic levels. In coastal lagoons, indeed, quantity and quality of sediment organic matter control rates of organic matter degradation, turnover rates (through breakdown of large macromolecules) and utilisation by benthic heterotrophic organisms (bacterial C production). Exo-enzymatic activities in all lagoons investigated were generally low, when compared to coastal marine systems, and lowest rates were observed in systems characterised by refractory organic pools. Our results indicate that the autotrophic contribution to the biopolymeric carbon pools, which influences the ratio of autotrophic to heterotrophic biomass, is a key factor regulating the functional efficiency of the benthic system. The structure of the benthic microbial loop varied according to the different characteristics of the lagoons: from a classical "detritus sink" system (i.e., the Marsala lagoon, where organic matter was highly refractory), to the "source" system (Lesina lagoon, which displayed an efficient C transfer to higher trophic levels, mediated by benthic bacteria). (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
Upwelling of cold. saline, and nutrient rich water was observed in late September 1999 along an east-west transect in the SW Kattegat. The Kattegat forms part of the transitional zone between the high saline North Sea and the low saline Baltic Sea. The upwelling occurred after an extended period of northward flow and eastern winds in the Kattegat, that changed into a southward flow as wind ceased. The upwelling was the result of a combination of high current speeds and bottom topography whereby the high-speed inflow water was forced towards the surface at the slope. Nutrient data show that the upwelling brought nutrient rich bottom water to the light exposed surface and a related strong (1943.5 ml(-1)) bloom of Pseudo-nitzschia pseudodelicatissima was observed. Surface (1.0 m) chlorophyll-a values increased from 3.7 to 10.0 mug l(-1) during upwelling. A frontal structure developed during the upwelling with raised fluorescence values at the front related to convergence. The present upwelling front was only indirectly related to the wind conditions and the front propagated off shore as compared to other upwelling fronts. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
The present paper deals with the morphodynamics of intertidal bars on Omaha beach, a macrotidal beach located along the Normandy coastline. During two years (defined here as medium-term time-scale), a monthly topographic monitoring has been conducted on this beach. An analysis of the morphological evolution of the ridge and runnel systems is performed and correlated to the forcing conditions (waves and tide) recorded on the lower foreshore. Our results allow to distinguish some morphodynamical evolution sequences with one stage of accretion and one stage of destruction of the bars. In order to discriminate these two stages, an energetic criterion is used. Accretion stages correspond to long periods of fair weather conditions (significant wave height, H-s < 1 m), when bars build up and migrate onshore with a rate under 0.4 m per day. On the opposite, destruction stages result from wave height increases during storms (H-s > 1 m). The destructive processes are modulated by tide level and pre-existing morphology. Our results show also a medium-term morphodynamic variability along the beach profile. Indeed, the upper beach bars are much more mobile than the lower beach ones. The drainage channel dynamic is also highlighted as a destabilizing factor which weakens the bar resistance to storm activity. Moreover, the construction and the evolution of intertidal bars correspond to short-term reorganisations of an intertidal sand volume which seems to be quite stable over a medium-term period. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Two samples of Aphanius fasciatus collected in the Pilo pond (northern Sardinia, Italy) and in an adjacent pool of small surface area were analysed morphologically (235 individuals) and genetically (a subsample of 58 individuals). The aims of the present study were (i) to test the hypothesis that different predation pressures may be associated with morphological and/or genetic differences between samples from each habitat and (ii) to assess the level of divergence between the two populations. Morphological analysis was based on the relative size of fins because it has been shown to be associated with predation pressure. The relative caudal fin area (caudal fin area/total body surface) was smaller in specimens from the pool, in both males and females, whereas no differences were found for the dorsal and anal fin areas. Caudal fins with higher aspect ratio (fin depth/fin length) were found in fish from the pool but not in the pond, due to a higher fin depth. We hypothesised that specimens from the pool would show smaller caudal fin area, since they are subject to lower predation pressure. Random amplification of polymorphic DNA (RAPD) analysis revealed a relatively high degree of both within- and between-sample genetic heterogeneity. The pond and pool samples exhibited heterozygosities, which did not differ significantly by t-test. Between-sample genetic divergence was highlighted by the coancestry coefficient (theta = 0.301 +/- 0.059, P < 0.001) and analysis of molecular variance (AMOVA) (variance between sites = 41%, P < 0.001). Genetic divergence between sites with a relatively high genetic diversity within both samples suggested that the population in the pool did not originate from a single colonisation event with a small number of founders. The genetic divergence between the two populations is consistent with their differences in fin size. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
Coral reef fishes often exhibit a high degree of structure in their distribution and abundance, but the factors that influence their spatial arrangement are poorly understood. This study sought to explain the spatial structure of coral reef fish communities in the Ryukyu Archipelago. southern Japan. Visual surveys of coral reef fishes were conducted at multiple stations across the fringing reef (from the inner reef flat to the outer slope) at each of three different islands; Aka, Ishigaki and Sesoko. Spatial variation in fish communities (within and among reefs) was then compared to changes in environmental variables (water depth, distance from the shoreline, reef zone, coral abundance and coral richness). Despite being small islands, the total species richness of coral reef fishes in the Ryukyu Islands was very high (>87 species per reef). Mean abundance of reef fishes was also very high (x = 2.26 +/- 0.20 S.E. fishes per m(2)), but more than 80% of all fishes were from the family Pomacentridae. The structure of fish communities was very consistent among reefs, but varied greatly among zones within each reef. On the reef flat, the fish community was dominated by the pomacentrid Chrysiptera cyanea and the acanthurid Acanthurus nigrofuscus. In contrast, the reef slope community was characterised by high densities of the pomacentrids Pomacentrus lepidogenys and P. richardsoni, as well as high densities of the acanthurid Ctenochaetus striatus. Canonical correspondence analysis showed that the structure of the coral reef fish communities varied in relation to reef zone, water depth, and distance from the shoreline, but these changes were not related to spatial variation in either coral abundance or coral richness. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
Although the use of deep-sea imagery considerably increased during the last decades, reports on nekton falls to the deep seafloor are very scarce. Whereas there are a few reports describing the finding of whale carcasses in the deep north-eastern and south-eastern Pacific, descriptions of invertebrate or vertebrate food-falls at centimetre to metre scale are extremely rare. After 4 years of extensive work at a deep-sea long-term station in northern polar regions (AWI-"Hausgarten"), including large-scale visual observations with various camera systems covering some 10 000 m(2) of seafloor at water depths between 1250 and 5600 m, this paper describes the first observation of a fish carcass at about 1280 m water depth, west off Svalbard. The fish skeleton had a total length of 36 cm and an approximated biomass of 0.5 kg wet weight. On the basis of in situ experiments, we estimated a very short residence time of this particular carcass of about 7 h at the bottom. The fast response of the motile deep-sea scavenger community to such events and the rapid utilisation of this kind of organic carbon supply might partly explain the extreme rarity of such an observation. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
Planktonic and benthic productivity and consumption were estimated to assess the availability of food to higher trophic-level consumers in the Ubatuba ecosystem on the SE coast of Brazil. The study area included waters from 10 to 100 m deep and covered 3800 km(2). The trophic compartments of the system were established on ecologically or taxonomically related species, considering their relative abundance and similarity of diets and habits. The compartments are phytoplankton, zooplankton, salps, bacterioplankton, cnidaria, polyplacophora, mollusca, carnivorous benthos, detritivorous polychaetes, other detritivorous benthos, penaeidea-caridea, brachyura, and echinodermata. Biomass, production, and consumption were estimated in summer and winter. Plankton biomass, production and consumption were higher in summer than in winter, mainly because of the presence of salps. Primary production was estimated as 1486 g wet weight m(-2) 3 months(-1) in summer and 704 g in winter. Total benthic biomass in summer (101 gww m(-2)) was twice that in winter (53 gww m(-2)), but its production and consumption were similar in both seasons. (C) 2003 Editions scientitiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
Primary production (PP) and, nitrate (QNO(3)) and ammonium (QNH(4)) uptakes were measured together with other environmental parameters from October 1999 to February 2001 in the Gulf of Trieste (N Adriatic Sea). Their trends showed a high variability because of the combined effects of meteorological conditions, water circulation and river discharges. PP ranged from 0.2 to 1.5.9 mumol C dm(-3) d(-1), whereas QNO(3) varied from 0.8 to 442 nmol N dm(-3) d(-1), showing a trend similar to that of carbon basically ascribable to the autotrophic activity. QNH(4) ranged from 20 to 1308 nmol N dm-3 d-' and it reached the highest values during the declining phases of phytoplankton blooms, indicating that bacterial community can also be involved in its uptake. Regenerated PP generally prevailed over the new production (depth-integrated f-ratios from 0.05 to 0.50). C/N uptake ratios by planktonic community (annual average of 16 +/- 11) showed the repetitive carbon overconsumption (23-33) during periods of high production, and lower values (2-13) during: the post-bloom phases and in the months of scarce autotrophic activity. Residence time of freshwater in the area (1 d in November and January, up to 23 d in July) indicated the fast export of low salinity waters in winter and their longer permanence in summer. These values were closer to the ammonium turnover times (1-34 d) than to the nitrate ones (2-831 d). Riverine nitrate load (3-67 t N d-') generally exceed the biological demand of this nutrient (uptakes from 0.2 to 8 t N d-'), whereas the ammonium load (0.1-33 t N d(-1)) was almost always insufficient (uptakes, from 2.6 to 33 t N d(-1)). These results evidenced the major role of physical transport and recycling processes to regulate, respectively, nitrate and ammonium availability in this shallow ecosystem. (C) 2003 Editions scientifiques et medicale Elsevier SAS and Ifremer/CNRS/IRD: All rights reserved.
During 1994-1999, the mesozooplankton community was sampled monthly in the upper sea layer (up to 100 m) along a cross-shelf transect of three stations in waters off Mallorca island. Copepods formed the most abundant group (54%) followed by appendicularians (17%), cladocerans and meroplankton larvae (13%). The abundance of all these groups decreased in the offshore direction but it was not the case for other zooplankton groups. A clear seasonal cycle was evident consisting of a general decrease of the abundance from the beginning to the end of the year. In addition to the general increase during late winter and spring, an absolute maximum was detected in May, particularly important at the neritic station and a relative maximum in March and October. During this annual cycle, the community structure was almost maintained. An interannual trend was also present, characterized by an overall decrease in the total zooplankton abundance from 1994 to 1999. Concurrent measurements of water and air temperature show that this trend was correlated with a warming of coastal waters of atmospherical origin. In particular. a marked minimum in zooplankton abundance was recorded during 1998, which was the warmest year registered. During 1997-1998, the warming was also associated with the presence of fresh, nutrient-poor southern waters of Atlantic origin. (C) 2003 Editions scientifiques et medicales Elsevier and Ifremer/CNRS/IRD. All fights reserved.
The macrobenthic community structure of the Valli di Comacchio (northern Italy) was described in order to assess the ecological conditions of the main basins through 2001. In addition, the biotic data set gathered in 1997-1998 was compared to achieve an estimation of the eventual recovery of the lagoonal benthic assemblages. Four permanent sites (PI, M4, M5 and M6), located along a gradient of sediment texture and confinement, and representing four different areas of the lagoon, were sampled quarterly in 2001 for macrofauna and sedimentary variables (organic content, phytobenthic chlorophyll-a, depth of the redox potential discontinuity layer), and fortnightly for water variables (temperature, salinity, dissolved oxygen and planktonic chlorophyll-a). Water and sedimentary variables were typical of eutrophic areas. A total of 52 macrobenthic taxa were identified and, on the basis of the species collected, differences in faunal distribution among the four areas were recognized, although less marked than in previous studies. Sediment trophic status and its seasonal dynamics in the Valli were crucial in deter-mining species distribution among the different areas. The comparison between 1997-1998 and 2001 biotic data indicated that conditions in the lagoon had improved, especially in the formerly most impaired, central area. In the Valli di Comacchio, the recovery of benthic communities after severe disturbance will probably take longer, even if sewage discharges have been removed I I years ago. Secondary disturbance due to scarce water circulation, sharp temperature and salinity fluctuations, release of toxic substances from sediments influenced animal assemblages along spatial and temporal scales. The interplay of these variables probably caused deviations from the expected improvement in benthic conditions. Nevertheless, clear signs of amelioration, particularly at the previously most impaired area, were detectable. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.
