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The southern coast of Hainan Island, China, is one of the most frequently hit areas of tropical cyclones in the Northwest Pacific regions. Although some of the extreme typhoon events were known in historical times, quantitative information on the timing and magnitude of paleo-typhoon events in this coastal area remains rare. In the present study, a large number of coral reef boulders were found on the Xiaodonghai reef platform, on the south coast of Hainan Island. Morphometric analysis of the boulders shows an exponentially fining landward trend, indicating a storm origin; a wave-induced current velocity of 2.41–5.71 m/s during the storm events is required to transport the boulders that were originally situated outside the reef edge. Based on the U/Th and 14C dating for the age-indicating samples taken from the boulders, seven major periods with intense typhoon activities were identified for the last 4,000 years, i.e., 1800–1500 BCE, 1200–900 BCE, 50–120 CE, 550–800 CE, 900–1000 CE, 1350–1900 CE, and 1910–2000 CE. A comparison with the regional typhoon records in terms of climatic parameters in the northwestern Pacific and the South China Sea regions indicates that the longitudinal variations of intense typhoon frequency were mainly controlled by El Niño-Southern Oscillation (ENSO), dominantly modulated by the Intertropical Convergence Zone. Because of the future warming climate, there will be a trend of enhanced typhoon risk for the southern Hainan Island coasts.

Sea level changes play an important role as an indicator of climate change. However, without climate change, the sea level itself shows strong regional patterns, both in space and time, that could deviate significantly from global averages. The spatial variability of sea level changes in Indonesia can be divided based on its drivers, i.e., climatic and seasonal weather-driven and non-climatic and geological-driven. Seasonally, the sea level in Indonesia is generally high in northwest monsoon and low in southeast monsoon. Nevertheless, there is a possibility of extreme natural phenomenon influences that generate anomalies and a thermosteric process that also affects the sea level. On the non-climatic and geological theory, the uniqueness of the tectonic setting in Indonesia will create spatial variations in regional sea levels, as both static and dynamic changes in a long period of time. Land subsidence is also often regarded as a significant contributor to the rise of relative sea level in coastal environments. Combined with the rise in sea level, land subsidence will escalate coastal flooding risks, contribute to shoreline retreat, and be further aggravated by anthropogenic forces such as groundwater extraction and land development. This scientific review will summarize the spatial variation of sea level rise in Indonesia, examines the underlying drivers that control it, and provides an overview of the combined sea level rise and land subsidence as a significant threat in Indonesia.

In the inner area of the Sea of Ariake, rearing experiments were conducted to examine how the survival rates of juveniles of three bivalve species (Anadara kagoshimensis, Ruditapes philippinarum, Atrina sp.) vary among sea areas and heights above the seabed. In three runs of the experiment, replicate samples of the three bivalves were kept in trays set at various heights above the seabed (range 0–40 cm) at one to six stations for 15–16 days. Results were as follows. (1) Survival rates varied among heights and stations more markedly for Atrina sp. than for A. kagoshimensis and R. philippinarum; (2) Atrina sp. always showed higher survival rates at greater heights above the seabed, whereas the other species did not always show this pattern. (3) Survival rates of Atrina sp. showed a different station-to-station variation pattern between experimental runs. (4) In statistical model selection, the spatial variations in the survival rate were not associated for either A. kagoshimensis or R. philippinarum with any of the environmental factors recorded (density of suspended solids, density of chlorophyll a, water temperature). In contrast, for Atrina sp. they were strongly and negatively associated with the spatial variations in density of suspended solids.

Highlights • Satellite data were used to characterize the oceanography of the Gulf of Guinea. • Ocean color CCI Chla offered unprecedented data coverage of the Gulf of Guinea. • Chla was modeled as a function of SST, SLA, winds, currents, EKE, eddies and fronts. • Chla was higher in upwelling conditions with cold SST, negative SLA, strong fronts. • The impact of river outflow on Chla was significant mostly from Nigeria to Gabon., The Gulf of Guinea represents a wide tract of the African coast with complex and rich coastal ecosystems undergoing various pressures. The seasonal variations of chlorophyll-a concentration (Chla) along the Gulf of Guinea (GoG) and their relations with physical oceanographic variables were analyzed using satellite observations covering the period 2002–2012. The effects of sea surface temperature (SST), sea level anomalies (SLA), winds, geostrophic currents, eddy kinetic energy (EKE), mesoscale eddies and fronts were considered on a monthly time scale. The analysis for each unit area was carried out on a chlorophyll index (IChla) computed as the product of the mean distance from the coast to the eutrophic threshold (1 mg m−3 isoline) and the average Chla in the eutrophic area. The study, based on satellite-derived Chla, was allowed by the unprecedented coverage given by the products distributed by the ESA Ocean Colour Climate Change Initiative (OC_CCI) resulting from the merging of data from several satellite missions. The physical variables served as potential predictors in a statistical Boosted Regression Tree (BRT) model. To account for the heterogeneous nature of the GoG, the analysis was conducted on eight systems that made up a partition of the whole region defined on the basis of the BRT model results and climatological properties. The western-most domain, from Guinea-Bissau to Sierra Leone, was associated with upwelling properties in boreal winter and appeared to share some characteristics with the overall Northwest African upwelling system. The region of Ivory Coast and Ghana also had upwelling properties but the main upwelling season was in boreal summer. In general upwelling conditions with cold SST, negative SLA, fairly strong frontal activity, and moderate winds, appeared as the environmental window most favorable to high IChla values. For these systems, the BRT model fitted the IChla data well with a percentage of explained total deviance D2 between 70% and 91% when using only physical oceanographic variables. Finally, the systems associated with the coasts of Nigeria to Gabon showed some mixed properties, with D2 values of 54–60%. Among these systems, a common feature seemed to be the importance of river discharge to explain IChla variations. Where possible (for the Niger River in the Nigeria system), the addition of river data as predictor in the BRT model resulted in a significant increase of D2 to 75%. Further progress is needed to understand the observed relationships and to predict how they can evolve in the face of climate change.

The Peruvian anchovy (Engraulis ringens) is the most important small pelagic of the Humboldt Current System (HCS), supporting the largest mono-specific fishery in the world. The spatial behavior of this species tends to be very dynamic at different spatial scales, influenced mostly by its biomass level and environmental factors. The aim of this study was to analyze temporal and spatial fluctuations in anchovy spatial distribution off Peru, based and modeled on acoustic data, focusing on large- and meso-scale spatial structures. We employed data from 41 scientific surveys (1994–2016) and Bayesian hierarchical spatial models to obtain the anchovy's spatial distribution, allowing us to identify spatial structures at specific scales. Our results showed similar temporal trends in the number of mesoscale structures, their areas and anchovy density, exhibiting altogether two breakpoints in the time series: ~1999 and ~2013. The last period (2013–2016) was similar to the earlier one (1994–1999), in terms of low values of mesoscale structure indicators. On the other hand, we identified four spatial scenarios differentiated by the aggregative behavior, which were highly influenced by seasons and El Nino events. Each scenario had recurrent, or fidelity, areas placed in different locations. For instance, for the ‘El Nino scenario’ a particularly coastal recurrent area was identified, which might be a refuge zone for this species during these unfavorable events. Finally, we assessed differences in biomass estimates of each scenario. The highest biomass values were estimated for the ‘Summer favorable scenario’ and the lowest ones for the ‘El Nino scenario’, which supports the MacCall's basin hypothesis for this species. This study expands the current knowledge of the Peruvian anchovy and it is a first step to understand the effects on this species of the last El Nino events (2014–2016) that occurred in the northern Humboldt Current System.

International audience; We have studied the heterogeneity of vertical profiles of biogeochemical components obtained from sediment core slicing. Sediment cores were collected in the intertidal zone of the Arcachon Bay and on the continental slope of the Bay of Biscay, at 550 and 1000m depth. At each station of the Arcachon Bay, five 1m-side zones were delimited at low tide. In each square, 3 cores were collected. Spatial heterogeneity on the continental slope was obtained from the study of 3 cores of multi-corer while 2 or 3 multi-corer deployments were used during the same oceanographic cruise. Similarity between profiles was determined to estimate the spatial heterogeneity at different scales. In the Arcachon Bay, results showed a spatial heterogeneity at a decimetre scale on apparently homogeneous areas. Despite the spatial variability, all the replicated profiles in Arcachon Bay sediments had similar trends, suggesting homogeneous benthic properties. However, a sampling with replicate cores handling is required for seasonal monitoring or study of biogeochemical mechanisms in coastal environments. We observe that the spatial variability on the continental margin of the Bay of Biscay is lower than in coastal environment of the Arcachon Bay. Heterogeneity is equivalent at a decimetre scale and at a hundred meters scale, which is the precision of the sampling positioning due to the drift of the boat and the tilt of the corer cable. In addition, our 10-year-long database for the Bay of Biscay showed that differences in the shape of profiles obtained in sediment cores collected at the same stations throughout this long period may not be interpreted in terms of evolution with time, because the observed variability is as high as the spatial heterogeneity.

Ecosystem engineers can modify habitat, creating structural microhabitats. This structural complexity can affect species richness. Marine ecosystem engineers are able to produce local effects in combination with environmental variables (e.g. to create more humid habitat during low tides). We tested the hypotheses that if there is a relationship between mussel morphology and environmental factors, mussels would be larger at warmer than at cooler locations, and in areas where 2 species of mussels overlap, size and biomass will decrease and density will increase. At a smaller scale, we predicted that there is a relationship between the assemblage structure and hardness of the substratum and sediment content of a mussel bed. Using a nested design, we measured density, biomass and size of 2 species of mussels, Brachidontes rodriguezii and Perumytilus (Brachidontes) purpuratus, and diversity of species associated with mussel beds at 2 rocky intertidal sites at each of 4 shores along the northern Argentinean coast. These variables were correlated with oceanographic conditions and local characteristics. Significant correlations were found between intertidal assemblages and local factors. The largest specimens of B. rodriguezii and P. purpuratus were found at the warmer shores. In areas where they overlapped, size, biomass and density of P. purpuratus were lower, although B. rodriguezii did not change. The mean abundance of invertebrates associated with a mussel bed showed significant differences among shores. These 2 species of mytilids coexist over a small area, and although these species are very similar in their biological and ecological function, the fauna associated with their matrices are very different. Fil: Arribas, Lorena Pilar. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Bagur Creta, Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Klein, E.. Universidad Simón Bolívar. Laboratorio de Sensores Remotos e Instituto de Tecnología y Ciencias Marinas; Venezuela Fil: Penchaszadeh, Pablo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Palomo, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina

10 pages, 7 figures, 2 tables, [EN] Short-term temporal variability in infaunal crustacean communities was evaluated against environmental variability. The area of study was located at two stations at 45 and 60 m depth under the influence of the Ebro River. Differences in the relative abundance of crustacean species between sites might be related to the distance from the river, with higher organic matter supply and finer mud content near the river. There was a marked seasonal variability linked to high phytoplankton production in spring, which supplied organic matter to the benthos, inducing higher crustacean abundance. In late summer there was a reduction in the infaunal crustacean abundance and species richness that could have been caused by two factors: the establishment of the thermocline, which could limit the availability of organic matter to the seabed, and the high water temperatures, which caused the production of phytoplankton exudates and accumulation of mucilaginous aggregates over the seabed. The 45-m site was under the influence of otter-trawl fishing and precisely in this area the seasonal variability was not observed, probably masked by the effects of trawling impact, [ES] Evaluamos la variabilidad temporal de la comunidad de crustáceos endobentónicos frente a la variabilidad ambiental a pequeña escala. El estudio se sitúa en la plataforma continental frente a la desembocadura del Rio Ebro, en dos estaciones de muestreo a 45 y 60 m de profundidad. Las diferencias en la abundancia relativa de crustáceos entre las dos estaciones pueden estar relacionadas con la distancia a la desembocadura del Ebro, con un mayor aporte de materia orgánica y mayor contenido de fango cerca del rio. Observamos una variabilidad estacional relacionada con la alta producción de fitoplancton en primavera, con aportes de materia orgánica al bentos favoreciendo una mayor abundancia de crustáceos. Al final del verano se establece la termoclina, pudiendo limitar el aporte de materia orgánica al bentos, y junto con las altas temperaturas, que originaron acumulaciones de exudados de fitoplancton en el fondo, pudo causar una reducción en la abundancia y riqueza específica. La variabilidad estacional no es tan marcada en la estación de muestreo a 45 m. Esta zona está impactada por la pesca de arrastre, que probablemente enmascara la variabilidad temporal

Fish assemblages of Ria de Aveiro coastal lagoon (Northwest Portugal) were studied from February 2012 and January 2013. Sampling were monthly conducted with a traditional beach-seine net (“chincha”) at 9 sites. Multivariate approach were used in order to analyse the spatial and temporal variation in fish community. A total of 58,201 fishes, weighting 249,540 g, were identified, representing 37 taxa and 21 families. Four taxa (Atherina spp., Dicentrarchus labrax, Liza spp., and Sardina pilchardus) were responsible for 94.7% and 85.4% of the total abundance, in number and weight. There were significant differences in fish community, in terms of fish number and weight, between sites and between months (ANOSIM, p

Benthic nematodes are widely regarded as very suitable organisms to monitor potential ecological effects of natural and anthropogenic disturbances in aquatic ecosystems. During 2008, the seagrass beds of Zostera noltii located in the Mira estuary (SW Portugal) disappeared completely. However, during 2009, slight symptoms of natural recovery were observed, a process which has since evolved intermittently. This study aims to investigate changes in patterns of nematode density, diversity, and trophic composition between two distinct habitat conditions: “before” the collapse of seagrass beds, and during the early recovery “after” the seagrass habitat loss, through the analysis of: i) temporal and spatial distribution patterns of nematode communities, and ii) the most important environmental variables influencing the nematode assemblages. The following hypotheses were tested: i) there would be differences in nematode assemblage density, biodiversity and trophic composition during both ecological conditions, “before” and “after”; and ii) there would be differences in nematode assemblage density, biodiversity and trophic composition at different sampling occasions during both ecological conditions. Nematode density and diversity were significantly different between the two ecological situations. A higher density was recorded before, but a higher diversity was evident after the collapse of Z. noltii. In spite of the disturbance caused by the seagrass habitat loss in the Mira estuary, the nematode trophic composition did not significantly differ between the before and after seagrass collapse situations. Despite the significant differences found among sampling occasions, a consistent temporal pattern was not evident. The response of nematode communities following this extreme event exhibited considerable resistance and resilience to the new environmental conditions.

Fish assemblages associated with Posidonia oceanica from three locations of the western Mediterranean (Mallorca, Formentera and Alacant, Spain) were sampled in order to assess their spatial variability at three different scales ranging from 100 km. Sampling was carried out using a beam trawl. Simultaneous sampling at these three spatial scales with the appropriate number of replicates implies a huge effort which is rarely possible to achieve. Consequently, we propose an arrangement of data coming from different sampling programs, after testing and making sure the specificities of each program cannot be confounded with the spatial variability. The two preliminary experimental designs adopted in order to combine the datasets were: (1) differences between two consecutive years were tested by sampling the same meadow (Formentera) in June 2001 and June 2002; and (2) differences attributable to the meadow structure were evaluated by sampling two meadows (Mallorca 2000 and Formentera 2001). The absence of any significant correlation pattern for univariate community descriptors and multivariate species-specific densities (i.e. individuals per hour) related to both between-year and within-location structural differences of the meadows, allow us to combine data from the three locations (Formentera 2001, Mallorca 2000 and Alacant 2000) in a single analysis aimed at determining how much variability is explained by the three spatial scales considered. The between-location scale (>100 km) is the most variable scale for species-specific densities (multivariate approach). Spatial variability at the smallest scale (

Spatial variation in the succession of phytoplankton in the Belgian Coastal Zone (BCZ) was investigated by monitoring phytoplankton biomass and community composition using microscopical cell counts, HPLC pigment analyses and in vivo fluorescence recordings. Monthly monitoring of phytoplankton community composition at five stations revealed a succession of three distinct diatom communities. The succession of these three communities was the same at each site, but the succession from the winter-spring to the summer community occurred one month earlier and the succession from the summer to the autumn community one month later at the SW than at the NE stations of the BCZ. Monthly monitoring of chlorophyll a at ten fixed sites and inspection of in vivo fluorescence recordings during various cruises of RV Zeeleeuw indicated that the spring bloom started about one month earlier in the SW part of the BCZ than in the NE part. The spatial difference in the onset of the spring bloom was ascribed to the higher water column turbidity at the NE coast compared to the SW coast. Although a Phaeocystis bloom occurred at all monitoring stations, a clear spatial variation in the magnitude of such blooms was observed, with more intense blooms at the NE coast than at the SW coast. A close relation was observed between the intensity of the Phaeocystis bloom and the availability of inorganic nutrients (N and P) before the onset of the bloom. Comparison of microscopical cell counts and CHEMTAX analysis of accessory pigment data indicated that HPLC analysis may be a useful tool for monitoring Phaeocystis in the North Sea. The presence of chlorophyll c3 containing diatoms, however, probably resulted in the detection of small quantities of Phaeocystis by HPLC-CHEMTAX analysis when microscopical analyses showed that the species was absent.

We investigated the abundance of the meiobenthos and the biomass and community structure of the nematodes in the central Arctic Ocean along two separate transects during 1991 and 1994. Meiobenthos abundances ranged from (100 to 600 individuals per 10 cm2, in the same order of magnitude as in other oligotrophic areas of the world’s deep ocean. Nematodes were the numerically dominant meiofaunal group at every station. Nematode biomass ranged from ( 1t o 48lg dry weight per 10 cm2. A combination of water depth and latitude explained 55% of the variability among stations in nematode biomass and 67% of the variability of total abundance, implying that both vertical and advective #uxes are important sources of food to the meiofaunal communities.The dominant nematode genus was Monhystera, a detrivorous/bacterivorous deposit feeder, suggesting that bacteria may play an important role in the food web of the meiobenthos in the Central Arctic. Multivariate analysis of genera abundances revealed di!erences among stations in the Eurasian and Amerasian Basins. During 1994, however, the deep stations in the Eurasian Basin were more similar to the other Amerasian stations, while the single deep station in the Makarov Basin was most similar to the other Eurasian Basin stations. The structure of meiofaunal communities in the central Arctic may provide insight into spatial variability in the Arctic Ocean. ( 2000 Elsevier Science Ltd. All rights reserved.

The mixing ratios of CO2, CH4, O-3, and SF6 were measured in 118 whole air samples collected onboard a Transall C-160 aircraft around the NH extratropical tropopause in the winters 1993-1994 and 1994-1995. The samples originate mainly from the upper troposphere (similar to 7 km) and partly from the lowermost stratosphere up to altitudes of 12 km. With help of 7-day back trajectories the potential temperature theta of an air mass in the free troposphere was established to be a reliable measure of the average latitude the air mass spent the last week before sampling, The potential temperature are thus interpreted in terms of a "representative latitude" allowing -1- for the creation of representative meridional trace gas profiles in the troposphere that show a lower scatter than if the data were plotted versus the sampling latitude itself and -2- for the distinction of different types of air masses, For example, by categorizing the sampled air masses by their potential temperatures and by their trace gas composition, the 300 K theta-surface was identified to separate cold polar air from warmer subtropical air. The 300 K theta - surface is thus found to mark the polar front in the wintertime upper troposphere and can be viewed as the lowest isentrope that allows quasi-isentropic cross-tropopause transport. The midlatitude upper troposphere was frequently affected by surface air resulting in a positive correlation of CH4, SF6, and O-3. In contrast, in the arctic upper troposphere and in the lowermost stratosphere, both CH4 and SF6 were negatively correlated with O-3. Surprisingly, variable CO2 levels (spanning similar to 14 ppm) found just above the ozonopause point to intensive mixing of tropospheric air into the lowermost stratosphere. From the high SF6 growth rate of nearly 7% per year a clear aging of the observed air masses since their entry into the stratosphere could be inferred. This SF6 age was rather high, for example around 2 years at an altitude of 11.5 km and thus just 3.5 km above the dynamical tropopause.

Foram estudados os padrões de densidade e diversidade específica dos anelídeos poliquetas da plataforma continental norte do Estado de São Paulo. A densidade de poliquetas foi maior na plataforma interna, especialmente na radial Sul. Nas radiais Central e Norte foram observadas variações temporais nas isóbatas de 20 e 35 m, com valores maiores no verão. Os valores de diversidade específica foram preponderantemente mais baixos na plataforma externa, no verão, e altos, no inverno, enquanto a plataforma interna apresentou padrões de diversidade mais complexos com flutuações sazonais em baixas profundidades. As densidades foram maiores em sedimentos pelíticos. Areias finas apresentaram valores mais altos de diversidade e riqueza. Sedimentos mais grossos apresentaram eqüitatividades maiores, porém, baixas diversidades. Os valores maiores de diversidade, nas estações mais rasas, foram devidos ao maior número de espécies e nas estações profundas, à maior eqüitatividade. Density and diversity patterns of the polychaetous annelids from the northern continental shelf of São Paulo State, Brazil, were studied. Polychaetous densities were higher in the inner shelf, mainly in the southern transect. Temporal variations were observed at the northern and central transects in the 20 and 35 m isobaths, with higher summer values. Diversity values were lower in summer and higher during winter in the outer shelf. The inner shelf presented more complex diversity patterns with seasonal fluctuations in lower depths. Muddy sediments presented higher densities; diversity and richness were higher in fine sand sediments. Coarser sediments presented the highest values of evenness but low diversity. The higher diversity values in the shallowest stations were due to the higher number of species and in the deepest stations to the great evenness.

Mahe, K., Amara, R., Bryckaert, T., Kacher, M., and Brylinski, J. M. 2007. Ontogenetic and spatial variation in the diet of hake (Merluccius merluccius) in the Bay of Biscay and the Celtic Sea. – ICES Journal of Marine Science, 64: 1210–1219. Analysis of the diet of trawl-caught hake (Merluccius merluccius) from three locations in the Bay of Biscay and the Celtic Sea in autumn 2001 showed that small hake fed almost exclusively on crustaceans (mainly euphausiids), but that there was a significant shift towards a fully piscivorous diet in hake >23 cm. A change in fish prey was also size-dependent, because smaller hake (30 cm). For all sizes analysed, conspecifics constituted 19.2%W of the diet and the frequency of occurrence of hake in the stomachs was 10.53%. Most hake prey were 0-group juveniles (

Fishing grounds off the northern coast of Mallorca Island (western Mediterranean Sea) are subject to very different fishing efforts as a result of both commercial and recreational activities. We analysed the variability at different spatial scales of the fishable community associated with shallow littoral rocky bottoms. Underwater visual censuses (UVC) were carried out in 3 localities that have different fishing pressure. Three sites were sampled within each locality, and nine 50 m long UVC transects were completed within each site. Multivariate correlograms showed that the transects were completely independent statistical units even when located less than 75 m apart. The spatial variability of the fish assemblage is remarkable. A redundancy analysis (RDA) revealed highly significant differences between the species relative abundance of the different localities. The bottom structure and rugosity were not detected to have any effect on the fish assemblage. The variability of the bottom structure at the below-locality level shows that these tests were powerful enough and that the effects of bottom structure were not confused with the effects of fishing pressure. Localities with lower fishing pressure showed significantly higher species richness (8.4 ± 0.3 and 8.9 ± 0.3 species 250 m-2) and abundance (54.6 ± 4.4 and 65.9 ± 4.1 ind. 250 m-2) than localities with higher fishing pressure (6.7 ± 0.3 species 250 m-2 and 41.1 ± 4.5 ind. 250 m -2). Serranus cabrilla and Symphodus tinca were significantly less abundant in the localities with higher fishing pressure. These results suggest that differences in fishing pressure may generate strong gradients of faunistic change even at relatively small spatial scales (5 to 10 km), and that the observed pattern emulates what would normally be expected to happen after protection measures are established in marine protected areas. © Inter-Research 2005.

An inventory of fish and epibenthic macrocrustaceans of the surf zones of sandy beaches along the Belgian coast was constructed. The surf zones were sampled intensively with a 2-m beam trawl in April–May 1996 (12 stations) and 26 species were recorded belonging to caridean shrimps (4), brachyuran crabs (5), cephalopods (1) and fish (16). The brown shrimp Crangon crangon dominated almost all samples (>80%). Total densities exceeded several times 250 ind 100 m−2 and 10 ind 100 m−2 if C. crangon was excluded. An east–west distinction as found in other (epi)benthic studies in deeper waters of the Belgian coast, was not found in the surf zone during this study. Spatial variation was mainly correlated with local characteristics such as turbidity of the water and the morphodynamic features of both the beach and the adjacent subtidal area.

During the course of 1996, the brackish to freshwater tidal reaches of the Schelde Estuary were sampled monthly along a longitudinal transect to study the origin and composition of phytoplankton communities in the freshwater tidal estuary. Variation in the phytoplankton community as a whole and its relation with the abiotic environment was analysed using multivariate analysis with variation partitioning. Of the variation in the species data 23·4% was spatially structured and a large part (13·8%) was explained by salinity or factors co-varying with salinity, with a marked species succession observed along the salinity gradient. Spatial variation not related to salinity (9·6%) was mainly situated within the freshwater tidal reaches, where in the uppermost stations phytoplankton was imported from the riverine tributaries while in the more downstream situated stations it was produced in situ . Riverine phytoplankton declined after import into the estuary where it was replaced by autochthonous, estuarine populations which were adapted to the low light climate and/or resistant to rotifer grazing. Of the species variation 27·8% was temporally structured. While riverine blooms appeared to be initiated by an increase in irradiance a decrease in river discharge in spring, estuarine phytoplankton only developed in summer, when temperature increased. Some potentials and limitations of the use of multivariate analyses with variation partitioning in pelagic estuarine environments are discussed in view of our results.