Sublittoral hard substrate communities off Helgoland

In the Helgoland region eight sublittoral hard substrate communities occur. These communities were stationary in time during the years 1987–1989. The major governing parameters are the available amount of daylight and the degree of exposure to water movement. In the photic zone, three communities are met with, one of which is widespread and appears to be independent of the exposure to water movement. Under exposed conditions, at the lower border of the photic zone, a second community is observed. A third community is established on erosive muschelkalk substrates. In the aphotic zone also, three communities are found. The distribution of these communities is related to the rate of water movement. One community is divided into three variants, with different preferences regarding the angle of inclination and nature of the substrates. In the artificially constructed harbours, where sedimentation exceeds erosion, two different communities have settled. In the community under moderately sheltered conditions many species are found which also occur in the natural photic zone. Under extremely sheltered conditions a group of species has become dominant which is very rare in the Helgoland region outside the quay-walls but which has been described as being characteristic for sheltered localities elsewhere.     

Meal Scheduling Modulation of Circadian Rhythm of Phototactic Behaviour in Cave Dwelling Fish

Phototactic responses of three groups, each of 16 cave fishes, were observed at 4-hr intervals beginning at 0900, following S days of acclimation inside specially designed aquaria. The latter consisted of two parts, a photic zone and an aphotic zone. The first group of fishes were fed ad libitum, while the second and third group of fishes were fed with minced mutton and/or liver delivered in the photic zone between 0700-1100, and in the aphotic zone between 1900-2100. The percentage of fishes present in the photic zone at a given time was used as a measure of their phototactic responses. Single cosinor analysis of these data has revealed, for the first time, a circadian rhythmicity in the phototactic behaviour of a cavernicolous organism. However, imposition of restricted feeding schedules shifted the peak time of the circadian rhythm in phototactic responses. Meal scheduling may thus be an effective synchronizer for this behavioural rhythm.     

Tidal reduction and its effects on intertidal hard-substrate communities in the Oosterschelde estuary

Developments of intertidal hard-substrate communities in the Oosterschelde estuary were examined in perpendicular transects between high-water line and low-water line in the period 1982–1992. Prior to the beginning of the Oosterschelde estuary works a typology of communities was established and an overall survey of the estuary was carried out. The communities contain flora (algae) as well as fauna. Due to asphalting of dikes in 1986, much of the surface of several communities has been destroyed. The originally well developed communities with large species-richness have not returned. The small reduction in tidal amplitude due to the construction of the storm-surge barrier had a minor effect on the zonation of communities. In the upper part of the intertidal zone the boundaries of the communities moved 0.5–1.0 m downward in the transects along the dike-slopes. At an average inclination of 18° this means a vertical shift of about 15–30 cm. This reflects the reduction of the tidal amplitude: the high-water line shifted ca 22 cm downward. In a number of places sedimentation has caused a reduction in the number of smaller seaweed species in the lower eulittoral zone. At monitoring locations presence of the original communities is rather unchanged. Rare species like Pelvetia canaliculata, Actinia equina and Gelidium pusillum have been able to maintain quite successfully.     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

The feeding strategies of Liza ramada (Risso, 1826) in fresh and brackish water in the River Tagus, Portugal

The stomach contents of samples of the mugilid Liza ramada (Risso, 1826), captured at Alcochete (brackish water zone of the Tagus Estuary) differed from those from Vala Nova (freshwater zone of the same estuary).
In the freshwater zone of the estuary the mullet ingested preferentially planktonic micro-algae, while in the brackish water they ate benthic micro-algae.
The stomach contents from Vala Nova showed a higher diversity of food items, compared with those from Alcochete. At Alcochete the Naviculales (numerical frequency, 82%) was the most representative order, while at Vala Nova it was the Coscinodiscales (61%) and the Chlorococcales (16%).
In fresh water, the stomach contents contained about 25–4% organic matter, while at Alcochete only 8.7% was found.
In the brackish water zone the ingestion rhythm was related to the tidal cycle, attaining a maximum during the high tide and a minimum at low tide.
At Vala Nova the mullet ate regularly throughout the day. showing a slight increase at dawn and dusk. Apparently, the fish remained inactive by night, at both locations.     

Metabolic shifts in hypersaline microbial mats upon addition of organic substrates

The responses of hypersaline microbial mats to the addition of acetate, glycolate or glucose were investigated using oxygen, pH and sulphide microsensors. Changes in community structure were investigated with molecular techniques. Acetate addition inhibited respiration in the photic zone, stimulated respiration in the aphotic zone and had no effect on gross photosynthesis. Glycolate addition strongly increased both respiration and gross photosynthesis in the photic zone. Thus, glycolate and acetate were probably consumed in those regions of the mat where these substrates are usually formed. Moreover, photosynthesis was only stimulated by increased respiration and concomitant CO2 production in the photic zone which indicates that the photosynthetic and respiratory populations must be present in close proximity to each other. Glucose addition had an unexpected negative effect on the microbial population, strongly inhibiting both respiration and gross photosynthesis within hours. After four days, oxygen profiles in the light were equal to those measured in the dark. After replacing the water phase with unamended water, photosynthesis and respiration recovered within a week. None of the physiological changes were accompanied by detectable shifts in the cyanobacterial or the overall microbial community. The mechanism of inhibition of photosynthesis by glucose requires further investigation.     

Distribution of particulate amino acids in the Bransfield Strait

Summary The depth distribution and composition of residual amino acids was determined in December 1980 in the Bransfield Strait. The major components were aspartic and glutamic acids together with alanine, glycine and serine. Non-protein amino acids were not found in significant amounts. On the average, the amino acids accounted for 25% of the total organic carbon and 50% of the organic nitrogen. Amino acid nitrogen/chlorophyll ratios indicated that in most euphotic zone samples phytoplankton in good physiological condition was present whereas heavily degraded material was found in deeper water layers. Statistical treatment and cluster analysis show distinct differences between euphotic and aphotic zone samples which could be used to characterize phytoplankton communities.     

Does microbial biomass affect pelagic ecosystem efficiency? An experimental study

Bacteria and other microorganisms in the pelagic zone participate in the recycling of organic matter and nutrients within the water column. The microbial loop is thought to enhance ecosystem efficiency through rapid recycling and reduced sinking rates, thus reducing the loss of nutrients contained in organisms remaining within the photic zone. We conducted experiments with lake communities in 5400-liter mesocosms, and measured the flux of materials and nutrients out of the water column. A factorial design manipulated 8 nutrient treatments: 4 phosphorus levels × 2 nitrogen levels. Total sedimentation rates were greatest in high-N mesocosms; within N-surplus communities, 1 µM P resulted in 50% increase in total particulate losses. P additions without added N had small effects on nutrient losses from the photic zone; +2 µM P tanks received 334 mg P per tank, yet after 14 days lost only 69 mg more particulate-P than did control communities. Nutrient treatments resulted in marked differences in phytoplankton biomass (twofold N effect, fivefold P effect in +N mesocosms only), bacterioplankton densities (twofold N-effect, twofold P effects in -N and +N mesocosms), and the relative importance of autotrophic picoplankton (maximum in high NY mesocosms). Multiple regression analysis found that of 8 plankton and water chemistry variables, the ratio of autotrophic picoplankton to total phytoplankton (measured as chlorophyll ) explained the largest portion of the total variation in sedimentation loss rates (65% of P-flux, 57% of N-flux, 26% of total flux). In each case, systems with greater relative importance of autotrophic picoplankton had significantly reduced loss rates. In contrast, greater numbers of planktonic bacteria were associated with increased sedimentation rates and lower system efficiency. We suggest that different microbial components may have contrasting effects on the presumed enhanced efficiency provided by the microbial loop.Correspondence to: J. D. Wehr.     

Influence of changes in salinity and light intensity on growth of phytoplankton communities from the Schelde river and estuary (Belgium/The Netherlands)

In the Schelde continuum, a succession in the phytoplankton community is observed along the transition from the river to the freshwater tidal reaches of the estuary and from the freshwater to brackish reaches of the estuary. The goal of this study was to experimentally evaluate the contribution of changes in salinity and light climate to this succession. In summer 2000 and in spring 2001, phytoplankton communities from the river, the freshwater tidal reaches and the brackish reaches of the estuary were incubated under high or low light intensities and exposed to a change in salinity. HPLC analysis was used to evaluate the response of different algal groups to changes in light intensity and salinity. When incubated at a light intensity corresponding to the mean underwater light intensity of the freshwater tidal reaches, growth of phytoplankton from the river as well as from freshwater tidal reaches was significantly lower than when incubated at a light intensity corresponding to the mean underwater light intensity of the river. The phytoplankton community from the freshwater tidal reaches did not appear to be better adapted to low light intensities than the phytoplankton community from the river. Although diatoms were expected to be less sensitive to a reduction in light intensity than green algae, the opposite response was observed. Freshwater and brackish water phytoplankton were negatively affected by respectively an increase or decrease in salinity. However, the effect of salinity was not strong enough to explain the disappearance of freshwater and brackish water phytoplankton between a salinity of 0.5 and 10 psu, suggesting that other factors also play a role. In the freshwater phytoplankton communities from the river and the freshwater tidal reaches, green algae and diatoms responded in a similar way to an increase in salinity. In the brackish water phytoplankton community, fucoxanthin displayed a different response to salinity than lutein and chlorophyll a.     

Circadian Variation in Phototactic Behaviour of Walking Indian Catfish, Clarias batrachus

Temporal organization in phototactic rhythm in male Clarias batrachus was studied in a choice chamber consisting of a photic zone and an aphotic zone. Results indicate that most of the fishes exhibited a statistically significant 24-h variation in the frequency of visits to the photic zone with a peak frequency at late night or early morning. Cosinor analysis of phototactic index (PI) values also yielded comparable results. This behaviour of C. batrachus shows similarity with its other activities, like air gulping, surfacing, foraging or predation that occur chiefly at night. The light intensity at the surface of a natural water body is more than at the bottom, even at night. Therefore, the peak phototactic activity observed in C. batrachus in the night or early morning could be attributed to its daily migration from the bottom to the surface of the water bodies. The results of the present study might be useful in aquaculture practice and inland fishing.     

Phytoplankton growth rates in the freshwater tidal reaches of the Schelde estuary (Belgium) estimated using a simple light-limited primary production model

During the course of 1996, phytoplankton was monitored in the turbid, freshwater tidal reaches of the Schelde estuary. Using a simple light-limited primary production model, phytoplankton growth rates were estimated to evaluate whether phytoplankton could attain net positive growth rates and whether growth rates were high enough for a bloom to develop. Two phytoplankton blooms were observed in the freshwater tidal reaches. The first bloom occurred in March and was mainly situated in the most upstream reaches of the freshwater tidal zone, suggesting that it was imported from the tributary river Schelde. The second bloom occurred in July and August. This summer bloom was situated more downstream in the freshwater tidal reaches and appeared to have developed within the estuary. A comparison between phytoplankton growth rates estimated using a simple primary production model and flushing rate of the water indicated that no net increase in phytoplankton biomass was possible in March while phytoplankton could theoretically increase its biomass by 20% per day during summer. Chlorophyllaconcentrations at all times decreased strongly at salinities between 5–10 psu. This decline was ascribed to a combination of salinity stress and light limitation. Phytoplankton biomass and estimated annual net production were much higher in the freshwater tidal zone compared to the brackish reaches of the estuary (salinity > 10 psu) despite mixing depth to euphotic depth ratios being similar. Possible reasons for this high production include high nutrient concentrations, low zooplankton grazing pressure and import of phytoplankton blooms from the tributary rivers.     

Astronomically controlled deep-sea life in the Late Cretaceous reconstructed from ultra-high-resolution inoceramid shell archives

The periodicity of the mutual position of celestial bodies in the Earth-Moon-Sun system is crucial to the functioning of life on Earth. Biological rhythms affect most of the processes inside organisms, and some can be recorded in skeletal remains, allowing one to reconstruct the cycles that occur in nature deep in time. In the present study, we have used ultra-high-resolution elemental ratio scans of Mg/Ca, Sr/Ca and Mn/Ca from the fossil, ca. 70 Ma old inoceramid bivalve Inoceramus (Platyceramus) salisburgensis from deep aphotic water and identified a clear regularity of repetition of the geochemical signal every of ~0.006 mm. We estimate that the shell accretion rate is on average ~0.4 cm of shell thickness per lunar year. Visible light–dark lamination, interpreted as a seasonal signal corresponding to the semilunar-related cycle, gives a rough shell age estimate and growth rate for this large bivalve species supported by a dual feeding strategy. We recognize a biological clock that follows either a semilunar (model A) or a tidal (model B) cycle. This cycle of tidal dominance seems to fit better considering the biological behaviour of I. (P.) salisburgensis, including the estimated age and growth rate of the studied specimens. We interpret that the major control in such deep-sea environment, well below the photic zone and storm wave base, was due to barotropic tidal forces, thus changing the water pressure.     

Microbial diversity of an anoxic zone of a hydroelectric power station reservoir in Brazilian Amazonia

Microbial diversity was evaluated in an anoxic zone of Tucuruí Hydroelectric Power Station reservoir in Brazilian Amazonia using a culture-independent approach by amplifying and sequencing fragments of the 16S rRNA gene using metagenomic DNA as a template. Samples obtained from the photic, aphotic (40 m) and sediment (60 m) layers were used to construct six 16S rDNA libraries containing a total of 1,152 clones. The sediment, aphotic and photic layers presented 64, 33 and 35 unique archaeal operational taxonomic units (OTUs). The estimated richness of these layers was evaluated to be 153, 106 and 79 archaeal OTUs, respectively, using the abundance-based coverage estimator (ACE) and 114, 83 and 77 OTUs using the Chao1 estimator. For bacterial sequences, 114, 69 and 57 OTUs were found in the sediment, aphotic and photic layers, which presented estimated richnesses of 1,414, 522 and 197 OTUs (ACE) and 1,059, 1,014 and 148 OTUs (Chao1), respectively. Phylogenetic analyses of the sequences obtained revealed a high richness of microorganisms which participate in the carbon cycle, namely, methanogenic archaea and methanotrophic proteobacteria. Most sequences obtained belong to non-culturable prokaryotes. The present study offers the first glimpse of the huge microbial diversity of an anoxic area of a man-made lacustrine environment in the tropics.     

Quantitative Importance,Composition, and Seasonal Dynamics of Protozoan Communities in Polyhaline versus Freshwater Intertidal Sediments

The quantitative importance and composition of protozoan communities was investigated in sandy and silty intertidal sediments of a polyhaline and a freshwater site in the Schelde estuary. Total biomass of the protozoans studied, integrated over the upper 4 cm of the sediment, ranged from 41 to 597 mg C m^–2 and was in the same order of magnitude at the polyhaline and the freshwater intertidal site. Nanoheterotrophs were the dominant protozoans, in terms of both abundance and biomass. Ciliate abundances appeared to be largely determined by physical constraints, namely, the amount of interstitial space and hydrodynamic disturbances. It remains unclear which factors control nanoheterotrophic abundances and biomasses, which showed comparatively little seasonal and between-site fluctuations. Salinity differences were clearly reflected in the protozoan community composition. The dominant role of sessile ciliates is a unique feature of sediments in the freshwater tidal reaches, which can be attributed to the dynamic nature of sedimentation and resuspension processes associated with the maximum turbidity zone. Based on biomass ratios and estimated weight-specific metabolic rates, protozoa possibly accounted for ~29 to 96% of the estimated combined metabolic rate of protozoan and metazoan consumers at our sampling stations in late spring/early autumn. The contribution of protozoa to this combined metabolic rate was higher at the sandy than at the silty stations and was mainly accounted for by the nanoheterotrophs. These data emphasize the potential importance of small protozoa in sediments and suggest that protozoa are important components of benthic food webs.     

Depth-stratified functional and taxonomic niche specialization in the ‘core' and ‘flexible' Pacific Ocean Virome

Microbes drive myriad ecosystem processes, and their viruses modulate microbial-driven processes through mortality, horizontal gene transfer, and metabolic reprogramming by viral-encoded auxiliary metabolic genes (AMGs). However, our knowledge of viral roles in the oceans is primarily limited to surface waters. Here we assess the depth distribution of protein clusters (PCs) in the first large-scale quantitative viral metagenomic data set that spans much of the pelagic depth continuum (the Pacific Ocean Virome; POV). This established ‘core'' (180 PCs; one-third new to science) and ‘flexible'' (423K PCs) community gene sets, including niche-defining genes in the latter (385 and 170 PCs are exclusive and core to the photic and aphotic zones, respectively). Taxonomic annotation suggested that tailed phages are ubiquitous, but not abundant (<5% of PCs) and revealed depth-related taxonomic patterns. Functional annotation, coupled with extensive analyses to document non-viral DNA contamination, uncovered 32 new AMGs (9 core, 20 photic and 3 aphotic) that introduce ways in which viruses manipulate infected host metabolism, and parallel depth-stratified host adaptations (for example, photic zone genes for iron–sulphur cluster modulation for phage production, and aphotic zone genes for high-pressure deep-sea survival). Finally, significant vertical flux of photic zone viruses to the deep sea was detected, which is critical for interpreting depth-related patterns in nature. Beyond the ecological advances outlined here, this catalog of viral core, flexible and niche-defining genes provides a resource for future investigation into the organization, function and evolution of microbial molecular networks to mechanistically understand and model viral roles in the biosphere.     

Bioerosion along a bathymetric gradient in a cold-temperate setting (Kosterfjord, SW Sweden): an experimental study

In the cold-temperate setting of the Swedish Kosterfjord, a 2-year experiment was launched in order to assess bioerosion rates and to investigate the endolithic borer communities in relation to light availability (relative bathymetry), hydrography and exposure time. The inventory of microendolithic traces, studied by SEM analysis of epoxy resin casts of planted bivalve shells, yields diverse ichnocoenoses comprising a total of 21 traces produced by boring cyanobacteria (7), chlorophytes (4), fungi (6) and traces of uncertain affinity (4). The link between the endoliths (biotaxa) and the traces they leave (ichnotaxa) is evaluated by the study of the boring organisms in situ by transmission light microscopy of planted Iceland spar and bivalve shells. Additionally, the activity of various macroborers (foraminiferans, polychaetes, echinoids, gastropods and sponges) is documented, adding to a distinct diversity maximum at 7 m water depth. A highly condensed photic zonation, due to the high latitude (59°) and eutrophic conditions, is recorded by the measurement of the Photosynthetically Active Radiation (PAR) and is confirmed by the bathymetric range of the photic related ichnocoenoses. At 1 m water depth, a mature shallow euphotic ichnocoenosis dominated by cyanobacteria and at 7 m, a deep euphotic ichnocoenosis dominated by chlorophytes, respectively, is developed after as little as 12 months exposure. With the vanishing light availability from 15 m downwards, the ichnocoenoses development is significantly slowed and only immature dysphotic and aphotic borer communities (dominated by fungi) are encountered. Strong fluctuations of salinity (down to 8%) and temperature (0–20°C) in the euphotic zone indicate most phototrophs present to be considerably euryhaline and eurytherm, while most endolithic fungi appear preferentially in the deeper, more stable marine waters.     

Phytoplankton structure in the White Sea after summer bloom: Spatial variability in relation to hydrophysical conditions

The species composition and phytoplankton biomass, concentrations of chlorophyll “a” (Chl) and nutrients, concurrent hydrophysical conditions were studied in the south part of the White Sea in July 10–15, 2012 during chlorophyll “a” decrease after summer peak. The water column stability varied, the concentration of dissolved silicon in upper mixed layer was closed to the range favorable for diatoms with exception of areas of intensive tide mixing and areas influenced by waters of Severnaya Dvina River. In surface layer the dinoflagellates dominated excepting of areas with intensive tide mixing where diatoms prevailed. Diatoms provided major contribution to biomass in different stations above, in and under pycnocline and in deep waters out of photic zone. Structural analysis has revealed three phytoplankton communities that corresponded to different depths: communities of photic zone, intermediate and deep layers. Extension of layers inhabited by different communities depended on water column stability and on genesis of water masses. Integrated values of phytoplankton biomass and Chl varied from 250 to 1188 mg С/m², and from 22 to 51 mg/m², correspondently.     

促淤等人为扰动对长江口滩涂湿地土壤微生物呼吸的影响

为阐明促淤和堤内农业生产对长江口滩涂湿地土壤微生物呼吸(SMR)的影响,在崇明东滩和九段沙湿地设置3个典型区域,研究了人为扰动和自然状况下湿地SMR的差异性,并通过分析不同类型湿地土壤的微生物活性和环境因子阐明了导致SMR差异的主要原因。结果显示,促淤区现有湿地SMR强度((0.41±0.22)mgCO·2g-·124h-1)高于自然状态区((0.07±0.02)mgCO·2g-·124h-1),且差异达到了极显著水平(P0.01);堤内不同农业生产模式导致的施肥强度差异对堤外湿地SMR也有一定影响。通径分析表明,促淤等人为扰动状态下湿地土壤微生物活性增强是导致其SMR较高的主要原因,其中土壤原核微生物多样性指数及蔗糖酶活性与SMR强度的关联性尤为显著。而促淤与堤内化肥施用所引起的已有滩涂湿地土壤环境条件的改变,特别是土壤含水量下降和无机氮含量增高是导致其微生物活性发生改变的重要原因。总体而言,促淤和堤内高强度施肥的农业生产模式一定程度上会增强堤外现有滩涂湿地的SMR,从而弱化其碳汇功能。     

Modern bryomol-sediments in a cool-water, high-energy setting: the inner shelf off Northern Brittany

Summary The inner shelf off Roscoff/North Brittany, France situated in the Western English Channel, provides a unique facility for studying modern cold water BRYOMOL-carbonate deposits in the North Atlantic. High tidal gauge with extreme strong tidal currents, which effect the well-mixed water column throughout the year, and strong, seasonal storms characterize the conditions of the area. The shelf is seperated in two carbonate production zones: Boulder fields and sand fields. The main production areas are the sand fields with an intensive epifaunal and infaunal colonization by bivalves and the bryozoan thickets ofCellaria spp. and their associated epifauna. The most beneficial and dominant strategies of the sessile benthos are erect flexible and encrusting growth habits. The study area is partitioned in two zones: (1) the coarse sediment blanket typified by active sediment generation and little accumulation, and (2) the shell dune Trezen ar Skoden, characterized by accumulated sediments. Sediment transport and distribution of facies areas are controlled by the strong semidiurnal tidal current regime and episodically severe storms. As a result of these high energy processes of redeposition the autochthonous sediment particles are physically reworked and redeposited while in calmer periods deposition and biological destruction of the components occur. The Holocene development of the sea level has been of crucial influence to the costal morphology and the establishment of different carbonate production centers. The benthic communities produce with their carbonate skeletons the first biogenic sediment and provide substrates for colonization of epi- and endofauna. Changes in the current patterns and the morphology of the sea bottom resulted in the origin of the shell dune Trezen ar Skoden.     

Measurements of import and export in the Krabbenkreek,a tidal area in the Oosterschelde (S.W. Netherlands)

Summary The Krabbenkreek is a tidal area of about 11.5 km², surrounded by dikes for 94%. Mudflats cover nearly 65% of the area and salt marshes cover 15%. The area is connected to the Oosterschelde estuary by a main channel, which allows the tides to reach the inner parts; a small channel draines the mudflats near the mouth directly to the estuary.In a series of 10 measurements the fluxes of material were observed in the two channels by measuring the flow velocities each half hour during two tidal cycles. The water was sampled concurrently. A rough calculation of the data indicated that the resulting masses of soluble and particulate material during a tidal cycle between Krabbenkreek and Oosterschelde are of the same magnitude as the error due to incorrect flow velocity measurements. A more refined calculation is under develoment, which together with checks on the flow measurements will reduce the error.A statistical analysis of the data on the soluble and particulate material gives an indication of the direction of the net flow. In this analysis the chloride is considered a conservative parameter and data of ebb and flood are treated separately. This analysis reveals that ammonia is imported over the year while nitrate is exported. Chlorophyll-a is exported throughout the year as is particulate organic carbon. Silicate is imported throughout the year. There is an import of phosphorus in spring and summer and an export during autumn and winter.