Macroinfauna community structure and biochemical composition of sedimentary organic matter along a gradient of wave exposure in sandy beaches (NW Spain)

Six sandy beaches on the North West coast of Spain, exposed to different wave action, were sampled in order to study the macroinfauna community and the biopolymeric fraction (proteins, lipids and carbohydrates) of sedimentary organic matter. According to McLachlan’s rating system (1980), three of them were classified as sheltered and the other three as exposed beaches. Sampling was carried out during August 2004 at three tidal levels: high, medium and low. Macroinfauna community and organic matter concentrations were found to be significantly different when sheltered and exposed beaches were compared. Macroinfauna diversity (H′), abundances and biomass became increasingly enriched along a gradient from exposed to sheltered beaches. Macroinfauna mean abundance was found higher in sheltered (ranked from 1535 ± 358 to 15062 ± 5771 ind m⁻²) than in exposed beaches (from 150 ± 41 to 5518 ± 1986 ind m⁻²). Macroinfauna biomass ranged from 3.2 to 14.7 g m⁻² and species richness from 25 to 27 in sheltered localities; while in exposed beaches, biomass ranged from 0.2 to 2.3 g m⁻² and the number of species from 5 to 14. The biopolymeric carbon concentration (BPC) was significantly higher in sheltered (from 84.7 ± 44.7 to 163.3 ± 34.8) than in exposed (from 30.3 ± 7.5 to 78.7 ± 12.3) beaches. The low hydrodynamic conditions of sheltered beaches favoured the settlement of organic rich fine sediments, being supported by the higher protein to carbohydrate ratio found in the exposed (from 23.5 ± 0.9 to 32.7 ± 4.4), rather than in the sheltered localities (from 6.2 ± 0.7 to 13.6). Mean macroinfauna abundances were higher at medium and low tidal levels in both sheltered and exposed beaches. Crustacea was found to be the main group inhabiting the upper part of both types of beaches, dominating all tidal levels of exposed sandy beaches. Mollusca and Polychaeta groups were dominant in sheltered beaches at the medium and lower levels. There was a significant negative relationship between the BPC and the beach face slope; thus, BPC decreased as the intertidal slope increased. It seems that exposed sandy beaches are mainly physically controlled, whereas hospitable sheltered beaches let other factors, such as biochemical compounds, enrich the benthic fauna scenery. Electronic Supplementary Material  Supplementary material is available in the online version of this article at and is accessible for authorized users Handling editors: K. Martens     

Composition and distribution of meiofauna,including nematode genera,in two contrasting Arctic beaches

The meiofauna of two tidal beaches, one exposed and one more sheltered, on Bjornoya (Bear Island) was investigated in summer 2000. Both meiofaunal densities and composition seem to be controlled by physical properties of the sediment, which in turn are controlled by exposure. The moderately and poorly sorted sediments in the sheltered beach were more abundant in terms of meiofaunal densities than the well sorted sediments in the exposed beach (254–481 individuals in 10 cm² vs 7–269 individuals in 10 cm², respectively). In total, seven higher meiofaunal taxa were found. Turbellaria were the numerically dominant taxon in the exposed beach. In the sheltered beach, Turbellaria also dominated, followed by Nematoda and Harpacticoida. The vertical distribution of the meiofauna was in accordance with what has been reported from other intertidal beaches. Nematoda were studied in detail and their densities ranged over 0.7–7.7 individuals in 10 cm² in the exposed beach and 2.7–186.0 individuals in 10 cm² in the sheltered beach. Nematodes were identified to genus level and a total of eight nematode genera were found. Sediment community respiration, measured as oxygen consumption, ranged between 2.3 cm³ O₂ m^–2 h^–1 in the exposed beach and 7.3 cm³ O₂ m^–2 h^–1 in the sheltered beach (respectively, the equivalent of 24 mg and 75 mg of organic carbon metabolised per day). Values from the sheltered site are within the range of results registered in much warmer localities.     

Long-term changes of intertidal and subtidal sediment compositions in a tidal basin in the northern Wadden Sea (SE North Sea)

Wadden Sea tidal flats are highly dynamic regarding the spatial distribution and the grain size composition of their sediments. From 2003 to 2006 surface sediments have been surveyed in an intertidal and a subtidal area within the tidal inlet Königshafen (south-eastern North Sea, northern Wadden Sea, island of Sylt) with the goal to gain information on short-term development trends in the grain size composition. The average grain size (Mean) becomes finer in the sheltered part of the intertidal survey area whereas a coarsening tendency can be observed in the more exposed part of the intertidal and especially in the subtidal survey area. The trend of the most frequent grain size (first Mode) shows the same spatial distribution pattern but is far less distinct. Thus, the changing Mean must be related to an increase in the deposition of fines in the sheltered part of the intertidal Königshafen as well as a general removal of fine-grained material in the exposed intertidal and subtidal Königshafen. In order to see long-term trends the surveys of 2003–2006 were compared to earlier studies conducted in 1932/1933, 1981 and 1989. A significant depletion of mud can be observed in the entire survey area. It is concluded that primarily changed hydrodynamics that may accompany ongoing climate change are responsible for this. However, the loss of fine-grained sediments is additionally amplified by a reduced vegetation cover and coastal protection measures.     

The maintenance of shore-level size gradients in an intertidal snail (Littorina sitkana)

Summary The size of many intertidal animals varies with tidal height. These size gradients could be produced by growth or survival varying with tidal height, or by animals moving to a preferred tidal level. The body size of the snail, Littorina sitkana, increases steadily with tidal height in rocky high intertidal habitats of British Columbia. To determine how size gradients were maintained in L. sitkana, I quantified how growth, survival, and snail movement varied with tidal height. I studied populations of L. sitkana found on sheltered pebble beach and exposed basaltic shelf habitats. Mark-recapture studies and experimental transplants showed that growth could not have produced the size gradients because snail growth rates in both habitats were as fast or faster at low tidal levels (where the snails were the smallest) than at high tidal levels. However, survival rates were lowest at low tidal levels. On pebble beaches, this was due to size selective predation on large snails by the pile perch, Rhacochilus vacca. On basaltic shelves, heavy wave action at low tidal levels may have caused the poor survival rates. Transplanted snails moved homeward on pebble beaches, but not on basaltic shelves. Reduced survival rates at low tidal levels cause size gradients in both habitats, and snail movement helps to maintain size gradients on pebble beaches.     

Intertidal meiofauna of a high-latitude glacial Arctic fjord (Kongsfjorden, Svalbard) with emphasis on the structure of free-living nematode communities

Meiofauna communities of four intertidal sites, two sheltered and two more exposed, in Kongsfjorden (Svalbard) were investigated in summer 2001 at two different tidal levels (i.e. the low-water line and close below the driftline, referred to as mid-water (MW) level). A total of seven meiofaunal higher taxa were recorded with nematodes, oligochaetes and turbellarians being numerically dominant. Mean total meiofaunal densities ranged between 50 ind. 10 cm⁻² and 903 ind. 10 cm⁻². Our data showed a clear decrease in total meiofaunal densities with increasing coarseness of the sediment. Total meiofaunal biomass varied from 0.2 g dwt m⁻² to 2 g dwt m⁻² and, in general, was high even at low meiofaunal densities, i.e. larger interstitial spaces in coarser sediments supported larger meiofauna, especially turbellarians. The results on the vertical distribution of meiofauna contrasted sharply with typical meiobenthic depth profiles on other beaches, probably in response to ice-scouring and concomitant salinity fluctuations. Oligochaetes were the most abundant taxon, with a peak density of 641 ind. 10 cm⁻² at Breoyane Island. They were mainly comprised of juvenile Enchytraeidae, which prohibited identification to species/genus level. Nematode densities ranged between 4 ind. 10 cm⁻² and 327 ind. 10 cm⁻². Nematodes were identified up to genus level and assigned to trophic guilds. In total, 28 nematode genera were identified. Oncholaimus and Theristus were the most abundant genera. The composition of the nematode community and a dominance of predators and deposit feeders were in agreement with results from other arctic and temperate beaches. Nematode genus diversity was higher at the more sheltered beaches than at the more exposed ones. Low-water level stations also tended to harbour a more diverse nematode communities than stations at the MW level. Differences in nematode community structure between low- and MW stations of single beaches were more pronounced than community differences between different beaches and were mainly related to resources quality and availability.     

Composition of organic matter in sediments facing a river estuary (Tyrrhenian Sea): relationships with bacteria and microphytobenthic biomass

The relationships between the biochemical composition of sediment organic matter and bacteria and microphytobenthic biomass distribution, were investigated along the coast of Northern Tuscany (Tyrrhenian Sea). Organic matter appeared to be of highly refractory composition. Among the three main biochemical classes, proteins were the major component (0.96 mg g^-1 sediment d.w.) followed by total carbohydrates (0.81 mg g^-1 sediment d.w.) and lipids (8.1 µg g^-1 sediment d.w.). Bacterial number in surface sediments (0–2 cm) ranged from 1.7 to 24.5 × 10⁸ cells g^-1 of sediment dry weight showing a strong decrease with sediment depth. In surface sediments, significant correlations were found between bacterial biomass and protein concentration. Bacterial activity (measured by the frequency of dividing cells) was significantly related to lipid concentration. Bacterial and microphytobenthic biomass accounted for 3.1 and 18.1% respectively of the sediment organic carbon. In surface sediments bacterial lipids accounted, on average, for 27 % of total lipids, whereas bacterial proteins and carbohydrates accounted for 2.5 and 0.5% of total proteins and carbohydrates, respectively.The benthic degradation process indicated that lipids were a highly degradable compound (about 35% in the top 10 cm). Carbohydrate decreased for 25.6% in the top 10 cm, whereas proteins increased with depth, thus indicating that this compound may resist to diagenetic decomposition.These data suggest that specific organic compounds need to be measured rather than bulk carbon and nitrogen measurements in order to relate microbial biomass to the quality of organic matter.     

Sediment-benthos relationships as a tool to assist in conservation practices in a coastal lagoon subjected to sediment change

This study explores the relation between sediment composition and intertidal macrobenthos populations in the Zwin nature reserve (Belgium and The Netherlands), a tidal lagoon that is included in the Ramsar list of wetlands of international importance and has been designated as Natura 2000 area, among others due to its function as wintering habitat for shorebirds that feed upon macrobenthic invertebrates. Species response models show highest biomass of these prey species in organically enriched cohesive sediments and a distinct decline in probability of occurrence for most species in coarse sediments. Further, the biomass of macrobenthos declined between 2003 and 2010 in the extensive low intertidal inlet channel concurrent with the coarsening of the sediment over time in this hydrodynamically stressed habitat. In contrast, macrobenthos biomass increased in a sheltered shallow intertidal habitat that acted as a catchment area for finer sediments, therefore facilitating the succession towards a higher elevated habitat with salt marsh vegetation establishment. Hence, spatio-temporal sediment dynamics decreased site quality for intertidal predators due to a reduction in feeding areas over time, and a change in physical sediment properties that alter the macrobenthos species occurrence and population biomass. This study thus illustrates that sediment transport dynamics may affect the functioning of coastal shallow soft-sediment habitats, like coastal lagoons. The presented macrobenthos species response models provide a tool to assist in management actions that enable the conservation of cohesive low intertidal habitats that provide a high food supply to shorebirds, fish and macrocrustaceans.     

Microphytic standing stocks at Kerguelen Islands (Subantarctic,Indian Ocean), annual variations in relation to environmental factors: II,intertidal and subtidal microphytobenthos

The microphytobenthic standing crop in marine coastal sediments from Kerguelen main island (from surface to 8 cm deep) varied in relation to the tidal position, grain size, and shelter of sediments. A time-series analysis was performed at three distinct sites: a sheltered fjord (PRAY), a moderately exposed embayment (PAF) and a deep fjord with higher open-ocean influence (PN). Temporal variations on all studied parameters were observed on intertidal, as well as on subtidal sediments, but with a great range in variations and pattern. Compared to phytoplankton blooms at the same location and stations, the microphytobenthos productive periods were not so marked, especially on intertidal sediments. Nevertheless, high productivity periods were in most cases linked to austral spring and summer (up to 30–50 g Chl a g^–1 dw, in intertidal sheltered sands; >170 g Chl a g^–1 dw, in sheltered subtidal muds). On subtidal muddy sites, the high phaeopigments concentrations (up to 195 g Phaeo a g^–1 dw at PRAY site) were attributed to kelp and epiphyte degradation and sedimentation, and also to macrofauna trophic influence, whereas at Portes-Noires fjord (PN) a Phaeophytine a late spring increase in 1991 was suspected to be of plankton origin. The PN site exhibited a lower productivity than at the other two sites, regardless of the tidal position of the sediment, due to a delayed annual cycle in surficial temperature and standing crop. Compared to the phytoplankton blooms, the microphytobenthos productivity at Kerguelen main island was less restricted in time and may occur throughout the year, not just to the benefit of the benthos food-chain, but also to the pelagic one via resuspension, as well as to filter feeders (i.e. mussels).     

Oxygen profiles in intertidal sediments of Ria Formosa (S. Portugal)

Microelectrode oxygen profiles were measured in intertidal sediments from Ria Formosa (S. Portugal), a very productive shallow coastal lagoon. Four intertidal sampling sites were selected according to different sediment characteristics. Individual profiles revealed a high degree of lateral variability on a centimeter spatial scale. Nevertheless, consistent differences were observed between oxygen profiles measured in atmosphere-exposed and inundated intertidal sediments: in organically poor sand oxygen-penetration depth varied from 3 mm in inundated cores to more than 7 mm in exposed ones, while in organically rich muddy sand and mud it remained between 0.5–2.0 mm. The oxygen input from inundated to exposed conditions was estimated for each sampling site. Semi-diurnal tidal fluctuation, leading to periodical atmospheric exposure of sediments plays a major role in the oxygenation process of intertidal zones of Ria Formosa.     

Dissolved and particulate organic matter in contrasting Zostera marina (eelgrass) sediments

The influence of seagrass Zostera marina on sediment characteristics was examined in two contrasting sediments, one organic-rich and one organic-poor. The presence of plants leads to reduced sediment redox potential in both sediment types compared to bare sediment with the largest effects in the organic-poor sediment. Z. marina stimulated the sulfate reduction rates in organic-poor sediment with ∼50% and higher pools of dissolved organic carbon (DOC) were found. In contrast, sulfate reduction rates were lower in vegetated compared to bare sites in the organic-rich sediment. Despite a low contribution of dissolved carbohydrate (DCHO) to the DOC pool (<5%), the seagrass vegetation was responsible for an increase of ∼50% in DCHO pools with a peak in the root zone suggesting that Z. marina supplied DCHO to the pore waters. The Z. marina meadows also enhanced the contribution of particulate carbohydrate (PCHO) to sedimentary particulate organic carbon (POC) pools by 6-14% compared to bare sediment. Although the PCHO pools were higher in organic-rich than organic-poor sediments, the analyses of carbohydrate composition revealed that three groups of neutral sugars including glucose, galactose and mannose+xylose were the major compounds of PCHO and contributed with >60% to sedimentary carbohydrate pools at both sites. Only glucose showed depletion with depth in the vegetated sediments, whereas the percentage of ribose and rhamnose increased indicating a selective degradation of labile carbohydrates in the meadows. Galactose and mannose+xylose appeared to represent a refractory part of carbohydrate that remained after degradation of the more labile components. The sugar content was rather constant with depth at the bare organic-rich sediment indicating that only recalcitrant carbohydrate pools were buried. There was less difference in the PCHO composition profiles between vegetated and bare organic-poor sediments.     

Distribution of Exopolymeric Substances in the Littoral Sediments of an Oligotrophic Lake

Bacteria and algae release exopolymeric substances (EPS) that perform a wide range of important functions in aquatic and terrestrial systems. In this study we measured EPS in sediments at nine littoral sites around a shallow oligotrophic basin, and tested whether the concentration and composition of EPS was related to sediment characteristics. The concentrations of both loosely bound (colloidal) and tightly bound (capsular) EPS carbohydrates ranged up to ~800 µg glucose equiv. cm^–2 and were well within the range of concentrations reported from marine intertidal flats, where EPS play an important role in stabilizing sediments, affecting nutrient exchanges between sediments and the water column, feeding benthic invertebrates, and sequestering and increasing the transfer of contaminants to food webs. Proteins were an important component of the EPS in these littoral sediments, with protein:carbohydrate ratios of ~0.4. In summer, the concentrations of most EPS fractions were positively related (P < 0.05) to the porewater and organic matter content of the sediments. Capsular EPS concentrations were lower in the fall, with a simultaneous increase in colloidal proteins but not in colloidal carbohydrates. This suggests that the carbohydrates in this colloidal EPS may be more labile than the proteins. Our results suggest that exopolymeric substances could be an important, but neglected, component of littoral sediments in lakes.     

Enumeration and speciation of enterococci found in marine and intertidal sediments and coastal water in southern California

AIMS: To determine the levels and species distribution of enterococci in intertidal and marine sediments and coastal waters at two beaches frequently in violation of bacterial water standards. METHODS AND RESULTS: Faecal indicator bacteria were extracted from sediment and enumerated using membrane filtration. High levels of enterococci were detected in intertidal sediments in a seasonal river and near a storm drain outlet. Low levels were found in marine sediments at 10 m depths and in surf zone sand. Bacterial isolates presumptively identified as Enterococcus on mEI media were speciated. The predominant species found in both water and sediment included Enterococcus faecalis, Enterococcus faecium, Enterococcus hirae, Enterococcus casseliflavus and Enterococcus mundtii. A number of isolates (11-26%) from regulatory water samples presumptively identified as enterococci on mEI media were subsequently identified as species other than Enterococcus. At both study sites, the distribution of species present in water was comparable with those in sediments and the distribution of species was similar in water samples passing and exceeding bacterial indicator standards. CONCLUSIONS: High levels of Enterococcus in intertidal sediments indicate retention and possible regrowth in this environment. SIGNIFICANCE AND IMPACT OF THE STUDY: Resuspension of enterococci that are persistent in sediments may cause beach water quality failures and calls into question the specificity of this indicator for determining recent faecal contamination.     

Estuaries as Filters: The Role of Tidal Marshes in Trace Metal Removal

Flux calculations demonstrate that many estuaries are natural filters for trace metals. Yet, the underlying processes are poorly investigated. In the present study, it was hypothesized that intertidal marshes contribute significantly to the contaminant filter function of estuaries. Trace metal concentrations and sediment characteristics were measured along a transect from the subtidal, over an intertidal flat and marsh to a restored marsh with controlled reduced tide. Metal concentrations in the intertidal and restored marsh were found to be a factor two to five higher than values in the subtidal and intertidal flat sediments. High metal concentrations and high accretion rates indicate a high metal accumulation capacity of the intertidal marshes. Overbank sedimentation in the tidal marshes of the entire estuary was calculated to remove 25% to 50% of the riverine metal influx, even though marshes comprise less than 8% of the total surface of the estuary. In addition, the large-scale implementation of planned tidal marsh restoration projects was estimated to almost double the trace metal storage capacity of the present natural tidal marshes in the estuary.     

The quantitative variability and monosaccharide composition of sediment carbohydrates associated with intertidal diatom assemblages

The extracellular secretions of epipelic diatoms (Bacillariophyceae) axe an important source of carbohydrates on intertidal sediments. For analytical purposes, sediment carbohydrates have been operationally separated into colloidal and bulk fractions that are often assumed to be similar in their chemical properties. However, there has been little investigation into the nature of the two fractions. In this study, carbohydrate fractions were sampledin situ, isolated, purified and biochemically characterised using gas chromatography-mass spectrometry (GC-MS). Both carbohydrate fractions were found to contain similar sugars although in different proportions. Glucose represented more than 80% of the monosaccharides identified in the colloidal carbohydrate fraction while only 37% of monosaccharides present in the bulk carbohydrate fraction. Colloidal carbohydrate concentrations showed short-term variability and were correlated with diatom biomass (as chlorophylla) suggesting the colloidal fraction is labile and may be of recent origin, perhaps representing diatom activity. Concentrations of the bulk carbohydrate fraction did not show significant short-term variation and was therefore more refractory. This combination of biochemical and field data suggested that the bulk and colloidal carbohydrate fractions were chemically and physically different. These findings have relevance to studies of estuarine carbon cycling.Abbreviations LTSEM Low-temperature scanning electron microscopy - GC-MS Gas chromatography-mass spectroscopy - EPS Extracellular polymeric substances     

The primary production of phytoplankton in the restored Maltañski Reservoir in Poland

Patterns in composition, abundance and diversity of the annelid fauna (Polychaeta and Oligochaeta) in 22 sandy beaches in Iceland were explored. The effect of exposure on annelid distribution was studied. A total of 5651 annelids were recorded from 160 core samples. Oligochaetes (chiefly Tubificidae) dominated the annelid assemblage whereas polychaetes represented a minor fraction. Polychaetes were relatively more abundant in exposed than in sheltered beaches, contrary to oligochaetes. Meiofaunal polychaete species were also more abundant in exposed than in sheltered beaches. Southwest beaches seemed more diverse in annelid species than northern ones. Annelid diversity did not differ between sheltered and exposed sites, but higher diversity was attained in fine sands at sheltered areas. Cluster analysis revealed large differences between beaches in the annelid community composition. The general patterns found suggest that beach exposure is a major factor conditioning macro- and meiofaunal polychaete and oligochaete distribution along the Icelandic coast.     

Responses of estuarine intertidal microphytobenthic algal assemblages to enhanced ultraviolet B radiation

As a result of ozone depletion, ground doses of ultraviolet B (UVB) radiation in the mid latitudes of the Northern Hemisphere have increased since the 1980s, and current predictions indicate no possible alleviation until at least post 2020. Mudflats and sandflats are important coastal-zone habitats, and support extensive biofilms of benthic microalgae (microphytobenthos). In intertidal situations, these assemblages are exposed to high levels of UVB radiation during periods of tidal exposure. Exposure of intertidal biofilms dominated by epipelic (mud-inhabiting) diatoms to 0, 0.18 or 0.35 W m⁻² UVB radiation for between 4 and 10 days resulted in no significant decreases in the maximum PSII quantum efficiency (F_v/F_m) throughout diel exposure periods. Although the quantum efficiency of electron transport (F_q′/F_m′) showed significant reductions early in some experiments, the major response was an increase in F_q′/F_m′ in UVB exposed biofilms. This increase in F_q′/F_m′ was suggestive of a protective vertical migration down into the sediment. Single-cell and whole biofilm fluorescence imaging demonstrated, for the first time, that motile diatoms are able to detect UVB radiation independently of UVA or photosynthetically active radiation (PAR) and migrate rapidly down (within 15 min) into the sediments to avoid it. This behavioural acclimation mechanism appears to prevent significant accumulation of UVB induced damage to the algae. UVB exposure had no significant effect of biofilm photosynthesis (measured by ¹⁴C carbon fixation), but did alter organic carbon allocation patterns, with significantly less new carbon allocated to intracellular storage (glucan) and extracellular colloidal carbohydrate fractions. Significant reductions in the sediment standing stocks of chlorophyll a (Chl a), colloidal carbohydrates, extracellular polymeric substances (EPS) were seen after 7 days of UVB exposure. This study showed that marine intertidal benthic diatoms use a behavioural strategy to avoid exposure to UVB and that this response is effective as a short-term protection mechanism against UVB damage. However, altered carbon allocation patterns feed forward over time into changes in biofilm biomass and sediment carbohydrate dynamics. This suggests that continual long-term exposure to UVB may impact on sediment carbon cycling and trophic interactions and on the stabilization of sediments by microalgal biofilms through their production of extracellular carbohydrates.     

Large scale patterns and trophic structure of southern African rocky shores: the roles of geographic variation and wave exposure

In this study we revise the biogeographic delimitation, and large-scale patterns of community structure of the intertidal rocky shores of southern Africa. We use binary (presence/absence) and per-species biomass data collected at fifteen localities and thirty-seven different rocky sites, encompassing the shores of southern Namibia, South Africa and southern Mozambique. Multivariate analyses revealed that the shores of southern Africa (south of 25°) can be divided into three main biogeographic provinces: the west coast or Namaqua province, the south coast or Agulhas province and the east coast or Natal province. The biomass structure of the intertidal rocky shores communities of southern Africa varied at a large scale, corresponding to biogeographic differences, while local-scale variation accorded with the intensity of local wave action. The average biomass of west coast communities was on average significantly greater than that of the south and east provinces. At a local scale, the community biomass on exposed shores was an order of magnitude greater than on sheltered shores, within all biogeographic provinces. Semi-exposed shores exhibited intermediate average biomass. The trophic structure of these communities varied significantly with wave action: autotrophs, filter-feeders and invertebrate predators were more prevalent on wave exposed than sheltered shores, whereas grazers were more abundant on sheltered and semi-exposed shores. Exposed shores were consistently dominated by far fewer species than semi-exposed and sheltered shores, independently of biogeographic differences. Within all biogeographic provinces semi-exposed and sheltered shores were more diverse than exposed shores. West coast intertidal communities therefore had high levels of biomass, but were consistently species-poor. Several working hypotheses that could explain these large and small-scale patterns are presented.     

Sulphate,dissolved organic carbon,nutrients and terminal metabolic products in deep pore waters of an intertidal flat

This study addresses deep pore water chemistry in a permeable intertidal sand flat at the NW German coast. Sulphate, dissolved organic carbon (DOC), nutrients, and several terminal metabolic products were studied down to 5 m sediment depth. By extending the depth domain to several meters, insights into the functioning of deep sandy tidal flats were gained. Despite the dynamic sedimentological conditions in the study area, the general depth profiles obtained in the relatively young intertidal flat sediments of some metres depth are comparable to those determined in deep marine surface sediments. Besides diffusion and lithology which control pore water profiles in most marine surface sediments, biogeochemical processes are influenced by advection in the studied permeable intertidal flat sediments. This is supported by the model setup in which advection has to be implemented to reproduce pore water profiles. Water exchange at the sediment surface and in deeper sediment layers converts these permeable intertidal sediments into a “bio-reactor” where organic matter is recycled, and nutrients and DOC are released. At tidal flat margins, a hydraulic gradient is generated, which leads to water flow towards the creekbank. Deep nutrient-rich pore waters escaping at tidal flat margins during low tide presumably form a source of nutrients for the overlying water column in the study area. Significant correlations between the inorganic products of terminal metabolism (NH₄ ⁺ and PO₄ ³⁻) and sulphate depletion suggest sulphate reduction to be the dominant pathway of anaerobic carbon remineralisation. Pore water concentrations of sulphate, ammonium, and phosphate were used to elucidate the composition of organic matter degraded in the sediment. Calculated C:N and C:P ratios were supported by model results.     

Microbial-Activated Sediment Traps Associated with Oncolite Formation Along a Peritidal Beach,Northern Arabian (Persian) Gulf,Kuwait

Identification of microbial communities within shoreline sediments and sediment precipitates from the Tigris-Euphrates delta (northern Kuwait) were determined by microscopic/nanoscopic studies, and by molecular analysis. Oncolites are syn-diagenetic carbonate precipitates that are surviving in a shallow subtidal to intertidal siliciclastic environment with periodically excessive hydraulic energy, extreme salinity (up to 47 per mil), and high concentrations of organic matter. X-ray diffraction techniques reveal that oncolite cortices are predominantly composed of calcite, quartz, halite and dolomite, associated with minor fractions of clay minerals. Quantitative analysis of the Corey Shape Factor reveals distinct morphological populations but with local overlap. A plot of the Equivalent Diameter vs. Corey Shape Factor provided the best indicator of the morphological relationships within the total oncolite population, indicating a hydrodynamically controlled morphological distribution defining intertidal and subtidal oncolite classes. Direct microscopic examination of the samples indicates that diatoms are the most abundant eukaryotic algae in subtidal sediments and within actively precipitating carbonate cements, especially the genus Navicula. In contrast, filamentous cyanobacteria from the genus Anabaena are most abundant in the intertidal zone sediments. The PCR-DGGE of the 16SrRNA gene of the cyanobacteria shows a higher diversity for this genus of bacteria in all sediment samples and that the cyanobacterial population in the diagenetically precipitating oncolites are closely related to the population found in the subtidal sediments. Dunaliella viridis dominates the culturable algae obtained from the four tidal zones. Our results indicate that a range of microbial populations are actively contributing to the formation of microbially-induced sedimentary structures in the extreme conditions of the southern Tigris-Euphrates delta.     

Macrofauna distribution and bioturbation on tidal confluences of the dutch Wadden Sea

Macrofauna density and bioturbation intensity (measured with X-ray radiography), were studied in the Dutch Wadden Sea near Ameland and in Mok Bay, Texel, in September 1988. The bivalveMacoma balthica and the polychaeteHeteromastus filiformis were widely distributed in the areas studied. The cockleCerastoderma edule and the polychaeteScoloplos armiger did not occur in areas with high clay content, while the molluscsHydrobia ulvae andMya arenaria preferred fine sediments. The polychaeteNereis diversicolor preferred the higher parts of the intertidal. In the Ameland area disturbance of primary sediment structures was highest near the shore and near the middle of the tidal confluence where physical reworking was low. The sheltered Mok Bay sediments were completely reworked by deposit-feeders. Bioturbation intensity and deposit-feeder (bioturbator) density were, however, not highly correlated. A number of stations showed higher bioturbation towards the surface and this may be related to the high abundance of near surface dwelling macrofauna, due to eutrophication and organic enrichment of the sediments in recent years.