Ecology of benthic foraminifers in the littoral zone of Iturup Island

The composition and abundance of present-day benthic foraminifers in the littoral zone of Iturup Island are examined. The littoral zone is surveyed on the sides of both the Sea of Okhotsk and the Pacific Ocean. The greatest species diversity and the maximum foraminifer abundance were observed on the bench and at the sites of attachment of seaweeds and aquatic plants on silted sands and on sands with an admixture of coquina, silt, and detritus from the adjacent coast. The minimum diversity and abundance are confined to the mouths of rivers and creeks; over rocky plates, where sediments cannot be retained and there are no attached seaweeds and aquatic plants; and in areas not protected from wind-wave action. It was stated that the foraminifer assemblages on the sides of the Sea of Okhotsk and the Pacific Ocean differ both in their species diversity and in their population density over the littoral zone. A morphological comparison between the species Buccella granulata and B. inusitata from different areas of the Sea of Okhotsk and the Pacific Ocean is presented.     

Seasonal dynamics of the populations of intertidal harpacticoids (Harpacticoida: Copepoda) in the White Sea

In May to October 2001, seasonal variations in the population structure of four species of intertidal harpacticoids—Paraleptastacus kliei, Huntemannia jadensis, Heterolaophonte minuta, and Stenhelia palustris—were studied at three sites in the middle intertidal zone of Chernorechenskaya Bay (White Sea) with different sediment compositions. At different sites, the changes in the harpacticoid abundance, and the times and amplitudes of the peaks were different. The features of the local dynamics of the population are determined both by the intensity of its reproduction at the reproductive habitats and by the intensity of subsequent migrations. A comparison of the data available on the seasonal dynamics of the intertidal harpacticoids at various latitudes allows one to suggest that they are mainly determined by the temperature regime.     

Provenance-related characteristics of beach sediments around the island of Menorca, Balearic Islands (western Mediterranean)

The island of Menorca, one of the Balearic Islands (Spain) located in the western Mediterranean, is characterised by a contrasting geology and landscape with two major geographic domains: (1) a southern region called Migjorn, comprised of Late Miocene calcarenites and limestones, and (2) a northern region known as Tramuntana, which is composed of folded and faulted Palaeozoic, Mesozoic and Tertiary (Oligocene) siliceous and calcareous rocks. Both domains are lined by numerous pocket beaches exhibiting a high variety of surficial sediment assemblages. Grain-size and compositional analyses revealed that cliff erosion and nearshore Posidonia oceanica meadows are the main sources of sediments consisting mostly of medium- to coarse-grained carbonate sands of marine biogenic origin, with variable amounts of terrigenous rock fragments and quartz. Based on distinctly different contributions of bioclastic material, biogenic carbonates and quartz, 320 sediment samples from 64 beaches were grouped into different facies associations dominated by either (1) biogenic sands, (2) biogenic sands with terrigenous contributions or (3) terrigenous sands with quartz. Nevertheless, there is a marked regional variability in sediment texture and composition. Thus, variable mixtures of carbonate and siliciclastic sediments characterise the beaches of the northern region, whereas the beaches of the southern region are composed mostly of carbonate sands of marine biogenic origin. An exception is the central sector of the south coast, which is enriched in quartz sand (~10 %); this can be related to outcrops of quartz-rich basement rock and also to rocks exposed in some northern drainage basins captured by southern streams since the Plio-Quaternary.     

Sediment compositions in offshore southern Taiwan and their relations to the source rocks in modern arc-continent collision zone

Modal analyses of 31 sand samples collected by piston coring document variations in sediment composition along and across the developing collision zone off southern Taiwan and help constrain sediment transport paths and, by inference, of sediment sources. Overall, sand composition from this region is dominated by lithic-fragment populations, with a QtFL average of Qt₂₇F₂₁L₅₂. Three geographic domains are based on morphotectonics and variations in sand composition: (1) South China Sea and the adjacent slope of the accretionary prism; (2) suture zone south of southern Taiwan and north of the Luzon forearc; and (3) the Luzon forearc basin (North Luzon Trough) and immediate adjacent slopes. Sands from the accretionary prism and the suture zone contain subequal amounts of sedimentary and metamorphic lithic fragments (Ls₅₁Lv₅Lm₄₅ and Ls₄₇Lv₅Lm₄₈), respectively, whereas sands from the forearc basin are dominated by volcanic lithic fragments (Ls₂₉Lv₄₉Lm₂₂). In addition, compositions of individual sand beds vary dramatically in the forearc basin. This heterogeneity indicates that sediments from different sources have been deposited sequentially, but do not typically mix during transport and deposition. Similar, but less dramatic, within-core variations occur over the accretionary prism.The major sediment input for the accretionary prism is from western Taiwan and is dominated by sedimentary and low-grade metamorphic lithic fragments. There appears to be a second sediment source, however, from southeastern China. This implies that a significant amount of sediment is the input from China to this region. The major component of sands in the suture zone is derived from Taiwan, but medium-grade metamorphic lithic fragments are rather sparse in these sands, considering the extensive and high-relief exposures of metamorphic rocks on the island of Taiwan. The major source of sands in the forearc basin is the active volcanoes of the Batan islands. Episodically, minor components appear to be fed to the forearc basin from the arcward slope of the accretionary prism, presumably by submarine mass wasting. This observation provides support for the hypothesized olistostromal origin for the Lichi Mélange of eastern Taiwan.     

Les carbonates associés à la macrofaune des sables fins littoraux en Méditerranée nord-occidentale

The carbonates associated with the macrofauna of shallow fine sands have been evaluated at six stations located at five different sites on the French Mediterranean coast. The carbonate content of forty species or zoological groups has been estimated. At each station the mean calcimass has been calculated during a year-long cycle, showing the participation of the different zoological groups, mainly molluscs and echinoderms. The comparison of calcimass and associated biomass shows that CaCO₃/AFDW ratio fluctuates between 1.6 to 19.3. These values are similar to those obtained in some rocky bottom communities. Calcimass values usually largely exceed biomass ones; therefore the carbon linked to carbonates cannot be excluded from the carbon balance including macrofauna, which are usually represented only by biomass organic matter. According to mean longevity of species providing CaCO₃, the annual carbonate production by macrobenthos in Mediterranean fine sands can be roughly estimated as being one third of its calcimass value.     

Recolonization of macrofauna in unpolluted sands placed in a polluted yachting harbour: A field approach using experimental trays

A field experiment using trays was conducted at Ceuta's yachting harbour, North Africa, to study the effect in recolonization of placing trays with unpolluted defaunate sediments (fine and gross sands with low contents of organic matter) inside an enclosed yachting harbour characterized by high percentages of silt and clay and high concentrations of organic matter. Sediment recolonization in the trays was mainly undertaken by the species living naturally at the yachting harbour, which recolonized both uncontaminated gross and fine sand trays (such as the crustaceans Corophium runcicorne, Corophium sextonae and Nebalia bipes, the mollusc Parvicardium exiguum and the polychaete Pseudomalacoceros tridentata). However, other species like the polychaetes Cirriformia tentaculata and Platynereis dumerilii, although also abundant in the yachting harbour, were unable to colonize the trays through transport of larvae and/or adults in the water column. The recolonization was very quick, and after the first month, the values of abundance, species richness, diversity and evenness were similar in the experimental trays and in the reference area (yachting harbour). Although the multivariate analysis showed that the species composition differed between the trays and the reference area, there were no significant differences in recolonization of gross and fine sands, indicating that other factors different from the granulometry are modulating the recolonization patterns.     

Molecular and isotopic compositions of bitumens in Silurian tar sands from the Tarim Basin,NW China: Characterizing biodegradation and hydrocarbon charging in an old composite basin

Biodegradation and oil mixing in Silurian sandstone reservoirs of the Tarim Basin, one of the largest composite basins in China, were investigated by analyzing the molecular characteristics and stable carbon isotopic signatures of low-molecular-weight (LMW) saturated hydrocarbons and high-molecular-weight (HMW) asphaltenes. Detection of 25-norhopanes and 17-nortricyclic terpanes in most Silurian tar sands from the Tabei Uplift in the Tarim Basin suggests a much greater degree of biodegradation here than in the Tazhong Uplift. This explains the relatively more abundant tricyclic terpanes, gammacerane, pregnane and diasteranes in tar sands from the Tabei Uplift than in those from the Tazhong Uplift. Hence, care must be taken when assigning oil source correlations using biomarkers in tar sands because of the biodegradation and mixing of oils derived from multiple sources in such an old composite basin. Asphaltenes in the tar sands seem to be part of the oil charge before biodegradation, depending on the relative anti-biodegradation characteristics of asphaltenes, the similarity in carbon isotopic signatures for asphaltenes and their pyrolysates, and the consistent product distribution for flash pyrolysis and for regular steranes in asphaltene pyrolysates, regardless of whether the tar sands were charged with fresh oil. According to the relative distributions of regular steranes and the relatively abundant 1,2,3,4-tetramethylbenzene significantly enriched in ¹³C, the oil sources for asphaltenes in the tar sands might be related to lower Paleozoic marine source rocks formed in euxinic conditions. Nevertheless, the relatively low abundance of gammacerane and C₂₈ regular steranes observed in asphaltene pyrolysates and residual hydrocarbons, within limited samples investigated in this work, made a direct correlation of oils originally charged into Silurian tar sands with those Cambrian source rocks, reported so far, seem not to be possible. Comparison of carbon isotopic signatures of n-alkanes in asphaltene pyrolysates with those of LMW saturated hydrocarbons is helpful in determining if the abundant n-alkanes in tar sands are derived from fresh oil charges after biodegradation. The limited carbon isotopic data for n-alkanes in LMW saturated hydrocarbons from the tar sands can be used to classify oils charged after biodegradation in the composite basin into four distinct groups.     

Fish assemblages in Tanzanian mangrove creek systems influenced by solar salt farm constructions

Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each haul covering 170 m²) within three locations in each creek, i.e. at the upper, intermediate and lower reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation, whereas there were no differences among the three sites in the undisturbed mangrove creek system. In addition, multivariate analyses showed that the structure of fish assemblages varied between forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across the season, we found no significant differences except for a tendency of a minor increase in fish densities during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops machnata, which were both found in relatively low abundances compared to the undisturbed areas. The conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm developments will decrease fish densities, biomass and species numbers as well as alter the overall fish assemblage composition in the salt farm area but not downstream in the creek.     

Spatial variability of epifaunal communities from artificial habitat: Shipwrecks in the Southern Bight of the North Sea

We investigated the cover, community structure and abiotic environment of nine shipwrecks lying at increasing distance from the Belgian coast. Results indicated that all shipwrecks were strongly dominated by cnidarians in terms of biomass and by amphipods in terms of abundances. Based on their epifaunal composition, three groups of shipwrecks could be determined. Metridium senile dominated a species poor community of the coastal sites. On the same sites, a Tubularia larynx community with a more species-rich assemblage was also developing. The T. larynx community had a lower biomass value (102 g AFDW m⁻²) and significantly lower species richness compared to the other sites. The coastal sites were characterized by periodic salinity decreases, large seasonal temperature fluctuation, high total suspended matter load and reduced current velocity. Channel water masses influence the offshore sites causing a more stable temperature and salinity environment, less turbid waters and high current speed. Tubularia indivisa dominated this community, with an average biomass of 229 g AFDW m⁻². Intermediate sites were also dominated by T. indivisa, but a higher biomass (424 g AFDW m⁻²) was observed. They showed intermediate results for the abiotic parameters and fast current velocities. Hypotheses for the observed variation in community structures are discussed in the light of the abiotic characterization of the shipwrecks.     

Spatial and seasonal variations in the ecological characteristics of the free-living nematode assemblages in a large microtidal estuary

This study has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large southern hemisphere microtidal estuary change spatially and seasonally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at this time and thus when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material (%POM) in the sediment. Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum.     

山东半岛东部海域表层沉积物元素组成及物源指示意义

通过对山东半岛东部海域表层沉积物常量、微量元素、有机碳(TOC)以及碳酸盐(CaCO₃)等指标的分析,研究了该海域表层沉积物元素组成特征及其控制因素,并对物质来源进行了探讨。结果表明,山东半岛东部海域表层沉积物元素的平均组成与上陆壳(UCC)相比Al,K,Na,Mg,Fe,Ca,Cu和Zn等元素,相对较低,而Mn,Co,Ni,Cr以及REE元素含量较高,Si和Ti与UCC的含量相当。研究区砂粒级沉积物轻重稀土分异明显,(La/Yb)_N值与韩国河流的非常相近;其余粒级沉积物LREE分异较弱,标准化曲线与黄河沉积物的具有相似性。研究区沉积物的元素含量主要受控于源岩组成,存在明显的"粒级效应"。除此之外,Fe-Mn氧化物、生物碳酸盐等因素对元素组成产生一定影响。沉积物物源判别结果显示,山东半岛近岸及其东南部沉积物主要来源于黄河,该区域沉积物分布受山东半岛沿岸流及近岸潮流影响。研究区东北部为残留砂,其沉积物元素组成特征与朝鲜半岛和鸭绿江沉积物组成相近,表明研究区东北部砂质区沉积物代末次冰期低海平面时可能由朝鲜半岛或鸭绿江供应。     

Trophic ecology of Mustelus schmitti (Springer, 1939) in a nursery area of northern Patagonia

Mustelus schmitti is an endangered endemic shark of the southwest Atlantic, and an important economical resource in Argentina, Brazil and Uruguay. The objective of this study was to describe the trophic ecology of M. schmitti in Anegada Bay, its feeding strategy and diet composition, along with the possible dietary shifts, due to season, sex, ontogeny and the different geographical features of the bay. Our results show that M. schmitti is a carnivorous opportunistic predator, feeding on a variety of benthic invertebrates. The diet presented seasonal and ontogenetic variations, while no differences in diet composition were observed between sexes or the different sampling sites. This species behave as a generalize feeder, with a wide trophic spectrum and a diverse diet.     

Settling velocity of sediments at high concentrations

New data on the settling velocity of artificial sediments and natural sands at high concentrations are presented. The data are compared with a widely used semiempirical Richardson and Zaki equation (Trans. Inst. Chem. Eng. 32 (1954) 35), which gives an accurate measure of the reduction in velocity as a function of concentration and an experimentally determined empirical power n. Here, a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds. The resulting values for n are compared against values derived from new and existing laboratory data for beach and filter sands. For sands, the appropriate values of n are found to differ significantly from those suggested by Richardson and Zaki for spheres, and are typically larger, corresponding to a greater reduction in settling velocity at high concentrations. For fine and medium sands at concentrations of order 0.4, the hindered settling velocity reduces to about 70% of that expected using values of n derived for spheres. At concentrations of order 0.15, the hindered settling velocity reduces to less than half of the settling velocity in clear water. These reduced settling velocities have important implications for sediment transport modelling close to, and within, sheet flow layers and in the swash zone.     

Profiles of DMSP,algal pigments,nutrients and salinity in pack ice from eastern Antarctica

Concentrations of dimethylsulphoniopropionate (DMSP) were measured in seven pack ice cores from three sites in eastern Antarctica to determine their relation to algal pigments, nutrients (nitrate, silicate and phosphate) and bulk salinity. The algal groups haptophytes, dinoflagellates and diatoms were identified in surface, interior and bottom assemblages in the pack ice cores using the photosynthetic marker pigments 19′-hexanoyloxyfucoxanthin (HEX), peridinin (PER) and fucoxanthin (FUC), respectively. DMSP concentrations were significantly correlated (P<0.01, Pearson) with chlorophyll-a (r=0.58), HEX (r=0.75), PER (r=0.79) and FUC (r=0.63) concentrations. The pool of DMSP within the pack ice (mean 107 nM) was contributed mainly by interior and bottom algal assemblages (mean 94 and 268 nM, respectively), whilst the surface algal assemblages were minor contributors (mean 18 nM). DMSP production and/or accumulation appears to differ between surface, interior and bottom pack ice algal assemblages due to differences in biomass, class composition, and possibly the unique environmental conditions experienced by each assemblage. In pack ice, diatoms appear to be important producers of DMSP, due to their dominance of algal assemblages.     

Accumulation and distribution of biogenic and pollutant hydrocarbons,pcbs and ddt in tissues of western mediterranean fishes

Data on hydrocarbons, PCBs and total DDT in muscle, liver and gonads of Mullas barbatus. Trachurus trachurus, Merluccius merluccius, Engraulis enchrasicholus and Micromesistius poutassou collected along the Catalan Coast (NW Mediterrenean) are reported for the first time. The species and the collection sites—off Barcelona to the north (Palamôs) and to the south (Ehro Delta)—were selected for the assessment of the effects of coastal pollutant sources on commercially valuable organisms.Mullus barbatus reflects the influence of local sources, and is therefore a useful bioindicator for organic pollutants. Despite some scattering of the results, concentrations are in general of the same order of magnitude for juvenile and adult specimens, although the pollutants considered exhibit different biological fates. Hydrocarbons are accumulated primarily in liver, whereas organochlorinated compounds are accumulated in gonads. Liver and muscle contents could reflect acute and chronic pollutants inputs respectively. The accumulation in muscle is more important for aromatic and chlorinated hydrocarbons than for the saturated ones, which are probably metabolized in the liver.     

Structure and seasonality in a Malaysian mudflat community

An assessment of community composition and the functional roles of the dominant species has been carried out in two intertidal areas of Malaysian mudflat dominated by natural populations of the arcid bivalve mollusc Anadara granosa.In addition to A. granosa, organisms of numerical importance are the venerid bivalve Pelecyora trigona, the neogastropod Plicarcularia leptospira, the mesogastropods Stenothyra glabrata and Cerithidea cingulata and the hermit crab Diogenes sp. The mesogastropod Natica maculosa and the neogastropod Thais carinifera may be of some importance to community organization but they are not numerically dominant. Annelids are conspicuous by their absence.The following trophic roles are ascribed to specific members of the community: A. granosa—facultative surface deposit feeder; P. trigona—suspension feeder; P. leptospira—scavenger; C. cingulata—deposit feeder/grazer; S. glabrata—deposit feeder/grazer; N. maculosa—predator; T. carinifera—predator; Diogenes sp.—scavenger/predator. S. glabrata is of particular interest because it appears to fill the niche occupied by mud snails of the genus Hydrobia in temperate mudflat systems.There is evidence of seasonality on the mudflats which points to a spawning of certain forms triggered by the major annual salinity depression at the time of the onset of the north-east monsoon in October/November. Concentrations of benthic chlorophyll a show no obvious signs of a seasonal fluctuation and the seasonality of the primary consumers is not thought to be related to food abundance. However there is some evidence of seasonality of reproduction in N. maculosa which preys on the seasonally reproducing bivalves.     

南海北部莺歌海岭头岬近岸烃类渗漏喷口分布及气体地球化学

Natural hydrocarbon seeps in a marine environment are one of the important contributors to greenhouse gases in the atmosphere,including methane,which is significant to the global carbon cycling and climate change.Four hydrocarbon seep areas,the Lingtou Promontory,the Yinggehai Rivulet mouth,the Yazhou Bay and the Nanshan Promontory,occurring in the Yinggehai Basin delineate a near-shore gas bubble zone.The gas composition and geochemistry of venting bubbles and the spatial distribution of hydrocarbon seeps are surveyed on the near-shore Lingtou Promontory.The gas composition of the venting bubbles is mainly composed of CO_2,CH_4,N_2 and O_2,with minor amounts of non-methane hydrocarbons.The difference in the bubbles' composition is a possible consequence of gas exchange during bubble ascent.The seepage gases from the seafloor are characterized by a high CO_2 content(67.35%) and relatively positive δ~(13)C_(V_PDB) values(-0.49×10~(-3)-0.86×10~(-3)),indicating that the CO_2 is of inorganic origin.The relatively low CH_4 content(23%) and their negative δ~(13)C_(V-PDB) values(-34.43×10~(-3)--37.53×10~(-3)) and high ratios of C_1 content to C_(1-5) one(0.98-0.99)as well point to thermogenic gases.The hydrocarbon seeps on the 3.5 Hz sub-bottom profile display a linear arrangement and are sub-parallel to the No.1 fault,suggesting that the hydrocarbon seeps may be associated with fracture activity or weak zones and that the seepage gases migrate laterally from the central depression of the Yinggehai Basin.     

Tubeworm-associated communities at hydrothermal vents on the Juan de Fuca Ridge,northeast Pacific

Hydrothermal vent communities on a mid-ocean ridge crest can be separated by large distances on separate segments. Heat sources, vent character, fluid chemistry and current patterns may differ markedly. This study examines whether vent community characteristics on three of the four southern segments of the Juan de Fuca Ridge are significantly different. Taxonomic composition and relative abundance of the fauna over 1 mm in size associated with vestimentiferan tubeworm bushes are examined from fifty-one collections. Among nearly 350,000 specimens, 37 taxa are recognized, most to species level. Another 14 taxa are meiofaunal in size classification. Species richness and selected diversity indicators are highest on Axial Volcano while animal density within the bushes does not differ significantly. Cluster analysis does not group collections by location, year of collection or vent temperature; collection substratum—basalt or sulphide—may influence clustering. The architecture of the tubes of tubeworm bushes appears to affect the numbers of species present and the resultant clusters. The tightly interwoven, knotted Ridgeia piscesae tubes found on Axial host twice as many species as tubeworm bushes with a less complex structure. Four species dominate most of the collections: two gastropods (Lepetodrilus fucensis and Depressigyra globulus) and two polychaetes (Paralvinella pandorae and Amphisamytha galapagensis). Other vent species are low in abundance (<1% relative abundance) and patchy in distribution. Four collections with no visible flow had markedly different assemblages representing a transition state from vent assemblages to normal deep-sea fauna. There are differences in community structure among the segments, but the causes for these differences are unclear. Higher diversity on Axial Volcano may be supported by a greater time of sustained venting, a larger venting area, water circulation contained within the caldera, or flow conditions that sponsor growth of more complex habitat.     

Macrobenthic zonation patterns along a morphodynamical continuum of macrotidal,low tide bar/rip and ultra-dissipative sandy beaches

The species composition, densities, biomass and zonation patterns of the macrobenthos of sandy beaches are greatly influenced by the morphodynamics and morphology of the beaches. Macrobenthic zonation patterns along a small-scale morphodynamic gradient, comprising eight Belgian beach sites, were investigated. By taking into account the dimensionless fall velocity (Ω) and the relative tidal range, the beach sites were ordered along the gradient from the ultra-dissipative beach type (UD) to the low tide bar/rip beach type (LTBR). The resulting beach state index varied between 1.8 and 4.2 and the beach profiles were related with the beaches' morphodynamic state.In total 35 macrobenthic species, mainly polychaetes and crustaceans, were encountered, varying between 19 and 23 species per beach site. The species composition was quite similar among beach sites, with Scolelepis squamata being abundant at all eight sites. Furthermore, the macrobenthic distribution patterns were mainly related to elevation at all beach sites. Some remarkable difference in metrics, largely related to the beach morphodynamics and the consequent hydrodynamics, were found. At the hydrodynamically benign and consequently macrobenthos-rich UD beaches, the highest macrobenthic densities and biomass occurred on the upper beach, while at the hydrodynamically harsh and thus macrobenthos-poor LTBR beaches, the maximum densities and biomass occurred lower on the beach. Species, typically occurring on the upper UD beaches, such as Eurydice pulchra, S. squamata, and Bathyporeia sarsi, were restricted to the sub-optimal middle and lower beach zone at LTBR beaches. Only Bathyporeia pilosa was found on the upper beach of both UD and LTBR beaches. The more robust polychaete Ophelia rathkei and the interstitial polychaete Hesionides arenaria were exclusively found in the hydrodynamically harsh conditions of the middle LTBR beach zone.     

Community patterns and temporal variation of picoeukaryotes in response to changes in the Yellow Sea Warm Current

Picoeukaryotes are important members of the surface ocean microbial community with high diversity and significant temporal and spatial variations in community composition. Little is known about the picoeukaryotic biodiversity and community in the Yellow Sea, where hydrologic conditions are very different with the influence of the Yellow Sea Warm Current (YSWC). Using Illumina high throughput sequencing targeting 18S rDNA, we investigated the composition of picoeukaryotes at a permanent monitoring site in the central Yellow Sea from 2011 to 2013. Alveolata, Stramenopiles, and Archaeplastida were the main super groups found. Prasinophytes were dominant in N-YSWC (not influenced by the YSWC) samples whilst YSWC (influenced by the YSWC) samples were dominated by different groups, such as MALV-II (novel marine Alveolata), MAST-3, MAST-4 (novel marine Stramenopiles), and Dictyochophyceae. N-YSWC samples were grouped together in nMDS (non-metric multidimensional scaling) using the Bray–Curtis method. Distances between each two YSWC samples were greater. Based on indicator operational taxonomic unit (OTU) analysis (IOA), indicator species of the YSWC were represented by Pseudochattonella farcimen, Florenciella parvula within the class Dictyochophyceae, and Phaeocystis cordata within the class Prymnesiophyceae. The findings in our study suggest that picoeukaryotic communities in the central Yellow Sea differ temporally in response to changes in the YSWC.