Microbial activity profiles in Tagus estuary salt marsh sediments

This study provides some results about microbial activity in salt marsh sediments. Microbial activity was determined by profiling extracellular enzyme activities in three Tagus estuary marshes and in two sediments horizons: surface layer (0–2 cm) and depth (8–10 cm). Five enzymatic activities were examined (β-glucosidase, cellulase, alkaline phosphatase, potential nitrification and nitrate reductase). All extracellular enzymatic activities were highest in the surface layer and decreased with depth. β-glucosidase and alkaline phosphatase prevailed both in surface sediments (1150 and 1200 ηmol h⁻¹ g⁻¹, respectively) and in deeper sediments (150 and 200 ηmol h⁻¹ g⁻¹, respectively). Microbial activities differed significantly between salt marshes. The marsh location in the estuary seemed to contribute to these differences: marshes located in the proximity of urbanised and industrial areas had higher microbial activities.     

The fishes associated with three intertidal salt marsh creeks in a temperate southern African estuary

This study compares the fish assemblages in a range of intertidal salt marsh creeks in the Kariega Estuary, South Africa, as well as highlighting any differences between the ichthyofaunal structure of the creeks and adjacent Zostera bed habitats. The superimposition of environmental variables on the creek biotic groupings (60% similarity level) indicated consistent relationships between both the creek water depth and mouth area with the major creek fish clusters. Water temperature, salinity and turbidity did not display any pattern which could explain the disparity between the ichthyofaunal groupings. The results also indicated that intertidal creeks form a unique littoral habitat within the Kariega Estuary, with ichthyofaunal compositions very different to those found in nearby eelgrass beds. Furthermore, intertidal creeks in the Kariega system appear to be similar to creeks found elsewhere in the world in that their fish assemblages are dominated by 0+ juveniles, have a conspicuous marine transient and estuarine resident component, and very few piscivorous representatives. These results also give weight to the hypothesis that southern African salt marsh creek habitats serve as temporary refuges to juvenile fishes, a role that has also been proposed in other parts of the world.     

Distribution and speciation of phosphorus along a salinity gradient in intertidal marsh sediments

We examined forms of solid phosphorus fractions in intertidal marsh sediments along a salinity (0–22%.) gradient in a river-dominated estuary and in a marine-dominated salt marsh with insignificant freshwater input. Freshwater marsh sediments had the highest ratio of organic N:P of between 28:1 and 47:1 mol:mol, compared to 211 to 311 molmol in the saltmarshes, which is consistent with a trend toward P-limitation of primary production in freshwater and N-limitation in salt marshes. However, total P concentration, 24.7±11.1mol P g dw^–1 (±1 SD) averaged over the upper meter of sediment, was greatest in the freshwater marsh where bioavailablity of P is apparently limited. In the freshwater marsh the greatest fraction of total P (24–51%.) was associated with humic acids, while the importance of humic-P decreased with increasing salinity to 1–23%. in the salt marshes. Inorganic P contributed considerably less to total sediment P in the freshwater marsh (15–40%.) than in the salt marshes (33–85%.). In reduced sediments at all sites, phosphate bound to aluminum oxides and clays was an important inorganic P pool irrespective of salinity. Inorganic P associated with ferric iron [Fe(III)] phases was most abundant in surface sediments of freshwater and brackish marshes, while Ca-bound P dominated inorganic P pools in the salt marshes. Thus, our results showed that particle-bound P in marsh sediments exhibited changes in chemical association along the salinity gradient of an estuarine system, which is a likely consequence of changes in ionic strength and the availability of iron and calcium.     

Environmental and behavioural factors affecting activity in the intertidal gastropod Hydrobia ulvae

Laboratory microcosms were used to investigate the mud snail Hydrobia ulvae (Pennant) bioturbation activities and behavioural changes in response to snail density, algal food, sediment moisture content, light regime and water cover conditions. Density-dependent kinetics of bioturbated muddy areas were described by von Bertalanffy equations, which provided reliable estimates of mud surface covering rates by snail tracks (m² h⁻¹ snail⁻¹). Snails need a wet habitat to be active either covered by seawater or by moving in fluid layers for low-tide conditions. Light and microphytobenthic biomass, which are less potent to affect snail activity, are positively interrelated to increase covering rates in the tested chl a concentrations within the range of 1-15 μg g⁻¹. Experimental results suggested us the relevance of microphytobenthos migration processes in affecting crawling activities of H. ulvae that appeared to adjust their foraging efforts in response to benthic algal biomass. Behavioural processes of H. ulvae, in terms of floating, crawling, burrowing and inactive snails, were described using a Markov model. Finally, an empirical model based on von Bertalanffy equations was proposed to describe kinetics of sediment covering by snail tracks under the influences of snail density, sediment moisture content, chl a concentrations and the four combinations of presence/absence of light and seawater. This model should provide a base for further development of a hydrosedimentary model to simulate the effects of H. ulvae bioturbation activities on the resuspension of the intertidal cohesive sediment-water interface for various in situ conditions.     

Decomposition in salt marsh ecosystems of the S.W. Netherlands: the effects of biotic and abiotic factors

Decomposition rates, determined with the litterbag technique in salt marshes of the S.W. Netherlands during the past decade are compared; the biotic and abiotic factors influencing these rates are identified and discussed.Tissue composition is the main variable affecting decay rates of halophytes, particularly variations in lignin content between plant parts and between species.Experiments in which the loss of the tensile strength of cotton strips was used as an index of cellulolytic decay, show that there is a conspicuous variation in decay rates on different sites in a salt marsh. Nonetheless, the locally varying environmental conditions within salt marshes of the S.W. Netherlands have less impact on the variation in decomposition rates of halophyte litter than the chemical make-up of the plant material.Larger fauna elements (> 300 m) may increase decomposition rates, but this effect is only limited and depends on location and litter type. The role of small fauna elements such as nematodes, which occur abundantly in association with halophyte litter, remains largely unknown.     

Anatomical adaptations and ionic homeostasis in aquatic halophyte Cyperus laevigatus L. Under high salinities

Salinity is extremely hazardous to agriculture worldwide and its expanding constantly. Soil of almost 100 countries facing salinity problem including Pakistan. Cyperus laevigatus also act as salinity indicator species is a naturally adapted halophyte dispersed in subtropical regions of world. Six populations of C. laevigatus were collected from different saline habitats to evaluate adaptations regarding anatomical and physiological characteristics. C. laevigatus is perfectly adapted to harsh environmental conditions like dry barren soils, saline lakes, hyper-saline wetlands and salt marshes. Ecological success of this species is due to plasticity in physiological and anatomical characteristics to adapt variable environmental conditions. C. laevigatus is a halophyte, exhibited increased biomass production in moderately saline habitat. Higher uptake of K⁺ occurs to compensate the uptake of Na⁺ ion contents, a striking feature of salt-tolerant and halophytic species. Accumulation of osmoprotectants like proline, free amino acids, soluble sugar and protein contribute significantly to osmotic adjustment. Stem thickness enhanced as salinity level of habitat increased to store water in parenchymatous tissues under physiological drought. Intensive sclerification in root cortex provide mechanical strength to plant as well as prevent the radial leakage of water. Well-developed aerenchyma, increased vascular bundle area, broader vessels, small and dense stomata are critical to cope with environmental hazards. Population of Jahlar lake showing maximum biomass production indicate that this species grows better in moderate salinities. Therefore, this species will prove very useful for revegetation of salt affected rangeland and prairies by direct growth of such halophytic ecotypes.     

Inconsistency in short-term temporal variability of microgastropods within and between two different intertidal habitats

Small-scale temporal variation in abundances of fauna in marine soft sediments has long been recognised. Many studies on rocky intertidal shores have, however, focused on larger fauna in single habitats and have primarily examined relatively long time-scales. The implications of small-scale variability are frequently not adequately addressed in the studies of changes in fauna over longer time-scales. Without knowledge of the magnitude of variation at smaller scales, comparisons across longer time-scales may be confounded. In this study, the temporal variability of a number of co-existing species of microgastropods in patches of two different intertidal habitats (coralline turf and sediment) in Botany Bay, New South Wales, Australia, was measured using a nested, hierarchical sampling design incorporating temporal scales of weeks, 1 and 3 months. In addition to habitats, there were also spatial scales of metres between plots and 100s of metres between the locations. There was generally a lack of consistency in the trends of variance for the three temporal scales at the smallest spatial scale of plots. In addition, the different species, including those that were closely related, showed different patterns of variation, depending on the habitat and site. These data show the importance of incorporating adequate scales of sampling in different habitats when analysing the distribution and abundance of microbenthos in intertidal habitats.     

Oxidation of elemental-S in coastal-dune sands and soils

Summary S-oxidation was studied in samples of (a) coastal sands lacking vegetation; (b) sands from beneath isolated stands ofAmmophila arenaria andHippophaë rhamnoides; and (c) dune soils obtained from beneath vegetation growing on mature dunes. S-oxidation in samples taken from dune environments was compared with the process in a fertile garden soil.Elemental-S was oxidized to SO ₄ ^2– in all samples, with S₂O ₃ ^2– being formed as intermediates. S-oxidation was most pronounced in the dune soil, followed by the garden soil,Ammophila arenaria andH. rhamnoides rhizospheres and finally the non-vegetated sand. The rate of S-oxidation thus generally increased with increasing C and N content, increasing vegetation cover and decreasing soil-sand pH.Maximum S-oxidation occurred at 30–37°C, but some of the intermediates appeared even at 45°C, presumably indicating abiotic S-oxidation at high temperatures. S-oxidation decreased the pH of the two soils studied, but did not markedly acidify the unvegetated or rhizosphere sands.     

嵊泗海岛不同底质潮间带春秋季大型底栖动物的群落格局

于2006年9月(秋季)和2007年4月(春季)对嵊泗海岛的不同底质潮间带断面设立的8个取样站采集的调查资料,采用ABC曲线方法和大型多元统计分析软件PRIMER5对嵊泗海岛大型底栖动物进行Bray-Curtis相似性聚类分析和非度量MDS标序,研究群落结构格局以及用物种多样性指数、物种均匀度和物种丰富度指数分析潮间带大型底栖动物物种多样性和群落种类组成,并对大型底栖动物的群落结构进行了初步研究。调查获得嵊泗海岛的不同底质潮间带大型底栖动物130种,其中多毛类31种,软体动物57种,节肢动物32种,棘皮动物4种,其它类6种。春、秋季嵊泗潮间带大型底栖动物多样性指数(H′)(F1,13=0.10,P=0.75)、物种丰富度(D)(F1,13=0.66,P=0.43)和均匀度指数(J)(F1,13=0.33,P=0.58)均无显著差异;不同底质嵊泗潮间带大型底栖动物多样性指数(H′)(F1,13=14.28,P<0.01)、物种丰富度(D)(F1,13=14.07,P<0.01)存在显著差异,而均匀度指数(J)(F1,13=1.62,P=0.23)无显著差异。群落结构聚类分析和MDS标序表明,8个取样站的群落可分为3组(Ⅰ、Ⅱ和Ⅲ组)。根据所调查嵊泗海岛潮间带的丰度和生物量资料做的ABC曲线分析表明,底栖动物群落受到了中等程度的污染或者扰动。     

Exchange of Cu and Cd across the sediment-water interface in intertidal mud flats from Ria Formosa (Portugal)

Depth profiles of Fe, Mn, (HS)_t, Cu and Cd concentrations in pore water were determined on a seasonal scale in intertidal sediments of Ria Formosa. Concentrations of Cu and Cd were also determined in near-bottom water during the short period that water inundates the sediment. A maximum near the sediment-water interface was observed in depth profiles of Mn and Fe concentrations followed by a decrease with depth. Otherwise, depth profiles of (HS⁻)_t were irregular but peak concentrations was observed below Mn and Fe maximum. Although subsurface maximum was observed at deeper layers for Cu and Cd, the profiles shape varied among sites and sampling dates. This suggests site specificity and alterations associated with early diagenetic reactions. In order to assess exchanges of Cu and Cd across the sediment water interface, diffusive fluxes and advective transport were estimated. Both contribute substantially to the daily transfer of Cd from intertidal sediments to the water column of Ria Formosa. In the case of Cu, the flux associated with tidal flooding (advective flux) was the major contributor. Presumably, the exchange of trace elements between the sediment-water interface in intertidal areas of macro- and meso-tidal systems are underestimated since do not take into consideration the pulse contribution associated with tidal flooding.     

Sublethal stress in the intertidal zone: tidal emersion inhibits photosynthesis and retards development in embryos of the brown alga Pelvetia fastigiata

The effect of tidal emersion on survivorship, photosynthesis and embryonic development was studied in 8 h old zygotes and 7 d old embryos of the intertidal brown alga Pelvetia fastigiata (J. Ag.) DeToni. Zygotes and embryos were outplanted for single low tides in the intertidal zone on the central coast of California (U.S.A.) during June, 1990. Both zygotes and embryos exhibited close to 100% survival when outplanted beneath the canopy of adult P. fastigiata. Embryos (7 d old) also exhibited high survival when outplanted in a red algal turf, the microhabitat where most successful recruitment occurs. However, zygotes (8 h old) experienced high mortality (65–90%) when outplanted in the turf microhabitat. Embryos and zygotes that survived emersion experienced sub-lethal stress that temporarily impaired light-saturated photosynthesis when plants were reimmersed in seawater. The effects of sub-lethal stress were more pronounced in 8 h old zygotes than 7 d embryos, and more severe in the turf microhabitat than beneath the adult Pelvetia canopy. Zygotes outplanted in the red algal turf did not re-establish net photosynthesis until at least 6 h after re-immersion. Photosynthesis was less inhibited in 8 h old zygotes outplanted beneath the adult Pelvetia canopy, and recovered to control (non-emersed) levels within 3 h of re-immersion. Embryos (7 d old) were able to achieve positive net photosynthesis immediately on re-immersion after emersion in the turf or canopy microhabitats. Emersion also retarded the rate of embryonic development in 8 h old zygotes, delaying the formation of primary rhizoids, which help to attach the plant to the substrate. For example, at 19 h post-fertilization, 75% of control (non-emersed) zygotes had developed rhizoids, compared to 3% and 30% for zygotes outplanted in the turf and canopy microhabitats. The different emersion responses of 8 h old zygotes and 7 d old embryos appeared to be related to their ability to tolerate cellular dehydration. Overall, our data suggest that the effects of sub-lethal stresses may have been underestimated in studies of intertidal ecology.     

Larval and juvenile fishes occurring with flood tides on an intertidal mudflat in the Tama River estuary, central Japan

Intertidal movements of fish larvae and juveniles on a mudflat in the Tama River estuary, central Japan, were investigated by comparing the abundance and sizes of fishes caught in the intertidal zone during flood tides with those in the subtidal zone during low tides. A total of 28465 individuals, belonging to 9 families and 20 species, were collected by small purse seine. Among the abundant species, planktonic larvae and juveniles of gobiids and Konosirus punctatus were more abundant in the intertidal zone at flood tide than the subtidal zone at low tide. Similar occurrence patterns were found in juvenile Plecoglossus altivelis altivelis and Lateolabrax japonicus, having fully developed swimming abilities. In contrast to these species, much higher abundances of epibenthic juveniles of 2 gobiids (Acanthogobius flavimanus and Gymnogobius macrognathos) were found in the subtidal zone at low tide, although they also utilized the intertidal zone at flood tide.     

The effect of wrack composition and diversity on macrofaunal assemblages in intertidal marine sediments

Wrack (dead, washed-up seaweed and seagrass) buried in soft substrata may increase the organic content and alter the physical structure of sediments. These effects may influence the composition and structure of macrofaunal assemblages in the sediment. Such influences can be expected to vary according to the type and amount of wrack as well as the presence of invasive seaweeds in the wrack. In this study, we deliberately buried different amounts of the invasive species Sargassum muticum in isolation or mixed to the native species Ulva sp. and Fucus vesiculosus, in two intertidal sandflats to test some hypotheses about the response of macrofaunal assemblages. We tested whether (1) diversity of detritus (i.e. different mixtures), and (2) the amount of detritus of S. muticum influenced the composition and the relative abundance of macrofaunal assemblages. We also assessed whether the sediment organic carbon and the biomass of benthic microalgae varied depending on the diversity of detritus and the amount of detritus of S. muticum. Finally, we tested if these effects of wrack were consistent across sites. Results indicated that buried wrack affected the composition and structure of macrofaunal assemblages in short-term (i.e. 4 weeks), but there were no differences depending on detritus diversity or the amount of S. muticum. In addition, sediment organic matter and microalgal biomass were not affected by the addition of wrack. They instead varied greatly among small spatial scales (i.e. plots). Wrack composition or abundance of the invasive species S. muticum played thus a small role in shaping the structure of macrofaunal assemblages or the biomass of benthic microalgae in these intertidal sediments, probably because these sediments are frequently affected by various inputs of organic matter and benthic assemblages are already adapted to organically enriched sediments.     

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.     

Spatial heterogeneity recognition in estuarine intertidal benthic macrofaunal communities: influence of sieve mesh-size and sampling depth

Estuarine intertidal soft-bottom macrobenthic infauna of the Tagus estuary was characterised using different mesh size sieves and sediment sampling depth. The study sampled 105 sites using a hand held 0.01 m² corer. The top layer (0–5 cm) was sieved through nested 1.0 and 0.5 mm meshes whereas the bottom layer (5–20 cm) was through a 1 mm mesh. The total survey took 26 taxa of more than 5800 individuals and a total wet weight biomass of over 650 g. The top layer, using both sieves, gathered 23 taxa (92% of the total), more than 5600 specimens (96%) but less than 8 g of biomass (1%) whereas the 1.0 mm sieve retained 21 taxa (91%), more than 1700 specimens (31%) and almost 7 g of biomass (1%). Abundance was dominated by small annelids, of which Streblospio shrubsolii was 68%, whereas biomass was dominated by molluscs, with the bivalve Scrobicularia plana representing 98%. Multivariate analyses showed an abundance pattern where the top layer data was very similar to that obtained with both layers. The bottom layer data were needed to accurately represent the total biomass pattern. The macrofaunal spatial pattern identified with the 0.5 mm sieve data differed from that identified by the 1.0 mm and was essential to discriminate a faunal assemblage located along the upper part of the shore. It was concluded that in order to characterize the macrofauna community structure, based on the presence/absence of taxa, the top layer and a 1.0 mm sieve would be sufficient. An abundance-based characterization requires the top layer and a 0.5 mm sieve whereas a biomass-based characterization requires data for both layers but it is sufficient to use the 1.0 mm sieve. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effects of two parasitoids on the life history and metapopulation structure of the intertidal snail Littoraria filosa in different-sized patches of mangrove forest

We describe differences in life history of the intertidal arboreal snail, Littoraria filosa, among patches of mangroves ranging in size from isolated trees to large stands several square kilometres in area. Recruitment of L. filosa occurred from mid spring (October) to early winter (June), recruits grew rapidly and copulating adults were found during the following September–April. Populations within large patches of forest were annuals; all or most individuals died between October–January (spring–midsummer). In contrast, those in smaller peripheral patches were more likely to survive over the summer but survival differed among patches and years. These differences in life history were caused by a parasitoid fly (genus Sarcophaga) that attacked L. filosa 10 mm and longer and was present in all large patches, but absent from, or rare, in smaller peripheral patches. Experimental introductions to isolated trees confirmed that the fly could kill L. filosa. Another sarcophagid parasitoid that attacked L. filosa from 4 to less than 10 mm long was also found in every patch. The combined effects of these parasitoids appear to determine the metapopulation structure of L. filosa. Most adults in large patches were killed by the larger fly during early summer. Summer recruits were often killed by the smaller fly within a month of settlement and when this happened effective recruitment of L. filosa was reduced to autumn. The planktotrophic larval stage of L. filosa lasts less than 1 month, so the source of autumn recruits to all patches must have been adults that survived the early summer, most of which were in small patches or on isolated trees. Consequently these ”peripheral sources” are likely to be important for persistence of the metapopulation of L. filosa. The results of this study demonstrate that metapopulation structure may be determined by complex interactions and that common models cannot be assumed to apply in all habitats. Received: 15 September 1999 / Accepted: 31 January 2000     

Iron in Oxidative and Reduction Processes in Marine Sands

The iron content and the ratio of bivalent to total iron in the labile acid-soluble fraction of iron were studied in sublittoral sands of Vostok Bay, Sea of Japan. Iron oxidation and reduction rates in sand sediment were measured in the laboratory. Trivalent iron almost always prevailed in the acid-extractable fraction in the natural environment. The most oxidized state of iron occurred in spring and was associated with a low water temperature and a high seawater oxygen content; the most reduced iron was found in fall during periods of low hydrodynamics and low oxygen concentration. In sand, iron is mainly reduced by bacteria; this process is slow and can be inhibited by adding chloroform. Oxidation of iron is mainly a chemical process and cannot be stopped by chloroform. In sand, the content of redox equivalents such as trivalent iron is much greater than in dissolved oxygen of pore water. It is assumed that labile iron in sands acts as a redox buffer, is oxidized by dissolved pore water oxygen at the periods of advective mixing, and is slowly reduced by benthic bacteria during anaerobic conditions.     

Effects of added manganic and ferric oxides on sulfate reduction and sulfide oxidation in intertidal sediments

Abstract Freshly precipitated iron or manganese oxides were added to surface sediments from a salt marsh and from the intertidal region of Lowes Cove, Maine. In the presence of added manganese, sulfate was formed under anoxic conditions, suggesting a manganese dependent sulfide oxidation. Sulfate formation was not observed with iron additions. Sulfate reduction was substantially but not completely inhibited by either metal oxide, even though both were added at levels well in excess though both were added at levels well in excess of natural concentrations. Manganese-catalysed sulfide oxidation was further documented using a combination of radiolabel, metal oxide, and inhibitor additions, Results from this study suggested that losses of radiolabelled sulfide could result in underestimates of gross sulfate reduction rates in the presence of significant manganic oxide concentrations. In addition, manganic oxides may facilitate the anaerobic regeneration of sulfate from sulfides.