Superficial Sediment Layer Research Articles

Response of meiobenthos to migrating ripples in sandy lowland streams

Stream sediments move at low flow forming migrating ripples. These ripples can cover substantial areas where benthic communities experience erosion-resting cycles of sand grains. Sediment surface and interstitial space is colonized by meiobenthos, an assemblage of microscopic invertebrates. Here we describe how sediment migration influences the structure of the meiobenthic community. We sampled migrating and stationary sediment patches in five streams. Sediments in migrating ripple patches were characterized by coarser grain size and higher oxygen concentration, but less organic matter and chlorophyll than stationary patches. Meiobenthos was more abundant in the superficial layer of stationary sediment compared to the underlying layer, whereas comparable abundances were observed in both layers of migrating patches. This suggests that ripple migration enhances the vertical mixing of interstitial communities. Among the environmental drivers measured, meiobenthos community structure was most related to sediment transport regime: Rotatoria were more abundant in migrating patches, whereas Chironomidae, Ceratopogonidae, Copepoda and Hydrachnidia were more abundant in stationary patches. Body-size structure was affected by sediment migration, with fewer larger organisms in migrating ripples. By modifying the distribution of benthic resources and of meiobenthic consumers, ripple migration likely affects energy flow paths through benthic food webs.

The 4GFOR model – Coupling 4G early diagenesis and benthic foraminiferal ecology

The 4GFOR model presented in this paper combines the OMEXDIA model of Soetaert et al. (1996) with four theoretical species of benthic foraminifera. The geochemical part of the model simulates the succession of early diagenetic redox reactions in the superficial sediment layers. The four theoretical foraminiferal species, each representing a group of biological species with comparable microhabitats, differ by their limitations with respect to oxygen and nitrate concentration and their ability to feed on different organic matter types. The foraminiferal model is a transformation model in which different proportions of four types of organic matter with different reactivity are attributed to each of the theoretical species. The model has been manually tuned and tested on a large data set from two stations, at 1000 and 550 m depth, in the Bay of Biscay. The model adequately simulates the vertical distribution of shallow, intermediate and deep infaunal species. The 4GFOR model can be used to test several hypotheses concerning foraminiferal ecology. The model has already allowed us to conclude that it is high unlikely that shallow infaunal taxa feed exclusively on the most labile part of the organic matter flux, since it was unable to reproduce the field observations while using this hypothesis. Another important conclusion based on our preliminary model results is that the absence of deep infaunal taxa close to the sediment surface may be explained by their decreasing competitiveness in well oxygenated environments. In the future, the inversion of the 4GFOR model may yield a powerful paleoceanographic tool, enabling us to reconstruct major limiting environmental factors (oxygen and nitrate concentrations; quantity and quality of the organic flux to the ocean floor) from benthic foraminiferal assemblage data.

Persistent effects of sand extraction on habitats and associated benthic communities in the German Bight

Abstract. Sea-level rise demands for protection measures of endangered coastlines crucial for the local population. At the island of Sylt in the SE North Sea, shoreline erosion is compensated by replenishment with sand dredged from an offshore extraction site. We studied the long-term effects of sand extraction on bathymetry, geomorphology, habitats and benthic fauna. Sand extraction created dredging holes about 1 km in diameter and up to 20 m below the ambient seafloor level. Directly after dredging the superficial sediment layer, inside the pits was dominated by coarse sand and stones. Hydroacoustic surveys revealed only minor changes of bathymetry > 35 years after sand extraction. Obviously, backfill of the dredging pits was very slow, at a rate of a few millimeters per year, presumably resulting from low ambient sediment availability and relatively calm hydrodynamic conditions despite high wave energy during storms. Thus, a complete backfill of the deep extraction sites is likely to take centuries in this area. Hydroacoustic surveys and ground truthing showed that the backfilled material is mainly very fine sand and mud, turning the previously coarse sand surface into a muddy habitat. Accordingly, grab samples revealed significant differences in macrozoobenthos community composition, abundance and species density between recently dredged areas (< 10 years ago), recovery sites (dredging activity > 10 years ago) and undisturbed sites (control sites). Overall, dredging turned the original association of sand-dwelling species into a muddy sediment association. Since re-establishment of disturbed benthic communities depends on previous re-establishment of habitat characteristics, the low sedimentation rates indicate that a return to a pre-dredging habitat type with its former benthic community and habitat characteristics is unlikely. Since coarse sand is virtually immobile in this area, a regeneration towards pre-dredging conditions is also unlikely without human interference (e.g., mitigation measures like depositing coarse material on the seafloor to restore the sessile epifauna).

Characteristics of secondary-ruptured faults in the Aso Caldera triggered by the 2016 Mw 7.0 Kumamoto earthquake

The 16 April 2016 Mw 7.0 Kumamoto earthquake caused prominent fault displacements and crustal deformation, not only around the main rupture faults but also around numerous secondary-ruptured faults. The physics and characteristics of such secondary faulting have not yet been studied in detail. We investigated a set of two secondary faults that appeared at the timing of the Mw 7.0 quake in the Aso Caldera by mainly using synthetic aperture radar interferometry and fault slip modeling. The two faults were found to be associated with surface displacement offsets of several centimeters or more, in the oblique sense of right-lateral and vertical motion. Fault slip inversions found that the slip was dominantly in normal sense with smaller contribution from the right-lateral component. The deeper limit of the slips was estimated to be around 1.3 km, which may coincide with the boundary between the superficial sediment layer and the basement rock. The shallowness of the slip and the difference in the dip angles of the main secondary fault and the Mw 7.0 seismogenic fault suggest separation of the two fault systems, although the fault strike and sense of motions were similar. The amount of slip on the two secondary faults was larger than that expected from the scaling law derived from seismogenic faults, which may indicate the difference in the physics of seismogenic and secondary faultings.

Tracking Mangrove Oil Bioremediation Approaches and Bacterial Diversity at Different Depths in an in situ Mesocosms System.

In this study, oil spills were simulated in field-based mangrove mesocosms to compare the efficiency of bioremediation strategies and to characterize the presence of the alkB, ndo, assA, and bssA genes and the ecological structures of microbial communities in mangrove sediments at two different depths, (D1) 1–10 cm and (D2) 25–35 cm. The results indicated that the hydrocarbon degradation efficiency was higher in superficial sediment layers, although no differences in the hydrocarbon degradation rates or in the abundances of the alkB and ndo genes were detected among the tested bioremediation strategies at this depth. Samples from the deeper layer exhibited higher abundances of the analyzed genes, except for assA and bssA, which were not detected in our samples. For all of the treatments and depths, the most abundant phyla were Proteobacteria, Firmicutes and Bacteroidetes, with Gammaproteobacteria, Flavobacteriales and Clostridiales being the most common classes. The indicator species analysis (ISA) results showed strong distinctions among microbial taxa in response to different treatments and in the two collection depths. Our results indicated a high efficiency of the monitored natural attenuation (MNA) for oil consumption in the tested mangrove sediments, revealing the potential of this strategy for environmental decontamination and suggesting that environmental and ecological factors may select for specific bacterial populations in distinct niches.

Microbial Community Structure and Functionality in the Deep Sea Floor: Evaluating the Causes of Spatial Heterogeneity in a Submarine Canyon System (NW Mediterranean, Spain)

Understanding community assembly and processes driving diversity in deep-sea environments is a major challenge in marine microbial ecology. The deep sea represents the largest ecosystem on Earth, but its remoteness makes the microbial community composition and functionality largely unknown. Moreover, microbial-focused studies comparing different deep-sea habitats like dynamic submarine canyons and slope ecosystems altogether are rare. The present work aims to study the deep-sea seafloor microbial communities (Bacteria and Archaea) of the Blanes Canyon and its adjacent western open slope (NW Mediterranean) at ca. 1500 m deep, in autumn and spring, and along the vertical sediment profile. Microbial assemblages were studied in terms of abundance, diversity (α and β), community structure and functional potential through 16S rRNA tag-sequencing to assess their adaptations to the canyon’s idiosyncrasy. Furthermore, the relationships of microbes with environmental variables and a potential predator (nematodes) were also assessed. We observed overall marked differences between canyon and open slope microbial assemblages, although their phyla composition was similar. Both the dominant and richest phyla showed significant differences in proportion between canyon and slope. Bacterial diversity was higher in the canyon than in the open slope, together with nematode abundances. Microbial assemblages were more heterogeneous and showed a higher temporal variability in the canyon than in the open slope. Microbial abundances along the vertical sediment profile showed high heterogeneity in the canyon while on the slope consistently decreased with depth. Nematode and microbial abundances were correlated in the more stable slope environments, while in the canyon phytodetritics inputs (Chl a and Chl a: phaeo) and organic carbon seem to play a role in controlling microbial diversity and abundance. Grain size was correlated with microbial abundances and explained part of the variability in the community structure. Predicted functional profiles differed per habitat and sediment layer, and specific metabolisms appear to be distinctively enhanced, such as aerobic pathways in the most superficial sediment layers in the canyon. Overall, we observed specific patterns of nutrient inputs, microbial composition, and predicted functionality, which may affect higher trophic levels (i.e, Meiofaunal nematodes). This study highlights the importance of canyon heterogeneity in shaping microbial communities.

A role for a superficial sediment layer in upward nutrient fluxes across the overlying water–sediment interface

A superficial sediment layer (SL) is the top 2–3 mm layer of surface sediment that may contribute to high upward nutrient flux. To study the characteristics and the biogeochemical processes in the superficial layer, the seasonal variation in the total phytopigments (chlorophyll a and pheo-pigments), total organic carbon (TOC), and total nitrogen (TN) of the surface sediments in a shallow coastal area, Shido Bay, were measured, and the influence of the superficial sediment layer on nutrient flux at the sediment–water interface was investigated. TOC and TN content were relatively constant for the SL and subsurface layers (0–1 and 1–2 cm) during the study period. In contrast, total phytopigments content was higher in the SL layer than in the subsurface layers. The results of upward nutrient flux experiments showed higher nutrient release within the whole sediment core (SL remaining) than the SL-less (SL removed) core. Moreover, high nutrient fluxes were observed during the high temperature season, indicating that seasonal variation in nutrient flux was regulated by temperature. Moreover, in the low temperature season, the SL seemed to absorb nutrients, probably because of microphytobenthos photosynthesis that took up the nutrients under the sufficient light penetration to the sea floor.

Distribution of high Zn concentrations in unvegetated and Typha domingensis Pers. vegetated sediments

Fil: Di Luca, Gisela Alfonsina. Universidad Nacional del Litoral. Facultad de Ingenieria Quimica. Laboratorio de Quimica Analitica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Experimental investigation on diffusive contaminant release from permeable sediment layer under unidirectional unsteady flow

The interfacial diffusive contaminant (phosphorus) release from permeable sediment layer into overlying water column under a unidirectional unsteady (periodic) flow condition was experimentally measured and analyzed. The experimental results indicate that the gross diffusive contaminant release rate is substantially enhanced as compared to that under a steady flow condition, and this enhancement trend is much more pronounced in an immediate release stage. The interfacial diffusive contaminant release rate tends to increase with the increasing flow velocity, decreasing period and augmenting amplitude for the case of the unsteady flow. The additional interfacial diffusive contaminant release under the unsteady flow condition may be related to the hydrodynamic response of the diffusive boundary layer to the flow unsteadiness of the overlying water, depending upon not only the periodic thickness variation of the diffusive boundary layer immediately above the sediment-water interface modulated by the temporal flow velocity of the overlying water column but also the intensified turbulent mixing between the overlying water and the pore-water within the superficial sediment layer induced by an alternate acceleration/deceleration fluctuation during each period.

The impact of increased oxygen conditions on metal-contaminated sediments part II: Effects on metal accumulation and toxicity in aquatic invertebrates

The present study evaluated the effect of increasing oxygen concentrations in overlying surface water on the accumulation and toxicity of sediment-bound metals in the aquatic invertebrates Lumbriculus variegatus, Asellus aquaticus and Daphnia magna. A 54 days experiment using three experimental treatments (90% O2 in overlying surface water, 40% O2 and a non-polluted control) was conducted. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured in the superficial sediment layer (0–1 cm). At each time point, accumulated metal levels as well as the available energy stores were measured in L. variegatus and A. aquaticus and each time D. magna was exposed to surface water in a 24 h toxicity test. Additionally metallothionein-like protein (MTLP) induction was quantified in L. variegatus. Oxygen induced changes in sediment AVS resulted in faster accumulation of metals from contaminated sediments in A. aquaticus, while no differences in toxicity in this species were observed. Ag, Cr, As and Co accumulation as well as toxicity in water exposed D. magna were clearly enhanced after 54 days, caused by oxidation of metal-sulfide complexes. Due to their feeding and burrowing behaviour, metal accumulation and toxicity in L. variegatus was not influenced by geochemical characteristics. Nevertheless, a rapid induction of MTLP was observed in both the 90% O2 and the 40% O2 treatment. The present study showed that elevated oxygen concentrations in overlying surface water can directly enhance metal accumulation and toxicity in aquatic invertebrates, however this is highly dependent on the organisms ecology and most dominant metal exposure route (water vs. sediment).

Leaf degradation of Salix humboldtiana Willd. (Salicaceae) and invertebrate colonization in a subtropical lake (Brazil)

AIM: To evaluate leaf degradation and invertebrate colonization of Salix humboldtiana Willd. in a subtropical shallow lake on the coastal plain of Rio Grande do Sul, Brazil; METHODS: Litter bags containing 6.85 g of leaves were incubated in the superficial layer of sediment in the littoral region for 1, 4, 7, 14, 32, 47 and 71 days; RESULTS: After 71 days, a loss of 51% of the initial leaf weight was observed (k = 0.0100 d-1). We estimated that it would take 300 days to lose 95% of the initial weight. A total of 16040 organisms and 35 taxa were identified. Caenidae (25.9%), Oligochaeta (19%), Ostracoda (13.8%), Hydracarina (9.8%), Tanypodinae (9.7%) and Coenagrionidae (7.7%) were the most highly represented taxa. We observed increases in density, richness and diversity of taxa over time, with a stabilizing trend noted in the taxa diversity. Regarding the functional trophic groups (FTGs), gathering-collectors accounted for 57.6% of the community, while predators (25%), scrapers (15.8%), filtering-collectors (0.88%) and shredders (0.73%) were also represented. The diversity and evenness of the FTGs had stabilized by day 14; CONCLUSIONS: S. humboldtiana detritus provides a favorable habitat for a sufficient duration to support a high density and diversity of aquatic invertebrates. The small percentage of shredders indicates the minor influence of the invertebrate community on the rate of detrital degradation. The main contribution of invertebrates to detrital processing comes from the consumption of fine particulate organic matter by gathering-collectors.

Living benthic foraminiferal assemblages along a latitudinal transect at 1000m depth off the Portuguese margin

The relationships between the quantity and biochemical composition of organic matter and the species diversity and community structure of living benthic foraminiferal assemblages have been investigated at four sites on the Portuguese margin (NE Atlantic). All of the sites are located at approximately 1000m depth. Two out of the four sites are located in the Nazaré and Cascais submarine canyons, while the other two are positioned on the adjacent open slope. The composition and vertical distribution in the sediment of the foraminiferal assemblages have been investigated in the topmost 10cm for the >150µm fraction and in the top cm for the 63-150µm size fraction. Foraminiferal abundance and species richness are related to the quantity and biochemical composition of the sedimentary organic matter, as well as to the stability of the sea floor. The open slope stations are characterised by a relatively low quantity and nutritional quality of organic matter. The faunas of the two open slope stations are much poorer than those found in Nazaré canyon. At both stations, there is a succession of shallow, intermediate and deep infaunal species, suggesting a fairly deep oxygen penetration into the sediment. At the northern open slope station, the faunal density is about two times lower than at the southern station, where the fauna is very largely concentrated in the uppermost half cm. This difference coincides with a lower nutritional quality of organic matter at the northern station. The faunas of the two canyons, where the quantity and nutritional quality of bio-available organic matter are higher, are very different. The rich fauna of Nazaré canyon is characterised by a strong dominance of intermediate and deep infaunal species (e.g. Melonis barleeanus and Chilostomella oolina) in superficial sediment layers, suggesting a low bottom-water oxygen concentration and a minimal oxygen penetration into the sediment. InCascais canyon themuch poorer faunas of the superficial sediment layers are characterised by the co-occurrence of shallow, intermediate and deep infaunal taxa, again suggesting a rather limited oxygen penetration into the sediment.We suggest that the relatively low densities in the Cascais canyon could reflect an early stage of ecosystem colonisation after a recent turbidite deposition.

Linking feeding activity and sediment reworking in the deposit-feeding bivalve Abra ovata with image analysis, laser telemetry, and luminophore tracers

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 351:139-150 (2007) - DOI: https://doi.org/10.3354/meps07147 Linking feeding activity and sediment reworking in the deposit-feeding bivalve Abra ovata with image analysis, laser telemetry, and luminophore tracers Olivier Maire1,*, Jean-Claude Duchêne1, Lionel Bigot2, Antoine Grémare1 1Université Pierre et Marie Curie-Paris 6 and CNRS, UMR7621, 66650 Banyuls-sur-Mer, France 2Laboratoire d’Ecologie Marine, ECOMAR, Université de La Réunion, Avenue René Cassin-BP 7151, 97715 Saint Denis Cedex, France *Email: olivier.maire@obs-banyuls.fr ABSTRACT: The quantitative relationship between activity (as detected by the comparison of grey levels in successive images using automated software) and sediment reworking in the deposit-feeding bivalve Abra ovata was investigated based on simultaneous and continuous measurements using laser telemetry, luminophore tracers, and image analysis. Total activity included both feeding (siphoning) and shell and/or foot activity. Sediment reworking was assessed through the measurements of surface sediment handling and vertical sediment mixing during 2 separate experiments. Surface sediment handling correlated positively with surface feeding activity. Shell and/or foot activity induced oscillatory movements of the superficial sediment layer but did not account for true vertical sediment mixing. Conversely, feeding activity induced intense vertical sediment mixing. Quantitative changes in feeding activity and vertical sediment mixing based on a biodiffusion model were positively correlated. These results underscore the importance of considering both the nature and intensity of infaunal activity when parameterizing models of sediment reworking. KEY WORDS: Abra ovata · Sediment reworking · Activity · Micro-topography · Laser telemetry · Luminophores · Biodiffusion · Image analysis Full text in pdf format PreviousNextCite this article as: Maire O, Duchêne J, Bigot L, Grémare A (2007) Linking feeding activity and sediment reworking in the deposit-feeding bivalve Abra ovata with image analysis, laser telemetry, and luminophore tracers. Mar Ecol Prog Ser 351:139-150. https://doi.org/10.3354/meps07147 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 351. Online publication date: December 06, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

The Contribution of Crab Burrow Excavation to Carbon Availability in Surficial Salt-marsh Sediments

Geomorphology, vegetation and tidal fluxes are usually identified as the factors introducing variation in the flushing of particulate organic matter (POM) from tidal marshes to adjacent waters. Such variables may, however, be insufficient to explain export characteristics in marshes inhabited by ecosystem engineers that can alter the quantity and quality of POM on the marsh surface that is subject to tidal flushing. In this study we evaluated the balance between transfer of buried sedimentary organic carbon (C) to the marsh surface due to crab excavation (measured from the mounds of sediment excavated from burrows) and outputs of C from the surface due to sediment deposition within crab burrows (estimated from sediment deposited within PVC burrow mimics), in a Southwestern Atlantic salt marsh supporting dense (approximately 70 ind m−2) populations of the crab Chasmagnathus granulatus. C excavation by crabs was much greater than deposition of C within crab burrow mimics. Per area unit estimates of the balance between these two processes indicated that crabs excavated 5.98 g m−2 d−1 and 4.80 mg m−2 d−1 of total and readily (10 d) labile C, respectively. However, sediments excavated by crabs showed a significantly lower content of both total and readily-labile C than sediment collected in burrow mimics. This indicates that ecosystem engineering by burrowing crabs causes a net decrease in the concentration of C in the superficial sediment layers and, thus, an overall decrease in the amount of C that can be washed out of the marsh by tidal action. Incorporating the in situ activities of ecosystem engineers in models of marsh export should enhance understanding of the function of marshes in estuarine ecosystems.

Effects of Copepods and Chironomids on the Abundance and Vertical Distribution of Nematodes in a Freshwater Sediment

ABSTRACT In the presence of copepods and chironomids the number of nematodes in a laboratory microcosm system was not influenced; however, the vertical distribution patterns in the sediment were influenced by the presence or absence of copepods and chironomids. The relative numbers of nematodes in 0–1 cm versus 1–5 cm sediment layer in copepod and copepod plus chironomid treatments were significantly higher than that for the controls. The vertical distribution of three dominant nematode species (Eumonhystera filiformis, Ethmolaimus pratensis and Tobrilus sp.) showed that the juveniles were more concentrated in the superficial sediment layer, whereas adults burrowed deeper into the sediment. Significant differences for the vertical distribution were found for adults of E. pratensis and for juveniles of E. filiformis and E. pratensis. Analysis of the macro- and meiozoobenthos of Lake Starnberger See indicated that nematode abundances were positively correlated with those of chironomids, oligochaetes, ostracods, and copepods.

Variations of the nutrient concentrations in the sediments of ponds under the slopes of different land use patterns in small red soil watershed

以我国南方丘陵区红壤小流域为研究对象,对不同土地利用方式坡面下的4个水塘底泥中养分含量作了分层比较研究(0-5 cm,5-10 cm,10-15 cm,15-20 cm,20-25 cm,25-30 cm)．结果表明:4个水塘底泥养分含量差异明显,在0-15 cm泥层有机碳、全氮、速效氮和全磷含量以邻近村庄的水塘(简称C塘)底泥最高,其次为板栗园坡下的水塘(简称B塘),水稻田坡面下水塘(简称S塘)和花生地坡面下水塘(简称H塘)最低;在15-30 cm泥层,有机碳和速效氮含量以B塘最高,而全氮和全磷含量则以C塘最高;有效磷含量除C塘0-15 cm底泥外,其余均为痕量．表明土地利用方式对其坡面下水塘底泥养分含量影响明显．各水塘底泥养分随泥层加深均呈递减趋势,其中全氮和速效氮减幅以C塘最大,分别为36．0%和38．7%,有机碳和全磷减幅则以B塘最大,为29．4%和31．9%;各塘底泥养分含量的最大降幅主要在浅层底泥,水塘养分积累加速表明近年来农村面源污染加剧．传统农业耕作方式的改变是农村水体底泥养分含量增加的主要原因之一．;Based on the low hill small red soil watershed in the Ecological Experiment Station of Red Soil of China Academy of Sciences, the variations of nutrient concentrations in the sediments(0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, 20-25 cm, 25-30 cm)of 4 ponds under the slopes of different land use patterns were investigated. The 4 ponds were B pond (locateal in the downside slope of Chinese chestnut land)，C pond (locateal in the vicinity of the village)，H pond (locateal in the downside slope of peanut land) and S pond (locateal in the downside slope of paddy field respectively. The results showed that： The nutrient concentrations in sediment of 4 ponds were differed obviously. The highest concentrations of TOC, TN, AN and TP in 0-15 cm sediment were appeared in C pond, and the lowest were in H pond. In 15-30 cm sediment, the highest concentrations of TOC and AN were found in B pond, while TN and TP were found in C pond. The concentrations of AP of the sediment in 4 ponds were trace except the 0-15 cm sediment in C pond with low level. This suggested that the land use patterns had significant effect on the nutrient concentrations in the sediments of the ponds. The nutrient concentrations of the sediments (0-30 cm) in 4 ponds all decreased from surface to bottom. The TN and AN with the maximal descent were found in C pond, and the TOC and TP were both in B pond. The most descents of nutrient concentrations in sediment in each pond appeared in superficial sediment layers. The accelerations of the nutrient accumulating in sediment indicated that the export of nutrient from each land use pattern had increased in recent years obviously, and one of the main causes of the nutrient enhancement in the sediment was the transform of the traditional agricultural cultivation fashions.

Variation of a benthic heterotrophic bacteria community with different respiratory metabolisms in Coyuca de Benítez coastal lagoon (Guerrero, Mexico)

The fluctuations of the number, biomass and composition of the heterotrophic community were studied daily for two days, according to depth, pH, Eh, O2 and organic carbon concentration within a zone of the canal between the Coyuca de Benitez lagoon (Guerrero, Mexico) and the coastal waters. At the three moments of the day studied (6 am, 2 pm and 10 pm), the oxygen concentrations in the overlying water and in the superficial sediment layer were near air-saturation in the diurnal samplings (582 microM at 6 am and 665 microM at 2 pm), and sub-satured during the night (158 microM). In the sediments, the models of vertical distribution of Eh and organic carbon distributions were very irregular due to the bio-perturbation of the benthic, meio- and macrofauna, whose activity allows the superficial organic carbon to migrate towards sediment deeper layers. Vertical distribution of the different viable bacteria populations seems to be related to the hydrodynamic patterns of the communicating canal and sediments heterogeneity. In the sediment column, the heterotrophic bacteria total number varied from 6.8 to 20.3 x 108 cells cm(-3). The highest heterotrophic bacterial biomass values were encountered during the diurnal samplings (39.2 microgC.l(-1) at 6 am and 34.4 microgC.(l(-1) at 2 pm) and the lowest during the night (9.7 microgC.l(-1). The fluctuations of viable heterotrophic bacteria populations with different respiratory metabolisms (aerobic, microaerophilic and anaerobic) can be explained by the existence of suboxic microniches that appear when particles of sediment are resuspended due to the water circulation and the benthic infauna excavating activity, that allows the supernatant water oxygen to penetrate through its galleries towards deeper sediment zones. The statistical analysis (Multiple lineal regression model r2 > or = 0.5) showed that the on the whole, the hydrological parameters are not influence over the bacterial number and bacterial biomass distribution (r2 < or = 0.5), Nevertheless, the variations of the heterotrophic bacteria community observed in the two days sampling, seem to be governed (with F-values of 0.6 to 0.9) by the irregular flows of bio-available organic material and the sediment porosity.

Population biology and distribution of the tanaid Kalliapseudes schubarti Mañé-Garzon, 1949, in an intertidal flat in southeastern Brazil.

The population biology and the spatial and temporal distribution of Kalliapseudes schubarti Mañé-Garzon, 1949, a common tanaidacean in mud flats and estuaries in southern and southeastern Brazil, was studied in the Araçá region, São Sebastião (SP), Brazil. This species showed a clustered dispersion in the area and the individuals were concentrated in the superficial sediment layer (5 cm). Higher densities of K. schubarti were recorded in areas characterized by moderately sorted fine sediment. Multiple regression analysis revealed a positive influence of the organic matter contents and a negative effect of the silt-clay contents on the abundance of K. schubarti. This species showed a marked temporal variation with very low abundance in winter and fall (March to August). Sexual dimorphism was evidenced with males being larger than females. Ovigerous females were also larger than pre-ovigerous ones. Sex ratio was skewed towards females. Seven cohorts were identified during the sampling period, the estimated longevity was 12 months, and no seasonal oscillation in growth was evidenced. The continuous reproduction, as evidenced by the presence of larval phases (manca II and neutron) and reproductive females throughout the year, and high fecundity among the tanaids associated with fast growth and limited longevity support the case for the opportunistic life strategy suggested for this species in the literature.

Relationship of non-specific commensalism in the colonization of the deep layers of sediment

The macrofauna of samples collected with a box-corer from northern Adriatic Sea muddy bottoms in five survey campaigns from 1985 to 1993 has been analysed separately in sediment strata of varying depth. Samples were collected before, during and after the dumping of large amounts of inert particulate material that covered the seabed and caused an almost total defaunation. After this disturbance the seabed was recolonized by a new community. This new community differed from the original one mainly on account of the abundance of Mysella bidentata, a small bivalve filter or surface deposit-feeder. In the original community M. bidentata was confined to the more superficial sediment layers (0–5 cm) at low population density. In the new community it was very abundant and evenly distributed even in the deep layers (5–20 cm). Analysis of species association performed on data from each of the 54 corer samples collected in the last sampling period, points to a marked association between M. bidentata and Nephtys incisa in deeper sediment layers. Deep layer colonization by Mysella in association with the burrowing polychaete N. incisa suggests a case of commensalism between these two species.

Regulation of b- and a-Glycolytic Activities in the Sediments of a Eutrophic Lake.

Temporal changes in a- and b-glucosidase activities, dissolved organic matter content, and bacterial biomass were studied in the superficial sediment layer of a eutrophic lake during the period of anoxia. The mean a- and b-glucosidase activities were 30.7 +/- 11.0 and 15.1 +/- 6.2 nmol h-1 g-1 of dry sediment, respectively. The specifc b-glucosidase activity seemed to be stimulated by carbohydrates (r = 0.80, P <0.05), whereas the specifc a-glucosidase activity was negatively correlated with the dissolved protein concentration (r = -0.72, P <0.10). To test the effect of organic matter on hydrolytic activities under controlled conditions, changes in specific activities were studied in relation to the concentrations of different types of organic matter: phytoplankton, polymers (proteins, cellobiose, and starch) and monomers (glucose and amino acids). The specifc a- and b-glucosidase activities were strongly induced by their natural substrates (starch and cellobiose, respectively) (P <0.05) and were not inhibited by glucose. Proteins inhibited these activities (P <0.05), whereas supplementation with amino acids had no effect on specifc glycolytic activities.