Predator–prey interactions between Dugesia gonocephala and free-living nematodes

1. Three groups of laboratory experiments clarified the role of nematodes as a potential food resource for the triclad Dugesia gonocephala. The first group measured the functional response of adult D. gonocephala feeding on juvenile or adult Caenorhabditis elegans. The feeding rates of D. gonocephala on adult and juvenile C. elegans followed a type II functional response. The maximum number of adult nematodes and juvenile nematodes eaten by a single D. gonocephala individual within 3 h was 94 and 197 nematodes, respectively. 2. A second group of microcosm experiments investigated the effect of D. gonocephala on the density and the vertical distribution of a nematode community in fine sand. The following treatments were performed: (i) microcosms with 400 nematodes and (ii) microcosms with 400 nematodes and one D. gonocephala. After 5 days, nematodes as a group, as well as the dominant species Tobrilus pellucidus and Trischistoma monohystera, showed no significant difference in vertical patterns between the treatments with and without D. gonocephala. 3. The third group of experiments determined whether grain size of the sediment (sand, fine gravel and coarse gravel) altered the ability of D. gonocephala to consume adult C. elegans. Sand and fine gravel reduced the predation effectiveness of D. gonocephala by 100%, whereas the predator consumed nematodes in coarse gravel (19 nematodes within 3 h).     

Laboratory experiments on the infaunal activity of intertidal nematodes

The impact of oxygen on the vertical distribution of an intertidal nematode community was investigated in a manipulation experiment with sediments collected from the Oosterschelde (The Netherlands). The vertical distribution of nematodes was examined in response to sediment inversion in perspex cores with or without the presence of an air-flushed silicone tube introducing oxygen to the bottom sediment layer. Following an incubation of 1 week, peak densities of nematodes were recorded in the deep layers of the sediment in cores with subsurface oxygenation. In contrast, this concentration of nematodes was absent in the cores that lacked bottom oxygenation and the majority of the total assemblage was still located in anoxic sediment layers. This suggests that oxidised sediments with traces of oxygen represent favourable conditions for nematodes and indicates that these nematodes are tolerant to short-term anoxia and burial. Observations on the species level suggest that oxygenation, primarily through its direct impact on geochemical properties of the sediment, may be an important factor governing the subsurface activity of nematodes.     

An experimental test of the effects of inorganic sediment addition on benthic macroinvertebrates of a subtropical stream

Inorganic sediments of terrestrial origin may impact stream macroinvertebrate communities. Although input of terrestrial sediments to streams may occur naturally, human-induced activities in the catchment amplify this input greatly. We used an in-stream experiment to investigate whether short-term additions of terrestrial sediments of two size classes affected stream macroinvertebrates. The experiment was designed in blocks to minimize the influence of flow velocity and other environmental variables. Four treatments were employed: (i) addition of fine sand (0–0.24 mm), (ii) coarse sand (0.25–0.8 mm), (iii) fine+coarse sand, and (iv) control (water only). Macroinvertebrates were sampled immediately after the addition of sediments (or water). The experiment consisted of 20 blocks. We analyzed the response of the macroinvertebrate fauna in terms of abundance and species richness. Since species richness is strongly dependent on number of individuals sampled, we also analyzed rarefied species richness. Community structure was evaluated using a distance-based Manova on presence/absence and abundance data. The addition of coarse and fine+coarse sand reduced the abundance and species richness of macroinvertebrates in relation to the control. The response in terms of rarefied species richness in the treatments did not differ from the control, indicating that reduction in species richness was a sampling artifact resulting from decreased sample abundance. The Manova analyses indicated that coarse-sand addition caused changes in both species composition and community structure. Addition of fine and fine+coarse sand affected only slightly species composition and community structure. We concluded that even short-term input of terrestrial sediments causes impacts on benthic macroinvertebrates, and recommend that land-use management of tropical catchments should employ practices that reduce input of terrestrial sediments to streams. Handling editor: K. Martens     

Responses of intertidal nematodes to short-term anoxic events

We investigated tolerance to, and activity of, nematodes in hypoxic and anoxic/partially sulphidic conditions and their ability for recovery after reoxygenation of anoxic sediment. To this end, sediments from an intertidal flat were incubated under oxic, suboxic and anoxic/partially sulphidic conditions for a 14-day period and the final density of nematodes, as a group, and of the most abundant species were assessed. In one treatment, oxygen was restored after anoxic incubation. The incorporation of ¹³C, originating from labeled algae added on top of the sediment, was taken as an indication of nematode activity.Short-term suboxic and anoxic/partially sulphidic conditions had similar structuring impact on the nematode community, reducing total densities by about one third. Survival in suboxic and anoxic/partially sulphidic conditions was species-specific. Daptonema setosum, D. tenuispiculum and Chromadora macrolaima, dominant in the oxic incubation, disappeared when the oxygen level was reduced. The density of the other dominant species was slightly reduced (Sabatieria pulchra), similar (Terschellingia communis) or even increased in the suboxic and anoxic conditions (Metachromadora vivipara). The activity level of these three species was, however, reduced under oxygen limitation. Our results are discussed in terms of the life-history strategies of these species.     

Wide variation in a tiny space: The microdistribution of meiobenthos in an artificial pond

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Meiobenthic distribution and nematode community structure in five European estuaries

Meiofauna from the intertidal zone of five European estuaries (Ems, Westerschelde, Somme, Gironde, Tagus) was investigated. Samples represented a cross section of various benthic habitats from near-freshwater to marine, from pure silts to fine-sandy bottoms. The meiobenthic community comprised everywhere a fauna strongly dominated by nematodes, with meiobenthic density increasing with increasing salinity. The Ems differed from the other estuaries due to the presence of a well developed community of Copepods, Gastrotrichs, large Ciliates and/or soft-shelled Foraminiferans in some sites. The Westerschelde stood out due to the near-absence of harpacticoid copepods and, as in the Tagus, the lower meiobenthic densities in the marine part of the estuary. For nematode community analysis, we also included data from the Tamar which were obtained from the literature (Warwick &; Gee, 1984). This resulted in the enumeration of 220 species, belonging to 102 genera, each with a characteristic distribution along the salinity, sedimentary and latitudinal gradients. Using the multivariate technique CANOCO, a zonation along these different physicochemical determinants was observed as well although salinity and sediment characteristic (scale of hundreds of meters to kilometers) proved to be more important in explaining community structure than latitudinal differences (scale of hundreds of kilometers). Nematode diversity was nearly entirely determined on the genus level and was positively related to salinity. Deviations from this general trend in the Gironde and the Tamar were attributed to sedimentary characteristics or to low macrobenthic predation. The presence of a typical opportunistic colonizing nematode species Pareurodiplogaster pararmatus in the low-salinity region of the Gironde could indicate (organic?) pollution or disturbance of the intertidal mud-flats.     

Patterns of food and microhabitat resource use by two benthic gobiid fishes

The mechanisms responsible for different patterns of habitat use by two benthic gobiid fishes, Acentrogobius sp. 1 and A. sp. 2, which displayed identical food use but resided in shallow and deep zones of coarse and fine sediments, respectively, in Lake Hamana, Shizuoka Prefecture, Japan, were investigated by field removal and laboratory sediment-grain size selection experimentation. Following field manipulation, involving removal of both species, the distribution patterns of each were found to be similar in both control and manipulated quadrats, suggesting their differential habitat use patterns may be the outcome not of competition but of differing preferences for habitat characteristics. Results of a sediment-grain size selection experiment in the laboratory suggested a weak preference of A. sp. 2 for fine sediment, while A. sp. 1 showed no grain size preference. The observed difference in the distribution patterns between these two species, therefore, may possibly have resulted from, at least in part, a combination of differences in their preference for sediment grain size and other habitat characteristics such as water depth.     

Community structure and spatial variability of marine nematodes in tropical Australian pioneer seagrass meadows

The spatial variability in the community structure of infaunal free-living marine nematodes of pioneer seagrass (Halophilaand Halodule) meadows within a deltaic mangrove estuarine system and a bay mangrove system in tropical north-eastern Australia were examined. Nematode mean densities were intermediate ranging from 609 to 2744 inds./10 cm². A total of 152 putative species from 94 genera and 22 families were found across the four sites. The communities exhibited a high degree of dominance by Terschellingia longicaudata, Catanema sp 1, Terschellingia sp 2 and Metalinhomoeus insularis.Non-metric multi-dimensional scaling (nMDS) revealed that intra-site variability was low. This was reinforced by 1-way MANOVA, showing no significant inter-station differences between the six most dominant species at each site. The main system difference was reflected by a greater percentage of the Desmodoridae combined with a reduction of the Linhomoeidae in the bay system. At a species level system differences were manifested by a stenohaline, brackish water nematode assemblage in the deltaic system (M. insularis, Terschellingoidessp 1, Pseudolellasp 1) and, by a stenohaline, marine nematode assemblage in the bay system (Catanema sp 1, Spirinia parasitifera, Actinonemasp 1). These communities represent `hotspots' of diversity within a wider, mangrove-influenced depauperate fauna. The high degree of dominance found in each community was countered by moderate diversity and this, combined with the high number and speciation of deposit-feeding species, suggests that nematodes were more abundant in the meadows due to the abundance of microbial food. Notwithstanding the different salinity/CaCO₃ regimes, these communities exhibit both intra- and inter-site homogeneity with dominance by a conservative, deep-dwelling guild. The fact that this homogeneity exists suggests that these small-bladed seagrass species may play a greater role (sediment stability, fine particle settlement, organic detritus) in influencing the infaunal nematode community than was previously thought.     

砂质潮间带自由生活海洋线虫对缺氧的响应——微型受控生态系研究

以青岛砂质潮间带自由生活海洋线虫为研究对象,建立微型受控生态系,研究缺氧对海洋线虫群落结构和垂直分布的影响,以及环境复氧后海洋线虫群落的恢复能力。研究结果显示,海洋线虫是耐低氧的小型底栖动物类群,可通过垂直迁移来耐受缺氧造成的不利条件。但是,海洋线虫通过主动迁出而耐受缺氧条件的特性具有种的区别。研究中Pseudosteineria sp1、Rhynchonema sp1等海洋线虫通过向有氧环境的主动迁移耐受缺氧条件;Thalassironus sp1却可通过自身耐受机制抵御缺氧条件,在缺氧生境中仍能保持较高的丰度。此外,研究结果显示,当表层海洋线虫暴露于缺氧环境时,其总丰度显著降低,种类组成发生改变。Pseudosteineria sp1对缺氧环境较为敏感,可暂时性地离开沉积物进入水层;而沉积物溶解氧恢复正常后,该种可以重新回到沉积物中。Daptonema sp1成熟个体及其幼龄个体对缺氧均具有较高的耐受性,是缺氧群落的绝对优势种。D.sp3则表现出对缺氧环境较高的敏感性。环境恢复正常,线虫群落丰度及多样性增加,Neochromadora sp1和Spilophorella sp1等具有机会种的特点,首先表现出丰度和繁殖能力的增加。但是线虫群落种类组成在受测时间内并未能完全恢复,群落结构的恢复需要更长的时间。     

Effects of organic enrichment on meiofaunal abundance and community structure in sublittoral soft sediments

In experimental mesocosms established at Solbergstrand, Oslofjord, Norway, organic enrichment was effected by the addition of powdered Ascophyllum nodosum (L.) Le Jol., in quantities equivalent to 50gC·m^?2 and 200gC·m^?2, to boxes of sublittoral soft sediment. After 56 days, the structure of the meiofaunal communities in these treatments was compared with that of the control boxes. At this time the meiofaunal communites at each level of organic enrichment were markedly different from each other and from that in the control sediment. The responses of the two major components of the meiofauna, however, were different. Although the abundance of nematodes was slightly reduced in the high dose treatment this was not accompanied by detectable changes in community structure. Harpacticoid copepods, on the other hand, increased significantly in abundance in the treatment boxes and showed a general trend towards increased dominance and decreased diversity with increasing levels of organic enrichment, although in the low dose treatment there was also an increase in the number of species present. It is also shown that the nematode/copepod ratio is unreliable as a biomonitoring tool and it is suggested that the differential responses in community structure between the nematode and copepod components of the meiofauna might be a better indication of stress at the community level.     

Sediment Burial Intolerance of Marine Macroinvertebrates

The marine environment contains suspended particulate matter which originates from natural and anthropogenic sources. Settlement of this material can leave benthic organisms susceptible to smothering, especially if burial is sudden i.e. following storms or activities such as dredging. Their survival will depend on their tolerance to, and their ability to escape from burial. Here we present data from a multi-factorial experiment measuring burial responses incorporating duration, sediment fraction and depth. Six macroinvertebrates commonly found in sediment rich environments were selected for their commercial and/or conservation importance. Assessments revealed that the brittle star (Ophiura ophiura), the queen scallop (Aequipecten opercularis) and the sea squirt (Ciona intestinalis) were all highly intolerant to burial whilst the green urchin (Psammichinus miliaris) and the anemone (Sagartiogeton laceratus), showed intermediate and low intolerance respectively, to burial. The least intolerant, with very high survival was the Ross worm (Sabellaria spinulosa). With the exception of C. intestinalis, increasing duration and depth of burial with finer sediment fractions resulted in increased mortality for all species assessed. For C. intestinalis depth of burial and sediment fraction were found to be inconsequential since there was complete mortality of all specimens buried for more than one day. When burial emergence was assessed O. ophiura emerged most frequently, followed by P. miliaris. The former emerged most frequently from the medium and fine sediments whereas P. miliaris emerged more frequently from coarse sediment. Both A. opercularis and S. laceratus showed similar emergence responses over time, with A. opercularis emerging more frequently under coarse sediments. The frequency of emergence of S. laceratus increased with progressively finer sediment and C. intestinalis did not emerge from burial irrespective of sediment fraction or depth. Finally, and perhaps unsurprisingly, the greatest ability to emerge from burial in all other species was from shallow (2 cm) burial. Although survival was consistently highly dependent on duration and depth of burial as expected, emergence behaviour was not as easily predictable thereby confounding predictions. We conclude that responses to burial are highly species specific and therefore tolerance generalisations are likely to be oversimplifications. These data may be used to inform environmental impact models that allow forecasting of the cumulative impacts of seabed disturbance and may provide mitigation measures for the sustainable use of the seabed.     

Microbial Food Webs in Marine Sediments. I. Trophic Interactions and Grazing Rates in Two Tidal Flat Communities

Abstract The role of grazing by marine sediment flagellates, ciliates, and meiobenthic animals in controlling production of their bacterial and diatom prey was investigated. Several novel or modified techniques were used to enumerate prey (bacteria and diatoms), measure bacterial production, quantify proto- and micrometazoan predators, and evaluate rates of bacterivory and herbivory. The results indicated that, in a temperate, marine intertidal flat composed of fine sand, colorless nanoflagellates, ciliates, and nematodes were the most important bacterivores. Together, these organisms were responsible for removing up to 53% of bacterial production, by grazing. The observed rates of bacterivory were high enough to hypothesize that periods of grazing control of bacterial production might occur regularly in similar habitats. Colorless microflagellates, ciliates, and nematodes had high rates of diatom consumption. The combined small diatom consumption rate was equivalent to 132% of diatom standing stock per day. Trophic interactions between diatoms and micro- and meiobenthos might be a factor limiting growth of small (around 10 μm) diatoms. In coarse sands of an open beach, all micrograzers except pigmented nanoflagellates were rare, whereas bacterial and diatom assemblages were rather abundant and active. In this type of sediment, the micrograzers were able to consume only a marginal percentage of bacterial production (<1%) and diatom standing stock (3.8%), thus playing a minor role in controlling the dynamics of their prey. Received: 11 June 1996; Accepted: 13 August 1996     

Reconciling root plasticity and architectural ground rules in tree root growth models with voxel automata

Dynamic models of tree root growth and function have to reconcile the architectural rules for coarse root topology with the dynamics of fine root growth (and decay) in order to predict the strategic plus opportunistic behaviour of a tree root system in a heterogeneous soil. We present an algorithm for a 3D model based on both local (soil voxel level) and global (tree level) controls of root growth, with development of structural roots as a consequence of fine root function, rather than as driver. The suggested allocation rules of carbon to fine root growth in each rooted voxel depend on the success in water uptake in this voxel during the previous day, relative to overall supply and demand at plant level. The allocated C in each voxel is then split into proliferation (within voxel growth) and extension into neighbouring voxels (colonisation), with scale-dependent thresholds and transfer coefficients. The fine root colonisation process defines a dynamic and spatially explicit demand for transport functions. C allocation to development of a coarse root infrastructure linking all rooted voxels depends on the apparent need for adjustment of root diameter to meet the topologically defined sap flow through this voxel during the previous day. The allometric properties of the coarse root system are maintained to be in line with fractal branching theory. The model can predict the dynamics of the shape and structure (fine root density, coarse root topology and biomass) of the root system either independently of soil conditions (purely genetically-driven) or including both the genetic and environmental effects of roots interacting with soil water supply and its external replenishment, linking in with existing water balance models. Sensitivity of the initial model to voxel dimensions was addressed through explicit scaling rules resulting in scale-independent parameters. The model was parameterised for two tree species: hybrid walnut (Juglans nigra × regia) and wild cherry (Prunus avium L.) using results of a pot experiment. The model satisfactorily predicted the root growth behaviour of the two species. The model is sparse in parameters and yet applicable to heterogeneous soils, and could easily be upgraded to include additional local influences on root growth (and decay) such as local success in nutrient uptake or dynamic soil physical properties.     

An insight into the feeding ecology of deep-sea canyon nematodes — Results from field observations and the first in-situC feeding experiment in the Nazaré Canyon

Submarine canyon systems provide a heterogeneous habitat for deep-sea benthos in terms of topography, hydrography, and the quality and quantity of organic matter present. Enhanced meiofauna densities as found in organically enriched canyon sediments suggest that nematodes, as the dominant metazoan meiobenthic taxon, may play an important role in the benthic food web of these sediments. Very little is known about the natural diets and trophic biology of deep-sea nematodes, but enrichment experiments can shed light on nematode feeding selectivity and trophic position. An in-situ pulse-chase experiment (Feedex) was performed in the Nazaré Canyon on the Portuguese margin in summer 2007 to study nematode feeding behaviour. ¹³C-labelled diatoms and bacteria were added to sediment cores which were then sampled over a 14-day period. There was differential uptake by the nematode community of the food sources provided, indicating selective feeding processes. ¹³C isotope results revealed that selective feeding was less pronounced at the surface, compared to the sediment subsurface. This was supported by a higher trophic diversity in surface sediments (Θ⁻¹ = 3.50 ± 0.2) compared to the subsurface (2.78 ± 0.6), implying that more food items may be used by the nematode community at the sediment surface. Predatory and scavenging nematodes contributed relatively more to biomass than other feeding types and can be seen as key contributors to the nematode food web at the canyon site. Non-selective deposit feeding nematodes were the dominant trophic group in terms of abundance and contributed substantially to total nematode biomass. The high levels of ‘fresh’ (bioavailable) organic matter input and moderate hydrodynamic disturbance of the canyon environment lead to a more complex trophic structure in canyon nematode communities than that found on the open continental slope, and favours predator/scavengers and non-selective deposit feeders.     

Comparison of the Levels of Bacterial Diversity in Freshwater,Intertidal Wetland,and Marine Sediments by Using Millions of Illumina Tags

Sediment, a special realm in aquatic environments, has high microbial diversity. While there are numerous reports about the microbial community in marine sediment, freshwater and intertidal sediment communities have been overlooked. The present study determined millions of Illumina reads for a comparison of bacterial communities in freshwater, intertidal wetland, and marine sediments along Pearl River, China, using a technically consistent approach. Our results show that both taxon richness and evenness were the highest in freshwater sediment, medium in intertidal sediment, and lowest in marine sediment. The high number of sequences allowed the determination of a wide variety of bacterial lineages in all sediments for reliable statistical analyses. Principal component analysis showed that the three types of communities could be well separated from phylum to operational taxonomy unit (OTU) levels, and the OTUs from abundant to rare showed satisfactory resolutions. Statistical analysis (LEfSe) demonstrated that the freshwater sediment was enriched with Acidobacteria, Nitrospira, Verrucomicrobia, Alphaproteobacteria, and Betaproteobacteria. The intertidal sediment had a unique community with diverse primary producers (such as Chloroflexi, Bacillariophyta, Gammaproteobacteria, and Epsilonproteobacteria) as well as saprophytic microbes (such as Actinomycetales, Bacteroidetes, and Firmicutes). The marine sediment had a higher abundance of Gammaproteobacteria and Deltaproteobacteria, which were mainly involved in sulfate reduction in anaerobic conditions. These results are helpful for a systematic understanding of bacterial communities in natural sediment environments.     

Barcoding marine nematodes: an improved set of nematode 18S rRNA primers to overcome eukaryotic co-interference

Nematodes form an important component of many benthic marine ecosystems and DNA barcoding approaches could provide an insight into nematode community composition from different environments globally. We have amplified nematode 18S rRNA sequences using standard nematode18S rRNA primers from environmental DNA extracted from intertidal sediment collected from New Jersey coast, USA to test whether the published marine nematode 18S rRNA sequences from GenBank and EMBL databases can effectively assign unknown nematode sequences into genus or species level. Most of the sequenced clones showed some degree of identities with published marine nematode 18S rRNA sequences. However, relatively very few of the sequences could be assigned even to genus level based on sequence assignment rule. In addition, other eukaryotic 18S rRNA sequences were found to be co-amplified with commonly used nematode 18S rRNA primers. We found that the majority of the current nematode 18S rRNA primers will co-amplify other eukaryotes if environmental DNA is the target template. We therefore designed a new set of nematode 18S rRNA primers and evaluated them using environmental DNA in intertidal sediment from the New Jersey coast. In total, 40 clones were screened and subsequently sequenced and all the sequences showed varying degree of identities with published nematode 18S rRNA sequences from GenBank and EMBL databases, and no obvious eukaryotic co-amplicons were detected with new primers. Only 13 out of 40 clones amplified with the new primer set showed 100% identity to published Daptonema and Metachromadora 18S rRNA sequences. The current molecular databases for nematodes are dominated by sequences from NW Europe and need to be more extensively populated with new full length 18S rRNA nematode sequences collected from different biogeographic locations. The new primers developed in this study, in combination with an updated nematode 18S rRNA sequence database, would help us to better investigate and understand the diversity and community composition of free-living marine nematodes based on DNA barcoding approaches during biodiversity or biomonitoring surveys on a global-scale.     

Nematode communities of Lake Tana and other inland water bodies of Ethiopia

Free-living nematodes from littoral benthic sediments of four lakes, two rivers and a hot spring in Ethiopia are studied. Populations of nematodes encountered are identified to the species level. The general nematode (generic and species) composition of the lakes, rivers and hot spring are appraised by giving special emphasis to the nematodes from L. Tana, i.e. three sites where different environmental factors come into play were considered. Gelda is a site close to a river inlet (River Gelda), Gedero is a site exposed to strong wind action while Zegie is a secluded site protected by a land mass from any strong wind action. Nematode communities were identified using classification and ordination techniques. The identified communities are then characterised with respect to species composition, biomass, density, diversity, size structure, feeding type and maturity index. Also, the vertical distribution of nematodes is examined at the community and species level. An attempt has been made to associate these variations with the considered environmental factors viz. site, water depth, sediment depth, median grain size and percentage of mud in the sediment.     

Effect of Crotalaria juncea Amendment on Nematode Communities in Soil with Different Agricultural Histories

Effect of sunn hemp (Crotalaria juncea) hay amendment on nematode community structure in the soil surrounding roots of yellow squash (Cucurbita pepo) infected with root-knot nematodes was examined in two greenhouse experiments. Soils were from field plots treated long-term (LT) with yard-waste compost or no yard-waste compost in LT experiment, and from a short-term (ST) agricultural site in ST experiment. Soils collected were either amended or not amended with C. juncea hay. Nematode communities were examined 2 months after squash was inoculated with Meloidogyne incognita. Amendment increased (P < 0.05) omnivorous nematodes in both experiments but increased only bacterivorous nematodes in ST experiment (P < 0.05), where the soil had relatively low organic matter (<2%). This effect of C. juncea amendment did not occur in LT experiment, in which bacterivores were already abundant. Fungivorous nematodes were not increased by C. juncea amendment in either experiment, but predatory nematodes were increased when present. Although most nematode faunal indices, including enrichment index, structure index, and channel index, were not affected by C. juncea amendment, structure index values were affected by previous soil organic matter content. Results illustrate the importance of considering soil history (organic matter, nutrient level, free-living nematode number) in anticipating changes following amendment with C. juncea hay.     

SSR and RAPID Profile Based Grouping of Selected Jute Germplasm with Respect to Fibre Fineness Trait

With an aim to develop mapping population on fibre fineness trait, grouping of 16 selected jute accessions, eight each from Corchorus olitorius and Corchorus capsularis which showed promising agronomic characteristics, was carried out using fibre fineness data and DNA fingerprinting using SSR and RAPID primers. Based on fibre fineness trait two subgroups depicting the fine and coarse fibre yielding accessions were obtained in each species. A total of 26 RAPID primers and 22 pairs of SSR primers yielded 277 and 41 scorable bands, respectively. High level of polymorphism was detected between fine and coarse fibre yielding jute accessions. Dendrogram showed that all the accessions formed two main clusters between C. olitorius and C. capsularis and each main cluster subdivided in two clusters containing fine and coarse fibre jute accessions. RAPID and SSR marker data-sets showed high levels of positive correlation (Mantel test, r = 0.97). Grouping of jute accessions based on morphological and molecular data was highly correlated. This study will be useful in future jute breeding programs.     

The Influence of Organic Material and Temperature on the Burial Tolerance of the Blue Mussel,Mytilus edulis: Considerations for the Management of Marine Aggregate Dredging

Rationale and Experimental Approach

Aggregate dredging is a growing source of anthropogenic disturbance in coastal UK waters and has the potential to impact marine systems through the smothering of benthic fauna with organically loaded screening discards. This study investigates the tolerance of the blue mussel, Mytilus edulis to such episodic smothering events using a multi-factorial design, including organic matter concentration, temperature, sediment fraction size and duration of burial as important predictor variables.

Results and Discussion

Mussel mortality was significantly higher in organically loaded burials when compared to control sediments after just 2 days. Particularly, M. edulis specimens under burial in fine sediment with high (1%) concentrations of organic matter experienced a significantly higher mortality rate (p<0.01) than those under coarse control aggregates. Additionally, mussels exposed to the summer maximum temperature treatment (20°C) exhibited significantly increased mortality (p<0.01) compared to those in the ambient treatment group (15°C). Total Oxygen Uptake rates of experimental aggregates were greatest (112.7 mmol m^-2 day^-1) with 1% organic loadings in coarse sediment at 20°C. Elevated oxygen flux rates in porous coarse sediments are likely to be a function of increased vertical migration of anaerobically liberated sulphides to the sediment-water interface. However, survival of M. edulis under bacterial mats of Beggiatoa spp. indicates the species’ resilience to sulphides and so we propose that the presence of reactive organic matter within the burial medium may facilitate bacterial growth and increase mortality through pathogenic infection. This may be exacerbated under the stable interstitial conditions in fine sediment and increased bacterial metabolism under high temperatures. Furthermore, increased temperature may impose metabolic demands upon the mussel that cannot be met during burial-induced anaerobiosis.

Summary

Lack of consideration for the role of organic matter and temperature during sedimentation events may lead to an overestimation of the tolerance of benthic species to smothering from dredged material.