Biogeochemical influence on carbon isotope signature in boreal lake sediments

The functional morphology of the feeding palps and prostomium of the spionid polychaetes Streblospio benedicti and S. shrubsolii was studied. Three functional groups of cilia of the feeding palps were found on both species – frontal cilia, latero-frontal cirri and lateral cilia. Frontal cilia line the food groove and transport food particles to the pharynx, and have been reported for all spionid polychaetes except species of the genus Scolelepis. Latero-frontal cirri deflect particles onto the frontal surface and have been observed in several spionid genera including Paraprionospio, Streblospio, Polydora and Dipolydora. Lateral cilia beat in continuous metachronal waves creating lateral vortices that potentially entrain suspended particles, and are known in Paraprionospio and Streblospio. The two species of Streblospio did differ in the distribution of prostomial papillae. These papillae are eversible and thought to function in particle selection as particles on the pharynx come in contact with the papillae. Prostomial papillae were restricted to the peripheral surface of S. benedicti and were widely scattered on all surfaces of the prostomium of S. shrubsolii. A conical tentaculate structure occurs between the branchiae of the first setiger of S. benedicti, but only a low raised elevation is present on S. shrubsolii.     

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.     

Optimal foraging by deposit-feeding invertebrates: Roles of particle size and organic coating

Summary Feeding experiments were conducted on marine, deposit-feeding benthic invertebrates to test the predictions of an optimal foraging model. Food item selection based on sediment particle size and presence or absence of an organic coating on particles was investigated. Animals displaying a wide range of feeding mechanisms were studied in particle size-selection experiments using artificial sediment of closely controlled size composition. Nine of 10 species from 4 phyla ingested smaller particles in greater proportions than the particles were present in the sediment. In experiments where animals fed on a mixture of two particle types, one with and one without a surface protein coating, 6 of 7 species from 3 phyla ingested preferentially the protein-coated beads. While these trends of selection of smaller particles and protein-coated particles follow qualitatively the predictions of the optimal foraging model, the animals did not ingest exclusively the preferred particle types. Mechanics of particle handling rather than behavioral responses to particle characteristics appear to offer the better explanation for the observed selection patterns. In particular, the results support strongly the recently proposed role of mucous adhesion in particle selection by deposit feeders.These and other results from studies of deposit feeders suggest that factors in addition to food item selection must be considered when testing the assumptions and predictions of optimal foraging theory. Specifically, feeding energetics are also affected by postfood-selection processes such as variation of ingestion rate. Furthermore, the effects of abiotic environmental factors on foraging behavior cannot be overlooked in evaluating the optimality of foraging behavior; variable water velocity affected differently the particle size selectivity of 3 sympatric polychaete species in these studies.Contribution No. 1239 from the School of Oceanography, University of Washington     

Community structure and food web based on stable isotopes (δN and δC) analysis of a North Eastern Atlantic maerl bed

Maerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources.     

Coating Soybean Seed with Oxamyl for Control of Heterodera glycines

Oxamyl coated on soybean (Glycine max (L.) Merr. cv. Elgin) seeds in solutions of 20, 40, 80, and 160 mg/ml had no serious deleterious effects on seedling emergence and growth when planted in sterile soil. Seedling emergence on day 3 was less than that of the uncoated control, but by day 7 emergence was equal to, or greater than, the control. Shoot and root growth from seed coated with oxamyl in 40 and 80 mg/ml solutions was greater than that of the control. In soil infested with soybean cyst nematode, Heterodera glycines, shoot weight of soybean plants from seeds coated with oxamyl in 80 mg/ml solution was 11 and 9% greater at weeks 3 and 7, respectively, than from uncoated seeds. Numbers of juveniles (J3 and J4) and adults of H. glycines observed on the roots of plants from oxamyl-coated seeds were 83, 42, and 49% less at weeks 3, 5, and 7, respectively, than numbers on the roots of the untreated control. Numbers of J2 extracted from the roots of plants from oxamyl-coated seeds were 75% less at weeks 5 and 7 than those extracted from roots of uncoated seeds. The numbers of J2 extracted from the soil planted to oxamyl-coated seeds were 51 and 33% less at weeks 5 and 7, respectively, than from soil planted to uncoated seed.     

Predaceous Behavior and Life History of Odontopharynx longicaudata (Diplogasterida)

The behavior of a California isolate of the predaceous nematode, Odontopharynx longicaudata de Man, was studied in water agar culture. When feeding on an Acrobeloides sp. the predator completed its life cycle in 13 to 14 days at 25 C. Optimum temperature for reproduction of the predator was 25 C, few individuals survived at 10 C, and 30 C was lethal. Males were necessary for reproduction, and at 25 C the sex ratio was about 1:1. All postembryonic stages were voracious feeders. A single female predator consumed 30 individuals of another Acrobeloides sp. in 1.5 days. Juveniles must feed in order to complete their development. Three modes of feeding were observed depending on the prey selected. A high degree of prey selectivity occurred; 6 of 17 nematode prey species were readily consumed by the predator, but there was little or no feeding on the remaining 11 species. Predation percentage varied with prey species. Consumption of Anguina pacificae and the two Acrobeloides spp. was almost 100%, consumption of A. amsinckiae, Pratylenchus vulnus, and Trichodorus sp. was 70-78%. Difference in final predator population densities was obtained after feeding on the two species of Acrobeloides. Final predator population densities increased linearly with increasing inoculum levels of the first Acrobeloides sp.     

Refinement of an adherence assay for the measurement of bacterial attachment to silica beads

An in vitro adherence assay [4] which utilised radiolabelled bacteria and silica beads was used to investigate firm and loose attachment of bacteria. A systematic evaluation of the effects of the assay conditions, including incubation vessel, bacteria to bead interaction, bead washing and bead weight, was carried out in an attempt to improve the reproducibility of adherence measurements. Four oral streptococcal strains (S. mutans NCTC 10449, S. sanguis NCTC 7863 and 10904, S. salivarius NCTC 8618) were studied with saliva coated and uncoated silica beads.Using the improved system, total bacterial adherence to uncoated beads was high (45–60% of bacteria present). While saliva coating of beads reduced total and firm adherence of all strains, these reductions were less marked (P > 0.005) for S. sanguis NCTC 10904.     

Lugworm exclusion experiment: Responses by deposit feeding worms to biogenic habitat transformations

On six 400 m² plots over 3 years, we excluded the sessile subduction and conveyer-belt feeding polychaete Arenicola marina which generates a pit-and-mound topography at the sediment surface from intertidal sands near the island of Sylt, Germany. This experiment was used to test whether other abundant deposit feeding polychaetes (the discretely motile and surface feeding ragworm Nereis diversicolor and the subsurface-feeding, motile orbiniid polychaete Scoloplos cf. armiger) benefit from competitive release. Ragworms took advantage from the absence of lugworms. Presumably they responded to a more stable and nutritious surface layer at lugworm exclusion plots (relief from inhibitive bioturbation). Contrary to this, S. cf. armiger was negatively affected by the exclusion of A. marina. It may have suffered from higher sulfide concentrations in the less irrigated and less permeable sediment where lugworms were absent. For adult worms of both species these results were consistent in 2 out of 3 years examined. Recruitment by N. diversicolor was highly variable between years and occurred either irrespective of experimental treatments or the response was inconsistent. Juveniles of S. cf. armiger benefited from the presence of A. marina and aggregated near lugworm tail shafts where inflow of oxygen rich water was high and sulfide concentrations were low. Biogenic habitat mediated effects of lugworms on both deposit feeders were in the same order of magnitude as abundance variation in space and time. Thus, A. marina was one of the key factors structuring the deposit feeding community. It is suggested that arenicolids modify the composition of the associated polychaete assemblage primarily through habitat transformation.     

Grazing-filtration as feeding mechanisms in motile specimens of Crepidula fecunda (Gastropoda: Calyptraeidae)

Quantification of ingestion by grazing and by filtration in Crepidula fecunda showed that during the motile phase of the life cycle (<28 mm in shell length), the species depends on both feeding strategies to supply it's energetic requirements. This species improves the energetic quality of the material ingested by exercising preferential selection for organic material from all the materials that are available on the substrate, with an average organic enrichment of 13%. The ontogenetic change in the relative importance of grazing and filter feeding appear to be species-specific within the genus; some species have motile forms in earlier life stages which need to move about the substrate to obtain food and locate aggregations of conspecifics. After growing to about 28 mm in length, C. fecunda become sessile females and depend solely on filter feeding to meet their nutritional requirements.     

Intraspecific density regulates positioning and feeding mode selection of the sand dollar Dendraster excentricus

Dendraster excentricus is a common sand dollar of nearshore benthic habitats along the west coast of North America, and has the ability to feed either on deposited or suspended food particles. Field surveys and manipulative experiments demonstrated that intraspecific density and sediment organic matter (SOM) content of sediments are among the factors that regulate the proportion of sand dollars that forage as deposit versus suspension feeders. High local density was associated with a lower proportion of deposit feeding animals in both field surveys and under controlled experimental conditions. Conversely, the proportion of deposit feeders was elevated in treatments in which SOM levels were subsidized, regardless of local density. These data fit Levinton's model of resource limitation in relation to deposit-and suspension-feeding communities, and expand the list of biological processes regulated through density dependence. Analyses of carbon stable isotope ratios (δ¹³C) of sand dollars and their potential sources of primary production suggest individuals rely primarily on suspended particulate organic carbon (POC) or drift macroalgae. Sediment organic matter was not a substantial source of carbon for most individuals. There was a significant inverse relationship between size and δ¹³C values; smaller individuals depended to a greater extent on macroalgae. There was no consistent relationship between isotopic ratios, feeding mode and density, which may be due to the high mobility of the species, their ability to respond rapidly to changing environmental conditions and the dynamic nature of their habitat. Our results suggest that biological interactions influence feeding mode of this species. This is a complementary mechanism to those described previously, in which physical factors such as flow and lift/washout have been shown to regulate sand dollar positioning.     

Influence of diet on pre-ingestive particle processing in bivalves: II. Residence time in the pallial cavity and handling time on the labial palps

Previous studies have demonstrated that bivalve molluscs respond to changing food conditions through processes such as preferential selection and ingestion of particulate matter. Little is known, however, about the underlying mechanisms accountable for these responses. To further explain feeding processes at the level of the pallial organs, we determined pallial cavity residence times, or the amount of time it took particles to travel from the inhalant aperture to the stomach, in two species of bivalves, Crassostrea virginica and Mytilus edulis, under conditions of differing particle quality, particle concentration, and temperature. From these residence times, particle-handling times on the labial palps were determined. Diets of three different qualities were tested, including Rhodomonas lens cells, particles prepared from ground Spartina sp. detritus, and a 50/50 mixture of both. Bivalves were delivered one of the three diets along with 10-μm fluorescent polystyrene beads (tracer), removed from feeding chambers at intervals from 30 s up to 20 min, and placed in liquid nitrogen to halt particle transport. Digestive systems of bivalves were then dissected and examined for the presence of tracer beads. Particle-residence times in the pallial cavity and handling times on the labial palps of C. virginica were significantly affected by changes in diet type. Particle-handling times on the palps decreased with increasing diet quality and ranged from 2.2 min (100% R. lens) to 22.8 min (100% ground Spartina sp.), accounting for 88% and 99%, respectively, of the total time particles spent in the pallial cavity. In contrast, diet quality had little effect on particle-residence times in the pallial cavity of M. edulis. However, residence times were affected by temperature and diet concentration. Temperature significantly affected residence times at particle concentrations of both 20 and 100 particles μl⁻¹, whereas particle concentration affected residence times at 20 °C, but not at 5 °C. Particle-handling times on the labial palps ranged from less than 1 to 5.5 min, depending on temperature and concentration, accounting for 50% to 82%, respectively, of the total time particles spent in the pallial cavity. We suggest that (1) observed interspecific differences in particle handling on the labial palps may be due to differences in palp morphology and function, and (2) particle sorting and selection on the labial palps is a rate-limiting step of pre-ingestive feeding processes in by bivalves.     

Chitosan coated alginate beads for the survival of microencapsulated Lactobacillus plantarum in pomegranate juice

This work studied the effect of multi-layer coating of alginate beads on the survival of encapsulated Lactobacillus plantarum in simulated gastric solution and during storage in pomegranate juice at 4°C. Uncoated, single and double chitosan coated beads were examined. The survival of the cells in simulated gastric solution (pH 1.5) was improved in the case of the chitosan coated beads by 0.5-2 logs compared to the uncoated beads. The cell concentration in pomegranate juice after six weeks of storage was higher than 5.5logCFU/mL for single and double coated beads, whereas for free cells and uncoated beads the cells died after 4 weeks of storage. In simulated gastric solution, the size of the beads decreased and their hardness increased with time; however, the opposite trend was observed for pomegranate juice, indicating that there is no correlation between cell survival and the hardness of the beads.     

Carnivory during Ontogeny of the Plagioscion squamosissimus: A Successful Non-Native Fish in a Lentic Environment of the Upper Paraná River Basin

This study evaluated feeding patterns and ontogenetic variations in a non-native fish species (Plagioscion squamosissimus) in an isolated lake in the Upper Paraná River floodplain. Quarterly samplings were performed from April 2005 to February 2006 using plankton nets to capture larvae, seining nets for juveniles, and gill nets and trammel for adults. Stomach contents (n = 378) were examined according to the volumetric method in which the volume of each food item was estimated using graduated test tubes or a glass counting plate. During early development (larval stage), P. squamosissimus consumed mainly Cladocera and Copepoda. Juveniles showed a more diverse diet, including shrimp (Macrobrachium amazonicum), fish, aquatic insects (Trichoptera, Ephemeroptera, Chironomidae and pupae of Diptera) and plants. It was notable the high proportion of cannibalism (23.3%) in this stage. Adults consumed predominantly shrimp and fish. The use of food resources varied significantly between development stages (ANOSIM; r = 0.458; p<0.005), showing changes in food preferences during ontogeny. The Similarity Percentage Analysis (SIMPER) indicated that Cladocera and Copepoda were responsible for the differences observed between the larval stages of pre-flexion, flexion and post-flexion. M. amazonicum and Chironomidae were responsible for the differences between juvenile and larval stages, while M. amazonicum and other fishes caused the differences between adults and other ontogenetic stages. These results are confirmed by the relationship between standard length and developmental periods (ANCOVA; r² = 0.94; p<0.0001). In general, there were low values of trophic niche breadth. The essentially carnivorous habit from the early stages of P. squamosissimus and the predominant use of M. amazonicum by adults have important roles in feeding patterns of the species, suggesting a major contribution to its success and establishment, especially in lentic environments.     

Aspects of the ultrastructure of the alimentary canal and respiratory ducts in Xenopus laevis larvae

The pharynx, intestine and respiratory duct of Xenopus laevis were examined by light and electron microscopy, at different stages of the metamorphic cycle, through climax. It is well known that preclimactic larvae are suspension feeders and that after climax specimens feed on solid food. It is shown that the histology of the pharynx and the alimentary canal changes in adaptation to the change in the mode of feeding. Suspension feeding utilises ciliary activity but after climax cilia have disappeared from the pharynx and alimentary canal, when new neuromuscular mechanisms are utilised in feeding. Other morpho-histological changes in various intestinal and respiratory tissues are likewise considered in terms of functional activity.     

Gut architecture,digestive constraints and feeding ecology of deposit-feeding and carnivorous polychaetes

Summary We analyze gut architectures of 42 species of marine polychaetes in terms of their anatomically distinct compartments, and quantify differences among guts in terms of ratios of body volume to gut volume, relative compartmental volumes, total gut aspect ratios and compartmental aspect ratios. We use multivariate techniques to classify these polychaetes into 4 groups: carnivores with tubular guts; deposit feeders with tubular guts; deposit feeders with 3 gut compartments; and deposit feeders with 4 or 5 gut compartments. Tubular guts, morphological expressions of plug flow, are common among deposit feeders and may allow relatively rapid ingestion rates and short throughput times. Median gut volume per unit of body volume in deposit feeders (31%) is twice that of carnivores (15%) and ranges up to 83% in one deep-sea species. Deep-sea deposit feeders tend to have relatively larger and longer guts than closely-related nearshore and shelf species. Guts of a number of deep-sea deposit feeders and nearshore and shelf deposit feeders from muddy environments are relatively longer and narrower as body size increases, suggesting that digestive diffusion limitations may be important. Gut volume scales as (body volume)¹ while ingestion rate scales as (body volume)^0.7. If diet and the chemical kinetics of digestion do not change appreciably, throughput time and thus the extent of digestion of given dietary components therefore must increase as a deposit feeder grows. Digestive processing constrainst may be most important in juveniles of species (especially those species with plug-flow guts) that are deposit feeders as adults.     

Hunting and predation in a fiddler crab

Fiddler crabs are known primarily to be deposit feeders. They eat detritus, bacteria, and other small particles of organic material found in the sandy or muddy substrate on which they live. They have highly specialized mouthparts used to separate edible matter from nondigestable material. Here we provide evidence of cannibalism and predation in a fiddler crab, Uca annulipes. We additionally provide the first evidence of a fiddler crab hunting shrimp and insects. This study is an exemplary reminder that, even though an animal may have evolved highly specialized feeding traits, this need not preclude it from opportunistically acting as a generalist feeder.     

Ontogenetic variation in the autecology of the greater earless lizard Cophosaurus texanus

We investigated the potential for ontogenetic resource partitioning within a population of the Texas earless lizard Cophosaurus texanus Results from focal samples, line transects, haphazard observations, and stomach flushes compiled in summer (July 1993) and autumn (September 1995) revealed differences in microhabitat use and diet between adults and juveniles Juveniles use rock perches more frequently than adult males, and consume smaller prey than adults No ontogenetic differences in thermal ecology were observed Diet differences between juveniles and adults may be attributed to the inability of juveniles to handle large prey items Differences between juveniles and adults in prey size and microhabitat use suggest ontogenetic variation in foraging, predator avoidance, and territory defense     

Effect of organic rice farming on planthoppers 4. Reproduction of the white backed planthopper,Sogatella furcifera Horváth (Homoptera: Delphacidae)

The reproduction ofSogatella furcifera was investigated in a chemically fertilized rice field and an organically farmed field. In the latter, the density of immigrants was significantly higher, while the settling rate of female adults and the survival rate of immature stages of ensuing generations were lower. The number of eggs laid by a female of the invading and following generations was smaller, and the percentage of brachypterous females in the next generation was also lower. Consequently, the density of nymphs and adults in the ensuing generations decreased in the organically farmed field. For an experimental comparison, potted rice plants were cultivated using seedlings and soil from the chemically fertilized or the organically farmed fields. WhenSogatella furcifera was reared on these plants, both the reproductive rate and the appearance rate of brachypterous female adults were lower in the organic treatment. Egg hatchability was also lower in the organic treatment. This experiment suggested that a specific nutritional condition in rice plants suppressed the population ofS. furcifera in the organically farmed field.     

Sulfasalazine release from alginate-N,O-carboxymethyl chitosan gel beads coated by chitosan

In the present study, spherical beads were prepared from a water-soluble chitosan (N,O-carboxymethyl chitosan, NOCC) and alginate with ionic gelation method. Then, swollen calcium–alginate–NOCC beads were coated with chitosan. To prepare drug loaded beads, sulfasalazine (SA) was added to the initial aqueous polymer solution. The effect of coating, as well as drying procedure, on the swelling behavior of unloaded beads and SA release of drug loaded ones were evaluated in simulated gastrointestinal tract fluid. The rate of swelling and drug release were decreased for air-dried and coated beads in comparison with freeze-dried and uncoated ones, respectively. No burst release of drug was observed from whole tested beads. Chitosan coated beads released approximately 40% of encapsulated drug in simulated gastric and small intestine tract fluid. Based on these results, the chitosan coated alginate–NOCC hydrogel may be used as potential polymeric carrier for colon-specific delivery of sulfasalazine.