Natural and Disturbance-Induced Demographic Variation in an Infaunal Polychaete, Nephtys incisa

Demography of the infaunal polychaete Nephtys incisa was investigated for periods of 1 yr prior to and following disturbance (dredge material disposal) at a site in central Long Island Sound, USA. Infaunal grab samples were taken at 5 stations 200 m to 3 km apart. The demography of populations at each station was based on age-classes spanning juveniles to adults 4 + yr of age. Age-specific survivorship and fecundity were based on changes in mean density of each cohort and a positive correlation between female size and egg production, respectively. Analyses of population matrix models indicated pre-disposal populations had positive population growth rates, despite differences in vital rates among stations. During the second year, population growth rates were reduced by 50%, below population maintenance levels, at each station, primarily due to recruitment failure across the entire study site. Population growth rates were reduced an additional 25% by disturbance at the dump site and next closest station (200 m away) due to decreased worm size and survivorship relative to other stations, and the absence of recolonization by worms \u3e 2 yr of age. Populations of N. incisa appear to experience several demographic \u27states\u27, related to periods of potential population growth, decline and recovery from disturbance. Based on analyses of related demographic parameters, there is a concomitant change in the contribution different age-classes make to population growth. During periods of growth 2-yr-old worms make the greatest contribution, older age-classes during declines, while younger age classes become important during recovery from disturbance. These differences result from temporal and spatial fluctuations in recruitment, individual growth and reproductive activity. Responses of long-lived marine infauna to disturbance likely depend on their current demographic state at the time of disturbance (reflecting demographic conditions such as size/age structure) and factors external to the population (e.g. environmental influences on settlement and recruitment or the type of disturbance]. In this case, the disposal of contaminated dredge material had a negative impact on vital rates and potential population growth of N. incisa at and 200 m away from the disposal site, but little or no effect on populations 400 m to 3 km away

Biotic Interactions Among Estuarine Infaunal Opportunistic Species

Biotic interactions among soft-sediment infauna were investigated in a small New England estuary in order to determine what effect(s) established opportunistic species had on subsequent recolonization. Interactions were defined according to successional models developed by Connell and Slatyer (1977), e.g. facilitation, tolerance and inhibition. Adults of the opportunistic polychaetes Streblospio benedicti, Polydora ligni and Hobsonia florida were added at 2 densities to separate cores containing defaunated sediment. These cores and control cores containing no worms were sampled at 10 d intervals for 40 d. Cores containing capillary tubes to simulate polychaete tubes were also deployed and sampled at 10 d intervals. Subsequent infaunal colonization densities of the polychaetes seeded to the cores - and also Capitella capitata, the amphipods Corophium insidiosum and Microdeutopus gryllotalpa and the anthozoan Nematostella vectensis - were analyzed for differences in recolonization with respect to the initial density of each of the established species. While more than 1 particular type of interspecific interaction operated during the study, the results indicate that the species could be divided into 2 groups, the polychaete and non-polychaete fauna. A predominance of inhibitory interactions (recolonization densities were significantly lower in cores with established species than in control cores) occurred among the polychaete fauna of the estuary. Some evidence of interspecific facilitation was found during initial sampling periods when overall densities of organisms were low. The effect of initial worm density on settlement inhibition was variable. The non-polychaete fauna appeared not to have been either positively or negatively affected by established species, thus suggesting some form of tolerance interaction or the lack of interaction. Cores containing simulated polychaete tubes generally had no effect on recolonization. Inhibitory interactions among opportunistic polychaetes may be due to intraspecific gregarious settlement and subsequent preemption of food and space resources. While biotic interactions among opportunistic species may play an important role in controlling successional dynamics, the specific type of interaction that occurs most likely depends on the species present, their density and habitat conditions. There appears to be no “characteristic” type of biotic interaction which influences soft-bottom successional dynamics

Responses of Estuarine Infauna to Disturbance. I. Spatial and Temporal Variation of Initial Recolonization

Responses to disturbance of estuarine infauna were studied to test the hypothesis that seasonality, the estuarine environmental gradient and sediment composition would significantly affect recolonization. The study was conducted in a small estuary located in southeastern Connecticut, USA, using controlled disturbance experiments and sampling of the ambient infauna. Species composition in experimental plots and ambient sediments usually did not differ, either on a seasonal or areal basis. Numerically dominant species usually included the polychaetes Streblospio benedicti, Capitella spp. and Polydora ligni, and the oligochaete Peloscolex gabriellae. Other species included the polychaetes Scoloplos fragilis, Hobsonia florida and Nereis virens, the hemichordate Saccoglossus kowaleski, and the amphipods Microdeutopus gryllotalpa and Corophium insidiosum. At times, densities of these species exceeded or were equivalent to dominant species densities in ambient sediments and experimental plots. There were usually significant differences in recolonization and ambient population dynamics due to seasonality and estuarine position. The effects of sediment composition on recolonization patterns of the various species were generally not significant. Seasonal trends in ambient and recolonization species densities were similar, with the highest responses to disturbance in the spring and summer. As ambient densities declined during the fall and winter, responses to disturbance did likewise. On an areal basis, the highest responses to disturbance occurred in the middle and upper portions of the estuary. Ambient densities followed a similar pattern, but peak densities in the early spring (May, 1979) were found in the lower portion of the estuary. Based on differences between ambient and recolonization population densities, only 1 species, Polydora ligni, exhibited a regular opportunistic response. Other species exhibited opportunistic responses, but in only 1 or 2 mo during the study. It is apparent, therefore, that species responses to disturbance were quite variable and no general pattern of recolonization could be applied to Alewife Cove with respect to seasonality and estuarine position. Due to this variation, and the historical component involved in recolonization of disturbed habitats, hypotheses correlating species responses to disturbance with life history adaptations may not be generally applicable to estuarine soft-bottom communities

Responses of Estuarine Infauna to Disturbance. II. Spatial and Temporal Variation of Succession

Infaunal successional patterns in Alewife Cove, a small estuary in southeastern Connecticut, USA, varied significantly seasonally and along the estuarine environmental gradient. Each study site exhibited different patterns of change in species composition and abundance. However, suites of species found during succession did not differ greatly from those found in ambient sediments. Species which exhibited the most variable population changes during succession were numerically dominant tubiculous polychaetes (Streblospio benedicti, Capitella spp., Polydora ligni], and an oligochaete (Peloscolex gabriellae). Other species which exhibited significant activity were the polychaetes Scoloplos fragilis, Hobsonia florida and Nereis virens, the hemichordate Saccoglossus kowaleski, and the amphipods Microdeutopus gryllotalpa and Corophium insidiosum. At certain times, densities of these species exceeded or were equivalent to dominant species densities in ambient sediments and experimental plots. Timing of disturbance greatly influenced succession. Succession after an early spring disturbance was characterized by peak species densities and numbers. Succession following a fall disturbance was abbreviated with few species at low densities, while after a summer disturbance intermediate trends were found. Classification analysis of similarity between ambient and successional community structure indicated that recovery to ambient conditions occurred rapidly in the lower reach (14 to 30 d), while successional changes in the middle and upper basins continued at least until the end of the winter. It is apparent that estuarine succession can be quite variable and that re-establishment of community structure may occur over various time scales with no set seral stages. The physical and biological processes appearing to be important determinants of estuarine succession include (1) timing of disturbance, (2) habitat in which the disturbance takes place, (3) reproductive periodicity of infauna, (4) ambient population dynamics which generate the pool of recolonizers, ( 5 ) abiotic and biotic factors (e.g. food and space resources that affect the preceding 4 factors)

Effects of Resident Species on Recruitment into a Community: Larval Settlement Versus Post-Settlement Mortality in the Oyster Crassostrea virginica

Laboratory and field experiments revealed that a variety of species of common, sessile invertebrates, including barnacles, ascidians, and bryozoans, affected the settlement and post-settlement abundance of the oyster Crassostrea virginica (Gmelin). While the nature of the effects varied, most species both reduced oyster settlement by covering and removing substrate available for attachment, and increased settlement on adjacent surfaces. The solitary ascidians Ciona intestinalis (L.) and Styela clava (Herdman), were found to be predators of oyster larvae. Post-settlement survivorship and growth were also strongly affected by the presence of sessile species. In most cases the effects were negative and correlated with the abundances of the species. Data suggest that competition for planktonic food was the mostly likely cause of reduced growth and survivorship. For many resident species, the combination of reduced oyster settlement on their own exposed surfaces, increased settlement on substrate adjacent to them, and decreased post-settlement survivorship in their presence resulted in these species having little effect on net recruitment. These results demonstrate the need for distinguishing interactions among benthic invertebrate populations during the period from settlement to recruitment

Effects of Inter-Specific Density and Food Supply on Survivorship and Growth of Newly Settled Benthos

Using a laboratory model system comprised of newly settled oysters Crassostrea virginica and established fouling species (Botrylloides sp. initially, and others including Styela clava and Ciona intestinalis as the experiment progressed), we tested how differences in food supply and competitor density may affect post-settlement surivorship and growth of sessile marine invertebrates over a 44 d period. After 15 d, results were mixed but indicated that both food and density conditions affected growth and survivorship significantly, with some suggestion of high food levels ameliorating high density effects However, 44 d after settlement, oysters had reduced survivorship and growth when competitors were present regardless of food level. This study suggests that localized food depletion by juveniles and/or adults of resident species may have a negative effect on recruitment in fouling communities, even when space is not limiting

The Texture of Surficial Sediments in Western Long Island Sound off the Norwalk Islands, Connecticut

Grain-size analyses were performed on 69 samples from western Long Island Sound. The relative grain-size frequency distributions and related statistics are reported herein. Descriptions of the benthic character from video tapes and still camera photographs of the bottom at these stations, and 33 others, are also presented. The southern and eastern parts of the study area are dominated by poorly sorted clayey silts that have nearly symmetrical distributions. Gravelly sediments are prevalent in the shallow northwestern part of the study area, but are also present in central part of the study area. Bands of sand, silty sand, and sand-silt-clay occur on the flanks of the gravelly areas

Determining the influence and effects of manufacturing variables on sulfur dioxide cells

A survey of the Li/SO2 manufacturing community was conducted to determine where variability exists in processing. The upper and lower limits of these processing variables might, by themselves or by interacting with other variables, influence safety, performance, and reliability. A number of important variables were identified and a comprehensive design experiment is being proposed to make the proper determinations

Evaluation of the bond performance in FRP-brick components re-bonded after initial delamination

The bond behavior between Fiber Reinforced Polymers (FRPs) and masonry substrates has been the subject of many studies during the last years. Recent accelerated aging tests have shown that bond degradation and FRP delamination are likely to occur in FRP-strengthened masonry components under hygrothermal conditions. While an investigation on the possible methods to improve the durability of these systems is necessary, the applicability of different bond repair methods should also be studied. This paper aims at investigating the debonding mechanisms after repairing delaminated FRP-strengthened masonry components. FRP-strengthened brick specimens, after being delaminated, are repaired with two different adhesives: a conventional epoxy resin and a highly flexible polymer. The latter is used as an innovative adhesive in structural applications. The bond behavior in the repaired specimens is investigated by performing single-lap shear bond tests. Digital image correlation (DIC) is used for deeper investigation of the surface deformation and strains development. The effectiveness of the repair methods is discussed and compared with the strengthened specimens.The first author acknowledges the financial support of the Portuguese Science Foundation (Fundacao de Ciencia e Tecnologia, FCT), through grant SFRH/BPD/92614/2013. Additional acknowledgement goes to Sika Poland for providing the PS polymer to the laboratory of the Minho University in Portugal

Screening nuclear field fluctuations in quantum dots for indistinguishable photon generation

A semiconductor quantum dot can generate highly coherent and indistinguishable single photons. However, intrinsic semiconductor dephasing mechanisms can reduce the visibility of two-photon interference. For an electron in a quantum dot, a fundamental dephasing process is the hyperfine interaction with the nuclear spin bath. Here we directly probe the consequence of the fluctuating nuclear spins on the elastic and inelastic scattered photon spectra from a resident electron in a single dot. We find the nuclear spin fluctuations lead to detuned Raman scattered photons which are distinguishable from both the elastic and incoherent components of the resonance fluorescence. This significantly reduces two-photon interference visibility. However, we demonstrate successful screening of the nuclear spin noise which enables the generation of coherent single photons that exhibit high visibility two-photon interference.Comment: 5 pages, 4 figures + Supplementary Informatio