Population Ecology of Polydora ligni (Polychaeta: Spionidae). I. Seasonal Variation in Population Characteristics and Reproductive Activity

A population of the polychaete Polydora ligni Webster was studied during 1982 and 1983 in Alewife Cove, Connecticut, USA, to determine seasonal changes in population characteristics. During early spring (March and April), the population was comprised of primarily large adults that had over-wintered. Females in this group exhibited the highest mean individual fecundity over the year (\u3e 2000 larvae per brood). However, total larval production at this time was low (5200 to 208 000 larvae m-2 per 14 d) due to low densities of adults. Population density increased slowly during spring as juveniles produced by overwintering adults recruited into the population and matured into adults. While mean individual fecundity of these adults was lower (≈ 1200 larvae brood-1), larval production peaked (≈ 884000 larvae m-2) due to their high density. Population abundance peaked coincident with peaks in larval production, decreased rapidly during late summer and leveled off during fall and winter. Population density was lower and fluctuated less in the second year of the study, but general seasonal patterns were repeated. Reproductive activity was continuous over the study period. The overall female-to-male sex ratio was 2.42 : 1,and females grew to significantly larger sizes than males. Besides fecundity, there were seasonal differences in the number of gametogenic segments per female and the number of eggs per capsule; there were no seasonal differences in the number of egg capsules per brood. Temporal changes in population characteristics of P. ligni differed to various degrees from those reported for related taxa and other opportunistic polychaetes. However, the general patterns were similar. Seasonal variation in the population characteristics of opportunistic polychaetes may cause responses to disturbance to vary because of changing dynamics in populations that act as sources of larvae. Seasonally varying dynamics may also be an important evolutionary determinant of opportunistic life history traits

Population Ecology of Polydora ligni (Polychaeta: Spionidae). II. Seasonal Demographic Variation and its Potential Impact on Life History Evolution

Seasonal demographic variation was studied in an estuarine population of the opportunistic polychaete Polydora ligni between May 1982 and November 1983 in Alewife Cove, Connecticut, USA. The demography of 15 cohorts settling during this period was analyzed using life cycle graph models. Cohorts settling in spring and early summer had the shortest life spans (≈ 10 wk); highest survivorship over all life cycle stages and adult females produced an estimated maximum of 6 larval broods. Early adult stages contributed most to population growth during this period, and the potential for population growth, λ, was the highest during the study. Late summer cohorts had low juvenile survivorship, life spans of ≈ 12 wk, and females produced a maximum of 8 broods. Later stage females contributed most to population growth, and λ values were usually ≤ 1, indicating population decline. Fall cohorts comprised 2 groups. Early fall cohorts reproduced only in late fall, as females growing into later stages during winter did not reproduce and died before reproduction resumed in spring. These cohorts had low fecundity, 4 to 6 broods female-1, and λ ≤ 1. One cohort settled at the beginning of winter and along with late fall cohorts overwintered to produce the following spring\u27s cohorts. Overwintering cohorts had low juvenile but high adult survivorship, extended times to maturity (≈ 14 to 20 wk), the highest mean fecundity, 4 to 8 broods female-1 and λ ≈ 1. The results indicate the demography of Polydora ligni exhibits 3 seasonal phases with respect to population growth over the year: (1) a spring/early summer growth period; (2) a late summer/fall transition phase; (3) a late fall/winter maintenance period. These demographic phases can be related to regular periodic changes in estuarine soft-bottom habitats and can influence the evolution of its life history traits. Seasonal life history patterns were consistent with predictions of life-history models centering on demographic selection. Seasonal changes in demographic selection may act to increase life-history flexibility in Polydora ligni, and in other infaunal opportunists, as a way of maintaining fitness with respect to periodic changes in habitat conditions. Such flexibility may either enhance or diminish its colonizing abilities. Seasonal demographic changes can influence the response of P. ligni to benthic disturbance as opportunistic potential falls off after early summer due to life-history shifts

The effects of intra-specific density and food supply on growth and reproduction in an infaunal polychaete, Polydora ligni Webster

In two laboratory experiments decreasing food supply and increasing intra-specific density generally had negative effects on growth and reproduction in the spionid polychaete Polydora ligni. These included longer maturation times at smaller worm size, longer times to deposition of the first brood of eggs and inter-brood period, and decreases in the number of gametogenic segments, egg capsules and fecundity. The number of eggs deposited per capsule was not affected by the treatments. Analysis of field data indicated a significant negative correlation between intra-specific density and fecundity, suggesting that the laboratory results reflect field conditions. Populations of opportunistic infauna, like Polydora ligni. may undergo periods of density-dependent population regulation, and their life histories may be shaped via density-dependent as well as density-independent selective pressures

Drift Algae in New Haven Harbor and Impacts on Benthic Communities

In 2009 the University of New Haven initiated studies to develop a contemporary database and assessment of the benthic ecology of New Haven Harbor. Previous studies were last conducted in the 1970s and 1980s (e.g. McCusker, and Bosworth 1979, 1981, Rhoads and Germano 1982). Benthic populations and communities are excellent indicators of environmental conditions and are regularly used for environmental assessment in estuarine and coastal waters (e.g. Pearson and Rosenberg 1978, Rhoads et al. 1978, Zajac and Whitlatch 2001, Mangi 2003). Given the inherent ability of the benthos to integrate sediment and water quality, many environmental indicators and indices to assess the degree and nature of environmental change have been developed based on marine macrobenthic taxa and communities (e.g. Weisberg et al. 1997, Borja et al. 2000). Our findings have been reported to the Quinnipiac River Fund Board (Zajac and Brown 2012), and also have been presented at the Biennial Long Island Sound Research Conference that was held at the end of October 2010, and at national and regional meetings in 2011. Briefly, these studies showed that there are a diverse set of benthic (seafloor) habitats within the harbor that support a surprisingly diverse pool of species although there are areas that are impaired. Additionally, comparison to data collected in the 1980’s suggest that there has been an overall shift in the benthic community characteristics in New Haven Harbor suggesting a long-term degradation due to the presence / increased abundance of organisms that are typical under disturbed conditions

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)

Determination of the modal parameters on the thin flat structures

This paper presents the investigation of modal parameters using the different approaches. The object of the examination is the simple structure such as flat rectangle plate is. Before starting the measurement, there have been calculated natural frequencies of the plate by analytical approach. Subsequently, the experiment part is performed. The appropriate measuring apparatus has to be applicated for the experimental analysis. First, there are evaluated modal parameters of the specimen, the so-called “frequency sweep” is used as the input signal for excitation. After that, the experimental harmonic analysis is performed according the obtained eigen frequencies from the modal analysis. In the final stage, the data from simulations and experimental measurement are compared

Food Webs in Long Island Sound: Review, Synthesis and Potential Applications

Understanding food web structure and dynamics of ecological systems is a key element in the development of more effective environmental assessment and management procedures. Although various components of the Long Island Sound (LIS) ecosystem have been studied in some detail, a framework for food web based research has been lacking. The objectives of this study were to: a) collect and review all pertinent data available in the scientific literature and technical reports on food web components and interactions in different sections of Long Island Sound; b) based on this review, refine initial conceptual food web models and extract pertinent data as available for input into the trophic modeling system Ecopath; c) using the Ecopath models constructed, identify apparent critical food web components and functional groups (particularly those influenced by human activities and management decisions) in LIS, their potential influence on ecosystem dynamics, important linkages along the food web, and the nature of the food web dynamics; and d) make an overall assessment of the gaps in our knowledge and recommendations as to how the work can be built on, and how information from food web analyses such as these and the models themselves, can be used to support management efforts focused on the vital resources of Long Island Sound