Patterns of resource utilization and coexistence in marine intertidal deposit-feeding communities

Patterns of foraging and distribution of 19 species of infauna! deposit-feeding annelids are described from several intertidal soft-substratum habitats. Two major feeding groups were recognized: surface and sub-surface foragers. In both feeding groups, between-habitat species richness was positively correlated with food-resource supplies in sediments...

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

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)

Enhanced growth of a filter-feeding bivalve by a deposit-feeding polychaete by means of nutrient regeneration

Sediment reworking and tube irrigation by the deposit-feeding polychaete, Clymenella torquata, reduced the quantity of particulate organic matter (POM) at the sediment-water interface and increased concentrations of dissolved nutrients (nitrite, ammonia, silicate, phosphate) in the water overlying laboratory microcosms. To determine the effect of these changes on growth of the filter-feeding bivalve, Gemma gemma, clams of the same initial size were grown under different laboratory conditions, representing all combinations of the following three treatments: (a) presence or absence of light, (b) presence or absence of C. torquata, and (c) proximity to C. torquata (clams living in sediment with worms or in sediment-filled microcosms positioned 1 cm above the worms).Clams grown in sediment with C. torquata, and in light, experienced less POM at the sediment surface than clams elevated in the water column, due to the burial of POM by accumulations of worm-defecated mineral particles. Among clams grown in the same tank, those in sediment with worms grew faster (p \u3c 0.1) than those elevated above worms, indicating that worm-induced POM reduction at the sediment surface, or factors correlated with it, were responsible for increased clam growth.Clams elevated above worms (in light) were exposed to higher concentrations of dissolved nutrients and microflora than control populations in another tank which did not contain C. torquata. Elevated clams grew faster (p \u3c 0.1) when worms were present in the tank than when worms were absent. Worm activity transported nutrient rich sedimentary pore water into the overlying water, apparently stimulating microfloral populations which supported improved clam growth. The effects of C. torquata on G. gemma growth may be one mechanism contributing to the common association of these species in New England sand flats

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

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 effects of infaunal biodiversity on biogeochemistry of coastal marine sediments

We tested the role of benthic infaunal functional diversity in regulating the biogeochemistry of nearshore sediments using laboratory microcosms. Single and multispecies assemblages of deposit-feeding polychaetes (Clymenella torquata, Spio setosa, and Leitoscoloplos fragilis) were used, and fluxes of oxygen and phosphate, as well as profiles of oxygen and pH in the sediment pore water, were measured. Significant differences in flux rates were found among treatments that were unrelated to polychaete abundance or biomass alone. Multispecies assemblages had lower flux rates of both oxygen and phosphate than rates calculated from the single-species treatments. Depthintegrated oxygen and pH profiles also showed significant differences between multispecies assemblages and selected single-species treatments. These differences were most likely from species-specific feeding and burrowing behavior and species-related interactions. Coefficients of variance for both oxygen and pH were highest for microcosms with no polychaetes and lowest for the assemblages, indicating a dampening effect of multispecies assemblages on porewater heterogeneity. When oxygen flux data was incorporated into a model of oxygen dynamics in Long Island Sound, results indicated that shifts in the benthic community composition could change sediment oxygen consumption rates sufficiently to disrupt the balance between the physical supply of oxygenated water and biological oxygen demand. The results of this study confirm the importance of benthic functional biodiversity to nearshore sedimentary processes and suggest that losses of functional diversity can have significant effects on ecosystem function

FOOD-RESOURCE PARTITIONING IN THE DEPOSIT FEEDING POLYCHAETE PECTINARIA GOULDII

Volume: 147Start Page: 227End Page: 23

SEASONAL CHANGES IN THE COMMUNITY STRUCTURE OF THE MACROBENTHOS INHABITING THE INTERTIDAL SAND AND MUD FLATS OF BARNSTABLE HARBOR, MASSACHUSETTS

Volume: 152Start Page: 275End Page: 29