No description available.

Monotypic stands of the macrophytes Peltandra virginica and Spartina cynosuroides, which shared a common boundary, were studied at Sweethall Marsh, a tidal freshwater marsh located on the Pamunkey River within the Chesapeake Bay estuarine system, Virginia. Compartmental models indicate that both Peltandra and Spartina take up, internally cycle, and release to the environment, significant levels of nitrogen and phosphorus. Models also suggest that Peltandra and Spartina and their associated sediment compartments are capable of regulating nitrogen and phosphorus fluxes through their uptake and storage capacity. Nitrogen use efficiency was significantly higher in the shoots and roots of Spartina compared to Peltandra, while rhizome use efficiency was slightly higher in Peltandra. Phosphorus use efficiency was significantly higher in shoots, roots, and rhizomes of Spartina than in Peltandra. Lower use efficiency in Peltandra demonstrates a greater demand of nutrient per unit biomass than Spartina. Nitrogen and phosphorus recovery efficiency was higher in Peltandra. Efficiency indexes suggest that although Spartina appears to use nitrogen and phosphorus more efficiently for growth, Peltandra recovers and stores these nutrients more efficiently. Peltandra shoot, root, and rhizome tissue nutrient levels appear independent of sediment nitrogen and phosphorus availability. Spartina shoot, root, and rhizome nitrogen levels, however, appear dependent on sediment total nitrogen and total phosphorus. The relationship of Peltandra tissue nutrient levels to sediment availability is explained in terms of the rhizome storage capacity and reallocation of nitrogen and phosphorus to support productivity patterns. Spartina, however, must rely more on de novo root uptake to meet nutrient demands. Shoot, root, and rhizome nitrogen and phosphorus standing stocks were strongly correlated in both Peltandra and Spartina while sediment standing stocks were not. Nitrogen to phosphorus ratios were higher in the shoots than the roots and rhizomes of both Peltandra and Spartina reflecting the levels of nitrogen required to support photosynthesis. Nitrogen to phosphorus ratios varied over the sampling period, however appeared to converge on an "optimum" ratio. The correlation of nitrogen and phosphorus suggests an interaction between these nutrients although this relationship is unclear. Apparently both Peltandra and Spartina reallocate, as well as require, nitrogen and phosphorus in certain ratios which maximize productivity, uptake, and carbon assimilation.

Continuous flow microcosms (50L volume, salinity 18-24 ppt) were used to examine the roles of heterotrophic protozoa and bacteria as phosphorus mineralizers. Nitrogen limitation was regulated by N:P supply ratios (5:1, 16:1) and growth rate was regulated by dilution rate (0.5, 0.25 volumes day&\sp{lcub}-1{rcub}&). Rates of carbon and phosphorus uptake from dissolved inorganic pools were determined using &\sp{14}&C and &\sp{lcub}32{rcub}&P tracer experiments and pre- and post-fractionation incubations. Based on uptake rates and on POP and POC values of the bacteria in the &<&1.0 &\mu&m fraction, mass balance estimates of bacterial mineralization were determined. An isotope dilution method was used to determine phosphorus mineralization in the unfractionated sample. Heterotrophic protozoan mineralization was calculated as the difference. Results showed that bacteria had a minor role as remineralizers of phosphorus, more often taking-up inorganic phosphorus than remineralizing it. Heterotrophic protozoa were the major remineralizers of phosphorus. Microcosm treatments with a greater supply of inorganic phosphorus over nitrogen had increased POP concentrations and increased phosphorus remineralization. The effect of dilution on phosphorus remineralization was temperature dependent. Greater remineralization occurred in the high dilution rate in the July through October experiments and less remineralization occurred in the high dilution rate treatments in the December and January experiments.

Seasonal occurrence and activity of heterotrophic nanoflagellates (HNANO or heteroflagellates) and bacteria were studied in a sheltered brackish water embayment of Chesapeake Bay wetlands (Virginia, USA) over a three year period (1981 - 1984). Epifluorescence direct counts and Scanning and Transmission Electron Microscopy (SEM and TEM) techniques were used for the description of organisms, enumeration, and biomass determinations. Seasonal bacterial growth rates and growth and grazing rates of bactivorous HNANO were estimated using diffusion chambers equipped with Nuclepore polycarbonate membrane filters in natural salt marsh tidal pools. Environmental monitoring of nanoplankton populations revealed a seasonal pattern of bacterial abundances with temperature while heteroflagellate abundances and growth rates showed no seasonal pattern nor correlation with fluctuations in bacterial densities. Heteroflagellate populations were dominated by 34 to 50 (mu)m('3) sized monads, choanoflagellates, bodonids, and Paraphysomonas sp., all found in varying abundances throughout the year. Blooms were concurrent with extended low tide or specific bacterial populations (i.e., cyanobacteria) typical of spring and autumn periods. Heteroflagellate growth in diffusion chambers reflected the environmental blooms and increased diversity of low water assemblages. Growth and grazing rates of heteroflagellates at ambient densities thus could account for 20 to 80% of daily bacterial carbon production. Although heteroflagellate ingestion rates did not regulate seasonal bacteria densities or vice versa, maximum growth of bacteria and heteroflagellates in chambers was closely coupled. Heteroflagellate grazing activity may regulate the rate of bacterial production by preventing substrate limitation and maintaining the population in an active growth phase. The seasonal study demonstrated the dynamic nature of nanoplankton populations during autumn and spring transitional periods. SEM photomicroscopy revealed that the dominant component of spring blooms may be composed of several members of the loricate choanoflagellate family, Acanthoecidae. Using modified EM techniques, eleven Acanthoecidae choanoflagellates species, identified from spring in situ chamber experiments, were described. In situ growth and grazing rates for the spring chamber populations ranged from 0.023 h('-1) to 0.196 h('-1) and 40 to 210 bacteria h('-1) respectively. These high rates represent an opportunistic response to optimum conditions and an expression of maximum grazing potential. (Abstract shortened with permission of author.).

Patterns in the distribution of feeding-biology categories of polychaetous annelids were used to characterize benthic habitats of the Middle Atlantic Bight. Feeding biology classifications were based on recent publications regarding polychaete feeding and on gut-contents analyses of polychaetes collected in the study area. Proportion of carnivorous polychaetes was greatest in coarser sediments, and decreased significantly with depth across the continental shelf. Surface deposit feeders numerically dominated most habitats. Abundance of surface deposit feeders decreased across the continental shelf and sharply increased at the shelf break, paralleling the pattern of water-column production. Proportion of subsurface deposit feeders was greatest in fine-sediment habitats, and increased significantly with depth and percent organic carbon across the continental shelf. Sessile polychaetes generally inhabited physically stable habitats of the study area. Proportion of sessile polychaetes was positively correlated with percent silt and clay and percent organic carbon. Feeding-morphology categories were generally less closely related to habitat differences than were feeding or motility categories. These results suggest that the diverse assemblages of polychaetes that inhabit topographic depressions of the Middle Atlantic Bight may be dependent on stability of sediment parameters. Furthermore, distribution and abundance of surface deposit feeders may depend on food resources from water-column production, and distribution of sessile polychaetes may be limited by physical disturbance.

In view of questions concerning the digestive and assimilative abilities of larval marine fishes, the changes in these processes with development, and their relationship with starvation-induced mortality; this study has three objectives: (1) to examine the morphological and histological development of the alimentary canal and associated structures of larval spot, Leiostomus xanthurus (Pisces: Sciaenidae); (2) to assess short-term carbon assimilation in discrete age cohorts of larval spot; and (3) to relate any changes in assimilation to development. The alimentary canal and associated structures of larval spot from hatching through transformation (metamorphosis) were examined using light microscopy. These findings were related to results of experimental-radiotracer studies of carbon assimilation in discrete age cohorts of larval spot. Cytological evidence suggested that the alimentary canal and associated structures were functional in first-feeding larvae after the completion of yolk-sac and oil-globule absorption, and changed little prior to transformation. There is no elaboration of tissues during the larval phase. Major development changes associated with transformation were accompanied by changes in habitat and feeding regime. The behavior of carbon-14 indicated that food was quickly digested and carbon assimilated following the ingestion of a uniformly labeled ration. A percentage of newly assimilated carbon entered rapidly into short-term metabolic processes and exited the larva via respiration beginning as early as 1 h after ingestion. Gut evacuation was complete within 6 or 7 h. Uptake, short-term retention, and loss of ('14)C were used to compute two parameters, carbon retention and carbon absorption, that were taken as relative indices of the coefficient of utilization and absorption efficiency. The relationships between these two indices of carbon assimilation and measures of development indicated that assimilative abilities did not improve with larval development. Because there were no major changes in alimentary canal tissues, this might be expected. The indices of assimilation were negatively related to larval condition factor and this relationship has important implications to larval growth and survival. Condition factor is an indicator of larval growth and robustness. Larvae that have been feeding well enough to survive, but less than optimally for maximum growth, apparently assimilate more carbon from a ration than do larvae with a better growth history. These results are plausible in evolutionary terms. Larvae may mitigate the risk of a patchy food distribution by fully utilizing available resources. Such compensatory mechanisms may be of great adaptive significance to pelagic marine larvae.

No description available.

No description available.

No description available.

Tidal freshwater wetlands represent a transitional wetland between tidal salt marshes and non-tidal wetlands. as such, they exhibit some of the vegetation characteristics of both systems. If the changes in the vegetation pattern favor the characteristics of one system over the other, the changes may be an indication of changes in the environmental conditions of the estuarine ecosystem that favors that system. Unfortunately, little is known of the temporal and spatial changes that occur in the vegetation patterns of tidal freshwater marshes of the mid-Atlantic coastal region. In 1987 a vegetation analysis was done on a 60 hectare section of Sweet Hall Marsh, a tidal freshwater marsh of Chesapeake Bay. The data was compared with that of a similar study completed in 1974 to determine the changes that may have occurred in the vegetation pattern of the marsh. The results found that there was no significant difference in the species diversity of the two studies. However, further analysis showed that there was a change in the plant species contributing to the diversity. Spartina cynosuroides, an oligohaline species that was not important in the 1974 study, had the fourth highest importance value in this study. The shift in species composition of Sweet Hall Marsh may reflect a shift in the marsh's environment from being historically that of tidal fresh water to one of being more transitional between oligohaline and tidal fresh water.