We applied the Floristic Quality Index (FQI) to vegetation data collected across a chronosequence of created wetland (CW) sites in Virginia ranging in age from one to 15 years post-construction. at each site, we also applied FQI to a nearby forested reference wetland (REF), for a total of 30 sites (15 created, 15 reference). We tested the performance of the index against a selection of community metrics (species richness, diversity, evenness, percent native species) and site attributes (age, soil physiochemical variables). The relationship between FQI and community and environmental variables was analyzed with Spearman's rank order correlation coefficient and Canonical Correspondence Analysis (CCA). Calculation of FQI with all species (including non-natives) did not increase the number of significant correlations (p<0.05) with community attributes and/or environmental parameters when compared with FQI based on native species alone. Further, vegetation layer-based FQI calculations improved the sensitivity of the index to differences in floristic quality between sites when compared with an "overall" index calculated across layers, and a modified, abundance-weighted FQI showed a unique correspondence with community and environmental variables in the CW herbaceous layer and REF herbaceous and shrub-sapling layers. These results suggest that a "natives only", layer-based version of the index should be used in wetland assessment in Virginia, and an abundance-weighted FQI may be a useful tool for assessing floristic quality in certain layers. An abundance-weighted format is perhaps desirable because such an index preserves the "heritage" aspect of the species conservatism concept inherent in floristic quality assessment, and also entrains the "ecology" aspect of site assessment based on relative abundances of the inhabiting species. FQI did not successfully relate CW sites to REF sites, bringing into question the applicability of the FQI concept in comparing created wetlands to reference wetlands, and the use of forested reference wetlands in general to assess vegetation development in created sites. Based on correlations with soil nutrient variables and ordination results, we propose a conceptual model of vegetation development in created wetlands described as the "Initial Conditions" model, which is expressed in terms of initial site conditions, soil chemistry, species diversity, and floristic quality.

Age and growth rates for salmon sharks (Lamna ditropis) in the eastern North Pacific (ENP) were estimated from seasonally formed bands in the vertebrae, and compared to previously published life history parameters for this species from the western North Pacific (WNP). Results of this study show that salmon sharks in the ENP achieve their maximum length at a faster rate, reach sexual maturity at an earlier age and achieve a greater weight-at-length than those in the WNP. Additionally, this dissertation shows that adult salmon sharks maintain a specific body temperature independent of changes in ambient temperature through a combination of physical and physiological means, and essentially function as homeotherms. Due to uncertainty in previous life history parameter estimates for sand tiger sharks (Carcharias taurus) in the western North Atlantic, age and growth rates were re-estimated using a larger sample size and captive individuals injected with oxytetracycline (OTC), a fluorescent skeletal marker. The results support a hypothesis that this species forms one pair of growth bands annually in the vertebral centra, whereas previous growth rate estimates were based on the formation of two bands per year. as such, the growth rate of this species is considerably slower than previously predicted and the population more susceptible to fishing mortality. Demographic analyses were conducted for salmon sharks in the ENP and WNP, and for sand tiger sharks (based on new life history parameter estimates) with uncertainty in vital rates incorporated via Monte Carlo simulations. Density-dependent compensation was included in models where fishing mortality was imposed by increasing sub-adult survivorship from output values generated by a previously published "Intrinsic Rebound Potential" model. The results indicate that both species are extremely vulnerable to fishing mortality and that no fishery should be implemented for sand tiger sharks or salmon sharks in the WNP. Salmon sharks in the ENP were the only population examined that indicated the potential to tolerate any fishing mortality. A comparison of growth completion rates and other life history parameters of ectothermic and endothermic sharks did not indicate that endothermic sharks achieve their maximum length at a faster rate than ectothermic sharks.

No description available.

Theory and small-scale experiments predict that biodiversity losses can decrease the magnitude and stability of ecosystem services such as production and nutrient cycling. Most of this research, however, has been isolated from spatial processes, such as dispersal and disturbance, which create and maintain diversity in nature. Since common anthropogenic drivers of biodiversity change, such as habitat fragmentation, species introductions, and climate change, are mediated by these understudied processes, it is unclear how environmental degradation will affect ecosystem services. This dissertation examines how diversity interacts with spatial processes to affect the magnitude and stability of ecosystem functions, using seagrass communities as a model system. Diverse communities were more resistant to colonization, but the order of species arrivals affected competition outcomes. as predicted, grazer metacommunities assembled from diverse species pools were more diverse at all scales, had larger grazer populations, and usually kept their primary food resource, epiphytic algae, at lower abundances than metacommunities assembled from smaller species pools. Counter to theory, increasing the number of mobile grazer species in these metacommunities increased spatial and temporal variability of producers and grazers. Effects of diversity on stability also differed qualitatively between patch and metacommunity scales. Moreover, allowing grazers to move among patches reduced diversity effects on production and modified relationships between grazer diversity and stability. Finally, dispersal significantly increased resistance to and recovery from a mimicked macroalgal bloom. However, diversity did not. None of the existing theories for biodiversity-ecosystem function relationships or consumer-resource metacommunity dynamics completely explained patterns observed in these experiments. Effects of diversity and dispersal on ecosystem functions were complex, but seemed to be influenced by habitat choice and synchronization of grazer and epiphyte dynamics among patches. Overall, these results emphasize the importance of incorporating spatial processes and trophic interactions into the study of biodiversity-ecosystem function relationships. This information is critical for conserving diversity and managing ecosystem services in light of the ongoing changes to regional species pools caused by anthropogenic disturbance.

The spatially complex lower Chesapeake Bay estuary is characterized by a variety of bottom types and hydrodynamic regimes. to account for this physically-induced variability a benthic habitat delineation scheme was developed based on existing knowledge of physical and geological characteristics. Within the context of this scheme a series of studies were conducted to identify biotic response to and interactions with the physical, chemical and geological gradients that characterize the lower Chesapeake Bay. These studies characterized organism distribution and abundance patterns within the lower bay and identified processes controlling those patterns. The biological community of the polyhaline basin habitat, an area characterized by moderate tidal, but little wave-induced bottom disturbance was defined and described for the first time. This community is characterized by large tube and burrow builders, epifaunal and commensal organisms, shallowly-distributed, short-lived species and deeply-dwelling predators. The basin is also the preferred habitat of overwintering blue crabs and an area where biotic sediment reworking generally exceeds physical reworking. The results of these studies suggest that within the lower Chesapeake Bay estuarine system, the relative importance of biological versus physical processes in maintaining the structure and dynamics of estuarine benthic communities will be greatest in the basin habitat.

No description available.

The relative contributions to organic matter production and the interactions between submerged vascular plants and their associated microalgae assemblages were investigated in seagrass communities characteristic of the lower Chesapeake Bay. The studies were conducted in three parts; the first compared production and respiration of the major autotrophic components in adjacent seagrass communities dominated by Zostera marina and Ruppia maritima, respectively. Annual production for the two communities differed; in the Z. marina area microalgal (i.e. phytoplankton and benthic microalgae) production dominated during the summer months, whereas in the R. maritima area, the macrophyte-epiphyte complex dominated throughout the growing season. Both areas exhibited high annual gross production rates (1580 gC m('-2) in the Z. marina area and 1000 gC m('-2) in the R. maritima area) of which the microalgae accounted for 45% and 36% in the two communities respectively. The ratio of net production to dark respiration (P/R) exceeded 1.0 for each of the components, suggesting export and/or burial of carbon from the system. The second series of studies investigated specific interactions between Z. marina and its epiphytic microalgae. Two sites were examined, where previous observations had been made of differing epiphytic colonization patterns. The two seagrass ecosystems differed markedly in epiphytic abundance, community structure, and productivity and respiration of the epiphytic complex. Based on gross morphological characteristics of the seagrass host, differences in nutrient conditions could exist at the two sites, where the hypothetically enriched site coincided with a flourishing epiphytic community. Effects of nutrient enrichment and light reduction on epiphytic growth were examined directly in the third phase of this study using controlled microcosm experiments. Both nutrient enrichment and light reduction led to enhanced epiphytic productivity and biomass, as well as increased light attenuation associated with epiphytic growth. Direct reduction in ambient light also stimulated epiphytic production relative to that of the seagrass host. Reduced abundance of plant leaves in the nutrient enriched systems perhaps indicated some signs of stress to Z. marina. This study suggests that nutrient enrichment and light reduction in the water column could increase epiphytic growth and production, possibly at the expense of the macrophyte.

The oxygen metabolism and exchange of nutrients between sediment and water were studied on a submerged sandy shoal in the York River, Virginia from March to December 1983. Particular emphasis was placed on the variability in metabolic estimates over different time scales. Variation in oxygen metabolism was examined over the photoperiod, between successive sampling days, between tidal condition (mid-day high vs. low tide), and among seasons. Morning NP was significantly greater than afternoon NP over the study. Mean hourly NP and R were significantly different between successive days in 4 of 6 tests, and 2 of 6 tests respectively. R was significantly higher on days with mid-day low tides (noon (+OR-) 2 hours). Mean hourly NP was 49% greater on days with mid-day low tides and R was 70% greater. Hourly NP and R were significantly different among seasons. R peaked in summer and NP in fall. Plots of mean hourly NP and R by month were made using all data for a given month and compared to plots made by randomly selecting a single measurement for each month. The latter plots are based on 12 data points, the former on 185 points. The two types of plots produced very similar annual rate estimates but differed radically in their depiction of seasonal changes. Within dark domes, hourly fluxes of ammonium and phosphate ranged from -21 (uptake) to 364 ug-at N m('-2) and -3 to 76 ug-at P m('-2). Nitrate + nitrite fluxes were generally small and erratic, comprising an average of only 15% of the total dissolved inorganic nitrogen flow. Releases of ammonium and phosphate peaked in summer, were an exponential function of temperature, and a linear function of respiration. Average ammonium release within transparent domes was only 25% of the average release in the dark domes, but phosphate fluxes were nearly identical to those in the dark domes. Nitrate + nitrite fluxes comprised an average of 17% of the total dissolved inorganic nitrogen flux of the transparent domes. Ammonium fluxes were significantly different between dome treatments, fluxes of the other nutrients were not significantly different.

Early life histories of alewife (Alosa pseudoharengus) and blueback herring (A. aestivalis), collectively known as river herring, are poorly documented for Chesapeake Bay populations. Improved knowledge of these early life histories potentially will aid fisheries, habitat and resource management. Investigations were conducted following two lines. First, alewife and blueback herring larvae reared from eggs were used to investigate methods for species identification and to validate the otolith increment method for age determination. Blueback herring larvae hatched from naturally-spawned eggs were reared to age 24 d. Alewife and blueback herring larvae hatched from artificially-spawned eggs were reared to age 32 d and age 37 d. Alewife larvae exhibited paired melanophores laterally along the notochord starting at about 15 mm SL, contracted xanthophores dorsally on the head, and lacked xanthochrome at the caudal fin base. Blueback herring exhibited one or two melanophores dorsally on the notochord starting at about 11 mm SL, relatively large xanthophores dorsally on the head, and xanthochrome at the caudal fin base. Other pigment variation was found. Estimated deposition of otolith increments was 1.16 and 0.90 increment d&\sp{lcub}-1{rcub}& for blueback herring larvae and 0.90 increment d&\sp{lcub}-1{rcub}& for alewife larvae. Increment enumeration was affected by otolith microstructure appearance, but estimated deposition did not differ statistically from one increment d&\sp{lcub}-1{rcub}&. Second, larval river herring distributions, abundances, growth rates, and hatch dates in the Pamunkey River tidal freshwater reach were analyzed. Distributions and abundances of zooplankton prey for river herring larvae were also analyzed. High abundances in two tidal creeks suggested that larvae occur in these areas from about late April to about mid-May. Larval river herring growth, pooled across seasons, was faster in the tidal creeks, 0.46 mm d&\sp{lcub}-1{rcub}&, than the mainstem river, 0.34 mm d&\sp{lcub}-1{rcub}&. Faster growth in the tidal creeks may increase survival by reducing the larval stage duration. Older larvae, pooled across habitats, grew faster than younger larvae, 0.59 mm d&\sp{lcub}-1{rcub}& and 0.35 mm d&\sp{lcub}-1{rcub}&. Larvae with relatively earlier hatch dates were associated primarily with the mainstem river while larvae with relatively later hatch dates were associated primarily with the tidal creeks. Zooplankton abundances were higher in the tidal creeks than the mainstem river.

No description available.