A two-year zooplankton survey of lower Chesapeake Bay was conducted from August 1971 to August 1973. Twenty-four stations extending from the Rappahannock River mouth to the Bay entrance were sampled each month, using paired bongo nets with a 202 μm mesh. Marine Cladocera comprised >68% of the total zooplankton during two months of the survey, and were 36-40% by number three other times. The mean abundance over the whole study area of all cladoceran species combined was >62,000 m-3 in August 1971 and was >1000 m-3 on six other occasions. Of the six species of marine Cladocera found, Podon polyphemoides was most eurythermal and euryhaline, being found in abundance at temperatures of 7-26°C and salinities of 11.5-27 0/00. It was found in all months of the year with a peak occurrence in May and a smaller peak in January. Peak densities of P. polyphemoides always followed periods of rapidly changing temperatures. Podon leuckarti was found only near the Bay mouth, nearly always at densities of latitude, cold water species which requires spring conditions for its emergence, restricting its appearance to the month of May in Chesapeake Bay. Podon intermedius occurred only in the bay mouth area, at densities of 18.3-26.4°C and a minimum salinity of 20.42 0/00. Although appearing to be a warm-water organism in Chesapeake Bay, the species is found at much lower temperatures elsewhere. An inverse temperature-salinity relationship may influence the worldwide distribution of this species, with its warm water occurrences being at relatively low salinities, and vice versa. Evadne nordmanni is a high-latitude species neeaing spring conditions to develop. It does not persist throughout the summer in regions where temperatures are >21°C for two months or more. E.nordmanni occurred from late winter through June, with a peak in May. It appeared throughout the study area with highest concentrations (>100 m-3) at the bay mouth at 15-19°C and 17-26 0/00-salinity. Evadne tergestina and Penilia avirostris usually occurred at densities of >100,000 m-3 at some stations, with a mean of 30,000 m-3 over the entire area. Densities of both species were greatly reduced by September and they disappeared in October. The species reappeared in August 1972 in greatly reduced numbers, being >1000 m- 3 only at the bay mouth. Numbers were higher in August 1973 but were still an order of magnitude less than in 1971. The freshwater runoff from Tropical Storm Agnes was responsible for the great reduction in populations of Podon polyphemoides, Evadne tergestina and Penilia avirostris in the summer of 1972 as compared to 1971 and 1973. Biological influences on cladoceran populations included predation by ctenophores, which limited P. polyphemoides to the bay mouth in June, and predation by chaetognaths, a probable cause of the great reduction in E. tergestina and P. avirostris densities between August and September. Day and night sampling over the entire study area and a 24-hour station at the York River mouth showed that Evadne tergestina releases its young from the brood pouch just before dawn. An individual of E. tergestina releases its first brood of young when two days old. The parthenogenetic reproduction of Cladocera makes them among the most opportunistic of marine zooplankters and is probably partially responsible for their comparative lack of speciation in marine waters. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

At the time of the Deepwater Horizon oil spill in 2010, very little was known about the inshore bottlenose dolphin (Tursiops truncatus) populations hit hardest by the spill. Without previous population demographic data impacts were challenging to assess. My dissertation was designed to build research capacity moving forward by helping to fill data gaps in the western Florida Panhandle. The first study presented here resulted in the first system-wide assessment of seasonal abundance, survival, and site fidelity patterns of bottlenose dolphins that inhabit the Pensacola Bay system. In contrast to a previous study that reported only 33 dolphins, results from mark-recapture analyses estimated abundance ranging from 220-310 individuals, which consisted of a high proportion (43%) of transients. The second study revealed fine-scale genetic population structure (detected using both microsatellite and mitochondrial DNA markers) among five inshore systems in the Florida Panhandle. Migration rates were variable among populations with higher gene flow moving from east to west than in the reverse direction, and into St. Andrews Bay than coming out of it. There was no evidence of sex-biased dispersal. Finally, a 100-year flood (20 inches over 30 hours) occurred unexpectedly in the middle of my field work, after which dolphins were seen with extensive skin lesions. The event resulted in a unique natural experiment from which to evaluate the potential impacts of sustained freshwater exposure on local dolphin population health. Despite the persistence of a near freshwater environment for several months, skin lesions were not widespread but extensive and persistent for only some individuals, the reasons of which remain unknown. This body of work offers an updated perspective on the ecological and evolutionary connectivity of inshore dolphin populations in the Florida Panhandle, information of which is crucial for understanding how to best manage populations and assess new potential threats moving forward.

No description available.

The objective of my research was to examine the physiology and behavior of metamorphosing oysters, Crassostrea virginica, and to investigate the effects of low oxygen stress on metamorphic processes. Specifically, I examined the effects of hypoxia (20% of air saturation) and microxia (&<&1% of air saturation) on settlement, survival, growth, morphology, metabolic rate and feeding on post-settlement oysters. All of the functions I measured were adversely affected by hypoxia and microxia, compared to normoxic controls. Survival times indicate that, like larvae and adults, post-settlement oysters are capable of anaerobic metabolism. The 2 week period following settlement is especially critical to recruitment. Low oxygen conditions increases mortality and have detrimental effects on the development and growth of post-settlement oysters. Oysters have the ability to feed at nearly all stages of settlement and metamorphosis. While hypoxic conditions reduce feeding only in the youngest metamorphosing oysters, microxic conditions affect all ages. Not only does weight-specific metabolism decrease as the oysters grow, but metabolic responses to low oxygen change from relatively oxygen independent to oxygen dependent. I conclude that oyster distribution may be influenced by low oxygen, especially in those areas that experience prolonged (24-48 h) hypoxia or severe microxic events. Low oxygen events may control recruitment into the adult population directly, because of larval settlement failure and post-settlement mortality, and indirectly, because of reduction in feeding, development rate, and growth of post-settlement oysters.

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.