No description available.

Abstract Background: Cusk-eels from the subfamily Neobythiitinae are one of the major groups of sound-producing fishes on the continental slope. Sounds have never been recorded from a member of this subfamily, and sonic anatomy is considered a proxy for sound production. As the first part of a study on the effects of depth on sonic anatomy, we examined three relatively shallow species from the upper continental slope. Methods: Three species (Hoplobrotula armata, Neobythites longipes and Neobythites unimaculatus) were examined for sonic anatomy (skeleton, swimbladder and sonic muscles), and sonic and epaxial muscle fibers were measured for diameter. Regressions of dimensions and weights of sonic muscles and swimbladders against fish total length and weight were compared to determine sexual dimorphism and relative development between species. Results: Four pairs of sonic muscles (two medial and two lateral) originate on the skull and insert on the medial swimbladder or on modified epineural ribs that attach to the lateral swimbladder. The medial and medial intermediate muscles are generally larger in males than females and are made of relatively small fibers (ca 10 um in diameter), and lateral muscles are generally larger in females and consist of larger fibers as in epaxial muscles. Medial muscles are considerably larger in Hoplobrotula armata than in the Neobythites species. Conclusion: Neobythitines from the upper slope have relatively well-developed sexually-dimorphic sonic systems, suggesting that males produce advertisement calls for courtship. There are major quantitative differences between species. We suggest that sound production involves tonic contraction of the large-fibered lateral muscle pair and oscillatory contractions of the smaller medial fibers setting the swimbladder into vibration. Hoplobrotula armata is probably capable of making more intense sounds than the Neobythies spp.

In the uppermost millimeters of shallow submerged coastal sediments, photosynthesis by microalgae and cyanobacteria during daylight hours can cause oxygen supersaturation of sediment porewater, leading to bubble formation. In shallow water depths, the seabed is affected by the pressure maximum beneath the wave crest and pressure minimum beneath the wave trough. While the photosynthetically-generated gas bubbles persist within the surface layer highly permeable sand sediments, they may be exposed to pressure pulsations caused by tides and passing surface gravity waves, because pressure is not significantly attenuated in the upper few centimeters of permeable sediments. The question arises, whether the tens of thousands of millimeter-size bubbles that are produced on sunny days in each square meter of nearshore sands respond to these pressure oscillations and if so, what consequences these responses may have. The main goals of the research thus were the demonstration of the bubble pulsation within the sediment and the quantification of the pore water flow, associated interfacial solute flux, and sand grain movement caused by the pulsation. The central working hypotheses tested in this research were: 1) Millimeter-size photosynthetic gas bubbles buried in the surface layer of submerged permeable coastal sands respond to passing surface gravity waves by volume changes leading to bubble volume pulsation. 2) This bubble volume pulsation causes pore water flows and thereby exchange across the sediment-water interface and an increase of the net solute flux from the sediment. 3) The bubble volume pulsation causes sand grain movement and thereby local sediment compaction, alteration of sediment surface topography and vertical transport of substances attached to the sand grains. These three working hypotheses were addressed in Thesis chapters 1, 2 and 3, respectively. In-situ video observations with a buried camera showed that the bubbles (1-3 mm diameter) buried in the surface layer ([less than] 10 cm) of nearshore sand respond to passing waves by volume pulsation and allowed estimation of the oscillating volume change of the bubbles visible in the sediment-cross section. These observations revealed bubble volume oscillation with compressions of 7.4% caused by ~1 meter water waves producing a temporary 10 kPa pressure increase. Laboratory measurements in a custom-built pressure tank confirmed the in-situ observations: Bubbles with 1.24 mm to 2.12 mm diameter (1 mm3 to 5 mm3), embedded in transparent Nafion[TM] sand sediment, at 1 m water depth were compressed by 8.7 ± 1.3 % of their volume when exposed to the same pressure increase of 10 kPa as produced by a 1 meter water wave. With an observed abundance of 50,000 bubbles m-2 in sandy Gulf of Mexico sediments, the pulsation of bubbles with 2 mm diameter produced by the passing of thirty 1 m-waves per minute (8.3% compression) could pump 31.3 L m-2 h-1 (or 750 L m-2 d-1) of water across the sediment-water interface. Once it was established that surface layer bubbles pulsate due to pressure oscillations associated with passing surface gravity waves at a rate consistent with Boyle's Law, the effect of pulsating bubbles on pore water movement and grain movement was investigated. Fluorescein dye tracer experiments conducted at the same wave frequency (0.5 Hz) and wave height (75-100 cm) showed a linear correlation (R2 = 0.99) between interstitial gas bubble volume and interfacial tracer flux. The pulsation of 200 five-microliter bubbles embedded in the top 2 cm of a 10 cm (L) x 10 (W) x 45 cm (D) wet sediment core (bubbles occupied 0.5% of the volume of the 2 cm thick upper sediment layer) increased interfacial flux initially (first 7 min) by a factor of 17 compared to the control experiment, where tracer transport was limited to molecular diffusion and some tracer release caused by the setup of the experiment. The increase of flux caused by the bubbles is produced by the oscillating water flow across the sediment-water interface that pushes pore water out of the sediment that then is mixed into the overlying water through dispersion and turbulence. At an observed in-situ abundance of 50,000 bubbles m-2, bubble pulsation can be estimated to increase solute transport across the highly-active sediment-water interface by a factor of 30 when compared to molecular diffusion. Over time, the intermittent movement of sand grains driven by the pulsating bubbles resulted in a tighter packing of the sand, with a decrease in pore space, and an overall downward migration of grains above and around the buried bubbles. Particle Image Velocimetry showed that the cross-sectional area around the bubble, in which grains were moved by its pulsation, decayed exponentially over time. In the natural environment, decompaction of the sediment surface layer by bioturbation and sediment resuspension by bottom currents counteracts the compaction caused by the bubble pulsation, resulting in a continuous cycle of compaction/de-compaction that keeps a substantial fraction of the grains in the surface layer moving. With observed in-situ abundances of 50,000 bubbles m-2 and an average bubble volume of 5 mm3, approximately 5,000 cm3 m-2 or 50% of the grains in the top 1 cm of the sand bed are moved by the pulsation of buried gas bubbles every hour. The movement and net downward migration of surface layer sand grains towards pulsating bubbles has broad implications for sediment physical characteristics, sediment geochemistry and pore water flow. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Sciences in partial fulfillment of the Doctor of Philosophy. / Fall Semester 2015. / October 29, 2015. / Bubbles, Coastal, Pressure, Sand, Sediment, Waves / Includes bibliographical references. / Markus Huettel, Professor Directing Dissertation; Janie Wulff, University Representative; Ian MacDonald, Committee Member; Jeffrey Chanton, Committee Member; William Dewar, Committee Member.

Persistent organic pollutants (POPs) such as the organochlorine pesticide hexachlorocyclohexane (HCH) may undergo atmospheric transport and accumulate in regions remote from the source. It is important to develop techniques to help apportion source and identify transport or transformation processes to which HCHs and other mobile POPs may be subjected. Molecular tracers such as compound specific stable isotope and enantiomer ratios (ERs) may prove valuable in studying POP fate and transport. The objective of this study was to further develop the use of these two novel geochemical tools to evaluate the sources, transport and environmental fate of POPs, in the context of studying the fate and transport of HCH, a globally distributed POP. In the first part of my study, I evaluated the potential for using stable isotope ratios to track POP source and transport, using HCH in laboratory simulations of global distillation. I compared the relative fractionation of carbon versus deuterium isotopes during air-water gas exchange along a strong temperature gradient. The hypothesis, that perdeuterated, but not necessarily carbon-labeled compounds would show measurable and significant fractionation during air-water transfer, was validated within the confines of the experimental system. The results suggest that it may be possible to use a dual tracer approach on a larger scale, in which carbon isotopes could be used to track POP source, while fractionation of deuterium may be used to track POP transport distance. In the second part of the study, I evaluated the potential for use of ERs to evaluate HCH biodegradation. The rationale was that most enzymatic processes are stereoselective, enantiomers of pesticides may microbially degrade at significantly different rates, leading to increased environmental persistence of the non-degradable isomer. to bridge the gap between microbial and chemical information on enantioselective processes, I measured microbial activity, abundance, concentrations and enantiomer ratios of HCH in air and surface waters of the York River estuary. HCH concentrations and ERs were related with microbial activity but there were seasonal variations in enantioselectivity suggesting that seasonal as well as spatial differences in microbial communities may affect HCH ERs. The relationship between microbial parameters and enantioselective degradation appears to be complex and warrants further study before ERs can be used as effective tracers of chiral POP transport.

No description available.

Following larval development in coastal waters, the postlarval stage, the megalopa, of the blue crab enters estuaries and colonizes juvenile/adult habitats. I examined the dynamics of the immigration of blue crab megalopae in the York River, Virginia. Plankton samples were collected nightly during flood tide in the York River Jul-Nov 1987, 1988 and 1989 to quantify variation in abundance of blue crab megalopae during the recruitment season. The abundance of megalopae was highly episodic, and significantly correlated with wind stress to the west (1987, 1988 and 1989), wind stress to the north (1989), and observed tidal range at Gloucester Point (1987 and 1988). These factors accounted for 22-56% of the variation in megalopal abundance. Megalopal abundance was not correlated with current speed, water temperature, salinity, or Chesapeake Bay subtidal volume. While in the estuary, megalopae vertically migrated in response to light and tide. Blue crab megalopae were more abundant during flood than ebb, indicating that megalopae selectively occupy flood waters. Ascent of megalopae into the water column appeared to be light limited. at night, megalopae were concentrated at the surface; during day, they were concentrated near the bottom in deep water, but apparently did not ascend from the bottom in shallow water. Thus, megalopae utilize flood currents for transport up the estuary while reducing the risk of predation to visual predators. Spatial patterns of abundance of megalopal and juvenile blue crabs were not consistent across habitats (plankton, grassbeds, or artificial settlement substrates) or time (days, months). Densities of megalopae and first-stage juveniles in grass beds correlated with megalopal abundance in the plankton; settlement on artificial substrates did not. Total juvenile abundance exhibited lower spatial and temporal variability in grass beds than that of megalopae or first-stage juveniles, suggesting that high variability in settlement is tempered by post-settlement processes. In laboratory studies, sand shrimp, Crangon septemspinosa, consumed &>&99% of available megalopae, while grass shrimp, Palaemonetes pugio, consumed 37% of megalopae in the first trial and 5% in the second trial. Predation by grass shrimp was not related to the rate of metamorphosis of megalopae, but may have been related to water temperature.

Juvenile weakfish Cynoscion regalis, life history was studied in the York River estuary, Virginia. to verify daily aging methods of juvenile fish, both male and female adults were induced to spawn by injection of 200 IU Human chorionic gonadotropin/Kg wet weight. Subsequent larval and juvenile fish were reared up to 275 days with wild plankton and a daily rotating diet of squid, liver, Anchoa mitchilli, and Menidia menidia. Otoliths and scales were examined for daily microincrements patterns. Otolith ring counts were highly variable (31% varied by &>& 15% among 3 counts). Two problems were evident: (1) Microincrements frequently split to form two increments; and (2) Otoliths from a size series of fish (6.12-13.1 mm) indicated that weakfish otoliths grew by bud formation rather than concentric deposition. Scale circuli showed little variation between counts (99.5% of 2 counts from an individual scale were the same). Daily scale deposition was suggested by rearing up to 100 days, after which ring deposition was less than daily, however further research is needed because only one fish was reared past 25 days. The advantages of scale circuli counting over otolith increment counting were increased precision and ease of preparation. Field samples were collected weekly from the York River channel, at night using a 4.9 m, 1.5 mm cod end, trawl, during the weakfish nursery period (Aug-Oct 1983). The new technique of daily aging by scales, was applied to 845 of 922 weakfish collected. Counts ranged from 3 to 100 circuli/scale. Three cohorts were defined from the 1983 0-age fish. Growth rates estimated from scales (0.76-1.13 mm/d) were similar to those from length frequencies (1.0-1.2 mm/d). Analysis of covariance showed a significant difference (0.05 level) in growth rates among cohorts and among stations, but third order interactions (station, cohort, growth rate) were not detected. Mortality/migration rates estimated from decline in mean catch were significantly different between cohorts 1 and 2 (0.05 level, t-test). Weakfish were first abundant as new recruits at the river mouth, and moved upriver as they grew. In the fall a reverse migration occurred. Birthdate frequency by station and date indicated that different cohorts used different areas of the York River.

No description available.

The genus Bittium in the Western Atlantic was studied to determine the number and distribution of extant species. Shells of adults and juveniles collected from Brazil to Canada, including the type specimens of B. virginicum, were examined and compared on the basis of length, lengthwidth ratio and varix presence or absence. Although intergrades of B. alternatum and B. varium probably existed in the middle Chesapeake Bay, along the Atlantic shores of the Delmarva Peninsula and New Jersey, and in western Long Island Sound prior to 1940, B. alternatum is now found from Shark River, New Jersey, northward and B. varium from Chesapeake Bay, s outhvlard. There are presently no Bittium between Shark River, New Jersey and Cape Charles, Virginia excepting the B. var.i·um in Chesapeake Bay. Destruction of the eelgrass habitat in the 1930's is the probable cause of :.the absence of Bi ttium in the area of former intergradation. Larger size and lack of a varix distinguish adult B. e1lterna.tum from adults of the smaller, more slender .!}.. var:l.um. Juveniles are more difficult to separate since neither species possesses the varix as juveniles, but juvenile B. alternatum are usually wider than juvenile B. var.ium and attain greater lengths before formation of an apertural canal with maturity. B. virginicum·is considered a growth form of B. varium.

The sandbar shark, Carcharhinus plumbeus, is the most abundant large coastal shark in the temperate and tropical waters of the northwest Atlantic Ocean. The Chesapeake Bay, Virginia and adjacent waters serve as a nursery ground for C. plumbeus as well as many other fauna. Characterizing the diet of a higher trophic level predator such as the sandbar shark sheds light on a small portion of the temporally and spatially complex food web in the Bay. This study describes the diet of the sandbar shark, highlighting differences in diet within various portions of the nursery area, as well as ontogenetic changes in diet. Stomach samples were obtained in 2001 and 2002 from 232 sharks caught in gillnets or by longline gear. Historical data from the Virginia Institute of Marine Science (VIMS) Shark Ecology program were also analyzed. Ontogenetic changes in diet were evident, with crustacean prey decreasing in importance and frequency with increasing shark size, and elasmobranch prey importance and frequency increasing with increasing shark size. While previous research in Chincoteague Bay, VA showed the blue crab, Callinectes sapidus, as the dominant crustacean in sandbar shark diet, the mantis shrimp, Squilla empusa, dominated the crustacean portion of the diet in this study. Differences in diet were mainly attributable to location of shark capture. Small juveniles (< 80 cm precaudal length) in the lower Chesapeake Bay ate significantly more fishes, whereas Eastern Shore juveniles ate more crustaceans. The type of crustacean consumed varied within areas of the Eastern Shore, with more portunid crabs consumed in waters near Wachapreague and more mantis shrimp consumed near Sand Shoal Inlet. This study was not able to detect any change in diet over time due to insufficient sample sizes and the effect of location.