Our Students and Their Research

Existing video data taken with the Video In Situ Settling Tube Apparatus (VISTA) was used to calculate particle sizes and settling speeds of suspended sediment particles found within the Estuarine Turbidity Maximum (ETM) region of the Chesapeake Bay. This information was used to determine the relationship between particle size and settling speed in order to calculate the fractal dimension, D3 and the reference particle diameter, dr. Observations of the settling speeds of suspended sediments in their natural environment have been estimated at 1 mm/s with fractal dimension values between 2 and 2.5. The preliminary results of this study show that particle settling speed increases with both size and depth, ranging between 0.5 and 4.5 mm/s and with sizes ranging between 71 and 549 microns. The calculated fractal dimension values decrease with depth ranging from 1.8 to 2.4, while the calculated reference particle diameter values increase with depth ranging between 0.5 and 4.9 microns.

The Eastern oyster, Crassostrea virginica is in trouble. The impact on the seafood industry and traditional fishing communities may be incalculable. Oysters play a vital role in helping to maintain water quality in estuarine ecosystems. Oyster reefs created by aquaculture can very rapidly take on the characteristics of healthy natural oyster reefs. The restoration of oyster reefs through aquaculture is an important part of the process of restoring the Chesapeake Bay. This study is to determine if there is a relationship between juvenile oyster size and resistance to mortality by desiccation to provide parameters of survival for oyster spat under transit conditions. Spat were marked to assure that replicates were easily identified. Replicates of each size class were subjected to timed desiccation in a drying oven. The percentage of dead oyster spat was determined after a recovery period. All data was plotted "raw" and then normalized using Microsoft Excel 2000 software. Our preliminary data analysis strongly suggests that there is a direct positive correlation between oyster-spat size and the spats resistance to mortality due to desiccation. A distinction occurs between <1mm and 3mm spat. This suggests that larger sizes (>3mm) may display an even greater tolerance to exposure.

Exposure of aquatic animals such Palaemonetes pugio to contaminated sediments of aquatic animals such Palaemonetes pugio can cause these animals to increase their metabolic rates and thus change their energy budgets to better cope with the higher accumulation of toxic contaminants in their bodies. Inability to cope with contaminated conditions can lead to increased mortality. To examine changes in the energy budget of the grass shrimp P. pugio under contaminated conditions, we exposed shrimp to a concentration of 12% Elizabeth River sediment. We looked for effects on survival, standard metabolic rate measured by mean oxygen consumption at rest, growth measured by RNA:DNA ratios, lipid storage, and reproduction. We found no significant difference between contaminated and reference tanks for survival, reproduction, or growth. We also found no significant difference between tanks for oxygen consumption rates with the exception of week six, where shrimp from the contaminated tanks had a lower metabolic rate. We found a significant difference between treatments for adult lipid content, with shrimp from the contaminated tanks having higher lipid content. Thus, we did not see any conclusive negative effects of exposure to contaminated sediments on the energy budget of P. pugio.

One of the most predominant problems facing the Chesapeake Bay and its tributaries today is that of excess nutrient loading, which can lead to several detrimental ecological effects. However, although the results of high nutrient concentration have been studied in detail, few quantitative studies on nutrient sources have been conducted. This paper concentrates on the development of a one-dimensional advection-diffusion model for the Choptank River, the largest Eastern Shore Chesapeake Bay tributary. The model is based on the salt balance equation:

Using salinity data collected from the CISNet cruises between 1999 and 2001, the diffusion coefficient K was calculated once with time dependence, and once without. Currently, it does not appear that time-dependence makes a significant contribution to the diffusion coefficient, but it may play a larger role in the final model. The preliminary results of the model show that a one-dimensional model can accurately estimate salinity in a well-mixed sub-estuary such as the Choptank River. In order to complete this nutrient transport model, the model will need to be calibrated with the CISNet data and verified with an independent data set. A conservative tracer will then be added to the model to represent transport. Finally, a non-conservative tracer will be added to represent nutrient transport.

Benthic organisms respond to chemical and physical cues that prompt them to settle or deter them from settling at a particular sedimentary site. Disturbance to the sediment from deposit-feeding, burrowing, human activity, or numerous other sources releases sulfides and ammonium from the lower sediment layers. Since these chemicals are often toxic to benthic animals, they can act as negative chemical cues for settling larvae or mobile meiofauna. In this experiment, ambient porewater ammonium concentrations in Tom's Cove in Chincoteague Bay, VA were manipulated through the burial of acrylatnide gels containing Ammonium sulfate in the muddy sediment in an intertidal zone. Porewater and sediment samples were taken above the gels four days later and analyzed for ammonium concentration and animal content, respectively. It was found that the porewater ammonium concentrations were successfully increased above the high ammonium gels, with significant difference from the control gels. There was also a significant difference in meiofaunal abundance above those two types of gels. Only nematodes and polychaetes were found in the samples. The results indicate that acrylatnide gels are useful for chemical manipulation in the field. They also reaffirm previous findings that ammonium is a negative chemical cue for settling meiofauna.

Seagrass beds may influence sediment biogeochemical cycling through enhancing nitrification, ammonification, phosphate regeneration, and sulfate reduction as compared to unvegetated sediments. In addition, seagrass health (i.e. die-back) may influence biogeochemical cycling as well. This study was conducted in Florida Bay and Chincoteague. In Florida Bay, I found that concentrations and rates were higher in healthy beds than in unhealthy ones for relative nitrate concentrations and ammonification. No difference in rates between vegetated and unvegetated sediments in Florida Bay were observed. In Chincoteague Bay, differences between vegetated and unvegetated for relative nitrate concentration and ammonification were observed. Sulfate reduction and phosphate regeneration were indeterminate for both study sites. Methods need to be further improved so that reasonable rates can be determined. Once improved, further investigation will be able to elucidate these processes.

Seagrass decline worldwide is generally attributed to eutrophication. However, in the future global climate change may increase sea-surface temperatures, increasing the frequency and severity of storms. Increase in severe storms may also cause an increase in overwash events along barrier islands. Overwash events increase deposition, burying seagrasses and altering their habitat. The seagrasses Zostera marina and Ruppia maritima occur in patchy distributions in Sinepuxent Bay, a shallow coastal barrier island lagoon south of Ocean City, MD affected by overwashes approximately every 5 to 7 years. We hypothesize that overwash events will cause a short-lived setback on local seagrass populations as they quickly recolonize the area. We determined through organic matter, grain size, and GIS analysis that an overwash in 1998 altered seagrass habitats by changing topography, sediment type, and bottom cover. However, new seagrass habitat is being created as seagrasses slowly recolonize the area.

An in-situ camera system was created to investigate particle size distributions and the dynamics of flocculated particles within the Estuarine Turbidity Maximum zone of the Chesapeake Bay. The Video In Situ Settling Tube Apparatus (VISTA) displayed images of sediments within a settling tube. The images were recorded and later transferred to a computer and analyzed to determine particle characteristics. A Laser In Situ Scattering and Transmissometry (LISST) was deployed simultaneously with the camera setup in order to validate the outputs of both instruments. The preliminary results indicate that the two instruments agree reasonably well, but the VISTA misses some of the larger particles. The dynamics of flocculated particles were evaluated by investigating the sources of macroflocs within the water column. Of the two cruises, one data set indicated that macroflocs are present due to resuspension from the current shear. The data from the second cruise concluded that macroflocs are actively forming immediately following the decrease in current shear when the maximum tides pass.

Weighted flow networks are structures that arise naturally when analyzing complex systems. The countable properties of unweighted networks are not easily generalized to weighted networks. One candidate measure of complexity is the number of roles, or specialized functions in a network. It is easy to identify the number of roles in a linear or cyclic unweighted network. There is only one logically consistent way to generalize the measures of nodes, flows, connectivity, and roles into weighted networks, and these generalizations are equivalent to indices derived from information theory and used by ecologists since the late seventies. Data from ecosystem networks suggests that ecosystems inhabit a narrow window of the parameter space defined by these measures.

To fully understand interannual variations in the sizes of fish populations, the relationship between abiotic (density-independent) and biotic (density-dependent) factors must be analyzed. Moreover, particular attention must be given to the influences of physical factors in the field, and how it influences fish behavior, and ultimately larval recruitment. Small-scale turbulence in the field has been found to increase prey encounter with planktonic predators. Feeding success, however, is limited to a certain threshold of turbulence for visual predators, where the probability of successful seizure of prey eventually decreases with increasing turbulence. The effects of turbulence on non-visual predators is not investigated as fully as the effects of turbulence on visual predators, but is a worthy topic to completely understand microscale turbulence effects on an entire food web. The purpose of this investigation is to analyze the effects of varying amounts of small-scale turbulence on the feeding success of the non-visual ctenophore predator, Mnemiopsis leidyi. Small ctenophores were exposed to varying amounts of turbulence in a novel turbulence chamber apparatus while being fed an identical Artemia salinia nauplii concentration for each turbulence condition. Ingestion rates were analyzed as the mean naupllii/gut, and standard error bars were used to compare ingestion rates among all tested turbulences (0 mm/s- 26.2 mm/s). It was observed that no significant effect of turbulence on ingestion rate existed, as a non-linear relationship was discovered. This counters expectations as non-visual predators were proposed to encounter continually increasing feeding success with increasing turbulence due to ingestion based on contact, not visual pursuit. Further turbulence investigations concerning other non-visual predators should be undertaken to confirm these findings.

Bacteria incubations carried out using samples collected from chlorophyll max., oxic/anoxic interface, and marsh sites in the Delaware and Chesapeake Bays were run to examine breakdown and consumption of the protein BSA, as well as total DOC consumption. Experimental and control incubations were run simultaneously, and 20.0mg of BSA was added to experimental incubations. Protein measurements were made using NanoOrange Protein Assay (Molecular Probes; Eugene, Oregon). Station 1 incubations (chlorophyll max.) were found to consume the most protein at the fastest rate. Station 2 (oxic/anoxic) incubations showed lower rates and total consumption, and station 3 (marsh) was observed to have the slowest rate of degradation. Bacteria populations in experimental incubations were higher than in controls. Overall, rates of BSA degradation were similar for all three sites (~ 4% h^-1), and may indicate excessive run times. Station 3 (marsh) samples were found to have high DOC content which could represent an abundance of terrigenous compounds such as humic substances, and may have affected results. The use of NanoOrange as a seawater protein assay reinforced expected trends found in this study. However as a relatively new protein assay, its abilities to accurately measure small amounts of protein using the method we employed is still uncertain.

The rate of predation and feeding behavior of the blue crab Callinectes sapidus on the soft-shelled clam Mya arenaria, in relation to the presence of artificial submerged aquatic vegetation (SAV) was examined in 1 m² raceway tanks at the Academy of Natural Sciences Estuarine Research Center in St. Leonard, Maryland. Two types of experiments were conducted. The first experiment tested whether individual crabs would exhibit different rates of predation in single habitat tanks, where the habitat is defined by zero, low, medium, and high SAV density. The second experiment gave each individual crab a choice of three habitats: zero, medium, and high density SAV. Crabs participating in this experiment were video monitored to observe their feeding efficiency by quantifying the proportion of time each crab spent in each habitat compared to the amount of clams consumed in each habitat. The results of the first experiment showed that when not given a choice of habitat, crabs do not display significantly different predation rates between habitats, indicating that clams were not benefiting from the potential refuge created by higher densities of SAV. However, when given a choice of habitat, the crabs showed preference for feeding where SAV was absent over medium and high SAV habitats, but did not display significant differences of predation between the medium and high-density habitats. This suggests that the clams are getting protection from the presence of SAV, but may not get enhanced protection as the density of SAV increases. The results of the video monitoring showed highly variable feeding efficiency and behavior between individuals.

Epiphytes are considered detrimental to seagrasses as they reduce the amount of light, i.e. photosynthetically available radiation (PAR) that reaches the plant surface. This study evaluated the possibility that epiphytes can also be beneficial to seagrasses by reducing the amount of UV-B that reaches seagrass leaves. As UV-B may not only negatively affect seagrasses but also their epiphytes, possibly eliminating a positive filtering effect, artificial seagrass leaves made out of a UV-B transparent material were deployed at Horn Point Cove (Ruppia maritime and high nutrients) and Chincoteague Bay (Zostera marina and low nutrients) under a UV-B screen as well as under natural conditions (unscreened). At days 1, 3, 5, 7 and 12 after deployment, the leaves were collected and transmittance of UV and PAR quantified. No significant difference was found in the epiphytic load of UV-B-screened and unscreened leaves, suggesting that the present UV-B levels are not detrimental to epiphytic growth on seagrasses. In contrast, epiphytes transmitted a significantly lower amount of radiation in the UV-B range than in the PAR range. Therefore, epiphytic layers are effective UV-B filters on seagrass leaves. This benefit of epiphytes is lost when PAR transmission is reduced to levels below the compensation point.