Our Students and Their Research

During the course of two months, a device was created and field-tested which continually samples atmospheric air for concentrations of ammonia and ammonium. Though still being refined, this sensor reliably measured nitrogen species during a variety of conditions: urban to rural settings, calm days to thunderstorms, dangerously high levels of ammonia/ammonium to next to nothing, and even while offshore in the Chesapeake Bay and Baltimore's Back River. Continual testing ranged in time from several hours to just under a week. All field-testing was carried out within the confines of the state of Maryland because it provided no death of infrastructural settings. Within the next several months this real-time sensor will be used as the primary data collection tool in a major study to model the fate and transport of ammonia/ammonium as a result of the changing agricultural trends on Maryland's eastern shore.

Sediment toxicity is a major area of current research in the Chesapeake Bay region. Much research has focused on the lethal effects of contaminants on benthic organisms. Sub-lethal effects of such contaminants, however, also need to be taken into consideration. To begin to understand the effects of these contaminants on a population of organisms, a long-term, multi-generational model named BAMM, Benthic Amphipod Multi-generational Model, was employed to focus on the sub-lethal effects of sediment contaminants on the amphipod Leptocheirus plumulosus.

The dinoflagellate, Pfiesteria piscicida, was exposed to varying levels of shear comparable to those found in its natural environment. The shear rates tested, produced by Couette devices, were 0, 1, 3, and 10 s^-1. P. piscicida and its in-culture prey, Storeatula major, were put in Couette devices at known concentrations and, at 24 hour intervals over 4 days, samples were withdrawn to measure the effect of shear on P. piscicida's growth and ability to graze on S. major. Additional experiments were conducted to determine how shear affected S. major, and how shear would affect a starved culture of P. piscicida. It was found that below 1 s^-1, shear was not significant on Pfiesteria growth. However, at 3 and 10 s^-1, shear significantly affected Pfiesteria growth. In the supplemental experiment testing the feeding rates of Pfiesteria after an hour of exposure to shear, the proportion of Pfiesteria with orange fluorescent inclusions (feeding cells) was dependent on the level of shear the specific treatment received.

The ingestion rates, clearance rates and selectivity of Neomysis americana on copepods, rotifers and phytoplankton were of key investigation. Since there was no significant difference in mysid length between all experiments mysid predation was not a result of various sizes but rather various prey. Mysids did prey on Thalassiosira weissflogii but it was so insignificant further consideration was extraneous. The functional response of N. americana on copepods was linear suggesting no saturation, whereas the function response of mysids on rotifers became logarithmic at concentrations exceeding 300 rotifers/liter. Ingestion rates significantly increased when copepods were offered in the presence of rotifers when compared to copepods offered alone; the same trend was seen for clearance rates. Rotifers offered in the presence of copepods showed no significant differences between rotifers offered alone. Clearance rates did, however, show a significant decrease suggesting that N. americana does prefer copepods to rotifers when presented with a choice. The presence of rotifers may be interfering with copepod escape and defense tactics resulting in greater mysid predation. Copepods may also be of greater nutritional value than rotifers to mysids. This investigation will act as a precursor for future studies applying these results in a non-turbid environment to the turbid waters of the Chesapeake Bay Estuary.

In recent decades, the populations of SAV in the Chesapeake Bay have decreased in number. A large factor in this decline has been the amount of nutrients deposited in the Bay by human sources, which in turn cause a buildup of algae that blocks light to the plants. In an attempt to determine how much epiphytic algae a plant can tolerate, artificial substrates were used to mimic actual plants. The first experiments were arranged to find whether an increase in nutrients resulted in higher levels of epiphytic growth. We found a correlation in the spring, but not in the summer. The second experiment compared epiphytic growth on the artificial substrate to the grassbed density it was placed in. We found that as bed density increased, epiphytic growth decreased. The ultimate goal is to determine at what level of epiphytic growth plants can survive. The reasoning behind the difference between spring and summer is a combination of factors, including differences in grazing, precipitation, temperature, and the source of nutrients.

It was hypothesized that desiccation will cause mortality in Crassostrea virginica (Eastern oyster) spat; small oyster spat are more susceptible to desiccation than larger spat; misting with ambient Choptank river water will reduce spat mortality; covering spat (thus reducing exposure to solar radiation) will decrease mortality; and decreased temperature/increased humidity will decrease mortality. These hypotheses were tested by subjecting spat of varying sizes and known ages to desiccation under various stressors. These included: direct exposure to atmospheric ambient weather conditions; exposure to the atmosphere while covered by a tarp thus preventing exposure to solar radiation; and exposure to ambient conditions with lessoned desiccation by providing a constant mist of Choptank River water flowing over the spat. The exposure times for each stressor ranged from 2-48 hrs. During the entire exposure time data loggers recorded the temperature, humidity, and solar radiation of the ambient conditions the spat were being exposed to. The results showed that desiccation did cause mortality in spat, and that the larger the individual spat, the longer it could to survive under any stressor. Positive correlations between decreased solar radiation, increased humidity, and decreased temperature were found. The spat positioned under the tarp faired slightly better than those under the mist of river water and both faired significantly better than those exposed to ambient conditions.
It was hypothesized that the mortality rate of Crassostrea virginica spat exposed to ambient conditions will decrease as their size increases and as their exposure time decreases was tested by subjecting spat of varying sizes and known ages to desiccation under various stressors. These stressors included direct exposure to ambient weather (sunny) conditions; exposure to the atmosphere while covered by a tarp thus preventing exposure to solar radiation; and exposure to ambient conditions with lessoned desiccation by providing a constant mist of Choptank River water flowing over the spat. The exposure times for each stressor ranged from 2-48 hrs. These stressors determined if various other factors (solar radiation, time of day, humidity, temperature, and a constant mist of sea water as compared to complete desiccation) would have any effect on the survival rate of the spat once removed from their natural environment. The results showed that the larger the individual spat, the longer it could to survive under any stressor. Positive correlations between decreased solar radiation, increased humidity, and decreased temperature were found. It was also determined that time of day did play a significant role in spat survival. The spat positioned under the tarp faired slightly better than those under the mist of river water and both faired significantly better than those exposed to ambient conditions.

The soft bottom coastal sediments of the Chesapeake Bay are inhabited by several species of macroinvertebrates. The geochemistry of the sediment is affected by the activities of the fauna within the sediment. It is important to understand how organisms affect the habitat in which they live inorder to understand how other species will be affected. The feeding behavior of a tentilid clam, Macoma balthica, in varying population densities was studied in laboratory conditions. The effects on nutrient flux, pore water, and primary production were analyzed in relation to population density.

The bioaccumulation of Hg, as methylmercury (MMHg), can reach toxic levels in top predatory fish that can be unsafe for human consumption. Over 40 states have fishing advisories due to the health risks associated with Hg. This research was completed to determine the HgT concentration in top predatory fish of MD reservoirs and investigate the relationships between Hg concentration and size. Large mouth bass and black crappie and/or bluegill species of fish were collected at five different reservoirs, and were analyzed for HgT. Large mouth bass was the only species that showed increased HgT concentrations with size class. Weight proved to be a better predictor of HgT concentrations, as four out of the five reservoirs showed a significant correlation between HgT and weight in large mouth bass. Only one reservoir was significantly different in terms of the amount of HgT in large mouth bass. In this study, we found that there were several large mouth bass from MD reservoirs that exceeded the common Hg advisory level (0.5 mg Hg/ kg fish tissue) and a few that approached the FDA action level (1.0 mg Hg/kg fish).

The fine-scale vertical distribution of zooplankton in an estuarine system was analyzed by addressing the following hypotheses: 1) Physical parameters such as low dissolved oxygen (DO), salinity, and temperature have an effect on the fine-scale vertical distribution of zooplankton. 2) Given that the copepod, Acartia tonsa is relatively sensitive to hypoxia, there will be a strong relationship between fine-scale vertical distribution of mesozooplankton and DO concentrations. 3) Given that the ctenophore, Mnemiopsis leidyi is relatively tolerant of hypoxia, there will not be a strong relationship between fine-scale vertical distribution gelatinous zooplankton and DO levels. 4) The greatest M. leidyi density will be found in the same fine-scale vertical layer as their prey, mesozooplankton. To test these hypotheses sampling was completed in the Patuxent River in July 1999 and in the mainstem of Chesapeake Bay in July 2000. DO, temperature and salinity were measured at 1m intervals using a YSI meter. Zooplankton samples and underwater video footage were attained at 2 meter intervals. Laboratory studies included identification and counting of the zooplankton samples and analysis of video footage in order to determine the ctenophore abundance in each depth interval. Zooplankton distribution data relative to DO concentrations supports the first hypothesis. There was a strong oxycline in Chesapeake Bay where DO concentrations where nearly anoxic below 10m. Zooplankton were not found below 10m in these severe oxygen conditions. However, when bottom DO does not reach stressful levels (that is, in the Patuxent River), zooplankton are distributed to lower depths. The second and third hypotheses were neither supported nor refuted. This is because in order to address these hypotheses DO levels had to be stressful (1-2 mg/L), but not lethal for ctenophores and zooplankton in a large part of the water column. These physical conditions never occurred in either the Bay or the River during sampling times. Distribution of zooplankton and ctenophores supports the fourth hypothesis. Both the Bay and River stations demonstrate an overlap in zooplankton and ctenophore peaks. The results received in this project can be used to further the study of the effects that low DO levels has upon the trophic interactions taking place in an estuarine system.

The effects of sediment disturbance on methylmercury production were studied at Mackall Cove, off the Patuxent River estuary, near St. Leonard, MD. The study consisted of six mesocosms and three treatments. The sediment was stirred twice over three weeks in the disturbed treatments. Porewater and sediment samples were taken to determine the concentrations of methylmercury, sulfate and sulfide. Deeply disturbed sediment (10 cm) was shown to have a significant increase in the production of methylmercury due to an increase in microbial activity.

Labyrinthilomycota spp. (or "Laby") is an unnamed species of the same phylum as the clam parasite QPX (quahog parasite unknown). QPX disease has been shown to cause mass mortalities in the clam (Mercenaria mercenaria). Research was conducted to determine if the cell-mediated immune system of M. mercenaria responds to this potential pathogen via chemotaxis, defined as directional migration of blood cells (hemocytes) along a concentration gradient of substances secreted by Laby. Test substances (i.e., live Laby cells, cell-free culture media, dead or lysed Laby cells, concentrated Laby proteins from culture media) were placed in the bottom of a blind-well chamber and clam hemocytes were placed in the top well, with a 5 micron pore size polycarbonate membrane separating the two wells. After an hour incubation, membranes were fixed, stained, and mounted, and cells were counted under 400x for the top and bottom sides of the membrane to determine the number of cells migrating through the membrane towards the putative chemoattractant. This information was used to calculate a chemotactic index, to compare control and experimental data. Preliminary results indicate that the presence of Laby cells does increase hemocytic chemotaxis, and that this response is dose-dependent. Results also indicate that hemocytes are responding more to a secreted chemoattractant, possibly protein, than to the Laby cell surface components. It is suggested that Laby cells secrete a mix of proteins, some that are attractive and some that are inhibitory to the clam chemotactic response. Since Laby is closely related to QPX, conclusions drawn from these experiments may be applicable to QPX as well.

Through the addition of sediment pore water extracted from various sites around the Delmarva Peninsula, the hypothesis was tested which stated that high-nutrient filtrate would stimulate growth of a local isolate of Prorocentrum minimum to a greater extent than would nutrient-poor filtrate. Growth rates of the dinoflagellate were analyzed over a period of 10-18 days amongst tubes containing pore water of varying nutrient compositions and concentrations from 18 sample sites. The sample sites were as well representative of a wide array of particle sizes and were situated in very diverse environments. Enhancement of the growth rate higher than the control was observed in 100% of experimental cultures, and some significance was found between growth rate enhancement and the existence of particular nutrients within pore water samples. Positive correlations between nutrient concentrations and physical characteristics of sediment demonstrate the possibility of classifying sample sites based on a variety of parameters. Results show the actual stimulation of growth from pore water examples and suggest that the nutrients within the benthos may serve as a source for pelagic algal growth.

Direct and enzymatic methods for urea determination were compared and analyzed for specificity. Organic nitrogen compounds (arginine and humics) were added to urea standards to measure interference in both methods. In the enzymatic method, urea concentration appeared to decrease with increasing arginine concentration. However, minor ammonia contamination in the arginine stock solution created uncertainty as to these results. However, the presence of arginine appeared to have no effect on the direct method. In the presence of humic material, the enzymatic method underestimated true urea concentrations, but the direct method was not as significantly affected. Pursuing a peripheral issue led to the conclusion that the enzymatic method underestimates urea concentrations under saline conditions. Urea standards and Pocomoke River samples were assayed using both methods. The enzymatic method underestimated urea concentrations relative to the direct method. Culture studies with the brown tide organism Aureococcus anophagefferens indicated that arginine is not an effective substrate for the organism's urease.

The calanoid copepod Eurytemora affinis is known to be highly adaptable in the dynamic conditions they encounter in the estuarine environments they inhabit. The geographic and seasonal distribution of the species is restricted, however, and could possibly be linked to osmotic limitations. These limitations involve both lethal and sublethal responses to salinity stress and are possibly related to salinity regime. Questions arise as to how osmotic demands created by different salinity regimes affect E.affinis individuals. These effects include sublethal responses such as reproduction and lethal responses involving maintenance costs. Possible salinity regimes populations encounter in estuaries are both pulsed and chronic and can have high, low, or optimal salinity levels. Under these parameters, E.affinis appears to have greater fecundity and survivorship in high salinity environments and in general, populations have relatively higher growth rates in varying vs. constant salinity regimes. Because salinity stress is often a major factor in many estuarine species' distribution, the response of E.affinis populations and individuals to different salinity regimes could be useful in explaining the factors limiting the distribution of the species in estuaries.

The accumulation of contaminants within the sediments of the Baltimore Harbor region has led to concern for their possible impact on aquatic ecosystems. In order to determine possible effects of contaminated sediment on three, co-occurring, indigenous species in the Chesapeake Bay we used 28d and 14d exposure tests. The three species studied were the benthic crustaceans, Palaemonetes pugio, Leptocheirus plumulosus, and Gammarus mucronatus. P. pugio and G. mucronatus were used in both 28d and 14d exposure tests, whereas L. plumulosus was only used in a 28d test. Organisms were exposed to diluted volumes of sediment from Colgate Creek (CC), a tributary in Baltimore Harbor. Contaminated sediments were mixed with the control substrate from Fishing Bay (FB) to make 25% CC and 50% CC concentrations. Reference sediments remained 100% FB. The responses of organisms, following the 28d and 14d exposures, were measured by quantifying changes in individual mass, mean reproduction, mean proportion survived, and standard metabolic rate for organisms in each of the three sediment treatments. The contaminated sediments showed no significant effects in measured response variables for P. pugio or L. plumulosus. Mean reproduction for G. mucronatus was significantly higher in the control sediments (FB) than in the contaminated sediments (CC). Standard metabolic rate values showed not significant differences between treatments implying that energy allocation for production was not altered. Effects on reproduction may have thus derived from mechanisms other than contaminant-driven energetic constraints. 14d exposures yielded similar survivorship results to that of the 28d exposure.

The Estuarine Turbidity Maximum (ETM), located at the head of many estuaries like the Chesapeake Bay, is a region of high turbidity and suspended particle concentrations. The ETM is a nursery area for larval fish and may concentrate zooplankton species. The goal of this study is to determine the spatial distribution of adult copepods and cladocera that are potential prey of fish larvae in and around the Chesapeake Bay ETM in both a wet (1998) and dry (1999) year. Plankton concentrations were analyzed from depth-stratified 1-m2 Tucker-trawl (280 micron mesh) samples that were taken at stations in the channel of the upper Chesapeake Bay. The study focused on the abundant calanoid copepods Eurytemora affinis and Acartia tonsa, and the cyclopoid parasitic copepod Ergasilus labricus. Cladocera analyzed were Bosmina longirostris and Daphnia pulex. Although total zooplankton concentrations were highest within and below the ETM zone in both 1998 and 1999, zooplankton distribution varied between species, year, and depth. Eurytemora and Ergasilus were concentrated in the ETM in 1998, but not in 1999. Acartia was concentrated below the ETM zone, and Cladocera were mostly found above the ETM. Vertical distribution varied among species, and between sexes of the same species. Changes in distribution and abundance of zooplankton in the ETM may have important consequences for higher trophic levels since the distribution of prey and parasitic copepods overlapped and was similar to that of larval striped bass and white perch.

The effects of diets consisting of the harmful algal bloom (HAB) species Pfiesteria piscicida (strain FDEPMDR23) and Prorocentrum minimum on the egg production and hatching success of the calanoid copepod Acartia tonsa were studied in laboratory experiments. These experiments were conducted in order to test the hypotheses that P. piscicida and P. minimum represent nutritionally deficient, or possibly toxic, diets to A. tonsa. A similar experiment was also conducted using the cryptophyte species Storeatula major since it was used as a food source to grow the P. piscicida. Each egg production and hatching experiment was run for 96h, which included a 48h acclimation period, a 24h experimental period, and an additional 24h period to allow eggs produced during the experimental period to hatch. Results obtained form the experiment using P. minimum as a food source show decreased egg production rates (expressed as eggs/female/day) and hatching success compared to diets consisting various diatoms and non-HAB forming dinoflagellates (information concerning these algal species was obtained from various sources cited within this paper). However, the P. minimum cultures used for this experiment were contaminated with S. major, so the results of this experiment cannot be directly linked to a diet consisting purely of P. minimum. Due to problems with copepod survival rates there is presently no data for the experiments involvingP. piscicida. or S. major. However, future experiments will be conducted to obtain this information. These results will also be combined with information on how these HAB diets affect the somatic growth of A. tonsa.