Our Students and Their Research

Aquatic microbial species have been proven to be difficult to culture and thus hard to study. The use of genetic analysis has begun to fill the knowledge regarding aquatic microbes. Analyses of ribosomal RNA genes in fosmid libraries constructed from bacterioplankton from surface waters of the Chesapeake Bay has revealed the presence of several groups of marine/estuarine microbes. Through PCR, sequencing, and phylogentic analysis, several aquatic bacterial groups have been identified. These include, but are not limited to Thiobacillus (Betaproteobacteria), Delftia (Betaproteobacteria), Verrucomicrobia, Synechococcus, Bacteroidetes, Paenibacillus (Firmicutes), and Actinobacteria.

Currently, the fate of medusa biomass after annual crashes of Chrysaora quinquecirrha populations in the Chesapeake Bay is unknown. A preliminary study on the effects of temperature on the swimming ability and mortality of the species is the first step toward understanding the eventual fate of this biomass. Such a study first requires the development of a large-tank experimental method. Our exploration in methodology to complete this study resulted in several readjustments in lighting and water exchange within the tanks. The start of the study was slowed by the local C. quinquecirrha population being low and consistently too small to sample. We speculate that this low population was caused by low salinities and thereby low strobilation rates in early summer. The following is a report on challenges faced when trying to run a large tank study on these gelatinous zooplankton once they were high enough in occurrence to sample.

The eastern oyster, Crassostrea virginica, is a culturally and socially valuable species that is declining rapidly in Chesapeake Bay. To estimate site-specific mortality rates from relative age class abundance, I generated cohort specific catch curves and compared the results to corresponding regional anthropogenic and environmental data, including harvest and August bottom dissolved oxygen, water temperature and salinity. Harvest and mortality, though there is high uncertainty (p = 0.67; α = 0.05), have a slight negative relationship. A strong negative relationship, though not significant (p = 0.06; α = 0.05), exists between dissolved oxygen and mortality. Despite what may be expected, there is a highly significant negative relationship between temperature and mortality (p = 0.01; α = 0.05). Salinity and mortality have a negative relationship (p = 0.13; α = 0.05). This suggests that of all the observed anthropogenic and environmental factors affecting oyster mortality, bottom temperature has the greatest influence on oyster mortality, followed by the effects of decreasing bottom dissolved oxygen levels, salinity and harvest.

Sediment cores were collected in St. Martin River and Blackwater National Wildlife Refuge (BNWR) to determine sediment accumulation rates and textural properties. One core was collected and analyzed from St. Martin (SM14), and two were collected and analyzed from the open-water area of BNWR (Lake Blackwater; cores BW3 and BW4). SM14 and BW4 have similar textural properties, consisting mostly of fine-grained mineral sediments. Also, the grain-size profile for BW4 shows upward fining, which is characteristic of channel-fill deposits, suggesting that BW4 was located in a relict river channel. In contrast, the other BNWR core (BW3) is mostly composed of organic material (i.e., peat), which is probably composed of eroded marsh material. The mass accumulation rate for BW3 is 0.5 g/cm2/y, which, if extrapolated to the entire Lake Blackwater area, would account for ~50% of the estimated export of sediment from the adjacent marshes by previous studies. The BNWR results demonstrate the high spatial variability present in Lake Blackwater sediments and the need for further research. In St. Martin River, the sediment accumulation rate at SM14 is ~3 mm/y, which is similar to the average rate of sea-level rise in the Chesapeake Bay region, indicating that this area is keeping up with sea-level rise. However, rapid population growth and high nutrient loading in recent years are likely to have impacts on shorter-term (<100 y) sedimentation processes.

Dimethylsulfoniopropionate (DMSP) is the precursor of DMS, which plays significant roles in the global sulfur cycle (Steinke et al., 2000). Dinoflagellates are among the highest producers of DMSP; this is of importance in coral-algal symbiotic relationships. Various coral species have been shown to contain DMSP, produced by their resident symbiotic dinoflagellates (Symbiodinium sp.) and under stressed conditions display the recognizable odor of DMS. DMS is formed from DMSP via the action of the enzyme DMSP lyase, which some, but not all algae contain. Although corals have been shown to contain DMSP, no investigations have been directed at determining its role and function within these organisms. Various roles and functions of DMSP, including as an osmolyte, anti-grazing chemical, nitrogen storage molecule and an antioxidant have all been proposed in other algal species. Given the pivitol role of elevated levels of oxidative stress preceeding bleaching, our focus was to determine the role and function of DMSP as an antioxidant. DMSP's breakdown products, DMS, acrylate and DMSO have been shown to be even more efficient antioxidants (Sunda et al., 2002) than DMSP or other coral antioxidants. It is currently unknown if the coral symbiotic algae (Symbiodinium sp.) contains DMSP lyase, which may allow for the production of these more efficient antioxidants. Current research is focused on determining baseline levels of DMSP in a variety of Symbiodinium sp. strains to investigate if some strains possess more antioxidant protection than others. These studies involved determining levels over an entire growth cycle, as DMSP is known to vary with growth cycle conditions in other species. We also investigated if Symbiodinium sp. contain the enzyme DMSP lyase. Our research demonstrated that levels of DMSP varied with Symbiodinium sp. strains; in all strains maximal levels were seen during the exponential growth phase at Day 14. Symbiodinium algal strain 830 with antibiotic addition displayed DMSP lyase activity similar to findings of Steinke et al. (2000). Future work will focus on DMSP lyase host involvement employing the tropical sea anemone, Aiptasia sp.

The sorption of the rare earth elements (REEs) on Ulva lactuca (Sea Lettuce) was investigated at different ionic strengths over a wide range of pH values (4 - 8.5). REE concentrations were measured using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS), and distribution coefficients (Ks) were calculated and plotted as a function of pH. In 0.5 M NaCl, the log(Ks) values are linear over the pH range 4 - 8.5. In 0.05 M NaCl, the log(Ks) values are linear from pH 4 5.5, followed by a sharp decrease and substantially decreased pH dependence between pH 6 - 8.5. Acid/base titration experiments were also conducted to determine the density of the functional groups on Ulva.
Additionally, Extended X-ray Absorption Fine Structure (EXAFS) was used to investigate the coordination chemistry of individual REE ions bound to functional groups on Ulva. This data was collected at Argonne National Laboratory (ANL) Advanced Photon Source in Argonne, IL.

While many storms travel through the Chesapeake Bay region, only two hurricanes in recent history have resulted in major flooding of the surrounding area. By passing to the west of the Bay, Hurricanes Chesapeake-Potomac (1933) and Isabel (2003) created strong southeasterly winds around the estuary, propagating water up the Bay and flooding the estuarial coast. More frequently however, hurricane paths travel along the east coast, causing northerly winds to push waters out of the estuary. Thus, it appears that local wind forcing, which is highly dependent on a storm's path, is a leading factor in the estuarial response to passing storms.
The Regional Ocean Modeling System (ROMS) is used to model the barotropic sea level response of the Chesapeake Bay due to passing hurricanes. Hindcast simulations are conducted for Hurricanes Isabel (2003) and Floyd (1999): two storms with similar intensities but distinctive paths. The predictions are compared with observed sea level data for several stations along the length of the estuary. The model predicts the storm surge for both hurricanes with good accuracy; however, results clearly show high sensitivity in the storm surge predictions with changes in the inputted wind stress field. It is therefore determined that a highly accurate wind field is vital to obtain more accurate model results. The model predicts major flooding in the upper bay for Hurricane Isabel, and a sea-level depression for Hurricane Floyd at the same latitude, indicating that in both cases local wind forcing dominates the storm surge dynamics, although at differing degrees.

Nitrogen is considered to be key in limiting growth and productivity. The involvement of nitrogen fixation by planktonic cyanobacteria and epiphytic cyanobacteria was investigated in association with several bay macrophytes with surrounding sediments and pelagic waters. Nitrogen fixation was measured by assessing the activity of the nitrogenase enzyme complex using the acetylene reduction assay by epiphytes on the blades, roots, and rhizomes of macrophytes including Myriophyllum spicatum, Potamogeton perfoliatus, Zostera marina, Ruppia maritime, Vallisneria americana, and Stuckenia pectinata. Rates of nitrogenase activity in the pelagic realm overall were lowest at a range of 0.044-11.4 nmol C₂H₄/g/h however, the highest rate was displayed in the cyanobacteria bloom at 629,000 nmol C₂H₄/g/h. Sediment seemed not to have high rates of nitrogenase activity ranging from 0.155-8.57 nmol C₂H₄/g/h and revealed no strong correlation to the organic content at R² = 0.0117 nmol C₂H₄/g/h. Seagrass blades, Zostera marina and Stuckenia pectinata yielded higher rates of nitrogenase activity at 544 and 204 nmol C₂H₄/g/h respectively. Overall nitrogen fixation was relatively higher in marine systems where nitrogen is limited and lower in fresher environments systems where nitrogen is sufficient and ultimately may be a source of "new" nitrogen.

Polybrominated diphenyl ethers (PBDE) are hydrophobic molecules that are used as flame retardants. There are three commercial mixtures produced: Penta-BDE, which is the most bioaccumulative, Octa-BDE, and Deca-BDE, which is the most commonly used.
PBDEs are found everywhere. They can be found in very high concentrations in sediment. Bioaccumulation of PBDEs and PCB 209 was assessed using the polychaete worm Nereis virens. Nereis virens were exposed to spiked sediment (1000ng/g dry sediment Penta-BDE, 2600ng/g dry sediment Deca-BDE, 2500ng/g dry sediment PCB 209) for 28 days. Bioaccumulation occurred from all three contaminants, with Penta-BDE accumulating the most. Deca-BDE was found to accumulate in Nereis virens in small concentrations. This accumulation of the Deca-BDE provides a possible pathway for the contaminant to enter the food chain.

The release of phosphate from Corsica river sediments is influenced by benthic organisms and redox status, specifically iron and sulfur biogeochemistry. Sediment-water column exchanges are less in 2006 than in 2001 at certain sites of the Corsica River though phosphate continues to flux out of the sediments. Differences in exchange data between sites may be influenced by variations in pH. History of the Corsica River includes periods of nutrient loading, and long core data suggests retention of phosphorus in these sediments. Iron oxyhydroxides and pyrite formation largely control retention of phosphorus in sediments.

Spatial changes in the composition of natural microbial communities are complex and highly variable. Although underlying mechanisms are poorly understood, it is believed that both dispersal and environmental conditions are important factors. The present study investigates the influence of dispersal and environmental conditions on the development of microbial communities in tributaries of the Choptank River watershed. An in situ experiment was also conducted to determine the distribution of airborne microbial communities across a wide spatial scale (<1m to >100 km). Community composition was determined via PCR amplification of bacterial DNA followed by denaturing gradient gel electrophoresis (DGGE). Community composition in the tributaries was predominantly influenced by environmental conditions, specifically agricultural land use within the catchment and presence of suspended sediment. However, the nonrandom distribution of airborne bacteria at the largest distance scales of our study suggests that dispersal may influence aquatic microbial community structure, although this effect is overwhelmed by environmental conditions in Choptank River tributaries.

Flow, erosion, and bioturbation affect sedimentation in rivers. Metals can react with sediment particles and be deposited with the sediment. The Corsica River in Maryland is highly polluted from erosion and waste disposal, amongst other things. To determine the changes in sedimentation in the Corsica River over the past 100 y, two cores were collected from different locations on the river. Both cores were analyzed for grain size using a Sedigraph, and an alpha counter was used to analyze ²¹⁰Pb. The downstream core was analyzed for the trace metals Pb, Cu, Zn, Mn, and Fe with a flame atomic absorption spectrometer. The results show that the downstream core has more sand in the surface layers, possibly from higher river flow. The upstream core has more clay and a higher sediment accumulation rate, indicating lower flow. Bioturbation is the primary cause of mixing in the top 12 to 16 cm of both cores. The increase in Pb, Cu, and Zn over time is directly related to the increase in industrialization and pollution. However, in recent years, the concentrations of Pb and Zn decrease due to pollution regulations. Mn concentrations correspond to concentrations of pyrite, suggesting that Mn is incorporated into pyrite. Fe concentrations show no pattern. Overall, the concentrations of all the metals analyzed were low relative to those of the Chesapeake Bay and Baltimore Harbor, suggesting that metals are not a major source of pollution in the Corsica River.

Organic matter cycling is a central process taking place in all types of ecosystems. The Arctic Ocean is no exception. In this study, sediments which represent one specific sector of the organic matter reservoir, in the Arctic were investigated. Two analysis methods were combined; the distribution of amino acids downcore to examine the history of organic matter inputs and processing together with ²¹⁰Pb to establish an age chronology. Three sediment cores (2, 4, and 7) crossing the continental shelf East of Barrow (EB), Alaska were analyzed. Results for sediment chronology found that the two near shore stations (EB-2 or EB-4) were well mixed over the sampling range (0-20cm) due it intense benthic activity and ²¹⁰Pb chronologies were not useful. The average sedimentation rate calculated for the EB-7 core collected in deeper waters was 0.0411 cm/year or 41.1 cm/1000 years.

Our results show that amino acids varied among all three cores. The three most abundant amino acids in the EB-2 sediment core included, glycine, serine, and valine; in the EB-4 core the most abundant amino acids were alanine, glycine, and serine; while in the deep water EB-7 sediment core showed glycine, serine, and aspartic acid with the highest concentrations. The percent total organic carbon was shown to remain stable through the intervals measured in the cores while the THAA concentrations showed fluctuation, suggesting varied carbon sources over the sediment accumulation history.

Blue crab (Callinectes sapidus) is common to a wide range of estuarine habitats along the eastern seaboard of the Americas. Despite its broad distribution, the abundances of crabs in several regions including in the Chesapeake Bay have declined due to explotation and habitat alteration. Resource managers have tried a range of tools and techniques to assess the status of the blue crabs in the Chesapeake Bay. Patterns of habitat-specific production are currently unknown. One technique for measuring habitat-specific production that has proven successful with fishes and other crustaceans is to measure short-term growth using the ratio of RNA:DNA in sample tissues of an organism. This technique has not been validated for blue crab. The objective of this project was to test experimentally the potential of this technique to assess habitat quality and growth of the blue crab in the bay. Crabs from a wide range of sizes were exposed to three food regimes for 7 days. After 7 d, muscle samples from three legs of each crab were extracted for nucleic acid analysis. Nucleic acids concentration in crabs was strongly affected by crab size, tissue type and ration. However, no significant relations were found between factors. As the exploratory nature of this project, other areas should have to be explored to improve this technique for later use in blue crab stock management.

Bacteria are central players in many important processes within aquatic ecosystems, yet little is known about the diversity, distribution and precise functions of these organisms. This is due mainly to the difficulty in culturing these organisms in the laboratory. However, the application of molecular techniques to the field of marine microbiology is beginning to unveil the mysteries of bacterial roles in marine systems. The DNA of cells can be directly examined without need to grow the bacterial cells. In this study a fosmid library was created storing the genetic information of bacteria present in surface waters of the mid Chesapeake Bay. Partial analysis of the library via ITS-LH-PCR and limited sequencing has revealed some of the diversity of bacterioplankton in the bay. 60% of the bacterial groups identified belonged to the actinobacteria class, which was traditionally associated with freshwater bacteria only. 25% of the species identified belonged to the bacteroidetes phylum, 9% to the Roseobacter group and 6% to the gamma subclass of the proteobacteria phylum. Further analysis of the library may reveal a greater diversity of species and the genetic information stored could even be used for other purposes in the future such screening for genes of particular interest or searching for the presence of antibiotic-producing organisms.

In the event of an oil spill, timely and informed response decisions must be made based on sound scientific research. In coastal areas, shallow water and rocky shoals serve as barriers to the use of recovery equipment and leave coastal life vulnerable to surface slicks. Dispersants could provide a solution to this problem; however, careful research must be conducted to determine the effects on benthic and water column life. This research studied the effects of chemically dispersed oil on the sensitive symbiotic soft coral Xenia elongata to determine toxicity levels in this common cnidarian. Three experiments were conducted testing the acute and sub-lethal toxicity of water accommodated fractions of Arabian Light crude oil (WAF), chemically enhanced water accommodated fractions (CEWAF), as well as the toxicity of the dispersant alone. A multi-tiered array of behavioral and physical endpoints were analyzed including pulse rate, pulse intensity, rigidity, as well as physical measurements of poly-aromatic hydrocarbons (PAHs), dissolved oxygen, chlorophyll content and DNA damage. The corals showed high sensitivity to both the chemically dispersed oil (CEWAF) and the dispersant alone. LC50s for dispersant alone were in the 50-60 range and concentrations at 25 ppm and higher produced strong adverse behavioral responses. In the acute experiment, 20 ppm dispersant treatments and CEWAF treatments at the 1 g oil/L with a 1:20 dispersant to oil ratio produced a complete paralysis of pulsing. All showed significant recovery in clean artificial sea water within two weeks with CEWAF treatments resulting in the slowest recovery. Chlorophyll levels and algal cell counts did not differ significantly between treatments when normalized to protein levels although there were lower levels of both protein and chlorophyll overall in the high acute CEWAF treatments. Further analysis of water and tissue samples will illuminate PAH uptake and accumulation levels as well as assess levels of DNA damage.

Methane is important to study because of its role as a greenhouse gas. In our attempts to solve environmental problems, it is important to fully understand the system we are dealing with so as to not inadvertently create a new problem, or add to a preexisting one. This study was focused on the relationship between denitrification and methanogenesis in areas dominated by agriculture. According to past lab studies, there should be a negative correlation between methanogenesis and denitrification in soils rich in nitrate. Three different farms were studied using a subset of 8 groundwater wells. Samples were taken and analyzed for dissolved methane, nitrogen gas, and oxygen. These variables were regressed to test the relationship predicted by the literature. Overall, there was found to be no significant correlation between methanogenesis and denitrification; however, there was a significant negative correlation found at one of the three farms when examined separately (r² = 0.58, p = 0.02). A highly significant inverse quadratic relationship was also found between the concentration of methane and the percent saturation of oxygen in the samples (r² = 0.33, p < 0.01). These results show that microsites in soils can produce methane despite high levels of nitrate and denitrification in the bulk soil properties.

This study examined the relationship between exposure to polychlorinated biphenyls (PCBs) and behavior and metabolic rates measured as oxygen consumption of juvenile snapping turtles, Chelydra serpentina. Two behavioral assays were done: a predator avoidance study and a foraging study. The turtles fed contaminated food were found be more active than those fed reference food in the first of three trials in the predator avoidance study. There was no significant difference found among treatments in the ability of juveniles to forage for live food. In the metabolism study the juveniles fed contaminated food were found to have higher rates of oxygen consumption than those fed reference food in two of three months. These results suggest that PCB contamination through food may affect the metabolism of the organism, but perhaps may not have a significant effect on behavior.

Aquatic microbial species have been proven to be difficult to culture and thus hard to study. The use of genetic analysis has begun to fill the knowledge regarding aquatic microbes. Analyses of ribosomal RNA genes in fosmid libraries constructed from bacterioplankton from surface waters of the Chesapeake Bay has revealed the presence of several groups of marine/estuarine microbes. Through PCR, sequencing, and phylogentic analysis, several aquatic bacterial groups have been identified. These include, but are not limited to Thiobacillus (Betaproteobacteria), Delftia (Betaproteobacteria), Verrucomicrobia, Synechococcus, Bacteroidetes, Paenibacillus (Firmicutes), and Actinobacteria.

Seagrass plays an important role in its ecosystem, but it has declined in the Chesapeake Bay to as low as 10% of historic levels. Increased seston concentrations, due to eutrophication and increased sediment loads, are believed to be the main cause of the seagrass decline because seston increases light attenuation, thereby decreasing photosynthesis. Oysters reduce seston concentrations through suspension feeding, and oyster reefs and breakwaters can also decrease seston through wave attenuation. A numerical model that included seagrass, waves, oysters, light, and seston (SWOLS model) was used to determine if oyster reefs and breakwaters could improve seagrass growth by reducing suspended sediment concentrations. Seagrass growth potential was calculated using different wave heights, the presence or lack of oysters and/or breakwaters, and two configurations of oyster reefs/breakwaters. Wave height was found to be the dominant factor influencing seagrass growth potential, with higher waves predictably causing decreases in seagrass growth potential. Breakwaters were found to improve seagrass habitat quality only in the presence of the highest wave heights simulated (0.4 m). Oysters did not affect seagrass growth in any of the simulations conducted, mostly likely due to their seston-dependent filtration rates which reduced filtration to less than 20% of full capacity in low (< 5 mg l^-1) and high (> 35 mg l^-1) suspended sediment concentrations. A dynamic phytoplankton component and wave reflection should be incorporated into the model in order to assess the influence of oyster filtration on both the organic and inorganic components of seston, and the effect of breakwaters on seagrass growth potential in high wave conditions.