Our Students and Their Research

In the recent years coastal marshes and submersed aquatic vegetation (SAV) beds within the Chesapeake Bay have been declining with rising sea level and warming of the bay. Understanding what is affecting deposition in the marshes could help the efforts being made to preserve them, and sediment provided from SAV diebacks could be playing a major role. A transect of cores, one within the SAV bed and four within the marsh, were taken and analyzed for median grain size and organic content. This along with ²¹⁰Pb dating was used to assess possible linkages between the SAV bed and the marsh. The SAV core was represented by large median grain size (1-2 phi) and low organic content (

This study examines two simple nitrogen loading models, an excel spreadsheet based nitrogen loading model and a web-based pollution runoff model, applied to two small watersheds within the larger Chesapeake Bay watershed. The values for nitrogen runoff generated by the models are compared to nitrogen runoff values from field studies. The Nitrogen Loading Model, NLM, overestimated the observed value by 17.5% while the Long Term Hydrologic Impact Analysis model, L-THIA, underestimated the observed value by 37%. For a watershed with an area of just over 36 km2 the NML predicted, 17,382 kg N/yr and the L-THIA model predicted 10,797 kg N/yr, field studies showed 14,789 kg N/yr. These results suggest the usefulness of the models for local management, but still require the input of specialists and continued field analysis to determine long-term impacts of land management decisions.

Due to the small size of bivalve larvae (<0.3mm), identification may be very tricky if not near impossible. However, based on the current understanding that bivalves build their shells out of calcium carbonate and lay down crystals in species specific patterns, a new technique using polarized light will revolutionize the way bivalve larvae are classified. This technique has shown to be highly accurate using larvae grown under controlled conditions, but previous studies revealed that field conditions increased the margin of error in larval recognition (Thompson 2011). In this present study, the oyster, Crassostrea virginica, will be raised under different conditions such as, temperature, salinities, and food concentration, to test whether growth conditions do in fact affect the accuracy of the polarized light analysis. Our results indicated that when experimental larvae were not included in the training set accuracy decreased drastically, which indicates that growth conditions may in fact alter the results of this technique.

Newell (2005) suggested that nutrient regeneration from bivalve communities independent of the underlying sediments is a critical yet not adequately understood dynamic. We evaluated this statement by adapting techniques used in sediment incubations and modifying them for the study of the nutrient balance associated with the oyster aquaculture. In order to assess chemical processes associated with off-bottom oyster floats, we examined for ammonium, nitrate, nitrite, phosphate, dinitrogen and oxygen fluxes. Our analysis indicates that oyster shells are covered with nitrifying organisms, and that nutrient transformations are correlated to the size of the oyster shell. The process of denitrification did not occur significantly in single oyster incubations and was not nitrate-limited.

The Amazon River plume has a significant impact on the biochemistry of the western tropical North Atlantic. It brings nutrients and organic matter to aquatic ecosystems where ocean currents structure communities. Therefore, in order to understand this biochemical impact we explore the physical aspects of the plume which dictate its interactions with the surrounding ocean waters. We specifically focus on quantifying plume volume and age, ultimately demonstrating the essential use of satellite data for both estimations. Additionally, the analysis of these two physical properties of the plume allows us to derive mathematical relationships correlating plume variables such as sea surface salinity, CDOM, and K490. We use these to improve on previous relationships of salinity and K490 and well as to quantify the decay of CDOM with salinity and time. In the end we gain an understanding of both the propagation of the plume and the fate of several biochemically relevant plume properties over time.

Atlantic menhaden (Brevoortia tyrannus) is an important fish to both the estuaries and coastal ecosystems it inhabits at different life stages. It primarily feeds on phytoplankton and zooplankton at different stages, thus it provides filtering and a food source to estuaries, and supports the largest fishery on the Atlantic coast. The recruitment of Atlantic menhaden to estuaries is highly variable. To begin to examine why that is, the spatial distribution of the larvae must be determined. To achieve this goal, I used bi-monthly ichthyoplankton survey data from Northeast Fisheries Science Center from 1971 - 2008. Results suggested that larval distribution shifted to the north in January-March, April-June, and July-September. However, the data from October through December showed a southerly shift. The relationship between the surface and bottom mean temperatures were also varied by time period. The January-March and July-September data showed northerly shift in abundance as water temperatures increased, the April-June data showed northerly shift in abundance as water temperatures decreased, and the October-December data showed southerly shift in abundance as water temperatures increased. Further research should examine the effects of large-scale climactic phenomena and other environmental factors on the spatial distribution of Atlantic menhaden larvae.

Fishing at maximum sustainable yield (MSY), theoretically, maintains the population at a size that maximizes production by removing only its surplus-production. However, the central assumption in MSY policies that excess production is "surplus" has been challenged. MSY policies do not consider the ecosystem consequences of removing this production. For example "surplus" production may also play a role in enhancing the resilience of individual populations and in supporting the production of predators. Here we determine the ecosystem impacts of fishing individual and small groups of species at their MSY in the Chesapeake Bay. Surplus-production assessment models and stock assessments were used to determine the MSY fishing mortality rate (F_msy). The consequences of F_msy policies for blue crab, striped bass, white perch, Atlantic menhaden, and Atlantic croaker were examined using the Ecopath with Ecosim (EwE)-based Chesapeake Bay Fisheries Ecosystem Model (CBFEM) developed by Christensen et al. (2009). We compared abundances of species within the ecosystem under a continuation of current exploitation patterns to abundances under MSY policies for the 5 target species individually and combined. We also examined MSY policies for a broader range of 10 species including bluefish, weakfish, summer flounder, alewife and herring, and oyster. We found that fishing multiple species and fishing menhaden at MSY had widespread impacts on the ecosystem through loss of the top predator striped bass. This suggests that applying MSY fishing policies to an entire ecosystem is an unsustainable level of exploitation, and that forage fish, that are either highly connected or constitute a large proportion of the biomass in the system, serve an important role in the ecosystem as prey to top predators. We conclude that the MSY for forage fish is lower than their individual MSY and that the MSY for the ecosystem is less than the sum of the individual species MSYs

A mass balance, control volume model of the Marinetics oyster farm in Cambridge, Maryland was constructed to predict the fluxes of biodeposits out of the farm and the biodepositon rate within the farm. A sequence of calculations at quasi-steady state approximate the entire tidal cycle. Equations expressing fluxes into and out of the control volume as well as internal sources and sinks are parameterized using field measurements. Measurement techniques include settling experiments, erosion experiments, current meter measurements and sediment trap deployments. Results indicate that the area is ebb dominated; ebb currents are stronger and the ebb lasts longer than during the flood. During the ebb tide a significant fraction of the biodeposits are predicted to leave the farm before hitting bottom. Accounting for resuspension more than doubles this export. During flood tide, less material is directly exported and much less is resuspended. Averaged over the tidal cycle, most of the biodeposits remain beneath the farm, but may be flushed out during infrequent wind and wave events.

Due to the rising sea levels in the Chesapeake Bay region, the Bay's coastal wetlands are being threatened. Wetlands are important ecosystems; they have strong moisture gradients, a distinctive zonation between flora and fauna, and hold an excellent archive of their own history. This archive of history can be retold using the micro-organisms, such as foraminifera, that are preserved in the sediment of the marshes. By using a statistical analyses, or transfer function, as a tool to quantify foraminifera species distribution and relate species assemblages to elevation, recent sea levels for a particular marsh can be reconstructed; the recent sea level trajectory of a marsh can aid in restoration priorities. Based on the information we gathered from our three study sites up and down the Bay, the data, r², and root mean squared error values show promise for future study with more data when relating species abundances to elevation. Due to the strong influence of salinity in an estuarine environment, we also tested the transfer function along a salinity gradient. Our salinity data is inconclusive and data from sample sites from outside our salinity range is needed to determine the possibility of utilizing the transfer function along a salinity gradient.

Oil spills frequently pollute marine ecosystems and necessitate a quick and timely response for effective cleanup. Recent cleanup efforts have shifted toward chemical cleanup with the addition of dispersants as an effective method of dispersing the spilled oil. However, these chemicals still threaten the health and survivorship of marine organisms and acute toxicity testing has been developed to quantify the toxicity of chemicals. No life stage of blue crab has been acutely tested with the most commonly used dispersant, Corexit 9500 (Deepwater Horizon). 48 hour static acute toxicity tests were performed on blue crab life stages zoea 3, 4, 5, 6, 8, megalopa and juvenile and LC₅₀ values were calculated using probit analysis. Preliminary results suggest that Corexit 9500 was found to be most toxic to zoea stages 3-4 and was less toxic as age progressed to juveniles. An anomaly was found in zoea 4-5 which had a greater LC₅₀ than zoea 5-6 due to changes in water and salinity conditions creating a threshold and non-dose-dependent pattern of mortality. Issues including control survivorship and blue crab aggression were encountered, and future blue crab experiments are necessary to accurately quantify the toxicity of Corexit 9500 to each blue crab life stage. This information can then be used for chemical companies to develop less toxic yet effective dispersants to treat future oil spills.

Picoplankton are plankton between 0.2 and 2.0 μm in diameter. Chlorophyll analyses are traditionally conducted using glass-mesh fiber filters (GF/Fs) with a nominal pore size of 0.7 μm, so chlorophyll measurements can be biased if picophytoplankton slip through the GF/F filter and are not counted. For this study, fourteen sites on the Potomac and Patuxent Rivers were sampled to determine what proportion of total planktonic biomass and primary productivity is accounted for by picophytoplankton that slip through GF/F filters. Water samples were filtered sequentially through a GF/F filter pad and then a polycarbonate filter membrane with 0.2-μm pores, isolating picoplankton between 0.7 and 0.2 μm on the polycarbonate membrane. Both filters were then analyzed for chlorophyll-a concentration, and light-dark oxygen evolution incubations were performed on both whole water samples and the GF/F filtrate. Picophytoplankton trapped on the polycarbonate filter were found to account for an average of 0.241% of total planktonic chlorophyll and 0.1% of modeled total planktonic primary productivity. These results suggest that picophytoplankton that are missed by GF/F filters are not significant contributors to planktonic biomass or primary productivity in these locations during the months when sampling occurred.

In order to predict future changes in the Earth's climate, we must thoroughly understand past and present variability in the system. Due to the lack of instrumental data prior to the mid-19^th century, it becomes necessary for paleoclimatologists to look at natural proxies such as coral cores in order to determine climatic events prior to instrumentation. Oxygen isotope ratios (δ¹⁸O) can be observed to determine the surface ocean temperature and hydrologic balance at the time of accretion of the coral's CaCO3 skeleton. In this study a core from a Montastraea faveolata specimen was analyzed for its oxygen isotope ratio in order to determine climatic behavior in the Caribbean from 1841-2001 and the results were compared alongside those of Kilbourne et al. (2008). The results received so far are only preliminary, but show a mean offset of 0.18±0.3‰ from 1841-1884 AD and 0.17±0.3‰ from 1957-2001 for the two cores, LPTA and LPPD, which is similar to the magnitude of intercoral variability found in other studies. The trend from 1841 to 2001 was -0.0013‰/year for this study, which is indistinguishable from the -0.0017‰/year found over the same time period in the data published previously from this reef tract (Kilbourne et al., 2008). More data is necessary to verify the claims made using this preliminary data, but these new data show that M. faveolata δ¹⁸O records are reproducible and confirm the strong warming signal in the Caribbean proposed Kilbourne et al. (2008).

We tested the ability of Hyla versicolor (grey tree frog) to depurate Ag, Cu, Zn, As, Cd, Se, Hg, V, Cl and Pb, introduced in 2 dosing levels through food, during various stages of metamorphosis. We also looked for biological consequences or stress in individuals, by measuring the metabolic rates of individuals at various stages along with growth rates. The control, low and a high dose treatments where conducted in quadruplicate, with each enclosure having 15 animals at the beginning of the experiment. Individuals were taken from each enclosure before the onset of metamorphosis, after hind leg had emergence, after front leg emergence and after complete metamorphosis. Analysis of trace elements in tissue was performed using ICP-MS after microwave digestion. Respiratory rates of individuals were tested before metamorphosis and after metamorphosis, using a closed-circuit microrespirometer. Among the elements tested, Ni, Cu and Zn showed decreases in concentrations between the tadpole stage and premetamorphosis in low and high dose treatments, which suggests that Hyla versicolor larvae are able to depurate these metals in the early stages of metamorphosis. However, concentrations of these elements increased during the final stage of metamorphosis, indicating that element mass loss exceeded depuration.

Due to its painful sting, dense blooms that clog fishing gear and pumps, and voracious predation of mesozoplankton and ichthyoplankton, the sea nettle Chrysaora quinquecirrha, is an important species in Chesapeake Bay. Temperature and salinity influence inter-annual variability in the distribution of sea nettles, but the causes of smaller scale, intra-annual variability, remain unknown. Current efforts at understanding patchiness include visual surface and vertical net-haul counts. Here, we compare the abilities of a digital video camera to capture images of sea nettles at the water surface to those of a human observer in an attempt to automate the observing process so that visual counts could be made more frequently in time and simultaneously at multiple locations to better comprehend this patchiness. Translucent plastic disks were deployed at different depths to determine the limit of the camera's depth of view. The results showed that the camera was not able to visualize the disks as well as an observer on location, and it likely will not provide a quantitative measure of sea nettle abundance; however, we feel that it can be used as a continuous semi-quantitative data collector, and the data can be analyzed for trends in variability of sea nettle abundance.

Nitrite can accumulate in the water in natural and hatchery settings and elevated levels are toxic to many fish. This study evaluated effects of 1 mg/L nitrite on methemoglobin, PCV (packed cell volume), hemoglobin and plasma chemistry in Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus). Juvenile fish (0.544 kg ± 0.126 SD) were divided into two treatment groups of chloride concentrations of 0 mg/L and 50 mg/L. The percent methemoglobin in the 0 mg/L chloride group was 81.936 (68.182, 87.719), median (1st quartile, 3rd quartile), at 96-hours post exposure and was significantly different from the 50 mg/L chloride group which had a percent methemoglobin of 7.895 (4.762, 10.811) (P < 0.05). Two weeks after removal from nitrite, elevated methemoglobin was observed in the 0 mg/L chloride group with a percent of 71.429 (62.963, 90.476). PCV decreased significantly in both groups (P < 0.05). The 0 mg/L treatment group dropped in percent PCV from 30 (29, 32) to 7 (5, 9) and the 50 mg/L treatment group dropped in percent from 29.5 (28, 32) to 15 (13, 18) over the duration of the study. Total hemoglobin decreased significantly from 6.6 g/dL (6.2, 6.8) to 5.6 g/dL (5, 7.1) in the 0 mg/L chloride group and from 6.2 g/dL (5.9, 6.6) to 4.3 g/dL (3.5, 5.3) in the 50 mg/L chloride group (P < 0.05). Nitrite resulted in severe hemolytic anemia and mortality of 60% in the 0 mg/L chloride group and was less severe with no mortality in the 50 mg/L chloride group. Nitrite accumulation at a chloride level close to 0 mg/L is toxic and multiple stressors can result in significant mortality.

Excessive anthropogenic nutrient inputs from both point and non-point sources have contributed to a number of problems currently plaguing the Chesapeake Bay. Nitrogen compounds in particular have resulted in extremely high levels of phytoplankton production, causing hypoxia, and increased turbidity in certain parts of the Bay. In this study, we explore how denitrification rates may be influenced by processes that occur naturally within an oyster reef community. We conducted a three day laboratory experiment with sediment core samples to quantify nitrogen flux rates in the presence of two oyster reef associated organisms; polychaete worms (Alitta succinea) and amphipods (Leptocheirus plumulosus, Melita nitida, Gammarus spp., and Apocorophium spp.). Our results indicate a significant enhancement of denitrification rates in the presence of both polychaetes and amphipods, however, due to unforeseen influences within amphipod treatments, we were unable to attribute flux rates entirely to the treatment. We conclude that oyster reef communities with high densities of polychaetes and amphipods significantly enhance removal of nitrogen compounds.

This study was designed to determine whether denitrification was occurring in stream beds within the Choptank River Basin. Denitrification was measured by the amount of excess N₂ found in the groundwater flowing into piezometers installed 20-60 cm below the stream bed of a channelized farm stream. I hypothesized that the groundwater flowing into the stream from adjacent lands was the primary source of excess N₂ in the stream sediments, meaning denitrification is primarily occurring in soils and groundwater distant from the stream and not within the streambed. My alternate hypothesis was that denitrification is occurring within the stream sediments and augments the vertical distribution of excess N₂ entering the stream from groundwater. Sampling in July 2010 produced results, which showed significant inverse correlations between NO₃, O₂, and excess N₂ that indicated an environment suitable for denitrification. However, excess N₂ concentrations decreased from 40 cm to the surface of the streambed, suggesting that advective loss to the surface waters flowing above was the most important process influencing the vertical distribution of excess N₂ concentrations. Thus, denitrification was only concluded to be occurring in the deeper layers at one sampling site.

Chicken manure-based fertilizers are extremely popular with not only the farming community, but everyday home-gardeners as well. These types of fertilizers are known to contain a suite of heavy metals (As, Ag, Cd, Cr, Cu, Pb, Ni, Se, V, and Zn) and organic compounds. Yet the effects that these contaminants have on the environment have not been well studied in a laboratory setting. For this study, grey tree frogs (Hyla versicolor) were assessed for toxicity to chicken manure-based fertilizer. Hyla versicolor was chosen, due to their availability, rapid developmental period, and their sensitivity to certain toxins. To determine the effects of heavy metals on H. versicolor two controls were set up (one containing sediment consisting of soil, the other containing no sediment), as well as two experimental groups. One experimental group contained sediment consisting of one hundred percent fertilizer, and the other containing an equal mix of fertilizer and soil. The frogs were closely monitored, and by the end of the experiment several heavy metals such as arsenic, copper, and lead were found to have accumulated at significantly higher concentrations in the fertilizer treated groups. However, many biological traits of the frogs were not significantly affected, including metabolic rate, lipid content, and rate of metamorphosis.

Establishing biomarkers for a particular species at a specific area is very important to determine the significance of contamination, and it can help identify pollutants and their source. There are many known types of PAHs in oil that are toxic to marine organisms hat range in their toxicity. Neptunea heros, an arctic whelk found in Northwest Alaska was used as a bioindicator to establish baseline levels to test for antioxidant and PAH exposure with a GST and EROD assay. Small activity were found in the EROD and GST assays, as compared to controls.