Current Research Projects

The eastern oyster, Crassostrea virginica, has historically been a species of tremendous importance to the Chesapeake Bay economically and ecologically and provides numerous ecosystem services, including water filtration, habitat and food for many other Bay species. Significant hatchery and aquaculture efforts are currently underway to recapture the economic and ecological benefits of a robust oyster population within Chesapeake waters, whether for human consumption or to promote improvements in water quality and benthic habitat. The presence of microplastics (MP) in Bay waters may negatively impact these efforts.

Anadromous alosine fishes (river herrings and shads) are critically important to ecosystem function, economies, and cultures of coastal communities, but have seen major declines in the mid-Atlantic region and the Chesapeake Bay in particular. We have developed and demonstrated the effectiveness of new monitoring tools for river herring (alewife and blueback herring) including environmental DNA (eDNA) and sonar image-based run counts that are rapidly improving our ability to study these species. However, additional eDNA monitoring of American shad and hickory shad, which lacks baseline data, is needed to establish habitat use in rivers across the mid-Atlantic.

Urban stormwater runoff remains on the of the primary sources of nutrients, sediments, and other pollutants in receiving waters, like the Chesapeake Bay. Stormwater best management practices (BMPs) and green infrastructure (SWGI) have been implemented in urban and suburban areas to re-establish ecosystem functions lost because of urbanization. SWGI treatment trains provide sequential infiltration and treatment of stormwater on the landscape prior to export into nearby waterways and groundwater.

The Anacostia River is among the most polluted tributaries in Chesapeake Bay. With substantial algal blooms and bacterial contamination, it has placed those who recreate on the water at considerable health risk. The first phase of a recently completed, multi-billion dollar infrastructure project, the Anacostia River Tunnel, which will retain and divert sewage and storm water effluent is due to be operational by March 2018. The tunnel project is award-winning from the perspective of the engineering community, but the environmental outcome is yet to be determined. While it may be years before the full infrastructure project is complete or full ecosystem recovery is seen, changes in phytoplankton and bacteria should be clearly evident in these first two years of project implementation.

Salinization is increasingly affecting many watersheds, significantly impacting drinking water resources and infrastructure, reducing stability and resilience of aquatic ecosystems, and potentially hindering stream and river restoration efforts. Salinization is related to deicer use on roadways with additional contributions from accelerated weathering of impervious surfaces, water softeners, and sewage. The concentrations of chloride observed in many urban streams in Maryland now exceed the limit of 250 mg/L established by the U.S. EPA for chronic toxicity to freshwater life. These observed ranges and extreme fluctuations in salinity can mobilize nitrogen, phosphorus, base cations, and toxic metals from sediments to streams due to enhanced ion exchange and solubility.

The recent exponential growth in established or planned US closed-containment Atlantic salmon production has been associated with over $1B investment into this aquaculture sector. The success of this dramatic expansion/investment in land-based, RAS salmon production requires a national, coordinated and interdisciplinary effort to ensure that current barriers are eliminated and efficiency and cost-effectiveness are attained. While major progress has been achieved in recent years in RAS technology, its scaling up may face biological, engineering, technological, economical and societal constraints that should be addressed via a fully integrated research, extension, outreach, education and workforce development network.

Rationale: To meet the increasing demands of the world’s growing population under sustainability constrains, optimization of aquaculture methods will be necessary to maximize cost-effective production and minimize ecological impact. One of the supreme strategies for large-scale commercial aquaculture operations is the use of infertile/sterile populations of farmed animals. Sterility carries environmental significance, as the infertile animals are not able to propagate and/or interbreed with wild stocks. In addition, sexual maturation is associated with a substantial decrease in somatic growth due to the diversion of energy into the development of the gonads.

We have developed an immersion-based method in fish to eliminate primordial germ cells (PGCs) by silencing a PGC-development-responsible gene, which resulted in the production of reproductively sterile fish. This proposal aims to transfer this fish sterilization technology to produce sterile diploid eastern oysters to avoid triploids mortality issues. The production of sterile diploid oysters without ploidy manipulation could retain the market advantage of sterile oysters and minimize performance compromise. We have identified several candidate genes in eastern oysters that are potentially indispensable for oyster PGC development. Our preliminary experiments by targeting one of the candidate genes, germ-cell-less (gcl), have yielded oysters that are in their third year.

Triploid eastern oysters are an important component of the Maryland aquaculture industry because of their fast growth and sustained high meat yield. Commercially, triploids are produced by mating tetraploid oysters with normal diploid oysters. Developing tetraploid stock is crucial to meeting the growing demand for Maryland triploid oysters. However, it is challenging to produce and maintain excellent tetraploid lines for the benefit of industry. In short, there is a clear and pressing need for triploid and tetraploid lines that have region-specific beneficial characteristics, especially tolerance to low-salinity environments. In this project, we will establish the first generation of tetraploid stock derived from Maryland local oyster populations.

A spectral library of remote sensing reflectance for major phytoplankton taxonomic groups in the Chesapeake Bay will be developed using measured and modeled inherent optical properties as inputs into radiative transfer equations (HydroLight TM). The spectral library will be used to develop a phytoplankton discrimination algorithm in order to distinguish major phytoplankton taxa and sediment types in Chesapeake Bay waters. Hyperspectral remote sensing reflectance spectra collected from an unoccupied aircraft system (UAS) or the upcoming hyperspectral satellite mission, PACE, can be used as inputs to the algorithm to effectively quantify and map phytoplankton taxonomic-specific biomass.

Coastal ecosystems are vulnerable to short term anthropogenic changes such as nutrient loading and longer-term changes such as sea level rise. Together these changes can alter these systems in ways that change the ecosystem services these systems provide. For example, estuaries bury carbon over time which in turn is a major controller for a habitable atmosphere. Carbon can enter estuaries through a number of processes such as photosynthesis, respiration, air-sea exchange, terrestrial runoff, and groundwater input. As it gets buried, it will undergo a series of microbially mediated processes which terminates in the production of methane, a potent greenhouse gas.

The net environmental impacts of oyster aquaculture are strongly related to the transport and fate of biodeposits, though little is known of their physical and biological properties. Biodeposits exported from aquaculture sites may result in net denitrification elsewhere while mitigating the impacts of organic matter over-enrichment at the aquaculture site. Consequently, the susceptibility of biodeposits to erosion and long range transport is key to determining the ecological effects of oyster aquaculture. Current oyster biodeposit models do not use realistic values of critical shear stress, (?c), or values of the cumulative suspended mass (CSM) available for export at aquaculture sites.

As Chesapeake Bay (CB) submersed aquatic vegetation (SAV) recover and oyster aquaculture operations in Maryland expand, the potential for these important shallow-water resources to spatially overlap and come into conflict is increasing. Until recently, the Code of Maryland Regulations has restricted installation of aquaculture gear in areas occupied by SAV and further requires that aquaculture operations cease if SAV expands into an existing lease. These regulations were intended to support SAV restoration under the assumption that aquaculture will impair SAV growth. However, the extent to which aquaculture is detrimental to SAV growth and the mechanisms by which it impacts SAV habitat are poorly understood at present.

While existing research addresses many of the important issues of oysters in Chesapeake Bay (CB), the fate and effects of resuspended oyster biodeposits in aquaculture areas on the nutrient, light, zooplankton and phytoplankton dynamics have not been taken into account when the use of oysters in mitigation of eutrophication in CB is examined. Currently, models do not include the effects of biodeposit resuspension on the ecosystem, nutrient dynamics and light and experimental data are not available.

Atlantic menhaden (Brevoortia tyrannus) is a migratory forage fish that plays a vital role in Chesapeake Bay and Mid-Atlantic marine ecosystems by linking production at lower trophic levels with piscivorous predators. Given the critical ecosystem services menhaden provide as forage, the Atlantic States Marine Fisheries Commission is currently developing an Ecosystem-Based Fisheries Management (EBFM) approach to stewardship of the menhaden resource. Managers and stakeholders are particularly interested in potential impacts of menhaden management on its primary predator, Atlantic striped bass (Morone saxatilis).

Though fish populations typical experience spatially varying mortality, abundance, and fishing pressure, stock assessments commonly model a population that is assumed to be well-mixed. When assumptions about population mixing are not met, these models can result in biased estimates. Spatial population estimates are particularly beneficial to the Chesapeake Bay as this region faces unique challenges as a result of climate change, fishing pressure, and land use within the watershed. Though the Chesapeake Bay supports many important commercial and recreational fisheries, few assessments have estimated abundance of fish within the bay. However, use of spatial models for fisheries management relies on the ability of these models to reliably estimate biological parameters.

The existence of spatial structure in populations of exploited marine fishes challenges our ability to develop reliable stock assessments. Using the northern stock of Black Sea Bass (BSB - Centropristis striata) on the US Atlantic coast as a model species, I will combine empirical and analytical approaches to explore the impacts of the spatial resolution of population and assessment models on the reference points generated by assessments. In this region, the distribution of BSB is highly structured during summer months when the fish are inshore, but the distribution is more widely dispersed when offshore in the winter.

Callinectes sapidus supports the most valuable commercial fishery in the Chesapeake Bay and its tributaries. Nationally, the average total dockside value of blue crab fisheries in Maryland, Virginia, North Carolina, Florida, Louisiana and Texas approaches $200 million. Interstate live blue crab transport has increased due to seasonal cycles of crab landings in the Chesapeake regions and changes in allocation of immigration permits for guest workers. The risk of spreading shellfish pathogens through commercial transportation of live seafood has drawn increasing attention, while the potential for blue crab pathogens to be spread by commerce may be underappreciated.

Identification and development of effective algaecides for commercial use is an active area of research, as the intensity and frequency of harmful algal blooms (HABs) are increasing worldwide. Although algaecides are a focus of HAB mitigation, there are still many unknowns. To this end, we propose the following objectives: 1) identify the algaecides released by barley straw with and without the use of white-rot fungi, Trametes versicolor, in the laboratory, 2) identify the impact of the algaecides on microcystin toxin production (toxin per cell/total toxin) and growth rate of the blue-green algae, Microcystis aeruginosa, and 3) compare algaecides found in the controlled laboratory setting to those found in Lake Williston post barley straw deployment.

Zooplankton are critical food sources for marine fish, and climate-driven changes in their abundance, diversity, and quality can have profound effects on larval recruitment and fisheries productivity in coastal oceans and estuaries. Despite the importance of prey for understanding variation in fisheries recruitment, accurate identification of zooplankton species remains challenging and a lack of information on prey quality and prey selectivity by fish may hinder the discovery of relationships between zooplankton and fish productivity. In Chesapeake Bay, two copepods, Acartia tonsa and Eurytemora carolleeae, are critical components of bay anchovy (Anchoa mitchili), larval striped bass (Morone saxatilis), and other fish diets.

Current efforts to restore natural oyster reefs and a growing oyster aquaculture industry in Maryland will serve to support an increased prevalence of oysters in Chesapeake Bay. While these activities will support continued commercial harvests and restored natural habitats, elevated oyster numbers will also lead to changes in estuarine biogeochemistry relevant to water quality restoration. Recent studies have illustrated that oyster communities are associated with extremely high rates of nitrogen removal and newly proposed BMP guidelines will serve to give nitrogen removal credits to aquaculture activities.

Although external nutrient load reductions have been a primary management strategy for Chesapeake Bay restoration, internal ecological processes, such as seasonal nutrient retention in submersed aquatic vegetation (SAV) beds, may also play an important, complementary role. However, we lack sufficient details about the factors controlling the magnitude of an important mechanism of SAV-mediated nutrient sequestration--particulate nutrient trapping--to make inferences about its importance relative to total loads to the system.

The Ostreid herpesvirus 1 (OsHV-1) and its microvariants are highly virulent pathogens that cause mass mortalities of oysters and pose a threat to the shellfish aquaculture industry globally. OsHV-1 causes economically devastating mass mortality events up to 100% in the Pacific oyster (Crassostrea gigas). However, OsHV-1 and its variants lack host specificity and are known to infect a range of bivalve species and be carried by the European green crab (Carcinus maenas). There is a lack of testing and research on the East coast of the United States, including in the Chesapeake and Maryland Coastal Bays where aquaculture is an important industry for food production and restoration efforts.

The aquaculture industry in Maryland is far from optimized partly due to the lack of knowledge relating oyster growth and morphology to the physical environment (flow and jostling). For sessile suspension feeders, such as oysters, water flow is critical to optimize under culture conditions as it regulates food delivery and waste export. Additionally, jostling may inhibit feeding activity and influence shell shape, the latter of which may influence product marketability. It is also unknown how different off-bottom cage types affect the flow regime. This lack of understanding is not unique to Chesapeake Bay waters but is a concern for oyster farmers globally.

Shellfish aquaculture represents a growing industry with strong potential for global expansion. However, biofouling poses a considerable concern to operations, with conservative estimates indicating farmers spend 5-10% of total costs on biofouling removal. Bioexcavators, such as mudworms, are especially problematic as they affect the condition of the oyster, and also leave behind an unsightly mud blister, which is offputting to the half shell industry which prizes pristine oyster shells. Desiccation, or aerial exposure of oysters and cages, has demonstrated marked success in mitigating biofouling, including bioexcavators, but has also been associated with a growth penalty in some desiccated oysters.