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Research

My current and recent projects are described below:

 

Earlier projects:

 

 

Short Descriptions of Current Projects:

The effects of diatom-produced polyunsaturated aldehydes on the microbial food wed in temperate and polar waters

Funded by NSF OCE

This project will conduct a set of field/laboratory experiments to address the following hypotheses with respect to microzooplankton (consumers between 20-200 µm) and diatom- produced polyunsaturated aldehydes:

I. Aldehydes will impair microzooplankton herbivory on diatoms and non-diatom phytoplankton. 

II. Aldehydes will reduce the growth rates of microzooplankton and non PUA-producing phytoplankton. 

III. In the presence of aldehyde-producing diatoms, copepods will switch to microzooplankton, whereas non- (mildly)- toxic diatoms will be an important food source for copepods. 

IV. The effects of aldehydes on microzooplankton and copepods will depend on the grazers' prior exposure to PUA. 

The experiments will include natural plankton, captured copepods, cultured Skeletonema marinoi (SM), including its aldehyde-producing strain, and synthetic aldehydes. To gain insights into complex interactions within planktonic communities, detailed information on their composition, abundance, and dynamics will be obtained using microscopy, flow-cytometry, and cytological methods. This approach will allow the PIs to draw conclusions about the role of diatom-produced aldehydes in phytoplankton-microzooplankton- copepod trophic interactions. The PIs will coordinate efforts and exchange information with the PUA study group at the Stazione Zoologica Anton Dohrn (Naples, Italy).

Intellectual merit: Diatoms are dominant autotrophic plankton in the ocean. Recent evidence indicates that microzooplankton are the dominant herbivores, whereas copepods often rely on microzooplankton as food, except during peak diatom production. The ability of microzooplankton to feed on large diatoms and grow as fast as their algal prey leads to the question of what allows diatoms to escape microzooplankton grazing control during the initial phases of their blooms and maintain the blooms until nutrient resources are depleted? Allelopathy is wide spread among phytoplankton. The cosmopolitan bloom-forming SM produces several aldehydes and has become a model organism in plankton allelopathy studies. Most studies on diatom cytotoxicity have been dedicated to inhibitory effects on reproduction and development of marine invertebrates, whereas surprisingly little information exists on its impact on key diatom grazers, microzooplankton. Preliminary results in the Chesapeake Bay show that aldehydes may induce cascading effects within planktonic communities. The proposed study will: (1) Improve our knowledge of the critical diatom-microzooplankton-copepod links in the coastal ocean; (2) Generate novel data on the effects of allelopathy on marine food webs; (3) Contribute to our understanding of broader patterns of marine ecosystems by comparing plankton structure and dynamics in the temperate Atlantic waters; (4) Advance biological oceanography through international collaboration.

Broader Impacts: One post-doctoral fellow, two graduate students and several undergraduate students at the Universities of Akron and Maryland will be trained as a result of this project. The project will attract motivated minority students into the program. The research will be extended to students in grades 7-12 and teachers via an interactive distance learning series in collaboration with the WVIZ Ideastream network. The PIs will continue an existing outreach partnership with the Great Lakes Science Center, where a recent electronic presentation dedicated to Arctic change and NSF-sponsored research was seen by ca. 45,000 visitors. The PIs will also work with the Cleveland Museum of Natural History to develop public programs, and with the National Inventors Hall of Fame STEM Middle School to develop a curriculum focused on polar research. Curriculum modules will be available as free downloads from a dedicated website. Broader Impacts, LLC, will evaluate these education and outreach activities.

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Copepod Population Dynamics in Hypoxic Coastal Waters: Physical and Behavioral Regulation of Resupply and Advective Losses

Funded by NSF OCE

The PIs will develop a mechanistic understanding of how circulation interacts with hypoxia-induced behavioral and physiological changes to affect the population dynamics of coastal zooplankton. They will do this by assessing two potentially contrasting mechanisms influencing the dynamics of the copepod Acartia tonsa in the hypoxic zone of Chesapeake Bay. The first hypothesis is that maintenance of copepod populations in the hypoxic region requires replenishment by advection (immigration) of animals through wind-driven lateral transport processes. The second, counteractive, hypothesis is that bottom water hypoxia alters the vertical distribution of A. tonsa, thereby making them more susceptible to advective losses from the region (emigration) via surface water transport in the estuarine circulation. They will take advantage of a current NSF-funded physical oceanography research program in Chesapeake Bay that will comprehensively measure and model axial and lateral water exchanges in the mid-Bay region. 

The present study will use the physical oceanography study site as a Controlled Volume (CV) in which the oceanographic exchanges of water and the driving mechanisms for those exchanges will be well defined. The PIs will conduct high-resolution spatial and temporal sampling of zooplankton and combine the data with measurements of copepod behavior, mortality and egg production in the hypoxic region. They will use an improved Individual-Based Model of the life history of A. tonsa coupled with the circulation to explore the combined effects of advection, behavior, egg production, and mortality on population dynamics. In addition to increasing our knowledge of the impacts of bottom water hypoxia on copepod populations in Chesapeake Bay, the study will improve our general understanding of the regulation of zooplankton populations by physical and biological processes and the impacts of hypoxia on secondary production and food webs in coastal waters. 

The project will enhance existing public education and outreach efforts so that the public can be better informed about the effects of hypoxia on Chesapeake Bay. This will be accomplished in part through the Center for Ocean Science Education Excellence (COSEE) Coastal Trends program (now the Horn Point Laboratory STEM Center Student Learning Activities program). The PIs will enhance an existing set of online education modules (http://www.teachoceanscience.net/) that focus on the causes and consequences of the Chesapeake Bay's "Dead Zone" through development of an online interactive version of their synthetic plankton model. The study also includes participation by undergraduate summer interns through a Research Experience for Undergraduates (REU) program. In addition, this research will contribute information toward the development and improvement of dissolved oxygen criteria for Chesapeake Bay, will support broad initiatives of the Chesapeake Bay Program by providing information on the role of zooplankton in supporting productivity of fisheries, and will contribute information to ecosystem-based fisheries management plans.

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Hypoxia in Marine Ecosystems: Implications for Neritic Copepods

Funded by NSF OCE

Participants may click here to acces a password protected site.

The occurrence of low-oxygen waters, often called "dead zones" in coastal ecosystems throughout the world is increasing. Despite these increases, the pelagic food-web consequences of low-oxygen waters remain poorly understood. Laboratory research has demonstrated that hypoxic water (< 2 mg l-1) can result in mortality, reduced fitness and lower egg production of planktonic copepods, a major link in food webs supporting pelagic fish. Observations in the sea indicate that hypoxic bottom waters usually have depressed abundances of copepods compared to normoxic waters (> 2 mg l-1). The gradient of declining oxygen concentration with respect to depth (oxycline) can be a critical interface in coastal pelagic ecosystems by altering the migratory behavior and depth distribution of copepods and their spatial coherence with potential predators and prey. This project will result in a mechanistic understanding of how behavior and fitness of copepods are affected by hypoxia. The PIs will compare bottom-up and top-down controls on the ecology of copepods in Chesapeake Bay waters experiencing seasonal hypoxia and those that are normoxic.

Specific objectives of this project are to: 1) analyze changes in migratory behavior and fine-scale (meter) distribution of copepods across the oxycline over hourly and diel time scales while simultaneously examining the distribution and abundance of their food (phytoplankton and microzooplankton) and predators (fish, gelatinous zooplankton); 2) estimate effects of hypoxia on the "fitness" of copepods using a suite of measurements (length/weight ratios, feeding, egg production, and egg hatching success) to develop condition indices of copepods captured at different times and depths in hypoxic and normoxic waters; and 3) evaluate effects of hypoxia on copepod mortality by hypoxia-induced, stage-specific copepod mortality in hypoxic bottom waters and by changes in top-down control of copepods from predation by fish and gelatinous zooplankton. Oxyclines may be a barrier to vertical migration of copepods and thus disruptive to predator avoidance behavior. Faced with increased predation risk from fish and jellyfish, copepods may seek refuge in hypoxic waters for part of the day and/or make short-term vertical excursions between hypoxic and normoxic waters. By regulating vertical migrations, copepods may increase utilization of microzooplankton prey concentrated in the oxycline. Hypoxic waters may elevate consumption of copepods by jellyfish and depress consumption by pelagic fish. This project will evaluate copepod distribution and migration behavior, individual fitness and stage-specific mortality in hypoxic and normoxic waters. It will examine food-web consequences of increased or decreased spatial coherence of copepods and their predators and prey in regions with hypoxic bottom waters and will contribute to fundamental understanding of food-web processes in eutrophic coastal ecosystems.

Collaborators:

  • Michael Roman, Diane Stoecker, & Ed Houde, University of Maryland Center for Environmental Sciences
  • Mary Beth Decker, Yale University
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Modeling the Impacts of Hypoxia on Ecologically and Commercially Important Living Resources in the Northern Gulf of Mexico

Funded by NOAA CSCOR

To assess the full impact of hypoxia on living resources of the Northern Gulf of Mexico (NGOMEX) requires a multi-scale (both time and space) and multi-stressor approach. This project proposes a framework to simultaneously account for direct and indirect effects of hypoxia, including their linear and non-linear interactions on key organisms to support ecosystem-based management in the NGOMEX. A battery of modeling approaches of varying complexity (individual - to ecosystem-level), spatial configuration (near-field plume to fine-scale spatial pelagic to entire NGOMEX), and temporal duration (hourly to inter-annual) will be employed to provide both understanding and forecast capabilities to the management community of the NGOMEX.

Multiple models will be used to evaluate:

  • What is the effect of the spatial extent and seasonal timing of hypoxia on fish growth, recruitment and production potential?
  • How does hypoxia affect food web interactions in the pelagic zone? Specifically:
    • How will hypoxia affect the spatial distribution and predator-prey interactions of mobile organisms and zooplankton?
    • How does hypoxia affect habitat quality and suitability for economically and ecologically important fishes?
  • How will management decisions on loadings affect fisheries through its impact on the timing and extent of hypoxia?
  • What is the potential of strong wind events (and their relationship to climate change) to re-aerate the water column and alter the interactions of fish and their prey?
  • What are the most effective tools to forecast food-web interactions, habitat suitability, and fish production in relation to hypoxia?

It is hypothesized that hypoxia in the NGOMEX can strongly impact pelagic food webs and production through unexpected, indirect pathways, potentially leading to changes in production potential (both positive and negative) of economically and ecologically important fishes. Our overall goal is to provide quantitative tools to probabilistically forecast the effects of hypoxia on the living resources in the NGOMEX. Direct linkages to fisheries management will ensure continued interaction with, and attention to, the critical management issues.

Collaborators:
  • Michael Roman, University of Maryland Center for Environmental Sciences
  • Stephen Brandt & Sarah Kolesar, Oregon State University
  • James Cowan & Kim deMutsert, Louisiana State University
  • Doran Mason and Craig Stow, NOAA Great Lakes Environmental Research Laboratory
  • Shaye E. Sable, Louisiana Department of Fishes and Wildlife
  • Aaron Adamack, University of Michigan
  • Fredrick Sutter, NOAA NMFS Southeast Regional Office
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James J. Pierson, Ph.D.
Research Assistant Professor

University of Maryland Center for Environmental Science
Horn Point Laboratory
2020 Horns Point Rd.
Cambridge, MD 21613
410.221.8218

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