| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | March 2, 2010 |
| Latest Amendment Date: | March 2, 2010 |
| Award Number: | 0961942 |
| Award Instrument: | Standard Grant |
| Program Manager: |
David Garrison
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | March 1, 2010 |
| End Date: | February 28, 2015 (Estimated) |
| Total Intended Award Amount: | $1,114,711.00 |
| Total Awarded Amount to Date: | $1,114,711.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
2020 HORNS POINT RD CAMBRIDGE MD US 21613-3368 (410)221-2014 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
2020 HORNS POINT RD CAMBRIDGE MD US 21613-3368 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | BIOLOGICAL OCEANOGRAPHY |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
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.
Broader Impacts: As hypoxia becomes more prevalent in estuarine and shelf waters, increased understanding of its effects on planktonic food-webs becomes essential for effective, ecosystem-based management. The effects of eutrophication and hypoxia are areas of research emphasized in the JSOST Ocean Research Priorities Plan. Information gained from this project will be critical for food-web modeling in development of fisheries ecosystem plans for Chesapeake Bay. In a broader sense, the research is needed to achieve goals in the Chesapeake Bay Program's "Chesapeake 2000" Agreement. The proposed research will support two graduate students and a postdoc. In addition, the Horn Point Laboratory is part of the mid-Atlantic NSF-COSEE program and this project will support the participation of two summer teacher interns. The Horn Point Laboratory also participates in the NSF Research Experience for Undergraduates (REU) program. REU undergraduate students will be involved in the proposed research. Dissemination of results to the public and environmental managers will be facilitated by the infrastructure of University of Maryland Center for Environmental Science's Integration and Application Network (www.ian.umces.com).
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The overarching goal of this project was to develop a mechanistic understanding of how the behavior and fitness of the copepod Acartia tonsa is influenced by low dissolved oxygen, or hypoxia. Copepods are microscopic crustaceans found in nearly all aquatic systems, and they are likely the most abundant animal on earth. A. tonsa is a species of marine copepod, with adults reaching approximately 1 mm in length, and it is found in estuaries and coastal systems throughout the world. Hypoxia is defined as dissolved oxygen < 2 mg L-1 at 18°C and we examined how hypoxia effects were expressed in the population abundance, distribution and food web in the Chesapeake Bay ecosystem. To unambiguously explore the effects of hypoxia on copepods it was necessary to understand or control for impacts of other factors that affected the copepods, including their predators and prey, and physical conditions of their environment. To accomplish this, we undertook a comparative approach in which data were collected from two stations – one more hypoxic than the other – over three seasons in two years. All data were collected on six research cruises conducted in 2010 and 2011 aboard the RV Hugh R. Sharp in the central region of the Chesapeake Bay that is most commonly affected by seasonal hypoxia.
We encountered a wide range of environmental conditions. In 2010, hypoxia was generally less severe than in 2011. However, in 2011, hurricane Irene and tropical storm Lee had significant impacts on conditions in the ecosystem, with less hypoxia, lower salinity, and cooler water observed after the storm passed. Anoxic water, in which dissolved oxygen was completely absent and sulfide was present in bottom waters, was observed in both years, but in 2010 it only was observed briefly in summer, whereas in 2011 it occurred in spring and summer. Bay anchovy and copepod abundances were higher in 2010 than in 2011, and jellyfish abundances were higher in 2011.
One major finding was that copepod mortality was higher under hypoxic conditions, due to both direct and indirect factors. First, during hypoxic conditions non-predation mortality was usually greater than predation mortality, meaning that more copepods died from other causes than being consumed. The severity of hypoxia affected the kinds of predators that dominated and contributed to copepod mortality. Juvenile anchovy predation was greater under less severe hypoxic conditions, and jellyfish, in particular ctenophores or comb jellies, were more important predators under more severe hypoxia. We found that male copepods occurred more commonly in hypoxic water than do female copepods, and we have hypothesized that this dichotomy is related to increased metabolic demand of females, an area for further study that we are pursuing.
An additional product of this work was an analysis of data on metabolic and respiration rates of the target copepod A. tonsa, to determine how temperature affects the ability of the copepods to cope with low dissolved oxygen. This research showed that when temperatures are high copepods likely experience oxygen stress even at oxygen concentrations above the definition of hypoxia. This result has indicated that consideration of metrics describing oxygen-limiting habitat is in order to provide an approach for developing organism-specific, oxygen stress metrics for plankton organisms.
This project contributed significantly to training of two graduate students, one Masters student who has graduated and a PhD student who is finishing her dissertation and degree requirements. Additionally, it contributed to the training of a postdoctoral scholar who has published two peer-reviewed papers based on data from the project. Analysis of data generated by this program is...
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