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 continuing and more insights into food-web effects of hypoxia will be forthcoming. Last Modified: 06/29/2015 Submitted by: James J Pierson
Principal Investigator: James J. Pierson (University of Maryland Center for Environmental Sciences)
Co-Principal Investigator: Michael R Roman
Co-Principal Investigator: Diane K Stoecker
Co-Principal Investigator: Edward D Houde
Research Publications
Journal of Plankton Research~2013~35~Elliott, David; Pierson, James; Roman, Michael~10.1007/s12237-013-9653-9~~~~~Copepods and hypoxia in Chesapeake Bay: Abundance, vertical distribution, and non-predatory mortality~~~~~~~
PLoS One~2013~8~Elliott, David; Pierson, James; Roman, Michael~10.1371/journal.pone.0063987~~~~~Predicting the effects of coastal hypoxia on vital rates of the planktonic copepod Acartia tonsa Dana~~~~~~~
Journal of Plankton Research~2013~35~Elliott, D. T., J. J. Pierson, M. R. Roman.~10.1093/plankt/fbt049~1027~~~~Copepods and hypoxia in Chesapeake Bay: Abundance, vertical position, and non-predatory mortality.~~~~~~~
PLoS ONE.~2013~8~Elliott, D. T., J. J. Pierson, M. R. Roman.~10.1371/journal.pone.0063987~e63987~~~~Predicting the effects of coastal hypoxia on vital rates of the planktonic copepod Acartia tonsa Dana.~~~~~~~