RUI: Ecophysiology of gelatinous zooplankton in hypoxic estuaries

Evergreen State College, Olympia WA

Investigators

Abstract

Estuaries are typically sites of natural hypoxia in summer for several reasons: lower freshwater inflows decrease turnover times, stratification increases, and increased surface primary production sinks to the bottom where it is remineralized thereby using up oxygen. Increased human population growth around the Puget Sound has increased the degree of hypoxia in the near-bottom depths of the estuary through increased nutrient influx and resulting eutrophication. Researchers in Chesapeake Bay have found that gelatinous zooplankton are able to survive in hypoxic bottom waters while their zooplankton prey (copepods and fish larvae) cannot tolerate such low levels of oxygen. This means that prey are concentrated in shallower zones while gelatinous predators can take advantage of the benefits of vertical migration. Therefore, increased hypoxia in estuaries due to human disturbances appears to alter pelagic food web structure by increasing the importance of gelatinous predators. This project will investigate the mechanisms that allow gelatinous zooplankton to survive at low oxygen levels. Previous research on the metabolic physiology of medusae, ctenophores, chaetognaths and other pelagic worms in midwater oxygen minimum layers has led the Investigator to propose several mechanisms whereby simple animals that do not have oxygen binding proteins or well developed circulatory systems may survive in low oxygen environments. Gelatinous zooplankters transferred from high-oxygen water to water depleted in oxygen leak oxygen into a closed chamber (Thuesen & Childress, unpublished; Thuesen & Lee, unpublished), and this project will describe and quantify the oxygen storage capabilities of mesoglea in the context of providing oxygen to gelatinous zooplankters during forays into hypoxic estuarine waters. This project will also investigate potential glycolytic adaptations in estuarine gelatinous zooplankton, including ctenophores, hydromedusae and scyphomedusae. The goals of this research are to (1) determine the oxygen regulatory abilities of gelatinous zooplankton; (2) measure the rate of oxygen release from mesoglea as a function of oxygen concentration in the surrounding water and determine if oxygen release is regulated by the organism; (3) determine the ratios of "oxygen storage potential" to metabolically active tissue through biochemical measurements and develop indices of hypoxia tolerance in gelatinous zooplankton to predict the abilities that different species may have for hypoxia survival; and (4) determine the role that anaerobic metabolism may have in the hypoxia tolerance of gelatinous zooplankton. The studies proposed here will complement studies on gelatinous zooplankton in hypoxic regions of the Chesapeake Bay through collaborations with scientists at the University of Maryland and the Estuarine Research Center of the Academy of Natural Sciences that will allow studies with specimens collected from hypoxic zones of the Chesapeake Bay. The proposed research will further our knowledge on the impact of hypoxia on Puget Sound food webs through collaborations with the Washington State Department of Ecology Marine Water Quality Monitoring Team. Students at The Evergreen State College will benefit through participation in this research through proposed RUI activities.