Gymnodinium breve in the Gulf of Mexico: Gyroxanthin-based Estimates of Carbon-Specific Growth Rates Under Varying Environmental ConditionsEPA Grant Number: R829369
Title: Gymnodinium breve in the Gulf of Mexico: Gyroxanthin-based Estimates of Carbon-Specific Growth Rates Under Varying Environmental Conditions
Investigators: Richardson, Tammi L. , Pinckney, James L.
Institution: Texas A & M University
EPA Project Officer: Hiscock, Michael
Project Period: November 15, 2001 through November 14, 2004 (Extended to March 1, 2006)
Project Amount: $100,387
RFA: Ecology and Oceanography of Harmful Algal Blooms (2001) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Water , Ecosystems
Determination of in situ growth rates of HAB-forming species is critical to an accurate description of bloom dynamics, but there are currently few reliable methods of directly determining growth rates on natural populations. Photopigment radiolabeling, a method for measuring carbon (C)-specific growth rates of phytoplankton, is based on the determination of synthesis rates of chlorophylls and carotenoids using photosynthetically-assimilated 14C as a radiotracer. This work will examine the use of radiolabeling of the biomarker pigment gyroxanthin as a diagnostic tool for determining growth rates of natural populations of the toxic dinoflagellate Gymnodinium breve (recently renamed Karenia brevis) in Texas and Florida coastal waters, and will examine effects of varying nutrient and light regimes on K. brevis growth rates.
We will use batch and semi-continuous cultures to assess growth rate responses of K. brevis. Batch cultures will investigate growth rate dynamics under varied environmental conditions, including varying forms and concentrations of nitrogen and three irradiance levels. Samples will be analyzed for inorganic nutrients, urea, cell counts, POC and PON, and photopigments, including gyroxanthin and total chl a. Semi-continuous cultures will allow an evaluation of the photopigment radiolabeling method under conditions of steady state growth, an important assumption of the radiolabeling technique. Growth rates derived from steady-state semi-continuous cultures will be defined as the "true" growth rate for comparisons with other methods. Once we have determined if the gyroxanthin radiolabeling technique gives satisfactory results, we will apply the technique to field investigations of the in situ growth rate of K. brevis off Texas and/or the Florida shelf. Work in the field will concentrate on measurements of K. brevis growth rates throughout the course of a bloom and in vertical profiles.
Why does K. brevis bloom? In order to address this question from a mechanistic perspective, we need to directly measure K. brevis growth rate responses in its natural environment. The fundamental question is whether or not these blooms are caused by changes in the physiology of K. brevis, such as an alteration in the population growth rate, or some alteration in their environment that allows this species to out-compete other members of the phytoplankton community. The gyroxanthin-based radiolabeling technique outlined in this proposal will likely prove invaluable as a tool for describing the ecophysiology of K. brevis under natural conditions. This research project will address concerns of phytoplankton physiologists as well as resource managers concerned with environmental limitations and controls of toxic dinoflagellate blooms in coastal waters. In light of the possible relationships between anthropogenic nutrient discharges, coastal eutrophication, and red-tide bloom formation, this project has the potential to enhance our understanding of the mechanistic relationship between growth, light, and nutrients for K. brevis and closely-related HAB species.