Tracy A. Villareal, Marine Science Institute, The University of Texas at Austin, R. Michael L. McKay, Dept. of Biological Sciences, Bowling Green State University, & Cynthia H. Pilskaln, Dept. of Oceanography, University of Maine,

This is a collaborative research project that will quantify nitrogen importation and excretion in the euphotic zone by vertically migrating Rhizosolenia mats, and will provide the first physiological data on mats below diver accessible depths. Rhizosolenia is a macroscopic diatom able to control their buoyancy through which they sink below the euphotic zone to acquire nitrate, store it in their vacuole, and then return to the surface for photosynthesis. This new production is based entirely on a biologically, rather than physically mediated transport of N.

During the summer 2002 30-day cruise to the Eastern Pacific Ocean, and In addition to SCUBA collections as a primary collection technique, two systems will be used for abundance estimates, sizing and mat collection. The first system is a Video Plankton Recorder (VPR) and the second is a Remotely Operated Vehicle (ROV). The ROV will be used to collect mats below diver accessible depths in order to compare deep mats with surface mats. This is a key, undocumented area of their life history and will provide closure look to our understanding of the migration cycle.

Nitrogen excretion occurs in phytoplankton as a result of Fe and/or light stress. These observations predict that N excretion will be common in Rhizosolenia mats in natural waters deficient in bioavailable Fe. This study will quantify inorganic and organic N excretion rates from these two stresses in both laboratory and field Rhizosolenia.

The contribution of our work to this project will be assessing cellular Fe status using Ferredoxin (Fd) index, that is an in situ immunological markers of Fe deficiency, in addition to biophysical Fe index (Fv/Fm). There is a possibility that this open ocean large diatom have inability to make Ferredoxin due to possible natural selection. To validate the Ferredoxin index as a measure of Fe stress in large oceanic diatoms, and determined N excretion rates by these taxa. The study will look for the petF (Ferredoxin) gene by means of Microsatellite technique and then sequencing of this gene.

These data will provide more information about the relationship between trace metal nutrient limitation, especially Iron, and macronutrient acquisition and assimilation. These studies will also calculate rates of biological N import and release for the eastern half of the central N. Pacific gyre by the entire migrating community. This is a fundamental contribution to our understanding of oceanic N cycles, and has direct relevance for both carbon and nitrogen cycling in the upper ocean.

Along with the Fd index, the effect of Iron binding legands on Fd Index for Rhizosolenia mainly and other diatoms will be studied. Also, I will study some of the marine bacterial strains capable of sensing iron deficiency in it's environment, and the effect of those bacterial strains on our diatom's ability of utilizing Iron existing in the same environment.