Tracy Villareal 

Professor, Department of Marine Science Research Professor, Marine Science Institute Ph.D., University of Rhode Island (1989)  M.S., Texas A&M University (1981)  B.S., Texas A&M University (1979) Home page

Phytoplankton Ecology

Harmful algal blooms, ciguatera, growth physiology of diatoms and brown tides, Ecology of oceanic phytoplankton, transport of nutrients via phytoplankton vertical migration, adaptations to oligotrophic gyres;

Research Interests

My research interests are in understanding the processes and interactions that structure phytoplankton communities. I have two major research areas: Harmful algal species (particularly ciguatera causing dinoflagellates and red tides) and  the autecology of the oceanic diatom species. My lab uses both field and laboratory studies to understand phytoplankton community responses. 

The harmful algal bloom work focuses on dinoflagellate driven events. We have a number of toxic species along the Texas coast but the dominant red tides species is Karenia brevis.. We are conducting a multi year survey of Texas coastal waters for K. brevis in order to understand its seasonal dynamics in this region and to support the development of satellite detection systems for the western Gulf. Such systems are already successfully deployed in the eastern Gulf of Mexico, but currently lack the ground-truthing required for validation in the western Gulf of Mexico.

Ciguatera is the most common form of seafood intoxication in the world, and is caused by toxins produced by the benthic dinoflagellate Gambierdiscus toxicus.  My work (funded by the NOAA program ECOHAB) is examining the growth and toxicity response under differing environmental conditions. In addition, we have discovered that oil production platforms located off the Texas coast harbor this dinoflagellate.  As a result, we are examining toxicity in local barracuda through a collaboration with Dr. R. Dickey’s FDA laboratory in Alabama.

My oceanic work has explored vertical migration in the largest known phytoplankton species. These taxa can range up to several millimeters in diameter. Despite being non-motile (lacking flagella), various dinoflagellates, diatoms and Prasinophytes appear to be capable of extensive vertical migrations. They regulate their buoyancy to sink to sub-nutricline depth (>100 meters), take up nitrate and then return to the surface for photosynthesis. My work has focused on understanding how buoyancy is regulated, growth rates, sinking rates, ascent rates, nitrogen assimilation, and the biogeochemical implications of this biologically mediated N flux. 

Selected Publications

Magaña, H.A. and T.A. Villareal.  2006.  The effect of environmental factors on the growth rate of Karenia brevis (Davis) G. Hansen and Moestrup.  Harmful Algae 5: 192-198.

Pilskaln, C.H., T.A. Villareal, M. Dennett, C. Darkangelo and G. Meadows.  2005.  High concentrations of marine snow and diatom algal mats in the North Pacific Subtropical Gyre:  Implications for carbon and nitrogen cycles in the oligotrophic ocean.  Deep-Sea Research I 52:2315-2332.

Wynne, T.T., R.P. Stumpf, M.C. Tomlinson., V. Ransibrahmanakul, and T.A. Villareal.  2005. Detecting Karenia brevis blooms and algal resuspension in the western Gulf of Mexico with satellite ocean color imagery.  Harmful Algae 4:992-1003.

Singler, H.R. and T.A. Villareal.  2005.  Nitrogen inputs into the euphotic zone by vertically migrating.  Rhizosolenia mats.  Journal of Plankton Research. 27(6):545-556.

Kubanek, J., E. Prince, M.K. Hicks, J. Naar, and T.A. Villareal.  2005.  Does the Florida red tide dinoflagellate use allelopathy to outcompete other phytoplankton.  Limnology and Oceanography. 50(3):883-895.

Adornato, L.R., E.A. Kaltenbacher, T.A. Villareal and R.H. Byrne.  2005.  Continuous in-situ determinations of nitrite at nanomolar concentrations.  Deep-Sea Research I 52:543-551.

Biegalski, S.R. and T.A. Villareal.  2005.  Correlations between atmospheric aerosol trace element concentrations and red tide at Port Aransas, Texas, on the Gulf of Mexico.  Journal of Radioanalytical and Nuclear Chemistry 263(3):767-772.

Cheng, Y.-S., T.A. Villareal, Y. Zhou, J. Gao, R.H. Pierce, D. Wetzel, J. Naar, and D.G. Baden.  2005.  Characterization of red tide aerosol on the Texas coast.  Harmful Algae 4:87-94.

Villareal, T.A.  2004.  Active fluorescence in the giant diatom Ethmodiscus (Bacillariophyceae) documented using single cell PAM fluorometry.  Journal of Phycology 40(6):1052-1061.

Montoya, J.P., C.M. Holl, J.P. Zehr, T.A. Villareal, and D.G. Capone.  2004.  High rates of N2-fixation by unicellular diazotrophs in the oliogotrophic Pacific Ocean.  Nature (London) 430:1027-1031.

Magaña, H.A., C. Contreras, and T.A. Villareal.  2003.  A historical retrospective of Karenia brevis (Davis) G. Hansen and Moestrup in the western Gulf of Mexico.  Harmful Algae 2:163-171.

Buskey, E.J., H. DeYoe, F. Jochem, and T.A. Villareal.  2003.  Effects of mesozooplankton removal on trophic structure during a bloom of the Texas brown tide:  A mesocosm study.  Journal of Plankton Research 25:215-228.

Villareal, T.A. and E.J. Carpenter.  2003.  Buoyancy regulation and the potential for vertical migration in the oceanic cyanobacterium Trichodesmium.  Microbial Ecology 45:1-10.

Bersano, J.B.F., E.J. Buskey, and T.A. Villareal.  2002.  Viability of the Texas brown tide alga, Aureoumbra lagunensis, in fecal pellets of the copepod Acartia tonsa.  Journal of Plankton Biology 49(2):88-92.

Villareal, T.A. and S. Morton.  2002.  Use of cell specific PAM-fluorometry to characterize host shading in the epiphytic dinoflagellate Gambierdiscus toxicus.  Marine Ecology 23:129-140.

Loret, P., T. Tengs, T.A. Villareal, H. Singler, B. Richardson, P. Mcguire, S. Morton, M. Busman, and L. Campbell.  2002.  No difference found in ribosomal DNA sequences from physiologically diverse clones of Karenia brevis (Dinophyceae) from the Gulf of Mexico.  Journal of Plankton Research 24(7):735-739.