<i>Trichodesmium</i> spp.: Numerical Studies of Resource Competition, Carbohydrate Ballasting, and Remote-Sensing Reflectance

<p>In recent years, a new appreciation for the role of diazotrophy in the oceans has emerged. This dissertation reports on three modeling studies designed to investigate ecological processes associated with <em>Trichodesmium </em>spp., the most conspicuous marine diazotroph: (1) characterization of a generalized model <em>Trichodesmium</em> and issues of macronutrient resource competition; (2) carbohydrate ballasting by <em>Trchodesmium </em>and implications for the formation of surface accumulations; and (3) the vertical distribution of <em>Trichodesmium</em> and implications for detection from space.</p> <p>The first study focuses on issues of nitrogen and phosphorus competition and ecosystem structure. It utilizes a simple ecosystem model that includes dissolved nitrogen and phosphorus plus two classes each of primary producers, grazers, and particulate detritus. In a monoculture submodel, the <em>Trichodesmium</em> biomass is most sensitive to the nitrogen: phosphorus compositional ratio and the senescence and gross growth rates. In the competitive model, <em>Trichodesmium</em> is adversely affected by competitors for model phosphorus, while the contribution of diazotrophy to fueling non-diazotrophy new production is limited by the concomitant lack of other nutrients. This model's outcome is most sensitive to the <em>Trichodesmium</em> gross growth and senescence rates. Experimental studies that would be particularly useful in this context include determination of the <em>Trichodesmium </em>half-saturation coefficient for phosphate, as well as quantitative co-occurrence data for <em>Trichodesmium</em> and <em>Macrosetella gracilis</em>.</p> <p>In the second study, an individual-based Lagrangian model is used to explore carbohydrate ballasting and its implications for <em>Trichodesmium </em>vertical distribution in quiescent waters. The model results indicate that mean population depth is controlled primarily by environmental conditions (incident irradiance and its vertical attenuation) and physiological rate parameters for ballast processes. Morphologic parameters have a greater effect on the amplitude of ballast-driven oscillations. Post-mixing quiescence, high incident irradiance, and high water clarity all encourage the formation of surface accumulations. Post-mixing quiescence produces a depth-segregated population, with the proportion ascending to the surface increasing as a function of water-column turbidity. This study provides insight into environmental and biological conditions that encourage <em>Trichodesmium</em> accumulation at the marine boundary layer and identifies key processes for further study.</p> <p>In the third study, a radiative transfer model is used to quantify the effects of <em>Trichodesmium</em> vertical distribution on remote-sensing reflectance, <em>Rrs</em>(λ). For the detection thresholds employed here, the model results indicate that surface accumulations of <em>Trichodesmium</em> can be detected when chlorophyll ≥1.5 mg m−3. For near-surface populations, <em>R rs</em> is most sensitive to chlorophyll concentration. For populations at 10–20 m depth, <em>Rrs</em> is most sensitive to population depth. Populations deeper than 20 m are not detected. These results, in conjunction with recent field surveys, indicate a detection rate of approximately 25%. These results have implications for ocean-color sensor and algorithm development and may have direct application to satellite estimations of N₂-fixation.</p> <p>In summary, these three modeling studies confirm the importance of <em>Trichodesmium</em> in marine ecosystems. Moreover, these studies identify critical areas in which future research is required for illumination of the role of <em>Trichodesmium</em> in elemental cycling and marine ecosystems.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Ocean & Earth Sciences

Year dc:date.available

2001

Author dc:creator

• Clayton, Tonya Denise

Contributors dc:contributor

• Eileen E. Hofmann
• Larry P. Atkinson
• David M. Karl
• John M. Klinck
• Curtis D. Mobley

• Ballasting
• Carbohydrate
• Remote sensing
• Resource competition
• Trichodesmium
• Ecology and Evolutionary Biology
• Oceanography

Statement dc:rights

• <p>In Copyright. URI: <a href="http://rightsstatements.org/vocab/InC/1.0/">http://rightsstatements.org/vocab/InC/1.0/</a> This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).</p>

Identifier

9780493564470

OAI identifier oai:identifier

oai:digitalcommons.odu.edu:oeas_etds-1115