Graduation Year

2006

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Pamela Hallock-Muller, Ph.D.

Committee Member

Kendra Daly, Ph.D.

Committee Member

Gary Huxel, Ph.D.

Keywords

nutrient cycling, translocation, mixotrophy, carbon, nitrogen

Abstract

Coral reefs thrive in nutrient-deficient environments yet function among the most productive ecosystems on Earth as a consequence of the symbiosis between coral hosts and their symbiotic zooxanthellae. The symbiotic unit (holobiont) can utilize both inorganic and organic sources of nutrients for the accumulation of carbon and nitrogen required for metabolism, growth, and reproduction. An iterative model was created to describe the flux of carbon and nitrogen between a host and its algae. The model design is based on a previously published conceptual model of algal symbioses; functions and values of input parameters are based on published studies of the coral species Stylophora pistillata. The model is designed to simulate responses of the coral, zooxanthellae and the holobiont to different environmental variables, either one at a time or changing simultaneously. Simulations presented are for default values based on previously published data for S. pistillata adapted to high-light (shallow-euphotic) and low-light (deep-euphotic) environments, and for single-variable manipulations of rates of a) host feeding, b) photosynthesis, and c) dissolved inorganic nitrogen (DIN) uptake. x Simulations examining feeding rates between 0% and 6.5% of host biomass indicate that biomass of both high-light and low-light adapted holobionts increase exponentially with increased feeding, with benefit to the high-light holobiont ~8 times greater than to the low-light holobiont. Increasing rates of photosynthesis illustrated that a low-light holobiont is carbon limited, is primarily dependent upon host feeding, and can benefit from a small increase in photosynthesis rate. Simulations examining rates of DIN input indicate that the high-light holobiont functions optimally when inorganic nitrogen input is very low. Increase in DIN up to 0.5% resulted in benefit to the holobiont, but more resulted in unrealistically excessive growth by the zooxanthellae until a function to maintain a fixed range for the host-zooxanthellae biomass ration function was included in the model. Simulations for the low-light holobiont did not indicate any benefit from DIN input. The model was originally designed using a spreadsheet-based program which frequently became overloaded when testing multiple variables. Modification of the model in software better designed for modeling is recommended for future work.

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