Graduation Year


Document Type




Degree Granting Department

Marine Science

Major Professor

Pamela Hallock-Muller, Ph.D.

Co-Major Professor

Kendra Daly, Ph.D.

Committee Member

Gary Huxel, Ph.D.


nutrient cycling, translocation, mixotrophy, carbon, nitrogen


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.

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


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.