Degree Granting Department
Pamela Hallock-Muller, Ph.D.
Kendra Daly, Ph.D.
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
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.
Scholar Commons Citation
Gaydos, Dana Joy, "Modeling the Advantages and Disadvantages of the Coral-Algal Symbiosis" (2006). Graduate Theses and Dissertations.