Document Type


Date of Degree

Summer 2016

Degree Name

PhD (Doctor of Philosophy)

Degree In


First Advisor

Ann F. Budd


Reef-building corals (Order: Scleractinia) are undergoing rapid taxonomic revision after molecular systematics disputed the relationships at all taxonomic levels within traditional classification. New morphological characters are being used to produce evolutionary relationships supported by molecular phylogenetics. While these characters are providing more congruent taxonomic relationships, their variation has not been fully explored. Additionally, phenotypic plasticity (changes in morphology resulting from environmental factors influencing the expressed phenotype despite a shared genotype) is prevalent amongst Scleractinia. In order to better understand the nature of these characters and explore their variation, I created a series of aquaria-based experiments designed to test the stability of these new morphological characters in response to differing environmental conditions. Light intensity and temperature were chosen as the environmental factors varied in these experiments on the basis of being a known trigger for environmentally-driven plasticity and their importance in calcification rate. In addition to aquaria-based phenotypic plasticity experiments I also examined a group (Family: Euphylliidae) within Scleractinia that had been divided by molecular phylogeny into two disparate groups. My research focused on morphological features viewed at magnifications observable by scanning electron microscopy (SEM) called micromorphology. Although variation in the skeletal micromorphology is observable, the new morphological characters that are used in taxonomy display only small amounts of variation caused by changing environmental conditions and were found to be stable for use in taxonomic studies. Additionally, I found a few micromorphological features distinguishing the two groups previously assigned to Euphylliidae including the shape of the septal margins and the fine-scale skeletal texture.


Climate change, Micromorphology, Microstructure, Phenotypic plasticity, Reef ecology, Scleractinia


xiii, 207 pages


Includes bibliographical references (pages 165-171).


Copyright 2016 Matthew A. Tibbits

Additional Files

Caulastraea Temp (266 kB)
Caulastraea Temp

Dipsastraea light (267 kB)
Dipsastraea Light

Dipsastraea Temp (535 kB)
Dipsastraea Temp

Euphylliidae specimen macro photos.pdf (654 kB)
Euphylliidae Specimen Macro Photos.pdf

Galaxea Temp (27 kB)
Galaxea Temp

Micromussa light (200 kB)
Micromussa Light

Micromussa light (349 kB)
Micromussa Light

Caulastraea 2D (136 kB)

Included in

Geology Commons