VARIATION AND PLASTICITY IN SCLERACTINIAN MICROMORPHOLOGY

Ocean acidification, localized disturbances, anthropogenic causes, and increased oceanic temperatures are threatening the viability of coral reefs. Disparities between morphology-based taxonomies and molecular phylogenies has only recently begun to be reconciled through the use of micromorphology and microstructure. Corals can display disparate morphology based on the environmental growing conditions. This plasticity is one potential cause of homoplasy within Scleractinia (Class: Anthozoa). While plasticity of macromorphology has been well-documented the plasticity of micromorphology is still poorly understood. The plasticity of coral micromorphology could cause problems in understanding coral relationships in deep time and for misidentifying species during conservation efforts. In order to examine the variations in skeletal micromorphology and the potential for plastic change influencing character states used in phylogenetics I examined hermatypic coral species grown in controlled environments. I tested the plastic response to temperature, light intensity, and pH levels in experimental aquaria and analyzed the specimens using Scanning Electron Microscopy (SEM) to examine the dentition, granulation, septal shapes, and other micromorphological features. I used Dipsastraea speciosa, Caulastraea furcata, and Galaxea astreata for these experiments. Each experiment used a single mother colony for each species in order to minimize genetic disparity. The species were chosen to represent both the robust and complex clades within Scleractinia. I found that micromorphology did display small variations due to phenotypic plasticity. These changes did not influence the currently used micromorphological characters and did not result in different character states from the same species or mother colony. While examining micromorphological characters for interspecific variation and confirming the consistency of the character states is still important to responsible taxonomy, micromorphological characters are stable for use in systematics.