As anthropogenic climate change is having large repercussions on scleractinian corals, it is important to understand how species will respond to future environmental change if we are to accurately predict how corals will function under new ecological conditions. However, coral species are quite variable, both among species, as well as within species, making it difficult to calculate outcomes if we do not understand within-species heterogeneity. One way in which coral species are variable intraspecifically is through color morphotypes. The aim of this study was to investigate the ecological consequence of intraspecific color variation in scleractinian corals, and was divided into two parts. First, chapter 2 focuses on physiological differences of color morphotypes in response to abiotic factors. Coral color (other than brown) is the result of fluorescent and non-fluorescent pigmented, host proteins, which protect corals from the detrimental effects of high light intensity and UV radiation, however, they degrade under increased thermal regimes. I hypothesized that color morphotypes would have dissimilar metabolic responses to temperature and light extremes due to the combined effects of photoprotective properties, yet thermal sensitivities of host pigments. Green, blue, and brown color morphotypes of the coral Porites rus from Moorea, French Polynesia, were subjected to a combination of temperature and light treatments, and responses were measured using four dependent variables-calcification, enzyme activity, net and gross photosynthetic maximum, and aerobic respiration. All three color morphotypes exhibited similar responses for all dependent variables measured, with no differences observed when exposed to temperature and light treatments. Although previous literature suggests that variable physiological responses should occur, color morphotypes of Porites rus did not exhibit any of these predicted responses, which may showcase the robust nature of this species. Second, chapter 3 investigates differences in biotic interactions between color morphotypes and other invertebrate taxa. A key survival strategy for mounding corals is the removal of sediment from the colony surface, and brown morphotypes of the Caribbean coral Porites astreoides shed sediment faster than green color morphotypes. I hypothesized that this dissimilar removal of sediment would affect the abundance and distribution of endolithic invertebrates that must first settle onto the surface of P. astreoides colonies in order to commence their endolithic lifestyle. Surveys were conducted in the US Virgin Islands National Park, quantifying the distribution, abundance, and taxonomic diversity of endolithic invertebrates inhabiting brown and green color morphotypes. Green colonies harbored greater proportions of endolithic invertebrates, as well as, greater densities of endoliths per colony than brown morphotypes. Color morphotypes also were inhabited by different proportions and densities of taxonomically diverse endoliths. This is the first time that color morphotypes of a coral species has been shown to harbor different communities of endolithic invertebrates, and may call for greater examination of the habitat provisioning traits offered within a species. Together, the results presented in this thesis show that color morphotypes may not exhibit physiological differences in response to temperature and light, but can have different biotic interactions with other taxa.
Thesis or Dissertation
Department of Biology, CSU Northridge