This study evaluated the spectral composition of the light microenvironment on shallow tropical reefs and how light reflected from high reflective surfaces (HRS) and low reflective surfaces (LRS) influenced coral physiology. On shallow reefs in Moorea and Taiwan, the intensity of reflected light was reduced ~20% over LRS compared to HRS, and its quality was modified through a depressed representation of red light. The effects of these contrasting regimes of reflected light were explored with two series of experiments. First, the photophysiology of massive Porites spp. and Pocillopora verrucosa on light and dark surfaces was measured at 3-m depth in the Moorea lagoon. Second, an aquarium tank was used to test for a growth response of Montipora stellata exposed to contrasting regimes of reflected light created under three categories of ambient irradiance mimicking shallow and deep water. For both experiments, the treatment surfaces were created with colored plates simulating HRS and LRS substrata. In the field, photosynthetic yield (φPSII) of massive Porites spp. and P. verrucosa was affected by the substratum reflectance, but the effect differed 3-fold between species. In the tank, growth of M. stellata was suppressed by the darkened surface under conditions simulating a deep-water environment, but the light surface mitigated this effect. The findings from this study conclude that the reflectance characteristics of the substratum can affect coral physiology in shallow water, and suggests that this affect could represent a previously overlooked mechanism mediating the interactions between reef corals and macroalgae.
Thesis or Dissertation
California State University