Phototropic adjustment of the foliaceous coral Echinopora lamellosa in Palau

We tested the hypothesis that foliose plates of Echinopora lamellosa (Esper, 1795) adjust their primary growth direction (or slope from the horizontal) when irradiance (light) is limiting. This hypothesis was tested at a coral-reef locality that is shaded daily by steep adjacent hills, restricting direct light to only a few hours each day (Iwayama Bay, Palau). The angle at which colonies received maximum light was measured using acetate film, and was compared with modeled estimates (using a simple global-light model). We show strong relationships between light and primary-colony gradients; with the foliose plates acting as parabolic antennae, predictably adjusting their primary gradients to optimize light capture.