Iwase, A., Sakai, K., Suzuki, A., & van Woesik, R. (2008) Phototropic adjustment of the foliaceous coral Echinopora lamellosa in Palau. Estuarine, coastal and shelf science, 77, 672–678. https://doi.org/10.1016/j.ecss.2007.10.022
Iwase et al. (2008) outline the concept of morphological adjustments by corals in response to wave action and light intensity. Many coral species have the ability to change their growth forms in response to light intensity while other coral species can only change their shape to a small extent. The coral species that express the latter for instance, may grow their branches toward the light or change the shape of their plates to maximize light intake. What previous studies didn’t focus on is the capacity of foliose corals (corals that can change shape to a small extent) in changing the shape of their plates to increase the number of tissue exposed to light.
The researchers measure the angle of colonies of Echinopora lamellosa at various elevations of steep hills where light intensity is highest. They also produce a light model calculating both sun elevation and shade at any time and any location.
Foliose corals can change how much tissue on plates are exposed to light and E. lamellosa in particular can slightly change shape to look like it’s leaning with its plates taking on the shape of parabolic antennas. However, results show that sunlight intensity isn’t necessarily the only factor, suggesting that atmospheric diffusion or other factors may play an important role as well.
Significance for Palau:
Palau has a very rich diversity of coral communities because of its decent variety of reef habitats and lagoons. Reef flats around specific islands are quite notable for housing diverse coral communities even though the somewhat clear water limits visibility from the surface to between 10 and 12 meters. The diversity at these conditions shows the incredible adaptability of corals in limited sunlight. The paper by Iwase et al. may highlight the importance of morphological adjustments of corals in Palau and around the world when sea level increases with climate change and less sunlight reaches the corals underwater. Additionally, higher pollution levels in the air or from nutrient runoff may further diffuse sunlight intensity although corals may adapt very quickly and survive until conservation efforts are directed to coral reefs.