Spectral and microspatial effects of altering light intensity on fluorescent proteins of Porites furcata: A hard coral from the tropical western Atlantic

Corals have evolved over millennia to become very effective at utilizing light for energy. No other animal is known to use light in an endosymbiotic relationship in the way that corals do. The mechanisms involved with the structure and function of energy obtained from light are yet to be fully understood. One thing that has been discovered and investigated is the production of fluorescent proteins within reef building corals. Corals use fluorescent proteins to enhance light trapping for more efficient harvesting of energy. Fluorescent proteins are also used for reducing light energy for photoprotection against damaging levels of light that could affect endosymbiotic dinoflagellates. This investigation characterized the spectral diversity of fluorescent proteins and their micro-spatial or cellular micro-structural changes in location in the tropical western Atlantic hard coral Porites furcata due to varying light intensities. Green fluorescent protein-like pigments (GFP-like protein) were discovered to be present in P. furcata , along with a phycoerythrin-like pigment. GFP-like proteins present in P. furcata did not change significantly in their steady-state (emission intensities) characteristics among the three light intensity treatments. GFP-like protein concentrations were significantly greater (p = 0.0015), by 50%, in the growing tip of the branches in P. furcata than other areas of the branch. In addition, granular chromophore cells, which are amoeboid shaped, were found in the gastrodermal tissues as well as the epidermal tissues. GFP-like protein was present in those gastrodermal chromophore cells in addition to the epidermal chromophore cells. Porites spp. are the only reef building corals to date known to have the amoeboid chromophore cells.