Coral Species and Their Photosynthetic Preferences

Our next project being carried out on our expedition is titled “Investigating the photosynthetic threshold of active radiation on coral community” and will be lead by Rosalie. This study aims to delve into a relatively understudied area in coral research to determine which species prefer which light conditions. Corals display a symbiotic relationship with zooxanthellae, which live within their cells. In this case the zooxanthellae photosynthesise, fixing carbon, providing nutrients allowing the coral to survive in a wide variety of nutrient conditions. In return, the corals provide the zooxanthellae with carbon dioxide, shelter and some organic nutrients. The majority of reef-building corals exhibit this relationship.

As the zooxanthellae require light to photosynthesise, we would expect to see more corals in areas of higher light penetration. However, different light characteristics may be favoured by different species. Photosynthetically Active Radiation (PAR) is radiation within the wavelength range of 400-700nm which can be used by photosynthesising organisms to produce energy. Zooxanthellae pass on photosynthetic products to the coral host allowing the coral to grow more.

During the 2017 Egypt Expedition, it was found that Photosynthetically Active Radiation (PAR) light penetration levels were a greater determining factor for the abundance of particular coral species than the depth of the environment. This coral study will determine how many hours per day a sampled environment needs to be above the photosynthetic threshold in order to support particular coral species in the Abu Sauatir reef.

During this study, PAR loggers will be left in specific sites for 24 hour periods. Around these sites photo-quadrats will be taken. The photo quadrats will be analysed and corals identified. The graphs produced by the PAR loggers will be analysed and number of hours the site spent above a photosynthetic threshold will be counted.

Message from Rosalie

I decided I wanted to do a coral study because I have always had a fascination with them. Along with the rest of the world, I am heartbroken by news of rapid coral bleaching around the world and I want to contribute to saving them. Knowing more about coral preferences to conditions can help us to rebuild lost colonies. Previous studies done on this expedition have investigated coral bleaching and the effect of light vs PAR on coral communities. I found these interesting and wanted to build upon them. I will be using data from the 2017 expedition to include a larger dataset in my results.